CA1045909A - Processes and products of sensitizing substrates - Google Patents

Abstract

Abstract of the Disclosure.- Sensitizing processes and the resulting new articles of manufacture, suitable for the production of metallized bodies, such as printed circuits, dials, nameplates, metallized plastics, glass, ceramics and the like, comprising bases coated with a halide containing aqueous sensi-tizing solution of pH 1.5-4.0 that deposits a layer of copper, nickel, cobalt or iron salts or salt compositions, which on ex-posure to radiant energy, such as heat, light, etc., is converted to a layer of metal nuclei which is non-conductive, but which is capable of catalyzing the deposition of metal onto the base from an electrodes metal deposition solution in contact with the metal nuclei.

Description

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1 Bnck~round of th~ Invclltion.- T~ 5 inv~n~lon rcl~t~

2 to novel and improv~d methods ~or mc~allizing bodics, c.g.,

3 lnsul~tlng suppor~s~ and to the produc~s ~Ihich result from such S methods.
S More particularly, the present invention relates to 7 imposing, by thermal or radiant energy, sensitive non-conductive 8 I metallic areas on the surfaces of such bodies which catalyze the 9 ~ deposition of strongly adherent and rugged deposits o~ electro-le$s metal.
11 . ~ . . ~ ~, 12 Although applicable whenever it is desired ~o apply a 13 metallic coating to a base, as for example, for decorative or 14 protective effects, or to make electrical conductors of a wide ¦ variety of shapes and con~igurations, the procedures for metal-¦ lization herein are particularly useful for making printed cir-17 ¦ cuits from readily available base materials, e.g., metal clad 18 1 Iaminates, resinous insulating laminated bases or porous non-19 1 conductive materials, e.g., fiberglass, paper, cloth, cardboard, I ceramics and the like.

22 It is a primary object of this invention to provide 23 bases sensitive to metaLlization by electroless plating and, 24 optionally, subsequent electroplated metal deposition, 26 ~
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- ````l! ) l PC-123C l 104~09 1 Another princlp;1l ob3cct of t~1is lnvention is to pro 2 vid~ improv~ments in mc~allization proccsscs in which a base is 3 sensitlzed to met~llization by electroless plating.
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S An addi~ional objec~ of this invention i5 ~0 provlde S base materials and processes for electroless metallization in 7 which there are e~ployed non-noble metal sensi~izers which are 8 much more economical in cost~ bu~ equivalent in per~ormance to 9 the noble metal-containing sensitizers used until now.
10 . .
11 Another object of this invention is to provide adher-ent elec~roless metal coàtings bonded to base materlals either 13 directly or through an intermediate, adhesive layer.

14 i Although the invention will be described with particu-16 lar reference to printed circuits, and although fabrication o 17 printed circuits constitutes a primary and preferred application, 18 ¦ it should be understood that the invention is not limited to 1g printed circuits but is applicable to metallizing surfaces 20 ~ broadly. .

2~ Heretofore, it has been known to employ a number o~

23 pretreatment or sensitization baths in effectlng the electroless 24 deposition of metals on various surfaces. All such prior art ~5 1¦ sensitization baths used commercially have been expensive because ¦ they depend upon a nob~e metal, e.g., palladium, platinum, gold, silver, etc., as the sensitizing component. In ~pite of the ¦

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1 expensc, howevcr, the prior art has stood ~ast in its Eeelin~ i 2 that precious mctals m~lst bc usecl if sensi~ization to ~lectroless 3 me~al dcpos1tion ~nd ~oo(l bond st~ng~h between the sens~tl~2d

4 sur~ace ancl the electroless deposit is to be achieved, In one embodimen~, 9uch prior ~rt noble met~l sensiti~ation baths are S used sequen~ially by providing firs~ a ilm of a Group IV m~tal 7 ion, e.g., stannous ion, and then a film o reduced precious metal, e.g., reduced palladium, on the surface, In another em-9 bodi~ent, un~tary noble metal baths are used, rom which there is deposited on the surface a ~ilm o~ colloidal noble ~etal or 11 a complex o~ noble metal which is later reduced.
12 ~
13 It has now been discovered that adherent electroless 14 metal deposits can be applied to a broad variety of insulating substrates without the need to use expensive noble metals, 17 In addition, the methods o~ this invention avoid the flash deposition of precious metals which sometimes causes loss l9 ¦lof bond strengths between the electroless metal and the base in 20 jlprior art procedures.
21 I ~`
22 ¦ When following the teachings herein, there can be 23 ¦obtained printed circuits of the highest quality using base 22246 ~ metals onl n all se-ps of their production.

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1 S~n~lry o~ thc Inv~nt~on.~ The present lnvention 2 involvcs metho(ls for scnsiti~in~ a basc for s~bsequcnt electro-3 less metal dcposltlon by stcps that includc deposlt:lng on said 4 base a layer of a radi~tion-s~nsitive co~posit~on by treating said base with a solution having a p~l bet~ecn about 1.5 and 4.0 S as well as a minor content by welght o~ at least one halide ion 7 of the group consisting of chloride, bromlde and iodide ions .
and compris~ng a reducible salt of a non-noble metal with the ..
9 cations of said metal present in a larger propor~ion of equlva-lents than said halide ions, a radiation-sensitive reducing 11 ¦ agent for said salt and a secondary reducer in an aqueous medium, 12 li and exposing said layer to radian~ energy to reduce said metal 13 !I salt to metallic nuclei thereby producing a non-conducting layer 14 ¦ on said base of said metallic nuclei capable of directly cata- ¦ :
15 ¦ lyzing the deposition on said nuclei of metal from an electro-16 , less metal bath, 17 I . :
18 Other aspects of this invention relate to the sensi-19 I tized articles in the form of the bases bearing the layer of 20 j radiation-sensitive co~position; and also to combination pro-21 1 cesses in which the oregoing procedure is followed by an 22 1 electroless metal treatment o~ the image-bearing substrate to 23 1 build up a layer of electroless mctal on the lmage. Stlll 24 jl other aspects are concerned with preferred materials, fonmu-25 ¦1 lations and process conditions, ~6~ .
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- . : ~: : . ' , PC-1~3C ~ 9 I ~cscri~tlon of the Invcntion.- Accordlng to the _. _ 2 present invcntiorl thcre arc provide~ new articlcs of manufacture 3 comprising a base an~ a laycr on the base, the layer comprislng 4 a mctal salt or metal sal~ composition which on exposure to radiant energy, such as heat, li~h~, elcctron be~ms, X-rays, etc., 6 is converted to a layer of metal nuclei ~hlch is non-conductive 7 and which is capable of catalyzing the deposition of electroless 8 metal from an elec~roless metal deposition solution in contac~
g with the base, the metal salt being selected from salts of copper, nickel, cobalt, iron or mixtures of any of the foregoing.
11 . .' : ,.
12 According to the present invention there is also pro-13 vided in a process for producing metallized ar~icles by contacting 14 ¦ a base sensitized to the reception of electroless metal with an 15 ll electroless metal deposition solution, an improvement which com- j 16 ¦I prises providing the base with a layer of a metal salt or metal l l 17 1l salt composition which on exposure to radiant energy, such as ¦ -18 1 heat, light, electron beams, X-rays, etc., is convertible to a 19 i non-conductive layer of metallic nuclei, and exposing the layer 20 1l to a suitable source of radiant energy so as to convert it to a 21 ~I non-conducting layer of metal nuclei ~hich are catalytic to the 22 ¦¦ reception of electroless metal, said metal sait being selected 23 j from salts of copper, nickel, cobalt, iron or mixtures of any 24 1 of the foregoing.
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26 j In carrying out the present inventlon, the base i9 27 clcaned, if necessary, t.,en coated with the metal salt, e,g,3 .. . . .
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PC-12~C I 1045909 1 1 by di~-coatillg in a solution Oe ~hc salt, on areas on which i~ i9 2 desired to dcposit metal el~c~rolessly. When it i5 desired to 3 ¦ metalllze only selected are~s of the surface of a body and/or 4 only selected intcrior portions thereo~, e,g " hole walls, suit-S able masking may be used to protect the areas whlch are to be 6 ~ree of the metal deposi~ during as well a5 after the coating 7 and reduction, 81 . .. :
9 ¦ ~mong the materials which may be used as bases in this 10 i invention are inorganic and organic substances, such as glass, ¦ ceramics, porcelain, resins, paper, cloth, and the like. Metal-12 ¦ clad or unclad substances o~ the type described may be used, 14 j For printed circuits, among the materiaLs which may be used as the bases, may be mentioned metal clad or unclad insu-16 1¦ lating thermosetting resins, thermopIastic resins and mixtures 17 I of the foregoing, including fiber, e~g., fiberglass, impregnated 18 I e~bodiments of the foregoing.

1911 , ',. ,, . I .' 20 ~1 Included in the thermoplastic resins are acetal resins;

21 !1 acrylics, such as methyl acrylate, cellulosic resins, such as 22 ilethyl cellulose, cellulose acetate, cellulose propionate, cellu-23 Illose acetate butyrate, cellulose nitrate, and the like; poly-~4i1ethers; nylon; polyethylene; polystyrene; styrene blends~ such 25 Ijas acrylonltrile styrene and co-polymers and acrylonitrile- !

