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Publication numberUS3904792 A
Publication typeGrant
Publication dateSep 9, 1975
Filing dateJun 27, 1973
Priority dateFeb 9, 1972
Publication numberUS 3904792 A, US 3904792A, US-A-3904792, US3904792 A, US3904792A
InventorsConlan Jr William A, Gulla Michael
Original AssigneeShipley Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Catalyst solution for electroless metal deposition on a substrate
US 3904792 A
Abstract
The invention disclosed herein is a catalyst for activating a substrate prior to electroless metal plating and to a process for making the same. The catalyst comprises the product resulting from the admixture of an acid soluble salt of a catalytic metal, a stannous salt, an acid and an extraneous source of halide ions. The extraneous source of halide ions provides an excess of halide ions in the catalyst formulation over that found in prior art formulations. The catalyst differs from prior art catalysts in the excess of halide ions and is an improvement as it may be used at a higher pH to catalyze substrates normally attacked by strong acids, is more stable and is adsorbed onto substrates to a greater extent than prior art catalysts.
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United States Patent Gulla et al. Sept. 9, 1975 [54] CATALYST SOLUTION FOR ELECTRQLESS 3,672,938 6/1972 Zeblisky 1 17/47 A METAL DEPOS T ON A SUBSTRATE 3,764,488 10/1973 Bernhardt 204/38 B [75] Inventors: Michael Gulla, Newton; William A.

Conlan, Jr., Attleboro, both of Mass.

[73] Assignee: Shipley Company, Inc., Newton,

Mass.

[22] Filed: June 27, 1973 21 Appl. No.: 374,093

Related us. Application Data [63] Continuation-impart of Ser. No. 224,742, Feb. 9,

1972, abandoned.

[52] US. Cl 427/304; 106/1 [51] Int. Cl. B44D 1/092 [58] Field of Search 117/213, 47 R, 47 A, 71 R,

117/130 E, 138.8 R, 160 R; 106/1 Primary Examiner-Thomas .1. Herbert, Jr. Assistant Examiner--Bruce H. Hess Attorney, Agent, or Firm-Robert L. Goldberg 5 7 ABSTRACT The invention disclosed herein is a catalyst for activating a substrate prior to electroless metal plating and to a process for making the same. The catalyst comprises the product resulting from the admixture of an acid soluble salt of a catalytic metal, a stannous salt, an acid and an extraneous source of halide ions. The extraneous source of halide ions provides an excess of halide ions in the catalyst formulation over that found in prior art formulations. The catalyst differs from prior art catalysts in the excess of halide ions and is an improvement as it may be used at a higher pH to catalyze substrates normally attacked by strong acids, is

[ References Cited more stable and is adsorbed onto substrates to a UNITED STATES PATENTS greater extent than prior art catalysts.

3,011,920 12/1961 Shipley 117/213 3,379,556 4/1968 Chiecchi 117/47 A 59 Clams 2 Drawmg F'gures Sn CONCENTRATION I A= A'= 0.05 moles 11m B= a'=o.13 u H TOTAL CHLORIDE CONCENTRATION (moles) 4s CATALYST SOLUTION FOR ELECTROLESS METAL DEPOSITION ON SUBSTRATE name of Michael Gulla and William A. Conlan on Feb. 1

9, 1972, now abandoned.

BACKGROUND OF THE INVENTION 1. Introduction This invention is directed to a formulation for catalyzing a substrate prior to electroless metal deposition.

2. Description of the Prior Art For electroless plating of substrates, especially for the plating of non-conductive substrates, it has been known for some time that chemically plated metal deposits of suitable thickness and adequate bond strength are commercially practical only if the substrate surface is properly catalyzed prior to metal deposition.

