CA1111407A - Preparation of solid precious metal sensitizing compositions - Google Patents

Abstract

Abstract of the Disclosure - Methods for the preparation of solid compositions soluble in aqueous media to produce clear sensitizing solutions for rendering surfaces receptive to the deposition of an adherent electroless metal comprise (1) precipitating a composition consisting of (a) a compound of an ion of a precious metal selected from a group consisting of the precious metals of the fifth and sixth periods of Groups VIII and IB of the Periodic Table of Elements, (b) a compound of a Group IV metal of the Periodic Table of Elements which is capable of two valence states and (c) a compound of an anion capable of forming a stable moiety with both valence states of the Group IV metal. Precipitation is from aqueous solution at an elevated pH or by cooling a hot saturated solution or melt. Alternately, the solid composition is formed by intimately blending the components in dry form. The compounds per se and methods for their use are also disclosed.

Description

1:1114~7 ., ,:

::, Generally stated, the subject matter of the present ~; - ~nvention relates to new a~d useful methods to prepare precious metal sensitizing compositions. More particularly, the invention relates to the preparation of solid compositions comprising a precious metal compound. Solutions prepared by dissolving the . novel solids are used to render surfaces of substrates catalytic - to the reception of an electroless metal.
, . -Background of the Invention - The electroless . deposition of a metal on either a metallic or non-m~tallic lC substrate usually requires pretreatment or sensitization of ; ~ the substrate with a precious metal composition to render it catalytic to the reception of such deposit. Various methods have evolved over the years employing particular sensitizing : compositions.
,~",,. , I I ~ I

.

. ' ~ll~L~7 ~C-31 L

1 Unitary bath sensitizers are known, e.g.,

2 Shipley, U.S. 3,011,920, but dry, stable solids, suitable to

3 prepare such baths by dissolution have not been feasible to

4 prepare, ship or store. Applicant herein has developed unitary bath sensitizers in a dry powder form, see, e.g., U.S.
6 3,672,923, assigned to the present assignee. These dry 7 sensitizers are desirable because shipping and storage costs 8 are minimized and process solutions are very simple to put 9 together (by dissolution, for example).

11 The methods for preparing sensitizers in dry solid 12 form known until now are somewhat disadvantageous, however, in 13 that they depend on heating and evaporating relatively large 14 quantities of water, often with the need also to provide for :., safe operation because of the liberation of acidic fumes.

17 It has now been found possible to provide solid 18 catalytic compositions by novel methods which do not require 19 evaporation of large quantities of aqueous media and/or acids.
Surprisingly, the solid compositions are different from and 21 superior to solid compositions produced by the prior art 22 methods.

24 Accordingly, it is a primary object of the present invention to provide new methods for producing solid sensitizer 26 compositions, the methods in general involving (i) precipitation 27 of the composition from aqueous media or a hot melt or (ii) 28 ~he formation thereof by intimately blending dry components of 29 the catalyst.

~ 7 1 Atditional objects and advantages will be set forth 2 in part in the description which follows, and in part will be 3 obvious from the desciption, or may be realized by practice of 4 the invention, the objects and advantages being realized and attained by means of the methods, processes, instrumentalities 6 and combinations particularly pointed out in the appended 7 claims.

9 Description of the Invention - To achieve the foregoing objects, and in accordance with its purposes as 11 embodied and broadly described, the present invention relates 12 to (i) precipitation and (ii) dry blending methods for the 13 preparation of solid compositions, dissoluble in media comprising 14 water to provide sensitizing solutions for rendering surfaces receptive to the deposition of an adherent electroless metal.
16 The solids comprise a composition consisting of three components:
17 ta) A compound f an unreduced icn of a precious 18 metal selected from the group consisting of the precious metals 19 of the fifth and sixth periods of Groups VIII and IB of the Periodic Table of Elements:
.
21 (b) a compound of a Group IV metal of the Periodic 22 Table of Elements which is capable of two valence states; ~nd 23 (c) an anion capable of forming a stable moiety 24 with both valence states of the Group IV metal, preferably the gram atomic ratio of components (a) to (b) to (c) will be 1:
26 at-least 1: at least 3, e.g., from about 1:1:3 to 1:6:24.

28 The term "solid" contemplates, e.g., dry but 29 hydroscopic powders, solid hard lumps (also very hydroscopic), a compacted precipitate or a paste, slurry or liquid comprising 31 1I predc~inantly tolid part~c es.

