Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~
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
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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.
1~
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.
17 .
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
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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.
19
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.
2~
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.
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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.
15 I
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
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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.
13 .
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.
17
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.
24
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.
11
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.
17
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
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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
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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.
28
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:
22
24
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.
28
29 Polysulfone may be prepared by the nucleophilic
s~bstitution reaction between the sodium salt of 2,2-bis
*trade mark
-15-
~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.
18
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.
17
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.
28
2g Polyphenylene oxide possesses a combination of useful
properties including: (1) a temperature range between about
*trade mark
-17-
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).
S
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.
13
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.
18
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.
29
*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.
23
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~ ;
5~5-1 9~3B .
. ' ~
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.
.
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.
18
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.
29
~.
~ 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.
12
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.
16
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.
26
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
18
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.
21
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.
29
~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.
11
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.
24
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.
11
12
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.
28
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.
24
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.
28
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.
16
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
27
28 ~or printed circuit application, copper deposits for use as the
29 bE~SiC conductor mnterial are usually 25um to 70um thick.
f~ ~2~
59S-198B
. ' ~
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.
16
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.
23
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.
27
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
-33-
, ~ ~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.
18
l9 In the drawings, similar reference numerals are used
to represent similar parts.
21
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).
14
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.
27
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
595-198B
l ¦ printed clrcuLt bonrd.
2 1
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.
18
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
1 EXAMPLE 1
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.
13
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.
23
24 EXAMPLE 2
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
1 EXAMPLE 3
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.
9 EXAMPLE 4
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.
18
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.
22
23 EXAMPLE 7
24 The procedure of example 1 is repeated except that
the following polymers are employed in lieu of polysulfone:
26 polyetherimide
27 polyetheretherketone
29
*trade mark
-43-
!
,~'
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 .