A common method for catalyzing a substrate prior to plating involves contact of the substrate with two solutions known in the art as a two-step catalyst. A process for metallizing utilizing this catalyst comprises contact of a substrate with a first aqueous solution ofa reducing agent such as stannous chloride followed by contact with a second solution of a catalytic metal salt such as palladium chloride in hydrochloric acid. The reducing agent reduces the catalytic metal salt in situ on the substrate surface to the catalytic metal thereby providing a catalytic surface receptive to electroless metal deposition-thereon. This procedure is employed successfully in many plating-on-plastic applications. However, it is subject to various disadvantages including poor adhesion between the substrate surface and a subsequently applied metal deposit. This is especially true where copper is to be deposited over copper such as in the manufactue of printed circuit boards where copper is deposited over both a plastic substrate and a copper cladding over said plastic substrate. Also, articles in the process of being plated using the aforesaid twostep catalyst must be re-racked subsequent to catalysis before proceeding to additional steps in the plating sequence to avoid contamination of the catalyst through dragin from preceding steps and rapid deterioration of the plating bath. Metal plate obtained using the twostep catalyst exhibits stardustingi.e. minor imperfections on the surface of the metal plate.

An alternative method for catalyzing a substrate prior to electroless deposition is also known and is disclosed and claimed in U.S. Pat-No. 3,01 1,920 incorporated herein by reference. In this method, a substrate is contacted with a colloidal catalytic solution formed by the admixture in acid solution of a catalytic metal salt, a stannous salt in molar excess of the catalytic metal salt and a hydrohalide acid. The catalytic metal may be selected from the group of silver, gold and the platinum family of metals. Palladium is the preferred catalytic metal. The excess stannous salt is believed to be responsible for stability of the colloid and prevents it from falling out of the formulation. The catalyst operates as a pH below about I and preferably well below 0. The limitation on the pH is due to the fact that the stannous salt hydrolyzes and precipitates at a pH of about 0.9.

Though this colloidal catalyst has been widely ac- .cepted and preferred for most applications, it is not without some difficulties. One such difficulty is that the highly acidic formulation attacks various substrate materials, especially plastic materials including the plastic racks used to carry the substrate through the plating sequence. Another difficulty is the volatilization of the hydrohalide acid which is undesirable from both 'a health standpoint and a quality control standpoint. Both of these problems could be overcome if the catalyst formulation could be prepared at a higher pH.

In U.S. Pat. No. 3,672,938, there is disclosed a process catalyzing a substrate prior to electroless metal deposition with a catalyst also formulated by the admixture in acid solution of a catalytic metal salt, a stannous salt in molar excess of the catalytic metal salt and a hydrohalide acid. This catalyst is said to differ from the catalyst of U.S. Pat. No. 3,01 1,920 in physical form, it being asserted that the catalyst of said patent is a true solution catalyst" rather than a colloidal catalyst as in the aforesaid U.S. Pat. No. 3,01 1,920. Regardless of its physical form, it is also highly acidic and suffers the same disadvantages as the catalysts of said U.S. Pat. No. 3.011.920.

Attempts have been made in the prior art to formulate a low acid, higher pH catalyst. Such attempts have been unsuccessful because the low acid catalyst has been formulated by the expedient of reducing the hydrohalide acid content. Such a reduction results in the formation of a precipitate at a pH of about 0.9 for a chloride system. This formation of precipitate is believed to be due to hydrolysis of the stannous ion with the formation of insoluble hydrolysis products. This results in loss of the catalyst. An example of this is shown in the aforesaid U.S. Pat. No. 3,672,938, Example V. where there is disclosed a catalyst having a total acid content of one milliliter of concentrated hydrochloric acid per liter of solution. This formulation is of no com mercial value as it is impossible to solubilize the stan nous salt and consequently, a stable colloid or catalyst in any other form cannot be prepared.

DEFINITIONS The following definitions are provided to assist in the understanding-of the ensuing text:

Catalyst formulation is the product resulting from the admixture of an acid soluble salt of a catalytic metal, a stannous salt in molar excess of the catalytic metal salt, an acid and an extraneous source of halide ions.

Catalyst component" refers to any one or more of the salts of the catalytic metal, stannous salt or acid used in making the catalyst formulation.

Actual halide ion concentration is the concentration of the halide ions in the catalyst formulation if any of the catalyst components are used in the form of a halide. This will be Zero if none of the aforesaid components are used in the form of a halide.