26 jbutadiene styrene co-polymers; polycarbonates; polychlorotri-27,l fluoroethylene; and vinyl polymers and co-polymers, such as 7 _ I

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~C-123C
Il ~O~S~9 1 1I vinyl acctat~, vinyl ~lcollol, vlnyl butyral, vinyl chlori~a~
2 vinyl chloriclc-ac~tn~e co-pol~ncr, vlnylidenc chloride and vinyl 3 ~onmal, ~mong the thenmosetting resins may be mcntioned allyl S phthalate; f~lrane, mel~mine-Eonnalclehyde; pheno} formaldehyde 7 and phenolfurfural co-polymcrs, alone or c~mpounded with bu~adiene acrylonitrile co-polymers or acrylon~trile-butadiene-styrene co-9 I poly~ers; polyacrylic esters; silicones; urea ~ormaldehydes;
epoxy resins; allyl resins; glyceryl phthalates; polyes~ers; and 11 the like.
12 ~
13 Porous materials, comprising paper, wood, iberglass, 14 cloth and fibers, such as natural and synthetic fibers, e.g,, 1 ~1 15 j~ cotton fibers, polyester fibers, and the like, as well as such 16 1l materials themselves, may also be metallized in accordance with `
17 ¦1 the teachings herein, The invention is particularly applicable 18 1I to the metallization of resin impregnated fibrous structures and 19 ii varnish coated resin impregnated fiber structures of the type 20 ~ degcribed.
~1 . ' .
' ' 22 The ba9es coated with catalytic metal nuclei generi-23 cally will include any insulating ma~erial s~-coated regardles8 ~, 24 ¦ Of shape or thickness, and includes t,hin fiLms and strlps a~
25 ¦I well as thick substrata, An adhesive layer can be on the bage~
26 , beneath the metal nuclel, e,g., an adhesive which is conventional 27 !i for this purpose in this art~ ` ¦

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lv~ssas I, 1 Thc bascs rcfcrr~ to hcrcin ~re ~r1organic or or~anlc 2 m~crials of thc type dcscrlbed ~hich have 3urface laycr com-3 prising mctallic nuclei whlch are catalytic to tha reception o 4 1electroless metal, "catalytic" in this sense referrin~ to an ¦
S ¦agent which is capable o~ reducing ~he me~al ions in an electro-1less metal deposition solution to mc~al.

The catalytic metals for use herein are selected fro~
9 Period 4 of Groups VIII and IB o the Period Table of the Elements: iron, cobalt, nickel and copper. Par~icularly pre ~ ferred is copper, When employing an iron salt as the reducible 12 l¦metal salt, a quick rinse in a suitable strong reducing agent, 13 1l such as sodium borohydride, after the exposure step ls usually 14 `! desirable for producing maximum density of the deposit.
1~ I . .'., 16 Tha catalytic metal, for example in t~e fonm of a solu- ;
17 jtion of the reducible salt or reducible salt c~mposition is ¦
18 11 applied ~o the base and then reduce.d on the surface o~ the base 19 liby application oE radiant energy, e,g,, heat, light, such as lultra-violet ligh~, electron beams, X-rays and the like. I
21 ¦1 multivalent, the reducible salt can be in any oxidation state, 22 ¦1 e,g " both, cuprous and cuprlc, ferrous and ferric, ions may be ~¦
25 ~ one manner of proceeding, a solution o a heat-26 jl reducible me~al salt, e.g., cupric formate, c d optionally a 27 1l developer, e.g., glycerine9 and a surfactant, in a solven~, such _ 9 _ ~, . , I .:
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1 !as water, i9 dlp-conted onto tha base, dricd ~n(l heated, e g., 2 lat 100 to 170~C., preferably at 130 to 140C., until the 3 coating has darkened in color, indicating the metallic salt has 4 been reduced to a non-conductive layer of coppcr nuclei The

5 base is now catalytic ~o the deposition of electroless metal on S t~e surface of the base and on the w~lls in ~ny holes in the 7 base, g In more detail, according to such a hea~-activiation proeess, the base, i necessary, is cleaned and pretreated by ll lone of the methods to be described. The clean base is dip 12 Icoated in one of the metal salt solutions, to be described in 13 jjdetail hereinafter, for a short time, e,g,, 1-3 minutes. The 14 ieoated base is then placed in a heated area, e.g , an oven ~or l~ 110 to 20 minutes, or until the metal salt is reduced to metallic -16 Inuclei. The temperature of heating can range from 100 to 170C "
l? jbut the preerred range ~s 130-140C. The reduction is con-18 ~sidered complete when the coating has darkened in color. The 19 l¦base is then removed ~rom the hea~ed area and allowed to eool.
20 jiThe coating is now catalytic to electroless metal deposition and 21 1I can be processed in known ways, as will be described hereinafter, 22 ¦I for the subsequent build-up of electroless metal plating,and, ¦
23 1 optionally, a top layer of electroplating, '241 . , .

25 ¦ In another manner of proceeding, a solution having a 26 1 p~l in the range of about 1.5 to 4.0 with a content of certain 27 j~halide ions (i.e., bromide, chloride and/or iodide ions) and q~ 10- I ~

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~0459Q9 1 comprlsln~ a metal ~alt c~npo~ition, e.~ " cuprlc fo~e, and a ~ -2 ¦light-scn~itive rcclucing ~gellt, a ~cond reducing agent, and 3 loptionally (for hard to wct surfaces) a surfactant, ln water is 4 ~coated on the base, drled and exposed to ult~avioiet light radia Ition to on~ a non-conductive layer of metallic nuclei. S~itable S llight-sensltive reducing agents are aromatic diazo compounds, iron 7 ~salts, e,g., ferrous or ferr~c oxalate, ferric ammonium sulEste, 8' Idichromates, e.g., ammoni~ dichromate, anthraqulnone disulonic 9 ¦1 acids or salts thereof, glycine (especially active under humid isurface conditions), L-ascorbic acid, azide compounds, and the like, as well as metal accelerators, e.g., tin compoundsl e.g., 12 Ij stannous chloride or compounds of silver, palladium, gold, mer-13 cury, cobalt, nickel, zinc, iron, etc " the latter group option-14 ally being added in amounts of 1 mg to 2 grams per liter, 15 ~
Among the second reducers are polyhydroxy alcohols, - ¦
17 Isuch as glycerol, ethylene glycol, pentaerythritol, mesoerythritol, 18 1,3-propanediol, sorbitol, mannitol, propylene glycol, 1,2-butane-19 ¦diol, pinacol, sucrose, dextrin, and compounds such as triethano-lamine, propylene oxide, polyethylene glycols, lactose, starch, 21 ethylene oxide and gelatin. Compounds which are also useful as 22' secondary reducers are aldehydes, such as ormaldehyde, benzalde-23 j~hyde, acetaldehyde, n-butyraldehyde, polyamides, such as nylon, 24 ;lalbumin and gelatin; leuco bases of triphenyl methane'dyes, such 25 ,ias 4-dlmcthylamino triphenylmethane, 4,4~,4"-tris-dimethylamino-26 1l triphenylmethane; leuco bases of xanthene dyes, such as 3,6-bis 27 ~ dimethyl~mino xanthene and 3,6-bls d~methylamino-9-(2-carboxyethyl) ~' -' ' '~

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t nthene; polyeth~rsl such as ~hylene glycol diethyl e~her, 2 ~ thylene glycol diethyl ether, tetraethylene glycol d;~e~hyl 3 ether, and the like. ¦
4 . . . .
A secondary reducer that is also a humec~ant, as exempl~fied by sorbi~ol, is generally preferred as a constituent ;
7 oi~ the treating solution, for the humec~ant, apparently by ¦ -8 ! reason of ~ moisture conditioning efect on ~he "dry" coating , :;
9 ¦ prior to developing, provides subs~antial aid in mainta~ning ~0 1 density of the metal coating on the base during a developing ¦ ;
I j step in which any unconverted radla~ion-sensîtive material in 12 the coating is washed of~ of the base. :~1 ~3 . . .
14 j Among the suitable surfzctants ar~ polyethenoxy non-15 11 ionic ethers, su~h as Triton X-100, manufactured by Rohm & ~aas 16 1 Co., and nonionic surfact~nts based on the reaction between nony~
7 phenol and glycidol, such as Sur~actants 6G and 10 manufactured 18 by Olin Mathieson Ccmpany , ~ 19 I . ' , . ' ': ' 2~ ! This tre~ting solution contains an acidifying agent tl in the fonm of an acid or acid salt for adjusting the pH of the 1 22 . aqueous solution to usually between about 2.0 and 4.0 (pre~erably :
l , ., , - 23 1 2 5 to 3.8~ and a ~mall quantity o iodide, br~mide or chloride . ~ ions~ 8~ that combination of additiv~s provides a surprising . ~;~
! 25 ~ effect in substantially inten~ifying the dens~ty of the coatin~ ' .I 26 ! ! that is formed subsequently by exposure of the treated substrate 2~ 1 eO radiant ~n~rgy~ Ad~usting the acidity do~s not always ¦

rc- 123C
~ ~LV4S~09 1 rc~uirc introducln~ an agent ~or ~hat purpose al~ne, becausc the 2 ~ ad~ustment may be accomplished wholly or partially by moans of 3 an acldic substance that has ~thcr ~unction~ a1so, as exemplified , 4 ~ by a light-sensitive re~ucing agent of an acidlc nature (e,~
ascorbic acidJ glycerine, ctc.) or by sane additives ~or intro-S ducing halide ions (e g " hydrochlor~c acid) Similarly, some 7 or all of the halide ions may be intro~uced as components o the 8 reducible metal salt (e g " cupric chloride).
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Among the many suitable acidic substances which may be 11 I ~mployed in controlling or adjusting the pH of the sensi~izing 12 j solution are ~luoboric acid, citric acid, lactic acid, phosphoric 13 ! acid, sulfuric acid, acetic acid, formic acid, boric acid, hydro-14 chloric acid, nitric acid and the like.

