CA1209026A - Polymer surfaced laminated blanks - Google Patents

Abstract

UNITED STATES PATENT APPLICATION

OF: DAVID C. FRISCH
WILHELM WEBER
FOR: POLYMER SURFACED LAMINATED BLANKS

Abstract of the Disclosure A blank and method for its manufacture which blank is useful in the preparation of printed circuit boards. The blank comprises an insulating substrate, typically impregnated with an epoxy resin and with reinforced fiber glass. Super-imposed and adhered to at least one surface of the substrate is a high temperature thermoplastic polymer film or sheet having a substantially uniform thickness between about 10 and about 500 microns. The thermoplastic polymer surface can be chemically treated to activate it and facilitate subsequent deposition of an adherent film of electrolessly deposited metal thereon. The circuits formed by such deposition are uniform, have excellent adherence of a conductor pattern to the thermpolastic polymer surface, have excellent electrical properties and resist heat in continuous use or when soldered.

Description

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Background of the In~lention l. Field of the Invention This invention relates in general ~o a blank and a method of its manufacture, the blank being suitable for use in the manufacture of printed circuit boards. More particularl7, the present invention relates to a blank comprised of an insulating substrate having a thin, high temperature, thermo-plastic polymer sheet or film superimposed and adhered to at least one surface thereof and a method of its manufacture.
This application relates to copending Canadian application Serial No. 350,711, filed April 25, 1980.
2. Description of the Prior Art Printed circuit boards generally comprise an elec-trically insulating substrate associated with one or more electrically conductive circuit patterns. Typically, the insulating substrate comprises a synethetic resin composition reinforced with non-conductive fibrous materials, for example, fibrous glass sheets or papers or webs or mats of glass fibers in either woven or unwoven form, or cellulose paper sheets; the electrically conductive circuit pattern may be a metal such as copper, nickel, cobalt, gold, silver or the like.
The use of insulating substrates to prepare printed circuits by electroless deposition techniques is well known.
For example, in the preparation of such printed circuits, adhesion of a copper conductor pattern to an insulating plastic support or base has been obtained by high pressure, high temperature lamination of copper foil to the base. After the lamination, the copper conductor pattern is established by etching away most of the copper to leave the desired conductor pattern. Frequently before etching, it is also necessary to - LB/~

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l electroplate additional copper to establish interconnections 2 between separate layers of etched conductor patterns. To over-

3 come adhesive difficulties and waste of copper associated --~ith

4 the techniques of lamination of copper foil and etching conductor patterns described hereinabove, the use of adhesives have been 6 proposed in U.S. patents 2,699,424 and 2,699,425, both to ~ieter 7 and also in U.S. patent 3,052,957 to Swanson. These adhesives 8 are receptive to and can be coated with a thin electroless metal film before the conductors are formed by electroplating. The adhesive, in the form of a film, then may be cross-linked and ll thermoset. These techniques have not been widely adopted because 12 the adhesion of the conductor to the insulating substrate is 13 geDerally poor, i.e., 0.7 newtons/mm conductor width. ~enerally, 14 the printed circuit industry requires at least 1.4 newtons/mm.
U.S. patent 3,625,758 to Stahl et al discloses thermosetting a 16 rubber-resin film before electrolessly depositing a metal in 17 order to improve adhesion. The insulating resinous film layer 18 adhered to the base has uniformly distributed therein particles 19 of i3 resin or rubber oxidlzable and/or degradable by suitable oxidizing chemicals. The peel strengths achieved according to 21 the techniques of U.S. patent 3,625,758 are, in general, excel-22 lent, i.e., 3.5 ne~7tons/mm.
~3 2~ The Stahl et al technique has been successfully employed in the printed circuits industry for a number of years.
26 Its main deficiency has been surface resistance. The surface 27 resistance of printed circuits employing the techniques dis-28 c]osed Ln thc above-mcntioned U.S. patcnt 3,625,758 have been 29 as low as 50~0 ;ne~ohm~i whcn condltioned according to ASTM
-30 D61~-61 Procedure C and rneasurcd on an insulation rcsistance ~%~26 , -l pattern as shown in IPC Test Method Number 5.8.1 (April, 1973) 2 (Institute for Interconnecting and Packaging ~lectronic Circuitry, 3 1717 ~oward Street, Evanston, Illinois 60202); reinforced, epoxy 4 resin impregnated substrates typically have a surface resistance of abou~ 100,000 megollms. As circuits have become more complex 6 ~ncl conductors spaced closer togetller, 10w surface resistance 7 becomes a problem.

9 The prior art adhesive techni~ues can also be better understood by the type of substrates used. Organic coatings ll and materials whose surfaces may be provided with electroless 12 metal deposits having commerc~ally acceptable adhesion, that 13 is, peel strengths of st least 1.2 newton~/mm oE ~idth, have l4 heretofore fallen into two distinct categorles according to the method of preparing them and the requisite chemical treat~
16 ment for insuring sufficiently adherent electroless metal plating 17 on them.
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lg A first type includes such products as the adhesives dls-21 closed in the aforementioned U.S. Patent No. 3,625,758, and 22 epoxy/phenolic blends with synthetic elastomers. Materials of 23 this first type typically contain a dispersed phase of synthetic 24 rubber such as butadiene or acrylonitrile butadiene copolymers with a matrix of materials such as epoxy/phenolic blends. The 26 material of the dispersed phase of such substrates is readily 27 degraded by oxidizing agents, such as chromic or permanganate 28 aolutions, while the matrix phase is less reactive to such 29 agents. Following the oxidation treatment, the substrate surface is microporous, resulting in greatly increased surface area.

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. ' , l The substrate surEace also hclS been transformed from hydrophobic 2 to hydrophlltc nnd i5 suLtnble for further processing in known 3 electrt)less metal plntlng procedures.

Substrates of this type, l.e., heterogcneous, dis-6 persed phase-mntrix phase materials, have previously been pre-7 pared by masticating prepolymer of the dispersed or reactive o phase material in solv~nt down to the desired molecular weight 9 or cha:in length, and thell blending the masticated prepolymer with the continuous phase or matrix phase materials in copious ll ~mounts of solvent. Such substrate materials normally comprise 12 Erom 65 to 80 ~eight percent solvent prior to their appllcat:lon 13 to base ~substrates as coatings, and, following solvent evapora-14 tion, typically comprise about 60 weight percent of unsaturated rubber as the dispersed phase and about 40 weight percent of a 16 thermosetting plastic matrix.
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18 A second general type of resinous substrates, such 19 as epoxy and polysulfone, includes materials having homogeneous single phafie. Forming a microporous surface on such substrates 21 requires a mandatory step preceding oxidation; polar and strained 22 sites that are selectively attacked in the oxidation steps must 23 be created, usually by contacting the homogeneous substrate with 24 a strong organic solvent, to permit preferential attack at these sitcs. This process of swelling the surface with an organic 26 solvent prior to attack by oxidizing atents has become known 27 as the "swell and etch" technique.
~8 29 In the "swell and etch" technique, the surface of 8 gl~qss reinforced epoxy resi~ impregnated lamin2te is first ~` ~2~Q~

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1 trentecl wlth a solvent and the~ w:Lth 3 strong oxldizer, e.g,, 2 chromlc ncLd, to etcll away pnrt of ehe surEace nn-l produce ~
3 mlcroporou3, hy(lrophi11c surEace suitable for adhel-ent electro-4 LeS9 metnl deposit:Lon, This tecllnique by itself did not give ncceptable surface resistance because the oxidation could be deep enougll to allow contamination oE the glass cloth laminate 7 core. To avoid this problem, manufacturers of glass cloth 8 reinforced epoxy resin impregnated laminates have produced ~ special grades of laminates with thick, epoxy resin "butter 1O C021~S~' over the glass fibers. Using such grades of laminates, 11 it has been possible to produce printed circuits with bond L2 strenstlls of 1.1 newtons/mm and an insulation resistance of 13 100,000 megohms. llowever, the variatLon oE the cure of the 1~) epoxy "butter coat" from one manufacturer to another and from lot to lot oE the same manufacturer requires the process to be 16 redcfined for each lot. For this reason, attempts to achieve 17 commercial production have not been successful. A further 18 disadvantage of chis process is the failure of the bond in 19 large areas of exposed metal during soldering.

.21 It is also well known that plastics may be electro-22 plated Eor the decorative arts by chemically conditioning them 23 iD strong oxidizing acids, e.g. ? chromic. Among the plastic 2~- materials that have been successfully plated are acrylonitrile-buLadielle-styrene copolymers, polyphenylene ox:ides, polysulfones, .76 ¦ polycarbonate6 and nylon. rhe majority oE these plastics are 27 ¦ not suitable for printed circuit board applications because they ?.o ¦ cannot resist the temperature oE soldering, i.e., about 260~C.
29 ior example, acrylonitr~le-butadiene-styrene has been proposed iO Eor use as a film in the mnnufacture of printed circuit boards 9.~ Z6

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1 but was not suitable because Whl:!O used in typical process io 2 the mnnuE.Ictllrc of circuit boards~ .Lts bond strength was only 3 I ncwton/m~ll und thè t)rLnted circuLt board cc.uld not ~ithstaDd 4 soltle~rinr/ temperAtures.

