Note: Descriptions are shown in the official language in which they were submitted.
: 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. .
24
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.
11
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.
24
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.
22
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,
PC-121C
3 S7
~ 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.
24
. 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,
14
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_ '
PC-121C
50 3 S7
. 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 ~
PC-121C
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
PC-121C
~ 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 . .
18
19 .
~2
24 . -
26
- 12 ~
PC-121C
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,
23
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 . ' ' .
11
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,
22
29
26
27 . .
~ 16 _
' .'
PC-121C
~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.
17
18
19 A typical electroless cobalt bath is described ln
22 the Ex~mpl 8s well ss a -cefal e-ecerole6s s~lver bsth.
Z3
27
- 17
PC-121C
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
23
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
PC-121C
~ ()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.
18
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~
PC 121C
~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
18
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.
27
_ 20 _
PC-121C
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 -
.
PC-121C
~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.
11
-12
- 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
26
27
. .
- 23 -
PC-121C
~ 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.
11
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.
23
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~
10503S7
~ 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,
11
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.
16
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.
23
24 PROCEDURE B
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 -
PC-121C
~ 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.
13
14 .
l6 ~ '
24
~26~
- 26 a -
PC-121C
3 57
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 -
PC-121C
~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.
21
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,
PC-121C
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 _
PC-121C
~ ~ 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 . ,
7 EXAMPLES 2 - 5
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.
21
22 EXAMPLE 3
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 .
~,,
- 31 -
PC-121C
1050357
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.
13
14 In all cases, substrates metallized in selected
areas accordlng to this invention are obtained.
6 .- . .
17 EXAMPLE 7
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
EXAMPLE 8
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~
EXAMPLE 9
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
1 EXAMPLE 10
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.
14
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.
61
? ¦ 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. .
21
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,
17
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
27
.'
~ 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.
13
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 .
23
~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,
3 TABLE I
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.
27
- 39 -
~ 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 -
PC-121C
3L~S~113S7
1 PROCEDURE F
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.
18
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
PC-121C
~IL0503S~
I the 21 ~tep S~sou~fer optical densi~y wedge with ~he ~llowing
2 resul ts .
4 TABLE II
~
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
24
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
11
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,
261
~ 43 _
PC 121C
~ ~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
12
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.
26
27 . .
..~
~05~357
1 TABLE II1
' 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
11
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
23
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-
.
- 46 -
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 .
7 I
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.
11
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
- 48 -
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,
11
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~
81
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.
14
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,
23
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~