PC-31 L ~ ~7 .
'.`

1 According to one feature of the invention, the 2 solid is prepared by precipitation from a mixture, e.g., a 3 solution comprising water, of the components (a), (b) and (c).
4 Preferably, prior to precipitation,an aqueous solution of com-ponents (a) and (c) will be mixed with an aqueous solution of 6 components (b) and (c) and the mixture heated at from 80C. to 7 its boiling point to permit substantial completion of the 8 formation of an especially active form of the sensitizer. .
Alternatively~ a composi_ion will be prepared from components at least one of which melts and dissolves the others, when 11 heated, and the solid will form in cooling.

13 - - Precipitation can-be induced by, e.g., raising 14 the pH to cause separation of the sensitizer. As will be -seen, precipitation can be made to occur after the sensitizer 16 i8 formed or simultaneously as it is formed, in the latter 17 case by carrying out the preparation in an alkaline solution.
18 In the former case, if the sensitizer solution is treated with 19 a basic reagent, e.g., an alkali metal hydroxide, e.g., NaOH, or an alkaline earth hydroxide, a carbonate, ammonium hydroxide, 21 an amine hydroxide, or, indeed, any reagent commonly employed 22 to raise pH, the sensitizer precipitates at a pH beginning 23 between 1.5 and 2. The precipitated sensitizer and any co-24 precipitated salts, e.g., Sn(OH)Cl, can then be separated from the aqueous liquor by filtration, centrifugation, decantation, 26 and the like. Of course,-the pH c~n-be raised even higher, 27 e.g., pH 5-11, to effect a more complete precipitation of the 28 salts. At the lower pH values, some of the salts may not be 29 completely precipitated and at the higher pH values, they may start to redissolve if an slkaline metal hydroxide is used.

PC-31 L 1 1111~7 1 1 These factors are easi'.y controllable however by observations 2 well within the skill of those in this art.

4 The solid sensitizer may also be made and precipitated simultaneously in an alkaline solution. Components 6 (b) and (c), e.g., SnC12, can be dissolved in water and treated 7 with enough base to render the solution alkaline. Then component s 8 (a) and (c), e.g., PdC12, can be added and a precipitate of 9 sensitizer will form and this can be recovered as described above.
1' 11 12 Alternatively, precipitation can also be induced 13 by preparing a "near" saturated hot solution and allowing it 14 to cool. The basic concept is to provide the sensitizer in a ¦ hot aqueous medium with a high concentration of salts. In the 16 ¦ case of Group IV metal halides, e.g., SnC12.2H20, which have 17 1 a relatively low melting point (37.7.C. for SnC12.2H20), or 18 ¦ the corresponding low melting germanium compounds, these act 19 ¦ as "hot melt" liquids after all of the excess water has been ¦ removed during preparation of the near saturated solution.
21 ¦ Excessive heat is avoided to preclude evaporating to dryness, 22 ¦ then the mixture is allowed to cool and the solid sensitizer 23 ¦ is formed. The mixture can, as is mentioned above, also be 24 I prepared in a "hot melt" fashion, i.e., without water being ¦ added. - -- --26 ¦ Obviously, as-will be~understood precipitation can 27 also be brought about by the-addition of a counter-ion, e.g., 28 triphenylarsonium ion, which combines with the solid composition 29 (in ionic form)-to cause it to precipitate.
~- -- --:-- -..

.

.,',~' ~
. ~

1~114~7 .
- A further preferrecl feature ls to produce the solid sensitizer by intimately blending solids comprising components (b) and ~c), e.g., SnC12, with components (a) and (c), e.g., PdC12. The intimate blend can be produced Ln any conventionaI fashion, but preferably ball milling will be used. Of course, other solid components can also be included, e.g., alkali metal halides, e.g., sodium chloride and solid acids, e.g., tartaric acid, and the like.
In all cases, the solid product can be stored for future use, preferably in a closed container to avoid air oxidation.