16 A wide variety of bromide, chloride and iodide salts 17 and other halide-generating water soluble compounds may be 18 utilized to provide part or all o the desired halide ion con-19 ¦ tent of the treating solution. These may include, inter alia, I salts of metals in general and these halogens as exempliied by 21 I cupric bromide, niclcel chloride, cobalt chloride, cupric chloride, 22 ¦ sodium iodide, potassium iodlde, lithiu~ chloride, magnesium 23 I iodide, magnesiu~ bromide, sodium bromide, potassium bromlde, 24 and the like, Bromide salts are preferred, as they produce a higher degree of sensitivity (i.e., darker and denser deposits) 26 on the substrate than the corresponding chlorlde in at le~st 27 j certain instances.

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10~909 ~ 'he hc~lid~ iO315 constitute only ~ minor proportion of the solute and may ty~)ically rancJe from about 0.0~$ to 1.6%
(preferably about 0.13 to 0.45~) based on the total w~ight of dissolved solids. Th~ amount o~ halogen may be stated otherwise as between about 0.~ and 25 milliequivalents of halogen per liter of the sensitizing solution, prefera~ly about 2.5 to 9 milli-~quivalents, e.g.~ 0.3-1.0 g./l. for cupric bromide. Increasing the proportions of the halide ions is usually undesirable as ~ ;
such increases appear to gradually diminish the sensitizing effect of the treatment below what is obtainable with the optimum amount. Also~ the proportion of these halide ions expressed as equivalents is less than that of the cupric or other reducible non-noble metal cations in the treating solution. For instance, the ratio of equivalents of such metal ions to halide ions is usually in the range of at least about 2:1 and preferably about 4:1 to 100:1.
The substitution of a compound yielding fluoride ions for a substantial proportion, but not all, of the iodide, ~bromide or chloride ions in some sensitizer formulations appears to increase the sensitizing effect somewhat. `~
; After exposure to ultraviolet light radiation for a short time the reduction to metallic nuclei is generally com-plete. If desired, the reduction can be further enhanced by heating at temperatures of up to about 130 to 140C. for 3 to 5 minutes more. For maximum density in the lsyer of metallic ~ `

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l nuclei, it is ~cncrnlly prcfcrn~le to dcvclop and rlnse ~he base 2 and carry out thc electrolcss mctal trca~mcnt descrlbcd herelnaEter 3 within a fcw hours aftcr such cxposure, espccially in ~he case o I -4 short cxposures to radiant energy. The base is now catalytic to 5 the deposition of electroless metal on the surface of tho base asld on the waLls in any holes in thc base in which metal nuclei are ~ exposed.

9 Typically, the autocatelytic or electroless metal de-position solutions for use in depositing electroless metal on 11 the bodies having a layer of catalytic metal nuclei prepared as 12 described herein comprisè an aqueous solution of a w~ter soluble 13 salt o the metal or metals to be deposited, a reducing agent or 14 !! the metal cations, and a complexing or sequestering agent for the 15 1¦ metal cations. The function of the complexing or sequestering ~
16 il agent is to form a water soluble complex with the dissolved ¦ ~-17 1 me~allic cations so as to maintain the metal in solution. The 18 function of the reducing agent is to reduce the metal cation to 19 metal at the appropriate time.

21 1 Typical of such solutions are electroless copper, nickel 22 1 cobalt, silver, gold, tin, rhodium and zinc solutions. Such 23 1 solutions are well known in the art and are capable of auto-24 ¦ catalytically depositing the identified metals without the use of 225 ¦ electricity.

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59~19 Typical of the electroless copper solutions which may be used are those described in U.S. Pat. No. 3,095,309, Con-ventionally, such solutions comprise a source of cupric ions, e.g., copper sulfate, a reducing agent for cupric ions, e.g., formaldehyde, a complexing agent for cupric ions, e.g., tetra-sodium ethylenediamine~tetraacetic acid, and a pH adjustor, e.g., sodium hydroxide.
Typical electroless nickel baths which may be used are described in Brenner, Metal Finishing, Nov. 1954, pages 68 to 76.
They com~rise aqueous solutions of a nickel salt, such as nickel chloride, an active chemical reducing agent for the nickel salt, such as the hypophosphite ion, and a comlexing agent, such as carboxylic acids and salts thereof.
Electroless gold plating baths which may be used are disclosed in U.S. Pat. No. 2,976,181. They contain a slightly water soluble gold salt, such as gold cyanide, a reducing agent for the gold salt, such as the hypophosphite ion, and a chelating or complexing agent, such as sodium or potassium cyanide. The hypophosphite ion may be introduced in the form of the acid or salts thereof, such as the sodium, calcium and the ammonium salts.
; The purpose o~ the complexing agent is to maintain a relatively small portion of the gold in solution as a water soluble gold complex, permitting a ., ~'''.

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1 rela~ivcly lnrge portion o the golc~ ~o remain out o solution as 2 ¦ ~old rcserve. T~e pH o the bath will be about 13.5 or bctween 3 I about 13 nnd 14, snd the ion ratio of hypophosphlte radlcal to 4 insoluble gold snlt may be between about 0.33 an~l 10:1. ' S Typical electroless cob~lt and electroless silver baths 7 are described in ~he Examples. Electroless tin, rhodium and zinc 8 baths are known by ~hose skilled in the art. ~ I
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A specific example of an electroless copper deposition ~ bath suitable ~or use will now be described:
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13 1i . . Moles/liter 14 Copper sulfate 0.03 1 15 Sodium hydroxide 0.125 I :
16 Sodium cyanide - 0.0004 ; 17 Formaldehyde 0.08 18 Tetrasodium I
l9 - ethylenediaminetetraacetate 0.036 Water Remainder i 21 11 ` . .
22 j This bath is preferably operated at a temperature of 23 ¦ about 55C. and will deposit a coating of ductile electroless ; 24 1i copper about 1 mil thick in about 51 hours.
25 ~j 26 il Utilizing the electroless metal baths o~ the type 27 , described, very thin conducting metal ~ilms or layers will be :~ 11 . I .

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ll iO4S9~9 1 11 laid do~n on t~e cn~nly~ic metal nuclcl. Ordinarily, the metal 2 films sup~ri~pose~ on ehe cataly~ic mc~al nuclei by elcctroless 3 metal deposition will ran~,e from O.l to 7 mlls in thickness, with 4 metal films havin~ a thickness of even less than O.l ~il being a S distinct possibillty.

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7 Among its embodiments, the present invention contem-8 plates metallized substrates in ~hich the electroless metal, e.g., 9 copper, nickel, gold or the like, has been further built up by ateaching an electrode to the electroless metal surface and electrolytically, i.e. galvanically,depositing on it more of the 12 ¦I same or different metal, e.g., coppe~r, nickel, silver, gold, ¦

13 li rhodium, tin, alloys thereof, and the like. Electroplating pro-14 j cedures are conventional and well known to those skilled in the 5 1 art, .

17 ~ For example, 8 pyrophosphate copper bath is commer-18 1 cially available for operation at a p~t of 8.1 to 8.4, a tempera-19 ¦ ture of 50C., and a current density of 50 amp./sq.ft. In 20 il addition, a suitable fluoborate copper bath is operated at a 21 Il pH o~ 0.6 to 1.2, a temperature of 25-50C., a~d a current 22 li density of 25 to 70 amp. per sq. ft. and is comprised o:
2311 ' ~:
24 il copper fluoborate Cu(BF4)2 , 225 - 450 g./l.

25 j fluoboric acid, ~tBF4 2 - 15 g./l.
26 ll borl~cid, N3bO3 12 - 15 g./1.

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?C~123C
~ 1()4~9~9 1 ¦ For printe~ circuit nppl~c~lon, coppcr d~posi~s for u.se as the 2 ¦ basic con~ctor m~ r~?al ~ro usunlly 0.001 to 0.003 ln. thlck.

¦ Silver may be deposi~ed galv~nically from a cy~nide ¦ ba~h opera~ed at a pH o 11.5 to 12, a temperature of 25-35C., ¦ and a current dcnsity of 5-15 ~mp./sq.ft. An illustrative ¦ galvanic silver bath i5 comprised of:
8 ~
9 ¦ 6ilver cyanide, AgGN 50 g./l, 10 ¦ po~assium cyanide, KCN 110 g./l.
11 ¦ potassium carbonateJ K2C03 45 g./l.
12 ¦ brighteners Variable 13 I .
14 ¦ Gold may be deposited galvanically from an acid gold 15 ¦ citrate bath at pH 5-7, a temperature of 45-60C., and a ¦
16 ¦ current density of 5-15 amp./sq.ft; An illustrative galvanic 17 gold bath consists of:

19 Sodium gold cyanide, NaAu(CN)2 20 - 30 g./l.
20 dibasic ammonium citrate 21 (N~4)2C6H507 25 - 100 g./l.

23 Nickel can be galvanically deposited at pH 4.5 to 5.5, 24 a temperature of 45G., and a current density o 20 to 65 26 1 ~ amp./sq.fc. the ba~h containinG:

, . i . . ~ .
,,' I -lg- l r i .
: -C-123C ' I
~ 4~ig~9 1 niclcel sulfl1~e, NiS04 6~120 240 g.ll.
2 nickel chloric1e, NiCl~ 61120 45 g./l.
3 boric acid, 113B03 30 g./l.

