CA2072398A1 - Method of preparing polymer surfaces for subsequent plating thereon and improved metal-plated plastic articles made therefrom - Google Patents
Method of preparing polymer surfaces for subsequent plating thereon and improved metal-plated plastic articles made therefromInfo
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- CA2072398A1 CA2072398A1 CA 2072398 CA2072398A CA2072398A1 CA 2072398 A1 CA2072398 A1 CA 2072398A1 CA 2072398 CA2072398 CA 2072398 CA 2072398 A CA2072398 A CA 2072398A CA 2072398 A1 CA2072398 A1 CA 2072398A1
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- layer
- enclosure
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Abstract
RD-21,551 METHOD OF PREPARING POLYMER SURFACES FOR SUBSEQUENT
PLATING THEREON AND IMPROVED METAL-PLATED PLASTIC
ARTICLES MADE THEREFROM
Abstract of the Disclosure Method of modifying an aromatic polymer surface to improve adhesion of a metal layer thereon and to the articles produced therefrom. The surface of the aromatic polymer such as polycarbonate, is nitrated by a contact with a nitrating solution such as a mixture of nitric and sulfuric acid and then hydroxylated by a contact with a hydroxylating solution such as ammonium hydroxide. The hydroxylated surface is thus chemically modified to become hydrophilic. The chemically modified surface is electrolessly plated with a primary metal layer. A secondary metal layer is then electrolessly or electrolytically applied on top of the primary metal layer until a metal layer of a desired thickness is attained.
The present invention further discloses articles such as an EMI shielded enclosure or a printed circuit board having metal layers as an EMI shield or a conductive metal trace pattern respectively.
PLATING THEREON AND IMPROVED METAL-PLATED PLASTIC
ARTICLES MADE THEREFROM
Abstract of the Disclosure Method of modifying an aromatic polymer surface to improve adhesion of a metal layer thereon and to the articles produced therefrom. The surface of the aromatic polymer such as polycarbonate, is nitrated by a contact with a nitrating solution such as a mixture of nitric and sulfuric acid and then hydroxylated by a contact with a hydroxylating solution such as ammonium hydroxide. The hydroxylated surface is thus chemically modified to become hydrophilic. The chemically modified surface is electrolessly plated with a primary metal layer. A secondary metal layer is then electrolessly or electrolytically applied on top of the primary metal layer until a metal layer of a desired thickness is attained.
The present invention further discloses articles such as an EMI shielded enclosure or a printed circuit board having metal layers as an EMI shield or a conductive metal trace pattern respectively.
Description
2~72398 RD-21 .551 ~ S~Bs~GuJENI
P~AT!NG T~IERI~O~J AND IMPRC~VEI) MEIAl,:PLAIEO PLA~Tl~
.ARTLÇ~L~S~ ADE IHJ~EFRC)M
The present invention is directed to improved methods of 10 plating metal on an organic polymer surface, ~nd to improvements in the quality of metal platcd organic polymer substrates.
Ever since the structural plastics have replaced metal in the enclosures used in clectrical applianc~s, microwave ovens, business machines, and other electrical/elQctronic products, 15 manufacturers have had to overcome problems caused by electromagn~tic interfsrence in general (EMI) and radio fre~uency interference (RFI) in particular. The Federal Communications Commission (FCC), since 1983, requires that the elec~rical products not exc~ed certain specified EMl/P~Fl levels. The FCC requirements ~o have been codified in the FCC regulation CRF 47, Part 15, Subsection J. The FCC requirements are met by reducing tha EMI/RFI emission from the electrical/electronic products by providing a shielding.
With the increased ssnsitivity o~ newer, higher-speed, and higher-frequency circuits plus a continued proliferation of electronic 25 devices worldwids, EMI shielding problems are becoming more demanding. This has placed greater ernphasis on high signai attenuation by the shielding medium.
The E~Al shielded enclosures are also used to protect delicate elec~ronic/electrical circuitry and componen~s enclosed 30 within the enclosure from damage by sxternal sources such as static ~lectricity or man-made high intensity EMI amission produced by an atmospheric nuclear explosion.
:
~0723~
2 RD-Z1,551 Electromagnetic and radio-fre~uency interference are often referred to as electronic nois~. Electronic noise may occur naturally from sources such as lightening or static electricity or from man-made sources such as radio signals, radio games, 5 computers, calculators, cash r~gisters, ~lectrical motors, automobile ignition systems, and all kinds of appliances, especially those that incorporate electronic compon~nts. A well-shielded enclosure enclosing the electrical components is often the quickest and most cost-effective w2y to suppres man-made electromagnetic 10 noise.
Enclosures for electrical components having metal oases, metal foil ctaddings, wire mesh scr~ens, applied coatings, magnetic materials, and a variety of alternative approaches have bean tried.
However, because of their cost advantages and ease of processing, 15 plastlc enclosures having metallized coatings have emerged as the dominant choice.
Printed circuit boards have b~come the dominant vehicle for mounting and interconnecting electronic components in order to manufactlJre a desired electronic circuit. The print~d circuit board 20 usually consists of a sheet of a dielectric substrate constructed from various fillsd or unfilled synthetic ma~erials. The substrate is provided with a pattern of thin mstat foil which functions as a conductive path on one or both sidcs. The paths or"traces" are usually formed of a conductive material such as copper, palladium, 25 nickel or gold. The traces collectively define all of th~ electrical connections betNeen components on ths boa~, and are routed between tha appropriate locations on the board.
Thermoplastics materials such as polycarbonates are particularly suitable for printed circuit board substrates because of 30 their strength, heat resistance, dimensional stability, and ease of moldability. I lowever, polycarbonate substrates are not easily provided with a strongly adherent rnetal trace. The printed circuit, i.e., the plated metai conductive path, can be dama~ed or separated from the substrate during the subsequent manufacturin~ steps or 35 during use of tha circuit board.
2~723~8 3 RD-21,~51 Currently, a number of approaches have been tried to solve the problem of applying metallized coatings onts the plastic enolosures or substrates. One involves adding an electrically conductive material to a polymer composition from which a shieldsd 5 enclosure is molded or formed. However, this method is limited by the type and the amount of conductive additives that can be incorporated into the polymer composition before the physical properties of the composition begin to dateriorate to unacceptable levels. Some work has been done in produGing parts made from 10 inherently conductive polymers, such as polyarylenes; however, these materials are intrinsically unstable.
A second approach invol~es ~he use of metal-loaded paints. Silver was popular before its rise in price. The paint industry has invcstigated all types of substitut~s, including carbon 15 black, copper and nickel. The most promising paints appear to be thoso loaded with nickel or copper. Howaver, painted EMI shields are fraught with a number of problems such as chemioal attack by the paint solvent on the underlying substrats, difficulty in environmentally safs disposal of the paint waste, flaking, 20 scratchin~ or scuffing of the painted surface, difficulty in controlling the thiokness of the painted surfaces, and the high cost of a painting operation.
Several attempts h~ve baen made to produce effective EMI shields at a reasonable cost. One of the most eff~ctive and 25 promisiny me~hods involves electroless plating of tha surfaces of the EMI shislded enclosures. Electroless or autocatalytic plating is defined as a deposition of a metal or alloy coating on a suitable substrate by a controlled chemical reduction that is catalyzed by the me~al or alloy being deposited. ~
30 J a~ K~ K, Page 213, lines 5-7. A great advantage of the el~ctroless plating solutions is their ability to deposit conductive metal films or layers on the properly prepared non-conductors and th~ir ability to uniformly coat any pla~abl~ objeGts. El~otroless plating p~rmits the deposition of pure-metal films onto a prepar~d 35 moided part surface. Electrolessly metal plated surfaces of the ~7239~
P~AT!NG T~IERI~O~J AND IMPRC~VEI) MEIAl,:PLAIEO PLA~Tl~
.ARTLÇ~L~S~ ADE IHJ~EFRC)M
The present invention is directed to improved methods of 10 plating metal on an organic polymer surface, ~nd to improvements in the quality of metal platcd organic polymer substrates.
Ever since the structural plastics have replaced metal in the enclosures used in clectrical applianc~s, microwave ovens, business machines, and other electrical/elQctronic products, 15 manufacturers have had to overcome problems caused by electromagn~tic interfsrence in general (EMI) and radio fre~uency interference (RFI) in particular. The Federal Communications Commission (FCC), since 1983, requires that the elec~rical products not exc~ed certain specified EMl/P~Fl levels. The FCC requirements ~o have been codified in the FCC regulation CRF 47, Part 15, Subsection J. The FCC requirements are met by reducing tha EMI/RFI emission from the electrical/electronic products by providing a shielding.
With the increased ssnsitivity o~ newer, higher-speed, and higher-frequency circuits plus a continued proliferation of electronic 25 devices worldwids, EMI shielding problems are becoming more demanding. This has placed greater ernphasis on high signai attenuation by the shielding medium.
The E~Al shielded enclosures are also used to protect delicate elec~ronic/electrical circuitry and componen~s enclosed 30 within the enclosure from damage by sxternal sources such as static ~lectricity or man-made high intensity EMI amission produced by an atmospheric nuclear explosion.
:
~0723~
2 RD-Z1,551 Electromagnetic and radio-fre~uency interference are often referred to as electronic nois~. Electronic noise may occur naturally from sources such as lightening or static electricity or from man-made sources such as radio signals, radio games, 5 computers, calculators, cash r~gisters, ~lectrical motors, automobile ignition systems, and all kinds of appliances, especially those that incorporate electronic compon~nts. A well-shielded enclosure enclosing the electrical components is often the quickest and most cost-effective w2y to suppres man-made electromagnetic 10 noise.
Enclosures for electrical components having metal oases, metal foil ctaddings, wire mesh scr~ens, applied coatings, magnetic materials, and a variety of alternative approaches have bean tried.
However, because of their cost advantages and ease of processing, 15 plastlc enclosures having metallized coatings have emerged as the dominant choice.
Printed circuit boards have b~come the dominant vehicle for mounting and interconnecting electronic components in order to manufactlJre a desired electronic circuit. The print~d circuit board 20 usually consists of a sheet of a dielectric substrate constructed from various fillsd or unfilled synthetic ma~erials. The substrate is provided with a pattern of thin mstat foil which functions as a conductive path on one or both sidcs. The paths or"traces" are usually formed of a conductive material such as copper, palladium, 25 nickel or gold. The traces collectively define all of th~ electrical connections betNeen components on ths boa~, and are routed between tha appropriate locations on the board.
Thermoplastics materials such as polycarbonates are particularly suitable for printed circuit board substrates because of 30 their strength, heat resistance, dimensional stability, and ease of moldability. I lowever, polycarbonate substrates are not easily provided with a strongly adherent rnetal trace. The printed circuit, i.e., the plated metai conductive path, can be dama~ed or separated from the substrate during the subsequent manufacturin~ steps or 35 during use of tha circuit board.
2~723~8 3 RD-21,~51 Currently, a number of approaches have been tried to solve the problem of applying metallized coatings onts the plastic enolosures or substrates. One involves adding an electrically conductive material to a polymer composition from which a shieldsd 5 enclosure is molded or formed. However, this method is limited by the type and the amount of conductive additives that can be incorporated into the polymer composition before the physical properties of the composition begin to dateriorate to unacceptable levels. Some work has been done in produGing parts made from 10 inherently conductive polymers, such as polyarylenes; however, these materials are intrinsically unstable.
A second approach invol~es ~he use of metal-loaded paints. Silver was popular before its rise in price. The paint industry has invcstigated all types of substitut~s, including carbon 15 black, copper and nickel. The most promising paints appear to be thoso loaded with nickel or copper. Howaver, painted EMI shields are fraught with a number of problems such as chemioal attack by the paint solvent on the underlying substrats, difficulty in environmentally safs disposal of the paint waste, flaking, 20 scratchin~ or scuffing of the painted surface, difficulty in controlling the thiokness of the painted surfaces, and the high cost of a painting operation.
Several attempts h~ve baen made to produce effective EMI shields at a reasonable cost. One of the most eff~ctive and 25 promisiny me~hods involves electroless plating of tha surfaces of the EMI shislded enclosures. Electroless or autocatalytic plating is defined as a deposition of a metal or alloy coating on a suitable substrate by a controlled chemical reduction that is catalyzed by the me~al or alloy being deposited. ~
30 J a~ K~ K, Page 213, lines 5-7. A great advantage of the el~ctroless plating solutions is their ability to deposit conductive metal films or layers on the properly prepared non-conductors and th~ir ability to uniformly coat any pla~abl~ objeGts. El~otroless plating p~rmits the deposition of pure-metal films onto a prepar~d 35 moided part surface. Electrolessly metal plated surfaces of the ~7239~
4 RD-21,5~1 substrates can be then easily electroplated to desir6d thickness, ei~her with the sam~ metal or with a different metal or alloy.
Thermoplastic materials such as polycarbona~es are particular~y suitable for making EMI shielded enclosures or holJsings due to their 5 high impact strcngth, heat resistance, dimensionai s~ability, and ease of moldability. However, polycarb~nate substrat~s can not be easily electrol~ssly plated or coated with a strongly adherent conductive metal tayer.
SevQral at~empts have been made to increase th~
10 adhesi~n of a conductive metal layer to polycarbonate substrates.
Adhesion is generally measured as a 4peel strengthn, i.e. a force requir0d to p0el an adherent metal iayer from an underlying substrate under controlled conditions. The controlled conditions are specified in The American National Standard Test titled ANSI/ASTM
15 D 3359-76, Measuring Adhesion by Tape Test.
One of the prior art me~hods for improving adhesion involves grit blasting the surface to provide a roughened profile on which the subsequently-applied me~als can be anchored. Other mcthods call for the use of chemical swellin~ agents or penetrants 20 to swell the surface prior to the application of a metal layer.
While such methods do increase adhesion, they are often not entirely satisfactory for several reasons. Such t~chniques result in structural degradation of the polymer moleeules disposed along the surface that results in decreasing the tensile as well the 25 impact strength of the underlying polymer substrate. The aforementioned structural degradation results from tha swelling and cracking s~eps to which the entire subs~rat~ material is cxposed, especially in those instances in which ths polymer contains fillers.
