CA1262576A - Porous bottom-layer dielectric composite structure - Google Patents

Abstract

POROUS BOTTOM-LAYER DIELECTRIC COMPOSITE STRUCTURE

ABSTRACT
A method for inhibiting the formation of blisters during the firing of intermediate layers of fired multilayer electronic components comprising the sequential steps of:
(1) applying to a substrate a first and second layer of finely divided particles of dielectric solids and glass dispersed in organic medium; and (2) firing the layers to effect volatilization of the organic medium therefrom, liquid phase sintering of the glass components and densification of both layers, the softening point of the glass, the particle size of the glass and the ratio of glass to dielectric solids in both layers being adjusted in such manner that when the layers are fired, the first layer is porous and the second layer is nonporous.

Description

TITLF~ PD-2250 POROUS BOTTOM-LAYER DIELECTRIC COMPOSIl`~ STRUCTURE

Field of Invention Thi~ invention relates to a 6mooth, hermetic, 6ubstantially bli~ter-free dielectric in a ceramic hybrid multilayer ci~cuit, and in particular to a dielectric ~tructure which inhihit6 dielectri~ and copper bli~tering in ceramic hybrid mul~ilayer ci~cuit~.

Backq~ound of the Invention Multilayer cera~ic thick film cir~uit hav,e been u6ed for many year6 to increase circuit functionality per unit of area. ~leretofore, mo~t of the dielectric material6 u6ed in multilayer circuits have been conventional monolithic thick ~ilm dielectric compo6itions. The~e are compri6e~ of finely divided particle~ of dielectric solid6 and inor~anic binde~s di~per~ed in an organic medium.
Such ~hick film materials are u6ually applied by screen printing, though they may be applied by other means as well. Thick film material~ of thi6 type are very important and will continue to be 60.
Howe~er, recent advance~ in circuit technolo~y have placed new demand~ on dielectric material6 for thi6 u6e in that the drive toward~
finer ~e601ution and higher reliability ha~ placed a premium on smooth~ bli6ter-free dielectric ~urfaces with good hermetlcity. Such ~urface~ would accept fine-re~olution thick-film or thin-fil~ conductor line~ ~ith a much lower probabili~y of circuit "Open6'l or CiLCUit "~hort6" to other conductor level6. In turn, t~ic~-film conduc~or line~ should not bli~ter upon the further refiring needed to ~J~

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~2~;~6 complete ~he thick-film multilayer, as this loss of adhe~ion dramatically reduce~ circuit reliability.
Dielectric blistering can occur upon initial firing of a hermetic, monolithic dielectri~ layer, especially over copper ~onductor. ~istorically, dielectric blistering has been eliminated by compromi6ing the herme~icity of the dielec~ric layer. On the other hand, conductor blistering, especially copper blistering, occurs upon either initial firing or ~ubsequent refirinq of copper over a hermetic, monolithic dielectric layer. Copper blis~ering can occur even if the copper i~ buried under subsequ~nt dielectric layer6. Once again, the historical ~olution eo copper blistering has been to compromise the hermeticity of the underlying dielectric layer, raising the po6sibility of ~hort circuitfi developing through the dielectric lay~r with time.
It appearz that dielectric blistering is primarily caused by premature sintering of the dielectric layer upon initial firing which traps ga~
generated at the interface be~ween the dielectric layer and the underlying CQpper layer. On the other hand, it appear~ that copper blistering i5 primarily cau~ed by diffusion of glass from the dielectric up into the copper metallization upon refiring. Thi~
glas6 seal6 over the copper metallization, which leads to copper blistering.
Notwithstanding the effectiveness of the prior art processes for applying a monolithic layer of ceramic dielectric, in many application~ there i6 a strongly unmet need for bli6ter-free ceramic dielectric layers which can be applied by either conventional methods, 6uch as screen printing, or as a laminated film where more exacting propelties are required.

Summary of_the Invention In its pri~ary aspect the invention i6 directed to a method for inhibiting the formation of bli&ter6 during the firing of intermediate layer~ of fiLed multilayer electronic components comp~i6ing ~he sequential ~tep~ of:
~ 1) applying to a ~ubstrate a firs~ layer of finely divided particles of dielectric ~olid6 and glas~ di6persed in or~anic medium;

(2) applying to the first disper~ion layer a fiecond layer comprising finely divided particles of gla~6 disper6ed in organic medium and

(3) firing the layers to effect vola~ilization o the organic medium therefrom, liguid phase sintering of the glas6 components and den6ification of both layers, the 60ftening point of the gla6s, the partlcle ~ize of the glas6 and the ratio of glas6 to dielectric solid6 in both layer6 being adjusted in 6uch manner that when the layer6 ~o are fired, the sintering of the glass in the layers i6 such that upon completion of firing both layers, the fir~t layer i6 porou~ and the second layer i~
nonporous, as measured by the Ink Adsorp~ion Te6t.
In another aspect, the invention i6 directed to a multilayer composite 6tcucture compri~ing (13 a substrate having adherent ~hereto (2) a fir~t di6persion layer of finely divided particle6 of dielectric 601id6 and gla6s di6perfied in organic ~edium, the first di6persion la~er having adheren~ thereto (3) a second di~per~ion layer of finely di~ided particle~ of dielectric solids and gla6s disper~ed in organic medium, which layer6 have been fired to effect volatilization of the organic medium ~2~

therefrom and liquid phase sintering of the glas6~
the 60ftening point of the glas~, the particle 8ize of the glas~ and the ra~io of glas~ to dielectric ~olid~ in both layer~ being adju6~ed ;n ~uch manner that when the lay~rs are fired, the ~intering of the glass i.n the layer~ is ~uch that the first layer i~
porous and the ~econd layer i~ nonporou~, as mea~ured by the Ink Ad~orption Test.
In a fur~her a~pect, the invention i~
directed to multilayer composite 6tructure compri~ed of a ~lurality of such two layer dielect~ic composite~ alternating with pat~erned elec~roconductive laye~s.
DETAI~ED DESCRIPTION OF THE INVENTION
A. Ceramic 501ids The invention i~ applicable to virtually any high melting inorganic 601id material. However, it i6 particularly ~uitable for making di6persions of dielectric 601id~ 6uch a6 alumina, titanates, zirconates and ~tannate6. It i~ also applicable to precur~or~ of such material6, i.e., solid materials whicb upon firing are converted to 6uch dielec~ric golids, and to mixtures of any of the~e.
Among the many dielectri~ ~olids which are likely to be u6ed in the inYention are BaTiO3, CaTiO3, SrTiO3, PbTiO3, CaZrO3~ BaZrO3, CaSnO3, BaSnO3, and A1203. A6 will be app~rent to tho6e 6killed in the cera~ic art6, the exact chemi~al composition of the ceramic ~olid~ to be u6ed in the composition of the invention i~ not ord;narily critical in the rheological sen~e. However, it i6 preferred that the ceramic solid6 not have ~welling charac~eristics in the organic di6per6ion since the rheological propertie~ of the di6Der~ion may be substantially changed thereby.

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5i7~i It has been found that the disper~ions of the invention mu~t contai.n no ~ignificant amount of ~olids having a particIe ~ize of le~6 than 0.3 ~m in order to obtain adequately complete burnout of the organic medium when the films or layers thereof a~e fired to remove the organic medium and to effect ~intering of the inorganic binder. However, none of the ceramic solids may exceed 20 ~m and, furthermore, at least 75 w~. % of the ceramic ~olids mu~t have a size o~ 1-10 ~m. ~hen the disper6ion~ are u6ed to make thick film paste~, which are u~ually applied by screen printing, the maximum particle ~ize mu6t not exceed the thicknes~ of the ~creen, and when the - dispersion i6 used to make dry film, the maximum particle ~ize mugt not exceed the thicknes~ of the fil~.
In addition, it i8 pre~erred that surface area/weîght ratio of the ceramic particles not exceed 10 m2/g for the reason that 6uch particles tend to afect adversely the ~intering characteristic6 of the accompanying inorganic binder. I i~ 6till fucther preferred that ~he 6urface area/weight ratio not exceed 5 m /g. Ceramic particles having a surface area/wei~ht ratio of 1-5 have been found to be quite ~5 &at;~fac~ory.
B. Inorqanic Binder The glas~ frit u6ed in the present invention aids in fiintering the inorganic cry~talline particulatefi and may be of any well known compo~ition which has a melting temperature below that of the ceramic solids. Neverthele~6. in order to get adequate hermeticity of ~he device~, it i8 preferred tha~ the glas transition temperature (Tg) of ~he inorganic binder be 550-825C and 6till ~ore ~5 preferably 575-750C. If melting take6 place below : - :

~2~5;76 ~50C, olganic material will likel~ be encapsulated and blisters will tend to form in the dielectric layer a~ the organics decompose. On the other hand, a glas~ transition temperature above 325C will tend ~o produce a porous dielectric when 6intering eemperature~ compatible with copper metallization6, e.g., 900C, are u~ed.
~ he glas~ frit6 preferably used are the vitrifying borosilicate frit~, such a lead borosilicate fcit, and bi~muth, cadmi~, baeium, ~alcium or other alkaline earth boro6ilicate frits.
The preparation of such glass frit6 i6 well known and con~i~t6, for example, in mel~ing together ~he constituent6 of the gla~s in the form of the oxide~
of the con6tituent6 and pouring such molten composition into water to form the frit. The batch ingredients may, of course, be any precu~60r compound that will yield the desired oxides under the u~ual conditions of frit production. For example, boric oxide will be obtained from boric acid, ~ilicon dioxide will be produced from flint, barium oxide will be produced from barium carbonate, etc.
The glas6e6 are prepared by conve~tional glas~making techniques, by mixing the desired ~S component6 in the desired proportions and heating the mixture to form a melt. As ic well known in the ar~, heating is conducted to a peak temperature and for a time such that the melt becomes entirely liquid and homogeneous. In the pcesent work, the componentfi are premixed by ~haking in a polyethylene jar with plastic balls and then melted in a platinum crucible at the desired temperature. The mel~ i8 heated at the peak temperature for a period of 1 to 1-1/2 hours. The melt is then poured into ~old water. The maximum temperature of the water during quenching i6 ' , , . .