Tin and rhodium and alloys can be ganvanically de-S posited by procedures descrlbed ln Schlabach et al, Printed and 7 Integrated Circuitry, ~1cGraw-Hill, New York, 1963, p. l46^l48.
8 I .
9 It is essential in carrying ou~ ~he process o ~his invention to use a clean base -- otherwise adhesion, a-; measured 11 by the work needed to peel the electroless Metal from the base, 12 I will be non existent. Ordinarily, this will require chemical 13 I cleaning and/or polarlzing the surface of the base With 14 ! adsorbent substrates, e.g., glass cloth, fabrics paper and the lS ¦¦ like, no special pretreatment is required, but the surace must 16 be clean.

18 If the base is a metal clad laminate, e.g., having holes 19 drilled through or punched therein, conventional cleaning methods 20 1 are used to remove all contaminants and loose particles. The 21 1 surface should be "chemically clean," i.e., free of grease, and 22 1 surface films. A simple test is to spray the surface with 23 distilled water. If the surface is chemically clean, the water 24 ¦¦ will onn a smooth film. If not, the water will break into 25 ~¦ droplets.

~ 20 ~- I : " .

: . , . . . : - . . .

) PC-123C ; lQ~59~)9 1 A basc can bc m3~10 clean by sc~lbbin~ with pumlce or 2 the like to remov~ hcavy soils; rinsin~ wlth wa~cr; and sub5c-3 quently rcinovin~ soiling due to organic substances with a suitable 4 alkaline cleaning compositionl e.g~:

6 sodium isopropyl

7 naphthalcne sulonate 3 g./l.

8 sodium sulEate 1 g./l.
sodium tripolyphosphate14 g./~.
. sodium metasilicate 5 g./l.
ll tetrasodium pyrophosphate27 g./l.
12 . ~ `
13 ¦ This operation is desirably perEormed at 160-180F.

The surfaces are exposed to the bath for 5 to 30 minutes.
16 Other suitable alkali cleaning compositions, detergents and soaps 17 may be used, taking care in the selection not to have the surface 18 ¦ attacked by the cleaner. If present, surface oxides can be re-

9 I moved from metal surfaces with light etchants, such as 25Z ¦
ammonium persulfate in water, or the cupric chloride etchant of 21 ¦ U S Pat. No. 2,908,557. On the other hand, if the shape of the 22 basc permits, a sanding operation with fine abrasive can also 23 be used to remove oxides.
2~ , Unclad resinous substrates, e.g., resinous, e.g., 26 epoxy resins, imprc~nated fibrous structurcs and varnish, e~g., 27 , epoxy resin varnish, coated resin impregnated fiber structures . I
~
, l ` `
~ - 21 ~
~

~4~9~9 ~re best provided with i~n additional surace treatment, e.g., the direct bonding pretreatment process of u.S~ Pat. NoO 3,123,038, to achieve strong adhesion o electroless metal deposits to the base.
This generally comprises treating the base with a suitable organic or inorganic iacid, e.g., chromic or sulfuric acid, or base solution to render it porous. In many cases it is desirable to also treat the surface with an agent, e.g., dimethyl formamide or dimethyl sulfoxide before or during the etching process. The e~fect of such treatment is to render the surface polar.
~epending upon the particular insuliating bases involved, other ion exchange imparting materials may be utilized to effect the aforementioned temporary polarization reaction. For example, acidified sodium fluoride, hydrochloric and hydrofluoric acids, chromic acid, borates, fluoroborates and caustic soda, as well as mixtures thereof, have been found effective to polarize the - various synthetic plastic resin insuliating materials described herein.
~20 In a typical procedure, after treatment with the polar-izing agents, the insulating bodies are rinsed so as to eli~inate any residua} agent, following which they are immersed in a solution containing a wetting agent, the ions of which are base 22 - `

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

;, . , , . . :: .. ::
: : , .

~0459~9 I cxch~n~d with tllc surface o thc insula~in~ basc to thereby im 2 part to the base rclatively lol~ chaincc1 ions which nlso are 3 capablc of chcmically linkin~ with precious metal lons or ionic 4 complexes containing precious met~l ions, Followin~ tr~atm,ent S with the weting a~ent, tl1e lnsulating bodies arc rinsed again S so as to eliminate the residual wetting agent solution.

9 SPECIFIC E~IBODIMENTS

The followin~ examples illustra~e the methods and 11 ¦ articles of this invention, They are not to be construed to 12 limit the invention in any manner whatsoever.
13 1 .. ' ~. .

, 16 A copper clad epoxy-gLass laminate having holes drilled 17 il in it for through hole connection is cleaned with a hot a1kaline ~8 li cleaner of the ~ype described above, and all loose particles are 19 ¦ removed, 20 . .
21 The clean laminate is dip coated Eor l 2 minutes in a 22 ~ solution of the following formulation:
23 cupric formate lO g, -I ' . 24 anthraquinone 2,6-disulfonic acld disodium salt 2 g.
26 1l water - lOO 8~
a7 1l glycerine l g-Il ~

PC-123C ,1 ~4X9Og 1 Thc coated substr~c i~ placed in an oven ~or 10-20 2 minutcs ~t 130~1~0C. to rcd~lc~ thc lnycr o~ copp~r ~al~ com-3 posi~ion to a layer of copper nuclci.
4 , ~The darkened substrate is rcmoved from the oven and S allowed to cool.

8 An electroless copper layer is deposited on the layer 9 of copper nuclei on the catalytic substrate by immersing it ln 1~ a bath at 55~C.~ the bath having the follo~ing composition:
11 . ' ,'' 12 ¦ cupric sulfate 0.03 moles/l.
13 j sodium hydroxide 0.125 moles/l.
14 1 sodium cyanide 0,0004 moles/L.
formaldehyde 0,08 moles/l.
16 1 tetrasodium ethylenediamine 17 1 tetraacetate 0.036 moles/l.
18 ¦ water remainder l~j . ' 20 1 The surface of the base and the walls of the holes in the base 21 ~ are covered with a firmly adherent layer o bright, ductile 2Z ~ el-ctro essly doposited copper.

2511 , ' Il . .
' . .

~ I - 24 - ~
71 ~ . ~ ' ` .

.. . - : ~ . i . , " ., . . ; ,. : ~ - .

1! ~0459v9 1 t; PROCEDURE B

3 The procedure of Procedure A is repeated, substituting ~ for the copper clad laminate base, an unclad epoxy ~mpregnated 5 ~;lass fibcr laminate ~Westinghouse M-6528). The base is acti-6 vated as follows:
7 . . .
a~ Treat the surface of the base by inmlersion for 1 9m~nut~ in a 1:1 volume mixture o~ 191,1-trichloroethane and io dimekhyl~formam~de (D~?), also containing 1 g.ll. of Su~actant Il 6G (~:)lin Corp. ), and drain for 10 seconds.
12 . ~ . .
13b. Place work piece in an "air exhaust chamber" for : ,~
14 li 2 minutes to selectively evaporate the t~ichloroethane leaving 1 li behind an even wet coating of D~IF.
16 jl . O ::
17 1~ c. Immerse the work piece in an activator solution at 18 li 45C.~ for lO minutes, the solution comprising: - ~: :
lg 1~ . .
20 ~¦ CrO3 lO0 g.tl. ~ :~
21 il ' Conc. ~2S04 300 ml./1 22 1I Water to make l liter . :`
23 j . (Heated at 100C. for l hour and cooled to 45C. ;-~
U I be~ore usej and drain for at least 30 seconds. : ~

251 . ~; ' 2611 -;~
27,~
, ~`

. . . .; . , : .. - . ,, .. . . .. ,, ~ ", . . . - ,, . ; ;

5~
PC-123C ~

1 1 d. Place worlc pi~cc in a ~irst ncutraliz~r for S
2 ~ minu~es nt roo~ tcn~pcrature, thc first ncutralizcr bath com-3 prising 4 .
sodium ~isulfite 20 g./l.
Surf~ctant 6G 1 g./l.
7 H2SO4 to pH 4.0 8 ¦ wa~er to make 1 liter 9 . .
t0 e. Immerse the work piece ~or 10 minu~es in a second 11 neutralizer bath of the same composition as d.
li I ~, 13 i ~. Rinse the work piece in cold running tap water ~or 14 10 minutes.
15 . . .
16 g. Place work piece i~ hot alkaline rinse at 93C.
17 ~ for at least 15 minutes, the al~aline rinse comprising 18 75 g./l. of NaOH and 0.5 g.ll. o~ Surfactant 6G in tap water.
'' 19 1 .
:~
h. Subject the work piece to a final rinse in cold 21 1 running tap water.
221 . ' ' :
23 1 i, Dry in air under normal room conditions.