Additionally, such surface preparations cause crack formation and 30 propagation at highly stressed areas such as at sharp cornars or edges of the 0nclosure being shielded. The pres~nce of such cracks invariably results in a poorly shielded enclosur~. As a result, a~
present, no viable and cost effeetive process of preparing the surfaces of an EMI/RFI shielded plastic enolosures for an electroless 3S metal plating exists.
207239~
5 RD~21,5~1 Therefore thc primary object of this invention is to provide a method of applying highly adherent metal layers on a surface of an aromatic polymsr substrate by chemically modifying the surface.
Another object of this invention is to provide a metal plated aromatic polymer substrate in the form of an EMI shielded enclosure wherein the noise genarated by the encloscd electrical/electronics componsnts is r~ducad to a desired level by the shielded ~nclosure.
Ye~ another object of the pressnt invention is to provide a polycarbonate substrate having nitrophenol polymer chain ends on the polymer chains exposed along the surface of ths substrate whereby the surfaca acquires a hydrophiiic ctlaract~ristic n0cessary for an electroless metal deposition.
Still another object of the present invention is to provide a printed circuit board comprising an electrically conductive electrolessly plated metai trace pattern disposed on a chemically modified surface of an aromatic polymsr substrate, the pattern having an improved adhesion to the surface of the substrate.
SlJmmarv of th~ Invention Th~ present invention is directed to a method of modifying an aromatic polymer surfaee to improvs adhesion of a metal layer ~n the surface comprises nitration of potymer molecules disposed on the surface by a nitrating solution followed by ammonolytic cleav0ge of nitrated polymer molecules by an ammonolytic solution and to the articles produced therefrom. The surface of the aromatic polymer, such as polyearbonat~, is nitrated by con~act with the nitrating solu~ion comprising nitrie and sulfuric acid. The nitrated surface is then contacted with ths ammonolytic solution such as ammonium hydroxids. Tho surfac~ is thus chemically modified to become hydrophilic, a desired condition prior to metallization of the surface.
207~398 B RD-21,551 Ths present invention aiso discloses a method for applying a metal layer on the surface, chemically modified by the aforemention~d method. A primary metal layer is electrolessly applied on the chemically modified surface. A secondary m~tal layer 5 iS then electrolessly or electrolytically applied on top of the primary metal layer until the metal layer of a desircd thickness is attained. A primary metal layer of copper followed by a secondary metal layer of nickel is the preferred choica.
The present invention further discloses articles such as 10 an EMI shielded enclosure or a printed circuit board having metal layers as an EMI shield or a conductive metal trace pattern respectively.
Detail~d_Q~scri~tion Qf th~ Inv~ntinn The present invention is directed to pre-treating a surface of an aromatic polymer substrate by chemically modifying its surface chemistry to improve adhesion of a metal layer deposited on the surface. Generally an adhesion bond between the 20 metal layer and the surface of the underlying substrate is established by an interfacial molecular contact between the metal layer and the surface. The interfacial molecular contact is directly proportional to the wettability of the polymer surface. The wettability of the polymer surface is defined in t~rms of an angle of 25 contact of a liquid droplet on the surface. A wettable (hydrophilic) surface will have a lower angle of contact (acute angle) than a non-wettable (hydrophobic) surface, which has a higher angle of contact (obtuse angle).
The process of this invention includes several steps. In 30 the first tYVo steps, the surface of a polymer substrate, such as an EMI shielded enclosure, is chemically modified before subjectin~ the surface to a rrietallization process. The surface is chemically modified by sequen~ially contacting the surface with the solutions disclosed hereinafter. In a third step, the chemically modified 35 surfacc is catalytically activated to permit electroless metal .
7 RD-21,551 deposition. tn a fourth step the catalytically activat~d surface is electrol~ssly plated with a ~netal lay~r of a desired thickness. In fur~her steps, the electrolessly plated surface may be electrolytically plated (electroplated) or electrolessly s (autocatalytically) plated with anothar layer of a metal sirnilar to ~he one underneath or a diff~rent metal. Th8 s~eps are normally interposed with rinsing steps.
The polymeric substrate disclosed in the present inventicn is substantialiy aromatic. As used hersin, the term 10 "substantially aromatic" denotes a polymer in which a substantial proportion of the mers (i.e. repeating monomer-derived units) contain aromatic moieties, such as benzene or napthal~ne groups. In general, at least about 40% by number of th~ mers, preferably at least about 90% and frequently 100%, contain an aromatic moiety.
5 The aromatic polymers forming the substrato can bo seleeted from a group consisting of polycarbonates, polyimides, poly(e~hyleno teraphthalates), poly(phenylene oxides), phonol formaldehydes, polystyrenes, polysulfones, and blends thereof. Preferred polymers used in the process of this invention are polycarbonatss, thosa 20 derived from bisphenol A being tho most pr~ferred.
Polycarbonates (PC) may be prepared by the reaction of dihydroxy aromatic compound such as bisphenol A with carbonyl chlorid~ in an int~rfacial process. This reaction may be carried out under basic conditions in the presence of an agu~ous and organic 25 phase. Aromatic polycarbonates have a recurring moiety having the forrnula, - O - Al - O - C -30 where A1 is an aromatic radical. Illustrative A1 radicals include those derived from bisphenol A, 2,2',6,6'-totramethyl bisphenol A
and l,l-dichloro-2,2-bis(4-hydroxyphenyl) ethylene. Typical polyearbonates pr~pared from these and other aromatic dihydroxy 2~7%~
8 RD-21 ,551 compounds are w~ll known in the art as illustrated by the following patents, incorporated herein by reference:
3,13~,008 3,334,154 4,073,814 4,217,438 3,157,622 3,635,895 4,130,548 4,239,918 3,169,121 3,737,409 4,19~,157 4,379,910 3,269,986 _ The polycarbonate resins are commercially produced as LexanX polycarbonate by General Elec~ric Company, Makrolon~
polycarbonate by Mobay Corporation ~nd Calibre~' polycarbonate by Dow Chsmical Company.
The aromatic polyimides, under the class of suitable 15 aromatie polymers, may be prepared by ~he rsaction of a diamine ~such as, m-phenylanediamine, 4,4'-diaminodiphenylmethane or 4,4'-diaminodiphenylether) with a dianhydride. Typical dianhydrides are pyrometallic dianhydrides, bis~3,4-dicarboxyphenyl) sulfone dianhydride, bis(3,4-dicarboxyphenyl) sulfide dianhydride and 2,2-20 bis[4-(3,4-dicarboxyphenoxy)phenyl]-propane dianhydrids. Because of the ether gr~ups present in the last-mentioned bisphenol A
dianhydride, polyimides derived therefrom are normally designated "polyetherimides". Polyimides and polyetherimides are also known in the art as illustrated by the following patents, incorporated 25 h~rein by reference:
3,356,691 3,850,965 3,983,093 4,118,535 3,422,064 3,933,749 4,048,142 4,297,474 3,803,0B5 3,944,517 4,092,297 4,331,799 3,847,867 3,968,083 4,107,147 4,332,929 3,847,86g 3.975.345 207~39~
g RD-21,5~1 The polyetherimid2 resins may be commercially produced as Ultem~9 polyetherimide by General Ele~ric Company.
Poiy(Ethylene terephthaiate) (PET) may be prepared by oxidizing paraxylene to produce terephthalic acid which is then 5 purifi~d either by reaction with methanol to form dimethyl ester of terephthalic aeid (DMT) or by further oxidation to form purified terephthalic acid (PTA). Ancth0r basic fced stream for PET is ethane, which is convertad to ethylsne oxide and then finally to ethylenc glycol (EG). PET is a condensation polymer produced by 10 reacting (DMT), or (PTA), and (EG) using a continuous melt-phase polymerization proc~ss, followed by a solid-state polymerization process that yields a highly crystali~e pelletized product.
The Poly(Ethylene tereph~halate) resins arc commercially produced by Eastman Kodak Company.
The poly(phsnylene oxide) polymers also known as polyphenylene ethers are prepare~ by known methods, typically by an oxidativo coupling polymerization of 2,6-dimathyl-phenol in~o a polymer characterized as 2,6-dimethyl-1,4-phcnylene ether.
The Poly(phenylene oxide) rcsins are commercially 20 produced as PPO~ by General Electric Company.
The polymer substrat~ disclosed in the present invention may also include various additives used for difFerent purposes. The additives incorporated in the aromatic polymer of the present invention are selected from the group consisting of flams 25 retardants, polymer chain initiators, polymer chain inhibitors, polym~r chain stabilizers, plasticizers, color pigments, ul~raviolet radiation absorbing agants, microwave absorbing agen~s, anti-static agsnts, impact modifiers, glass fibers, glass beads, carbon fib&rs, internal mold release agents, anti-oxidan~s, fillsrs, chemical 30 blowing agents, silica, mica, and mixtures thereof.
In the first step of this invention, the surfaces of the enclosure, preferably of polyc~rbonate, are contaoted for an effective ~ime a~ an effeetive temperature wi~h a nitrating solution of an cffective concentration for nitrating the exposed surfac~. As 35 usad herein, ~effective time, temper~ture and conGentration" relate 20723~8 1 0 RD-21,551 ~o a period of duration and degrs~s of temperature and concentration r~sp~ctively required to achieve a level of nitration sufficient to prQducs a desired degree of ch~mical modification on the surfac~. In the presence of nitronium ions (N02') the aromatic rings at nd near 5 the surface undergo an electrophilic attack that results in having the nitro group substitutsd in the aromatic ring. I~ is expect~d that due to the activating powar of the carbonate functi~nality, ortho su~stitution predominates. Since the nitronium ion is highly raactivs, the rate of nit!ation is fast and a significant portion of the 10 aromatic rings of the polymsr chain segments disposed alon~ tha surfaces will be nitrated. However at som~ depth from tha surface no nitration occurs. As a result a si~gl~ polymer may contain chain segments disposed in superior position from the exposed surface that are nitrated and some that are in inferior position from the lS exposod surface that are not nitrated. The nitration step schematically is shown in the structural representation below, O\ o o a \ ~~ O-C-( n -~0 C{~ ~C O~
~ ~ac~a1~
N~i2 ~}l-~ O-C-~I-~O-C-IJ~
(b) ¦ o n o~N NO2 ~) 11 ~ ~ il G~ f=( ~ ~ ~c-o~ ~aC-~ ~
~ ' 11 R~ 551 The nitrating solution includes a mixture of nitrating agents selected frorn the group consisting of nitric acid, acetyl nitrate, dinitrogen pentoxide, metal nitrate, nitronium tetrafluroborat2 and dehydrating agents selected frorn the group s consisting of sulfuric acid, acetic anhydride, trifluoroacetic anhydride. The nitrating solution of the preferred embodiment comprises a mixture of one part of ni~ric acid dissolved in watcr at a conc~ntration of at least about 60% by weight to about 7~% by wei~ht, pref~rably at ~bout 60% by weight, with two parts of 10 sulfuric acid dissolved in watsr at a concentratiorl of at laast about 90% by weight to at about 95% by weight, preferably at about 90% by weig ht.
Before the nitration of the surfaces of the enclosure it may be neeessary to clean the surfacos ultrasonically or with a 15 solvent such as ~vater, detergent such as for oxample MicroE9 made by International Products Corp. or with a solvent having solvent charac~eristics similar to Freon~9 1,1,2-trichloro-1,1,2-trifluor~ethane but is safe to the environmant. Ths cleaning step removes greases, oils and particulate mattar such as dust particles 20 from the surfaces. The effective time during whioh the nitrating solution is contacted with the surfaces is at about 0.5 to about 20 minutes, preferably for about 2 to about S minutes. The su~aces may be contacted with the nitrating solution by aither immersing the enclosure in a bath containing the nitrating solution or by 25 spraying or painting the solution on the desired surfaces of the enclosure if it is desirous for cosmetic reasons to provide an EMI
shield coat only on the innar or hidden surfaces or walls of the FMI
enclosure. The spraying or painting methods are well known in the art. The temperature ~f the nitra~ing bath or the sprayed nitratin~
30 solution is preferably maintaincd at about 10C ~o about 8ûC. Thos~
skilled in the art will r~adily realize that by manipulating the conccntrations and thc temperature of the nitrating solutions, the tim~ of contact may optimized for particular processing conditions.
The nitrating bath is preferably stirred during the nitrating step to 35 improve the efficiency of the chemical reaetion. The nitrated 2~72398 1 2 RD-21,5~1 surfaces are then rinsed with water to romove any remaining nitrating solution from adhering to them. Tha surfaces after the nitration are still hydrophobic.
A s~c~nd step of the invention is provided by contacting 5 the nitrated polymer molecul~s disposed on th~ surface for an effective time at an effective temperature with an ammonolytic solution of an effective concentration for ammonolytic cleavage of the nitrat~d polymer molecules. As used h~rein, "effec~ive time, temp~rature and concentration" relate to a period of duration, 10 dagrees of temperature and concantration respectively required to achieve a level of ammononolysis sufficient to produce a desired degree of chemical modification polymer molecules on the surface.
Typically the ammonolytic solution includes a mixture of water and a compound from tha group consisting of ammonium hydroxide and 15 tetraalkylammonium hydroxides. The ~mmonolytic solution of the preferred embodiment comprises arnmonia dissolvod in water at a concentration of about 0.001% to about 30% by weight, preferably at about 3% to about 8% by weight. The ammonolytic sohJtion, if needed, may also contain a pH adjuster, such as alkali metal 20 hydroxide.