6 Molded polyslllfones have been used in very limited

7 quantities as printed circuit base material, but only in high

8 frequency applications where the low dielectric constant and

9 dissipation factor of the po]ysulfone is required. Circuit base materials consisting of polysulfone have not achieved 11 wide usage because of the extreme processing difficulties and 12 the high price of the resin system. In processing molded 13 polysulfone bases for use as printed circuit substrates, it is 1~l necessary to anneal or stress relieve a minitnum of 2-l~ hours;
6-8 hours ls preEerred. These laborious steys àre required two 16 or more times during a cycle. Over-annealing tlle polysulfone 17 mflterials also must be avoided to prevent embrittlemeDt thereof 1~ or other deleterious effects.

Summary of the Invention 21 1. Objects of the Inventlon .. . _ _ 22 It is ao object of this invention to provide improved 2~ methods for Eorming subs~rates Eor adherent metallization and 24 improved subfitrates for the electroless deposition of metals thereon.
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27 ~n obJect of this invention is to provide new and 28 improved insulating blanks having a sorface which can be 29 activated to receive electroless metal.

``~` ~ 9~26 595-198~

l Aoother obJect o~ th:Ls invention is to provlde rugged 2 and durable metallLzod obJects from such :Lnsulating blanks.

A fuLtller object of thls lnventlon is to make from such blallks prLnted circult boards, lncluding one-layer, two-6 layer ancl multi-layer boards, which are provided with conductive 7 passageways, o 9 ~n object of the present invention is to provlde lO ¦prlnted circuits utilizing such blanks, the circuits having 11 ¦high surface resistance, excellent bond strength between the 12 ¦surface of the circuit and the electrolessly deposited metal 13 ¦ndhered thereto, excellent stability at soldering temperatures, 14 ¦reproducible methods of manufacturlng, and field repairabillty.

16 ¦ An object of thls invention i8 to provide an insulat-17 ¦ing blanlc with an improved adhesive Eilm surface which can be 18 ¦readily applied with good electrical and solder-shock resistance 19 ¦properties.

?O l 21 ¦ Another object of this invention is to provide a blank 22 Isuitable for the preparation of printed circuit boards, the ~3 ¦ blauk comprising an insulating substrate having adhered to a 2',1 surface thereof an extruded film composed of an aromatic poly-2S ether polymer such as a sulfone polymer having a uniEorm thick-26 ness between about lO and about 500 microns.

~7 ~8 It is an obJect Or thls lnventlon to provide a method 29 oE manufacturing a blank suitable in the preparation oF printed circuit boards, which includes laminatlng a film composed ot an .~, ~ Z6 SC,5--190~
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1 nromntlc polyether polymer such ns a sulfone polymer to an 2 lnsul1tlng substrate wLthout the need for seconclary annealing 3 ~t~s.

An object oE this invention is to provide a method 6 Or manu~act~lring a blank suitable in the preparation of printed circuit boards~ the blank having a surface layer of stress 8 relieved polysulEone laminated to an insulating substrate.

Anotller ob~ect of this invention is to provide a 11 multi-layer circuit board with controlled impedence for high 12 speed logic and other controlled impedence uses.
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14 An obiect of this invention is to provide an adhesive or bonding means between a metal layer such as a circuit pattern 16 and a reinforced thermoset plastic base.

lo Additional obieets and advantages of the invention 19 will be set forth in the description, or may be realized by praetiee of the invention, the objeets and advantages being 21 realized and attained by means of the methods, proeesses, 2~ instrumentalities and eombinations particularly pointed out 23 in the appended claims.

2S 2. ~rief ~escription of the Invention ~6 To achieve the foregoing obiects, and in accorclance 27 with its purpose, as embodiecl and broadly deseribed, the present 2~ inven~ion provides an improved blank and method for lts pre-29 paration, nn improved metal clad insulating substrate and method iO of its manufacture, :Lmproved methods oE produeing printed cireuit :^~ ~

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. ' 1 bo~irds cmploylllg thc :lmprove(l blnnlcs alld the improved cLrcult 2 lo;~r<ls Inrllu~cl thercby. ~s ~Lll le cLear Erom the Eollowillg 3 dCscLipt.iOtl~ there 1R used in the mnnufacturc of circuit boards 4 of thLs invention certain blanks containing a thin surface layer S oE a thermoplastic resin with an aromatic backbone.

7 By "B-Stage", as used throughout the specification 8 an(l claims, is meant that condition of a composition where some 9 but noe all of the active molecules are croxs-linked and the LO composition is still softened by heat.

12 By "C-Stage", as used throughout the specification 13 and claims, is meant that condition where a compositlon has 1~ xubstantially reached the final stage of polymerlzation where cross-linking becomes general and the composition assumes a 16 thermoset, is substantially insoluble and infusible.

18 The laminated blanks of the present invention and 19 methods of thelr preparation represent an improve~lent over the insulating substrates heretofore employed. The methods of 21 ¦ this invention utilize thermoplastic, organic, high temperature 22 ¦ polymer~ as the surface layer~s) of a blank. The surface layer 23 I has a thickness above about 10 microns, preferably above about 24 ¦ 25 microns, and most preferably above about 50 microns; the 25 ¦ thickness of the polymer surface layer is below about 500 microns, 26 ¦ pre~erably below about 125 microns and most preferably below 27 ¦ about 75 microns. One or more plies of a thermoplastic polymer 28 ¦ ¦ is superimposed and laminated onto one or more plies of a 291 "~-Stage", resin impregnated reinforcement, such as glass, cloth 30~ or paper, under heat and pressure to form a rigid printed wiring . -10-~ 6 595-l98B
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l bonrd substrate. An advnntage of this invent:Lon ls that it 2 ell1ninates the problems associated wlth the prior art methods 3 oE cc)at.lng g.L21ss clotl1 surface sheets to yielc1 n "C-Staged"
4 lDm:L111tc exhibit:Lng 9 25-50 micron epoxy "butter coat" or "re.s.Ln-r.Lch" layer.

7 The present invention provides a simple and 8 economical method of preparing (blanks) insulating substrates having substantially plnnar surfaces which surfaces may be lO ¦ adaptecl to receive a layer or pattern of conductive metal by ll ¦ electroless deposltion techniques. In one aspect, this 12 ¦ invention relates to an insulating substrate suitable Eor use 13 ¦ in printed circuits and the method of its preparation which 14 ¦ met11od comprises:
15 ¦ providlng thermoplastic films or sheets having a 16 substa1ltially uniform thickness between about lO and about 500 17 microns, the thermoplastic material having an aromatic backbone l8 that does not liquify or decompose at a temperature of 245C
l9 after five seconùs exposure at the temperature;
provi~ing a fibrous sheet or web impregnated with a 21 thermosettable resin or plies of ~he impregnated fibrous sheets 22 or webs;
23 super:imposing at least one of said iilms or sheets 24 on at least one of said plies of thermosettable resln impregnated fibrous sheets or webs; and 26 consolidating, preferably between planar press plates, 27 the assembly so produced and curing the thermosettable resin 2~ by he21tinp~ uncler pressure.
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l In flnothe1 nspect, thLs invcntion relates to a blank 2 ¦ su~tnblc for usc in printed cLrcllLts whlch comprlses:
3 ¦ nn Lnsulntlng substrate havln~ ndhered to a surface 4 ~hcreof or oppositc surface6 thereof a thermoplastlc or~anlc I1Lgh temperature polymer hnving a thickncss between about 10 6 and about 500 microns, the polymer having an aromatic backbone 7 that does not liquify or decompose at a temperature of 2~5~C
8 after five seconds exposure at the temperature.

In still another aspect, this invention relates to ll a laminate and the mcthod of its prepnration as subsequently 12 described herein which laminate comprises the blan~ as described 13 hereinabove and further including a layer oE an electroconductive l~ metnl superimposed on and adhered to the polymer surface layer(s).
~'he surface layer of polymer Eilm serves as an adhesive means 16 between the electroconductive metal layer and the relnforced 17 thermoset substrate. Consequently, to laminate a metal to a 18 reinforced polyester substrate, for example, a metal film and l~ thin thermoplastic film may be pressed together with a reinforced polyester substrate to bond the three together or the therrno-21 plastic film surface of the blank may be treated with an oxidiz-22 ing media or a plasma to produce a hydrophlllc surface receptive 23 to subseque11t metallization.
~4 In anotl1er aspect, this invention relates to a multi-26 layer printed circuit board and method of its preparat~on which 27 method comprises thc steps of:
28 providing an insulating substrate having a circuit 29 pattern ad11cred to at lcast one surface thereof;
applyin~ a layer oE pPlysulfone film over the circuit ~ ~2~99~i 595-193B ¦
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1 paetc.rn(s);
2 trt!atlllg the polysulfone surEacc!(s) w:Lth a solvtnt and 3 oxldl7.lllg ~Igent to render s3~tl surface(fi) microporous and hyclro-l~ phllLc; an(l clectrolessly depositing a metal onto the treated 6 surE~lcc(s).

