CA1050357A - Process for the formation of real images and products produced thereby - Google Patents

Abstract

Abstract of the Disclosure.- Non-conductive real images are formed on substrates by depositing reducible metal salt compositions thereon from an aqueous acidic solution of pHl.5-4 containing bromide ions and exposing the coated substrates to radiant energy to reduce the metal salt to metallic nuclei and to produce a real image of metal, which is intensified and built up by electroless metal deposition. The metal salt com-position can either by selectively deposited and then exposed or uniformly deposited and then selectively exposed, to produce the real image.

Description

: PC-121C
~)503S7 ~ ~ nd o~ the Invention ~ Thi~ invention relates

2 to novel and improved methods for selectively metallizin~

3 bodies and to the products which result from s~ch methods.

4 . .
More particularly, the prPsent invention rel~t~s t~
1mposing, by thermal or r~diant energy, re~l ima~es c~mpr~slng 7. non-conductive metallic are~s on the surfaces o~ s~(ch bodies.
8 Such images are then made clearer and built up w~th deposi~s .
9 of electroless metal.
11 Although applicable whenever it is desi~ed to ~pply a 12 met~llic coating to a substrate, as or ex~mple, for decor~tive 13 or protecti~re effects, or to make electr~c~l conduc~ors of a 14 ~ide variety of shapes and configurations, the procedures for mètallization herein are particularly useful for making real 16 images on a variety of base materials, e.g " resinous insulating .
17 laminated bases or porous non-conductive materials, e.~., cloth9 18 fiberglass, paper, cardboard, ceramics and the likeO
19 .
It is a primary object of this invention to provide a 21 process to produce real images on substrates, which c~n be.
22 bullt up by electroless plating and, optionally~ subsequent 23 electroplated metal deposition. .

25 Another principal object of this invention ~ to provide 26 lmprovements in metallization processes ~n which a base is 27 selectively sensitized to metallization by electroless pla~ing.

- 2 - ~

PC~121C
~5~ 3 ~ An a~ditional objec~ o~ this in~ention i~ to provide 2 base materlals and processes or selective elec~roless metalliza 3 tion in which there are employed non-nobl~ me~al ~ensitizer~
4 which are much more economlcal in cost, b~t equlvalent in per~ormance to the noble metal-containing sens~ti~ers used untll now, 8 Another object of this invention i~ ~o pro~de adherent 9 electroless met~l coatin~s bonded in selected areas to base materials.

12 The desired selectivity can be obt~ined according to 13 this inveQtion either by treating predetermined areas of the 14 substra~e by well-known techniques such as printing, free-hand drawing, lithographing, silk screening, embossing w~th textile 16 rollers, and the like, or by treating the ent~re ~urface and 17 selectively exposing predetermined ~reas through a mask~
18 through negatives, with heated dies9 and the like, or by 19 treating the entire surface and selectively exposing predeter-mined areas through a mask, through negatives~ with heated dies, 21 and the like.
22 . .
23 It has.now been discovered that an electrole~s metal 24 deposit can be selectively and adherently applied to a sub~tr~te The method uses a re~l lmage in selected areas on the surface, 26 the image being cataly~c to the build up o a metal layer there 27 on by elec~roles~ me~al deposition. The real image comprises _ 3 _ l(~S~357 n non-conduetlve layer o~ me~nl nuclei, Althou~h the proc~8.q cnn produce real im~ge~ or prin~ o~ ~ny kind~ lts selectivlty 2 f~cilitates the production o current conduc~or llne~, plate~
3 or termin~ls, as in the manu~cture o~ printed circ~it~ and 4 con~ributes to the decoratlve or deslgn process, ~8 in $he manufacture of name pl~tes diflls and other met~ ed pla~tlcs~

In all c~ses, when following the teachings herein) there are 7 obtained outstanding, unexpectedly h~h bond strengths between 8 the electroless metal and the base, as well as e5ccellent resolu-9 tion o~ the image formed.
10 .
11 Summary of the Invent~on.-. The p~e~ent invention involves 12 ~ method ~or selectively metallizing insulating ma~erials t~ith 13 real images b.y steps that include depositin~ on said substrate a 14 layer of a radiation-sensitive composition by treating the sub-15 strate with a so~ut ion havin~ a pH be~ween ab~ut l.5 and 4.0 as 16 well as a minor content by wei~ht o~ at least one halide ion ofth 2 17 group consisting of chlorid~ bromide an~ iodide ions and comprisi B
18 a reducible salt o a non-noble metal with the c~tions of said 19 met~l present in a larger proportion of equivalents than.said halide ions, a radiation^sensitive reducing a~ent for said salt 21 and a second~ry reducer in an a~ueous med~um; exposin~ sa~d layer 22 to radlant energy to reduce said metal salt to metallic nuclei .
23 thereof and wherein at least one of said treatin~ and exposin~
24 steps is res~icted to a selected p~ttern on sald substrate to produce a non-~con~ucting real im~ge o~ ssld met~llic nuclei In 26 said selected pattern ~nd cnpable of directly c~t~lyzln~ the de-27 posit~on thereon o met~l ~rom an electroless m~al bath.

~-i2iC
~5O 3 ~ 7 ~ Other aspects of thi~ inventlon relats ~o e combination 2 process ln which the foregoing procedure i8 followed by an 3 elec~roless metal treatmen~ o~ the image-be~ring ~ubstr~te 4 to build up a layer of electroless metal on the lm~gs a~ well as to certain apertured intermediate articles th~t h~e been S coated with the radiation-sensitive compo~lt~on bu~ not exposed . 7 to activating radiation. Still other aspects R~e concerned B with preferred materlals, formulations and proce~.conditlons.
g Descr_ption of the Invention.- According to t~e present 11 lnvention,substrates are metaLlized by either:
12 . . ~i) providing selected areas o the subs~rate 13 with a layer of a metal salt compos~tion which on exposure 14 to radiant energy is converted to metallic nuclei and exposing the layer to radiant energy to produce a non-conducting, real 16 image of a desired pattern or 17 (ii) providin~ the substrate with ~ layer of 18 a metal salt.or metal salt composition which on selective 19 exposure to radiant energy is converted into metal nuclei and exposing the layer to radiant energy to produce a non-conduct~
21 ing, real image of a desired pattern, and building up the 22 pattern by contacting the metallic nuclei with an electroless 23 metal deposition solution.

In carrying out the present invention9 the substrate 26 is cleaned, if necessary, then provided with a layer of the ~7 metal salt or metal salt composition9 e.g., by printing or PC~121C
~05~357 ~ othcr~i~e marking ~elected area~ of the 3ubstrate, e,g, 9 with 2 ~ solutlon of the 6alt or the ~alt composltion, or by use of 3 su~table masking to protect the areas which ~re ~o be free of 4 the image deposit during a~ well as a~ter the coa~lng and reduction. On the other hand, the en~ire subs~ra~e may be 6 co~ered with a layer of the metal salt or metal s~lt composition 7 and selected areas only may be reduced by expedlent~ such as 8 exposure to radiant energy through a mask or by ~pplieation of 9 a heated die, and the like.
11 Among the ma~erlals which may be used a~ b~ses in this 12 invention are inorganic and organic subs~rates, such as glass 9 13 ceramic~ porcela~n, res~ns, paper, cloth, ~nd the like. Unclad 14 laminated resinous structures, molded resins and lamillated resins may also be used.
i~ . .- - .
17 Among the materials which may be used as the bases9 18 may be mentioned unclad insulating thermosetting resins, 19 thermoplastic resins and mixtures of thc foregoing, including fiber, e g., flber glass, impregnated embodiments of the 21 foregoing.

23 Included ~n the thermoplastic resln8 are acetal resins;
24 acrulics~ such as methyl ~crylate, cellulosic resins9 such as 25 ethyl cellulose, cellulose acetate, cellulose propiona~e, 26 cellulose acetate butyrate, cellulose nitrate, and the like;

27 polyethers; nylon; polyethylene; polystyrene; s~yrene blends, ~ such as ~crylonitrile styrene copolymers and acrylonitrile-2 butadiene styrene copolymers; polycarbonate3; polychloro-3 trifluoroethylene; and vinyl polymer~ nnd c~polymer8, such ~g 4 vlnyl acetate, vinyl alcohol, vinyl butyr~l7 vinyl chloride, v~nyl chloride~acetate copolymer, ~inylidene chlor~de ~nd 6 vinyl formal.
. 7 B Among the thermosettin~ resins m~y be mentlohed allyl 9- phthalate; furane, melamine formaldehyde; phenol formaldehyde and phenol furfural copolymers, alone or comp~unded with buta-11 diene ~crylonitrile copolymers or acrylonitrile~butadiene-sty-12 rene copolymers; polyacrylic esters; silicones; urea formalde^
hydes; epoxy resins; allyl resins; glyceryl phthala~es; poly-14 esters; and the like.