It is theorized, without dependence thereon, that ammonolysis occurs wh~n ammonia (NH3) reacts with the aryloxycarbonate carbon bond proximal to tha aromatic ring having the substituted nitro group. The aforementioned bond site is ~5 expected ~o be where a cleavage occurs as the nitro group can resonance stabilize the deveioping charge. Initially it is axpected that ammonia reacts to form a hydroxyl (-OH) and a urethana (H2NC(O)O-) group. However urethane is apparently unstable under the reaction conditions and it further reacts with ammonia to form 30 urea (H2N~O)NH2) and ano~her hydroxyl group. The polycarbonate polymer chains containing the nitro ~roups are fragmented to yield nitrobisphenol A and urea. The non-nitrated polymar chain sgments anchored to the bulk of the polymer substrate are terminated with nitrophenol and phenol moieties. The overall resulg of the 35 ammonolysis is sch~matically shown below, ;
207~8 1 3 RD-21,5~1 ~l_~O-C~ o (b) n ~ NO2 ~
~ ~I-a~-~l-a~
~¦ aoc~ ~OH NO2 0 (c) o n HO~¦ ~ OH ll ~ ~1 a ~1 a + H2N c ~2 The effsctive time during which the ammonolytic 5 solution is contacted with the nitrated surfaces i5 at about 1 minute to about 24 hours, preferably about 2 to about 6 minutes. The nitrated surfaces may b~ contacted with the ammonolytic solution by either immersing the enclosure in a bath containin0 the hydroxylating solution or by spraying or painting the solution on the o desired nitrated surfaces of the enclosure if it is desirous for cosmetic reasons to provide an EMI shield coat on the inner or hidden surfaces or walls oF the EMI enclosure. The spraying mathods are well known in the art. The temperature of ~he hydroxylatin~ bath or the spraycd hydroxyla~ing solutisn is pr~ferably maintained at about 5 5C to about 65C. Those skilled in the art will readily reaiize that by manipul~ting the concentrations and the temperature of ths ammonolytic solutions, the time of contact may be optimized for particular processing conditions. The ammonolytic bath is preferably stirred during the ammonolytic step to improve the 20 efficiency of the chernical reaction. As a result of the ammonolysis ~723~8 1 4 RD-21,5~1 surfaces of tha polycarbonate substrate turn d~ep yellow with some evidence of surface dissolution. The ammonolyted surfac~s ar~ then rinsed with water to remove any remaining ammonolytic solution adhering to them. Thc rinsed surfaces are hydrop~ilic, smooth to touch and have pale yellow color. If the arnmonolyted surface is placed in an aqueous solution of a dilute acid, it app~ars nearly colorless. Howcver if the hydroxylated surface is placed in an aqueolJs solution of a dilute base it appears yellow. This pH
dependent shift is rapid and reversible and thereby demonstrates the presence of nitrophenol functionality disposed along the polycarbonate surfaces. According to the M~rck Index, the compound o-nitrophenol is used as a pH indicator (a pH of 5.0 appears colorless whereas a pH of 7.0 appears yellow). X-ray Photoelsctron Spectroscopic anaiysis an~ static Secondary lon mass Spectroscopc analysis of the chemically modifie~ polymer confirms tha presence of nitropheno! moieties. It is undorstood that the present invention is not dependent on the aforementioned mechanism. Ths mechanism, to the extent disclosed, provides for a better understanding of the invention.
If a rougher surface is desired, an alkali m~tal hydroxide may bc added to the ammonlytic solution. Potassium hydroxide is pre~errad. The roughened surface may provide greater adhasion of subsequent m~tal layers applied thereto by allowin~ some mechanical adhesion in addition to the chemical adhesion. In 25 general, the alkali metal hydroxide should be added to th~
ammonlytic solution in an amount rangin~ from about O.OO~M to about 10M, pr~ferably about 0.5M to about 3.0M. Preferably the ammonlytic solution containing thc alkali metal hydroxide is contacted with the nitrated surfaces for about 5 to about 20 30 minut~s. The preferred temperature of the ammonlytic solution containing the alkali metal hydroxide should be about 30C ~o about 50C.
In the third step, th~ chemically modified surfaces are catalytically activated by the methods well-knowr~ in the art and 35 desGrib~d, for example, in the U.S. Patent 3,5B9,916, as well as in 2~7239~
1 5 RD-21,551 the U S Patents 4,873.136 and 4,842,S46 to Foust et al., and in the U.S. Patent 4,775,449 to Dumas et al., all aforementioned patents being incorporated h~rein by reference. For ~xample, the substrate may be catalytically activated by contacting with an acid solution of a precious metall such as palladium chlorid~ in hydrochloric acid, for a period of time suffioient to cause the catalytic activation of the substrata surface, wherein the palladium is adsorbed 011 the exposed surfaces.
It is oft~n useful ~o begin the activation of the substrate by treatment with ~n additive which aids in adsorption of the plating catalyst. Such additives are well-known in the art~
Exemplary aids to catalyst adsorption include Shipley 1175A, a produc~ of the ~hiplcy Company, and Met~x 9420, a produc~ of the MacDermid Corporation. Immersion in about 0.1% to about 5% by volume of ~ither of these agents in water for about 1 minute to about 10 minutQs at a temperature of from about 40C to about 80C
is usually sufficient. Although such a treatment is not deem3d critical to the present invention, its use often snhances the uniform deposition of electrolessly applied m~tals onto the substrate.
One illustrative activation techniqua involves imm~rsing the substrate in a solution of Shiplcy Cataprcp'19 404, a product of the Shipley Company. This solution provides a protecting a~ent for the plating catalyst subsequently appliod, and compris~s sodium bisulfate and Yarious sùrfactants. The subs~rate may th~n bo immersed in a solution of Shiplsy CatapositB' 44, which contains the Cataprep~' 404 ingredients, tin, and palladiurn, which is the electroless plating catalyst. The substrate may also be imrnersed in a solution of Macuplex'D ~-34-C made by MacDermid Inc. having palladium/tin particles in colloidal form. A~tar a water rinse, the substrates may ~hen be immersed in a solution of Shipley Cuposit~9 Aco~lerator t 9, a fluoroboric acid-containin~ formulation used to separate tin from the plating catalyst.
Activation and plating process~s suitable far the presen~ invention ar~ also described in the application of W.T.
Grubb et al., European Patent No. EP 27Z,420, and incorporatsd .
. .
.
20723~8 1 6 RD-21,5~1 herein by r~ference, and also in U.S. Patents 3,011,920 and 3,841,881, issued to Shipley and Feldstein et al., respectively, both of which ar~ also incorporated h~rein by reference. A water rinse generally follows the activation step.
Aft~r surface activation and rinsing, the fourth step of the present invention, namely aiectrol~ss plating of a primary metal layer, can be undsrtaken. Illustrative metals used to form the metallization layer includo copper, palladium, nick~l, silver, platinum, cobalt and gold. Copper is usually the m~tal of choice when forming a printed circuit. A composite of a copper lay0r followed by a nickel layer is the preferred choice in preparing an EMI shielded ~nclosure. The nick~l layer is typically used to protect the EMI copper layer shield from corrosion and abrasion.
The adhesion mechanism between the modified polymsric chain and metal (M), though not fully understood, is believed to be as shown in the structural representation below, o NO
C-~¦.~ OH
~ M
o ~ N-O:
Electroless baths are wall-known in ~he art and are gsnerally described in the Kirk-C)thnlçr ~f Ch~nnical Techn~lo~, 3rd Edition, Volume 8, th~ contents of which ar~
incorporated herein by reference. The s~lection of a particular bath or ~lectroless platin~ process is not cri~ical to the present invention. Thc contents of the bath and the particular plating parameters, ~.9., temperature, pH, and immersion time, will of 207~3~8 1 7 FiD-21,5~1 course depend on the particular plastic serving as th~ substrate, and also upon th~ particular meta7 being deposited thereon.
Suitable plating baths includ~ tha Shipley Cuposit'~ 250 system, the Enthone~ 408 and the Enplate(9 Ni-426 syst~ms, latter two made by Enthone Inc. Furthermor~, the Grubb et al. application and Dumas et al. patent, mentioned ab~ve, list suitable electroless plating formulations. Immersion times, bath t~mperatures, and other operating parameters can be dctermined and c~ntrolled accordin~ to manufacturers' suggestions in ord~r to deposit the metal layer of a desired thickness in a desired duration of time.
Those having ordinary skiil in tha plating art will be able to determins the most appropriate plating regim~n for a particular situation .
The polycarbonate surface may ba subjectecl to a hcat treatm~nt after an alectrol0ss deposition of the metal. Ov~n hea~ing of the ~ntire articl~, i.*., substrate with metal thsr~on, is sufficient, although any hoating method is suitable. Typically, this heat treatment is carried out at a temperature rangin3 from about 45C to about 170C for about 5 minutes to about ~20 minutes, with higher temperatur~s within the above ran~e g~nerally compensating for shorter duration, and vice versa. The aforemention~d hcat treatment is prefarebly carried sut at 120C. Although the mechanism is not und~rstood, the h~at treatm~nt app~ars to reduce thc tim~ required to attain optimal adhesion.
If anoth~r layer of metal is to be elsctrolytically applied on th~ surface, e.g., by electroplating, the above-d~scribed heat treatment can in some instances be cmitted if a heat treatrnent is employed after the plating of more of the me~al, as doscribed below.
However, preferably the heat treatment is provided prior to electrolytic deposition of metal. Some of the embodiments inolude a heat treatment prior to the alcctrolytic d~position of metal (i.e., after the electroless d~position), aiong with another h~at treatm~nt after ~he final laycr of metal has bscn appJied, as described balow.
Even though electroplating is one of the methods for applying a secondary or a second metal layer, an el~ctroless plating 2~723~8 1 8 RD-21 ,551 as described above, is the preferred choice. The substrate is usually cleaned prior to immersion in the electroplating bath. The cleaning can be pe~ormed by rinsing the substrate with a dilute solution of a strong acid, such as 10% by weight of sulfuric acid in water.
Electroplating or electrolytic plating baths are well known in the art and are described, for example, in U.S. Patent 4,555,315, incorporated herein by reference, although tha particular electroplating bath used is not critical to the present invention. The choicQ of course d~pends in part on tho parti~ular metal being deposited. Suitable metals include those described for the electroless deposition. Furthermore, thoss ~killed in the art appreciats that the particular bath contonts will depcnd upon some of the factors considered for the elcctroless deposition of metal described above. Typically, th~ electroplating bath for copper is operated at a temperature ranging from about 16C to about 38C, with a cathode current density in the ranse of about 1 ASF to about 80 ASF. A description of baths for plating copper or various other metals is given in the Kirk-Q~er referencc desuibed above, in Vol. 8, beginning on pago 8Z6. Baths used to ap~y a layer of coppcr to the slectrol2ssly applied layer typically includ~ an aqueous acidic copper olectrolyte such as those of th~ acidic copper sulfate or acidic copper fluoroborate type; h~lide ions, such as chloride and/or bromidQ ions; and various other components well-known in the art.
The thickness of this second metal layer will of cours~ dep~nd upon the desired end use of the metal-coated substra~e.
As also described in the aforementioned applic~tion of Grubb et al., and in the patent of Foust ~ al. the metal applied on ~he polycarbonat~ substrate may be in the form of a pattern. Exemplary pattarning methods are also described in U.S. Pa~nt 3,562,005, issued to DeAngelo et al., incorporat~d herein by referenGe. Ano~her -technique suitable for use herein is disclosed in the aforemention~d Grubb et al. application. This resistless technique involves the photopatterning of an organic substrate by first exposing ~he substrate to electromagnetic radiation followed by ~reatm~nt with a 3S precious metal compound to catalytically activate the surface. The 20723~8 1 9 RD-21,551 metallic pathway formed after electrolessly plating the activated surface will tightly adhere to the underlying polymer subs~rate because of the chemical modification traatmsnt disclosed in the present invention.
Th~ electrolessly metallized layer when us~d as an EMI
shi~ld is preferably about ~wo micrometers in thickness. In other embodiments, such as a printed circuit board, tha el~ctrolessly metallized lay~r prepared by the method of this invention usually has a thickness of about 1 microme~ers tn about 5 micrometers and an electrolytically appiied layer thereon is at l~ast about 5 micrometers in thickness.
An article prepared by the m~thod of this invention comprises an aromatic substrate preferably of polycarbonat~, means to improve adhesion of a mstal on a surface of said substrate comprising modifying said substrata b~ contacting said surface with a nitrating solution followed by contacting with a hydroxylating solution, and a metal laycr disposed on said surface. The metai layer comprises an eiectrolessly applied primary layer on the pretreated surface. Additional secondary metal layars rnay be electrolessly or electrolytically applied on top of the primary metal layer until a desired thickness is attained. The present invention contempla~es various combinations of metal layers such as a single copper layer, a primary copper layer followed by a secondary nickel layer or a primary nick~l layer followed by a secondary copper layer and a tertiary nickel layer.
Ar~icles of various cmbodiments of this invention are suitablo as EMI shielded enclosures, printed cirouit boards or housings having an EMI shield and a printed circuit board wherein th~
circui~ board is an integral part of the housing and contains metallic layers as described herein as a printed circuit pattern or ~trace~.
An article of rnanufacture of tha preferred embodiment of tha present invention comprises an enclosure of an aromatic polymer, such as polycarbonata, having surfaces of ~he walls of ~he enclosure chemically treated by the process of the present invention to improve electroless deposition and a first metal layer, preferably 2~72398 2 0 RD-21,551 copp~r, thereon. A second metal layar, prefsrably of nickel, may be disposed on top of the first metal layer, the second layer b~ing electrolessly or electrolytically applied on the first lay~r. As stated earlier, the second layer is preferably deposited by the 5 slectroless metal deposition. Both the metal layers disposed, if so desired, on the interior sides of the walls of th~ enclosure, have a predetermined combined thickness in accordance with the requirements set forth in the FCC regulations for noise by reducing ~n intensity of nois~ emitted by th~ elec~rical components enclosed o within the snclosure to a desired lavel. The combined thickness of the first and second metal layers is adjusted to meet the FCC
re~uirements. The shielding of the enclosure may bs also used to protect the electrical components enclosed within the shictded enclosure from electro-magnetic radiation of a specified range of 15 frequency of about 1 KiloHertz to about 10 GigaHertz.
In another embodiment of the presan~ invention, an articl~ suoh as an EMI shielded ~nclosure having thre~ metal layered EMI shields. Preferably the first layer is an electrol~ssly applied first nickel layer on the surfaces of thc walls of the enclosure, ~he 20 second layer being an electrolessly applied or olectrolytically applied ~opper disposed on top of the ~irst nickel layer and ths third layer being electrolessly applied or ~lactrolytically applied second nickel layer disposed on top of the second layer.
Still another embodiment is a flat or thr~e-dimensional 25 printsd circuit board (PCB~ of the prssent invention is disclosed.