25 1 The activated base i9 sensiti~ed and an electroless 1 26 lj copper layer is deposited thereon by the method of Procedure A.
271 . .
., I . ' ~ - 26 ~

- ~O~S9(~ ~
_ROCE'DURE C
The process of Procedure A is repeated, substituting an activated epoxy glclss lamirla~e as the base (Procedure B) and a metal salt bath of the following composition:
cupric formate 10 ~
wate r 100 ml.
glycerine 6 g. .: :
surface active agent ~:
(Triton X-100) 1 g. ;.~:~
~10 There are obtained electrolessly metalized bases .
according to this invention.
PROCEDURE D .
A clean polarized epoxy-glass laminate (Procedure B) is dip coated into a metal salt solution of the formula~
cupric formate 10 g. ;
anthraquinone 2,6-disulfonic acid disodium salt 2 g. ~ ~
water 1000 ml. : ::
glycerine 10 g. `: `;
-20 and allowed to dry at 50 - 60C. for 5 minutes. ; ~

.~ ., . ",. ~; ~
. , ,.~,.,- ,.
";','`'~:

'.~
: - 27 ~

. ~ . - : ~.

S9(~9 I ~ Th~ substrate is exposed to ultrav~olet lizht ~or l ~o minutes, fon~in~ a l~yer o~ copper nucl~i. The substrate is 3 heated ~or 3 ~o S m~nutes at 130 to 140C. A layer of copper is 4 bu~lt up in the nuclei by electrolessly depositing copper onto the subst~ate from a bath as described ~n Procedure A.
6 .' 7 Instead of a resinous body~ paper or a woven fabric can .
be used. .
91 ' ' ' ~:

10 1 EXAMPL~S 1-4 ~11 1 . . .
~2 ~ The method of Procedure D is repeated (without heating) ', 13 substituting the following reducible salt solutions:
14 . . . .
15 ¦ ~ EXAMPLE 1 ~6 I .
17 I cupric formate . 10 g. :
18 11 anthraquinone 2,6-disul~onic.
19 1l acid dîsodium salt 3 g.
20 il : water 450 ml. . :
21 i ' glycerine 30 ml~ .

22 1 citric acid . 30 g~
23 ~t~nno~s chloride 1 g.
24 -: 1uorocarbon wetting agent(fluorinated alkyl polyoxy-ethylene ethanol) . (3-~ Co., FC-170) 0.25 g. :

27 1 : , ~:~
. ' '` ' . . ' - 28 ~

.
.. . ;: ~ - - : .

. ,l PC 123' ~' 1~45~ g 1 ~X~IPLE 2 , 2 . .
3 Prepare Part A:
~ cupric ~ conat~ 15 g.
. water 200 g, S Prepare Part B:
7 ~luorocarbon wettin~ atent .
8 ~FC~170) 0.1 g.
glycerine 30 g.
citric acid 30 g. :
Il I anthraquinone 2,6-disul~onic 1~ ¦ acid disodium salt 2 g.
~3 ¦ stannous chloride 1 g.
14 ~ ~ater 250g. ~
15 ¦ Mix A and B .
16 ~ . . :;.
17 ¦ EXAMPLES 3 AND 4 18 . .
19 ~ Prepare Part A: `;
20 ~ cupric acetate 15 g.
21 ¦ ' cupric nitrate 15 g. . :~
22 ¦ water 200 g. 200 g. .

~5 ~
26 11 .
27 ' . `

~; I - 29 -1' .' , ' ' ' . ':~, : ' ' : :' ::: : ~ , . . '`: `. ' :

::: . : . .. - . ~ . .~:: . . - . : : :: .

` ) PC-123C 1 ~4S9 1 Prcpare Pnrt U:
2 wetting agcnt ~FC 170)0.25 ~Ø25 ~;
3 ~lycerine 30 ~. 30 g.
4 citric acid 30 g. 30 g.
. anthraquinone 2,6-disulfonic S acid disodium salt 3 g. 3 g.
7 water 250 g. 250 g.
8 stannous chloride 1 g. 1 g.
9 Mix A and B
. ' :~
I1 ¦ EX~MPLE 5 12 I . ~ .
13 The process of Procedure A is rcpeated, substituting :.
14 j for the cupric ormate solution, the ~ollowing solution using 15 i L-ascorbic acid as the sensitiæer:
16 ~ . - .

17 ¦ cupric acetate 4 g `;~
18 ¦ L-ascorbic acid 5 g.
'9 1 pentaerythritol 2S g.
20 1 . sorbitol 30 g.
21 j citric acid 20 g.
22 ¦ stannous chloride 0.5 g.
23~ Surfactant 6G 0.5 g.
24j; water (to make) 1000 ml, 2511 , ' .' ' 26`1 A substrate metallized according to this invention 27 is obtained. ~ `

j _ 30 ~
i . ' .,: . , . . .. , -~ PC-123~ 4S~O~ , ' ' ~' I ~ r~.~ 6 2 The proce~lurc oE Examplc l is rcpcatcd, sub3~1tutln~ ~or 3 the electrol~ss copper solution, an el~ctroless niclcel solu~ion:
4 .
nickel chlorlde 30 g. :~
3 sodi~lm hypophosphite 10 g.
glycollic acid 25 g. .
8 sodium hydroxide 12.5 g, 9 water 1000 ml. . ~ .
'~ ' 10 . ' ':

11 The p~ i5 adjusted to 4.5 and the bath temperature is ~.

12 maintained at 95C. A nickel layer is built up on the copper ! `;

13 nuclei. . .

14 EXAMPLE 7 .16 The procedure of Example l is repeated, substitutlng for :
17 the electroless copper solution, an electroless cobalt solution:
18 .
19 ¦ cobalt chloride 30 g.
20 1 sodium hypophosphite 20 g.
21 1 sodium citrate dihydrate 29 g. .
22 ¦ ammonium chloride 50 g.
23 ¦ water (to make) 1000 ml. .
24 . .
The p}l is adju.sted to g.5 and the bath temperature ~s ~`
26 maintained at 90C. A cobalt layer is built up on the copper 27 1 nuclal.

! I ~:

I PC-123~, iL~ 59~39 I EXAMPrE 8 2 The proccd~re oE E~nalplc 1 is rcpeated, substiCuting for 3 thc clectroless coppcr sol~ltion, an electroless gold solution:
gold chlorid~ hydrochlorlde 6 trlhyclrate 0.01 mole/l.
7 sodium potassium tartrate 0.014 moletl.
8 cl~methyl amine borane 0.013 mole/l.
9 sodium cyanide 0.4 m~le/l.
I0 , wat&r q. 9. a.d.
11 . . . ,~'~,.' I~ The pH is adjusted to 13 and the bath temperature is 13 ¦ maintained at 60C. A gold layer is built up on the copper I4 ~ nuclei.
IS

17 The procedure of Example 1 is repeated, substituting 18 for~the electroless copper solution, an electroless silver l~ ¦ solution:
silver nltrate l,7 g, 21 sodlum potassium tartrate 4 g.
22 1 sodium cyanide 1.8 g.
23 I dimethyl amine borane 0.8 g.
24 I water (to make) , 1000 ml.

26 jj The p~l ls ad~ustcd to 13 and the bath temperature ls 27 maLntained at 80C. ~ sllver layer is built up on the copper 28 i' nuclel.
~....... I
_ I - 3~ -'$1 11 .' , . : ' :.J

' , I~C-123`~045909 ' 1Non-con~ ctlvc lnycrs of niclc~l, cobalt and iron n~lclei 2 form~d in slmil~r M~nncr can nlso b~ bullt up ~g descri~ed 3 for the coppcr n-lclei in thc~e cxamples with clectroless 4 nickcl, cobalt, gold ancl silver.
S . :, All such metallized substratcs having a layer of 7 electroless metal on top o the nuclei can ~urther be built 8 up with an electroplated layer o~ copper, silver, gold, nickel, 9 cobalt, tin, rhodium and alloys thereoE, using the baths and conditions described hereinabove.
~1 I . `;''' 12 1The above disclosure demonstrates that the present 13 1 process provides for the reduction of a layer o~ metal salt to 14 1 a layer of metallic nuclei by means of radiant energy such as ! 15 ¦~ heat or light, The layer of nuclei has been shown to be cata-;~' 16 1l lytic to adherent electroless metal deposition-and this metal ' can be iurther built up in thickness with electroplated metal.~

19 ¦¦ XAMPLE 10 20 1l A resinous laminated base is polarized according to ¦
21 li Procedure B. Holes are provided in the base at preselected 22 1l cross over points. The base is coated with a metal salt 23 1l solution of the following ~ormulation . 24 11 ~ . .

. 25 . .
26 ~ .

. : I - 33 ~ ~ ~ ! ~
~ . .

-`!1 `
PC-123~ 1 ~(~45~09 1 cuprlc acct~te 8 ~.
2 an~hraqu~none 2,6 disulfonlc 3 ncid disoclium salt 16 ~, 4 pentncrythritol 50 g.
sorbltol 60 g.
6 cItrlc acid 40 g.
7 stannous cllloride 0.5 g 8 Surfactant 6G 1 g.
g .
. ~ ' I0 The base is allowed to dry at 50-60C. for 5 minutes.
11 ~ha dry coating on the upper surface of the base is then exposed 12 to an ultraviolst light source for 2 minutes. Ultraviolet 13 light is also directed down into the hole walls. Next, the 14 unexposed metal salts are removed with a warm water rinse.