The products can be broken up and co-mixed with other conventional dry addition agents such as salts, e.g., NaCl, NaHSO4, and the like, dry acids, such as tartaric acid, citric acid and the like, stannous chloride, germanium chloride, lead chloride or other halides, and the like, :
surface active agents such as perfluorosulfonic acids and the like, stabilizers , . ...
and so forth all can be added. All such products can later be dissolved in ; water or an acid solution for use as a sensitizer solution in accordance with ` the teachings typically set forth in the above-mentioned Zeblisky patent, .;
` U.S. 3,672,923.
:
The sensitizers with which the instant invention is concerned are formed reversibly. Therefore, an excess of component (b) with respect to component (a) appears to enhance their formation. It has been fo~nd, however, that too much of an excess of component (b) results in a reduced sensitizing ':' ~ ' .~, 7 _ ' ' ''' PC-31 L 1111~7 1 eapability. Below a ratio of 3 gram atoms of component (b) 2 for each mole of precious metal, the anion, while 3 ¦ formed, is difficult to stabilize. On the other hand, if the 4 ¦ amount of component (b) is in excess of about 100 gram atoms ¦ per mole of precious metal compound sensitizing activity is 6 ¦ noticeably reduced. In practice, a solution containing a 7 ¦ relatively large excess of component (b) is preferred for long 8 I operating life. Best results are obtained when an excess of 9 ¦ component (b) is present in an amount to provide from about 1 5 to 70 gram atoms of component (b) for each mole of precious 11 I metal in the total composition.

13 In addition to preferring compositions which contair 14 a relatively large excess of component (b), it is preferred to use a large excess of component (c) to solubilize the compositior .
16 In the most preferred embodiments, this will be introduced in 17 the form of a halogen compound, preferably an alkali metal halid ¦' 18 e.g., NaCl or NaBr or a trihalotin (II) compound, e.g., SnC13~ , 19 or as HCl. Extremely large exeesses of this component do not seem to be detrimental to sensitizing activity. As to HCl, this 21 seems to serve a two-fold purpose: it provides both a large 22 excess of Cl- ion and also H+ ions, both assisting in the 23 solubilization of the powdered product. Low pH alone, as 24 produced, for example, by fluoboric acid does not solubilize the powder unless excess component (c) too is present, e.g., 26 sodium chloride can be added. A high excess of eomponent 27 (e), e.g., sodium ehloride alone, 25 to 100 moles per mole of 28 eomplex, helps dissolve the sensitizer and any excess component 29 (b). However, for example, if component (bj is stannous chlorid or a oirilar h~tr~l~zable oslticn which forcs a basie salt, 11114~7 . , `','.'' 1 e.g., Sn(OH)Cl, unless acid too is-present to prevent hydrolysis, 2 an insoluble hydrolysis product is formed which appears to 3 adsorb the composition causing it to be inactive as a sensitizer.
4 Accordingly, in preferred embodiments, to prevent hydrolysis of the Group IV metal, i.e., component (b), acid will be added.
6 High concentrations of acid are preferred, as will be explained 7 hereinafter.

9 While it should not be construed as limiting the invention, it is believed that the reaction which occurs between 11 the metals and the anion results in the formation of more than 12 one and possibly several compounds. Empirically, these can be 13 depicted as including complex anions of the formula: .
14 (MeSn2x8)-2; (MeSnX6)-2;
(Me2Sn4X14)~4; (Me2Sn4X16) 16 (MeSnsX14)~3; (Me3SngX20)-4; or 17 (Me2Sn4Xlg) 4; (MeSn4X12H) ; or .
18 mixtures thereof, wherein Me is Ru, Rh, Pd, Os, Ir, Pt, Au or a 19 mixture thereof, and X is halogen, i.e., fluorine, chlorine, bromine, or iodine; preferably chlorine or bromine. Preferred 21 complexes ars those wherein Me is Pd or Pt, and X is chlorine.

23 The concentrations of the components of the com-24 position are expressed interms of gram atomic ratio. Therefore, the gram atomic ratio of precious metal to Groûp IV metal to 26 anion of the compositions most preferred in the present invention , 27 is at least from about 1:1:3 up to, for example, 1:6:24, or 28 higher.