8 Any thermosettable resin known for use in preparing 9 insulating substrates for printed circuits may be employed in applicanes' method and blank provided lt or they produce, together 11 with the other materials employed, tlle desired properties in the 12 fLn:;shed substrates. Examples are allyl phthalate. furane, allyl 13 reslns, glyceryl phthalates, silicones, polyacrylLc esters, 14 phenol-formaldehyde and phenol-furfural copolymer, alone or com-pounded with butadiene acrylonitrile copolymer or acrylonitrile-16 butat]iene-styrene copolymers, urea-Eormaldehyde, melamine-17 formaldehyde, modified methacrylic, polyester and epoxy resins.
1o Phenol-formaldehydes may be used if requirements of use are not 19 str:ingent, Epoxy resins are preferred when stringent properties are required. For impregnating the fibrous sheets or webs 21 utilized in applicants' methods, the thermosettable resin may 22 be employed in any convenient form and manner, but a varnish 23 is preferably employed wherein the resin is dispersed or dis-24 solved in a suitable medium. The weight of resin solids in the.
varnlsh is not gcnerally critical, but it is selected to achieve 2S epoxy glass cloth compos.Ltes comprising about 35 to 70~, e.g., 27 about 35 to about 55% resin soldis by weight.

2~ The insulating base of this invention need not be organlc. Thus, it could be made of inorganic insulatlng 1 materials, e.g., inorganic clays and minerals such as ceramic, 2 ferrite, carborundum, glass, glass bonded mica, steatite and 3 ~he like.

Suitable thermoplastic film mnterials are high 6 temperature thermoplasti-: polymers havLng an aromatic backbone 7 and whlch do not liquify or decompose at a temperature of about 245C after five seconds exposure at such a temperature. Such 9 polymers are "aromatic polyether polymers" which are thermo-plastic polymers characterized by recurring aromatic and ether 11 units in the polymer chain. Representative, but not limiting 12 examples, include sulfoDe polymers, polyetherimides, polyether-13 etherketones, polycarbonates, polyphenylene oxides and the like.
14 Specific examples include polycarbonate, polysulfone having the following recurring unit:

~ ~ 1 3 V ~ 50 polyethersulfon~ having the followlng recurring unit:

26 polyphenylsulfone; polyphenylene oxide; Noryl thermoplastic resin 27 (Noryl is a trademark for a molding and extruding resin based 28 on phenylene oxide technology and commercially available from 29 General Electric Co., Polymer Products Operation, Pittsfield, Massachusetts); ULTEM*, a commercially available polyetherimide *trade mark .~l sold by General Elec~ric;and PEEK, a commercially available 2 po1yetheretherketone sold by ICI.

4 As can be fieen in the structllral formulas set forth here:lnabove, recurrlng aromatlc and ether units /-ppear in the 6 polymer chains.

8 Certain grades of these thermoplastics in molded 9 sheets, rods and/or film forms can be treated to render the surfaces of these materials receptive to adherent metal deposi-ll tion. These materials have been used widely in the decorative, 12 automotive, electronic component, med~cal appliance, food pro-13 cesslng and diary equipment industr~es. For illustrative pur-14 po6es, the following discussion will be directed to certain grades of polysulfone (commercially available as `UDEL polysulfone 16 from Union Carbide Corporation, 270 Park Avenue, New York, New 17 York 10017). It is known that the various grades of polysulfone l8 are characterized by toughness, low creep, and long term thermal 19 and hydrolytic stability, including years of continuous service in boiling water or steam, and in air in excess of 150C, with 21 little change in properties. Polysulfones qualify for Under-22 writers' Laboratories Thermal Index ratings of 150C; they main-23 tain their properties over a temperature range from -100C to 24 above 150C. They have a heat deflection temperature of about 174C at 264 psi (1.8 MPa) and about 181C at 6 psi (41 KPa).
26 Long term thermal aging at 150-200C has little effect on the 27 physical or electrical properties of polysulfones.

29 Polysulfone may be prepared by the nucleophilic s~bstitution reaction between the sodium salt of 2,2-bis *trade mark ~Z~ 2~;

(4-hydroxypheDyl) propane and 4,4'-dichlorodlphenyl sulfone.

2 The sodium phenoxide and groups are rescted with methyl chloride 3 to terminate the polymerization. This controls the molecular 4 welr,llt of the polymer and contributes to thermal stability.
S
6 The chemical structure of polysulfone is characterized 7 by the diary] sulfone grouping. This is a highly resonating 8 ~tructure, in which the sulfone group tends to draw electrons 9 from the phenyl rlngs. The resonance is enhanced by having oxygen atoms para to the sulfone groupO Having electrons tied 11 up in resonance imparts excellent oxidation resistance to poly-12 sul~ones. Also, the sulfur atom is in its highes~ s~ate of 13 oxidation. The high degree of resonance has two additlonal 14 effects: it increases the strength of the bonds in~olved and fixes this grouping spatially into a planar configuration.
16 This provides rigidity to the polymer chaln, which iB retained 17 at hi~h temperatures.

19 The ether linkage lmparts so~e flexlbili~y to the 29 polymer chaln, glving lnherent toughness to the material. The 21 sulfone and ether linkages connecting the benzene rings are 22 hydrolytlcally stable. Therefore9 as lndicated previously 23 hereinabove, polysulfones are resistant to hydrolysis and to 24 aqueous acid and alkaline environments.
~5 26 Suitable grades o polysulfone according ~o the 27 present invention include an unfilled grade such as the P-1700*

28 series which is used for in~ection molding or extrusion; a 29 higher molecular weight series for extrusion applications, such as the P-3500 series; and a mineral filled polysulfone useful *trade mark l for plating appllcations such as the P-6050 series (the P-1700, 2 P-3500 and P-6050 series all commerclally available from Union 3 Carbide Corporation, 270 Park Avenue, New York, New York 10017).

Polycarbonates as employed herein are linear, low-6 cry~talline, big11 molecular weighe (about 18,000) aromatic poly-7 ether polymers ln which the linking elements are carbonate 8 radical6. Polycarbonates poss~ss a combination of very useful 9 properties including~ very high impact strength (16 ft.-lb.lin. no~ch) combined with good ductillty, (2) excellentll dimen6ional stabili~y combined with low water absorption (0.35%
l2 immersed in water at room temperature; boiling water immersion l3 does not cause dimensions to alter by more than 0.001 in/in), 14 (3) high heat distortion temperature of about 135C, (4) superior heat re6lstance showing excellent resistance to thermal oxidative l6 degradation, and (5~ good electrical resistance.

18 Polyphenylene oxide may be prepared via oxidative l9 coupling of phenols. By oxidative coupllng is mean~ a reaction of oxygen with ac~ive hydrogens from different monomer~ to 21 produce ~ater and a dimerized molecule. If the monomer has two 22 active hydrogens, oxidative coupling continues resulting in 23 polymerizatlon. The polymer structure of polyphenylene oxide 24 is characterized by a high degree of symmetry, no strongly polar groups, rigid phenylene oxide backbone, a high glass 26 transition temperature ~21C) and no other observable transi-27 tions in the range of -273C to 210C.

2g Polyphenylene oxide possesses a combination of useful properties including: (1) a temperature range between about *trade mark l -180C and about 180C, (2) excellent hydrolytic stability, 2 (3) dimensional stability with very low water absorption, low 3 creep and a high modulus, (4) excellent dielectric properties 4 over a wide range of temperatures (-180C to 180C).
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6 It is believed that Noryl*thermoplastic resin would 7 also be a suitable high temperature thermoplastic polymer useful 8 in the present invention. Noryl*thermoplastic resin is a tough, 9 rigid material which maintains its mechanical properties over a wide temperature range. It also exhibits excellent dimensional ll stability with low creep and low moisture absorption. Nory~
12 thermoplafitic resin exhlbits excellent hydrolytic stability.

14 Polyetherimides and polyetheretherketones are available in film form, laminatable and capable oE being circuiti~ed.
l6 Becaùse of their desirable prop~rties, they are suitable polymers l7 for use herein.

l9 The laminated thermoplastic polymer films of this invention provide a high performance adhesive means suitable for 21 printed circuit applicatioD with reliable properties and 22 performance super-or to that obtainable ~ith the resin-rich 23 and rubber thermoset adhesive blends of the prior art. The 24 thermoplastic film surface(s) of the blanks of this invention have a substantially uniform thickness and can be chemically 26 treated by techniques known in the art to achieve excellent 27 adhesion of subsequent deposits of electroless metal during 28 the manufacture of printed circuit boards.

*trade mark ~.~ ~.. .

8D ~ ~Z()90Z6 1 It it: gencrully knvwn that thcse high temperature 2 polymcrs, speclfically polysulEones, when used by tilemselves 3 ln grea~er thickness than the extruded films re~luire prolonged 4 secondnry annealing bakes to prevent stress cracking. Typical recommendations for annealing conditions are two to four llours 6 and up to nine hours at l70C prior to processing. An additional 7 extended annealing cycle is required after machining tilC mate-8 rial prior to etching the surface for subsequent metal deposi-9 tions. The advantages of using rigid molded polysulEone are limited to those users who have stringent electrical requirements 11 at higll frequency applications. In suCll cases, the polysuifone 12 material is ideally suited but requires that the laborious 13 annealing steps be performed in order to render these materlals 1~ processlble. Ilowever, as subsequently described herein, anneal-1~ ing and production of the blank and/or laminate of this invention 16 occur simuleaneously in one step. It has been found that when 17 tlle thermoplastic polymer films of this invention, such as poly-1~ sulfone, were laminated to an insulating substrate according 19 to the present invention, the thermoplastic polymer films sre stress relieved during the laminating cycle. This eliminates 21 the need for the previously mentioned laborious and time ~2 consuming secondary annealing s~eps.