16 Porous materials, comprislng paper, wood, Fiberglass, 17 cloth and fibers9 such as natural and synthetic fibers, e.g. 9 .
l8 cotton fibers, polyester flbers~ and the like, may also be l9 metallized in accordance with the teachings herein. The 20 invention is particularly applicabIe to the metallizat~on 21 of resin, e.g" epoxy resin, impregnated fibrous structures 22 and varn~sh, e.g., epoxy resin v~rnish, coated xesin impregnt~d 23 fiber structures of the ~ype described.

. Th~ substrates selectively covered with a real image 26 compriQing catalytic met~l nuclei generically will include 27 ~ny insulating material so covered, regardless of shape or ~ ~S~ 3 57 lA thickne~s, and include~ thln 1lm~ ~nd ~rIps n~ well ~9 thick substrata, 2 The b~ses reerred to herein are inorganlc or org~nic 3 materials o~ the type described which havc a re~l lm~e in 4 ~he ~orm of a sur~ace layer comprisin~ me~llic n~tcle~ whlch are catalytic ~o the reception of elec~roless ~e~al, "ea~alytic"
6 ~n this sense reerring to an agent wh~ch i~ capable of reducin~
7 the metal ions in an electroless metal deposltion solutlon to 8 metal.
9 The real images produced herein comprise me~all~c nuclei ~n which the metals arP selected from Groups VI~ and IB o~ the ll Periodic Table of ELements, These include ~old,.~ilver, iri-12 d~um, platinum, palladium, rhodium, copper~ nickel, cobalt and 13 ron~ Preferred metals are selected rom Pèriod 4 of Groups 14 VIII and IB; iron, cobalt, nickel and copper, Especially pre-15 ferred for th~ production of the real image is copper. ~hen .
16 employ~n~ ~n iron s~lt as th-~ re~ucible metal salt, a gu~ck .
17 rinse in a suitable strong reducin~ agent, such as sodium 18 borohydride, after the exposure step is usually desirable for 19 producin~ ma~imum density of the image.
- Tf desired, the substrate can be coated with an tl adhesive which is conventi~nal for this purpose in this i~1d 22 before be~n~ coated wlth the compositions of this invention.
23 In producing the re~l ~mage~ the metal i~ reduced ~rom 24 its salt sr a composition of the salt in si~u in selected Z5 ~reas on the surf~cQ of the base by npplication o radiant -26 energy, e~:., heat or light, such as ul~ra~iolet llgta~ ~nd 27 vi~ible ligh~, x~rays, elec~ron bcnms, and the like,, . ..

~OS03S7 In one manner o pxoceedf ng, ~ ~olution o~ ~ hea~-re~
2 ducible metal salt, e,g., cupric formate, and op'cionally a 3 developer~ e.g" glycerine, alld ~ surfact~nt- in w~te~ is 4 selectively coated onto the bsse9 dried and hea~ed$ e.g., at 100 to 170C., preferably at 130 to 140~C., ~ntiL the surface layer has darkened in color9 indlcatlng the metalllc 7 salt has been reduced to a non-conductive r~al ~m~e comprising, g e,gr, copper, nickel, cobal~ or iron nuclei. The base is now 9 catalytic to the deposition of electroless metal~ e.g.~ copper, nickel, cobalt, gold or silver, on the sur~ce of the base and 11 on the walls in any holes in the base. A~tern~tively, the 12 en~ire base is provfded with alayer of the salt and the image 13 is formed by heating selected area~, as w~th 8 hot die, In more detall, according to such ~ heat-activatlon 16 proce~s, the base, if necessary, is cleaned and pretreated by .
17 one of the methods to be described. The clean base is printed 18 in selected areas with one of the metal salt solutions, to be 19 described in detail hereinsfter, for ~ short time, e.g., 1-3 minutes. The base and layer thereon is then placed in a heated 21 area, e.g., an oven for 10 to 20 minutes9 or until the metal 22 salt is redueed to form a real image comprising metallic nuclel. .
23 The temperature of he~ting can range from 100 to 170C.~ but .
24 the preferred range is 130~140C~ The reduction ls considered completed when the coating has darkened in color. The base with 26 the image thereon is then removed from the heated area and 27 allowed to cool. The ima~e is catalytic to electroless metal _g_ ' . deposition ~nd cnn be processed in known way~, ~8 ~ill be 2 described herein~ter, for the ~ubseq~ent build-up of 3 electroless me~Rl plating and, optionally, a ~op l~yer o 4 electropl~ing. Alterna~ively, the entire ba~e can be provided with a l~yer of the metal salt and the image produced by hea~ing selected areas.

8 In another manner to proceeding9 a 501utl~n h~vinæ a 9 pH in the range of about 1.5 to 4.0 wi~h ~ content o~ certain halide ions ~i.e., bromide, codide and/~r chlorid~ ions) 11 and comprising a metal sal~ composition, e,g., cuprlc formate, 1~ nnd a llght-sensitive reduclng agen~, a second reducing agent, 13 and optionally ~for hard.to wet sur~aces) R surfactant, ln 14 water is selectively printed on the base, dried and exposed o ultraviolet light radiation to form a re~1 image of me~llic lS nuclei. Suit~ble light-sensitive reducing agen~s are aromatic 1~ diazo compounds, iron salts, e.g., ferrous or ~erric oxala~, ferr c 18 ammonium sulfate, dichromates, e.g~, ammonium dichrom~te, l9 anthr~quinone disul~onic aclds or salts thereof, glyeine 20 (especially active under humid surface conditions), L ascorbic.
21 acid, azide compounds, and the like, 8S well as metfll accelera-2t tors, e.g., tin compounds, e.g., ~tannous chloride, or compounds 23 of silver, palladiumD gold, mercury, cobale9 nickel, ~inc, iron, 24 etc., the latter group optionally being ~dded in trace amounts of 1 mg. to 2 g. per l~ter. Among the second reducers are 26 polyhydroxy alcohols~ such as glycerol 9 ethylene glycol, penta- .
27 erythritol9 mesoerythrltol, 1,3-propanediol, sorbitol, mannLtol, . ~ 10 ~

1(~5CI~S7 propylene glycol, 1,2-butflnediol, pinacol, sucro~et dextrl~, 2 and eompounds such as trie~hanolamine, propylene oxide, poly-3 ethylene glycols, lactose, starch, ethylene oxlde ~nd gelatln.
4 Compounds which are also use~ul as secondary reducer~ ~re aldehydes, such as ~ormaldehyde, benzaldehyde, ace~ldehyde, 6 n-butyraldehyde, polyamides, such as nylon, ~lbu~in and gelatin;
7 leuco bases of tripllenylmethane dyes~ 3uch AS 4-d~methylam~no 8 triphenylmethane, 4,4',4"~tris-dimethylamino-trlphenylmethane;
9 leuco bases of xanthene dyes, such as 396-bi~ dim~thylamino xanthene and 3,6-bis dimethylamino-9-(~-carboxyethyl)xanthene;
11 polyethers, such as ethylene glycol diethyl ether, diethylene 12 glycol diethyl ether, tetraethylene glycol dimethyl ether, and 13 the like. Among the suitable surfactants ~re polyethenoxy 14 non-ionic ethers, such as Trito~X-100, manuactured by Rohm &
Haas Co~, and non-ionic surfactants based on the reacti n be-16 tween nonyl phenol and glycidol, such as Surfactants 6 nd 17 lO anufactured by Olin Mathieson Company 18 .
19 This treat~ng solution contains an acidifying agent in 20 the form of an aeid or acid salt for adjusting the pH of 21 the aqueous solution to usu~lly between about 2.0 and 4~0 2~ (preferably ~.5 to 3.8) snd a 8mall q~antity ofiodide, bromide or 23 chloride ions, as that combination of additives provides a 24 surprisin~ effect in substantially intensifyin~ the lmage that is formed subsequently by exposure of the treated substrate 26 to radiant energy~ AdJustin~ ~he ~cidity does not always 27 require intr~ducin~ an agent for ~hat purpo~e alone, because ~ L~)50357 the ad~ustment may be accomplished wholly or parti~lly 2 by me~ns of an scidic subst~nce that has other functions ~lso, 3 as exemplifled by a light-sensi~ive redu~ing a~ent ~ an aeidic 4 nature (e,g., ascorbic acid, gl.ycine, etc.) or by ~ome additlves

5 for introducin~ halide ions (e,~,, hydrochloric ac~d). Simil~rl ,

6 some of the halide ions mAy be introduced a8 componen~s o the

7. reducible metal salt (e.g. 9 cupric chloride), B
9 Among the many suitable acidic substancP~ ~hich may be employed in controlling or adjusting the pH of ~he sensitizing Il solution are fluoboric acLd, citric acid, 12~ic ~cid, phosphoric 12 acid, sulfuric acid, ~tic acid, form~c acid, boric acid, ¦ hydroch ric ac id, nitric ac id, and the ~likc .

6 . .

19 .