., ' PC-31 L 11114~7 1 As is explained above, it is a preferred feature - 2 of this invention when preparing particularly preferred 3 sensitizing solutions, most notably those containing complexes 4 of palladium, stannous chloride, to em?loy an excess of Group IV
.: . 5 metal and a large excess of the anion, (c) with respect to ,;~ 6 components (a) plus (b). Especially preferred is to use the 7 same anions as component (c).
. 8 9 In one manner of proceeding, the compositions are prepared by heating the salts of the precious metals and a 11 Group IV metal salt in an aqueous solution of suitable acid 12 and inducing precipitation. Among the acids that may be 13 mentioned are hydrochloric acid, hydrofluoric acid, sulfuric 14 acid! citric acid, acetic acid, and the like. Preferably, the . 15 anion of the inorganic acid corresponds to the anion of the salt 16 of the precious metal, or to the anion of the Group IV metal 17 salt. Where the anions of the precious metal salt and the Group 18 IV metal salt are the same, tha anion of the acid should pre-19 ferably correspond to the common anion of the salts. Where the ; 20 anion of the precious metal differs from that of the Group IV
, 21 metal salt, the anion of the acid preferably corresponds to the 22 anion of the precious metal salt. However, acids having anions 23. which differ from the anions of the precious metal salt or of 24 the Group IV metal salt may also be used. The hydride anion, H-, can be part of the complex. Preferred anions are Cl- and . 26 SnC13.
'; 27 - 28 In essence, the solid comprises a compound which is 29 formed between the metals and the anion. The preferred paIladiu~
chloride tin chloride iolld c _ ound produced by this Lnvention .~' ' ` ' ' ", ':~

-. ' ' 1~114~7 is acid soluble. Solld compositlons comprising the catalyst may be dlssolved, then dlluted to levels of concentratlon whlch can easily and reproduclbly be directly formulated into actlve sensitizing solutions. In other words, the ; invention makes avallable stable sensltizing solutions comprising slgnlflcantly lower concentrations of precious metal compound than can be produced by other known methods, excluding, of course, the methods of U.S. patents No. 3,682,671 (Aug. 8/72) and No. 3,672,938 (June 27/72) and the technique of above-mentioned Zeblisky, U.S. 3,672,923.
The sensitizing solution prepared by diluting the solid compositlon comprises an acldic aqueous solution of a precious metal as defined above consisting of (a) a precious metal compound, (b) a Group IV metal com-pound and (c) a compound of an anion. Among the precious metals that may be employed are palladium, platinum, gold, rhodium, osmium, iridlum and mixtures of these metals. The lnorganlc and organlc acld salts of these metals, and of the Group IV metals, such as the chlorldes, bromldes, fluorides, fluo-borates, iodides, nitrates, sulfates and acetates of stannous tin, titanium and germanium among others may be used. Other acid salts of the precious etals and Group IV metals will readily suggest themselves to those skilled in the art. The salts are preferably soluble in water, or in organic or in-organic acid aqueous solutions. Among the salts, the chloride is preferred,both for the precious metal, and the Group IV metal compound. The preferred precious metals and Group IV metal are palladium or platinum, particularly palladium, and stannous tin. In the sensitizing solution bath the precious metal concentration should be from at least about 0.003 to about 1.5 grams~
liter of olution. While the higher .

PC-31 L ~ , 111 14~7 ,," , . .
- 1 end of this range causes sensitization to be completed in very ..;. .~ ~.
: 2 abbreviated periods of time, e.g., ten seconds, the lower end 3 of this range is normally more economic.

S As is explained in Zeblisky, U.S. 3,672,923, above-6 mentioned, highly active sensitizing solutions are prepared . 7 by dissolving such solid compositions a liquid acid or a 8 mixture of water and an acid, until the concentration of compo-9 nent (a) has been reduced to a concentration of from about 0.000 f lO grams/liter to about 1.5 grams per liter.

12 The sensitizers render surfaces receptive to the 13 deposition of an adherent electroless metal by known procedures.
14 For example, the particular acidic precious metal solutions render conductive and non-conduct ve materials receptive to the 16 deposition of electroless copper, nickel, cobalt, palladium, 17 gold or silver, and especially to copper or nickel.
18 In use, the concentration of the acid in the l9 sensitizing solutions depends upon the strength of the acid employed. The concentration of the acid should be at least 21 sufficient to prevent hydrolysis of the Group IV metal, at the 22 final concentration. A suitable lower limit is 0.001 Normal.
23 At the upper end, the concentration of the acid may be as high 24 as 15 ~ormal, or even higher. When strong acids are used, the concentration of the acid in the sensitizing solution varies 26 between about 0.02 and 7.5 Normal, preferably the pH is usually 27 1.5 or lower. When weak acids are used, the concentration of 28 the acid in the sensitizing solution approaches the upper limit 29 given hereinabove. The concentration of acid in the sensitizing 30 solution should, of cours also be high enough to solubilize .