24 According to a method of applicants' invention, the 2S blank is formed by arranging impregnated plies of the insulating 26 substrate and extruded thermoplastic film or sheets in the form 27 of the laminate nnd ]amLnating the same under heat and pressure, ~ for example, at 160C and 1.4 MPa up to 60 minutes. 'The lamina-29 tlon step can b'e carried out ln a conventional press using con-ditions known fvr preparing thermosettable resin impregnated ~2~ ;
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1 lam:Lnntcs W.ttll sub6t,lnt:Lally pla11ar surfaces. A suitl1ble c~lrc 2 cyc.l.c is 10-60 m:lnutes nt 120-180C and 1.5 to 10 MPa.

4 Although the blank of thls invention. has been 5 clcscribed hereinabove in conJunction with an extruded, high .
6 I:emperature thermoplastic polymer used in a press lamination 7 procedure, other methods of manufacturing the blank of this invention may be employed. For example, a laminated insulating 9 substrate may be dlpped into a polysulfone adhesive to bulld up a layer of polysulfone on its surface(s) by drying steps or an ll extended higll temperature, thermoplastic film may be laminated 12 to an insulatlng substrate employing polysulfone as an adhcsive.
13 It :ls well known that a 2-5 percent solution of polysulfone ln 14 mctllylene chloride can be used to achieve a strong bond at room temperature. A polysulfone film, for example, may be clad to 16 an insulating substrate by dipping the film and substrate in 17 the polysulfone-methylene chloride solution, air drying for 15 18 seconds, and then assemb1ing them in a jig and placing them l9 under a pressure of about 500 psi for 5 minutes.
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21 After removal from the press plates or the like 22 employed in the lamination step described hereinabove, the blank 23 thl1s formed may be cmployed in the manufactur.e of priDted circuit 24 boards which comprise an insulating base material. In another ~5 preferred embodiment, a thin metal film may be superimposed on 26 one or more surfaces of the blank and adhered thereto to form a 27 laminate.
28 . .
29 Elanks of thc type described hereinabove could be used to prepare one-layer, two-layer and multi-layer printed ~ Q;~

l circuit boards with and without plated through holes in the 2 manner more particularly described hereinafter.

4 In one method of producing printed circuit boards, A "semi-additive" technique is employed. The insulating blank 6 oE this invention is cut to size and holes are prepared therein 7 by drilling, punching, or the llke. The surface of the blank is 8 sub~ected to a preetch-solvent attack on an abrasive treatment 9 thereon. It is believed that the surface of the blank may be mechanically roughened before the oxidizing treatment. The ll mechanical roughening would replace solvent pretreatment. A
12 typical mechanical roughening is grit blastlng the surface of 13 the blank with a slurry of abraslve particulat.e matter such as 14 sand, aluminum oxide, quartz, carborundum, and the like, sized finer than lO0 U.S.A. Sieve Series mesh. The solvent attacked 16 board is then mechanically and chemically trea~ed with an 17 oxidiæing solution to activate the surface of the blank.

19 A conventional electroless plating process is employed to deposit a thin conductive layer of copper on the activated 21 surface of the blank and in the holes. A temporary protective 22 coating or resist is employed to silk srreen print a circuit 23 pattern having 0.35mm lines; the temporary resist is heat cured.
24 The circuit pattern is built up by electroplati~g a metal onto the exposed areas of the substrate. The temporary resist is 26 removed and the thin layer of electroless metal which had been 27 covered by the mask is etched away with an acid. A permanent 28 registered solder mask is printed onto the blank and heat cured.
29 Then, the blank is wave or dip soldered.

~ 2~

l Alternatively, the temporary protective coating may 2 be a photoreslst. In such a case, the subsequPnt steps would 3 be pho~o-imaging and then developing the lmaged reslst to cure 4 it prior to the electroplating step.

6 In anotller method of producing printed circuit boards, 7 a "fu11y additive" technique i9 employed. A suitable insulating 8 blank accordin~ to the present invention is prepared having a 9 polysulfone, polyethersulfone, polycarbonate, polyetherimide or polyetheretherketone surface layer laminated to a suitable ll insulating base such as an epoxy-resin-fiber glass reinforced 12 base. Holes with a distance between centers of about 2.5mm 13 or less typically are formed in the blank at preselected sites.
14 The blank and walls of the holes are surface pretreated by deep lS etching with a conventional chrome acid oxidizing solutlon to 16 prepare the surface of the blank and the walls of the holes 17 chemlcally and physically. A photo-imaging technique described 18 in U.S. patents 3,772,078; 39907,621; 3,925,578; 3,930,962; and l~ 3,994~727, all to Polichetta et al, is then employed.
The blanks and holes are completely 21 coated with an aqueous ultraviolet light reducible, copper 22 complex and dried. An ultraviolet light photo~image is formed 23 by brief projection or contact printing on the sensitized sub-24 strate. The unexposed light reducible coating is washed off and the image is flxed by brief exposure to an electroless 26 "strike" bath to provide a permanent background resist leaving 27 the desired circuit pattern exposed, the pattern having as low 28 as about 0.2mm between lines.

~.

~ 9~Z~

1 A metal such as copper is electrolessly deposited onto 2 the exposed pattern and in the holes until a circuit is built 3 up to the desired thickness, e.g., about 1-5 mils (25-125 4 microns). The circu:Lt is protected from corrosion by coating lt wLtll rosin lacquer or solder coating the blank.
fi 7 Unclad blanks of this invention are best provided with 8 an additional surface treatment, e.g., the direct bonding 9 retreatment process of U.S. patent No. 3,723,039, to achieve strong adheslon of electroless metal deposi~s to the ll blank.

13 This generally comprises treating the blank with a 14 suitable organic or inorganic acid, e.g., chromic or sulfuric acid, or base ~olution to render it porous. In many cases 16 lt is desirable to also treat the surface with an agent, e.g., lt dlmethyl for~amide or dimethyl sulfoxide before or during the 18 etching process. The effect of such treatment is to resder the 19 ~ùrface polar.

2l Suitable solvents and blends thereof for swelling poly-22 sulfone in particular include dimethyl Eormamide, acetophenone, 23 chloroform, cyclohexanone, chlorobenzene, dioxane, methylene 24 chloride and tetrahydrofurane.

26 Depending upon the particular surface of ehe blanks, 27 other ion exchange imparting materials may be utilized to effect 28 the aforementioned temporary polarization reaction. For example, 29 acidified sodium fluoride, hydrochloric and hydrofluoric acids, chromic acids, borates, fluoroborates and caustic soda, as well SqS-l98B

l as m:Lxturc~R th;~ret)r, have ~een Eound effective to polarlzo the vnrlou~; synt1-etlc ihermopl;1stLc insulatLng materinls deseribed 3 hereLn.
b In one type of procedure, after treatment with the 6 polari~ing ngents, the insulating bodles are rinsed so as to 7 eliminate any residual agent, following which they are immersed 8 in a solution containing a wetting agent, the ions of whlch are 9 base exchanged with the surface of the insulating blank to thereby impart to the blank relatively long ehained ions which ll alsn are eapable of chemically linking with prevLous metal ions 12 or lonic complexes conta:ining precious metal ions. Following 13 treatment with the wetting agent, the insuLating bodies are 14 rinsed ngain so as to eliminate the residual wetting agent ].5 solution.

17 In the semi-additive method of producing printed l~ circult boardæ, an eleetroplating tehcnique is employed. A
l~ ¦blank according to present invention is pretreated for about three to six minutes in a dimethyl fol:mamide solution to promote 21 adhesion of metal to the surface of the blank after an etching ~2 step. The blank is then etched for about three minutes at about 23 55C to 65~C in a highly..oxidizing solution. This changes the 24 surface of t1-e blal1k from glossy to hazy while providing sites ~5 for chemical linking of the surface of the blank to metal.
~S I~fective etching (microscopic crazing and cracking) occurs due 27 to tl1e combination of the liquid pretreatment and the oxidizer 28 contnct:Lng the surface(s) of the blank of this invention. With 29 dimethyl formamide solution, a low chromic acid may be used. If a high chromic ncid were used with dimethyl formamLde solutio11, ~j ~ Q~6 595~198B

1 mncroclnzin~ oultl occur dcstroylng btth adlleslon nnd ~ood sur-2 ~nce apl)earallce~ The etched and pretreated blnok i9 cat~lyæed 3 hy ImmersLon in soluLlons accord:Lng to V.S. patent ~1,020,197 4 nt nlllbicrlt temper,lture for 1-3 minutes. Dur:Lng such immersions, S copper catalytic sites nre deposited over the entire blank 6 including on the walls of holes in the blank in order to cata- .
7 lyze the subsequent deposition of electroless metal.