~2 24 . -- 12 ~

0S0 3 S ~
A wlde vflriety o bromide, chloride and iodide salts and 2 other halide generating water ~oluble compounds m~y be utilized 3 to provide part or all of the desired hfllide ion content.o the 4 treating solution. These may include, inter ~lia, 8~1ts o~ metal in general and these halogens a~ exempliied b~ cupri~ bromlde, n.~ckel chloride, cobalt chloricle, cupric chloride, ~odl~m iodide, 7 sodium bromi~e, potassium iodide, sodium lodldej 11thium chloride,

8 magnesium chloride, magnesium iodide, potasslum bromide, magnesiu

9 bromide, and the like. Bromide salts are preerred, as ~hey produce a higher degree of ~ensitivity (i.e., darker and denser 11 images) on the substrate than the corresponding chloride in at 12 least certain instances. .-13 `
14 The halide ions constitute only a mlnor proportion of ~he solute and may typically range from about 0,045 to 1.6%
16 (preerably about 0.13 to 0.45%) based on the tot~l wei~ht of 1~ dissolved solids. The amount of halo~en may be stated otherwise 18 as between about 0.9 and 25 milliequivalents of halo~en per 19 liter of the sensitizing solution, preferably about 2.5 to 9 mllliequivalents e.~., 0.3-.1.0 ~.ll. for cupric b~omide.
21 Increasin~ the proportions of the halide ions is usually 22 undeslr~ble as such increases appear to gradually diminish 23 the sensiti~ing effect of the trestment below what i~ obtainable 24 with the optimum amountO Also, the proportion of these halide ions èxpressed as equivalent3 is less than ~ha~ of the cupric 26 or other reducible non-noble metal catiorls in the treating 27 solution. For instance~ the ratio of equivalents of such metal ~-121~ l i 050 3 ~7 ~ ¦ions to halide ions i8 usu~lly in the ~an~e of a~ le~st about 2 ¦ 2:1 and pre~erably about 4:1 to 100:1.

4 ¦ The ~ubstitution o a compound yield~n~ fluorld~ ion~
¦ for ~ subst~ntial proportion, but not all, o~ the lodide, 6 ¦ bromlde or chloride ions in some sensit~zer formul~tlons ~ppears 7 ¦ to in~rease the sensitizirlg effect somewhst.
~ I .
~ ¦ After exposure to ultr~violet li~ht radiation for a ¦ short time, the reduction to metallic nuclei is generally 11 ¦ complete, Sometimes, the reduction can be furt~er enhanced 12 ¦ by heatin~ at a temperature of up to about 130~C. for a few 13 ¦ minutes more.
14 I `
15 ¦ Alternatively, instead o selectively printing~ if the 16 -base is eoated all over with the metal salt composition and 17 exposed through a positive or negative of an originaL pattern 18 or photograph, there will form a real image on selected portions 19 of t~e surface from which the b~ckground ean be remo~ed by washing out the unexposed (unreduced) portion .of the ~etal layer 21 e.g., in running water for about 5 to 10 minutes. The real ~2 image on the base is reinforced by deposition of electroless 23 metal from a solution onto the image so as to build up metsl 24 on the base ~nd, in suitable instances, on the walls in any holes in the base in which metal nucle~ have been formed by 27 exposure to ultr~violet light.

P~-12lC
~OS~357 In all case~ the co~ting of metal ~alts should be dry 2 before selective exposure to radiant energy, Otherw$se~
3 ima~es may reverse, In all such embodimcnts~ the ~etal 4 accelerators described above w:Lll provide enhanced rates o 5 ima~e formation, For maximum tmage den~i~y, it ls generatly preferable to develop and rin~e the substrate snd ~rry out the 7 electroless metal treatment descrlbed hereinafter wlthin a few .
8 hours after such exposure, especially in the ca~e of short 9 exposures to radiant energy, 11 Typically, the autocatalytic or electroless metal 12 deposition solutions for use in depositing electroless 13 metal on the bodies having a real image comprised of catalytic 14 metal nuclei prepared as described herein comprlse an aqueous solution of a water soluble salt of the metal or ~etals to 16 be deposited, ~ reducing agent ~or the metal cations, and a .
17 complexing or sequestering agent for the metal cations.
18 The funetion of the complexi.n~ or sequesterin~ a~ent is to 19 form a water soluble complex with the dissolved metallic catLons so as to malntain the metal in solution, The function 21 of thc reducin~ a~ent is to reduce the metal cation to metal 22 at the appropriate time, 24 Typical of such solutions are electroless copper~
electroless niclcel, electroless cobalt, electroless sil~er 26 and electroless gold solutions. Such solutions are well known 27 in the ar~ and are capable of autocatalytically depositing the 28 identified metals withou~ the use o electricity, _,s~ .

P~-121C
~ ~ 5~ 3 S 7 Typical o~ the electroless clpper ~olu~ions which 2 may be used are tho~e described in U.S. P~tent Mo. 3509~3~3 4 Conventionally, such 601u~ions comprise a sourc~ ~ cupric ions, e,g., copper sul~te, a reducing ~gen~ for ~p~ic ~n~, e.g,, formaldehyde, a complexin~ agent or ~prl~ lon~ e.~. 9 ~ tetrasodium ethylenediamine-~etraace~ic ~cld, ~nd A pH
8 adjuster, e.g., sodium hydroxide, 9 . ' ' .

12 Typical eleccrole~s nickel bach~ wh~ch may ~e used 13 aredescribed in Brenner9 Me~sl Finishing, November 1954, 14 pages 68 ~o 76. ~hey comprise l~ aqueous solu~ions of a nickcl salt, such as nickel ~hloride, 16 ~n active chemical r~ducing agent for the nickel sal~, such .
17 ~s the hydrophosphite ion, and a complexin~ ~ent, such ElS
8 ¦ carboxyli c ids snd ~alt~ there~f, 27 . .
~ 16 _ ' .' ~05035'7 2 Electrol~ss gold plating baths whlch m~y be u~ed are 3 disclosed in U.S. Pa~ent No, 2,976,181, 4 ~hey cont~in ~ sllghtly wa~er 8~1uble S gold salt, such a~ gold cyan$de, a reducing a~n~ a~ the gold sal~, uch as the hypophosphi~e ion, and ~ ~h~lati~& ~r ~om-7 plexing ag~nt, such as sodium or potassi~ cy~nide. ~`he 8 hypophosphitc ~on may be ~ntrcduced ln the form ~ the ac~d 9 or salts thereof, s~ch as ~he sod~um, ~alcium ~nd the ~mmonlum salt~. The purpose of the complexing ~gent iR to m~n~a~n a 11 rela~ively small portion of the gold in 801~ion ~ a ~ater 12 ~oluble gold complex, permlttlng a re~a~ively lar~e por~ion of 13 the gold to remain ou~ of solutlon as gold reserve. ~he pH
14 o~ the bath will be about 13.5 or betw~en ~bout 13 and 14, and ~he ion ratio of hypophosphite radical to ins~luble gold salt 16 may be between sbout 0.33 and 10:1.

19 A typical electroless cobalt bath is described ln 22 the Ex~mpl 8s well ss a -cefal e-ecerole6s s~lver bsth.

50 3 S~7 A specific example of an electrole~a copper depo~i~lon 2 bath suitabl.e for use is a~ follows:
3 Moles/li~er.
4 Copper sulfate 0,03 Sodi~m hydroxide 0.125 6 Sodium cyanide 0,~004 7 Formaldehyde 0.08 8 Tetra*odium 9 ethylenedinminetetraace~ate 0,036 ~ater Remainder 1~
12 This bath is preferably oper~ted at a temperature of 13 about 55C. and will deposlt a coating of ductlle electroless 14 copper about 1 mil thick in about 51 hours.

16 Utilizlng the electroless metal baths of the typ~ .
1~ de~cribed, very thin conducting metal films or layers will be 18 laid down on the image comprising metal nuclei. Ordinarily, 19 the metal fi~ms super-imposed on the image of metal nuclei by electroless metal deposition will range from O.l ~o 7 mils in 21 thickness, wlth mPtal films having a thickness of even less 22 than O. l mil beirlg a discinct possibilityO

24 Among it~ embodiments, the present invention contempl~tes 25 metallized substr~tes in which the electroless metal, e,g 26 copper, nickel, cobalt, silver, gold or the like, has been 27 further built up by attaching an electrode to the electroless ~ ()5~357 metal surfncQ and electrolytlcally, l.e.~ galvanically depo~lt~
2 ing on it more of the same or df fferenk metal, e.g., copper, 3 nickel, cobalt, silver9 gold, rhodium, tin, alloys thereo, 4 and the like. Electrolytic ptating procedures are convention~l and well known to those skilled ln the art, 6 .
7 For example, a pyrophosphate coppe~ b~th is commercially 8 available for operating a~ a pH of 8O1 to ~49 a temperature 9 of 50C., and a current density of 5û amp./sq.ft. ln addition, a sui~able fluoborate copper bath is operated at a pH of 0.6 11 to 1.2, a temper~ture o~ 25-50C,, and a current density of 12 25 to 75 amp. per sq. t. and is comprised of:
13 copper fluoborRte Cu(BF4)2 ~ 225 - 450 g. /1, 14 fluoboric acid, HBF4 ~ 2 - 15 g. /1~, boric scid, H3B03 - 12 - 15 g. /1. For printed circuit 16 application, ~opper deposits for use as the bssic conductor 17 material are usually 0.001 to 0.003 in. thick.