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~2~5~6 kept as low as ~ossible by increasing the water-to-melt ratio. The crude frit after separation from wa~er i~ freed of residual water by drying in air or displacing the water by rinsing with methanol. The crude frit i8 then ball ~illed for 3-5 hours in alumina containers using alumina balls.
Alumina contamination of ~he fri~ i~ not wi~hin the observable limit of x-~ay diffraction analysis.
After discharging the milled-fcit ~lurry from the mill, excess solvent i~ removed by decantation and the frit powder is air dried at room ~emperature. The dried powder is then screened through a 325-mesh ~creen to remove any large particles. The inorganic binder, like the ceramic ~olids, ~hould ha~e a surface-to-weight ratio of no more than 10 ~2Jg and at least 75 wt. % of tbe particles ~hould have a particle ~ize of 0.3-10 ~m.
It i~ preferred that the 50% point of the inorganic binder, which i8 defined a~ equal parts by weigh~ of bcth larger and smaller particles, be equal to or le~fi ~han that of the ceramic ~olids.
Sintering rate i~ related directly to the ratio of inorganic binder ~o ceramic solid~ and inversely to Tg and particle 6ize of the inorganic binder. The acces6ible variables for adju~ting the hermeticity of a dielectric layer include, but are not limited to, (1) inorganic binder/ceramic 601id~ ratio, (2) gla66 tran~ition temperature of the inorganic binder, (3) par~icle 6;ze, and 54~ firing temperature.
C. Oraanic Pol~meric Binder A6 set ou~ hereinabove, the binder component of the di~per~ion of the invention is an orqanic polymeric ~inder ~elected from the group con~isting of ~1) homopolymers and copolymers of Cl 10 alkyl acrylate~, Cl_10 alkyl methacrylates, alpha-methyl-~26:2 S~

styrene and 0-2 wt. ~ ethylenically unsaturated carboxylic acid, amine or silane-containing compound6, (2) homopolymer6 and copolymer6 of Cl 10 mono-olefins, (3) homopolymers and copolymer~ of Cl 4 S alkylene oxide and mixture6 thereo~, the binder compri6ing 5-25 wt. % ba~i6 total inorganic 601id~.
The above-de~cribed polymer6 include homo-polymers a6 well as random copolymer~ and higher multipolymer~. The relative quantity of carboxylic acid or amine di~tributed along the polymer chain~
~hould be no more than 2.0 wt. %. Beca~se they are cleaner bu~ning in low oxygen atmosphere~, methacrylie polymer6, e~pecially eoly~methyl methacrylate)~ are preferred over acrylic polymer~.
lt i6 preferred that the comonomer6 containing functional moieties not exceed 10.0 wt.
of any one polymer or 2.0% in the polymer mixture to avoid flocculation of the di6persed cer~mic ~olid6.
In some in~tance6, it has been observed that polymer mixture~ having as low as 1.8~ acid-containing monomers may be borderline or even unsatisfac~ory with re~pect to di~per6ion characteri6tic6. In mo6t instances of thifi kind, such polymer~ can~
nevertheles~ ill be u~ed in the invention by emplo~ing a more polar ~olvent. Thu6, while a polymer mixture containing a6 much as 2.0%
monomer-containing functional groups can be u6ed, such polymer mixtures having only 1.5~ functional ~onomer~ are preferred. No more than 1.0 wt. ~ of ~uch functional monomer~ till further preferred.
It i~ also preferred Por the same rea60n that none of the polymer6 contained in ~he polymeric mixture contain more than 10.0 wt. % functional comonomer.
Thus, the polymeric binder can be a mi~ture of 3~

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polymers, some of which contain no functional moieties at all and ~ome of which con~ain as much a6 10.0 wt. ~ functional comonomer6 60 long as the content of functional comonomer~ in the total mixture i~ within the range of 0.2-2.0 wt. ~. On the other hand, it is preferred that the polymeric binder be comprised ~ostly of methacrylic polrmers as defined above which contain 0-5.0 wt. % func~ional comono~er.
5uitable sopolymerizable carboxylic acid~
include ethylenically un~aturated C3 6 monocarboxylic acids ~uch as acrylic, methacrylic and crotonic acid6 ~nd C4 10 dicarboxylic acids such as fumaric, itaconic, citaconic, vinyl succinic and maleic a~id6 as well as their half ester6 and, where appropriate, their anhydrides and mixtures thereo~. Because they are cleaner burning in low-oxygen atmospheres, methacrylic polymer~ are p~eferred over acrylic polyme~.
It is, of course, recognized that certain amine con~tituents cannot be incorporated in the chain directly by copolymerization of the amine-containing monomer but may be incorpo~ated indirectly by po~tpolymerization reaction of a pendant reac~ive moiety of the polymer chain. Illustrative of thi6 are primary amines which can be added by reaction oE
glycidyl compound~ with pendant carboxylic acid group~ in the presence of ammonia. ~hu~, as u6ed herein, the term "ethylenically unsaturated amine" i6 intended to include polymer6 derived from both amine-containi~g comonomers a~ ~ell as other comonomer6which have besn postpolymerizationally reacted to form a~ine group6 ~hereon. Primary, secondary and ~ertiary amine~ are each effective in a ~imilar manner. Suitable comonomers for direct incorporation of pendant amine group6 into the binder polymer chain ~2~ 5~

include diethylaminoethyl methacrylate, dimethylamino-ethyl methacrylate and t-butylaminoethyl metha~rylate.
Sui~able comonomers which yield pendant functional ~oieties ~uitable fo~ postpolymerization reaction to incorporate amine functionality include the aboYe-described ethylenically un~aturated viz.
epoxides 6uch a~ glycidyl acrylate or glycidyl methacrylate.
Wi~hin the above-descr;bed limits for the nonacidic comonomer~, it i~ pre~erred that the alkyl acrylate or methacrylate con6titute at lea~t 75 and preferably 80 wt. % of the polymer.
The polymeric binder can contain up eo about 10 wt. ~ of other nonacrylic and nonacidic comonomers ~uch a~ styrene, acrylonitrile, vinyl acetate, acrylamide and ~he like, 60 long as the previously di~cu6sed compositional criteria are ~et as well as the physical criteria mentioned below. EIowever, it i6 preferred to use not more than about 5 wt. ~ of ~uch monomer6 becau~e they are more difficult to burn out cleanly. At pre6ent, the use of ~uch other comonomer~ is not known to add to ~he eficacy of the ~opolymer6 in their application to the invention.
However, 6uch comonomer~ in the above-li6~ed amounts do not detract from the effectivenes~ of the polymer~
60 long as all ~he compo~itional and phy6ical property criteria are met.
In addition to the above described acrylic and methacrylic polymer6, variou~ polyole~ins &uch a6 polyethylene, polypropylene, polybutylçne, polyi~o-butylene, and ethylene-propylene copolymer can al60 be u~ed. Al~o u6eful in the invention are the 60-called polyether~ which ar~ polymer6 vf lower alkylene oxide6, 6u~h a polyethylene oxide, polypropylene oxide and polybutylene oxide, and cellulo~e ether~.

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In addition to the above-de~cribed compo6itional parameters, certain phy~ical prope~tie~
of the polymeric binder are, of cour~e, important.
In particular, it will be recognized by those skilled in the photore~ist art that the plasticized unexposed binder polymer mu~ be ~ub~tantially developable in wha~ever solven~ developer i6 u6ed. On the other hand, the photohardened binder must have ~ufficient solvent resi~tance ~hat it i6 no~ washed off by the developer solvent.
Polymers meeting ~hese criteria can be made by those 6killed in the art of acrylate polymeri2ation by conventional ~olution polymerization techniques.
Typically, such acidic acrylate polymers are prepared by combining an alpha, beta-ethylenically unsaturated acid with one or more copolymerizable vinyl monomQ~s in a relatively low boiling (75-150C) organic solvent to obtain a 20 to 60% solution of the monomer mixture, then 6ubsequently causing the monomar~ to polymerize by the addition of a polymerization catalyst and hea~ing the mixture at the reflux temperature of the 601ution at atmospheric pressure. After the polymerization reaction i8 essentially complete, the refiulting acid polymer olution i6 cooled to room temperature and 6amples are removed to determine the vi6cosity, molecular weight~ acid equivalent, etc. of the polymer.
D Photoinitia~ion SY6tem .

Suitable photoinitiation systems are those which are thermally inacti~e but which genera~e free radical6 upon expo6ure to actinic light at or ~elow 185C. These include the subs~ituted or unsubstituted polynuclear quinone6 which are compounds having two in~racyclic carbon atoms in a conjugated carbocyclic ring 6y~tem, e.g., 9,10-anthraquinone, 2-methylanthra-, ~.

25'76 12quinone, 2-ethylan~hraquinone, 2-tert-butylanthra-guinone, octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanth~enequinone, benz(a)an~hracene-7,12-dione, 2,3-naphthacene-5,12-dione, 2-methyl-1,~-naphthoquinone, l,~-dimethyl-anthraqu;none, 2,3-dimethylanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, retenequinone, 7,~,g,10-tetrahydronaphthacene-S,l~-dione, and 1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione.
Other photoinitiators which are also useful, ~ven though some may be ther~ally active at ~emperatures as lo~ as ~5C, are described in U.S. Patent Z,760,863 and include vicinal ketaldonyl alcohols - such as benzoin, pivaloin, acyloin ethers, e.g., benzoin methyl and ethyl ethers, benzil dimethy:L
ketal; a-hydrocarbon-substituted aromatic acyloins, including -methylbenzoin, a-allylbenzoin and a-phenylbenzoin. Photoreducible dyes and reducing agents disclosed in U.S. Patent6 2,850,445, 2,875,0~7, 3,097,096, 3,074,974, 3,097,097, and 3,145,104, as well as dyes of the phenazine, oxazine, and quinone classes, Michler'6 ketone, benzophenone, 2,4,5-triphenylimidazolyl dimer~ with hydrogen donor~
including leuco dyes and mixtu~es thereof as ~5 described in U.S. Pa~ent~ 3,4Z7,161, 3,~79,185, and 3,549,367 can be used a6 initiators. Also useful with photoinitiators and photoinhibitor~ are ~ensitizer6 disclosed in U.S. Patent 4,162,162. The photoinitiator or photoinitiator ~ystem i~ prese~t in 30 0.0~ to 10~ by weight based on ~he total ~eigh~ of the dry photopolymeriz~ble layer.
E. Photohardena le _o omer The photohardenable monomer component of the invention is comprised of at least one addition 35 polymerizable e~hylenically unsaturated compound - .

~26;~5~6 i having at least one polymerizable ethylenic group.
Such compounds are capable of forming a high polymer by free radical initiated, chain propagating addition polymerization. Preferably, the unsaturated compound (monomer) has at least two term;nal et'hylenically unsaturated groups, e.g., 2 to 4 group's. ~he monomeric compounds are nonga~eou~. That i8, they have a normal boiling point above 100C and a plasticizing action on the organic polymeric binder.
Suitable monomer~ which can be used alone o~
in combînation with other monomer~ include t-butyl acrylate and methacrylate, 1,5-pentanediol diacrylate and dimethacrylate, N,N-diethylaminoethyl acrylate - and methacrylate, ethylene glycol diacrylate and dimethacrylat0, 1,4-butanediol diacrylate and dimethacrylate, diethylene ~lycol diacrylate and dimethacrylate, hexamethylene glycol diacrylate and dimethacrylate, 1,3-propanediol diacrylate and dimethacrylate, decamethylene glycol diacrylate and dimethacrylate, 1,4-cyclohexanediol diacrylate and dimethacrylate, 2,2-dimethylolpropane diacrylate and dimethacrylate, glycerol diacrylate and di~ethacrylate, tripropylene glycol diacryla~e and dim~thacrylate, glycerol triacrylate and trimethacrylate, trimethylolpropane triacrylate and trimethacrylate, pentaerythritol triacrylate and trimethacrylate, polyoxyethylated trimethylolpropane triacrylate and ~rimethacrylate and similar compound a~ d;~closed in U.S. Patent 3,380,831, 2,2-di(p-~0 hydroxyphenyl)-propane diacrylate, pentaerythritol tetr~a~rylate and tetramethacrylate, 2,2-di-(p-hydroxyphenyl)-propane dimethacrylate~ triethylene glycol diacrylate, polyoxyethyl-2,2-di-~p-hydroxy-phenyl)propane dimethacrylate, di-(3-methacryloxy-3S 2-hydroxypropyl) ether of bi~phenol-A, di-~2-57~