9 Electroless metal is then deposlted on the activated surface and in the holes oE the blank typically at ambient ll temperature or about 52C (about 30C for nickel) for about 8 12 m:lnutes for sufficient metal deposition to make the surEace of 13 thc blunk conductive. Following this step, the metal coated 14 board is imprinted with a desired circuit by a photoresist technique. According to the photoresist technique, a photosensi-16 tive coating is applied to the surface of the blank. The photo-17 sensitive coa.ing may be of the type that polymerizes or lo depolymerizes on exposure to ultraviolet light. A positive or 19 negative transparency, respectively of the circuit, is then used to form a background resist whioh in turn outlines a circuit 21 pattern on the blank. Copper or another electroconductive metal .22 ¦is electroplated onto the pattern to a desired thickness such as 23 1--5 mils in about 1/~-2 hours. The pattern may then be solder 24 p]ated Contact areas such as edge connectors may be electro-plated with noble metals such as gold> silver, etc.

21 It is believed, however, that polycarbonate is not 28 suitable for the electroless deposition of copper or nlckel 29 ¦ because the p~l of the deposition solutions would be too high for satisfnctory results with polycarbonate resins :Ln that -1 partlcular embodlment.

3 The acid conditioner typically used for etching 4 acrylonitrile-butadiene-styrene substrates is satisfactory for polysulfone substrates. A typlcal composition of this acid on 6 a wei~ht ba8is: 60% H2S04, 10% H3P04, 1% CrO3 and 30% H20.
7 During etching, the chromium that comes in contact with the 8 pretreated polysulfone surface is reduced from Cr 6 to Cr 3.
9 When most of the chromium is reduced, the acid is no longer as 0 effective in improving adhesion of metal coatings. For this 11 reason, it is desirable to have as much chromium in the acid 12 conditioner as possible. However, wieh dimethyl formamide as 13 the preconditioner bath, chromic acid contents above about 14 3% result in macrocrazing and poor adhesion. A preferred acid conditioner for the polysulfone surface(s) is, therefore, 16 (on a weight basis): 55.9% of 96% H2S04, 10.4% of 85-87%
17 H3P4~ 3% of CrO3 and 30-7% of ~2 19 In an alternative "fully additive" technique for producin~ printed cirruit boards, a suitable blank according 21 to the present invention is prepared typically having a 22 distance between hole centers of about 2.5mm or less. The 23 blan~ and walls of the holes are activated using known seeding 24 and sensitizing agents such as stannous chloride-palladium chloride,activators. A permanent protective coating or resist 26 is screened to produce a permanent background resist leaving 27 the desired circuit pattern exposed, the pattern having spacing 28 as low as about 0.35mm between conductor lines. The resist is 29 cured and copper is electrolessly deposited on the exposed pattern and in the holes.

~2~(3 ;26 ",. ~ I

1 The blank according to the present invention may 2 alternately be catalytic, i.e.~ ha~ing catalytic materials 3 distributed throllghout its surface durin~ extrusion oE the 4 thermoplastic Eilm surface of the blank. In the aforementioned 5 Lecllnlques for manufacturing printed circuit boards, this would 6 elimlnate the need for a separate seeding and sensitizing 7 sLep. ~ncorporation of catalytic materials into the surface 8 of the therllloplastic film may be accomplished by the technique 9 disclosed ln U.S. patents 3,546,009; 3,560,257; 3,600,330 and example 1 of ~.S. patent 3,77~,758 (a palladium chloride 11 catalyst). In another embodi-12 ment of the present invention, the high temperature film may 13 be employed as an adhesive means for bonding decorative metallic 14 coatings to plastic, reinforced thermoset substrates. One application, for example, would be rims adapted to hold tires 16 such as automobile tires. Reinforced, thermoset polyester 17 substrates have been proposed for this purpose but are very 18 difficult to plate with metals. Standard metallizing techniques 19 cannot be used effectively since the polyester surface is not oxidizable and electroplatable. The polyester substrates may be 21 electroplated with a metal layer according to the present inven-22 tion. Typically, such substrate has been or may be shaped by 23 molds. According to this invention, a thermoplastic film is die 24 cut, laid into the mold used to form a reinforced wheel rim so that the outer surface of the wheel rim constitutes the thermo-26 plastic, and then molded to the substrate upon application of 27 heat and pressure. Alternately, the thermoplastic film may be 2~ applied under heat and pressure with a shape applicator to the 29 molded and shaped reinforced, polyester substrate. Subsequently, ~0 an electroless copper layer may be deposited on the thermoplastic -- ~2~

5'~5-I9~1~

1 LL1m surface layor oE the substrate, fo1lowad by a layer of 2 o10c~ropl.1ted copl)or al)prox:ln1;1toIy 0.3 mils thick, a layer of 3 ole(:trol-1atc(l 1lIcke1 approxInately 0.3 mLls tllick and a 1ayer 4 oE clIromt! appr(ximately 0.02 mils thick.

~mong the matericlls which may be used as insulnting 7 substrates for the blallks and/or laminates of this invention 8 are inorga1lLc and organic substances, such ns glass, ceramics, 9 ¦ porcelaiD, resins, paper, cloth and the like.

10 l

11 ¦ For printed circuits, among the materials which

12 ¦ preferably are used as the insulating substrates for the blanks,

13 ¦ mny be mcntioned insulating thermosetting resins, thermoplastic l~ I resins and mLxtures of the foregoing, including fiber, e.gO, lS ¦ fiberglnss, Impregnated embodiments of the foregoing.

16 .
17 Included in the thermoplastic reslns are acetal lc3 resins; acrylics, such as methyl acrylate; cellulosic resins, .19 such as cellulose triacetate; and polycarbonates, polycllloro trifIuoroethylene, polyesters and polyimides.

22 Arnong the thermosetting resins may be mentioned allyl 23 phtllalate; furane, melamine-forrnaldehyde; pheDol formaldehyde 24 antl pheno1furfural copo1ymers, alone or eompounded with butadiene 2S acry]onitrile copolymers or acrylonitrile-butadiene-styrene copolymers; polyacrylic esters; si]icones; urea formaldehydes;
27 epoxy resins; allyl resins; glyceryl phthalates; polyesters;
28 alld the like.

~0 ~ ~2~3;~6 1 Porous materials, comprising paper, wood, fiberglass, 2 cloth and fibers, such as natural and synthetic fibers, e.g., 3 cotton fibers, polyester fibers, adn the like, as well as such 4 materials themselves, may also be metallized in accordance with the teachings herein. The invention is particularly applicable 6 to the metallization of blanks having a surface comprised of a 7 high temperature thermoplastic polymer and an insulating sub-8 strate comprised of resin impregnated fibrous structures and 9 varnish coated resln impregnated fiber structures of the type described.

12 The blanks will include any insulating material coated 13 with the thermoplastic polymer film form, regardless of shape

14 or thickness, and includes thin films and strips as well as thick substrata. An adhesive layer can be on the blank. The 16 blanks can include metals such as aluminum or steel which are 17 coated with insulating layers of thermoplastic polymers. Where 18 the conductive pattern is only to be on upper and lower surfaces 19 the blanlc may optionally be coated with extruded thermoplastic films. If the conductive pattern is to include plated through 21 holes it may be preferably to first provide the me~al blanks 22 with holes and coat the blank by powder fusing techniques such 23 as fluidized bed.

Typically, the autocatalytic or electroless metal 26 deposition solutions for use in depositing electroless metal 27 on the activated surface(s) of the blanks comprise an aqueous 28 solution of a water soluble salt of the metal or metals to be 29 deposited, a reducing agent for the metal cations, and a com-plexing or sequestering agent for the metal catlons. The \ ~
1 function of the complexing or sequestering agent is to form a 2 water soluble comp]ex with the dissolved metallic cations so 3 as to maintain the metal in solution. The function oE the 4 reducing agent is to reduce the metal cation to metal at the al)proprLate time.

7 Typical of such solutions are electroless copper, ~ niclcel, cobalt, solver, gold, solutions. Such solutions are 9 well known in the art and are capable of autocatalytically 0 depositing the identified metals without the use of electricity.

13 Typical oE the electroless copper solutions which may 14 be u~ed nre those described in U.S. patent No. 3,095,309.
Conventlonally, such solutions comprise a source oE cupric ions, 16 e.g., copper sulfate, a reducing agent for cupric ions, e.g., 17 formaldehyde, a comple~ing agent Eor cupric ions, e.g., tetra-18 sodium ethylenediamine-tetraacetic acid, and a pW adjustor, 19 e.g., sodium hydroxide.
21 Typical electroless nickel baths which may be used ~2 are described in Brenner, Metal Finishing, Nov. 1954, pages 68 23 to 76. They co~prise aqueous 24 solutions of a nickel salt, such as nickel chlorlde, an active chemical reducing agent for the nickel salt, such as the 26 hypophosphite ion~ and a complexing agent, such as carboxylic 27 acids and salts thereof.

29 Electroless gold plating baths which may be used are disclosed in ~.S. patent 3,589,916 . They contain 1 an aqueous alkallne solution of a 2 water soluble salt of gold, a borollydride or amine borane 3 reducing agent, a complexing agent for gold and a small, effec-4 tive stabilLzlng amount of a cyanlde compound in Rn amount bstween about 5 mlcrograms ancl 500 milligrams. The p~l of the bath wlll be between about 10 and 14.