19 Silver may be deposited electrolytically ~rom a cyanide bath operated at a pH of 11.5 to 12, a temperature of 25-35C., 21 and a curren~ density of 5-15 amp. Isq. ft . An illustrative 22 electrolytic silver bath is comprised of:
23 silver cyanide~ AgCN - 50 g./
24 pot,assium cyanide~ KCN - 110 g,/l.
potassium carbonate,K2C03 - 45 g,/l.
26 brightener - Variable 2~

~l)S03S7 Gold may be depo~ited electrolytically from an acid 2 gol.d citrate bath at pH 5~7, a temperature o 45~60~C,, and 3 current density of 5-15 amp D /sq ~ ft. An ilLust~ative electro-4 lyti~al gold bath consls~s of:
Sodium gold cyanide, NaAu(CN)2 - 20 ~ 30 g./l, b dibasic ammonium citrate ~ (N~4)2C6H507 - 25 - 100 g./l, 9 Nickel can be electrolytically deposited ~t pH 4.5 ~o 5.5, a temperature of 45C., and a curren~ density of 20 to 11 65 amp./sqOt~ the bath containlng:
12 nickel sulfate, NiS046H~0 - 240 g~
13 nickel chloride, NiC126H20 - 45 g./l.
14 boric acid, H3B03 o 30 g./l. Tin and rhodium and alloys can be electrolytically deposited by procedures 16 described in Schlabach et al~ Printed and Integrated Circuitry~ .
17 McGraw-Hill, New York, 1963, pages 146-1480 19 It ~s essential in carry~ng out the process of this invention to use a clean substrate - otherwise adhesion, as 21 measured by the work needed to peel the electroless metal from 2t the substrate, will be non-existentD Resinous bases will bene-23 fit from chemically cleanin~ and/or polarizing the surface.
24 With adsorbent substr~tes, e.g " glass cloth, fabr~cs paper, and the like, no spec~al pretreatment is required~ but the 26 surface must be clean.

_ 20 _ 1a~503S7 ~ If the base ls a reslnou~ lamlnate9 e.g., having hole~

2 drilled through or punched therein, conventional cleaning 3 methods are used to remove all con~amlnan~ and 1008e part~cle8 4 The surface should be "ohemically clean", l.e,~ free of ~re~Qe, and surface films. A ~mple test i~ to ~pray the surface ~th S distilled waterO I the sur~Bce i8 chemically cl~n, the wa~er 7 wlll ~orm a smooth film~ If no~, ~he wate~ wlLl break ~nto 8 droplets.
A base can be made clean by scrubbin~ with pumice or 11 the like to remove hea~y soils; rinsing with water; and 12 subsequently removing soiling due to organic substances with a 13 suitable alksline cleaning composition, e.g,:
14 sodium isopropyl naphthalene sulfonate - 3 g./l.
16 sodium sulfate ~ 1 g./l.
17 sodium tripolyphosphate - 14 g./l.
18 sodium metasilicate - 5 g./l.
19 tetrasodium pyrophosphate - 27 g. /lr 21 This operation is desirably performed at 160ol80F.
22 The surfaces are exposed to the bath for 5 to 30 minutes.
2; Other suitable alkali cleaning compositions9 detergents and 24 soaps m~y be usedD taking c~re ~n the selection not to have the sur~ace a~tacked by the cleaner~ If present, surface 26 oxides can be removed from met~l surfaces with light etchants3 27 such as 25% ammonium persulfate ln water, or the cupric chloride ~ 21 -.

~5~357 ~ e~ch~nt o~ U.S. Pa~ent No. 2,908,557. On the other h~nd, 2 i ~he ~h~pe oP the b~se permi~ 3andir,g opeta~orl with 3 fine abra~ive can al80 be used ~o remove oxlde~ .
~ .' .
Some resinou~ subs~rat~s, e.~ p~xSr re~n ~mpre~ ted S fibrou~ structures and epoxy resin varni~h c~ed re~ln lm~
7 pregnated fiber s~ructures benefit from ~n addlt:~n~l sur~ce 8 treatment~ e.g., . a direct bonding pre~reatment process.
9 This helps to achieve strong adhesion of electroless metal deposits to such bases.

- 13 This generally comprises treating the base wlth a 14 sui~ble organic or inorganic acid, e,g., chromic a~d and/or 15 sulfuric acid or ~ ba~e solution to render ~t porotts, In 16 mRny caseQ, it i~ desirsble ~co also treat ~he surf~ce with ~r~
17 agent, erg., d~methyl formamide or dimethyl ~ulfox6de befc)re 18 or dur~ng the etching proces~. The e~ece vf such trea~ments 19 is to render the curface ~emporarily polar.
21 Depending upon the particular insulating base~ involved, 22 other ion e,~ch~nge imparting materials may be util~ed to 23 effect ~he aforementioned pol~rization reactiOn. ~or example, 24 acidi~ied 30dlU~ fluoride, hydrochlo~ic and hydrofluoric 25 acids9 chron1ic acid, borates, 1tloborates ~nd caustic sod~, 26 as well as mixtures thereol', have been found effecti~e to 27 polarize the v~rious synthetic plsstic resin insula~ing mRterisls described herein. a.~-PC~121C . I
~OS03S7 In a typlcal procedure, a~ter treatment with the polariæa 2 tion agents, such resinous insulating bodies are rinsed so as 3 to eliminate any residual Rgen~s~ followlng whlc~ ~hey are 4 immersed in a solution containing a wet~ing agent, th~ ion6 of which are base exchanged with the surace o ~he ln~lati~
S base to thereby impart to ~he base relatl~ely lon& chained 7 ion~ which also are capable of chemically linklng with precious 8 metal io~s or ionic complexes containing preciou~ me~l ions.
9 Following treatment with the wetting agent, the ln~ulating bodies are rlnsed again ~o as to eliminnte the residual wetting 17 agent co tton.

~O , I

. .

~ 357 . ~ - The . following examples l-llustrate the me~hods ~nd articles o .. 3 this lnvention. They are not to be construed to lim~t ~he invention in any manner whatsoever.
: 5 PR~CEDDRE A
7 An epoxy-glass Laminate having hole8 drilled in it for 8 through hole connections is cleaned with a hot alkaline cleaner 9 of the type described above, and all loose par~cle~ are removed.

12 A diagram is block prlnted on the clean laminate using 13 as the "ink" a solut~on of the following formulation:
14 cupric formate ~ 10 g.
anthraquinone 2,6-disulfonic.
16 acid disodium salt - 2 g.
17 water - 100 ml.
18 gly~erine -~1 g.
lg The printed substrate is placed in an oven for 10-20 21 minutes at 130-140C. to produce a real image by reduelng the 22 copper salt to copper nuclei.

24 The substrate ha~ing a darkened real ima~e on its surface is removed from the oven and allowed to cool.

~7 . - 24 -~ Zl~

~ An electroless copper layer i3 deposi~ed on ~he real 2 image by immersing the substrate in ~ bath ~t 55~C~, ~he ~ath 3 having the follow~ng composition:
4 cupric sula~e ~ 0.03 moles/10 sodium hyds~oxide - 0,125 moles/l, 6 sodium cyanide - 0~0004 moles/l.
. 7 formaldehyde - 0.08 moles/l.
8 tetrasodium ethylenediamine 9 tetraacetate 0.036 moles/l.
water - remainder, 12 Seleeted areas of the base, corresponding to the real 13 image9 and the walls of the holes in the base are covered 14 with a ~ilmly adherent lsyer of bright, duc~ile electrolessly deposited copper.

17 The procedure is repeated, except that the entire .
18 base is dip-çoated with the metal salt solution and air dried.
19 The real image is formed by applying a heated d~e ~o the surface, the elevated portions of the die in contact with the 21 surface heatin~ selected areas thereo, A substantislly .
22 similar ar~icle is obtained.