14methacryloxyethyl) ether of bisphenol-A, di-~3-acryloxy-2-hydroxypropylj ether of bisphenol-A, di-(2-acryloxyethyl) ether of bisphenol-A, di-(3--methacryloxy-2-hydroxypropyl) ether of 1,4-butanediol, triethylene glycol din~ethacrylate, polyoxypropyltrimethylol pLopane triacrylate, butylene glycol diacrylate and dimethacryla~e, 1,2,4-butanetriol triacrylate and trimethacrylate, 2,2,g-~ri~ethyl-1,3-pentanediol diacrylate and dimethacrylate, l-phenyl ethylene-l,~-dimethacrylate, diallyl fumarate, styrene, 1,4-benzenediol di~ethacrylate, 1,4-dii~opropenyl benzene, and 1,3,5-trii60propenyl benzene. A1BO useful are ethylenically un~aturated compound6 having a molecular weight of at least 300, e.g., alkylene or a polyalkylene glycol diacrylate prepared from an alkylene glycol of 2 to 15 carbon~ or a polyalkylene ether glycol of 1 to 10 ether linkages, and tho6e disclosed in U.S. Patent 2,927,022, e.g., those having a plurality of addition polymerizable ethylenic linkages particularly when pre~ent a6 terminal link~ge~. Particularly preferred monomers are polyoxyethylated trimethylolpropane triacryla~e, ethylated pentaery~hritol triacrylate, dipentaerythritol monohydroxypentaacrylate and l,10-decanediol dimethylacrylate. The un~aturated monomeric component i8 pre~ent in an amount of 5 to 45% by weiqht ba~ed on the total weight of the dry photopolymerizable layer.
~inor amounts of other component6 can be pre~ent in the photopolymeri2able compo6ition6, e.g., pigment~, dye~, thermal polymerization inhibitor~, adhe6ion promoter6, 6uch a~ organosilane coupling agent6, plasticizer~, coating aids such a6 polyethylene oxide~, etc. 60 long a~ ~he ~i;2~
i photopolymecizable compo~itions retain their e6sential propertie~.
F. Orqanic Medium The main purpose of the organic medium i~ to 6e~ve a~ a vehi~le for disper~i~n of the finely divided ~olids of ~he compo~ition in ~uch form tha~
ie can readily be applied to a ceramic or other substrate. Thu~, the organic medium ru~t fir6t be one in which the solid6 are dispersible with an adequate degree of ~tability. Secondly, the Lheological properties of the organic medium mu~t be ~uch that they lend good application properties to the di~per6ion.
When the di6pec6ion i~ to be made into a f;lm, the organic medium in which the ceramic 601ids and inorganic binder are di6per~ed con6i~t~ of ~,he above-de~crlbed polymeric binder, monomer and initiator which are dissolved in a volatile organic 601vent and, optionally, other dis~olved materials such as pla~ticizers, ~elease agent6, disper6ing agent~, st~ipping agent~, antifo~ling ayent~ and wetting agent~.
The solvent componen~ of the organic medium, which may be a mixture of 601vent~, is cho~en so aQ
to obtain complete solution therein of the polymer and ~o be uf ~ufficiently high volatility to enable ~he 601vent to be evaporated from the di~per6ion by the application o~ relatively low level6 of heat at atmospheric pres6ure. In addition, the ~olvent mu~t boil well below the boiling point and decsmpo~ition ~empera~ure of any other additive~ contained in the organic medium. Thu~, ~olvent& having atmo~pheric boiling point6 below 150C are u~ed mo~t frequently.
Such ~olvent~ include benzene, acetone, xylene, methanol, ethanol, methylethyl ketone, l,l,l-tri-~ . , 5~

16chloroethane, tetrachloroethylene, amyl acetate, Z,2,4-triethyl pentanediol-1,3-mono-i~butyrate, toluene, methylene chloride, and ethyllene glycol monoalkyl and dialkyl etherfi ~uch as ethylene glycol mono-n-propyl ether. For casting films, methylene chloride is particularly preferred becau~e of it~
volatility.
Frequently the organic medium will al~o contain one o~ more plasticizer~ which ~erve to lower the Tg of the binde~ polymer. Such plasticizer6 help to as~ure good lamination to ceramic ~ubstrates and enhance the developability of unexposed area~ of the compositio~. However, the u6e of such material~ i~
- preferably minimized to reduce the amount of organic material~ which must be removed when the films ca~t the~efrom are fired. The choice of plasticizerB i6, of cour~e, dete~mined primarily by the polymer which must be modified. Amon~ the plasticizerz which have been used in various binder sy~tems are diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, dibenzyl phthalate, alkyl pho6phate6, polyalkylene glycol~, glycerol, poly(ethylene oxide~), hydeoxy ethylated alkyl phenolD tricre&yl phospha~e, ~riethyleneglycol diacet~te and polye6ter pla6ticizers. Dibutyl phthalate is ~requently used in ac~ylic polymer sy6tem6 because it can be used effectively in relatively ~;mall concentrations.
The photosensitive compo~ition6 of the invention will frequsntly be employed a6 the photo6ensitive layer of a resist element in which ~he pho~osenitive layer i~ coated upon a 6upport film.
In conventional photore~i~t element~, it i6 nece~sary, or at lea~t highly de6irable, to protec~
the photo~en~itive layar by a removable coversheet in 3~

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~5~6 order to prevent blocking between the photo~en$itive layer and the rever6e surface of the support when they are s~ored in roll form. It i~ also de6irable to protec~ the layer laminated ~o a ~ubstrate by means of the removable support film during imaging expo~ure to prevent blocking be~ween the layer and th~ phototool.
The photopolymerizable compo~i~ion is coated upo~ ~he 6uppor~ film at a dry coating thickne~s of 1~ about 0.0004 inch ~~0.0010 cm) to about 0.01 inch (~0.025 cm) or more. A suitable strippable 6upport which preferably has a high degree of dimen~ional ~tability ~o temperature change~ may be chosen from a wide variety of f ilms compo6ed of high polymer6, e.g., polyamides, polyolefin~, polye6ters, vinyl polymer~, and cellulo~e ester~ and may have a thickne66 o~ from 0.0005 inch (~0.0013 cm) to ~.008 inch (~0.02 cm) or mare. If exposure i~ to be made before removiny the 6trippable 6upport, it mu6~, of cour~e, transmit a ~ub~tantial raction of the ac~inic radiation incident upon it. I~ the ~rippable 6Upport is removed prior to expo~ure, no such re~triction6 apply. A particularly ~uitable 6uppo~t i~ ~ransparen~ polye~hylene terephthalate Z5 f ilm having a ~hickness of abou~ 0.001 inch (~0.0025 cm) .
When an element contains no removable, protective cover6heet and i6 to be ~tored in roll form, the Leverse side of the ~trippable 6upport 3~ preferably ha~ applied thereto a thin relea6e la~er of a ~aterial such as wax or ~ilicone to prevent blockin~ ~ith the phv~opolyme~izable stratum.
Alternatively, adhe6ion to the coated photopoly-merizable layer may be preferentially increa6ed by flame treating or electrical di~charge treatin~ the 6uppor~ 6urface to be coated.

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:

57~

5uitable removable, protective coversheet~
when used may be chosen from the same group of high polymer film6 described above and may have the same wide range of thicknesses. A coversheet of 0.001 inch ~~0.0025 cm~ thick polyethylene i~ especially suitabl~. Supports and coversheet6 as described above provide good plotection to the pho~opolymeriz-able resist layer dur;ng ~torage prior to use.
It i~ preferred ~hat the weight ra~io of the inorganic ~olids (diele~tric and glass) to o~ganic~
be within ~he ca~ge of 2.0 to 8.0 and, more preferably, f~om 2.6 to 4.5. A ratio o~ no ~ore than 8.0 is necessary to obtain adequate disper~ion and rheological properties. HoweYer, below 2.5, the amount of organics which must be bucned o~f i6 excessive and the quality of the final layers suffers. The ratio o~ inorganic solids to oLganics i~ dependent on the particle 6ize of the inorganic ~olids, the organic compo~ents and on surface pretreatment of the inorganic ~olids. When the particles are treated with organo6ilane coupling agent~, the ratio o~ inorganic 601id~ to organics can be increa~ed. It i~ peeferred to use a lower level of organicG to mini~ize firing defect~. It i8 especially important that the ratio of inorganic6 to or~anics be as high as po~,ible.
On the other hand, when the di6persio~ is to be applied a~ a thick film paste, conventional thick fil~ organic.media can be used with appropriate rheological adjustment~ and the use of lower vola~ility ~olvents.
When ~he compo~itions of the invention are formula~ed as ~hick film composition6, they will usually be applied to a &ubstrate by means of ~creen 3~ printing. Therefore, they must hav0 appropriate 5~6 I

vi6co~ity 60 that they can be pas~ed th~ough the ~creen readily. In addition, they should be ~hixotropic in order that they set up rapidly af~er being 6creened, thereby giving good resolutiom.
While ~he rheological properties are of pri~ary importance, the organic medium i~ preferably formulated al~o to give appropriate wettabili~y of the ~olids and the sub~trate, good drying rate, deied film streng~h ~ufficient to with6tand rough handling and good firinq ~roperties. Satisfactory appearance of the fi~ed composition is also i~portant.
In view of all these criteria, a wid~
variety of inert liquids can be u6ed a~ organic - ~edia. The organic mediu~ for most thick ~ilm composition~ i8 typically a ~olution of resin i~ a solvent and, frequently, a ~olvent 801ution containing both lesin and thixoteopic agent. The solvent usually boils within the range of 130-350C.
Especially fiuitable re6in~ for this purpo~e are polymethacrylates o lower alcohols and monobutyl ether of ethylene glycol monoacetaee.
The mo~t widely u6ed ~olvents for ~hick film applications are terpenes 6uch as alpha- o~ beta-terpineol o~ mi~tures thereof with other solvent~
6uch a~ kero~ene, dibutylphehalate~ butyl Carbitol*
butyl Carbi~ol acetate, hexamethylene glycol and high boiling alcohols and alcohol e6ters. Various combination~ of these and other ~olvent~ are formulated to obtain the desired vi~c06ity and vola~ility requirement6 Por each application.
Among the thixotropic agent~ which are ~ommonly u~ed are hydrogenated castor oil and derivative6 thereof. It i6, of course, not always nece~ary to incorporate a thixotropic agen~ s;nce ~5 the solven~/re~in propertie6 coupled with the shear * denotes trade mark 25;~

thinning inherent in any suspension may alone be ~uitable in this regard.
The ra~io of organic medium ro inorganic solids in the disper6ions can vary con6iderably and depends upon ~he ~anner in which the dispersion is to be applied and the kind of organic meclium used.
Normally, to achievs good coverage, the dispersion6 will contain complementally ~y weight 60-90% 601id6 and 40-10% organic medium. Such dispersion6 are usually of semifluid consistency and are referred to commonly a~ "paste6".
The paste6 are conveniently prepared o~ a three-roll mill. The visccsity of the pastes is - typically within the following ranges when measured lS at room temperature on Brookfield vi6cometers at lo~w, moderate and hig~ shear rates:
Shear Rate ~Sec~l) ViscositY SPa.
0.2 100-50~0 300-2000 Preferred 600-1500 Most e~eferrecl ~- 40-400 100-250 Pre~erred 140-200 Mo6t preferred 10-25 Preferred lZ-18 Most preferred The a~ount and type of organic medium (vehicle) utilized i6 determined mainly by the final desired formulation viscosity and print thickne6s.
In ~he ca6e of photo~en~itive material6, variou6 dyes and pigment6 may al~o be added ~o increase vi~ibiliey of the photo image. Any colorant used, however, ~hould preferably be transparent to the actinic radiation used, although it may be opaque 2~:i7~

to or 6trongly absorb other radiation in the vi6ible or W ~pectral region.
In addition to the many para~eters of propertie~ and compo~i~ion described above, it i~
e~$en~ial ~hat all of the co~ponent6 - both inorganic and organic - be substan~ially free of halogen~. The rea~on for this i~ that under normal firing condition~, halogenated com~ounds cause corro~ion of adjoining conductive layers as well as the ~urface6 of the furnace in which they are fired.