Maximum component halide ion concentration" is the concentration of halide ions that would be in the catalyst formulation if each of the catalyst components were usedin the form of the halide.

Total halide ion concentration is the required amount of halide ions in the catalyst formulation in accordance with this invention.

, Extraneous halide ions and like terms mean a source of halide ions other than iodide ions in addition to those supplied by the catalyst components. The concentration of the extraneous halide ions is equal to the difference between the total halide ion concentration and the actual halide ion concentration.

Excess halide ions" are halide ions in the catalyst in excess of the maximum component halide ion concentration and the concentration of the excess halide ions is equal to the difference between the total halide ion concentration and the maximum component halide ion concentration. The concentration of the excess halide ions equals the concentration of the extraneous halide ions when all of the catalyst components used to make the catalyst are in the form of the halide.

Precipitation point" is the pH at which a precipitate forms in the catalyst formulation rendering the catalyst unsuitable for use. This precipitate is believed to be hydrolysis products of the stannous salt.

SUMMARY OF THE INVENTION The catalysts described herein are improvements over catalysts such as those described and claimed in the aforesaid U.S. Pats. Nos. 3,01 1,920 and 3,672,938 in that they have greater solution stability, better absorption properties and, if desired, a decreased hydrogen concentration with a correspondingly higher pH.

The invention is predicated in part upon the discovery that the halide ions play a significant role in the functioning of the catalyst and that the catalyst is improved when the concentration of the halide ions is increased beyond that concentration found in prior art catalysts by the addition of an extraneous source of halide ions. The improvements resulting from excess halide ions comprise improved stability and adsorption properties and solubilization of the stannous salt or retardation of the precipitation point. Accordingly, catalysts of increased pH can be formulated thereby providing catalysts suitable for use with materials readily attacked by strong acids.

A catalyst composition in accordance with this invention comprises the product resulting from the admixture of( l an acid soluble salt of a catalytic metal, (2) a solution soluble stannous salt in molar excess of the catalytic metal salt, (3) an acid and (4) an extraneous source of halide ions in an amount sufficient to provide an excess of halide ions in the formulation. The catalyst formulations of this invention have a pH of less than about 3.5 dependent upon the stannous content as will be explained in greater detail below.

DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 graphically represents precipitation point ofa series of catalysts as a function of pH; and

FIG. 2 graphically represents the precipitation point of a series of catalysts as a function of stannous ion concentration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The catalysts of this invention are formulated substantially with materials and in proportions such as those described and claimed in the aforesaid US. Pat. Nos. 3,01 1,920 and 3,672,938. The acid soluble salt of the catalytic metal is a salt of any of those metals known to exhibit catalytic properties in chemical plating. Such metals include the precious metals, golld and silver and members of the platinum family. Palladium is generally found to be the most satisfactory of these catalytic metals for the activation of a non-conducting 4 substrate, particularly a plastic substrate, and therefore constitutes the preferredembodiment of this invention. silver, gold and rhodium constitute lesser preferred embodiments of the invention as some difficulty is encountered in the preparation of the catalyst due to limited solubility of the salts of these metals in solution.

The particular salt of the catalytic metal used is not critical and may comprise the halides such as those described in the aforesaid US. Pat. No. 3,01 1,920 as well as such other salts such as the nitrate, sulfate and the like. Salts other than halides are suitable as halide ions will be introduced into solution by the extraneous source of halide ions. Preferably, the salt is the halide having an anion common to that of the other catalyst components. It should be noted that when the halide salt is used, some halide is introduced into solutions, but because of the low concentration of the catalytic metalsalt used, this amount is generally negligible.

The amount of the catalytic metal salt is not critical and is primarily governed by cost and functional considerations. Thus, though up to 5 grams per liter or more of the catalytic metal salt is possible, it is desirable to maintain the quantity of the salt as low as possible from a cost consideration without sacrificing the functional properties of the catalytic formulation. Typically, the amount of the catalytic metal salt in a madeup bath does not exceed 2 grams per liter of solution and more preferably ranges between about 0.1 and l gram per liter of solution.