The procedure o Procedure A ~ s repeated substitutin~
26 ~or the laminated base, an unclad epoxy impregnated glass 27 fiber laminate (~estinghouse M-652 . The base is activated . _25--P~-L~l~
~ OS~ ~ S 7 as ollows:
2 a, Treat the ~ur~ace of the bas~ by immer~ion ~or l 3 minute in a l:l volume mixture o l,l,l-trlchloroethane and 4 dimethy1~ormsmide (DMF), also containing 1 g./l. of Surfactant 5 6G (Olin Corp.), and drain for l0 seconds.
6 b. Place the work piece in an "~ir exh~u~ eh~mber~

? for 2 minutes to selectively evapora~e the trlchlo~ hane 8 leaving behind an even wet coating of DMF.
c. Immerse the worlc piece in an activa~or ~ol~ion at 45C. for l0 minutes, the solution comprising:
11 CrO3 - 100 g. /1 1~ Conc.H~SO4 - 300 ml./l.
13 Water - to make l liter 14 (Heated at 100C. for l hour and cooled to 45C.
before use~.
16 abd drain for at least 30 seconds.
17 d. Place workpieces in a first neutraliæer for 5 minutes at room temperature, the first neutralizer bath comprising 19 20 ~./l. sodium bisulfite l ~./l. Surfartant 6Ç
21 H2~04 to pH 4.0 22 ~ater to make.
23 e, Immerse the worlc piece for l0 minutes in a second neutra-2~ lizer bath of the same composition as d.
~. Rinse the work piece in cold runnin~ tap water for l0 26 minutes.
t~ 27 ~ - 26 -~ 3 5~
g, Place work pieces ln hot alkaline rinse a~ 93C, for 2 at least 15 minutes, the alkaline rinse comprlsing 75 g./l. of 3 NaOH and 0~5 g.¦l. of Surfactant 6G in tap water, h. Sub~ect the work plece a flnal rinse in cold runn~ng S tap water.
i. Dry in alr under normcll room condition.s.

9 The selected areas o the activated base are covered with a real image and an electroless copper layer is deposited 12 ¦¦ on the ima by the procedure of Procedure A.

14 .

l6 ~ ' ~26~
- 26 a -PROCEDURE C
, . ..~..
2 The procedure of Procedure A i~ repeated, 6ub~tltut~n~
3 an activated epoxy glass lami.nate as the ba8e (Prooedure 4 B) and the image~ are ormed from metal ~alt b~t~8 of ~h~
following composition:
S cupric forma~e ~ 10 g.
7 water - 100 ml.
8 glycerine - 6 g.
surace active agent

- 10 (Rohmi& ~aas~ Tr~ton X~100) ~ 1 g.

11

12 There are obtained electrolessly metalLized subs~rates

13 according to this invention.

14

15 . PROCEDURE D
lC A clean, polarized epoxy-glass laminate (Procedure B) .
17 Is dip coated with a metal salt solut~on of the formula:
18 cupric formate - 10 g.
19 anthraquinone 2 ,6-d;sulfonic acid disodium salt - 2 g.
21 water - 1000 ml.
î2 glyeerine - 10 g, 23 and allowed to dry at 50-60C. for 5 minutes, ~4 The substrate Ls exposed through a photographic negative 26 to ultraviolet light for l to 2 minutes, ~orming a real image 27 f copper. To build up the real image and ~o enhance contrast, . ~ 27 -~05~3S7 . the substrate is then heated for 3 ~o $ minutes ~t 130 to a 140C~
~` 3 4 - ~XAMP~E 1 . No heating step is needed with the ~110wing a~ternat~Ye : 6 formulation:
? cuprlc acetate - 8 g, 8 .pentaerythritol ~ 50 g.
9 eitric ac~d - 40 g.
1~ anthraquinone 2 ,6-disulfonic 11 acid disodium salt - 16 g.
12 stannous chloride - 0.5 g.
13 Surfactant 6G
14 (Olin Corp. ) - 1 g, . 15 water (to make) ~ 1000 ml.
1~ ' ., .
17 The unexposed portion o~ the surface layer is removed 18 from the substrate by rinsing in water. The metallic image 19 is buile up by electrolessly depositing copper onto the substrate from a bath as described in Procedure.A.

2Z Instead of selective exposure, paper is selectively 23 covered by free hand printing with a desi~n using the same .
24 cupric acetate solution as an lnk. A real image of copper 25 ls formed after exposure to light, corresponding to the deslgn.¦
26 This 19 built up with an electroless copper deposit.
2? . .
28 Instead of epoxy-gla9s laminates, paper~ woven f~brics, 10503~ii7 I cardboard~ cerAmlc~ and glas~ can be used as the ~ubstrate~.

3 Flexible printed c~rcu:Lts are m~de by ~his me~hod ~s 4 follows: .
a. treat a bibulouQ paper or flexible plast~
6 film substrate with the met~]L salt solutlon; ~.
7 . b, dry ~or 5 to 10 Minutes Rt 60~C.;
B c~ expose the dry eoating through a negat~ve to 9 an ultraviolet llght source;
do develop by removing the unexposed me~al s~lt~
11 under a warm water rinse;
12 eO immerse the treated paper of plastic film into 13 an electroless copper solution and plate up ~o th~ deslred 14 thickness of metal;
f. neutrali~e the treated paper on film~ wash and

16 dry; and

17 g. coat the treated paper ar f~lm with a polymerizable .

18 resin and polymerize t~e resin.

19 ~0 In another variation of the proces~, th~ substrate is 21 printed with the solution to form 8 clrcuit pattern, then 22 exposed to ultraviolet light without a pattern to form a 23 real image corresponding to the design. The metal is 24 electrolessly deposited untLl a sufficient am~nt o metal has been built up to serve as a common cathode for 26 electroplating. Alternatively, the base is covered all 27 over with the met~l salt coatlng and expose~ to ultraviolee . ~ _ ~9 _ ~ ~ S0 3 S7 I light without a pattern, a thin electrole~s met~L plate i8 2 deposited to serve as a common cathode~ Then~ ~ negative 3 prin~ or mas~ ls applied and the metal i~ built up by 4 electrolytic plating. The background electroles~ metal c~n then be removed by a quick etch.
S . , 8 The procedure of Example 1 is repea~ed (~ithout 9 heating) substituting the follow~n~ reducible salt solutions:
11 EXAMPLE_2 .
12 . cupric formate - 10 g.
13 anthraquinone 2,6-disulfonic 14 ac~d disodium salt - 3 g.
wa~er - 450 ml.
16 glycerine - 30 ml.
17 cltric acid - 30 g.
18 st~nnous chlorid~ - 1 g.
l9 fluoroca ~ on wetting agent (3-M Co., ~C-17 - 0.25 g.

23 Prepare Part A:
24 cupric gluconate - 15 g.

26 water - 200 g. .
2~ .

_ 30 -PC-lZlC
~5~35~
~ Prepare Part B:
2 fluorocarbon wetting ~gent 3 ~FC-170) - 0.1 g.
4 glycerine - 30 g.
citric acld - 30 g, S anthraquinone 2,6-disulfonic 7 acid disodium sal~ - 2 g. .
8 stannous chloride - 1 g.
Q water - 250 g.
. Mix A and B.
11 .' `12 . E~AMPLES 4 AN~ 5 . ., , .., ~
13 Prepare Part A:
14 : cupric acetate 15 g.
cupric nitrate 15 g~
16 water 200 g. 200 gA ' .
17 Prepare Part B:
18 wetting agent (FC~170)0.25 g. 0~25 g~
19 glycerine , 30 g~ 30 ~.
citric acid 30 g. 30 g.
21 snthraquinone 22 ~,6-disulfonic acid ~3 . disodlum salt 3 g, 3 g.
24 water 250 g. 25 g.
2S stannous chloride1 g. l g. .
26 A and B are then mixed.
27 .
~,, 1 EXAMPL~ 6 2 The procedure o Procedure D is repea~ed, ~ub~itut~ng 3 for the cupric formate solution) ~he follow~ng ~olution:
4 cupric acetate - 4 g L-ascorbic acid - 5 g~
S pentaerythri~ol - 25 g.
7 sorbitol - 30 g. .
8 citric acid - 20 g, 9 stannous ~hloride - 0.5 g.
Sur~ac~ant 6G - 0.5 g.
1~
12 wa~er ~to make) ~ 1000 ml.

14 In all cases, substrates metallized in selected areas accordlng to this invention are obtained.
6 .- . .

18 The procedure of Example 1 is repeated, substituting 19 for the electroless copper solution, an electroless nickel solution:
21. n~ckel chloride - 30 g.
22 sodium hypophosphite - lO g.
23 . glycollic acid - 25 g.
24 sodlum hydroxide - 12.5 g.
wster (to make~ ~ 1000 ml.

~7 .
.

. - 32 -PC~121C
05~ 3 S~f 2 The procedure o~ Example 1 ls repea~ed, ~ub~tituting 3 for the electroless copper solution, an electroles~ cobalt 4 solution:
sobal~ chloride - 30 g.
S sodium hypophosphite - 20 g. .
7 sodium citrate d~hydrate - 29 g, 8 ammon~um chloride - 50 g.
9 water (to make) - 1000 ml.
"' 10 11 The pH is adjusted to 9~5 and the bath temperature is 12 maintained at 90C. A cobalt layer is built up on tbe 13 copper image.
1~

16 The procedure of Example 1 is repe~ted, substituting .
17 for the electroless copper solution9 an ele~troless gold 18 solu~ion:
19 gold chloride hydrochloride trihydrate - 0, 01 mole/l . . .
21 . sodium potas~ium tartrate 0, 014 mole/l.
2t dimethylamine borane - 0.013 mole/l.
23 sodium cyanide - 0.4 g.'/l. .
24 water - q.s.a.d.
. .
26 The pH is ad~usted to 13 and the bath temperature is 27 ma~ntaine~ a~ 60C~ A gold layer is built up on the copper 28 image. ~3~_ .