:`
. , .
' ' ' ' PC-31 L lill4~7 "
l the salts of the precious metals and the Group IV metal and 2 also be high enough to render the solution suitable for use 3 as a sensitizer for the material being treated. Care should 4 be used in selecting the acid concentration to insure that the specimen being treated is not adversely attacked or corroded 6 by the treating solution.
8 . In use, the Group IV metal ion concentration may 9 vary widely but must be maintained in excess of a stoichiometric amount based on the amount of precious metal ions present in 11 the sensitizing solution. Normally a large excess of, for 12 example, stannous chloride, is maintained to allow for air 13 oxidation of the stannous ion. Illustratively, concentrations 14 of as high as 50 grams per liter of stannous chloride are not detrimental to the effectiveness of the sensitizing activity 16 of the diluted solutions.

18 In use, the sensitizing solutions resulting from 19 dilution of the solids prepared by the present invention may contain additional agents to-stabilize the solution, e.g., 21 against the effects of atmospheric oxidation. Such agents will 22 include the use of additional quantities of the Group IV metal, 23 as for example, additional stannous chloride may be added to a 24 palladium-stannous chloride sensitizing solution, as well as compounds, such as organic hydroxy compounds (ols), dihydroxy 26 compounds (diols) and polyhydroxy compounds (polyols), the 27 fluorinated hydrocarbon wetting agents and hydrogen fluoride.
28 One result of the addition of such compounds to the sensitizing 29 ~olution is the inhibition of oxidation of the Group IV metals and the subsequent reduction of the precious metals.
.

~ 14~7 1 The stabilizers, if solid, can be compounded with the solid ,: 2 sensitizer or they can be co-precipitated therewith by mixing : 1 3 solutions and evaporating the solvents.

Illustrative of the conductive and non-conductive, 6 metallic and non-metallic surfaces which can be plated uniformly 7 with adherent electroless metal by use of the sensitizing 8 solutions produced by diluting the solids prepared by the present 9 invention are plastic surfaces and surfaces of metallic copper, iron, nickel, cobalt, silver, gold and alloys thereof, such as 11 brass, s~erling silver and the like. The present invention can 12 be employed to render a surface catalytic to the reception of 13 such metals as copper, nickel, palladium, cobalt, silver, gold 14 and the like.

16 Such sensitizers lead to practically complete 17 avoidance of the deposition of a flash coating of precious metal 18 from the sensitizing bath. A flash coating of precious metal 19 normally leads to a low grade of adhesion. Also, avoidance of such deposition economically conserves the precious metal.
21 Solid sensitizers can also be incorporated into a plastic base 22 for the preparation of pre-sensitized substrates.

24 Description of the Preferred Embodiements - The following examples are provided for illustrative purposes and 26 may include particular features of the invention. However,-the 27 examples should not be constured as limiting the invention, many 28 variations of which are possible without departing from the 29 spirit or scope thereof.

..,''.,,.
:.

," ' . .
, ;:. ...
, .. . .
,., :
- , : ' ' :

~ PC-31 L 11114~7 -~-, 2 A solid composition, dissolvable to provide a 3 sensitizing solution is prepared.

A first solution is prepared comprising the 6 following ingredients:
7 palladium chloride (g.) 10 8 hydrochloric acid (37%,ml.) 200 9 water to make total tml.) 500 11 The palladium salt dissolves slowly in the acid-12 water mixture.

14 A second solution is prepared comprising the lS following ingredients:
16 stannous chloride dihydrate 800 grams 17 hydrochloric acid (37%) 500 ml.

19 The first solution is added to the second with 20 agitation and the mixture is heated to 85C. and then boiled 21 in a well ventilated place for 1.5 hours, during which time it 22 changes color from blue or purple, through green, then straw-23 yellow and, finally, brown.

The mixture is allowed to cool. The mixture is 26 diluted with 15 parts of water and the pH is raised by the addi-27 tion of NaOH during which a gray precipitate forms, pH 1.5 to 28 2. Additional ~aOH is added, keeping the mixture cooled to 29 about 23C., and the gray precipitate disappears and only a black precipitate remains. The mixture is centrifuged and '.' . . ' '~
: :
, :
:
, ~ ~ ~C-31 L i 1~114~)7 1 washed with alkali solution. There is obtained a solid composi-2 tion according to this invention, which is a black powder. The 3 black solid is diluted with sufficient 4 N HCl and adding 4 SnC12.H2O to produce an active sensitizing solution, which contains Pd ion at a concentration of 0.5 g./l., SnC12.2H20 at 40 6 g./l. and including 0.04 g./l. of FC-95 surface active agent.