The PCB may b~ of positive or a negative image type. The PCB
comprises an aromatic polymer substrate, preferably of polycarbonate, whose surfaces have been chemically treatsd in accordance wi~h the process of the presen~ invention to improve 30 adhesion of an electrolessly applied first m~tal layer, followed by an el~ctrolessly applied or an electrolytically applied second metal layer disposed on top of first metal layer, whersin the firs~ and sacond metal layers provide a pattern of traces of d~sired thickness with which to provide ~lectrical interoonnection between electrical 2~723~8 21 RD-21,551 components disposed on the PCB and the external electrical maans.
The preferred metal layers are of copper.
The adhesion between the surfaces of the substrates used in the aforementioned articlss and the metallized layer directly in contact with the surfacas may ba enhanced by increasing the roughness of the surfaces. As mentioned earlier, tho surfaco roughness may be incr~ased by adding the alkali m0tal hydroxide to ths amrnonlytic solution. The surface having rough texture should improvs mechanical adh~sion between the surfaces and th~
me~allized layer dir~ctly in contact with the rough~ned surfaces.
In these examples, adhesion of the matal to the substrate was evaluated by applying ASTM D33~9-78, Mathod B Cross-Cut Tape Test mentioned earlier. Method B, summarized below, comprises:
1. cutting, with a sharp knife blada, a cross hatch pattern in single pass uniformly applied strokes through th~ rnetal layer disposed on the substrate area being evaluated by the test;
2. removing the debris genarated during the cutting procedure;
3. eveniy applying over the cross hatched area tha recommended adhesive tape, having an adhesive strength of 36 ~ 2.5 ounce par inch;
4. pulling the tape away from the area a~ 9O to the surface in one quick stroke; and 5. checking the tape for any metal flakes.
A classification of 5 means no metal layer was flaksd off ths surface whereas a classification of O means greater than 65% of the metal layer was flaked off th0 surface~ The intermediat~
range of classification denotes percentages of flaking occuring batween greater than O% to less than 65%. The classification values for each tape are obtained and then averaged.
Tha present invention will be further understood from th~ description of specific axamples which follow. These examples are int~nd~d for illustrativ~ purposes only and should no~ be construed as a limitation upon the broad~st aspacts af the invention.
All liquid ratios are by volume, unless othanNise indicated.
2~7239~
2 2 RD-21,5~1 E~dm~2b~
A plaque, of 2 inches x 3 inches x 1/8 inches in size, s molded of Lexan(~ polycarbonate BE2130A, was treated as follows:
The substr~te was u!trasonically cleaned for 5 minutes at 24C in a solution comprising 2 volume percent of Micro~9 detergent and 98% by volurne of deionized water. The substrate was subsequently rinsed with watsr and air dried. The substrate was 10 immersed in the nitrating solution, compri~ing 1 part by volume of nitric acid (assay (HNO3~70-71%) and 2 parts by volum~ of sulfuric acid (assay (H2SO4) 95.S-96.5%), at 23C for 3 minutes. The substrate was then rinsed in tap water for less than on~ minute, follcwed by a 5 minute rinse in tap water at 65C, and then cooled to 23C.
The sample was then immersed in a solution, comprising 1 part by volume of ammonium hydroxide (sssay (NH3) 2~.0-30.0%) and 1 part by volume ef deionizsd water at 23C for 4 minutes, and subsequently rinsed in tap water at 23C for 5 minutes. The 20 substrate was oatalyzed by a 2 minute immersion into a solutien at 23C comprising 77.2% deionized water, 22% hydrochloric acid (assay (HCI) 36.5-38.0%), and 0.8% of Macuplex0 D-34-C containing colloidal palladium/tin particles that adsorb ont~ th~ substrata surfaca. The sample was subsequsntly rinsed with water for 1 25 minu~e and thsn imrnersed in an accelarator, a solution comprising 1 part by volume Shipley Cuposit~9 Accelera~or ~9, and 5 parts by volume deionized water. The substrate was then rinsed in ~ap water for about 2 minutes.
The sample was metallized with Enplate(~ Ni-426, a low 30 phosphorus eleetrolsss mstal fcrmul~tion. The ba~h was formulated per ths recommendatiQn by the manufacturer and was maintained at 54C: 1 1C and at pH 6.1-S.2. The substrate was immersed in this bath for I hour. The plated article w 5 removed and rinse~ in tap water for about 2 minutes and then air dri~d. Th~ nickel thickness 35 was determined to be 3.1 micrometers by x-ray fluorescenee on a 2~723~
2 3 RD-21,551 Seiks SFT/156 x-ray instrurnent made by Seiko Instruments and Electronios, Ltd. The adhesion of the metal coating was measured by using a tape test as psr the procedurss outlined in ASTM D3359-78 Me~hod B. A cross-c(lt tool made by Precision Gage & Tool Co. was s used to ~cribe a grid of 10 x 10 - 1 milimeters x 1 milimeters squares. Tap~ was ~venly appliad against the grid and removed in a manner consist~nt with the test procedure. Th~ observation of the scribed area showed that the matallization was completely smoo~h and no flaking of any parts of the squares was observRd thereby o indicating an ASTM adhesion classification of 5. The sample was baked in an air oven for 30 minutes at 80C + 2C. Th~ sample was then removed and ailowed to cool to 23C and the adhesion of the metal coating was rechecked in the manner as outlin2d above. An adhesion classifica~ion 5 was again obtained.
E~mQ~:~
Various grades of Lexan~9 polycarbonate were processed under various conditions using the nitrating and the hydroxylating solutions of the composition disclosed in Example 1. Th~ specific parameters are summarized in Table 1 shown hereafter.
24 RD-21, 551 I . .. . _ ~-U~C l '1:3) a~
~ ~ O
1~ .~ ~D g _ ~ ¦ tC~ O~ N ~N O U) _ N N C~ ~o _ nl ,~ I N N _ _ C~.i _ . -- N -- -- N ~ N U~ t') _ O ~. ~
O , . ~ ID D ~`
N I Æ~ O O O O O C O Q O ~ O O O ~ O c~ E ~ ~B
tD ~ . . .. __ I . ..... ~ ~
~D _ ~ O O 1~ 0 U) U~ O U~ O U~ _ ~ ~ O
IIJ ~ ~ N N ~'~ ~ _ -- N _ _ _ CD _ C~
., ~
.C _ 11~ N It 11~ In U) U> U~ N Nl N C~J ~ 3 ¦ . o~ ~ N
. ~ ~ ~ o ~ ~c o ~ _ U) U~ ~ b :~ E
'91 ' ~ ' E
.' '1: ~________________ ~o o = ~ ---- . ~ T ~ ~
~ ~ _ u) u~ u~ In It'~ u) ~ ~ t~ r-- I~ t~ ~') N ~ t ~ --o n~
. . . ~L ~ E ~ ~L
T - u~ io ~ E
_ . . ~ E ~ o~
C 1` _ N U~ ~ ~0 ~ p~ ~ ~ ~ co E ~ E E
~ 1 . _ . . E E o " E
9~ '';1 --~ ~ 0 .. . . . ~ l O ID ~q u~ N I U~ D~ E ~D
m I ~ ~ N N ~ q- N N N N N Nl IN N N N c ~ 0 V tn ~
~ __ ~ ~;~ V ~
Z _ _ ~ ~ 1~ N N C'~ N ~ ~ C~ N N ~ $ O y~ N
. _ _ a~ ~3 "> "I ~ _ t~7 ~D .. , o~ ~ N N N N ~ N N ~ O O N N ~ N N ~ ~ n O ~ ~ Z E
~ --~ - 9 ~ N C C a~ 3S a m E e~ Q--N ~ U) I~ E ~ c E ~ ~8 ~ F
LL ~ . U~ e~
20723~
2 5 RD-21,551 Nons of the substrates in thc aforementioned examples were cleaned prior to the nitration step. All the rinses unless othenNiss stated wers in flowing tap wat~r at about 15C. The nickel plating baths were maintainsd at a pH of about 6.1-6.3.
~am~
Th~ substrate sample of example 6, shown in Table 1, was provided a furth~r treatment after nickai platin~. The afor~mention~d substrate was baked at about 85C ~ ~C for about ono hour. Once the substrate cooled, the adhesion of the metallized layer was checked. The quali~ of ~hs adhesion classification remained at 5. Subsequently, thc substrat~ sampla was plac~d in a chambcr partially filled with deionized water. The samplc was held in the chamber above tha water level. The chamber was then closed and placsd into an oven, maintained at about 65C ~ 2C and about 100% relative humidity. The adhesion of the metal coating was checked by the aforementionsd ASTM tape t~st method after 1, 3 and 10 days of exposure to the environment within the chamber. In all the cases, the adh~sion classification of 5 was obtain~d.
E~ ,.
The sample of sxample 7, as shown in Table 1, was a plaque having a size of 21/2 inches x 1/2 inches x 1/8 inches. The plaque was secured in a stainlsss steel jig so ~ha~ 3400 pounds per squaro inch of bending stress could be applied on the plaque. The sample under stress w~s then proc~ssed according to th~ st~ps disclosed in Table 1. Upon completion of ~he step cf electroless mctallization, the stressed surface of the plaque was viewed at a magnification of 45 times the normal size using a light microscope.
No cracks, crevices or other adverse effects resulting frum an application of bending stress were observed on the strcssed metalliz~d areas of the plaque. The plaqus was rsmovad from the jig and mount~d in a clear epoxy solution so ~ha~ a cross-section of the metallized area could be made, once tha ~poxy solution hardened.
The cross-section was then viewed at a magniflcation of 1000 times the normal size using a light microscop~. No cracksl crevices ~, ~723~8 2 6 RD-21,551 or other adverse effects w~re observed in either the metallized layer or on the surface of thc substrat~.
~1e 1~
A plaque molded from Lexan'!9 polycarbonate ML6000 was 5 treat~d using the various chemical solutions described b010w. The substrate was immersed, without cla~ning, into the nitrating solution of Table 1 for 6 minu~es at 2~C; water rinsed for 1 minute;
immersed in the aqueous ammonia solution of Table 1 for 6 minutes at 25C; water rinsed for 5 minute; catalyzed fcr 6 minutes at 25C;
10 water rinsed for 1 minute; immersed in th~ acceterator for 5 minutes, and finally water rinsed for 5 minutes. Th~ plaque was then electrolessiy plated with copper- using a Shipley Cuposit~9 251 electroless copper bath, formulated as per the recommendations by tha manufactur~r. The plaque was immersed in the electroless 15 copper bath for 7 minutes while the bath was stirred and maintained at 40C t~ 1C. The plaqua was then water rins~d and air dried. The thickness of copper layer deposited on the substrate was measured by x-ray fluoresc~nce and was determined to b~ 1.5 micrometers in thickness. Tha copper layer on the substrat~ was than metallized 20 with a layer of nick~l, usin3 an alectroless nickel bath as described in exampl~ 1. Tha substrate was immersed in th0 electroless nick~l bath for 5 minutes while the bath was maintained a~ 50C i 1C. The substrate was water rinsed and air drisd. The thickness of nickel layer depasited on top of th~ copper layer was measured by x-ray 25 fluorescence and was determined to be about 0.7 micrometers in thickness. The ASTM tapa test was performed in a manner deseribed in example 1, and an adhesion classification 5 resulted. The EMI
shielding effectiveness was measured by The Dual Chamber Method (ASTM Fs-7-83) developed by Th~ American Society of Testing and 30 Materials. Attenuation values were measured at 30 MegaHertz, 100 MegaHer~z, 300 MegaHertz, and 1000 MegaHertz, producing values each in excess of 60 decibals, 70 decibals, 79 decibals, and 73 decibals respectively. It should b~ stated that the aforementiolled attenuation values arc well within th~ present FCC requirements 35 regarding the EMI shielding.
2~72398 27 RD-21 ,551 ~3m~Q~
A plaque of Lexan~ polycarbonate BE2130A, having a siz~
of 2 inches x 3 inches x 1/8 inches, was proc~ssed under the conditions disclosed in Example 1 during the nitration. Tlle sample s was then rins~d in water and imm2rs~d in an aqueous solution comprising 25 part by volume nf ammonium hydroxide (assay NH3 28%) and 2.0M of potassium hydroxide for 15 minutes at 23C. Tha sampl~ was thcn rinsed and driod. The surfac~ finish (roughness) of ~h~ ammonolyzed surface was measur~d by usin~ a Slaan Dektak ll 10 Surface Profil2 Measurin~ System (version 2.3 profilometer with a diamond tip submicron stylus~, supplied by Sloan Technology Corporation, Santa Barbara, California. Th~ surface finish was measured at + 0.5 ~lM. For comparison, th~ surfaco finish of th~
ammonolyzed surface of the sample in Example 1 was maasured at :~
15 0.1 IlM. Thus, a fivefold increase in sufface roughn~ss was obtain~d by adding potassium hydroxide to the ammonolytic solution.
The ammonolyzad surface of example 19 was then catalyzQd and electrolessly plated. The sample was immersed for 2 minutes in an aqueous catalyzing solution comprising 0.8% by volume 20 of Macuplex0 D-34-C and 22% by volume of HCI (37%). The sample was then rinsad in deionized water for 1 minute and than immersed in a solution comprising 1 part by volume of Shipley Cuposit~
Accelerator 19 and 5 parts by volume of deionized water. The sample was then wator rinsed ~or 2 minutes, nickel plated for 20 25 minutss using an Enplate~9 Ni~26 nickel/phosphorus bath at 50C, water rinsed for 2 minutes, copper plated for 8 m;nutes using a Shipley Cuposit'!9 251 copper bath at ~C, water rinsed for 2 minutes, nickel plated for 3 minutes at 50C: in ~he aforemantioned nickel bath, water r,nsed for 3 minutes, and then air dri~d. The 30 ASTM tape t~s~ was performed in a mann~r described in Example 1, and an adhesion classific~tion 5 r~sulted it will b~ understood that the for~going description is only illustrativ~ of tha present inv~ntion and it i5 not intanded that the invention be limited ther~to. Numerous variations, changes, 35 substitutions, and modifications will now ooour to thos~ skilled in 207239~
2 8 RD-21,5~1 the art which come within ths scope of the pres3nt invantion without departing ~rom the spirit and scop~ thereof. Accordingly, it is intended that th~ invention be limited only by the scops of the appended elaims.