G. Relation~hiD Between The Underlyinq And Overlyin~ Layer 6 The proper functioning of the invention requires that the underlying and overlying layers in the dielectric structure be properly related with respect to porosity.
When fired individually on a 96.5% alumina ~ubstrate, the underlying layer must be porous.
However, the overlying layer must be non~orou~, or hermetic under like firing condition6. In additiQn, the ~tructure may have one or more intermediate layer~ which can be either porou~ or nonpoLous. The intermediate layer6 can be compri~ed of glass particles alone or they may al80 contain particle6 of ceramic ~olids a~ well. The composition of the gla66 and/or ceramic ~olid~ in the intermedia~e layer6 may be ~he ~ame or different than the compo6ition of the adjoining layer~. The preferred test for deter~ining the relative poro~ity o~ an individually firad dielec~ric layer i6 the Ink Ad~orption Tezt which ifi de~cribed hereinbelow.
The gradient-poro~ity dielectric ~tructure inhibits dielectric blistering by facilitating ~he ven~ing of ga~ generated at the dielectric-underlying , :.
.
, .
~ -.

;;2~

copper interface during the fir~t firing of the dielectric structure. Ge~erally once the dielectric is fired, it i~ ~ufficiently rigid to re~ist bli~tering on refire. To prevent die]ectric blistering ~he underlying porous layer can be relatively thin, with the preferred range being 0.20 ~Q 2 time~ the thicknes~ of the overlying hermetic~
layer. The overlying layer can contain up to 100 inorgani~ binder to give an extremely hermetic dielectric ~tructuce overall.
The invention inhibit~ copper blistering by re~arding diffusion of the inorganic bindel into the overlying copper. Copper is 6ufficiently ductile tD
bli6~er on refire. To prevent copper blistering it i~ preferred that the underlying layer be 0.20 to 2 times the thickne6s of the overlying layer. The overlying dielectric layer should only contain ~u~ficient inorganic binder to bring the overall dielectric ~tructure into the preferred range of hermeticity. A method of mea6uring the hermeticity o~ the overall dielectric Btructure i6 the ~et Dis6ipation Factor test (the Wet DF test)0 A particularly preferr~d compo6ition an~
therefore best mode for practicing invention is one in which the first and second dielectric layer~ ha~e the following composition~:
Fir6t Layer ta) finely divided particle~ of ceramic 601id~ having a 6urface area-to-weight ratio of no more than 10 m /g and at lea6t 75 wt. % of the particle6 having a çize of 0.5-10 micron, and (b) finely divided par~icles of inorganic binder having a gla6s transition temperature of 550-~Z5C, a surface area-to-weight ratio of no more than 10 m /g and at lea6t 75 wt. ~ of the 5~7 particles having a size of 0.3-10 micron, the volume ~ of (b) being 30%-70% of total inorganic solids, and (c) an organic binder selected from the group consisting o ~1) homopolymers and copolymers of Cl 10 alkyl ac~ylates, Cl 10 alkyl methacryl-ate6, alpha methylstyrene and 0-2 wt. %
e~hylenically unsatu~ated carboxylic a~id, (2) homopolymers and copolymers of Cl 10 mono-olefin~, (33 homopolymer6 and copolymer6 of Cl 4 alkylene oxide ~4) cellulose ethers, and admixtures thereof, the organic binder compri~irlg 1-25 wt. % on the basis of to~al inorganic 601icl~.

Second LaYer The overlying coating composition con~is~s es~entially of (a) finely divided particle6 of ceramic solids having a 6urface area-to-weight ~atio of no more than 10 m /g and at least 75 wt. S of the particles having a ~ize of 0.5-10 micron, and (b) finely divided particles of inorganic binder having a gla6~ transition temperature of 550-825C, a ~urface area-to-weight ratio o~ no ~ore than 10 m /g and at lea6t 75 wt. ~ of the particle~ ha~ing a size of 0.3-10 mic~on, the volume t of (b) being 50~-100% of total inorgani~
solids, and (~ an organic binder 6elected from the group consi~ting o~ (1) homopolymers and copolymers of Cl 10 alkyl acryla~e~, Cl 10 alkyl methacryla~e6, alpha methyl~ty~ene and 0-2 wt. % ethylenically un~aturated carboxylic acid, (2) homopQlymer~ and copolymers of Cl 10 mono-olefin~, (3) homopolymers and copolymer~ of Cl 4 alkylene oxide ~L2~ ;76 (4~ cellulose ethers. and admixtures ~hereof, the organic binder compr;~ing 1-25 wt. % on the basi6 of total inorganic ~olids.
The underlying layer 8 distinguished from the overlying layer in that the underlying layer, if individually fired onto a 96.5~ alumina substrate, will absorb and retain ink in the Ink Ad~orption Te~t, while the individually fired overlying layer will not.
H. Test Procedures Ink Ad~orption The Ink Ad~orption Test is carried out a~
- follows. The test piece i~ held horizontally. A
drop of non6mear ruhber-stamp blue ink (Ranger Product6 Company, Red Bank, NJ) i~ placed on the dielectric surface and allowed to stand 30 second6.
The ~est part i6 then held vertically in a ~tream o~
cold tap wa~er for 30 ~econd6, followed by a stream 20 of acetone Por 15 seconds, in the attempt to wash o~f the ink. Area6 of ink retention which are traceable to di6tinct defect~ such as blisters or dirt, should be ignored. If there i~ no visible ink retention on the dielectric surface, the dielectric i~ deemed 25 nonporou~. If there i~ vi~ible ink retentivn on the dielectric sur~ace, the dielectric i~ deemed porous.

aPacitance, Dry Di6fiiPation Factor ~DF)~
and Wet Dis~ipation Factor (Wet DF) A capacitor is formed fro~ the dielectric ~ructule compri6ing (a) a copper di6k having an area of 1 cm and a contact tab ~upported on an alumina substrate, (b) a gradient-poro~ity dielectric 6tructure overlying the copper di6k but leaving the 35 contact tab expo~ed, and (c) a ~econd coppe~ disk o~

.:
,.
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~2;;~:~76 the s~me size overlying the dielectric structure and having a contact tab rotated 90-180 degrees with respsct to the lower ~ab.
Capaci~ance and dry DF are measured a~ 1 kHz u6ing a Hewlett-Packard HP4274A multi-frequency LCR
meter. The thicknes6 of the dielec~ric is mea~ured with a Sloan Dektak IIA Profilome~er. It may alternately be measured on a light-section microscope or on an SEM photograph of a sectioned capacitor.
All capacitors are held at least 15 hours after firing before making electrical ~easurements. I~ i~
common that the dis~ipation factor (DF) decreases by 0.5-2% within this holding time period. However, capacitance is generally unaffected during this lS period.
The dielectric constant i6 calculated using the equation:
R ~ C t where C is the capacitance of the capacitor A - is the area of small electrode in contact with the diele~tric layer t - i~ the thickness of the dielectric layer.
Wet DF is determined by placing a drop of water on the upper copper di~k 60 that i~ wet6 the di6k but not the contact tab. After 6tanding for 30 ~econd6, DF is determined in the usual manner. The dielectric i8 considered to be hermetic when the wet DF is le~ than 1%. Below 0.5% i6 preferred.

Insula~ion Re i~tance (IR) In~ulation resi~tance is measured using Super megohm meter Model R~ 170 (Biddle InstLument6, AV0, L~d.. ~.K.). Insulation resistance measurements .

5~3~
i are made after charging the capacitor with 100 VDC.
Each number i~ the average of at lea~ 10 mea~urement~.

Breakdown Voltaqe The BLeakdown Voltage test (al~o called the dielec~ric-6trength ~e~t~ con~i~t~ of the application of a voltage higher ~han rated voltage for a ~pecific t;me between mutually insulated portions of a co~ponent part or between in~ulated portions and ground. Thi6 is u~ed to observe whether the componen~ pa~t can o~erate 6afely at i~6 rated vol~age and with~tand momentary overpotential~ due to ~witching, surge~, and other ~imilar phenomena.
~lthough thi~ te6t i~ often called a voltage breakdown or dielectric-strength test, it i6 not intended that thi~ te~t cau6e in6ulation brealcdown or that it be u6ed for detecting corona. Rather it 6erve6 to detecmine whether in~ulating materials and ~pacings in the component part are adequate. When a component part i6 faulty in the6e respect6, application of the te~t voltage will re~ult in ei~her di~rup~ive di~charge or deteriora~ion. Di6ruptive di6charge i8 evidenced by fla6hover (6urface di6char~e), sparkover (air discharge), or breakdown (puncture di6charge). Deterioration due to exce6sive leakage current~ may change electrical parametee6 or phy6ical characteri~tic6. Dielectric hreakdown i~
reported in volt6/mil or volt~/cm of dielectric ~hicknes~. Dielectric layer6 are de6igned to have 6u~ficient thicknes~ to provide a maxgin of ~afety well below the breakdown of the electric. The te6t i6 conduc~ed in accordance wi~h MIL-STD-202E, 16 April 1973.

2~

Electromiqration Resi6tance (EUR) The leakage current determined in the elec~co migration resi~tance (EMR) ~e6t empirically measures the cross-sectional area of open poro~ity in the dielectric which i6 permeated by electroly~e.
Screen printed conductor patterns of 9924 thick film copper are made with a 6.25 cm2 area with a eab extending from this square to the edge of the 2" x 2"
alumina fiubstrate. After the part~ are fired, the dielectric is applied over thi~ except for the tab at ~he edge of the part. After thi~ i~ fired, the part~
are te~ted within a period of 18 to 24 houz6. The te~t part~ are mounted ~ertically in stirred lN
~odium chloride 60 that the 6.25 cm pattern i8 immersed. A platinum anode i~ also immersed in the electrolyte and an electric field of 10 volts DC is applied across the part which ifi inserted into a prewired connector. The current flow through the part is maintained for 5 minutes and the leakage current is recorded from a multi-range microammeter wired in serie6 wi~h the test piece.

~ea 6U rement of Glass T
Tg is determined from ~he linear ther~al ~5 expansion curve of the premelted frit a6 mea6ured by ASTM de6ignation C ~72-81, I'Linear Thermal Expan~ion of Porcelain Enamel and Glaze Frit~ and Fired Ceramic Whiteware Produ~t~ by the Dilatometer Method".

EXAMPI.ES
C ~ ~o~r ~AT~
In the examplefi which are set out below, the following component ma~erials were used having ~he indicated ~roperties:

~;~6;Z~;716 A. Inorqanics Glass frit A: PeLeo( ) glass #3467 ball milled in wa~er, fractionated and dried ~o give a surfa~e area of 1.3-2.2 m2~g and a particle ~ize di~tribution of 90~ point B.9 - 10 ~m 50% point 5.1 - 5.B ~m 10~ point 2.4 - 2.8 ~m Composition (component mole %~:
lead oxide (5.6), silicon dioxide (68.1), boron oxide (4.7)~ alumina (6.5), calcium oxide (11.1), sodium oxide (2.8) and pot,as6ium oxide (1.3).
Glas6 frit ~: FecrQ(l~ glasfi #3467 with a surface area of 3.1-4.9 m2/g and a particle 6ize distribution of 90% point 4.2 ~m 50% point 2.1 ~m 10% point 0.8 ~m Composition the same as gla~6 frit A.
Glas~ frit C: Ferro( ) glas6 ~3467 ~all milled : in water, fractionated and dried to give a &urface area of 3.9-4.6 m2/g and a particle 6ize distribution of 90% point 3.0 - 4.0 ~m 50% point 2.1 - 2.7 ~m 10~ point 1.1 1.3 ~m Composi~io~ the same as gla frit A.
Glas~ fcit D: Glass h~ving a particle 6ize distribution of ::
: 28 -go~ po;nt 12.0 ~m 50% point 5.5 ~m 10~ point 1.7 ~m Composition (component mole %):
magne~ium oxide (4.0) ~ilicon dioxide (39.8), boron50xide (~.7), alumina (7.8), calcium ox~ide ~8.5), titanium dioxide (10.0), zinc oxide (11.8~, and barium oxide (13.5)~
Alumina A: Alcoa A-14 aluminum oxide ~A1203) with a surface area ranging from 3.0 to 4.5 m2/g and a par~icle ize di~tribution of 90% point 3.5-4.0 ~m 50% point 2.0-2.5 ~m 10% point 0.8-1.3 ~m Alumina B: Alcoa A-14 aluminum oxide tA1203) ball milled in water with pH
adju~ted to 4.0 u6ing acetic acid, fractionated and dried to ~iv~ a ~urface area ranging from l.0 ~o 2.1 m2/g and a particle 6ize di6tribution o~
90~ point 4.~-7.6 ~m 50% point 3.0-9.9 ~m 10~ point 1.5-2.7 ~m Alu~ina C: Alcoa A-14 aluminum oxide (A1203) ball milled in water with pH
~dju~ted to 4.0 u~ing aceti~ acid, fractionated and dried to ~ive a : surface area of 2.9 m2/g and a partisle 6ize di~t~ibution of % point 3.8 ~m 50~ point 2.6 ~m 10* point l.9 ~m :

: : ~
;

:

. .