9 A solid composition, dissolvable to an active sensitizing solution is prepared and simultaneously precipitated.
,''.- 11 12 Add 8.5 g. SnC12 to one liter water. Add a sol-13 ution of NaOH until the precipitate formed redissolves. Add 14 approximately 10 g/l. more NaOH. Add 4 g. PdC12 from a solution containing 50 g/l. PdC12 and 5 ml./l. HCl. A black precipitate 16 forms. The precipitate is separated from the solution as a 17 solid sensitizer.

19 For use the precipitate is dissolved in a solution of hydrochloric acid and stannous chloride to produce a solution 21 with the following formula:
22 0.5 g./l. PdC12 23 100 ml./l. HCl 24 55 g.ll. SnC12.

27 A solid sensitizer is prepared under "near"
28 saturation conditions:

25 ml. of a solution containing 260 g.ll. PdC12 ,," I

. ' , ' -- ' ' .
.

:

PC-31 L l 111~4~7 , 1 and 400 ml./l. HCl is added to 40 ml. of a solution containing 2 800 g./l. SnC12.2H2O and 500 ml. HCl and placed in a flask. The 3 mixture is boiled very slowly for one hour. Sufficient heating 4 must occur to boil off excess free HCl and water; but excessive heat must be avoided to avoid overheating the sensitizer which 6 "scorches" it and renders it less active. After t'ne heating 7 step, the mixture is allowed to cool. A solid sensitizer product 8 is formed upon cooling. A solid product is formed because the 9 excess free water and HCl have been boiled off during the heating step. SnC12.2H20 which melts at 37.7~C. keeps the mixture in 11 a liquid form during the ?atter part of the heating step provide 12 excessive amounts of heat are not applied. When the mixture is 13 cooled to room temperaturs, the SnC12.2H20 freezes and the 14 sensitizer mixture becomes a solid product.
16 For use as a highly active sensitizer, the solid 17 catalyst product is dissolved in a solution of stannous chloride, 18 hydrochloric acid, and FC-95 to produce a solution of the 19 following composition:
PdC12 0.5g.
21 SnC12 25 g.
22 FC-95 wetting agent 0.05 g.
23 Hytrochloric acid (37%) 350 ml.
24 Water (to make) 1000 ml.

27 A solid catalyst is prepared under "hot melt"
28 conditions. A mixture is prepared comprising .625 g. of PdC12;
29 3.48 g. of NaCl and 32 g. of SnC12.2H2O. The mixture is heated 30 and the SnC12.2H2O melts and dissolves the other components.

~ ~ 6)7 .
1 After keeping the melt heated for about 1 hour, it is cooled and 2 solidifies. The solidified catalyst is dissolved in a solution 3 of stannous chloride, hydrochloric acid and FC-95 wetting agent, 4 as described in Example 3 to produce an active sensitizer composition.

8 A solid sensitizer is prepared by the intimate 9 blending technique, as follows:
'~'' 10 .
11 40 g. of SnC12.2H20 is plac d in a ball mill jar 12 with 0.5 g. PdC12. The mixture is ball milled for 48 hours 13 using flint balls. A solid catalyst product is obtained.

For use, the catalyst material is dissolved in 16 one liter of 4 Normal HCl.

19 A solid sensitizer is prepared by first making a solution comprising the following ingredients:
21 Gold chloride solution 2,' - 5 cc.
22 Stannous chloride 2H20 - 17 grams 23 Hydrochloric acid (37%) - 50 cc.
24 Water - to 1000 cc.
The stannous chloride is dissolved in water and the hydrochloric 26 acid is added. Then the gold chloride solution is added with 27 agitation. A small amount of precipitate forms and is removed 28 by filtration. Then the pH is raised by adding NaOH until 29 formation of a precipitated gold-stannous chloride compound ls cnmpleee. This ls rec e~ed and drled, ~d can thereafteF

:. . ' ~

11114~7 be redissolved in water to produce an active sensitizing 2 solution as described above.

A solid sensitizer is prepared by making an ~ 6 aqueous solution comprising:
: 7 Palladium chloride - 1 gram 8 Fluoboric acid (49%) - 50 cc.
9 Stannous fluoborate - 10 cc.
Water - to - 1000 cc.

12 The pH is raised by adding NaOH until formation 13 of a palladium-stannous fluoborate precipitate is substantially 14 complete. This is recovered and dried, and can thereafter be redissolved in water to produce an active sensitizing solution 16 as described above.
17 . .