Thermoplastic materials such as polycarbona~es are particular~y suitable for making EMI shielded enclosures or holJsings due to their 5 high impact strcngth, heat resistance, dimensionai s~ability, and ease of moldability. However, polycarb~nate substrat~s can not be easily electrol~ssly plated or coated with a strongly adherent conductive metal tayer.
SevQral at~empts have been made to increase th~
10 adhesi~n of a conductive metal layer to polycarbonate substrates.
Adhesion is generally measured as a 4peel strengthn, i.e. a force requir0d to p0el an adherent metal iayer from an underlying substrate under controlled conditions. The controlled conditions are specified in The American National Standard Test titled ANSI/ASTM
15 D 3359-76, Measuring Adhesion by Tape Test.
One of the prior art me~hods for improving adhesion involves grit blasting the surface to provide a roughened profile on which the subsequently-applied me~als can be anchored. Other mcthods call for the use of chemical swellin~ agents or penetrants 20 to swell the surface prior to the application of a metal layer.
While such methods do increase adhesion, they are often not entirely satisfactory for several reasons. Such t~chniques result in structural degradation of the polymer moleeules disposed along the surface that results in decreasing the tensile as well the 25 impact strength of the underlying polymer substrate. The aforementioned structural degradation results from tha swelling and cracking s~eps to which the entire subs~rat~ material is cxposed, especially in those instances in which ths polymer contains fillers.
Additionally, such surface preparations cause crack formation and 30 propagation at highly stressed areas such as at sharp cornars or edges of the 0nclosure being shielded. The pres~nce of such cracks invariably results in a poorly shielded enclosur~. As a result, a~
present, no viable and cost effeetive process of preparing the surfaces of an EMI/RFI shielded plastic enolosures for an electroless 3S metal plating exists.
207239~
5 RD~21,5~1 Therefore thc primary object of this invention is to provide a method of applying highly adherent metal layers on a surface of an aromatic polymsr substrate by chemically modifying the surface.
Another object of this invention is to provide a metal plated aromatic polymer substrate in the form of an EMI shielded enclosure wherein the noise genarated by the encloscd electrical/electronics componsnts is r~ducad to a desired level by the shielded ~nclosure.
Ye~ another object of the pressnt invention is to provide a polycarbonate substrate having nitrophenol polymer chain ends on the polymer chains exposed along the surface of ths substrate whereby the surfaca acquires a hydrophiiic ctlaract~ristic n0cessary for an electroless metal deposition.
Still another object of the present invention is to provide a printed circuit board comprising an electrically conductive electrolessly plated metai trace pattern disposed on a chemically modified surface of an aromatic polymsr substrate, the pattern having an improved adhesion to the surface of the substrate.
SlJmmarv of th~ Invention Th~ present invention is directed to a method of modifying an aromatic polymer surfaee to improvs adhesion of a metal layer ~n the surface comprises nitration of potymer molecules disposed on the surface by a nitrating solution followed by ammonolytic cleav0ge of nitrated polymer molecules by an ammonolytic solution and to the articles produced therefrom. The surface of the aromatic polymer, such as polyearbonat~, is nitrated by con~act with the nitrating solu~ion comprising nitrie and sulfuric acid. The nitrated surface is then contacted with ths ammonolytic solution such as ammonium hydroxids. Tho surfac~ is thus chemically modified to become hydrophilic, a desired condition prior to metallization of the surface.
207~398 B RD-21,551 Ths present invention aiso discloses a method for applying a metal layer on the surface, chemically modified by the aforemention~d method. A primary metal layer is electrolessly applied on the chemically modified surface. A secondary m~tal layer 5 iS then electrolessly or electrolytically applied on top of the primary metal layer until the metal layer of a desircd thickness is attained. A primary metal layer of copper followed by a secondary metal layer of nickel is the preferred choica.
The present invention further discloses articles such as 10 an EMI shielded enclosure or a printed circuit board having metal layers as an EMI shield or a conductive metal trace pattern respectively.
Detail~d_Q~scri~tion Qf th~ Inv~ntinn The present invention is directed to pre-treating a surface of an aromatic polymer substrate by chemically modifying its surface chemistry to improve adhesion of a metal layer deposited on the surface. Generally an adhesion bond between the 20 metal layer and the surface of the underlying substrate is established by an interfacial molecular contact between the metal layer and the surface. The interfacial molecular contact is directly proportional to the wettability of the polymer surface. The wettability of the polymer surface is defined in t~rms of an angle of 25 contact of a liquid droplet on the surface. A wettable (hydrophilic) surface will have a lower angle of contact (acute angle) than a non-wettable (hydrophobic) surface, which has a higher angle of contact (obtuse angle).
The process of this invention includes several steps. In 30 the first tYVo steps, the surface of a polymer substrate, such as an EMI shielded enclosure, is chemically modified before subjectin~ the surface to a rrietallization process. The surface is chemically modified by sequen~ially contacting the surface with the solutions disclosed hereinafter. In a third step, the chemically modified 35 surfacc is catalytically activated to permit electroless metal .
7 RD-21,551 deposition. tn a fourth step the catalytically activat~d surface is electrol~ssly plated with a ~netal lay~r of a desired thickness. In fur~her steps, the electrolessly plated surface may be electrolytically plated (electroplated) or electrolessly s (autocatalytically) plated with anothar layer of a metal sirnilar to ~he one underneath or a diff~rent metal. Th8 s~eps are normally interposed with rinsing steps.
The polymeric substrate disclosed in the present inventicn is substantialiy aromatic. As used hersin, the term 10 "substantially aromatic" denotes a polymer in which a substantial proportion of the mers (i.e. repeating monomer-derived units) contain aromatic moieties, such as benzene or napthal~ne groups. In general, at least about 40% by number of th~ mers, preferably at least about 90% and frequently 100%, contain an aromatic moiety.
5 The aromatic polymers forming the substrato can bo seleeted from a group consisting of polycarbonates, polyimides, poly(e~hyleno teraphthalates), poly(phenylene oxides), phonol formaldehydes, polystyrenes, polysulfones, and blends thereof. Preferred polymers used in the process of this invention are polycarbonatss, thosa 20 derived from bisphenol A being tho most pr~ferred.
Polycarbonates (PC) may be prepared by the reaction of dihydroxy aromatic compound such as bisphenol A with carbonyl chlorid~ in an int~rfacial process. This reaction may be carried out under basic conditions in the presence of an agu~ous and organic 25 phase. Aromatic polycarbonates have a recurring moiety having the forrnula, - O - Al - O - C -30 where A1 is an aromatic radical. Illustrative A1 radicals include those derived from bisphenol A, 2,2',6,6'-totramethyl bisphenol A
and l,l-dichloro-2,2-bis(4-hydroxyphenyl) ethylene. Typical polyearbonates pr~pared from these and other aromatic dihydroxy 2~7%~
8 RD-21 ,551 compounds are w~ll known in the art as illustrated by the following patents, incorporated herein by reference:
3,13~,008 3,334,154 4,073,814 4,217,438 3,157,622 3,635,895 4,130,548 4,239,918 3,169,121 3,737,409 4,19~,157 4,379,910 3,269,986 _ The polycarbonate resins are commercially produced as LexanX polycarbonate by General Elec~ric Company, Makrolon~
polycarbonate by Mobay Corporation ~nd Calibre~' polycarbonate by Dow Chsmical Company.
The aromatic polyimides, under the class of suitable 15 aromatie polymers, may be prepared by ~he rsaction of a diamine ~such as, m-phenylanediamine, 4,4'-diaminodiphenylmethane or 4,4'-diaminodiphenylether) with a dianhydride. Typical dianhydrides are pyrometallic dianhydrides, bis~3,4-dicarboxyphenyl) sulfone dianhydride, bis(3,4-dicarboxyphenyl) sulfide dianhydride and 2,2-20 bis[4-(3,4-dicarboxyphenoxy)phenyl]-propane dianhydrids. Because of the ether gr~ups present in the last-mentioned bisphenol A
dianhydride, polyimides derived therefrom are normally designated "polyetherimides". Polyimides and polyetherimides are also known in the art as illustrated by the following patents, incorporated 25 h~rein by reference:
3,356,691 3,850,965 3,983,093 4,118,535 3,422,064 3,933,749 4,048,142 4,297,474 3,803,0B5 3,944,517 4,092,297 4,331,799 3,847,867 3,968,083 4,107,147 4,332,929 3,847,86g 3.975.345 207~39~
g RD-21,5~1 The polyetherimid2 resins may be commercially produced as Ultem~9 polyetherimide by General Ele~ric Company.
Poiy(Ethylene terephthaiate) (PET) may be prepared by oxidizing paraxylene to produce terephthalic acid which is then 5 purifi~d either by reaction with methanol to form dimethyl ester of terephthalic aeid (DMT) or by further oxidation to form purified terephthalic acid (PTA). Ancth0r basic fced stream for PET is ethane, which is convertad to ethylsne oxide and then finally to ethylenc glycol (EG). PET is a condensation polymer produced by 10 reacting (DMT), or (PTA), and (EG) using a continuous melt-phase polymerization proc~ss, followed by a solid-state polymerization process that yields a highly crystali~e pelletized product.
The Poly(Ethylene tereph~halate) resins arc commercially produced by Eastman Kodak Company.
The poly(phsnylene oxide) polymers also known as polyphenylene ethers are prepare~ by known methods, typically by an oxidativo coupling polymerization of 2,6-dimathyl-phenol in~o a polymer characterized as 2,6-dimethyl-1,4-phcnylene ether.
The Poly(phenylene oxide) rcsins are commercially 20 produced as PPO~ by General Electric Company.
The polymer substrat~ disclosed in the present invention may also include various additives used for difFerent purposes. The additives incorporated in the aromatic polymer of the present invention are selected from the group consisting of flams 25 retardants, polymer chain initiators, polymer chain inhibitors, polym~r chain stabilizers, plasticizers, color pigments, ul~raviolet radiation absorbing agants, microwave absorbing agen~s, anti-static agsnts, impact modifiers, glass fibers, glass beads, carbon fib&rs, internal mold release agents, anti-oxidan~s, fillsrs, chemical 30 blowing agents, silica, mica, and mixtures thereof.
In the first step of this invention, the surfaces of the enclosure, preferably of polyc~rbonate, are contaoted for an effective ~ime a~ an effeetive temperature wi~h a nitrating solution of an cffective concentration for nitrating the exposed surfac~. As 35 usad herein, ~effective time, temper~ture and conGentration" relate 20723~8 1 0 RD-21,551 ~o a period of duration and degrs~s of temperature and concentration r~sp~ctively required to achieve a level of nitration sufficient to prQducs a desired degree of ch~mical modification on the surfac~. In the presence of nitronium ions (N02') the aromatic rings at nd near 5 the surface undergo an electrophilic attack that results in having the nitro group substitutsd in the aromatic ring. I~ is expect~d that due to the activating powar of the carbonate functi~nality, ortho su~stitution predominates. Since the nitronium ion is highly raactivs, the rate of nit!ation is fast and a significant portion of the 10 aromatic rings of the polymsr chain segments disposed alon~ tha surfaces will be nitrated. However at som~ depth from tha surface no nitration occurs. As a result a si~gl~ polymer may contain chain segments disposed in superior position from the exposed surface that are nitrated and some that are in inferior position from the lS exposod surface that are not nitrated. The nitration step schematically is shown in the structural representation below, O\ o o a \ ~~ O-C-( n -~0 C{~ ~C O~
~ ~ac~a1~
N~i2 ~}l-~ O-C-~I-~O-C-IJ~
(b) ¦ o n o~N NO2 ~) 11 ~ ~ il G~ f=( ~ ~ ~c-o~ ~aC-~ ~
~ ' 11 R~ 551 The nitrating solution includes a mixture of nitrating agents selected frorn the group consisting of nitric acid, acetyl nitrate, dinitrogen pentoxide, metal nitrate, nitronium tetrafluroborat2 and dehydrating agents selected frorn the group s consisting of sulfuric acid, acetic anhydride, trifluoroacetic anhydride. The nitrating solution of the preferred embodiment comprises a mixture of one part of ni~ric acid dissolved in watcr at a conc~ntration of at least about 60% by weight to about 7~% by wei~ht, pref~rably at ~bout 60% by weight, with two parts of 10 sulfuric acid dissolved in watsr at a concentratiorl of at laast about 90% by weight to at about 95% by weight, preferably at about 90% by weig ht.
Before the nitration of the surfaces of the enclosure it may be neeessary to clean the surfacos ultrasonically or with a 15 solvent such as ~vater, detergent such as for oxample MicroE9 made by International Products Corp. or with a solvent having solvent charac~eristics similar to Freon~9 1,1,2-trichloro-1,1,2-trifluor~ethane but is safe to the environmant. Ths cleaning step removes greases, oils and particulate mattar such as dust particles 20 from the surfaces. The effective time during whioh the nitrating solution is contacted with the surfaces is at about 0.5 to about 20 minutes, preferably for about 2 to about S minutes. The su~aces may be contacted with the nitrating solution by aither immersing the enclosure in a bath containing the nitrating solution or by 25 spraying or painting the solution on the desired surfaces of the enclosure if it is desirous for cosmetic reasons to provide an EMI
shield coat only on the innar or hidden surfaces or walls of the FMI
enclosure. The spraying or painting methods are well known in the art. The temperature ~f the nitra~ing bath or the sprayed nitratin~
30 solution is preferably maintaincd at about 10C ~o about 8ûC. Thos~
skilled in the art will r~adily realize that by manipulating the conccntrations and thc temperature of the nitrating solutions, the tim~ of contact may optimized for particular processing conditions.
The nitrating bath is preferably stirred during the nitrating step to 35 improve the efficiency of the chemical reaetion. The nitrated 2~72398 1 2 RD-21,5~1 surfaces are then rinsed with water to romove any remaining nitrating solution from adhering to them. Tha surfaces after the nitration are still hydrophobic.