15 ¦ The base is then exposed to an electroless copper solution

16 (as described in Procedure A), and eiectroless copper is deposit-

17 1 ed on the walls of the holes and also on the upper metal film. ! :~

18

19 1 Next, if desired, the base can be connected as an elec~

20 1I rode in an electrolytic metal deposition solution to deposit ¦

21 aclditional metal on the walls of the holes and also the upper

22 surace.

23 .

24 EX~IPLE 11

25 ¦ A resinous insulating base is provided with A uniform

26 1l laycr of an adhesive by d~p coating in the following

27 I composition:

~ . . ..

ss~
1 ¦: acrylonitrile-butadiene copolymer 2 (Paracry~ CV~ manu~actured by 3. NAugat~ck Chemical Div.) ~2 g~
~ phenolic res~n (SP-8014, manu~actured by ~.
6 Schnectady Chemical Co.) 14 g.
7 methyl ethyl ke~one 1200 g~ ~:
8 . ;~
The adhesive coated base is heated until cured, 10 1 treated with a chromie-sulfonic solution then dipped into the 11 metal salt formula~ion o~ Example 10. ~::
12 . ~:
13 The base is dried at 55-60C for 5 minu~es, then ex-14 posed to ultraviolet light for two minutes, forming a layer of ~5 1l copper ~uclei on ~he adhesive layer. The base is then exposed 16 ¦ to an electroless copper solution tas described in Example 1), and -17 j electroless copper is deposited on the nuclei layer on the adhesive 18 1 ~oat~ng.
19: 1 Next, i desired, the base can be connected as an 20 j electrode in an electrolytic metal deposition solu~ion to deposit:
21 1 additional m~tal.
22 . . .
23 ~ ~ The polarization treatment described above provides a 2S l very active surface to which the meta~ salt ~trongly adsorbs and 25j ultimately there is ~formed a strong bond 4etween ~he base and~:
26'j the electrolessly:deposited metal. ~:

PC-123C '!
~)4S~9 1 EX~MPLE 12 3 Startin~ with abou~ 800 ml. oE wa~er, another metal 4 salt sensitizin~ formulation is prepared by addlng the other ¦
constit~lents one at a time in the order lis~ed hereina~ter and 6 thoroughly mixing the solution under yellow light. ~:
7 . .
8 sorbitol 120 ~.
2,6-anthra~uinone disulfonic acid disodium salt 16 g.
cupric bromide 0.5 g. l :
l cupric acetate 8 g.
12 Surfactant 6G . 1.5 g.
13 water sufficient for 1 liter 14 li aqueous fluoboric acid - 40% sufficient to adjust pH to 16 After preparation at room temperature, this solution is em- :
17 ployed in treating the several substrates described in Procedure 18 j D while following in general that method both in the sensitizi~lg 19 ¦¦ and subsequent processing steps, including electroless copper t 20ljdeposition 21 ,~ In the case of a clean, polarized epoxy-glass laminate with 22 1l perforations therein, the panel is imm~rsed for 3-5 minutes in 23 1l a bath of the above solution maintained at 40C., drained with 24 1l careful removal of excess solution from the holes, dried, 25 I normalized at room tempcrature and 30-60V/O relative humidity, 26 i exposed to ultraviolet radiation and dcveloped by immersion for 27 ' 2 minuees in a tank containin~ cold running tap water; all o~ , ;

I - 36 ~

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

,, I
PC-l23r ~ 459~9 1 , which steps nrc pcr~orme~ undcr yellow light. The cxposu~ to 2 ultraviolet li~llt is carried ou~ in a two-slded Scanex II Printer ~ ~
3 provided with a 4800 wat~ air-cooled mercury vapor lamp on each ! ~ II
4 ~ide and situated 8 inches away from the vacuum frame with th~
exposure set at 4.5--$.0 feet per minute.
6 . .
7 In repeatin~ the treatment with another p~nel under t~le .
8 same conditions except for omittiug the cupric bromide and fluo- ' 9 j bbric acid from the metal salt sensitizing solution3 it is ob-served that a considerably denser layer of copper nuclei is 11 formed on the epoxy-glass laminate with the formulation o~ this 12 example than with the fo ~LLation devoid o~ halide and fluoboric 13 ¦ acid. ¦ :
14 .
15 1 It has been observed thst the sensitizer solution of 16 , this invention is quite stable and can be employed for periods 17 jl of more than six months with only a little attention, such as 18 1l ~iltering th~ solution each wor~ day and checking its specific 9 i! gravity along with a weekly check and adjustment as necessary to 20 il maintain a pH of 3.5 at 20C., a metal salt content equivalent to 21 !1 7.8 to 8.5 grams of cupric acetate per liter and an anthraquinone Z~ 11 sa1t oontent of 15 to 16 grams per llter. ¦

24!l ~ I
25` ~

27 ~

!

I

IPROCI.DUR~ E

3.Numerous samples of clean, polarized epoxy-glass 4 laminates arc subjccted to steps of sensitization through ' exposure and development of layers of copper metal nucle~ similar I
6 to those o~ Example 12 except for employing different sensitizing 1 .
7 baths and an exposure of 2 minutes ~o a 1500-watt ultraviolet 8 light source in forming test images through a Stou~fer 21-step tablet or optical wedge.
10 . , . :.
11The composition of the control sensitization bath is:
12 . .
13 ~orbitol 120 g.
14 ~nthraquinone 2,6-disulfonic ¦ acid disodium salt 16.2 g.

.. 16 potassium bromide . 1,0 g. .
17 cupric acetate 9OO g. ¦~
18 Surfactant 6G 1.5 g, . ::
: ~ater suf~icient for -- 1 li ter 20 j pH ' 4.62 211 . . . . ' ~, 22 ¦ The Stouffer tablet is a mask having 21 small squares 23 1 of graduated optical density for the graduated transmission o~
24 : light through different squares in the series. These squares 25 il ran~e in density from a completely transparent square desi~natcd ;:~ :
26 ~I No. 0 and permitting 100~/o transmission of ultraviolet light to an 27 ! opaque square No. 20 that transmits no light. After development '- 11 ' I '."''~.' ~ 38 ~ I

:-: , :: : . , : :. . .,.-- : .

~045~9 `

1 and drying oE the exposed lamina~c sur~accs, they are examined 2 to observc the number of square tcst images visiblc on the lamin-3 ates as a measure of thc efEectiv~ness of the sensitizing trea~-4 ment. A product with a sensitivity rating of at least 5 images is desirable, and ratings of 7 or more are preerred.
6 ` .
7 EX~ ES 13-30 8 .
9 Varying amounts of a number of diferent acids are 10 i1 thoroughly mixed with separate baths of the sensitizing formula-11 tion of Procedure E to adjust the mixtures to various pH levels 12 ! in illustrsting the important effect of acidity in the treating 13 1 solutions employed in the present process. For comparative 14 ! purposes, Trials I and II and their data are included. ¦
. .
16 1 In each of the following examples, one or more specimens 17 of the epoxy-glass bases are treated at each specified pU value, ;
18 il processed and rated according to Procedure E; and the specific 19 ~ data and results Qre set iorth in the table hereinaEeer.

22 ~
24i . ' ' . ,., 25 1 . . : '" `

~1 - 39 : . . . :
'~ . ' : . ' ' ! . :

~.-~o~s~s T~BI.E I
Individual I Sp~c im~n Averagc . Scnsi~ivity S~nsitivity 2 Exnm~le Aci(~ Addi~ivc pll Rn~in~,s Rat$n~
3- Control none 4.62 6 5 7 6.0 4 I* citric acid 1.4 3 5 5 4.~
13 citric acid 2.05 6 6 7 6.3 6 14 citric acid 2.1 7 - ~ 7.0 l 45 g./liter .
7 1 . .
8 1 15 citric acid 2.4 8 - - i8.0 22.5 g~ll.

i6 citric acid 2.5 10 lO 11 10.3 11 17 citric acid 2.6 10 - - 10.0 12 ~ 10.0 g./l, 13 1 18 citric acid 2.92 8 9 ll 9.3 14 l 19 ~ citric acid 3.5 8 8 9 8.3 ;~
15 1l 20 citric acid 3.96 8 8 lO 8.6 :' :
16 ,i II* fluoboric acid 1.06 0 0 0 Q -~ 4~/7 aqueous 17 ¦ 21 fluoboric acid 2.20 8 10 9 . 9.0 :-18 1 22 fluoboric acid 2.5 3 10 9 9.0 19 j 23 fluoboric acid 2.90 ~ 10 9 10.5 20 j 24 fluoborLc acid 2.96 8 lO' ll 9.6 .
2l ~ 25 fluoboric acid 3.5 - 10 10 lO.0 . - :
22 1 26 fluoboric acid 3.7 7 7 7 7.0 .:
23 1¦ 27 fluoboric acid 4.0 7 8 8 ' 7.7 24 l~ 28 phosphoric acid 2.05 8 _ _ 8.0 ~ 80% aqueous 25 1l : 200 drops/liter . ¦
26 . 29 phosphoric acld 3O15 10 - - 10.0 ll 140 drops/l.
27 ,! 30 sulfuric acid 2.0 7 _ ~ 7,0 ! ~1 il I
2B *Tri~l runs for comp~rison of results. I ~
!! - 40 ~ !