, .
.

;2~76 Alumina D: Alcoa A-14 aluminum oxide (A1203) ball milled in water with pH
adjusted to 4.0 us;ng acetic acid, frac~iona~ed and dried to gi~e a ~urface area ranging from 1.4 ~o 1.7 m2~g and a particle si~e dis~ribution of 90~ point 5.9 6.2 ~m 50~ poin~ 4.0 - 4.4 ~m 10~6 point 2 . 2 - 2 . 7 ~m Alumina E: Showa AL-45-A aluminu~ oxide ~A1~03) wi~h a ~urface area of 3.1 ~2/g and a particle ~ize di~tribution of - 90% point 2.5 ~m 50~ point 1.0 ~m 10% point 0.4 ~m Pigment: Cobalt aluminate (CoA1204).

B. PolYmeric Binders Copolymer of 9B~
methylmethacrylat~e, 2%
methacrylic acid M~ = 25~, acid No. 9, inherlent vi6co~ity* 0.183 ~f 0 . 011, T = 106C
g copolYmer of 95.5%
methylmethacrylate, 4.5%
ethyl a~rylate, ~ = 50M, Tg = 96CC, inherent VlscO6i~y 0.399 ~ 0.~11 (*) Inherent vi6c06ity of a solution that con~ains 0.25 g polymer in 50 ml o~ methylene chloride : measured at 20C u~ing a No. 50 Cannon-Fen6ke vi~cometer.
C. Monomer~
~EOTA 1000: Polyoxyethylated ~rimethylolpropane ~: tri~acrylate: Mw = 1162 ' ;
,: ' .: :: .
., ~ , , 57~

Chemlink( )176: E~hylated pentaerythritol triacrylate (Sartomer) Mw = 326 D. Pla~ticizer~
Dibutylphthalate Santicizer( ~ 261 Alkyl Benzyl Phthalate E. Initiator6 ~i~hler'~ ketone: 4,~'-bi~-N,N-dime~hyl-aminobenzophenone Benzophenone Irgacure( )651: benzil dimethylketal F. Others Re~olution and Exposure Latitude Improvement Di-t-bu~ylmethane nitroso dimer ~ntioxidant lonol~ ): 2,6-di-t-butyl-4-methylphenol Coatin~ Aid Polyox ~) WSRN-3000 Polyethylene oxide;
~ = 200M

Prepara~ion of Dielectric Film~
A~ Preparation of Mill Ba6e All of the ceramic component~, glass frit, alumina, pigment and any other inorganic ~aterial are mixed with copolymer of methylmethacrylate~me~hacrylic acid (98/2) and/or AB di&persant combined with ~ethylene chloride. The mixture i ball mill~d in a mill jar half-filled with burundum Salumina) cylinders 0.5 inch (1.27 cm) in both diameter and length for 4 to 16 hour6. The dispersion i8 filtered through a 325-mesh screen or a 20 ~m dep~h filter.
The fil~ered dispersion is ~tirred or iar-rolled until coated.

. "
: ' ~ '` ~ ' ' ~.

~2~25~

B. Pceparation of Coating DisPersion The percent ~olid~ i~ determined in order to calculate the amount of other component6 to be added. After all the additional component6 are put in ~olution, exces~ solvent is removed by mechanically stircing the dispersion in a ~ented area and allowing solvent to evaporate until a visco~ity of 700-900 cps, is reached a~ determined with a Brookfield vi~cometer using a #6 sp;ndle a~ 40 rpm.
The disper6ion i~ filtered ~hrough a 325-mesh screen.

C. Coa~inq Proceduce The di~persion is extrusion-die or knife coated onto a polyethylene terephthalate film ~upport. The film is pas~ed through an air impingement hea~er at 95-175F ~35-79C) before it is wound up with a polyethylene cover6heet.

D. Proce~6 Condition~
Care is taken ~o avoid dirt contamination in the proces~ of pre~aring coating compo~ition~ and in preparing dielectric parts ~ince such contamination can lead to defects in the fired dielectric. The process work i~ prefecably done in a cla~s-100 clean room. The film iB laminated to degreased alumina part6 that contain a fired conductor pattern. The parts are degreased ultra60nically in Chlocothene (l,l,l-trichloroethane) and baked in a vacuum oven at 50-100C to remove the degrea6ing ~olvent. The film is laminated with a vacuum laminator, or hst~roll laminator, manufactured by We~tern ~agnum Co..
Hermosa Beach, C~ with roll6 covered with neoprene rubber having a Durometer rating of 50 when heated to the lamination temperature of 100-110C. ~he Durometer rating i~ an arbitcary scale which denote~

~l26Z~76 cesistance to penetration. The film i5 laminated to ~he part at a ~peed of 0.5-l.0 ft (15.2-30.5 cm)/min. More than one pa6s through the laminator can be used to as~ure better adhe6ion and conformation around copper metallization~.
The part6 are exposed with a ~ollimated HTG( ) UV exposure 60urce aftar a 60-sec nitrogen purge or vacuum draw-down. The optimum exposure time is de~e~mined from an exposure ~eries ~hat indicate6 the best expo~ure to yield the co~rect &ize via~ or photofo~med holes in the dielectric after development.
The exposed pacts are developed using a spin developer using a ~-8 sec, 50 p~i spray of chloroth~ene developer with the part ~pinning at 2$00 rpm, ~ollowed by a 2-lO ~ec air stream at 50 p6i to dry the part.
The developer i~ sprayed perpendicular to the ~pinning part. A flat-spray jet pattern wa~ obtained with a 0.125 in (0.31B cm) JJ air atomizing nozæle from Sprayin~ Sy~tems Co., ~heaton, IL with setup J23 a~ described in Industrial Catalog 27. The solvent flow may be 50 to 2000 mL/min, preferably 300 mL/min. The nozzle-to-part di6~ance may be 0.5 in (1.27 cm) to 8 in (20.35 cm) with a typi~al distance being 1.5 in (3.~1 cm).
~5 The developed part~ are dried in a forced draft oven at 75~C for 15 min and fired in a fuLnace with peak temperature of 900C to 950C over a two-hour cycle. In firing the composition of the invention, they are expo6ed to a 6ub6tantially nonoxidizing atmo6phere up to the gla~s tran~ition ~emperature of the inorganic binder and to an eaaentially comple~ely nonoxidizing atmosphere during ~he 6in~ering pha~e oE the fir~ng s~ep.
~y the term "6ubs~antially nonoxidizing atmo~phere" i6 meant an atmo~phere which contaln~

, :
.

?~62~
3~
insu~ficient oxygen to effect any ~ignificant ~xidation of copper metal, but which neve~thele~s contains ~ufficient oxygen to effect oxidation of the organic material~. In prac~ice, i~ has been found that a nitrogen atmosphere of 100-1000 ppm 2 i~
appropriate in the ple6intering phase of the firing ~tep. From 300 to 800 ppm 2 i8 pref erred O The amount of oxygen i6 increased as the thickne~s of the dielectric layer increases. Por one layer of dielectric film that fire~ out to 25 ~m, 100 to 400 ppm 2 i6 fiufficient. For two layer~ of dielectLic film that fires out to 50 ~m. 200 to 800 ppm 2 i~
preferred. On the other hand, the essentially completely nonoxidizing atmosphere used during the lS ~la~6 ~intering 6tep of the firing 6tep refers to a nitrogen atmosphere ~ontaining only re~idual amount6 f 2~ e.g., about 10 ppm. It i~ preferred to fire the compo6ition oP the invention at low heating rates in order to minimize phy6ical defect~ in the fi~ed layer.
The fired par~ are te6ted for hermeticity by determining the wet di~6ipation factor ~DF) by application of water on top of capacitor6 made therefrom. The capacitance (K) in pi~ofarad~ i~
measured and the relative dielectric con~tant i~
calculated. The capacitors are compri6ed of an underlying copper metalliza~ion, 40-50 ~m thick fired dielectric, and an overlying copper metallizati~n.
The complete dielectric 6tructure can be obtained by firing the underlying and overlying layer6 individually, or by cofiring the complete ~tructure. A top layer film optimi2ed for le~s light ab60rption than the bottom layer can be used ~o that adequate light penetration ~hrough the bottom layer ~2~576 i~ obtained. This allows formation of vias with vertical sidewalls. ~lter~atively, the fir6t layer of dielectric can be exposed but not developed before the second layer is laminated ~hereon. Then, after the ~econd layer is laminated and exposed, both layers are developed simultaneou~ly.
Using the above-described component~ and procedures four different photosensitiYe dielectric films were prepared having the compositions indicatea in Table 1 be~ow:

~5 12~2s76 Table 1 - Composition and ProDertie6 of Films Film Desianation A B
Mill Base (g) S Glas~ Frit A 231.43 75.0 Alumina ~ 128.57 50 Cobalt aluminate 0.34 0.12 Copolymer of 98/2 17.3 6 methylmethaccylate/
methacrylic acid (Mw=
25M; Tg 105C, acid #9) Methylene chloride230.5 80 Glas6/alumina, ratio, wt. 1.8 1.5 Drv Film (wt. %) Glas6 Frit A 47.64 44.46 Alumina A 26.46 29.64 Cobalt aluminate 0.07 0.07 Copolymer in Dispersion 13.43 13.43 Dibutylphthalate 5.75 5.75 Ethylated pentaerythritol 5.75 5.75 triacrylate Polyoxyethylated trimethylol - -propane triacrylate Benzophenone 0.75 0.75 Michler 1 6 ketone 0.05 O.OS
Di-t-butylnitroso 0.10 0.10 methane dimer Benzil dimethyl ketal - -Table 1 - (continued) Film Desiqnation C D
Mill Base (g) Glass Frit A 231.43 216 Alumina A 128.57 144 Cobalt aluminate 0.3~ 0.3 Copolymer of 98/2 17.3 17.3 methylmethacrylate/
methacrylic acid (Mw=
25M: Tg 105C, acid #9) Methylene chloride 230.5 230.5 Glass~alumina ratio, wt. 1.8 1.5 r~ ~ilm (wt. %) Glass Frit A 47.64 44.46 ~lumina A 26.46 29.64 Cobalt aluminate 0.07 0.07 Copolymex in Dispersion 12.43 13.43 DibutylphthalatQ 5.75 5.75 Ethylated pentaerythritol - -triacryl~te Polyoxyethylated t~imethylol 5.75 5.75 propane triacrylate Benzophenone 0.75 0.75 Michler' 6 ketone 0~05 0.05 Di-t-butylnitroo 0.10 00.10 methane dimer Benzil dimethyl ketal1.00 Fil~s 1 through 4 were 1.8 mils (45.7 ~m) ~hick unfired.
and 1 mil (25.4 ~m) ~hick fired.

,:...~. ,,:, -`~

:,, ' .