A s~c~nd step of the invention is provided by contacting 5 the nitrated polymer molecul~s disposed on th~ surface for an effective time at an effective temperature with an ammonolytic solution of an effective concentration for ammonolytic cleavage of the nitrat~d polymer molecules. As used h~rein, "effec~ive time, temp~rature and concentration" relate to a period of duration, 10 dagrees of temperature and concantration respectively required to achieve a level of ammononolysis sufficient to produce a desired degree of chemical modification polymer molecules on the surface.
Typically the ammonolytic solution includes a mixture of water and a compound from tha group consisting of ammonium hydroxide and 15 tetraalkylammonium hydroxides. The ~mmonolytic solution of the preferred embodiment comprises arnmonia dissolvod in water at a concentration of about 0.001% to about 30% by weight, preferably at about 3% to about 8% by weight. The ammonolytic sohJtion, if needed, may also contain a pH adjuster, such as alkali metal 20 hydroxide.
It is theorized, without dependence thereon, that ammonolysis occurs wh~n ammonia (NH3) reacts with the aryloxycarbonate carbon bond proximal to tha aromatic ring having the substituted nitro group. The aforementioned bond site is ~5 expected ~o be where a cleavage occurs as the nitro group can resonance stabilize the deveioping charge. Initially it is axpected that ammonia reacts to form a hydroxyl (-OH) and a urethana (H2NC(O)O-) group. However urethane is apparently unstable under the reaction conditions and it further reacts with ammonia to form 30 urea (H2N~O)NH2) and ano~her hydroxyl group. The polycarbonate polymer chains containing the nitro ~roups are fragmented to yield nitrobisphenol A and urea. The non-nitrated polymar chain sgments anchored to the bulk of the polymer substrate are terminated with nitrophenol and phenol moieties. The overall resulg of the 35 ammonolysis is sch~matically shown below, ;
207~8 1 3 RD-21,5~1 ~l_~O-C~ o (b) n ~ NO2 ~
~ ~I-a~-~l-a~
~¦ aoc~ ~OH NO2 0 (c) o n HO~¦ ~ OH ll ~ ~1 a ~1 a + H2N c ~2 The effsctive time during which the ammonolytic 5 solution is contacted with the nitrated surfaces i5 at about 1 minute to about 24 hours, preferably about 2 to about 6 minutes. The nitrated surfaces may b~ contacted with the ammonolytic solution by either immersing the enclosure in a bath containin0 the hydroxylating solution or by spraying or painting the solution on the o desired nitrated surfaces of the enclosure if it is desirous for cosmetic reasons to provide an EMI shield coat on the inner or hidden surfaces or walls oF the EMI enclosure. The spraying mathods are well known in the art. The temperature of ~he hydroxylatin~ bath or the spraycd hydroxyla~ing solutisn is pr~ferably maintained at about 5 5C to about 65C. Those skilled in the art will readily reaiize that by manipul~ting the concentrations and the temperature of ths ammonolytic solutions, the time of contact may be optimized for particular processing conditions. The ammonolytic bath is preferably stirred during the ammonolytic step to improve the 20 efficiency of the chernical reaction. As a result of the ammonolysis ~723~8 1 4 RD-21,5~1 surfaces of tha polycarbonate substrate turn d~ep yellow with some evidence of surface dissolution. The ammonolyted surfac~s ar~ then rinsed with water to remove any remaining ammonolytic solution adhering to them. Thc rinsed surfaces are hydrop~ilic, smooth to touch and have pale yellow color. If the arnmonolyted surface is placed in an aqueous solution of a dilute acid, it app~ars nearly colorless. Howcver if the hydroxylated surface is placed in an aqueolJs solution of a dilute base it appears yellow. This pH
dependent shift is rapid and reversible and thereby demonstrates the presence of nitrophenol functionality disposed along the polycarbonate surfaces. According to the M~rck Index, the compound o-nitrophenol is used as a pH indicator (a pH of 5.0 appears colorless whereas a pH of 7.0 appears yellow). X-ray Photoelsctron Spectroscopic anaiysis an~ static Secondary lon mass Spectroscopc analysis of the chemically modifie~ polymer confirms tha presence of nitropheno! moieties. It is undorstood that the present invention is not dependent on the aforementioned mechanism. Ths mechanism, to the extent disclosed, provides for a better understanding of the invention.
If a rougher surface is desired, an alkali m~tal hydroxide may bc added to the ammonlytic solution. Potassium hydroxide is pre~errad. The roughened surface may provide greater adhasion of subsequent m~tal layers applied thereto by allowin~ some mechanical adhesion in addition to the chemical adhesion. In 25 general, the alkali metal hydroxide should be added to th~
ammonlytic solution in an amount rangin~ from about O.OO~M to about 10M, pr~ferably about 0.5M to about 3.0M. Preferably the ammonlytic solution containing thc alkali metal hydroxide is contacted with the nitrated surfaces for about 5 to about 20 30 minut~s. The preferred temperature of the ammonlytic solution containing the alkali metal hydroxide should be about 30C ~o about 50C.
In the third step, th~ chemically modified surfaces are catalytically activated by the methods well-knowr~ in the art and 35 desGrib~d, for example, in the U.S. Patent 3,5B9,916, as well as in 2~7239~
1 5 RD-21,551 the U S Patents 4,873.136 and 4,842,S46 to Foust et al., and in the U.S. Patent 4,775,449 to Dumas et al., all aforementioned patents being incorporated h~rein by reference. For ~xample, the substrate may be catalytically activated by contacting with an acid solution of a precious metall such as palladium chlorid~ in hydrochloric acid, for a period of time suffioient to cause the catalytic activation of the substrata surface, wherein the palladium is adsorbed 011 the exposed surfaces.
It is oft~n useful ~o begin the activation of the substrate by treatment with ~n additive which aids in adsorption of the plating catalyst. Such additives are well-known in the art~
Exemplary aids to catalyst adsorption include Shipley 1175A, a produc~ of the ~hiplcy Company, and Met~x 9420, a produc~ of the MacDermid Corporation. Immersion in about 0.1% to about 5% by volume of ~ither of these agents in water for about 1 minute to about 10 minutQs at a temperature of from about 40C to about 80C
is usually sufficient. Although such a treatment is not deem3d critical to the present invention, its use often snhances the uniform deposition of electrolessly applied m~tals onto the substrate.
One illustrative activation techniqua involves imm~rsing the substrate in a solution of Shiplcy Cataprcp'19 404, a product of the Shipley Company. This solution provides a protecting a~ent for the plating catalyst subsequently appliod, and compris~s sodium bisulfate and Yarious sùrfactants. The subs~rate may th~n bo immersed in a solution of Shiplsy CatapositB' 44, which contains the Cataprep~' 404 ingredients, tin, and palladiurn, which is the electroless plating catalyst. The substrate may also be imrnersed in a solution of Macuplex'D ~-34-C made by MacDermid Inc. having palladium/tin particles in colloidal form. A~tar a water rinse, the substrates may ~hen be immersed in a solution of Shipley Cuposit~9 Aco~lerator t 9, a fluoroboric acid-containin~ formulation used to separate tin from the plating catalyst.
Activation and plating process~s suitable far the presen~ invention ar~ also described in the application of W.T.
Grubb et al., European Patent No. EP 27Z,420, and incorporatsd .
. .
.
20723~8 1 6 RD-21,5~1 herein by r~ference, and also in U.S. Patents 3,011,920 and 3,841,881, issued to Shipley and Feldstein et al., respectively, both of which ar~ also incorporated h~rein by reference. A water rinse generally follows the activation step.
Aft~r surface activation and rinsing, the fourth step of the present invention, namely aiectrol~ss plating of a primary metal layer, can be undsrtaken. Illustrative metals used to form the metallization layer includo copper, palladium, nick~l, silver, platinum, cobalt and gold. Copper is usually the m~tal of choice when forming a printed circuit. A composite of a copper lay0r followed by a nickel layer is the preferred choice in preparing an EMI shielded ~nclosure. The nick~l layer is typically used to protect the EMI copper layer shield from corrosion and abrasion.
The adhesion mechanism between the modified polymsric chain and metal (M), though not fully understood, is believed to be as shown in the structural representation below, o NO
C-~¦.~ OH
~ M
o ~ N-O:
Electroless baths are wall-known in ~he art and are gsnerally described in the Kirk-C)thnlçr ~f Ch~nnical Techn~lo~, 3rd Edition, Volume 8, th~ contents of which ar~
incorporated herein by reference. The s~lection of a particular bath or ~lectroless platin~ process is not cri~ical to the present invention. Thc contents of the bath and the particular plating parameters, ~.9., temperature, pH, and immersion time, will of 207~3~8 1 7 FiD-21,5~1 course depend on the particular plastic serving as th~ substrate, and also upon th~ particular meta7 being deposited thereon.
Suitable plating baths includ~ tha Shipley Cuposit'~ 250 system, the Enthone~ 408 and the Enplate(9 Ni-426 syst~ms, latter two made by Enthone Inc. Furthermor~, the Grubb et al. application and Dumas et al. patent, mentioned ab~ve, list suitable electroless plating formulations. Immersion times, bath t~mperatures, and other operating parameters can be dctermined and c~ntrolled accordin~ to manufacturers' suggestions in ord~r to deposit the metal layer of a desired thickness in a desired duration of time.
Those having ordinary skiil in tha plating art will be able to determins the most appropriate plating regim~n for a particular situation .
The polycarbonate surface may ba subjectecl to a hcat treatm~nt after an alectrol0ss deposition of the metal. Ov~n hea~ing of the ~ntire articl~, i.*., substrate with metal thsr~on, is sufficient, although any hoating method is suitable. Typically, this heat treatment is carried out at a temperature rangin3 from about 45C to about 170C for about 5 minutes to about ~20 minutes, with higher temperatur~s within the above ran~e g~nerally compensating for shorter duration, and vice versa. The aforemention~d hcat treatment is prefarebly carried sut at 120C. Although the mechanism is not und~rstood, the h~at treatm~nt app~ars to reduce thc tim~ required to attain optimal adhesion.
If anoth~r layer of metal is to be elsctrolytically applied on th~ surface, e.g., by electroplating, the above-d~scribed heat treatment can in some instances be cmitted if a heat treatrnent is employed after the plating of more of the me~al, as doscribed below.
However, preferably the heat treatment is provided prior to electrolytic deposition of metal. Some of the embodiments inolude a heat treatment prior to the alcctrolytic d~position of metal (i.e., after the electroless d~position), aiong with another h~at treatm~nt after ~he final laycr of metal has bscn appJied, as described balow.
Even though electroplating is one of the methods for applying a secondary or a second metal layer, an el~ctroless plating 2~723~8 1 8 RD-21 ,551 as described above, is the preferred choice. The substrate is usually cleaned prior to immersion in the electroplating bath. The cleaning can be pe~ormed by rinsing the substrate with a dilute solution of a strong acid, such as 10% by weight of sulfuric acid in water.
Electroplating or electrolytic plating baths are well known in the art and are described, for example, in U.S. Patent 4,555,315, incorporated herein by reference, although tha particular electroplating bath used is not critical to the present invention. The choicQ of course d~pends in part on tho parti~ular metal being deposited. Suitable metals include those described for the electroless deposition. Furthermore, thoss ~killed in the art appreciats that the particular bath contonts will depcnd upon some of the factors considered for the elcctroless deposition of metal described above. Typically, th~ electroplating bath for copper is operated at a temperature ranging from about 16C to about 38C, with a cathode current density in the ranse of about 1 ASF to about 80 ASF. A description of baths for plating copper or various other metals is given in the Kirk-Q~er referencc desuibed above, in Vol. 8, beginning on pago 8Z6. Baths used to ap~y a layer of coppcr to the slectrol2ssly applied layer typically includ~ an aqueous acidic copper olectrolyte such as those of th~ acidic copper sulfate or acidic copper fluoroborate type; h~lide ions, such as chloride and/or bromidQ ions; and various other components well-known in the art.
The thickness of this second metal layer will of cours~ dep~nd upon the desired end use of the metal-coated substra~e.
As also described in the aforementioned applic~tion of Grubb et al., and in the patent of Foust ~ al. the metal applied on ~he polycarbonat~ substrate may be in the form of a pattern. Exemplary pattarning methods are also described in U.S. Pa~nt 3,562,005, issued to DeAngelo et al., incorporat~d herein by referenGe. Ano~her -technique suitable for use herein is disclosed in the aforemention~d Grubb et al. application. This resistless technique involves the photopatterning of an organic substrate by first exposing ~he substrate to electromagnetic radiation followed by ~reatm~nt with a 3S precious metal compound to catalytically activate the surface. The 20723~8 1 9 RD-21,551 metallic pathway formed after electrolessly plating the activated surface will tightly adhere to the underlying polymer subs~rate because of the chemical modification traatmsnt disclosed in the present invention.
Th~ electrolessly metallized layer when us~d as an EMI
shi~ld is preferably about ~wo micrometers in thickness. In other embodiments, such as a printed circuit board, tha el~ctrolessly metallized lay~r prepared by the method of this invention usually has a thickness of about 1 microme~ers tn about 5 micrometers and an electrolytically appiied layer thereon is at l~ast about 5 micrometers in thickness.
An article prepared by the m~thod of this invention comprises an aromatic substrate preferably of polycarbonat~, means to improve adhesion of a mstal on a surface of said substrate comprising modifying said substrata b~ contacting said surface with a nitrating solution followed by contacting with a hydroxylating solution, and a metal laycr disposed on said surface. The metai layer comprises an eiectrolessly applied primary layer on the pretreated surface. Additional secondary metal layars rnay be electrolessly or electrolytically applied on top of the primary metal layer until a desired thickness is attained. The present invention contempla~es various combinations of metal layers such as a single copper layer, a primary copper layer followed by a secondary nickel layer or a primary nick~l layer followed by a secondary copper layer and a tertiary nickel layer.
Ar~icles of various cmbodiments of this invention are suitablo as EMI shielded enclosures, printed cirouit boards or housings having an EMI shield and a printed circuit board wherein th~
circui~ board is an integral part of the housing and contains metallic layers as described herein as a printed circuit pattern or ~trace~.