8 Typical electroless cobalt and electroless silver 9 systems are we]l known.

11 A specific example of an electroless copper deposition 12 bath suitable for use will now be described:
13 N,N,N'-N' tetrakis (2-hydroxy-propyl 14 ethylenediamine) 18 g./l.
cuso4- 5H 0 10 g./l.
16 Forma]dehyde (37% solution) 4 ml./l.
17 Wetting Agent (GAFAC-RE*610) (commercially available from 18 GAP Corporation) (believed to 0.01 g./l.
be a phosphate ester of alkyl-19 phenolpolyethylene oxide) Sodium hydroxide to desired pH
21 (12-13) 22 Sodium cyanide (NaCN) 25 mg./l.
23 2-mercapto benzothiazole10 mg./l.

This bath is preferably operated at a temperature of 26 about 52C, and will deposit a coating of ductile electrolPss 27 copper about 35 micorns thick in about 18 hours.

29 Utilizing the electroless metal baths of the type described, very thin conducting metal films or layers will be *trade mark "`; -31-~E~15~ 1 _~.~ ., ~ ~ ~ ~t~ ~ 2 595-19~
.

l laid dowll on the surface of the blank. Ordinarily, the metal 2 f:LIms ;uperiml)osed on thc surEace of tlle blank by electroless 3 a~etnl dellos:lt:lt)n will rangi? from 2.5 to 100 microns in thickness, ~ with metal fllllm~ hllv:ln~ a thiclcness of even less than 2.5 microns belng n distinct possibillty.

7 Among its embodiments, the present invention contem-8 plates metallized blar.ks in which the electroless metal, e.g., 9 copper, nickel, gold or the like, has been further built up by attaching an electrode to the electroless metal surface and ll electrolytically, i.e., galvanically depositing on it more of 12 the same or dlfferent metal, e.g., copper, nickel, silver, gold, 13 rhodlum, tin, alloys thereof, and the like. Electroplating 1~l procedures are conventional and we:Ll-known to those skilled in the art.

17 ~or example, a copper pyrophosphate bath is commer-18 cially available Eor operation at a pH of 8.1 to 8.5, a tempera-l9 ture of 50C, and a current density of 50 amp./sq. ft. In addition, a suiLable acid copper sulfate bath is operated at a 21 pH of 0.6 to 1.2, a temperature of 15-50C, and a current 22 density of 25 to 70 amp. per sq. ft. and is comprised of:
23 copper sulfate, CuS04-5H20 GO-120 g./l.
~4 ¦ su~fur;c acid, H2S04 160-18 g./l.
25 ¦ llydroc11loric acid, IICI 1-2 mg./l.

26 ¦ bri&hteners and wetting agents optional 28 ~or printed circuit application, copper deposits for use as the 29 bE~SiC conductor mnterial are usually 25um to 70um thick.

f~ ~2~

. ' ~

l SLlver mny be deposited galvaniefl11y from a eynnide 2 blltll operated at a p}l of 11.5 to 12, n te1llper~ture of 25-35C, 3 a1ld a currel1t de11slty of 5-15 amp./sq. ft. An illustratlve l~ g~llVAlliC sil\~er bat11 is eomprised of:
sllver eyaoide, A CNSO g./l.
6 potassium eyanide, KCN 110 g./l.
7 potassium carbonate, K2C03 45 g./l.
8 brighteners variable Gold may be cleposited galvanically from an acid gold 11 citrute bath at pll 5-7, a temperature of 45-60C and a eurrent 12 density of 5-15 amp./sq. ft. An illustrative galvanic gold bath 13 eonsists of:
14 Sodium goLd cyanide, NaAu (CN)2 20-30 g./l.
dibasic ammonium citrate (NH4)~C611507 100 g./l.

17 Niekel ean be galvanically deposited at pU 4.5 to 5.5, 18 a temperature of 45C, and a current density oE 20 to 65 amp./sq.
19 ft., the bath containing:
niekel sulfate, NiS04 6H20 240 g./l.
21 nickel chloride, NiC12 6H20 45 g./l.
22 boric acid, H3B03 30 g./l.

24 Tin and rhodium and alloys can be galvanically deposited by procedures described ln Schlabach et al, Printed and Integrated 26 C.ircuitry, ~1cGraw-Uill, New York, 1963, p. 146-148.

28 Other objects and advantages of the invention will 29 be set forth in part herein and in part will be obvious herefrom or may be learned by practice with the invention, the same being , ~ ~2~ZEi 595-19813 . .

1 rcal:lzed and attained by mcans of the lnstrumcnt;llities and 2 comblnatlons poLnted out ln the appendet1 cla:lms.

Thc invention is more fully described hercil-aFter wlth rercrencc to the accompanying drawings which illustrate 6 certntn embo~ Dents o the invention and together with the 7 specification serve to e~plain the principles of the invention.

9 Yigs. 1-5 illustrate procedures ~-,bich can be used to produce printed c:ircuit boards from insulating blanks produced 11 in accor(lance w;th the teachings herein;
12 Fig. 6 illu~strates a prod~lction process apparatl1s 13 for making n blank in a roll-to-roll fashion following the 14 tcachings of this invention; and lS Fig. 7 illustrates a production process apparatus 16 for mtlking 1 blank in a roll application of polysulfone to a 17 rigid substr;lte.

l9 In the drawings, similar reference numerals are used to represent similar parts.

22 Referring to Fig. lA, there is shown an insulating 23 blank 10 according to the present invention. The insulating 24 blank lO comprises a thermoset resin inner core 12 and outer surface layers of polysulfone film 14. The core 12 is ca~alytic 26 for deposition of electroless metal. The polysulfone film 14 27 also is catalytic for electroless deposition. In Fig. 113 holes ~8 16 and 1~3 are drilledthrtJugll the blank 10. The blank 10 is ~9 thell immerscd :in a pre-etched solvent followed by a chemical treatmellt with an acid etch such as 20 g./l. CrO3, 350 mg./l.

~ Q~6 595-]981j l H2S0~, 50 g./l. NaF at a temperature betwecll 45 and 65C to 2 e~pose Lhc catalyst and activate the surface of the blank 10 3 ns sllown ln T'Lg. IC. A photores.Lst 2tl is appl:Led (sllown in 4 FLg. Il)) on u surface o~ the blanlc to mask areas th.lt will not be sul)t:e~luen~1y copper plated. Copper is then elcctrolessly 6 deposi~ed, by methods known in the art througll the holes 16 and 7 18 and onto the exposed surfaces of the blank 10 to form a 8 copper conductive pattern 22 about 35 microns thick on the 9 exposed surface of the blank and on the walls of the holes 16 and 18 as shown in Fig. lE. The photoresist 24 is then stripped ll as shown Ln Fig. lF, A registered soLder mask 30 then may be 12 applied over the circuit pattern leaving holes 16 and 18 exposed 13 (Fig, lG).

lS Fig, 2 illustrAtes a fully additive method of pro-16 ducing a printed circuit board. Referring to Fig. 2A there 17 is shown All insulating blank 10 according to the present 18 invention, The insulAting blank 10 comprises an epoxy resin-19 fiberglass reinforced inner core 12 and outer surface layers of polysulfone film 14. In Fig. 2B a llole 16 is drilled in the 21 blank, The blank and walls of the hole 16 are surface pretreated 22 by deep etching with a conventional low chrome acid etchant such 23 as (on n weight basis): 55.9% of 96% H2SO4, 10.4% of 85-87%
24 H3P04, 3% of CrO3 and 30.7% of H2O, to prepare the surface oE
the bl~nk 10 and the walls of the hole 16 chemically and physi-26 cslly, The blank 10 and hole 16 are then completely coated with 27 an aqueous ultraviolet light reducible copper comp]ex 20 and 28 dried (Fig. 2C). An ultraviolet light photo-image is Eormed by 29 brief projection or contact printing via screen on the sensitized surface 1~, The unexposed light reducible coating 20 is washed ~Z~9~;~6 595-l~8B
.

1 allcl the Lm.lge~ ~2 is ft~cd by brieE c~posure to an e]ectroless 2 "sLrLl;e" bnth as sllowll ln Flg 2D, leavlllg the cleslred ctrcuit 3 pLIttcrll c~ro!.e(l. ~q sho~n in Fi~!. 2E, copper i5 electrolessly 4 clepositc(l on~ he pattern and the hole l6 ulltil a circuit 28 Ls built up to the (Icsired thicklless, typically nbout l-5 mils 6 in about 18-20 hotlrs.

8 Fig. 3 illustrates an "electroplating" method of 9 producing printed c:ircuit boards. In Fig. 3~ there is shown an insulating blank 10 accordin~ to present invention, having 11 an inner core 12 an(l polysulfone surface layer 1~ as describecl 12 previously herin with respect to Figs. 1 and 2. As illustrated 13 :Ln ~'ig. 3B, the blank lO is pretreated for about 3-6 minutes in 14 a dlmethyl rormamide solution to promote adhesion of metal to the surface 14 of the blank 10 after an etching step. In Fig.
16 3C, the blank 10 is etched Eor about three minutes at about 17 35~C to about 70C in a h:ighly o~idizing solution. This chnnges 18 the surface of the blank from glossy to haæy while providing 19 sites 18 for chemical linking of the surface of the blank 10 to metal. The etched and pretreated blank 10 is activated by 21 im1nersiou in a stannous and palladium chloride activator solution 22 wllich may be at ambient tempernture for I to 3 minutes, each, 23 as shown in Fig. 3C. During such immersion, palladium sites 24 20 are deposited over the entire blank 10, including on the walls of the holex (not shown) in the blank 10 in order to catalyze 26 the subscquent ~eposition oE electroless metal.