19 A solid sensitizer is prepared by making an aqueous solution comprising:
21 Palladium chloride - 4 grams 22 Sulfuric acid (98%) - 140 cc.
~23 Stannous sulfate -20 grams 24 Water - to -100 cc.

26 The pH is raised by adding NaOH until formation 27 of a palladium-stannous sulfate precipitate is substantially 28 complete. This is recovered and dried, and can thereafter be 29 redissolved in water to produce an active sensitizing solution as described above.

'~ :

, ~ , 111~4~7 2 A solid sensitizer is prepared by making an 3 aqueous solution comprising:
4 Platinum chloride - 1 gram Stannous chloride - 20 grams 6 Hydrochloric acid (37%) - 40 cc.
7 Water - to - 1000 ml.

9 The pH is raised by adding NaOH until formation of a platinum-stannous chloirde precipitate is substantially 11 complete. This is recovered and dried, and can thereafter 12 be redissolved in water or in aqueous acid to produce an active 13 sensitizing solution as described above.

16 One gram of platinum chloride is placed in a ball 17 mill jar with 20 grams of stannous chloride dihydrate. The 18 mixture is ball milled for 48 hours using flint balls.
19 A solid catalyst product is obtained, which can be dissolved in one liter of 4 Normal HCl for use as a sensitizing solution.

23 Add 8.5 g. of SnC12-2H20 to one liter of water.
24 Add a solution of NaOH until the precipitate which forms redissolves. Add about 10 g./l. more of NaOH. Add 4 g. of 26 rhodium chloride and collect the black precipitate which forms.
27 For use, the precipitate is dissolved in a solution of hydro-28 chloric acid and stannous chloride to produce a concentration 29 of 0.5 grams/liter of rhodium chloride.

"

~ 11114~7 ., 2 A solution is prepared comprising:
3 Palladium bromide - 1.75 grams 4 Acetic acid (99.5%) - 880 cc.
Stannous bromide -30 grams 6 Water - to -1000 cc.

8 .The pH is raised by adding NaOH until formation 9 ¦ of a palladium-stannous bromide/acetate compound precipitate is substantially complete. This is recovered and dried, and 11 thereafter is redissolved in aqueous acid to produce an active 12 sensitizing solution as described above.
13 l A solution is prepared comprising:
16 Palladium iodide ~ 2.50 grams 17 Hydrochloric acid (37%) - 880 cc.
18 Stannous iodide -60 grams 19 Water - to -1000 cc.

21The pH is raised by adding NaOH until formation 22 of the palladium-stannous iodide/chloride compound precipitate 23. ~s substantially complete. This is recovered and dried, and 24 thereafter is redissolved in aqueous acid to provide an active 26 sensi~izing solution as described above.
~' . , 228 . ' 29 .

;

, .

111~7 i PC-31 L
~:,. . .
1 Substituting for the palladium chloride, stoich-2 iometrically-equivalent amounts of the following: ruthenium 3 chloride (RuC13); rhodium chloride (RhC13); osmium chloride 4 (OsC13); iridium chloride (IrC13); and platinum chloride (PtC14) will provide solid compositions according to this invention 6 containing, respectively, ruthenium, rhodium, osmium, iridium 7 and platinum.

Sensitizing solutions are prepared by taking 11 appropriate weights of the solid compositions from Examples 12 1-4 and dissolving them in a mixture comprising 490 ml. or 37 13 percent hydrochloric acid and 490 ml. of water. The resulting 14 solutions will contain about 0.6 grams/liter of palladium in the form of an active palladium-stannous chloride complex and 16 will have good catalytic activity.
? .
18 It is noted that while the use of stannous chloride 9 i8 preferred in the practice of thepresent invention, other stannous tin compounds such as, for example, stannous fluoborate 21 and stannous sulfate, as well as other Group IV metal compounds, 22 e.g., the analogous germanium and lead compounds, are also 23 suitable for use in the seeding, i.e., sensitizing compositions 24 described herein and in equivalent concentrations.
26 To demonstrate sensitizing activity, panels are 27 immersed in the solutions prepared from the dissolved solids.
28 These contain from 0.0005 to 2.5 grams/liter of precious metal.
29 After a suitable period of time, the panel surfaces including 30 any side walls of the apertures defined therein are thoroughly ~ ' . , ' . .