An article of rnanufacture of tha preferred embodiment of tha present invention comprises an enclosure of an aromatic polymer, such as polycarbonata, having surfaces of ~he walls of ~he enclosure chemically treated by the process of the present invention to improve electroless deposition and a first metal layer, preferably 2~72398 2 0 RD-21,551 copp~r, thereon. A second metal layar, prefsrably of nickel, may be disposed on top of the first metal layer, the second layer b~ing electrolessly or electrolytically applied on the first lay~r. As stated earlier, the second layer is preferably deposited by the 5 slectroless metal deposition. Both the metal layers disposed, if so desired, on the interior sides of the walls of th~ enclosure, have a predetermined combined thickness in accordance with the requirements set forth in the FCC regulations for noise by reducing ~n intensity of nois~ emitted by th~ elec~rical components enclosed o within the snclosure to a desired lavel. The combined thickness of the first and second metal layers is adjusted to meet the FCC
re~uirements. The shielding of the enclosure may bs also used to protect the electrical components enclosed within the shictded enclosure from electro-magnetic radiation of a specified range of 15 frequency of about 1 KiloHertz to about 10 GigaHertz.
In another embodiment of the presan~ invention, an articl~ suoh as an EMI shielded ~nclosure having thre~ metal layered EMI shields. Preferably the first layer is an electrol~ssly applied first nickel layer on the surfaces of thc walls of the enclosure, ~he 20 second layer being an electrolessly applied or olectrolytically applied ~opper disposed on top of the ~irst nickel layer and ths third layer being electrolessly applied or ~lactrolytically applied second nickel layer disposed on top of the second layer.
Still another embodiment is a flat or thr~e-dimensional 25 printsd circuit board (PCB~ of the prssent invention is disclosed.
The PCB may b~ of positive or a negative image type. The PCB
comprises an aromatic polymer substrate, preferably of polycarbonate, whose surfaces have been chemically treatsd in accordance wi~h the process of the presen~ invention to improve 30 adhesion of an electrolessly applied first m~tal layer, followed by an el~ctrolessly applied or an electrolytically applied second metal layer disposed on top of first metal layer, whersin the firs~ and sacond metal layers provide a pattern of traces of d~sired thickness with which to provide ~lectrical interoonnection between electrical 2~723~8 21 RD-21,551 components disposed on the PCB and the external electrical maans.
The preferred metal layers are of copper.
The adhesion between the surfaces of the substrates used in the aforementioned articlss and the metallized layer directly in contact with the surfacas may ba enhanced by increasing the roughness of the surfaces. As mentioned earlier, tho surfaco roughness may be incr~ased by adding the alkali m0tal hydroxide to ths amrnonlytic solution. The surface having rough texture should improvs mechanical adh~sion between the surfaces and th~
me~allized layer dir~ctly in contact with the rough~ned surfaces.
In these examples, adhesion of the matal to the substrate was evaluated by applying ASTM D33~9-78, Mathod B Cross-Cut Tape Test mentioned earlier. Method B, summarized below, comprises:
1. cutting, with a sharp knife blada, a cross hatch pattern in single pass uniformly applied strokes through th~ rnetal layer disposed on the substrate area being evaluated by the test;
2. removing the debris genarated during the cutting procedure;
3. eveniy applying over the cross hatched area tha recommended adhesive tape, having an adhesive strength of 36 ~ 2.5 ounce par inch;
4. pulling the tape away from the area a~ 9O to the surface in one quick stroke; and 5. checking the tape for any metal flakes.
A classification of 5 means no metal layer was flaksd off ths surface whereas a classification of O means greater than 65% of the metal layer was flaked off th0 surface~ The intermediat~
range of classification denotes percentages of flaking occuring batween greater than O% to less than 65%. The classification values for each tape are obtained and then averaged.
Tha present invention will be further understood from th~ description of specific axamples which follow. These examples are int~nd~d for illustrativ~ purposes only and should no~ be construed as a limitation upon the broad~st aspacts af the invention.
All liquid ratios are by volume, unless othanNise indicated.
2~7239~
2 2 RD-21,5~1 E~dm~2b~
A plaque, of 2 inches x 3 inches x 1/8 inches in size, s molded of Lexan(~ polycarbonate BE2130A, was treated as follows:
The substr~te was u!trasonically cleaned for 5 minutes at 24C in a solution comprising 2 volume percent of Micro~9 detergent and 98% by volurne of deionized water. The substrate was subsequently rinsed with watsr and air dried. The substrate was 10 immersed in the nitrating solution, compri~ing 1 part by volume of nitric acid (assay (HNO3~70-71%) and 2 parts by volum~ of sulfuric acid (assay (H2SO4) 95.S-96.5%), at 23C for 3 minutes. The substrate was then rinsed in tap water for less than on~ minute, follcwed by a 5 minute rinse in tap water at 65C, and then cooled to 23C.
The sample was then immersed in a solution, comprising 1 part by volume of ammonium hydroxide (sssay (NH3) 2~.0-30.0%) and 1 part by volume ef deionizsd water at 23C for 4 minutes, and subsequently rinsed in tap water at 23C for 5 minutes. The 20 substrate was oatalyzed by a 2 minute immersion into a solutien at 23C comprising 77.2% deionized water, 22% hydrochloric acid (assay (HCI) 36.5-38.0%), and 0.8% of Macuplex0 D-34-C containing colloidal palladium/tin particles that adsorb ont~ th~ substrata surfaca. The sample was subsequsntly rinsed with water for 1 25 minu~e and thsn imrnersed in an accelarator, a solution comprising 1 part by volume Shipley Cuposit~9 Accelera~or ~9, and 5 parts by volume deionized water. The substrate was then rinsed in ~ap water for about 2 minutes.
The sample was metallized with Enplate(~ Ni-426, a low 30 phosphorus eleetrolsss mstal fcrmul~tion. The ba~h was formulated per ths recommendatiQn by the manufacturer and was maintained at 54C: 1 1C and at pH 6.1-S.2. The substrate was immersed in this bath for I hour. The plated article w 5 removed and rinse~ in tap water for about 2 minutes and then air dri~d. Th~ nickel thickness 35 was determined to be 3.1 micrometers by x-ray fluorescenee on a 2~723~
2 3 RD-21,551 Seiks SFT/156 x-ray instrurnent made by Seiko Instruments and Electronios, Ltd. The adhesion of the metal coating was measured by using a tape test as psr the procedurss outlined in ASTM D3359-78 Me~hod B. A cross-c(lt tool made by Precision Gage & Tool Co. was s used to ~cribe a grid of 10 x 10 - 1 milimeters x 1 milimeters squares. Tap~ was ~venly appliad against the grid and removed in a manner consist~nt with the test procedure. Th~ observation of the scribed area showed that the matallization was completely smoo~h and no flaking of any parts of the squares was observRd thereby o indicating an ASTM adhesion classification of 5. The sample was baked in an air oven for 30 minutes at 80C + 2C. Th~ sample was then removed and ailowed to cool to 23C and the adhesion of the metal coating was rechecked in the manner as outlin2d above. An adhesion classifica~ion 5 was again obtained.
E~mQ~:~
Various grades of Lexan~9 polycarbonate were processed under various conditions using the nitrating and the hydroxylating solutions of the composition disclosed in Example 1. Th~ specific parameters are summarized in Table 1 shown hereafter.
24 RD-21, 551 I . .. . _ ~-U~C l '1:3) a~
~ ~ O
1~ .~ ~D g _ ~ ¦ tC~ O~ N ~N O U) _ N N C~ ~o _ nl ,~ I N N _ _ C~.i _ . -- N -- -- N ~ N U~ t') _ O ~. ~
O , . ~ ID D ~`
N I Æ~ O O O O O C O Q O ~ O O O ~ O c~ E ~ ~B
tD ~ . . .. __ I . ..... ~ ~
~D _ ~ O O 1~ 0 U) U~ O U~ O U~ _ ~ ~ O
IIJ ~ ~ N N ~'~ ~ _ -- N _ _ _ CD _ C~
., ~
.C _ 11~ N It 11~ In U) U> U~ N Nl N C~J ~ 3 ¦ . o~ ~ N
. ~ ~ ~ o ~ ~c o ~ _ U) U~ ~ b :~ E
'91 ' ~ ' E
.' '1: ~________________ ~o o = ~ ---- . ~ T ~ ~
~ ~ _ u) u~ u~ In It'~ u) ~ ~ t~ r-- I~ t~ ~') N ~ t ~ --o n~
. . . ~L ~ E ~ ~L
T - u~ io ~ E
_ . . ~ E ~ o~
C 1` _ N U~ ~ ~0 ~ p~ ~ ~ ~ co E ~ E E
~ 1 . _ . . E E o " E
9~ '';1 --~ ~ 0 .. . . . ~ l O ID ~q u~ N I U~ D~ E ~D
m I ~ ~ N N ~ q- N N N N N Nl IN N N N c ~ 0 V tn ~
~ __ ~ ~;~ V ~
Z _ _ ~ ~ 1~ N N C'~ N ~ ~ C~ N N ~ $ O y~ N
. _ _ a~ ~3 "> "I ~ _ t~7 ~D .. , o~ ~ N N N N ~ N N ~ O O N N ~ N N ~ ~ n O ~ ~ Z E
~ --~ - 9 ~ N C C a~ 3S a m E e~ Q--N ~ U) I~ E ~ c E ~ ~8 ~ F
LL ~ . U~ e~
20723~
2 5 RD-21,551 Nons of the substrates in thc aforementioned examples were cleaned prior to the nitration step. All the rinses unless othenNiss stated wers in flowing tap wat~r at about 15C. The nickel plating baths were maintainsd at a pH of about 6.1-6.3.
~am~
Th~ substrate sample of example 6, shown in Table 1, was provided a furth~r treatment after nickai platin~. The afor~mention~d substrate was baked at about 85C ~ ~C for about ono hour. Once the substrate cooled, the adhesion of the metallized layer was checked. The quali~ of ~hs adhesion classification remained at 5. Subsequently, thc substrat~ sampla was plac~d in a chambcr partially filled with deionized water. The samplc was held in the chamber above tha water level. The chamber was then closed and placsd into an oven, maintained at about 65C ~ 2C and about 100% relative humidity. The adhesion of the metal coating was checked by the aforementionsd ASTM tape t~st method after 1, 3 and 10 days of exposure to the environment within the chamber. In all the cases, the adh~sion classification of 5 was obtain~d.
E~ ,.
The sample of sxample 7, as shown in Table 1, was a plaque having a size of 21/2 inches x 1/2 inches x 1/8 inches. The plaque was secured in a stainlsss steel jig so ~ha~ 3400 pounds per squaro inch of bending stress could be applied on the plaque. The sample under stress w~s then proc~ssed according to th~ st~ps disclosed in Table 1. Upon completion of ~he step cf electroless mctallization, the stressed surface of the plaque was viewed at a magnification of 45 times the normal size using a light microscope.
No cracks, crevices or other adverse effects resulting frum an application of bending stress were observed on the strcssed metalliz~d areas of the plaque. The plaqus was rsmovad from the jig and mount~d in a clear epoxy solution so ~ha~ a cross-section of the metallized area could be made, once tha ~poxy solution hardened.
The cross-section was then viewed at a magniflcation of 1000 times the normal size using a light microscop~. No cracksl crevices ~, ~723~8 2 6 RD-21,551 or other adverse effects w~re observed in either the metallized layer or on the surface of thc substrat~.
~1e 1~
A plaque molded from Lexan'!9 polycarbonate ML6000 was 5 treat~d using the various chemical solutions described b010w. The substrate was immersed, without cla~ning, into the nitrating solution of Table 1 for 6 minu~es at 2~C; water rinsed for 1 minute;
immersed in the aqueous ammonia solution of Table 1 for 6 minutes at 25C; water rinsed for 5 minute; catalyzed fcr 6 minutes at 25C;
10 water rinsed for 1 minute; immersed in th~ acceterator for 5 minutes, and finally water rinsed for 5 minutes. Th~ plaque was then electrolessiy plated with copper- using a Shipley Cuposit~9 251 electroless copper bath, formulated as per the recommendations by tha manufactur~r. The plaque was immersed in the electroless 15 copper bath for 7 minutes while the bath was stirred and maintained at 40C t~ 1C. The plaqua was then water rins~d and air dried. The thickness of copper layer deposited on the substrate was measured by x-ray fluoresc~nce and was determined to b~ 1.5 micrometers in thickness. Tha copper layer on the substrat~ was than metallized 20 with a layer of nick~l, usin3 an alectroless nickel bath as described in exampl~ 1. Tha substrate was immersed in th0 electroless nick~l bath for 5 minutes while the bath was maintained a~ 50C i 1C. The substrate was water rinsed and air drisd. The thickness of nickel layer depasited on top of th~ copper layer was measured by x-ray 25 fluorescence and was determined to be about 0.7 micrometers in thickness. The ASTM tapa test was performed in a manner deseribed in example 1, and an adhesion classification 5 resulted. The EMI
shielding effectiveness was measured by The Dual Chamber Method (ASTM Fs-7-83) developed by Th~ American Society of Testing and 30 Materials. Attenuation values were measured at 30 MegaHertz, 100 MegaHer~z, 300 MegaHertz, and 1000 MegaHertz, producing values each in excess of 60 decibals, 70 decibals, 79 decibals, and 73 decibals respectively. It should b~ stated that the aforementiolled attenuation values arc well within th~ present FCC requirements 35 regarding the EMI shielding.
2~72398 27 RD-21 ,551 ~3m~Q~
A plaque of Lexan~ polycarbonate BE2130A, having a siz~
of 2 inches x 3 inches x 1/8 inches, was proc~ssed under the conditions disclosed in Example 1 during the nitration. Tlle sample s was then rins~d in water and imm2rs~d in an aqueous solution comprising 25 part by volume nf ammonium hydroxide (assay NH3 28%) and 2.0M of potassium hydroxide for 15 minutes at 23C. Tha sampl~ was thcn rinsed and driod. The surfac~ finish (roughness) of ~h~ ammonolyzed surface was measur~d by usin~ a Slaan Dektak ll 10 Surface Profil2 Measurin~ System (version 2.3 profilometer with a diamond tip submicron stylus~, supplied by Sloan Technology Corporation, Santa Barbara, California. Th~ surface finish was measured at + 0.5 ~lM. For comparison, th~ surfaco finish of th~
ammonolyzed surface of the sample in Example 1 was maasured at :~
15 0.1 IlM. Thus, a fivefold increase in sufface roughn~ss was obtain~d by adding potassium hydroxide to the ammonolytic solution.