~:6~;7~

3~ ;
~XAMP7~ES 1 AND Z
example~ 1 and 2 illu~trate the difference in ad60rption properties between a porous and a nonporou~ layer.
In Example 1, Film A was laminated ~o a degreased, 3'tx3" 96.5% alumina sub~trate, exposed overall, developed, and fired. ~or Ex,ample 2, Film B
was laminated to a deglea6ed, 3"x3" alumina ~ub~trate, exposed overall, developed, and fired. Proce~6 conditions used for the ~abri~ation p~ocedure were as follow~:
Lamination: Substrates preheated to 105C, 110C roll-lamination at 0.5 ft~min Expo6ure: 60 ~e~. exposure in HTG( ) expo~ure unit Development: l,l,l-tcichloroethane ~prayed on part spinning at 2500 rpm for 6 ~ec. followed by a 2 6ec. air stream for drying Oven drying: 75C for 15 ~in Firing: Nitrogen belt furnace with les6 than 1000 ppm oxygen: peak tempera~ure 900C, 2 hr. ~ycle.
Gas flow was 315 cu ft/hr. -The fired film of Example 1 did no~ vi6ibly ad~orb ink, indicating a low degree of porosity. The fired film of xample 2 ad60rbed ink, indicating a high degree of poro6ity.

:

2S~6 Example 3 illu~trates a dielectric formed fro~ a porou~ layer over a nonporou~ layer. Example

4 illu~trate~ 3 dielectric formed from a nonporous laye~ over a po~ou~ layer. The performance of the two dielectric ~tructures i6 compared.
For ~xample 3, a multilayer s~ructure wa~
fabricated on a degreased~ 3"x3" 96.5% alumina substrate by laminating, exposing overall, developing and firing F;lm A; laminating, exposing ove~all, developing and firing Film B; and laminating, imagewi~e expo~;ng, developing and firing a pho~o~e~-~itive conductive copper film compo~ition.
For Example 4, a multilayer 6tructure was fabricated on a degrea6ed, 3"x3" 96.5% alumina ~ub~rate by laminating, expo~ing overall, developing and iring Film B; laminating, exposing overall, developing and ~iring Film A; and laminating, imagewi6e expo6ing, developing and firing a photosen-sitive conductive copper film compo~ition.
The proces6e6 for applying Film6 A and 9 area6 given in Example~ 1 and 2.
The compo~ition of the photosen~itiYe conductive copper film compo~ition i~ given in Example 6 of U.S. Patent 4 598 037, of J.J. Felten, granted 1986 July 01.
Lamination, expo~ure, development and drying conditions are the ~a~e a~ for Film6 A and B.
The copper compo6ition was ~ired under the same condition~ a~ Films A and B, with the exception that the oxygen c~ntent of the furnace atmo6phere wa6 reduced to les~ than 500 ppm. The copper image covered about 30~ of the dielectric 6urface: thi~
image cons;6ted of a ~arieey of lines and ~quares.
~5 No bli6tering of the copper metallization wa~ pLe~ent ~pon eithe~ multilayer upon completion.

~9 , :

~L2~7~

4~ i ~owever, after four refires the multilayer of Example 3 wi~h the nonporous botto~ layer showed more than 25 copper bli~ters. The multilayer of Example 4, with the porous bottom layer, had no copper blisters after 10 refires.

XAMPI.E 5 Example 5 demonstra~es that the electrical performance of the dielectric structu~e does not degrade with refiring.
Films ~ and B were fabricatecl into fou~
capacitors by laminating, imagewise-exposing, developing, drying and firing Film B atop a copper conductive metallization; laminating, imagewise-lS exposing, developing, drying and firing Film A atopthe fired Film B; and imaging and fieing upper conductor copper metallization.
The proce6se~ for applying Films A and B are as given in Examples 1 and 2. The processe6 for applying the upper and lower conductors are a~ given in Examples 3 and 4.
Upon completion, no copper nor dielectric blistering appeared in any capacitor. Upon eight refires, ~o copper nor dielec~ric blisterin~ appeared in any CapaCitOL.
Upon completion, the highest wet DF of any capacitor was 0.4%, with the average wet DF being 0.~5%. Upon eigbt r~fires to 900C in a 6ubs~antially nitrogen atmo~phere, each of the four capacitor6 had a wet DF of 0.2%.

E~AMPLE 6 Exa~ple 6 illustrate~ tha~ structures with nume~ous layers can be fabricated withou~ blister6.
Example 6 also illu~trates that the inve~ion operates with various conductor elemen~6.

~' ' ~ ' ' . :
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~L~625~

A ten-layer structure was fabricated on a l"xl" 96.5~ alumina ~ubstrate by this method. Copper was applied and fired overall. The following ~equence of ~teps was then repeated three time6 to complete the multilayer: laminate and fire Film D
overall, laminate and fire Fil~ C overall, apply and fire copper metallization overall.
Dielectric la~ination condit;ons were a~ in ~xamples 1 and 2. There wa~ no exposure nor development. Firing conditions for the dielectric were as in Example~ 1 and 2. The fir~t and ~hird conductor layerz were photosensitive conductive copper film composition, laminated and fired as de~cribed in Examples 3 and 4. The second and fourth conductor layers were 6creen-printed copper paste composition, f;~ed to 900C in a belt furnace with a nitrogen atmosphere containing less than 10 p~
oxygen.
NeitheL copper bli~tering nor dielectric blisterin~ appeared in any layer of the multilayer struc~ure.

EXAMPLES 7 and 8 The6e examples show the utility of a thin, porous bottom layer in preventing blisters from occurring in the fired dielectric.

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~2~ 6 ~2 Table 2 ComPOSiSion and ProPerties of Dielectric kilm6 Film ~esiqnation E F
_ ~ill Ba~e ~g) Glass frit B 1708 51.47 (f2857) Alumina ~ ' 1552 ~I252~) Alumina ~1~2 73 53 (I2528 settled) Cobalt aluminate 3.08 0.12 - Du Pont Elvacite~ ) AB Di6per6ant (RCSF-5123~
MW=10,400 =5,600 13.76% by weigh~ in 6~0.5 8 to 1 methylene chloride/toluene 59.0~% by weight in - 5.72 toluene Methylene chloride 1275 ~0.0 GlassJalumina ratio 1.1 0.7 (by wt.) 1 sample baked in air at 550C for 24 to 56 hr6 to remove carbonaceou6 contaminant6 6ample wet, ~agnetically separated 3 USP 4032698 Formula 1 where Q i6 polymethyl ~ethacrylate The re6t of the organic components were di~solved in methylene chloride and filtered through a 1 ~o 2 ~m filter. For Pilm ~ all but the copolymer and ~2 , 2~;~6 ~ 3 polyethylene oxide solutions were rotary evaporated ~o dryness be~ore added. For Film F a stock solution of all the components ~o be added except for the polyethylene oxide was used.
F i Is De~i~n-J: j~ E F
Dry Film (w~
Glass frit 38.76 30.46 Alumina 35.2~ 43.51 Cobalt aluminate0.07 0.07 AB Dispersan~ 2.0 2.0 Copolymer of 95.5% 10.53 10.39 methylmethacrylate ~.5% ethyl acrylate~
M =50M, T =96C
30.6% by wt. solution in methylene chloride Polyoxyethylated4.60 4.67 t~imethylol Propane triacrylate MW=1162 Dibutyl phthalate3.75 3.~0 San~icizer(3)261 Alkyl 3.80 3-~4 benzyl phthalate (~onsanto) ~ichler's ketone0.05 0.04 Benzophenone 0.75 0.78 di-t-butylnitrosomethane 0.10 0.10 dimer ~onol(5) 0.20 0.19 Polo~ SRN 3000 0.15 0.15 polyethylene oxide 1. a4% by wt. Bolutio~
in me~hylene chloride .
. .;

For Film F an aliquot of a stock 601ution was used having the following composition:
q, Copolymer in Film E 216.0 Polyoxye~hyla~ed trimethylol 97.1 propane triacrylate MW=1162 Dibutyl phthala~e ~8.9 5anticizer(3)261 B0.0 Michler's ketone 0.89 Benzophenone 16.07 di-t-butylnitrosomethane d;mer 2.14 Ionol(~) 3.g3 ~ethylene chloride ~oo The mill base for Film E was jar rolled in a 2.3 gal (8.81) mill jar containing 19.55 lb6. (8.87 20 kg) burundum cylinders (0.5 in, l.Z7 cm) for 16 hr~.
at 48 revolutions per minute. The mill base for F;lm F was jar rolled for 16 hrs. at ~0 ft. $24.4 m) per minu~e in a 237 ml mill jar containing 242 g of 0.5 in (1.27 cm) burundum cylinder6).
The dispersions were mechanically stirred with a stream of nitrogen over the container to remove exces6 methylene chloride to obtain a vi~co~ity of 700 to 900 Cp6, a determined with a Brookfield vi6cometer. The difiper6ion6 were filtered through 20 ~m depth filters and stirred 810wly overnight to remove air from the dispersion. Pilm E

~%~x~
~ 15 waa e~stru~ior~ eoate~ to a tblckne~ of 1. 8 mil~
(0.0046 ~R) and 1.5 ~ 0.003~ ~m) on 1 ~ 0.0025 c~ silicbne-treated polyeehylene t~rephthalat~ and on 0 . 5 ~ 0 . 0012 c~ polyethylene ee~ephthal~te .

5 The fil~a ~a~ dri~d iLn th~e~ a f~ (2.q4 ~ lorlg d~ye~
zone6 wi~h the fiirst 20n~ at 120P (~I~.g~C), the ~econd zone at 1~0~ (60-C) al~d th~ thlrd ~on~ ~It ~00F (93~3C)o Tbe COdltiD9 s~eed ~a~ 25 ft. (7.62 m) p~r ~inute. ~he 1.~1 loil (O.Oû4~ c~ thi~k f~l~ o~
10 the two different ~upport 1~heet8 were lalainat~d to~ether ~t 7 . 62 al~inute at 60 psi ~4 . 2 kg/c~n2) at 150F 65.6C). Fi~ F ~æ~ coated on ~ Talboy~ coat~r on q~S Myl~r(a~ 10.48 ~ 0.0012 c~) polyethylene tsreph1:halate fil~ 3t 6 fe (1.83 cm~/mln with a 2.0 15 1 0.005 cl~) doctor knife to g~Ye ~ thickne~ of 0 ~ 6 ~ 0 . 0015 CDI~ . The ~e~eratule~ of zon~s 1 and 2 we~ 35C and 71C, re~pe~tively.
Por E:xar~pl~ ilm E that ~a~ 3.6 ail~
(0.0091 em~ th~ck wa~ lalainated at 1 ft/a~n with a 20 hot ~ol~ lar~inator to ~ ~ir~d 2 ~ c 2 1~ ~5.0~ ~m x S.05 c~) copper conductor layer at 1050C which, wa~
prepared from a copper fil~ !18 ael~eribed il~
U.s. Patent 4,598, 037.
: . . . The part~ w~re expo~ed 40 se~ wi~ a~
25 HTG~7~ W sou~ce and ~evelopea ~-10 ~8C in ~ spl~
de~teloper wi~h c~loroth~ne. The parts w~re irea a~
4 peak ee~per~tu~e of 950C oYer a two houl: cycle.
The f ~re~ d~electri~ containea 27~7 bl~ter~ per par~. Th~6 co~trol indi~ateE; ~he propenaity of the 30 ~lngle ~o~po~ition to give bli~eer~ when ~lred ov~r ~opper .
E`or Example 8, P`ilm ~ waE; lar~inat~d ~:o t~o ~ayer~ of 1.5 ~il thielc ~lm ~ all of which wer@ ho~
roll lar~nated together at 105~C ~t 1 tS~ he 35 cover6heet ~ttached to Filal F ~da~ Ee~oved and thi6 ~5 , : ., . .