PC-~lC
105~3S7 2 The procedure of Ex~mpLe 1 i8 repe~ted~ ~ub3titu~ing 3 for the electroless copper ~olu~ion, an electroless s~lver 4 solution~
S silver nitrate - 1O7 g.
S sodlum po~assium ~ar~ra~e - 4.0 g.
7 sodium cyanide - 1.8 g. .
8 dimethyl~mine bo~ane 0.8 g.
9 water (to make) - 1000 ml.
11 The pH is adjusted to 13 and the bath temparature is 12 maintained at 80C. A silver layer is bu~lt up o~ the 13 copper image.

lS EXAMPLE 11 i6 Starting with about 800 ml~ of water, another metal 17 salt sensitizing formulation is prepared by adding the other 18 constituents one at a time in the order listed hereinafter 19 and thoroughly mix;ng the solution under yellow light.
sorbitol - 120 g. .
2l 2,6-anthraquinone 22 disulfonic sciddiso~ salt - 16 g.
23 cupric bromide - O. 5 g.
24 cupric acetate - 8 g.
Surfactant 6G - 1. 5 ~. .
26 water - sufficient ~or 1 liter 27 fluoboric acid - 40% - sufficient to adju~t pH to 3.5, ~ 34 -PC-121C I .
I 1~50357 ¦ After preparation.at room temperature~ this ~olution 2 ¦ i8 employed in treating the varlous ~ubstra~es de8cr~bed 3 ¦ in Example 1 while following :Ln general the procedure of 4 ¦ that example both in the sensiLtizing and ~ubRequ~nt processin~

¦ steps, including electroless cleposit~on.

? ¦ In the case of a clean, pol~rized epoxy-~3.~ lam1n~e with perforations ~herein, the panel is immersed ~or 3-5 mln~
utes in a bath of the above solution maintained a~ 40C., drain-ed with care~ul removal of excess solution ~rom t~e holes, 11 dried, normalized at room temperature and 30~6~% re~ative 12 humidity, exposed to ultraviolet radiation through a mask and 13 developed by immersion for 2 minutes in a tank containing cold I running tap water; all of which steps are perormed under yellow light. The exposure to ultraYiolet light ls carried out in a 16 two-sided Scanex II Printer provided with a 4800 watt air .
17 cooled mercury vapor lamp on each s ide and situated 8 inches away 18 from the vacuum frame with the exposure set at 4.5-5.0 feet pe~
19 minute through a pattern mask wherein the desired conductor areas are exposed to the 11ght. .

22 In repeating the treatment wi~.h another panel under 23 the same conditions except for omitting the cuprlc bromide and .
24 fluoboric acid from the metal salt sensitizing sol-ltion? it is ~5 observed that a far more intense metal nuclei image is formed on 26 the epoxy-glass laminate with the tabulated formulation of this 27 example than with the formulation devoid of halide and fluoboric 28 acid, 5 Y(~ 1(;
~ ~5~ 3 57 1It h~s been observed thnt the sensit~er ~olution 2 of this inventlon i8 qulte stable and can be employed ~or 3 peri.ods of more than 8iX months wlth only 8 little sttentlon~

4 such as flltering the solution each worlc day and checking its specific ~r~vity alon~ with 8 weekly check ~nd adjustment as S necessary t~ maintain a pH of 3,5 at 20C., 8 metal ~lt con~ent 7 equivalent to 7.8 to 8.5 ~rams per liter of cupri~ ~cetate and 8 an anthraquinone salt content Or lS to 16 gra~s ~er 1~ter.
~' 10P~OCEDURE E
__ 11Numerous samples of clean, polarized epoxy-gl~ss ((FR-4)) 12 laminates are subiected to steps of sensitization ~hrough 13 exposure and development of imagcs similar to those of 14 Example 11 except for employing different sensitizlng baths and 15an exposure of 2 minutes to a 1500-watt ultraviolet li~ht source 16 through a StoufPr 21-step table~ or optical wedge, 18The composieion o~ the control sensitization b~th is:
l9 sorbitol 120 g.
anthraquinone 2,6-di-21 sulfonic acid disodium salt 16.2 g.
22 potassium bromide 1.0 g.
23 cupric acetate g,o g.
24 Surf~ctnnt 6G l~l g.
~ater su~ficlent for 1 liter 26 pH 4.62 .' ~ 3~ ~

PC-~21C
~0 50 3 S7 I The Stouffer table~ $s a m~sk hav$ng 21 3mall squares 2 of graduated optical density ~or the graduated kransmission 3 of light ~hrough different squares in the ~erie~. Th~se ~quare8 4 r~nge ~n density from ~ completely tr~nsp~rent ~quare des~nated No. 0 and permitting 100% transmission of ultr~violet llght to an opaque square No, 20 tha~ transmi~ na ligh~. Af~er 7 develvpment and drying of the exposed lamlnate surf~ce~, ~hey 8 are examined tG ob~erve the number o~ square lm~ges ~lsible 9 on the laminates as a measure of ~he effec~i~eness of the sensi~iz~ng treatmen~. A prod~lct with a ~nsiti~ity rating of 11 at least 5 images is desirable, and ratings of 7 or more are 12 preerred.

14 ~ _ LES 12 - Z9 Varying amounts of a number of di~ferent ac~ds are 16 thoroughly mixed wi~h separate baths of the sensiti~ing formula- .
17 tion of Procedur~ E to ~d~ust the mixture~ to various pH levels 18 iQ illustrating the important effect of acidity in the treating 19 solutions employed in the present process. For comparative purposes~ tr~als I and II and their data are included.

22 .

~4 In each of the following examples, one or more specimens 26 of the epoxy-glass bases are tre~ted a~ each specified pH value, 27 processed and r~ted according to Procedure E; and the specific ~ 37 ~ .
.

PC-12~C
~s~357 1 da~a ~nd re~ult~ are ~et ~orth in Table I hereln~~er, Ind ivld~lal Spec ~men A~erage Sens i~ ivi~y S~ns itivlty ~5 ~ Ac~d Addltive pH ~~ ~J
- . ... _ .
? Control none 4.62 6 5 7 6.0 S I* citric 1.4 3 5 S 4.3 9 12 citric 2 . 05 6 6 7 ~, 3 13 c itric 2 . l 7 - - 7 . O
11 45 gO /l iter '12 14 c itric . 8 - ~ . O
. 22.5 ~. ~liter ~.4 13 .
14 15 citric 2.5 10 10 11 10.3 .
~5 16 c itric 16 10 . O g . /liter 2 . 6 10 ~ ~ 10 . O .
17 17 citric ?.92 8 9 11 9.3 1~ 18 citric 3 . 5 8 8 9 8 . 3 19 19 c itric 3, 96 8 8 10 8 . 6 21 . ., . .
22 II* fluoboric 1.06 00 0 0 40% aqueous , .
23 20 fluoboric 2 . 0 810 9 9 . O
~4 ~1 fluoboric 2 . 5 810 9 9 0 0 i5 22 fluoboric 2 . 90 ~10 9 10. 5 26 23 fluoboric 2 . 96 8lO 11 9 .6 27 24 fluoboric 3.5 -10 10 lO.O

PC l~lC
3L05~357 1 TABLE I (cont'd) . Individual 3 Specimen Average Sen~ivi~y Se~sitivity 4 Example Acid Additive fluoboric 3.7 7 7 7 7.0 S 26 fluoboric 4~ a 7 8 ~ 7 . 7 7 27 phosphoric 2.05 8 - - 8.0 -- 80% aqueous.
8 200 drops/liter 9 28 phosphoric 3O15 10 - - 10.0 140 drops/liter 11 29 sulfuric 2.0 7 - - 7.0 ~2 .
13 * Trial runs -~ for comparison o~ results.
14 . .
In preparing the treatin~ solutions of Tablc I, 16 turbidity is sometimes encountered In the control and other .
17 bflths having a pH of the order o~ 3.5 or higher, whereas the 18 more ~cid mixtures are c1ear. However, this does not pose 19 ~ny serious problems, for the turbidity is usually rather sll~ht

20 and docs not interfere with sensitiz~tion; moreover the suspended .

21 ¦ solid ma~ter may be easily filtered out of the li~uid.

22 . . .

23 Another observation is that darker images ~i.e., denser t4 deposits) are obtained with sensitizing solutions containin~
i5 either fluoboric or citric acid rather than phosphoric or 26 sulfuric acid.