28 ~ layer of electroless metal 22 is deposited on the 2~ ~ctivated surface 14 and in the holes ~now shown) of the blank 3Q 10, typically at ambient temperature for about 8 minutes in ~`
1 order to render the surface of the blank electrically conductive 2 (as shown in Fig. 3D)r In Fig. 3E a desired circuit is imprinted 3 by a photoresist technique onto the metal coated blank 10. A
4 photosensitive coating 24 is applied to the surface of the blank.
The photosensitive coating 24 may polymerize or depolymerize on 6 exposure to ultraviolet light. A positive mask 26 is then used 7 to form n background resist which in turn outlinPs a circuit 8 pattern on the surface of the blank 10 (as shown in Fig. 3E).
9 In Fig. 3F copper 28 is electroplated onto the pattern to a desired thickness such as 25-70~m. In Fig. 3G, the background 11 resist is stripped and the conductive background film of copper 12 removed by etching.
13 _ 14 In Fig. 4, there is shown an additive method for manu-~5 facturing a multi-layer printed circuit board. In Fig. 4A, 16 printed circuit pattern 102 is adhered on insulating blank 100.
17 A polysulfone film 104 is superimposed and bonded over the 18 printed circuit pattern 102 (Fig. 4B). A hole 106 is then drilled 19 through polysulfone film 104, printed circuit pattern 102 and the insulating blank 100 (Fig. 4C). The surface of the poly-21 sulfone film 104 is adhesion promoted via the "swell and etch"
22 technique described previously herein. The "swell and etch"
23 technique also removes smears from the drilled hole edges of the 2~ (copper) circuit pattern 102. The polysulfone film surface 104 is activated by dipping in a palladium and tin solution. In 26 Fig. 4D, a photoresist image 110 is imposed on the outer surface 27 of the polysulfone film 104. The exposed film surface 104 and 2~ the hole(s) 106 are electrolessly plated with copper 112 to a 29 thickness of about 35 microns (Fig. 4E). In Fig. 4F, the photo-resist image 110 has been stripped providing the multilayer ~ ~ ~%~ 6 l ¦ printed clrcuLt bonrd.

3 ¦ tn PLg. 5, there i9 shown a semiaddLt1ve method of 4 ¦ m;lnuructurLnG a multL-layer printed circuit board. In Fig. 5A, 5 1 InLank 200 :Ls clnd on opposite surfaces with copper 201. An 6 ¦ lnterlor circuit pattern 202 is etched with a suitable etchant 7 ¦ and covered with a layer of polysulfone 204 (Fig. 5B). A hole 8 216 is drilled througll the blank 200. The blank 200 is adhesion 9 promoted with chromic acid and ac~ivated in palladium and tin solution. Then, an electrolessly (!eposited copper film 111 is ll applied onto the polysulfone surface 204 and in the hole 216 12 to a thickness of about 2 microns (Fig. 5C). A photoresist image 13 210 is applied and additional copper 212 i9 electroplated to 1~l provide a copper layer having a thickness of about 35 microns (Fig. 5D). In Fig. 5E, the photoresist image 210 is removed and 16 the copper film 211 under the photoresist 110 is etched away 17 with a suitabie etchant.

19 In Pig. 6, there is shown a mbthod for making an 2~ insulating blank 10 according to the present invention. There 21 are shown feed rollers 100, 102 and 104. Wound on roller 100 22 is a flexible support carrier 106 with a thickness of about 23 8mm, the carrier being woven glass, non-woven glass, dacron, 24 rayon, cellulose paper and the like impregnated with resins!

preferably thermoset resins such as epoxy, but high temperature 26 thermoplastics, e.g., polyimides and polycarbonates may also be 27 used. Wound on feed roller 102 is a thermoplastic film 108 28 having a thickness of 1-5mm. Wound on feed roller 104 is a 29 thermopl;1stic film having a thickness of about 1-5mm. Th~
thermoplastic film may be polysulfone, polyethersulfone, .f- I 3L~26 ~
595-19~
. , l I-olyphQnylene cxlde or polycarbonate.
~ .
3 Also 3hown ara combining take-up rollers 110 which ~ ap1)1y heat and pressurc to the laminate passilig therebetween.
S A tempcrature of about 160-200~C and a pressure of about 6 30-400 N/mm is typically applied between rollers 100. Exiting 7 from the rollers is a flexible laminated thermoplc~stic support carrier wl-ich when thermoset becomes the insulating blank 9 according to the present invention.
`' 10 ll In ~ig. ~, there is shown a roll application to a 12 ri~Lc1 substrate, i.e., 1.6mm thick epoxy gl~ss cloth reinforced 13 l~mL11ate. There are shown feed rollers 100, 102 and 104.
14 ~ound on rollers 102 and 104 are respective thermoplastic films lS 108 having a thickness of 1-5mm. The thermoplastic fil1n 108 16 may be polysul;Eone, polyethersulfone, polyphenylene oxide or 17 polycarbonate. Also shown are comblning take-up rollers 110 18 which apply heat and pressure to the laminate passing there-19 between. A temperature of about 160-200~C and a pressure of about 30-400 N/mm is typically applied between rollers 110. An 21 insulating base 12 passes between rollers 110 and the thermo-22 plastic film 108 is laminated to opposed surEaces of the base 23 12 under heat and pressure to form ~he blank i0 which is severed 24 from the web after exiting from the rollers 110. Optionally, the insulating base 2 is coated with a polysulfone adhesive 26 comprised of po]ysulfone dissolved in solvent.
27 .
28 The following examples illustrate at least one of 2t~ the best modes of the insulating blanks, printed circu:lt boards and methods of the present inventioo AS presently understood.

r h 2 8 Plies of glass cloth impregnated with 45-55% by 3 weight epoxy resin were placed in a printed circuit laminating 4 press with a sheet oE extr~lded polysulEone fLlm 50um thick on top and bottom. The extruded polysulfone film was made from 6 lldel P-1700'~polysul~one resin (cosnmercially available from 7 Unlon Carbi~le Cnrporation, EngLneering Polymer Division, 270 8 Park Avenue, New York, New York 10017). A laminating tempera-9 ture of 175C, a pressure of 600 psi (4.1 MPa) and a dwell time in the ho~ press of 15 minutes were employed. After 15 ll minutes, the press was cooled to room temperature and the blank l2 was removed.

14 The blank was processed into a printed circuit board employing the following steps: (1) Through holes were drilled l6 in the blank; (2) The blank was brushed to remove drilling 17 debris (it :Ls noted that no annealiDg and/or oven baking was 18 reguired after drilling); (3) The blank was immersed in dimethyl l9 formamide-waLer solu~ion (specific gravity of 0.955-0.965) for 3-6 minutes; (4) The blank was rinsed in hot water for 45 21 seconds; (5) The surface of the blank was adhesion promoted at 22 a temperature of 55~C for a time period of 7 minutes with the 23 following solutlon: CrO3-20 g/l, H3PO4-100 ml/l, H2SO4-600 24 ml/l, and*FC-98-0.5 g/l (FC-98*is an anionic perfluoroalkyl ~5 sulfonate commercially available from 3M Company, Commercial 26 Chemicals Division, St. Paul, Minnesota); (6~ The blank was 27 rinsed in still water, (7) Cr~VI] was neutralized with a solu-2B tion containing 10% H2O2 and 157D H2SO~; (8-11) The blank was 29 rinsed with water, immersed successively in 2.5 M HCl, a seeder solution (the seeder solution described in example 1 of *trade mark ~2~

~, 1 I~.S. patent 3,961,109 and an 2 accelerator, 5~ IIBF4; (12) Copper was electrolessly deposited 3 onto the blank (electroless copper solution is described in 4 U.S. pate~t 3,095,309) to a thickness of 2.5 microns; (13-14) rhe cnpper clad blank was rlnsed with water and dried at 125C
6 for 10 mlnutes providing a copper clad blank (as shown in Fig.
7 3D)-9 A printed circuit board was manufactured using such 0 copper clad blank by techniques well known in the art, i.e., a background resist image was printed, a copper circuit pattern 12 was electroplated using the copper bath described previously 13 herein (page 28), the resist was stripped and the background 14 copper was etched away (see Figs~3E-3G).

A peel strength of 1.7 N/mm was measured for the 17 printed circ~it board. A solder float test was also employed.
18 A one-inch square copper pattern (the printed circuit board) 19 produced according to this example was floated on 260C molten solder for 10 seconds. The sample was removed for examination 21 of potential blisters and/or delamination of the copper pattern 22 (from the blank). No blistering or delamination was detected.

Example 1 was repeated except a laminating pressure of 26 400 psi (2.8 MPa) and a dwell time on the laminating press of 27 1 hour were used. A final peel strength of 2.4 N/mm was measured 28 and a one-inch square copper pattern sample floated in 260 29 molten solder for more than 10 seconds without blistering or delaminating.`

~Z~ 6 2 Example 1 was repeated except that a laminating 3 pressure nf 200 psi (1.4 MPa) and a dewll time in the laminating 4 press of 5 minutes were employed. After laminating, the blank wns stabLllzed at l60C Eor 1 hour :Ln a circulating hot air 6 oven to prevellt shrlnkflge and warping during processing. A
7 fLnal pee] strength of 1.9 N/mm was measured.