- . , : ' ' ,' ' ' ,' ', ' ', 'C-123C l O ~ ~ 9 ~ g , I
1 In prep.~rin~ thc trcating solutions of thc foregoing 2 examplcs, turbidity is sometimes cncoun~ered in the control and 3 othcr baths having a pH of the order of 3.5 or higher whereas the 4 more acid mixtures are clear. Tlowever, this does not pose any serious problems for the turbidity is usually rather slight and 6 does no~ interfere with sensitization; moreover the suspended 7 solid matter may be easily ~iltcred out of the liquid.
8 .
9 Another observation is that darker images (i.e;, denser deposits) are obtained with sensitizing solutions containing 11 1 either fluoboric or citric acid rather than phosphoric or sulfuric 12 acid.
13 . . . .
14 By means of additional experiments wherein clean glass slides rather than laminates are processed according to Procedure 16 il E ~ith several of the solutions in the table of examples and t~en 17 I subjected to the same abrasion test, it can be demonstrated that 1~ 1I solutions containing fluoboric acid or phosphoric acid as the 19 lacid additive produce deposits with stronger adhesion to the glass 20 !!substrate than treating agents containing citric or sulfuric acid.
21 11 In some instances, it may be desirable to employ a mixture of 22 ~Itwo or more acids (e.g., citric and phosphoric acids) for ad-23 1j~usting the pH of the sensitizing solution in order to obtain a 24 " product having a combination of desired properties9 such as a 25 idense me~al coating that exhibits superior adhesion to the base.

~7 ~ 9~9 1 Furthcr illustra~ions of the processes and prod~1cts 2 o~ this invcntion arc set in the examp'les tabulatcd herelnafter 3 for varyin~ the proccssing under cont~olled and comparabl~ j 4 conditions, particularly in respcct ~o d~monstra~in~ thc ~f~ects S of varintions of acid and halid~ agen~s and concentrations 6 thereof by addition of the syeci~ied substances to stock .
7 1 sensitizing solutions Al~hough, gen~rally employing the 8 ¦ technique of Procedure E unless otherwise indicated, the follow-9 , ing examples differ from those o~ TabLe I in including an 10 1 elèctroless copper deposition step in a "copper strike bath"
11 i with a subsequent sensi~ivity rating observation of the dried 12 : srticle as a better.evaluation.
131 . ..

15 1 . ' 16 1 For more acidity comparisons, a stock sensitizer .:; ' 17 i solution is made up as beore, but without the addition'of ~ny 18 1 acid. The pH is 4.78, and its composition in grams per liter :
19 1j of aqueous solution is:
20 j .
21 sorbitol ' l20 . ' 22 1 2,6-anthraquinone 23 j ' disulfonic acid 24 j disodium saLt ' l6 25 1 cupric acetate 8 .
26' cupric bromide 0.5 27, Surfactan~ 6G 2.0 ~:

. . . ... ~ : . : :: : , : , , .: .

- , . .. :.. i:
- :: : :. . .. . : . . 1 ..

!

PC~l23C !
~5909 1 Thc pll of s~mplcs of this stock solution i5 then ad-2 Just~d ~o spcciEic valucs with suitnblo nmounts of citric, 3. lactic, and fluoboric acids. ~dditionally, scveral high pil 4 samples were pr~pnred, usin~ sodi~ln) hydroxide ~o adjust the p11.

S .
6 Test panels oÇ clean, polarized epoxy-glass laminates 7 are isensitized in those solutions, dried, exposed, developed 8 and immersed in an electroless copper bath. The drying cycle is three minutes and exposure to UV light consists of two passe~ ¦
10 1 on a Scanex II photoprinter, one at a setting o 4.6 feet per 11 11 minute, and the other at 13.0 feet per minute. PaneLs are 12 jl developed in cold running water for 60 seconds, and then immersed ;
13 il immediately in a room temperature copper strike bath for 20 14 1l minutes. Photosensitivity is detenmined by exposure through the 21-step Stoufer optical density wedge with the following 16 1~ resu1ts, 201 . .

24l ~ .
2s! . .
26!
771 ~

`~`!~ - 43 - ;
- j :

l 10~59~9 . l`ABl.E: X I
1 Exilmplc ~cid ~ Bcfore (~1 S t rikc ~ er Cu Stritce 2 Control none 4 . 78 3 4 3. 31 fluoboric 4.00 7 7 4 32 fluoboric 3.75 8 33 fluoboric 3,50 9 8 6 34 fluoboric 3.00 . 8 8 7 35 fl~oboric 2.50 7 7 8 36 fluoboric 2.00 6 - 6 37 1uoboric l.50 6 6 10 1' rrial III fluoboric 0.ô2 4 3 11 38 lactic4~00 6 7 12 39 lactic3.75 8 8 13 1 40 lactic3.50 8 8 14 i 41 lactic3.00 7 7 15 1l42 lactic2.50 7 7 16 1 43 lactic2.00 6 6 17 i 44 lactic1,60 3 . 3 : j 45 citric4.lO 7 7 19 i 46 citric3.70 lO 8 20 11 47 citric3.48 ll 9 21 1 48 citric3.00 8 7 22 1 49 citric2.~0 7 7 23 50 citricl.90 7 6 1 20 g,/l. , 24l 5l citric1.68 6 5 l . 30 g./l.
52 citric1.62 6 4 o ~./1.
26 ~Trial IV (NaO11)6.40* 2 l 27 ! Tri~l V (NaO11)11.50* 0 I! ¦

28 Not~: *At a p~ of 6.4, a precipitate formed; this redissolved . ~
.- ~ at the higher pH. I ::
~1 ~! - 44 -- .. , . . . - , ~. .. . .. .. . ;.. . . , . . - . .. . ..

. . . . . . ... .. .. . . .. . .

. `!! !

PC 123C I ~

From considera~ion o~ the T~ble I and II e~ampl~, it 2 is evident that treatin~ solutions containin~ the aforcsaid halide 3 ions and acidic materinl improve the ~ensitizing insulating sub-4 stra~es a~ pH levels in the range o~ about 1.5 to 4.0 and that a S significan~ly hi~h~r degree o sensitization i9 realized with a : 6 pH o 2.0 to 4.0 (particularly between 2.5 and 3.8) than i5 ob .
7 tainable ~ith more acid or less acid solutions under comparable conditions.
9I . . ~.
10 ¦ EXAMPLES 53-64 ,~
11 1 ~ ' 12 1 In demonstrating the results obtainable wi~h Procedure 13 ~ F using mixtures or halides other than cupric bromide, anqther ¦ aqueous stock solution is made up without the addition of cuprlc 15 1 bromide or acid. The composition in grams per 11ter of solution ' .
16 is: . ~.
17 , .
18 sorbitol 120 19 216-anthraquinone disulfonic 20 1 , acid disodium salt 16 21 1 cupric acetate 8 .
22 Surfactant 6G 2 23 . .
24 Variou~ halide compounds are then added to samples o~
25 ¦ this stock solution in such quantity as to provide a halide ion 26 concentration of ~.5 m~illiequivalents which is cquaL to 0.5 g./l.
27 I!of.cupric bromide. The p~ of each sample is then ad~usted to 3.50J
.

P~-123C
~ .

1 i nccessary, using fluoboric ncid. In Exnmple 54, more than 4.5 2 millieq~ivalcnts o~ hydrochlor~c acid is cmployed to accomplish 3 thc dual Etmction of providln~ halide ions and adjusting thc .
.~ acidity of the s~nsitizing bath; hence no fluoboric acid is S incorporated into this solution. The halide mixtures of Examples 6 63 and 64 contain 2.25 milliequivalents of each of the cupric 7 bromide and the sodium fluoride or ioclide liter of sensitizer solut~on.

IS ~ ~

,3 2s I
26 . ~ -:
. . . -':
27 . ::
- 46 - 1~
I, ~ . ~:
~ . ` .

~` PC-123C I
~LO~ Og Tl~BLE I I I

3 Example llalide p~l _nsit vity ~atin~
4 I Con~rol none 3.50 3 5 ¦ 53 HCl 3.50 4 6 1 54 HCl* ~.50 4 7 1 55 CuC12 3.50 6 8 56 HI* 3.40 4 57 Nal 3.50 7 58 NaI** 3.50 6 1l Trial VI MaI 6.00 2 12 Trial VII NaI 11.5 2 13 59 KI 3.30 6 14 6~ KI 1.50 0 61 bromine-water 3150 , 7 16 62 . CuBr2. . 3.50 17 63 CuBr2~NaF 3.50 9 ~18 ~4 CuBr2~NaI 3.50 7 19 1 . , . ;
¦ *HCl or HI in larger amount as the sole acid.

21 ~ *~Sensitizing solution filtered before use.
23 1 . . :~
24 1 . , . .
25 1 .

27 ~ : ~ . ;
~ ~ ~ ~ . ~
~ -47 - ~

~1 104S909 1 `
1 Trinls wlth scnsitizing sol~tions cmploying fluorid~
2 ions ns thc solc hnlide do not appear to increase sensitlzatlon 3 ovcr the control. Wnlile io~idcs alone tend to precipitate part 4 of thc coppcr con~ent of the sensitizer as cuprou~ iodide, this does not int~rfere, in most instances, wi~h the production o 6 1 good coating. Moreover, the precipitate may be removed by 7 j iltering.