~ 0S0 3 5 7 1 By mean~ of additlonal experimen~s wherei~ cle~n glas~
2 slides rather than laminates are processed ~ccordlng to 3 Procedure E with several of the solutions in the t~ble of 4 examples and ~hen sub~ected to the same ~rflsion ~e~, it can be demonstrated that solutlons conta~ning 1uobo~c ncid or S phosphoric acid a5 the acid addi~ive produce lm~ge~ with 7 stronger adhesion to the glass substrate ~han tre~tlng a~ents containing citric or sul~uric acld. In some inst~nces, it may 9 be des~rable to employ a combina~ion of two or ~ore acids (e,g., citric and phosphoric acids) for adjusting the pH of 11 the sensitizing solution in order to obtain a product having 12 a combination of desired propertias, such ~s a dense image that 13 exhlbits superior adhesion to the base.
14 . ` .
Further illus~ratlons of the proces~es and p~oducts 16 of this invention are set in the examples tabulated hereinafter 17 for varying the processing under controlled and comparable 18 conditions, particularly ~n respect to demonstratlng the effects 19 of variations of acid and halide agents and concentrations thereof by addition of the specified subst.ances to stock 21 sensitizing solutions. Although, generally employing the 22 technique of Proc~dure E unless otherwise indlcated9 the 23 following examples differ from those of Table I ~n includin~

24 an electroless copper depos~tion step in a "copper strlke bath"
with a subsequent sensitivity ratln~ obser~at~on of the dried 27 article as a better evaluation.

~ 40 -3L~S~113S7 For more acidity comp~risons, a ~ock sen8ltizer 3 801ut~on i5 made up a3 before, but withs:ut the addition o any 4 ~cld, The pH is 4. 78, and ~t~ Composi~ion in gr~rns per liter 5 o~ 8queous 8 01u~ :lon is:
~ sorbitol 120 7 2 ,6~anthraquinone 8 disulfonic acid 9 disodium salt 16 cupric acetate 11 cupric bromide 0.5 12 8urfactant 6G . 2,0 1~ .' 14 The pH of samples.of this stock golution is then adjus~ed to specifie values with suitable amounts of citric, lactic, 16 an~ fluoboric acids. Additlonally, seversl high pH samples 17 were prepared, using sodium hydroxide ~o ad~ust the pH.

19 Test panels of clean, polarized epoxy-glass lami.nates are sensitized in those solutions~ dried, exposed, developed 21 ,and immersed in an eleetrole~s copper bath. The drying cycle is 22 three minutes and exposure to UV li~ht consists of two pa~se~
23 on a Scanex II photoprlnter, one at a setting of 4.6 feet per ~4 minute, and ~he other ~t 13.0 feet per m~nute, Panels are dev~loped in cold running water for 60 seconds, And then immersed ~6 immediately ln a room temper~ture copper strike bath for 20 27 minutes. Photosensitivity is determlned by exposure through ~IL0503S~
I the 21 ~tep S~sou~fer optical densi~y wedge with ~he ~llowing 2 resul ts .

~
S Example Acid pH Be~ore Cu Stx ike A~te~ Cu Strike . - .
7 Control none 4. 78 3 4 .
8 30 fluoboric4 . 00 7 7 9 31 fluoboric3 . 75 8 32 fluoboric3 . 50 9 8, 5 11 33 fluoborlc3 . 00 8 8 12 34 fluoboric2 . 50 7 7 13 35 fluoboric~ . 00 6 6 14 36 ~luoboric l o 50 6 - 6 T~al III fluoboric 0.82 4 3 i6- . ~ . .
17 37 lactic 4, 00 6 7 18 38 lactic 3. 75 8 8 l9 39 lactic3 . 50 8 8 4~ l~ctic3 ~ 00 7 7 21 41 lactic2 . 50 7 7 2~ 42 lactic 2, 00 6 6 23 43 lac t ic1 . 6 0 3 3

25 44 cit~i~ 4. 10 7 7

26 45 cit~ic 3. 7~ 10 8 2? 46 citric 3~48 11 9 - 42 ~

P~
` 1~5~357 I TABLE II ~cont~d) 2 .
3 ~ Acld pHl~efure Cu S ~ril~: A Et.` r Cu trl~
47 citric 3.00 8 7 48 citric 2.50 7 7 S 49 cltric 1.90 ' 7 6 2~ g./1.
7 50 citri/ 1.68 6 5 8 51 citric 1 62 6 4 40 g./l.
9 Trial IV (NaOH) 6.40 2 1 Trial V (NaOH) 11.50* 0 12 Note: * At a pH of 6 . 4, a precipitate formed; this 13 redissolved at the higher pH.
14 :~
16 E`rom consideration of the Table I ~nd II examples, 17 it is evident that treating solutions containing the aforesaid 18 halide ions and acidic material improve the sensitlzing 19 insulating substrates at pH levels in the range of about 20 1.5 to 4.0 and that a significantly higher degree o sensitizatiol .
21 is realized with a pH of 2.0 to 4~0 (particularly between 2.5 22 and 3.8) than is obtainable with more acid or less acid solutions /5 under comp abl~ conditions, ~ 43 _ ~ ~S~3 57 1 EXAMP~ES 5~63 2 In demonstra~ing the results ob~ainable with ProcPdure F
3 us~ng mixtures or halides other than cupr~c bro0ideg nnother .
4 aqueous stock solution is madle up withou~ ~he add~.tion o~
S cupric bromide or acid. The composition ln ~r~ms per liter of 6 5 01ut ion is:
7 sorbltoi 12(~ .
B 2,6-an~hraquinone disulfonic 9 ~cid disodium salt 16 cupric acetate 8 11 Surfactant 6G 2 13 Various halide compounds nre then added to samples 14 of this sto~k solution in such quantity a~ ~o provide a halide ion concentration of 4.5 milliequivalents which i~ equa~ to i6 O.S g./l. of cupric bromide~ The pH of each sample is then . .
17 adjusted to 3.50, if necessary, using ~luobori~ acid, In 18 Example 53, more than 4.5 milliequivalents of hydrochloric 19 acid is employed to accomplish the dual function of providing 20 halide ions and adjust~ng the acidity of the sensitizing bath;
21 hence no fluoboric acid is incorporated into this solution, 22 The halide mix~ures of Ex~mples 62 ~nd 63 contain 2.25 milli-23 equivalents of each of the cupric brom~de and the sodium fluoride .

F iodide per liter of sensitizer solutioA.

27 . .
..~

~05~357 ' Sensit:lvity 2 ~ Halide pH Ratin~
3 Control none 3.50 3 4 52 HCl 3,50 S 53 HCl* 3,50 4 54 ~uCl2 3.50 6 7 55 HI* 3.40 4 8 56 NaI 3.S0 7 9 57 NaI** 3.50 6 10 Tr~al VI NaI 6.00 2 11 Trial ~II NaI ll.S
1~ 58 KI 3.30 6 13 59 KI 1.50 0 14 . 60 bromine- 3.50 . 7 15 ~ water 16 ¦ 61 ~uBr2 3.50 8 .
17 1 ~2 CuBr2~NaF 3.50 9 18 ¦ 63 CuBr2~NaI 3.50 7 lQ ¦* HCl or HI in l~rger amounts ~s the ~ole acid.
.20 1 21 ¦ Trials with sensitiz~ng solutions employin~ fluoride 22 ¦ ions as the sole halide do not appear to increase sensitization 23 ¦ over the control. While iodldes alone tend to prec~pitate part 24 ¦ of the copper content of the sensitizer as cuprous iodide, 25 ¦ this does not interefere in most instances with the production 26 ¦ of good images; moreover, the precipit~te may be removed by . 2? 1 filterlng. .

- 45 ~

, ~ a5~)357 I ¦ EXAMPLES 64-7~
2 ~ For appraising the effect o~ halide concentrat~on ln 3 ¦ sensitizer soltulons, ~ large batch of ~he ~tock solu~ion 4 ¦ of Examples 52-63 is prepared and 40% aqueous ~luobor~c acid 5 ¦ is added to lower the pH to 3~50. This batch i8 t~len dlvided ¦ in~o ten baths and cupric bromide i~ dissolved wl~h through 7 ¦ mixing in the proportions speciied in Table I~, ~hen epoxy-¦ glass laminates are trea~ed and evaluated as in Proeedure F
9 ¦ with the ~ollowlng results:
IABLE IV

Sensiti~lty Rating After 12 Example CuBr2~g./1. pH u Strike______ 13 Control 0 3.50 2 14 64 0.5 3.5~ ~

1.0 3.5~ 7 i6 66 1.5 3.5~ S .
1? 6 7 l . 75 3 O 50 6 18 68 2 . 0 3 . 50 S
19 69 2.5 3.50 6 3.0 3.50 4 21 71 4.0 3.50 3 22 72 5 . 0 3 . 50 0 24 From the data in Table IV, ~t i9 ~pp~rent that the concentration of halide ion is important for improving the 26 efficiency of sen~itizing baths, Amounts of halide ion~ above 27 about 25 milliequivalents per liter markedly reduce sensitiza-.

I l~S0357 1 ¦ tiorl. Accordingly, it i8 desir~ble ~o Iceep the cupric bromlde 2 ¦ s~oncentration be~ween nbout 0, l and 2.5 grams p~r liter, and 3 ¦ preferably be~cween abou~ 0.3 ~nd l.O g./l. Similarly desirable 4 ¦ proportions for other bromide or hallde agen~s may b~ computed 5 ¦ from the ranges for cupric bromide on ~ chemlcal equivalent 6 ¦ 'basis .

