Note: Descriptions are shown in the official language in which they were submitted.
1:1114~7
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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.
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~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.
16
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.
23
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.
PC-31 L
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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.
27
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
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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.
12
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.
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1~114~7
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- 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
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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.
12
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,
PC-31 L
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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.
22
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.
29
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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
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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
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- 1 end of this range causes sensitization to be completed in very
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: 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.
11
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
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PC-31 L lill4~7
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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.
17
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.
.
PC-31 L
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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.
23
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.
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- 1 EXAMPLE 1
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.
13
14 A second solution is prepared comprising the
lS following ingredients:
16 stannous chloride dihydrate 800 grams
17 hydrochloric acid (37%) 500 ml.
18
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.
24
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
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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.
8 EXAMPLE 2
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.
18
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.
26 EXAMPLE 3
27 A solid sensitizer is prepared under "near"
28 saturation conditions:
29
25 ml. of a solution containing 260 g.ll. PdC12
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PC-31 L l
111~4~7
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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.
26 EXAMPLE 4
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.
17
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PC-31 L
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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.
7 EXAMPLE 5
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.
14
For use, the catalyst material is dissolved in
16 one liter of 4 Normal HCl.
17
18 EXAMPLE 6
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
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11114~7
PC-31 L
be redissolved in water to produce an active sensitizing
2 solution as described above.
4 EXAMPLE 7
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.
11
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 . .
18 EXAMPLE 8
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.
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PC-31 L
1 EXAMPLE 9
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.
14
EXAMPLE 10
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.
21
22 EXAMPLE 11
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.
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PC-31 L
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1 XAMPLE 12
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
14 EXAMPLE 13
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 .
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i PC-31 L
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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.
EXAMPLE 14
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
22
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:` 11114~7
PC-31 L
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 .
24
: ~
23