The ammonolyzad surface of example 19 was then catalyzQd and electrolessly plated. The sample was immersed for 2 minutes in an aqueous catalyzing solution comprising 0.8% by volume 20 of Macuplex0 D-34-C and 22% by volume of HCI (37%). The sample was then rinsad in deionized water for 1 minute and than immersed in a solution comprising 1 part by volume of Shipley Cuposit~
Accelerator 19 and 5 parts by volume of deionized water. The sample was then wator rinsed ~or 2 minutes, nickel plated for 20 25 minutss using an Enplate~9 Ni~26 nickel/phosphorus bath at 50C, water rinsed for 2 minutes, copper plated for 8 m;nutes using a Shipley Cuposit'!9 251 copper bath at ~C, water rinsed for 2 minutes, nickel plated for 3 minutes at 50C: in ~he aforemantioned nickel bath, water r,nsed for 3 minutes, and then air dri~d. The 30 ASTM tape t~s~ was performed in a mann~r described in Example 1, and an adhesion classific~tion 5 r~sulted it will b~ understood that the for~going description is only illustrativ~ of tha present inv~ntion and it i5 not intanded that the invention be limited ther~to. Numerous variations, changes, 35 substitutions, and modifications will now ooour to thos~ skilled in 207239~
2 8 RD-21,5~1 the art which come within ths scope of the pres3nt invantion without departing ~rom the spirit and scop~ thereof. Accordingly, it is intended that th~ invention be limited only by the scops of the appended elaims.
Claims (45)
1. A method of modifying an aromatic polymer surface to improve adhesion of a metal layer on said surface comprises nitration of polymer molecules disposed on said surface by a nitrating solution followed by ammonolytic cleavage of nitrated polymer molecules by an ammonolytic solution.
2. The method of claim 1 wherein said nitrating solution comprises a mixture of nitrating agents selected from the group consisting of nitric acid, acetyl nitrate, dinitrogen pentoxide, metal nitrate, nitronium tetrafluoroborate and dehydrating agents selected from the group consisting of sulfuric acid, acetic anhydride, trifluoroacetic anhydride.
3. The method of alaim 2 wherein said nitrating solution comprises a mixture of one part of nitric acid dissolved in water at a concentration of at least about 60% by weight with 2 parts of sulfuric acid dissolved in water at a concentration of at least about 90% by weight.
4. The method of claim 2 wherein said nitrating solution is contacted with said surface for about 0.5 to about 20 minutes.
5. The method of claim 2 wherein said nitrating solution is at a temperature of about 10°C to about 80°C.
6. The method of claim 1 wherein said ammonolytic solution comprises water and a compound selected from the group consisting of ammonium hydroxide and tetraalkylammonium hydroxides.
7. The method of claim 6 wherein said ammonolytic solution comprises ammonia dissolved in water at a concentration of about 0.001% to about 30% by weight.
8. The method of claim 6 wherein said ammonolytic solution is contacted with said surface for about 1 minute to about 24 hours.
9. The method of claim 6 wherein said ammonolytic solution is at about 5°C to about 65°C.
RD-21,551
RD-21,551
10. The method of claim 1 wherein said aromatic polymer is selected from the group consisting of polycarbonates, polyimides, poly(alkene terephthalates), poly(phenylene oxides), phenol alkyaldehydes, polystyrenes, polysulfones, and blends thereof.
11. A method of metallizing a surface of an aromatic polymer substrate comprises:
nitration of polymer molecules disposed on said surface;
ammonolytic cleavage of nitrated polymer molecules; and application a metal layer on said surface.
nitration of polymer molecules disposed on said surface;
ammonolytic cleavage of nitrated polymer molecules; and application a metal layer on said surface.
12. The method of claim 11 wherein said step of applying said metal layer comprises:
electrolessly-applying a primary metal layer on said surface;
electrolessly or electrolytically-applying a secondary metal layer on top of said primary layer.
electrolessly-applying a primary metal layer on said surface;
electrolessly or electrolytically-applying a secondary metal layer on top of said primary layer.
13. The method of claim 11 wherein said aromatic polymer substrate is a polycarbonate substrate.
14. The method of claim 11 wherein said metal layer comprises copper, nickel, gold, silver, platinum, palladium, cobalt or a combination thereof.
15. The method of claim 11 wherein said metal layer comprises a copper layer proximately positioned to said surface followed by a nickel layer on top of said copper layer.
16. The method of claim 11 wherein said metal layer comprises:
a first nickel layer proximately positioned to said surface;
a copper layer on top of said first nickel layer; and a second nickel layer on top of said copper layer wherein said copper layer is sandwiched between said first nickel layer and said second nickel layer.
a first nickel layer proximately positioned to said surface;
a copper layer on top of said first nickel layer; and a second nickel layer on top of said copper layer wherein said copper layer is sandwiched between said first nickel layer and said second nickel layer.
17. The method of claim 11 wherein said metal layer is applied on said surface to form an electromagnetic interference shield.
31 RD-21,551
31 RD-21,551
18. The method of claim 11 wherein said metal layer on said surface is patterned to form a printed circuit pathway of a printed circuit board.
19. The method of claim 11 wherein said aromatic polymer surface having said primary metal layer thereon is heat treated at a temperature of about 45°C to about 170°C for about 5 minuted to about 120 minutes, prior to applying said secondary metal layer on said primary layer.
20. A method of modifying a polycarbonate surface to improve adhesion of a metal layer applied on said surface comprising:
contacting said surface for about 2 minutes to about 5 minutes with a mixture of one part nitric acid dissolved in water at a concentration of at least about 60% by weight with 2 parts of sulfuric acid dissolved in water at a concentration of at least about 90% by weight, whereby said surface is nitrated; and contacting said surface for about 2 to about 6 minutes with a solution of ammonia dissolved in water at a concentration of about 3% to about 8% by weight, whereby said surface becomes hydrophilic and thereby improves said adhesion.
contacting said surface for about 2 minutes to about 5 minutes with a mixture of one part nitric acid dissolved in water at a concentration of at least about 60% by weight with 2 parts of sulfuric acid dissolved in water at a concentration of at least about 90% by weight, whereby said surface is nitrated; and contacting said surface for about 2 to about 6 minutes with a solution of ammonia dissolved in water at a concentration of about 3% to about 8% by weight, whereby said surface becomes hydrophilic and thereby improves said adhesion.
21. An article comprising:
an aromatic polymer substrate having ammonolytically cleaved aromatic polymer containing nitro groups disposed on a surface of said substrate; and a metal layer disposed on said surface.
an aromatic polymer substrate having ammonolytically cleaved aromatic polymer containing nitro groups disposed on a surface of said substrate; and a metal layer disposed on said surface.
22. The article of claim 21 wherein said metal layer comprises:
an electrolessly applied primary metal layer disposed on said surfaces; and an electrolytically applied or an electrolessly applied second metal layer disposed on top of said first layer.
an electrolessly applied primary metal layer disposed on said surfaces; and an electrolytically applied or an electrolessly applied second metal layer disposed on top of said first layer.
23. The article of claim 21 wherein said first metal layer is copper.
32 RD-21,551
32 RD-21,551
24. The article of claim 21 wherein said first metal layer is nickel.
25. the article of claim 21 wherein said aromatic polymer substrate is a polycarbonate substrate.
26. An article comprising:
an aromatic polymer substrate having ammonolytically cleaved aromatic polymers containing nitro groups disposed on a surface of said substrate; and an electrolessly applied metal layer disposed on said surface.
an aromatic polymer substrate having ammonolytically cleaved aromatic polymers containing nitro groups disposed on a surface of said substrate; and an electrolessly applied metal layer disposed on said surface.
27. An article of claim 26 wherein said metal layer is copper or nickel.
28. An article comprising:
a polycarbonate substrate having ammonolytically cleaved polycarbonate polymers containing nitro groups disposed on a surface of said substrate; and a metal layer disposed an said surface.
a polycarbonate substrate having ammonolytically cleaved polycarbonate polymers containing nitro groups disposed on a surface of said substrate; and a metal layer disposed an said surface.
29. The article of claim 28 wherein said metal layer comprises:
an electrolessly applied first nickel layer disposed on said surface;
an electrolessly applied or electrolytically applied copper layer disposed on top of said first nickel layer; and an electrolessly applied or an electrolytically applied second nickel layer disposed on top of said copper layer.
an electrolessly applied first nickel layer disposed on said surface;
an electrolessly applied or electrolytically applied copper layer disposed on top of said first nickel layer; and an electrolessly applied or an electrolytically applied second nickel layer disposed on top of said copper layer.
30. An EMI shielded enclosure for electrical components comprising:
a polycarbonate enclosure having walls with an inner and an outer side wherein surfaces of said walls have ammonolytically cleaved polycarbonate polymer chains containing nitro groups; and a metal layer disposed on said surfaces wherein said metal layer reduces intensity of noise emitted by said electrical components enclosed within said enclosure to a desired level.
33 RD-21,551
a polycarbonate enclosure having walls with an inner and an outer side wherein surfaces of said walls have ammonolytically cleaved polycarbonate polymer chains containing nitro groups; and a metal layer disposed on said surfaces wherein said metal layer reduces intensity of noise emitted by said electrical components enclosed within said enclosure to a desired level.
33 RD-21,551
31. The enclosure of claim 30 wherein said metal layer comprises:
an electrolessly applied first metal layer disposed on said surfaces: and an electrolytically applied or an electrolessly applied second metal layer disposed on top of said first metal layer.
an electrolessly applied first metal layer disposed on said surfaces: and an electrolytically applied or an electrolessly applied second metal layer disposed on top of said first metal layer.
32. The enclosure of claim 31 wherein said first metal layer is copper.
33. The enclosure of claim 31 wherein said second layer is nickel.
34. The enclosure of claim 30 wherein said metal layer is disposed on said inner side of said wall.
35. The enclosure of claim 30 wherein a thickness of said metal layer is in accordance with said intensity of noise emanating from said enclosure.
36. An EMI shielded enclosure for electrical components comprising:
a polycarbonate enclosure having wails wherein surfaces of said walls have ammonolytically cleaved polycarbonate polymer chains containing nitro groups; and a metal layer disposed on said surfaces wherein said metal layer protects said electrical components from damage by an electro-magnetic radiation of a specified range of frequency.
a polycarbonate enclosure having wails wherein surfaces of said walls have ammonolytically cleaved polycarbonate polymer chains containing nitro groups; and a metal layer disposed on said surfaces wherein said metal layer protects said electrical components from damage by an electro-magnetic radiation of a specified range of frequency.
37. The enclosure of claim 37 wherein said metal layer comprises:
an electrolessly applied first metal layer disposed on said wall; and an electrolytically applied or all electrolessly applied second metal layer disposed on top of said first metal layer.
an electrolessly applied first metal layer disposed on said wall; and an electrolytically applied or all electrolessly applied second metal layer disposed on top of said first metal layer.
38. The enclosure of claim 36 said specified range of frequency is about 1 KiloHertz to about to GigaHertz.
39. A printed circuit board comprising:
34 RD-21,551 a polycarbonate substrate having ammonolytically cleaved polycarbonate polymer chains containing nitro groups disposed on surfaces of said substrate; and an electrolessly applied first metal layer disposed on said surfaces; and an electrolytically applied second metal layer disposed on top of said first metal layer wherein said first and second metal layers are a pattern of traces which provides electrical interconnections between electrical components disposed on said printed circuit board and external electrical means.
34 RD-21,551 a polycarbonate substrate having ammonolytically cleaved polycarbonate polymer chains containing nitro groups disposed on surfaces of said substrate; and an electrolessly applied first metal layer disposed on said surfaces; and an electrolytically applied second metal layer disposed on top of said first metal layer wherein said first and second metal layers are a pattern of traces which provides electrical interconnections between electrical components disposed on said printed circuit board and external electrical means.
40. The printed circuit board of claim 39 wherein said first and second metal layers are copper.
41. The printed circuit board of claim 39 wherein said substrate has a positive image.
42. The printed circuit board of claim 39 wherein said substrate has a negative image.
43. An enclosure for electrical components comprising:
a polycarbonate housing having unitarily constructed walls and a substrate wherein surfaces of said walls and said substrate have ammonolytically cleaved polycarbonate polymer chains containing nitro groups disposed on said surfaces;
a metal layer disposed en said surfaces of said walls wherein said metal layer provides an EMI shield; and an electrically conductive metal trace pattern disposed on said surfaces of said substrate which provides electrical interconnections between said electrical components disposed on said substrate and external electrical means.
a polycarbonate housing having unitarily constructed walls and a substrate wherein surfaces of said walls and said substrate have ammonolytically cleaved polycarbonate polymer chains containing nitro groups disposed on said surfaces;
a metal layer disposed en said surfaces of said walls wherein said metal layer provides an EMI shield; and an electrically conductive metal trace pattern disposed on said surfaces of said substrate which provides electrical interconnections between said electrical components disposed on said substrate and external electrical means.
44. The enclosure of claim 43 wherein adhesion between said metal layer and said surfaces is further enhanced by adding rough texture to said surfaces.
RD-21,551
RD-21,551
45. The invention as defined in any of the preceding claims including any further features of novelty disclosed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/744,043 US5180639A (en) | 1990-10-26 | 1991-08-12 | Method of preparing polymer surfaces for subsequent plating thereon and improved metal-plated plastic articles made therefrom |
| US744,043 | 1991-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2072398A1 true CA2072398A1 (en) | 1993-02-13 |
Family
ID=24991199
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2072398 Abandoned CA2072398A1 (en) | 1991-08-12 | 1992-06-25 | Method of preparing polymer surfaces for subsequent plating thereon and improved metal-plated plastic articles made therefrom |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2072398A1 (en) |
-
1992
- 1992-06-25 CA CA 2072398 patent/CA2072398A1/en not_active Abandoned
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