8 ¦ Also, unsatisfactory results are ob~ained when attempts 9 ¦ are made to repeat Examples 64-72 with the cup~i~ ace~ate ¦ omitted from ~he sensitizer, This is interpreted as an Il ¦ ~ndication that the number of equivalents of copper or other cat-12 ¦ ion of the reducible non-noble metal salt should be in excess 13 ¦` of ~he number of equivalents of halide ion in the sensitizing 14 ¦ solution. In general, a substantial excess is preferred, as ¦ exempli~ied` by a 5:1 or greater ratio of metal: halide 16 ¦ equivalen~ weights.
17 ¦ I~ is further evldent rom the foregoing data that both 18 ¦ the acidity Ievel ~nd halide lon concentration must be within the 19 ¦ afore~aid limited ranges to obtain the full benefits of the ¦ present inven~ion. A combination effect is involved here, as 21 ¦ neither factor alone can provide those fldvantages. The data in 22 ¦ Table~ I and II demonstrate that substantial losses in the sensi-23 ¦ tizing effect occur when the pH of the sensitizer is below 1.5 or 24 ¦ above 4.0 even with a preferred amount o halide in solution.
25 ¦ In Table IV, marked reductions in sensitlzation are noted even 26 ¦ with the pH at the pre~erred 3.5 level for solutions containing 27 ¦ either no copper bromide or ~n excessive quantlty~ e.g ~ three

28 ¦ or more grams per liter.

l - 47 -~C-121C
~05~1357 1The non conductive real images of nlckel, cobalt, iror 2 and silver prepared as described above c~n al~o be bullt up 3 as described for the copper images in the~e ex~mples wi~h 4 electroless nickel, cobalt, gold and sil~er.

7All such ~mages having a layer ~ electrole~ ~e~al 8 on top, can further be built up with an electroplated layer o~
9 copper, silver, gold, nickel, cobalt, tin, rhod~um and alloys thereof3 using the baths and conditlons descrlbed hereinaboYe.

12The above disclosure demDnstrates that the present 13 process provldes for the selective reduction of a metal 14` salt to metallic nuclei by means of radiant energy such as heat o~ light. The formation of a real ~mage o a printed lB circu~t or other type of pattern formation has been demonstrated 17 both by p~int~ng and by selectively exposin~ the dry coatin~
18 of the metal salt to UV radiation, through a negative in the 19 presence of a light sensitive compound and a reducing agent.
The positive, visible image has been shown to be.catalyt~c 21 to electroless ~etal deposition and this metal can be uscd to 22 build up conductor thickeness or increased current carrying 23 capacity or to incre~se the thickness of the pattern. In 24 contrast to prior ark techniques, the metallic image produced 25 by this process require5 no addltional development steps, ~7 pc~ c l 1 ~ 03S~

2 It i~ obvious that if ~he metal salt i~ reduced to ~t~
3 met~llic state in the holes of a printed circult sub~trate 4 board, si~ultaneously with the circuit pattern belng pr~nted on the surface o the base material, the holes walls w~ll be S rendered ca~alytic to electroless metal deposltlon and there 7 will be formed electrically interconnect~g p~thways ~or 8 circuitry on both sides of the base materlals, 12 It ~ possible to make interconnection through the 13 holes, around the edges o~ the boards and through slots 14 made in the base material. A un~que advantage of the present process is that only the portion of the hole which is expused 16 to activation is sensitized and beco~es catalytic. If, for 17 example, a negative of a conductor line passes over a hole or 18 a slot, positive, slightly enlarged, catslyzed image will form 19 on opposite sldes of the hole walls. This perm~ts electroless metal deposition to take pl~ce only on the exposed areas in 21 the holes. It is possible ln this way, with shadlng, or 22 example, to make multiple connections through the same hole, 23 thereby redu~ ing the number of holes requlred to make lnter-24 connections of individual conductors ~rom outside surfaces 25 of the circult boards.

27 .
.
- - 49 ~ ~ .

L ~ L ~ l 3 ~ 7 1 ¦ Sub~trates c~n include epoxy-gl~ss laminnte3~ polye~ter 2 ¦ film, ceramics, paper~ or other substrfltes having oxidi~able, 3 ¦ e.g., adhesive-coated sur~acesg and the llke, The dlrect 4 ¦ bonding treatment described flbove provide~ a ~ery ~ctive 5 ¦ surace to which the metal s~lt ~trongly 3dsorb~ and ultimately S ¦ there is formed a strong bond between the base ~nd the 7 ¦ electrolessly deposited metal~

9 ¦ In addition to printed circuit boards, posi~ive repro-10 ¦ ductions of photographs can be made from negat~ves onto ll ¦ paper and then metallized by electroless deposition. The 12 process is capable of producin~ high resolution, and is not 13 unduly sensitive to long exposures.

A secondary reducer that i~ ~lso ~ humectant, as 16 exempli~ied by sorbitol, is generally preferred as a const;tuent 17 ~ the trea~ing solution, forthehumectant, apparently by reason 18 of a moisture conditioning effect on the "dry" coatin~ prior to 19 developing Thi~ provides substantial aid in maintaining image density in exposed areas of the coating on the base during the 21 developing step in which unexposed areas of the costin~ are 22 washed off of the base, 24 The invention in its broader aspects is not limited by the specific steps, methods, compositlons and improvements 2~ shown and described herein, and departures may be made wlthin 27 the scope o~ the accompanying claims without departing from 28 ¦¦ the pri ples thereof. -S~

Claims (36)

CLAIMS:

1. In a process for selectively metallizing insulating substrates with real images, the steps which comprise depositing on said substrate a layer of a radiation-sensitive composition by treating the substrate 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 iodine 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, exposing said layer to radiant energy to reduce said metal salt to metallic nuclei thereof and wherein at least one of said treating and exposing steps is restricted to a selected pattern on said substrate to produce a non-conducting real image of said metallic nuclei in said selected pattern and capable of directly catalyzing the deposition thereon of metal from an electroless metal bath.

2. A process as defined in Claim 1 wherein said radiant energy comprises heat, light, X-ray radiation or electron beams.

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

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

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

6. A process as defined in Claim 5 wherein said metal salt is reduced to metallic nuclei by selective exposure to ultraviolet radiation.

7. A process as defined in Claim 1 wherein said substrate is thereafter exposed to an electroless metal bath to build up a layer of electroless metal on said image.

8. A process as defined in Claim 1 wherein the said electroless metal is of the group consisting of copper, nickel, cobalt, gold and silver.

9. A process as defined in Claim 7 wherein the treated substrate is dried before the exposure to radiant energy, and said substrate is rinsed after said exposure to radiant energy and prior to the exposure to said electroless metal bath.

10. A process as defined in Claim 7 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, gold and silver.

11. A process as defined in Claim 7 wherein said salt is reducible copper salt and said electroless metal is copper.

12. A process as defined in Claim 7 wherein said substrate is a non-metallic resinous substrate with a polarized surface.

13. A process as defined in Claim 1 wherein said substrate is a porous material.

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

15. A process as defined in Claim 1 wherein said secondary reducer is a polyhydroxy alcohol.

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

17. A process as defined in Claim 7 wherein said liquid medium also contains citric acid and said secondary reducer is a polyhydroxy alcohol of the group consisting of glycerine, sorbitol, pentaerythritol and mesoerthritol.

18. A process as defined in Claim 1 wherein a substrate having at least one hole therein is subjected to said process to produce said image on at least a selected area on the wall surface of said hole.

19. A process as defined in Claim 18 wherein said substrate is thereafter exposed to an electroless metal image on said wall surface in producing a metal conductor extending through said hole.

20. 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.

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

22. A process as defined in Claim 20 wherein said solution contains cupric bromide.

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

24. A process as defined in Claim 23 wherein said secondary reducer comprises sorbitol.

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

26. An article which comprises an insulating substrate, an aperture in said substrate, at least a selected area of the wall surface of said aperture being coated with 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.

27. An article as defined in Claim 26 an area of an outside surface of said substrate is coated with said radiation-sensitive composition in the form of a predetermined real image.

28. An article as defined in Claim 26 wherein said substrate is a porous material.

29. An article as defined in Claim 26 wherein a polarized wall surface underlies said radiation-sensitive composition.

30. An article as defined in Claim 26 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, dichlromates, anthraquinone disulfonic acids and salts, glycine and L-ascorbic acid.

31. An article as defined in Claim 20 wherein said secondary reducer is a polyhydroxy alcohol.

32. An article as defined in Claim 26 wherein said 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.

33. An article as defined in Claim 26 wherein said radiation-sensitive composition contains a bromide compound.

34. An article as defined in Claim 26 wherein said radiation-sensitive composition contains between about 0.13 and 0.45% cupric bromide based on the weight of said coating.

35. An article as defined in Claim 26 wherein said radiation-sensitive composition contains a humectant.

36. An article as defined in Claim 35 wherein said secondary reducer comprises sorbitol.