A blank made according to example 1 was used. Follow-11 ing the first 10 steps of example 1, the seeded blank was printed 12 with Riston 129 (Riston 129 is a trademark for a dry film photo 13 polymer resi~t commercially available from E.I. duPont deNemours 14 & Co., Wilmington, Delaware) to leave a desired circuit pattern

15 exposed. The blank was immersed in an acceleration tstep 11 of l6 example 1) and electrolessly copper plated (step 12 of example 1) 17 to a thickness of 35 microns.

l9 EXAMPLE 5 An epoxy glass laminate, G10 FR* (G10 FR* is commercially 21 available from Norplex Division of UOP Inc., LaCross, Wisconsin), 22 was clad with 35~m thlck copper foil top and bottom. A copper 23 circuie was etched in the foil by laminating with Riston 1206 24 (0.6 mil thick dry film photopolymer commercially available from E.I. duPont deNemours & Co., Wilmington, Delaware), exposing 26 to ultraviolet light through a negative, developing out the 27 unexposed Riston 1206 with l,l,l-trichloroethane, etching the 28 copper with ammoniacal cupric chloride and removing the remain-2~ ing Riston 1206 with methylene chloride.
3~
*trade mark ~ 3~

1 A polysulfone adhesive was prepared by dissolving 2 p~llets of Udel P-1700 NT polysulfone resin (commercially 3 available from Union Carbide Corporation, 270 Park Avenue, 4 New York, New Yorlc Inol 7) in methylene chloride. The etched panel was dippel ln the polysul~one solution and air dried.
6 A 7$~1m thLck po]ysu~folle foil was laminated to the adhesive 7 coate(l double sided panel in a press at 175C for 10 minutes 8 at 200 psi (1.4 MPa).

Through holes were drilled in the panel and the 11 debris was removed by brushing. The panel was converted into 12 a mul~i-layer printed circuit board following the procedure 13 of example 1 except that the adhesion promotion time was only 14 two minutes.

16 EXAMPLE 6 ~7 A single layer of epoxy impregnated glass cloth was 18 placed between two sheets of 25~m polysulfone foil and laminated 19 in a press at 400 psi (2.8 MPa) at 175C for 10 minuLes. This produced a flexible blank useful in the manufacture of printed 21 circuit boards.

24 The procedure of example 1 is repeated except that the following polymers are employed in lieu of polysulfone:
26 polyetherimide 27 polyetheretherketone *trade mark !
,~' 595-198~ .

1 :tt should be nt~(lcrstood by those skilled in the 2 2~rt th;lL v2~rio~l5 lDodl~icntloll9 IllDy be m2)(1e in the present 3 .Lnve2lt:Lol1 wLtllout dcparting from the spirit and scope thereof 4 ;lu descr:Lbed :Ln tlle specificat:Lon and defined in thc nppen(lcd C l I i 111 B, ~1 ~0 223 ' ' ' ' .
- 24 .

. .

28 . .
29 .

Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A blank suitable for use in the preparation of a printed circuit board by electroless deposition which comprises an insulating substrate having adhered to at least one surface thereof a thermoplastic organic high temperature polymer having a thickness between about 10 and about 500 microns, the polymer being selected from the group consisting of polyetherimides and polyetheretherketones.

2. A blank as claimed in claim 1 wherein said polymer is a polyetherimide.

3. A blank as claimed in claim 1 wherein said polymer is a polyetheretherketone.

4. A blank as claimed in claim 1 wherein said insulating substrate is comprised of an organic material.

5. A blank as claimed in claim 1 wherein said insulating substrate is comprised of an inorganic material.

6. A blank as claimed in claim 5 wherein said inorganic material is selected from the group consisting of inorganic clays and minerals.

7. A blank as claimed in claim 4 wherein said organic material is selected from the group consisting of thermosettable resin, thermoplastic resin and mixtures thereof.

8. A blank as claimed in claim 7 wherein said insulating substrate further includes fiber impregnated thermosettable resin.

9. A blank suitable for use in the preparation of a printed circuit board by electroless deposition which comprises:
(a) extruded thermoplastic films or sheets having a substantially uniform thickness between about 1 and about 5 mils, the thermoplastic material being selected from the group consisting of polyetherimides and polyetheretherketones;
(b) a ribrous sheet or web impregnated with a thermoset resin or plies of the impregnated fibrous sheets or webs;
(c) at least one of said extruded thermoplastic films or sheets laminated onto at least one of said plies of thermoset resin impregnated fibrous sheets or webs.

10. A printed circuit board which comprises an insulating base having a separate surface layer comprised of a high temperature thermoplastic film having a thickness between about 10 and about 500 microns, the thermoplastic being selected from the group consisting of polyetherimides and polyetheretherketones, and a metallic circuit pattern adhered to the surface layer of said insulating substrate.

11. A blank as claimed in claim 10 wherein said polymer is a polyetherimide.

12. A blank as claimed in claim 10 wherein said polymer is a polyetheretherketone.

13. A printed circuit board which comprises an insulating base having a core comprised of epoxy resin impregnated fiberglass and phenolic resin impregnated paper and a separate and discrete surface layer comprised of polyetherimide or polyetheretherketone having a thickness between about 10 and about 500 microns, and a metallic circuit pattern adhered to the surface layer of said insulating substrate.

14. A method of preparing a blank suitable for use in the manufacture of a printed circuit board which method comprises:
(a) providing extruded thermoplastic films or sheets having a substantially uniform thickness between about 1 and 5 mils, the thermoplastic material being selected from the group consisting of polyetherimides and polyether-etherketones;
(b) providing a fibrous sheet or web impregnated with a thermosettable resin or plies of the impregnated fibrous sheets or webs;
(c) superimposing at least one of said films or sheets on at least one of said plies of thermosettable resin impregnated fibrous sheets or webs; and (d) consolidating the assembly so produced and curing the thermosettable resin by heating under pressure.

15. The method of claim 14 wherein said polymer is a polyetherimide.

16. The method of claim 14 wherein said polymer is a polyetheretherketone.

17. A method as claimed in claim 14 wherein said consolidation step takes place at a temperature between about 120°C and about 180°C and a pressure between about 1.5 MPa and about 10 MPa.

18. A method as claimed in claim 14 wherein planar press plates are employed in the consolidation step.

19. A method of preparing a laminated suitable for use in the preparation of a printed circuit board, which method comprises:
(a) extruding thermoplastic films or sheets having a substantially uniform thickness between about 1 and about 5 mils, the thermoplastic material having a catalyst uniformly therein and being selected from the group consisting of polyetherimides and polyetheretherketones;
(b) providing a fibrous sheet or web impregnated with a thermosettable resin or plies of the impregnated fibrous sheets or webs;
(c) superimposing at least one of said films or sheets on at least one of said plies of thermosettable resin impregnated fibrous sheets or webs;

(d) consolidating the assembly so produced and curing the thermosettable resin by heating under pressure;
(e) pretreating the polymer surface with a polar solvent capable of swelling the outer layer of the polymer to promote adhesion of metal to the surface of the polymer after an etching step;
(f) etching the polymer surface in a highly oxidizing solution at a temperature and for a time period sufficient to expose the catalyst; and (g) electrolessly depositing a metal on the exposed catalytic surface of the blank.

20. A method of preparing a laminate suitable for use in the preparation of a printed circuit board, which method comprises:
(a) extruding thermoplastic films or sheets having a substantially uniform thickness between about 1 and about 5 mils, the thermoplastic material being selected from the group consisting of polyetherimides and polyetheretherketones;
(b) providing a fibrous sheet of web impregnated with a thermosettable resin or plies of the impregnated fibrous sheets or webs;
(c) superimposing at least one of said films or sheets on at least one of said plies of thermosettable resin impregnated fibrous sheets or webs;

(d) consolidating the assembly so produced and curing the thermosettable resin by heating under pressure;
(e) pretreating the polymer surface with a polar solvent capable of swelling the outer layer of the polymer to promote adhesion of metal to the surface of the polymer after an etching step;
(f) etching the polymer surface in a highly oxidizing solution at a temperature and for a time period sufficient to provide sites for chemical linking of the polymer surface to a metal;
(g) activating the pretreated and etched surface of the polymer by immersion of the polymer surface in a stannous and palladium solution for a time period sufficient to deposit palladium sites over the surface of the blank; and (h) electrolessly depositing a metal on the activated surface of the blank.

21. A method as defined in claim 19 wherein said polar solvent is dimethyl formamide solution.

22. A method as defined in claim 20 wherein said polar solvent is dimethyl formamide solution.

23. A method as defined in claim 20 wherein the oxidizing solution is chromic acid and wherein said electrolessly deposited metal is copper or nickel.

24. A method of preparing a multi-layer printed circuit board which method comprises the steps of:
(a) providing a circuit pattern on at least one surface of an insulating substrate;
(b) applying a layer of polyetherimide or polyetheretherketone thermoplastic film over the exposed circuit patterns;
(c) treating the thermoplastic surfaces with a solvent and oxidizing agent to render said surfaces microporous and hydrophilic; and (d) electrolessly depositing a metal onto the treated surfaces.