. ~
~: :
.. .- ~ .
:.-, :` 11114~7 1 rinsed with water to entirely remove the excess sensitizing 2 solution therefrom. Conventional electroless plating baths are 3 then used for the deposition of the adherent metal after 4 sensitizing the plating surface. Typically, electroless copper deposition may be followed by electroplating with copper or 6 other metals to build up copper thicknesses of 0.001 to 0.002 7 inch or greater.

9 As one embodimer.t, in the printed circuit industry, electroless copper is ordinarily deposited on the sensitized 11 surfaces of apertures formed in plastic insulation sheets which 12 have conductive copper foil laminated on both top and bottom 13 surfaces, and thereby conductive pathways between the top and 14 bottom and produced.

16 Although the invention has been described and 17 illustrated by reference to particular embodiments thereof, 18 it will be understood that in its broadest aspects, the invention 19 is not limited to such embodiments, and that variations and substitution of such equivalents may be resorted to within the 22 scope of the appended claims.
23 .

: ~

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for the preparation of a solid composition capable of dissolution in a medium comprising water and forming when dis-solved in said water a sensitizing solution for rendering a surface receptive to the deposition of an adherent electroless metal, the steps comprising:
(i) preparing an aqueous solution of:
(a) a compound of a precious metal selected from the group consisting of the precious metals of the fifth and sixth periods of Groups Viii and IB of the Periodic Table of Elements;
(b) a compound of a Groups IV metal of the Periodic Table of Elements which is capable of two valence states; and (c) a compound of an anion capable of forming a stable moiety with both valence states of the Group IV metal;
(ii) reacting said compounds in said aqueous solution;
(iii) precipitating from said aqueous reacted solution a solid composition comprising the reacted compounds of (a), (b) and (c) by (1) raising the pH of the solution to at least between 1.5 and 2 or higher, or (2) carrying out said preparation of said solution at an alkaline pH; and (iv) separating said solid composition so precipitated from said aqueous solution.

2. A method as defined in claim 1 wherein precipitation is carried out by heating and evaporating water from said mixture until sub-stantial saturation is reached, and by cooling and precipitating the cooled mixture.

3. A method as defined in claim 1 wherein component (b) comprises a low melting compound comprising tin or germanium and the pre-cipitation is carried out by heating said mixture until at least one com-ponent melts and dissolves the others, and by then cooling and precipitating said reacted compounds from the cooled mixture.

4. A method as defined in claim 1 wherein sufficient excess of component (b) is included in said aqueous mixture to provide from 3 to 100 gram atoms of component (b) per gram atom of precious metal in the total composition in said aqueous mixture.

5. A method as defined in claim 4 wherein said excess of component (b) is selected to provide from 5 to 70 gram atoms of component (b) per gram atom of precious metal in the total composition in said aqueous mixture.

6. A method as defined in claim 1 wherein component (a) comprises a compound of palladium.

7. A method as defined in claim 6 wherein component (b) comprises a compound of tin.

8. A method as defined in claim 7 wherein component (c) comprises a halide compound.

9. A method as defined in claim 8 wherein component (c) comprises a halide compound in large molar excess of components (a) plus (b).

10. A method as defined in claim 1 wherein component (a) is a compound of platinum.

11. A method as defined in claim 9 wherein component (b) is a compound of tin.

12. A method as defined in claim 1 wherein component (c) comprises a halide compound.

13. A method as defined in claim 12 wherein said halide com-pound is an alkali metal halide, a polyhalotin (II) compound or a mixture thereof.

14. A method as defined in claim 12 wherein component (b) includes sodium chloride.

15. A method as defined in claim 1 wherein said solid com-position includes an anion of the formula:

(MeSn2X8)-2 ; (MeSnS6)-2;
(Me2Sn4xl4)-4; (Me2Sn4xl6)-4;

(MeSn5X15)-4; (MeSn8X20)-4; or (Me2Sn4X18)-4; (MeSn4X12H) or a mixture thereof, wherein Me is Ru, Rh, Pd, Os, Ir, Pt, Au or a mixture thereof, and X is halogen.

16. A method as defined in claim 15 wherein Me is Pd.

17. A method as defined in claim 16 wherein Me is Pt.

18. A method as defined in claim l5 wherein X comprises chlorine.

19. A method for the preparation of a substrate which is receptive to the deposition of an adherent electroless metal thereon, said method comprising dissolving a solid composition prepared according to the method of claim 1 in a medium comprising water to produce a sensitizing com-position, contacting the substrate to be electrolessly plated therewith, and removing any excess sensitizing composition therefrom.