81 . . ~-g F.X~LES 65-73 10 . .' 11 For appraising the effect of halide concentration in 12 sensitizer solutions, a large batch of the stock solution o~
13 1 Examples 53-64 is prepared and 40% aqueous fluoboric acid is 14 1l added to lower the pH to 3.50. This batch is then divided into 15 j¦ ten baths and cupric bromide is dissolved with thorough mixing 16 1l in the praportions speciied in Table IV. Then epoxy-glass ~
17 1l laminates are treated and evaluated as in Procedure F with the --18 i following results:

201 ' I ' 22 ~
241 . , .

26j .

27,j . ~, PC-12~ :
~ 5~
,~
1 T~BI.E IV, Sensitivity Rating ~fter 3. Example ~ pH Cu Strike ~ ~ . .................. ~ .
Control 0 3.50 2 6 65 0.~ 3.50 8 . :.
7 66 l.0 3.50 7 ~.
8 67 1.5 3.50 6 .
9 68 1.75 3.50 6 10 1 69 2.0 ~.50 6 11 70 2.5 3.50 6 12 71 3.0 3,50 ~ .
13 72 4.0 3.50 `~ 3 14 73 , 5.0 3.50 0 . .
16 From the data in Table IV, it is apparent that the concentration of halide ion is important for impro~ing the ¦ .
18 jlefficiency of sensitizing baths. Amounts o halide ions above 19 i1about 25 milliequivalents per liter marlcedly reduce sensitiza-20 !i tion. Accordingly, it is desirable to keep the cupric bromide 21 !!concentration between about O.l and 2.5 grams per liter, and 22 111pre~erably between about 0.3 and l.0 g.jl. Similarly desirable 23 ¦Iproportions for other bromide or halide a~ents may be computed ~ ::
24 i~from the ranges for cupric bromide on~a chemical equivalent 25 1 basis.
2~ 11 27 j . . ~ .

. . - . . . ~

PC-1~3/
1~4S9~9 1 Also, unsatisfnctory rcsults arc obtaincd wilcn nttcmpts 2 arc made to r~pc~t the Tablc IV cx~mplcs with the cupric acotate 3 omitt~d from thc sensitizer. This is interpretcd ~s an indication 4 that the number oE equivalents o coppcr or othcr catlon of the rcducible non-noble metal salt should be in excess o~ the number 6 of equivalents of halide ion in the sensitizing solution. In 7 ¦ general, a substantial excess is preferred, fas exemplified by a 5:1 or greater ratio of metal: halide ecluivalent weights.

g I
10 1 It is further evident ~rom the foregoing data that both 11 the acidity level and halide ion concentration must be within ¦ !

12 ¦ the aforesaid limited ranges to obtain the full benefits o the 13 f present invention, A combination e~fect is involved here, as 14 1 neither ~actor alone can provide those advantages. The data in 15 1 Tables I and II demonstrate that substantial losses in the 16 ~ sensitizing effect occur when the pH of the sensitizer is below 17 1 1.5 or abo~e 4.0 even with a preferred amount of halide in 18 1l solution. In Table IV, marked reductions in sensitization are 19 1l noted even with the pH at the preferred 3.5 level for solutions 20 jlcontaining either no copper bromide or an excessive quantity, 21 ¦ e.g., three or more grams per liter.

23 1 The invcntion in its broader aspects is not limited by 24 the specific steps, methods, compositions and improvcments shown 25 11 and dcscribed herein, and dcpartures may be made within the scope 26 of thc accompanying claims without departing ~rom the principles 27 !! thereo.
il ~

1l _ 5~

Claims (38)

Claims:

1. In a process for producing metallized articles by contacting a base sensitized to the reception of an electroless metal with an electroless metal deposition solution, the steps which comprise depositing on said base a layer of radiation-sensitive composition by treating said base with a solution having a pH between about 1.5 and 4.0 as well as a minor content by weight of at least one halide ion of the group consisting of chloride, bromide and iodide ions and comprising a reducible salt of a non-noble metal, with the cations of said metal present in a larger proportion of equivalents than said halide ions, a radiation-sensitive reducing agent for said salt and a secondary reducer in an aqueous medium, and exposing said layer to radiant energy to reduce said metal salt to metallic nuclei thereby producing a non-conducting layer on said base of said metallic nuclei capable of directly catalyzing the deposition on said nuclei of metal from an electroless metal bath.

2. A process as defined in Claim 1 wherein said base is a porous material.

3. A process as defined in Claim 1 wherein said base is a non-metallic resinous base with a polarized surface.

4. A process as defined in Claim 1 wherein said base is a metal clad insulating base.

5. A process as defined in Claim 1 wherein said metal salt is reduced to metallic nuclei by exposure to light.

6. A process as defined in Claim 1 wherein said metal salt is reduced by exposure to ultraviolet light.

7. A process as defined in Claim 1 wherein said salt is of the group consisting of reducible salts of copper, nickel, cobalt and iron.

8. A process as defined in Claim 1 wherein said reducing agent is a light-sensitive reducing compound of the group con-sisting of iron salts, dichromates, anthraquinone disulfonic acids and salts, glycine and L-ascorbic acid.

9. A process as defined in Claim 8 wherein said secondary reducer is a polyhydroxy alcohol.

10. A process as defined in Claim 1 wherein said radiation-sensitive reducing agent comprises anthraquinone 2,6-disulfonic acid disodium salt.

11. A process as defined in Claim 10 wherein said liquid medium contains citric acid and a polyhydroxy alcohol secondary reducer of the group consisting of glycerine, sorbitol, pentaerythritol and mesoerythritol.

12. A process as defined in Claim 1 wherein said base is thereafter exposed to an electroless metal bath to build up a layer of said electroless metal on said layer of metallic nuclei.

13. A process as defined in Claim 12 wherein the treated base is dried before the exposure to radiant energy and said base is rinsed after said exposure to radiant energy and prior to the exposure to said electroless metal bath.

14. A process as defined in Claim 12 wherein said electroless metal is of the group consisting of copper, nickel, cobalt, silver, gold, tin, rhodium and zinc.

15. A process as defined in Claim 12 wherein said salt is of the group consisting of reducible salts of copper, nickel, cobalt and iron, and said electroless metal is of the group consisting of copper, nickel, cobalt, silver, gold, tin, rhodium and zinc.

16. A process as defined in Claim 12 wherein said salt is a reducible copper salt and said electroless metal is copper.

17. A process as defined in Claim 1 wherein said solution contains between about 0.9 and 25 milliequivalents of said halide ions based on the total weight of said solution.

18. A process as defined in Claim 1 wherein said solution contains bromide ions.

19. A process as defined in Claim 17 wherein said solution contains cupric bromide.

20. A process as defined in Claim 1 wherein said solution contains a humectant.

21. A process as defined in Claim 20 wherein said secondary reducer comprises sorbitol.

22. A process as defined in Claim 1 wherein the PH
of said solution is between about 2.5 and 3.8.

23. An article which comprises a base bearing a layer of a radiation-sensitive composition having a minor content of at least one halogen of the group consisting of chlorine, bromine and iodine and comprising a reducible salt of a non-noble metal with the content of said metal amounting to a larger proportion of equivalents than said halogen, a radiation-sensitive reducing agent for said salt, a secondary reducer and an acid.

24. An article as defined in Claim 23 wherein said base is a porous material.

25. An article as defined in Claim 23 in which said base is a non-metallic resinous base having a polarized surface underlying said layer of radiation-sensitive composition.

26. An article as defined in Claim 23 wherein said base is a metal clad, non-metallic base.

27. An article as defined in Claim 23 wherein said reducing agent is a light-sensitive reducing compound of the group consisting of iron salts, dichromates, anthraquinone disulfonic acids and salts, glycine and L-ascorbic acid.

28. An article as defined in Claim 23 wherein said salt is of the group consisting of reducible salts of copper, nickel, cobalt and iron, and said reducing agent is a light sensitive reducing compound of the group consisting of iron salts, dichromates, anthraquinone disulfonic acids and salts, glycine and L-ascorbic acid.

29. An article as defined in Claim 23 wherein said radiation-sensitive composition comprises a reducible copper salt, anthraquinone 2,6-disulfonic acid disodium salt as said radiation-sensitive, reducing agent, stannous chloride, citric acid and a secondary reducer of the group consisting of glycerine, sorbitol, pentaerythritol and mesoerythritol.

30. An article as defined in Claim 23 wherein said secondary reducer is a polyhydroxy alcohol.

31. An article as defined in Claim 23 wherein said metal salt is of the group consisting of reducible salts of copper, nickel, cobalt, iron and mixtures thereof capable of reduction to a non-conductive layer of nuclei of said metal and capable of catalyzing the deposition of electroless metal from an electroless metal deposition solution in contact with said nuclei.

32. An article as defined in Claim 31 wherein said radiation-sensitive composition is sensitive to radiant energy of the group consisting of heat, light, X-rays and electron beams.

33. An article as defined in Claim 31 wherein said electroless metal is of the group consisting of copper, nickel, cobalt, silver, gold, tin, rhodium and zinc.

34. A process as defined in Claim 33 wherein said metal salt is a copper salt and said electroless metal is copper.

35. An article as defined in Claim 23 wherein said radiation-sensitive composition contains a bromide compound.

36. An article as defined in Claim 23 wherein said radiation-sensitive composition contains between about 0.13 and 0.45% cupric bromide based on the weight of said layer.

37. An article as defined in Claim 23 wherein said radiation-sensitive composition contains a humectant.

38. An article as defined in Claim 27 wherein said secondary reducer comprises sorbitol.