2S7~

was laminated to f ired copper parts as descr;bad above . When this three layer composite was f ired as the two layer composite of the ~ame composition, only 0. 3 blisters per part were obtained, i.ndicating t~e utility of the thin, porous bottom layer.

Thi~ example demonstra~es excelleDt hermeticity of 50 llm f ired dielectric comprised of two ~op layer~ of the same compo~ition over a thin, 10 porous bottom layer in accordance with the invention.

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~3L;24~257~

rrable 3 comPosition of Dielectric Film Film Desiqnation G _H _ Mill Base (g~
Glas6 frit of Film E 62.~ 51.47 Alumina of Film E. but62.5 73.53 not baked at 550C
Cobal~ aluminate 0.12 0.12 AB Dis~er~ant of Film E 14.37 14.37 23.52% in 3.7 to 1 methylene chloridettoluene Methylene chloride 69.0 69.0 ~he di~per~ion was mill.ed and filtered a~ Fil~ F.
Dry Film (wt. %) Gl~s6 ~rit 37.00 30.47 Alumina 37.00 43.53 Cobalt aluminate 0.07 0.07 AB Di~per6ant 2.0 2.0 Copolymer of Film~ E and F 10.45 10.45 30.0~ wt. % i~
methylene chloride Polyoxyethylated 3.06 3.06 t~i~ethylol ~ropane triacrylate ~W=1162 Dibutyl phthalate 4.62 4.62 Alkyl benzyl phthalate 4.62 4.62 of Film E
Michler ' 6 ketone 0.04 0.04 Benzophenone 0.76 0.76 di-t-butylnitrosometha~e 0.04 0.04 dimer : .

:,:

~2 Ei2576 Table 3 (continuedl Fil Desiqnation _ G H _ Mill Base (g) Ionol( ) 0.19 0.19 Polox~ ) WSRN 3000 0.15 0.15 Dispersions G and H were coated on a Talboy6 coater as Film ~ bu~ with G coated to a dry thickne6s sf 1.5 mils (0.0038 cm) with a 4.5 mil knife on 1 ~il (0.0025 cm) polyethylene terephthala~e. Two layerR
of G were laminated together after removal of the polyethylene coversheets. A layer of H was lamina~ed to thi~ co~posite after removal of the polyet.hyl2ne coversheet of H and one of tbe polye~hylene terephthalate coversheet~ of G. The lamination6 were done with a hot roll laminator at 105C at 1 Et (30.S
cm)/min. The three layer film was vacuum laminated at 105C with a Du Pont Vacrel( ) SMVL-100 vacuum laminator after a 45 sec draw-down to preheated parts that were previou~ly cleaned in an ultrasonic bath containing methylene chloride. The parts contained a fired ~creen printed conductor pattern of Du Pont ~hi~k f ilm 9924 copper ~aste. The part~ were exposed 60 sec with an HTG( ) Bour~e a~ 16 ~w/c~ and spin developed for 9 ~ec in chlorothene. After a 15 min bake-out in a 75C fo~ced draft oven the parts ~ere fired at 1.7 în (4.3 c~)/min with a peak temperature of 950C. The paLt6 were te6ted in the EMR (Electro ~igration Resi&tance) te~t to dete~mine the her~eticity oP ~he dielectric over the copper pattern. A leakage current of 4.4~0.7 ~m/cm2 wa6 obtained wi~h a 10 volt DC current u~ed in the te6t, None of the parts had any visible leaks with examination under a micro~cope when the dielectri~

:
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"
: ' :

" ., . '- .: . ':

~ 9 surface wa~ covered wit~ 1 N ~odium chloride ~olution and a 9v battery connected to the tab of the underlying copper layer and ~o ~he wet dielec~ric ~urface. Minor ~urface defect~ of 0.1/cm2 were obtained w;th an average ~i2e of 0.5 mil but none cau~ed any leaks to the copper layer.

ExamPl e 10 This example ~how~ low leakage current, high insulation resistance and high breakdown vol~age for two mil thick fired dielectric containing a porous bottom layer.
Table ~
Preparation of Dielectric Film Film Desiqnation I_ J__ Mill Ba~e (g) Glass frit of Film Efi2.50 51.47 20 Alumina ~f ~ilm G - 73.53 Alumina C 62.50 Cobalt aluminate 0.12 0.12 AB Dispersant of Film E
23.5~ in 3.7 to 114.38 25 methylene chloride/toluene 59.04 wt. % in toluene - 5.72 Methylene chloride 69.0 80.0 The disper~ions were milled and filtered as Film F. Aliquots of 1-2 ~m ~iltered 6tock solution of ~he same composition a6 in Film ~ were u&ed. Por I a 1.9~ wt. S solid~ 601ution o~ Polyox(~) ~S~N 3000 in methylene chloride was used and for J a Z.38 ~. %
solid~ solution wa~ used.

~2~2~7~

Both Polyox~ 3 ~olution~ wer~ prefiltered through 1-2 ~m filters.
Film Desiqnation I J _ Dry Film (wt. %) Glass frit 37.00 30.46 Alumina 37.00 43.51 Cobalt aluminate 0.07 0.07 lo AB Dispersant 2.00 2.00 Copolymer of Film E and 10.38 10.39 and Film F
Polyoxyethylated 4.66 4.67 trimethylol propane tria~rylate MW=1162 Dibu~yl phthalate 3.79 3.79 Alkyl benzyl phthalate 3.84 3.85 of Film E
Michler'~ ketone 0.04 0.04 Benzophenone 0.7a 0.77 di-t-butylnitrosomethane 0.10 0.10 dimer lo~ol(~) O.lg 0.19 2S Polox~ ) WSRN 3000 0.15 0.15 Part6 ware prepared as with Example 9. The EMR parts gave leakag0 current~ of 11~1.8 ~AJcm .
Another serie~ of EMR part~ were prepared but a top copper pattern~ the same afi the underlying pattern was applied ~o ~hat the tab6 were 90 ~o each other.
The ~ame thick ~ilm copper pa~te and firing were u6ed f or ~hi~ top conductor layer. The in~ulation resiStance at 100 volt~ for these 50 ~m part6 was 4.5~0.9 x 10 X ohm~. The dielectric constant was 7.8~0.1. The breakdown voltage was 2300~700 ~ol~s.

::

~. ~

5~6 Example 11 This example shows ~he utility of a high glas~/alumina ratio top layer over two layer6 of the composition in Example 10 which improves hermeticity and gives a ~moother surface.
Table 5 CQmPOSitiOn Of Dielectric ,Film Film Desianation K _ Mill Base (g~
Glass frit A 113.64 Alumina of Example 9 11.36 Cobalt alumina~e 0.12 AB Diæpersant of Film E 4.14 65.2 wt. % in toluene Methylene chloride 80.0 The di~per6ion was milled and filtered a6 in Film F.

~5 .

.

i Table 5 continued Film Desiqnation K
Dry Film (wt. %) Glass Frit 62.41 ~lumina 8.32 Cobal~ aluminate 0.07 AB Di6per~ant 1.53 Copolymer of Films E and F12.04 Polyoxyethylated 5.38 trimethylol Dropane triacrylate M~-1162 Dibutyl phthalate 4.36 Alky} benzyl phthalate of 4.42 Film E
Michler's ketone 0~05 Benzophenone 0.58 Di-t-butylnitro60methane 0.12 dimer lonol(5~ 0.22 Polyo~t ) WSRN 3000 0.20 The diRpersion was coated with a 1.5 mil doctor knife to yield a dried ~ilm thickne~6 of 1.2 mil6. The Talboy~ dryer zone~ were 38C and the film wa~ coated on a ~ilicone treated polyethylene terephthalate cover~heet. Part~ were prepared as i~
~xample 9. Film K wa6 laminated to Fil~ I. A ~hird layer of Film J was laminated to the layer of Film I. The cover~heet of Film J was removed and ~hi6 compo~ite film wa~ laminated to part~, expo~ed, .
., ~" ' ., ' ~2~25~

developed and fired a6 de~cribed in Example 9. The leakage current in the EMR test was Z.4+0.9 ~Afcm .
The center line average ~urface roughne~s over copper using a Dektak IIA ~urface analyzer was 16.B+l.O ~in 5 ~4275A) for the resultant high gloss surface. The ~urface roughness for Example 8 was 26.6~2.9 ~in (6770A~. This compari60n 6howg the effect on surface roughness of the high glas~/alumina ratio film of the composition in Table 5.
Exam~les 12 and 13 The examples show that compositions L over M
of Example 12 do not bli~ter when fired over copper where a~ film of Example 13 does. Thi6 demonstrate~
that the thin, porou~ bottom layer is also effective in retarding bli~ter6 in dielectric that fires out to 25 ~m.
Table 6 ComPO6itiOn of Dielectric Film for Example 12 Film Desiqnation L_ M
Mill Base (g) ~las frit A of Film K 1723 1169.7 with 0.5 wt. ~ of Yg893 silane (Union Carbide~
~lumina D with 0.5 wt. % 1435.3 1671.7 Y98B3 ~ilane ~Union Carbide) Cobalt alumina~e 2.91 2.h ~B Di6persant of Film E 33.1 29.8 3~ 5906 wt. % in toluene Methylene chloride 1769 1592

6~76 Table S - continued Film Desi~nation L M_ Dry Film (wt. %) Glas6 Frit 41.45 31.29 Alumina 34.55 4~,7~
Cobalt aluminate 0.07 0.07 AB Di~persant 0.48 0.4R
10 Copolymer of Pilms E and F 11.0211.02 Polyoxyethylated 4.25 4.25 trimethylol Dropane triacrylate MW=1162 - Dibutyl phthalate 3.50 3.50 15 Alkyl benzyl ~hthalate ~.50 3.50 of Film E
MichleL'~ ketone 0.04 0. 04 Benzophenone 0.70 0.70 20 Di-t-bu~ylnitro60methane 0.10 0.10 di~er Ionol~ ~ 0.18 0.18 Polyox( ) WSRN 30000.16 0.16 Bth L and M disper6ion6 were ball milled 4 hrs. at 50 revolution6 per minute a6 Film E.
Di~persion M was extrusion-die coated at 80 ~t (24.4 ~)~min to a dry thickness of 0.6 ~il S0.0015 cm) from a di~per6ion ~i~c08ity of 730 centipoi~e on ~ilicone treated polyethylene ~erephthalate. The first dryar zone was 43C and the third wa6 93~C. The 6econd zone was at room temperature. Di~per6ion L wa6 coated a~ M on 0.48 mil ~0,0012 cm) polyethylene terephthalate at a dry film thickne~ of 1.2 mil~
:

''; ~

:
:

~625~

(0.0030 cm) with the ~ame drying temperature in ~he f ;r~t zone as for Film M but at 104C in the third zone . The f ilms were laminated togetlle~ a'c 65 . 6C at the coating 6peed of 80 ft ~24.4 m)/min at 60 psi (4.2 kg/cm ). The compo~ite film was laminated with underlying, expo6ed 20 sec and deve;Loped ~nd fired a~ Example 7 to yield fired dielectric wi~h 0.1 blister6 per cm and a leakage current of 26+14 ~Atcm . The dielectric ~hickne~6 of 25 ~m i~ more 10 prone ~o dirt and copper related defect~ than 50 ~m dielectric of previous example6. The ;mportance of ~he thin porou~ bottom layer is eviden~ with EMR
pa~t prepared entirely wi~h Pilm N for Example 13.
- The fired part~ had 2.4 blisters/cm2 and a leakage current in the ~MR test of 316 ~cm .
Table 7 PreParation of Di lectric Film for Example 13 Film Desiqnation N _ 20 Mill Ba~e (g) Gla~6 fri~ C with 1709.4 0.5 wt. % of Y9883 silane (Union Carbide) Alumina D with 0.5 wt. % 1554 Y9883 6ilane (Union Carbide) Cobalt aluminate ~.o AB Dispe~sant of Film E 39.9 51.25 wt. % solid~ in toluene 30 Methylene chloride 1827 3~

-~2~2~;~76 Table 7 - continued . .
Film Desianation N
Dry Film (wt. %) 5 Glas~ Fri~ 39.81 Alumina 36.19 Cobalt aluminate 0.07 A8 Dispersant 0.48 Copolymer of Films E and P 11.00 Polyo2yethylated 4.25 ~rimethylol propane t~iacrylate MW=1162 Dibutyl phthalate 3.50 Alkyl benzyl phthalate 3.50 Michler'~ ketone 0.04 Benzophenone 0.70 Di-t-butylnitro~omethane 0.10 dimer Ionol~s) 0.18 Polyox( ) HSRN 3000 0.16 The disper6ion was prepared a6 Film E. The di~persion visc06ity wa~ 730 cp6 before coating and the wt % solids was 67.9%. The film was coated as Film E ~o a dey thickne6~ of 1.8 mil6 o~ 1 mil (0.0025 cm) polye~hylene terephthalate ba~e.

ExamPle 14 Thi example ~hows that hermetic 15 ~m fired dielectr;c can be obtained with a ~wo laye~
dielectric film containing a high glass/alumina ratio top layer or an all gla~s top layer (with no alumina) and a thin porou~ bottom layer.

:.

"~

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~2~S~i Table 8 Composition Of ~ielec~ric Film Film Desianation 0 P Q
Mill Base (g) Gla~ frit of Film E 113.~51.47 125 but not 550C baked Alumina E Showa AL-45-A 11.36 - -Alumina of Film F but - 73.53 550C baked Cobalt aluminate 0.12 0.120.12 AB Dispersant of Film E 5.32 5.32 5.32 63.5 wt. ~ of solids in - toluene Methylene chloride 6a .168.1 68.1 ~: ~
, ' ;~' ' '' :

i ~8 Table 8 - continued Film De~iqnation Q Q
~E~ m wt. %) Glass frit 63.6428.82 70.00 Alumina 6.364l1.18 Cobalt aluminate 0.070.07 O.C7 AB Dispe~sant 1.~91.89 1.89 Copolymer of 12.2412.24 12.24 Films E and F
Polyoxyethylated 3.593.59 3.59 trime~hylol ~ropane ~riac~ylate MW=11~2 Dibutyl phthalate 5.415.41 S.41 Alkyl benzyl phthalate 5.41 5.41 S.41 Michler'~ ketone 0.050.05 0.05 Benzophenone .O.B90.89 0.89 Z Di-t-butylnitrosomethane 0.05 0.05 0.05 dimer IOnOlts) 0 ~ 0.2Z 0.22 Polyox( ) WSRN 30000.170.17 0.17 ..
:

.

F'or Films 0, P, and Q, aliquots of 1-2 ~m filtered 6tock solution was used having the following compo~ition:
(~ ) Copolymer of Film E 216 Dibutyl phthalate ~5.48 Alkyl benzyl phthalate 95.48 Polyoxyethylated 6~.25 trimethylol propane triacrylate M~=1162 ~ichler's ketone 0.83 Benzophenone 15.72 Ionol(~) 3.92 Di-t-butylnitrosomethane dimer0.83 Polyox( ) ~SRN 3000 3.10 Methylene chloride 852 The di6persions were prepared as Film P and coated as Film F with Film 0 coated on 0.48 mil (O.Q012 cm) polyethylene terephthalate with a 1 mil ~0.0025 cm~ knife to a dry film th;ckne~6 of 0.5 ~il (0.0012 c~). Film P wa6 coated on 1 mil (0.0025 cm) polyethylene terephthalate to a dry film thicknes~ of 0.6 mil ~0.0015 cm) with a 2.0 mil (0.005 cm) doctor knîfe. Film 0 wa6 hot roll laminated to Film P ~t 105C a~ 1 ft (30.5 cm)/mi~ and the coversheet of Fil~ P removed and the compo~ite film vacuum laminated to fired 9924 thick film copper EMR
pattern~ as in ~xample 9. The part~ were expo6ed 60 ~,~6;2,5~

sec and developed 8-10 ~ec and fired a~ Example 9 to give 2 part~ with a leakage current in the EMR te~t of an average of 2.5 ~A/cm and one part ~ha~ had a leakage current of 161 ~A/cm due to defect~ that are more prevalent in thinner dielectric a~ de~cribed in ~xample lZ. The ~urface roughnes~ over copper a8 determined in Exa~ple 11 wa~ 21.6~2.4 ~ in (5,500A~.

ExamPle 1~5 Film Q wa~ coated as Film 0 but to a dry thickne~6 of 0.75 mil ~0.0019 cm). Film Q ~a~
laminated to Film P and expozed, developed and fired a~ described for Example 14. The leakage current was 6.6 ~A/cm for one part but another paL~ with vi6ible de~ect~ had a leakage cu~rent of 94 ~A/cm . Thifi example 6how~ that a top layer containing no alumina can yield hermetic dielectric but the parts arQ
6u~ceptible to defect6 resulting from dirt contamination in the layer~.

Example 16 A bottom layer containing a higher melting glas~ frit, F2860 with a Tg of 655C compared to 590C for the glas6 frit of Film E and a eoftening point of 720C compared to 660C for the gla~ frit of Film E can be used az a thin porou~ bottom layer to retard bli~ers even though the volume glas6/alumina ratio i6 higher in the bot~om layer than in the ~op layer. In the previou6 examples the bottom porou6 layer ~ontained lower volume gla~s/alumina ratio than the tvp layer.

Table 9 Composition of Dielectric Film DisPersion Desiqnation Rl R2 ~ill 8ase ~g) Glas6 frit D 125 Alumina of Film O - 125 Cobalt aluminate 0.12 0.12 ~B Di~persant o Film E 13.83 13.83 24.4 wt. ~ in 3.5:1 methylene chloride:toluene Methylene chloride 69.5 69.5 Rl and R2 were milled a~ Film F. Aliquot6 of each were mixed to achieve a 1.3 glass/alumina weight ratio. 56.15 g of Rl at 59.59 wt % solid6 wa6 mixed with 40.44 g of R2 at 63.65 wt ~ 601id6. 49.2 g of a atock 601ution prepared a6 for Film P at 37.68 w~ % ~olids was used. The di~persion was coated as Film F with a 1 mil (0.0025 cm) knife to obtain a dry thicknes6 of 0.6 mil (0.0015 cm) on 1 mil (0.0025 cm) polyethylene terephthalate.

' Table 9 - continued Film Desi~nation ~Y~ (wt. %) Glass Frit 41.81 Alumina 32.16 Cobalt aluminate 0.07 A~ Dispersant 2.0 Copolymer of Films E and F 10.39 Polyoxyethylated 4.67 trimethylol ~ropane triacrylate ~ =1162 Dibutyl phthalate 3.79 ~lkyl benzyl phthalate3.85 of Example 7 Michler'~ ketone 0.04 Benzophenone 0.77 Di-t-butylnitrosomethane0.10 dimer Ionol(s) 0.19 Polyox( ) WSRN 3000 0.15 ~5 The coated film was laminated to two 1.5 mil (0.003B cm) thick layels of Film I of Example 10, all laminated together a~ de6cribed in Example 9. The co~po6ite film was ~acuum laminated to EMR te~t patterns a~ in Example 9 with R underlylng. The part~ were exposed, developed and fired a~ Exampl0 9 to give fired dielectric with no bli6ter~. When the two layer~ of Film I of Example 10 are fired without the thin, porous bottom layer, ove~ the coppe~ EMR
pattern~. 2.1 blister6~cm2 occur.

Thi~ example ~hows that the composition of Example 9 can be used with screen printed coppel to prepare multilaye~ without blisters occurring in buried lay~rs with multiple refires. A ~tructure wa~
prepared of a 6cre~n printed 9924 copper layer that wa6 fired at 900C over an alumina ~ub~tra~e. To thi~, a fiIm of Example 9 was laminated, exposed, developed and ~ir~d a6 de~cribed in Exampl@ 9.
sesond 6creen printed coppel layer was applied as the firs~ laysr and thi~ was fired at 900C. Three ~ore dielect~ic layer~ were applied on top with the ~ame process conditions a6 for the f ir~t dielectric layer. Two additional firings at 900C followed each dielectric fire. This wa6 done to corre~pond to firing of a via fill and an overlying copper layer even though these materials were not applied. With thi~ procedure the ~econd fired copper layer wa~
refired nine times. No bli6ters occurred in the buried layer6 of thig multilayer.

A multilayer wa6 prepared as in Example 17 but with two 1.4 mil thick piece~ of Film I of Example 10 a~ the dielec~ric. Since ~hi~ composition doe~ not contain a poroug bottom layer, large bli~ters appearing a~ delaminations occurred with ~iring of the ~econd dielect~ic layer. Thi~ example indicates that bli~ter6 in buried copper layers occur with multiple refires when glas6y film~ such a~ Film I of Example 10 are u~ed without a porou~ bottom layer.

(1) Trademark of Ferro Corporation, Cleveland, OH
for gla~ frit.
(2~ Trademark of Sartomer Co.. ~e~,t Che6~er, PA, fo~ acrylate monomer~.
(3~ Trademark of Mon~anto Indu6~rial Chemicals Co., St. Loui~, ~0 for pla~ticize~.
3 Trademark of Ciba-Geigy Corp., YaLdsley, NY
for curing agent6 ac~ivated by ultraviolet light.
(5) Trademark of Shell Chemical Co., Hou~ton, T~
1~ for hindered phenolic antioxidant6.
(6) Trademark of Union Carbide Corp., Morristown.
NJ for wa~er-~oIuble e~hylene oxide polymer re6in~.
(~) The Hybrid Technology Group Inc., San Jose.
CA.
(~) Trademark of E. I. du Pont de Nemour6 and Company, Inc., for acrylic re~ins.
(3) Trademark of E. I. du Pont de Nemour and Company, Inc., for dry film 601der ma6k.
0 (lo) Trademark of E. I. du Pont de Nemour and Company, Inc., for polye~hylene ~ere~hthalate film.

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:............. ,

Claims (9)

1. A method for inhibiting the formation of blisters during the firing of intermediate layers of fired multilayer electronic components comprising the sequential steps of:
(1) applying to a substrate a first layer of finely divided particles of dielectric solids and glass dispersed in organic medium;
(2) applying to the first dispersion layer a second layer comprising finely divided particles of and glass dispersed in organic medium and (3) firing the layers to effect volatilization of the organic medium therefrom, liquid phase sintering of the glass components and densification of both layers, the softening point of the glass, the particle size of the glass and the ratio of glass to dielectric solids in both layers being adjusted in such manner that when the layers are fired, the sintering of the glass in the layers is such that upon completion of firing both layers, the first layer is porous and the second layer is nonporous, as measured by the Ink Adsorption Test.

2. The method of claim 1 in which the second layer also contains finely divided particles of dielectric solids.

3. The method of claim 1 in which at least one intermediate dielectric layer of finely divided particles of glass dispersed in organic medium is applied to the first layer, the intermediate layer upon firing being either porous or nonporous as measured by the Ink Adsorption Test.

4. The method of claim 1 in which the two dispersion layers are co-fired.

5. The method of claim 1 in which the two dispersion layers are fired sequentially.

6. The method of claim 1 in which the dispersions are in the form of pastes and are applied by screen printing.

7. The method of claim 1 in which the dispersions are in the form of solid films and are applied by lamination.

8. The method of claim 1 in which the substrate is electrically insulative.

9. The method of claim 1 in which the substrate is comprised of an electrically conductive layer supported on an electrically insulative substrate.