The particular stannous salt used to formulate the catalyst is likewise not critical and in addition to a stannous halide, other stannous salts are suitable such as stannous nitrate and stannous acetate. As with the salt of the catalytic metal, the stannous halide having an anion common to that of other catalyst constituents is preferred. When a stannous halide is used, a source of halide ions is introduced into the catalyst formulation though this amount by itself does not provide sufficient halide ions for purposes of this invention.

The amount of stannous salt used is not critical provided stannous ions are present in the catalyst formulation in molar excess of the catalytic metal ions. In this respect, as in the prior art, the molar ratio of the stannous ion to the catalytic metal ion may be as low as 2:1, but preferably varies between 10:1 and 40:1 and may be as high as :1.

The hydrohalide acids, other than hydriodic acid, are preferred for purposes of this invention. However, results in terms of stability and catalytic activity with hydroflouric acid are marginal. Hydrobromic acid is better and hydrochloric acid provides the best result. Accordingly, the term hydrohalide acid as used herein is intended to mean principally hydrochloric acid, but also. includes hydrohalide acids other than hydriodie acid with the realization that these other acids provide only marginal results. It should be further realized that the term hydrohalide acid means the presence of hydrogen ions and halide ions in solution though the hydrogen ions may be derived from any other acid that does not have an anion detrimental to the catalyst .formulation. Thus sulfuric acid, as an example, may be used as a source'of hydrogen ions with all of the halide ions being supplied by the extraneous source of halide lOnS.

The amount of acid used may be substantially less than in the commercially acceptable formulations of the prior art. In the prior art, the concentration of the acid had to be sufficiently high so as to provide a catalyst having a pH of less than 1 and typically was so high as to provide a catalyst having a pH below 0. Using hydrochloric acid as an example, as much as 12 moles per liter of solution were used. In accordance with this invention, though such high concentrations of acid can be used, the acid concentration can be reduced to a level whereby the pH of the catalyst is as high as 3.5. Accordingly, for purposes of this invention, an operative range for the acid is from saturation to that amount that results in a solution pH of 3.5 and in the preferred embodiment of the invention, the acid is used in an amount sufficient to provide a pH ranging between 1 to 2.5. It should be noted that though catalysts can be for mulated with a pH as high as 3.5, this is principally accomplished when the stannous ion concentration is rel atively low. consequently, the stability of catalysts at this high pH is not entirely satisfactory for storage of catalyst for long periods of time.

From the above description, it can be seen that all of the catalyst componentsi.e., the catalytic metal salt, the stannous salt and the acid, may or may not be used in the form of their respective halides though in a preferred embodiment of the invention, they are all halides having a common anion, most preferably chloride. With reference to the definitions set forth above, if all catalyst components were in the form of the halide, the resulting halide concentration, referred to as the maximum component halide ion concentration, would not be sufficiently high to obtain the improvements in the stability and adsorption properties and the retarded precipitation point. Obviously, if one or more of the catalyst components were used in a form other than the halide, then the actual halide ion concentration would be lower than the maximum component halide ion concentration and still insufficient to obtain the improvements noted above.

In accordance with the invention described herein, an excess of halide ions is provided in the catalyst formulation, above the maximum component halide ion concentration, by the addition of an extraneous source of halide ionsv The amount of the extraneous halide ions added is equal to at least the difference between the actual halide ion concentration and the required total halide ion concentration.

In determining the required total halide ion concentration, different considerations apply dependent upon whether the pH of the catalyst is below or above the precipitation point, the pH at which a precipitate formswhich precipitate is believed to be insoluble hydrolysis products of tin.

With regard first to catalyst formulations having a pH below the precipitation point in the absence of the extraneous halide ions, the total halide ion concentration required is not critical, it being understood that the higher the total halide ion concentration, the greater will be the stability and adsorption propertiesof the catalyst though the improvements in these properties are sometimes difficult to ascertain, especially with those catalysts having a high hydrogen ion concentration-e.g., a concentration such that the pH of the catalyst is below 0. In general. at a pH below the precipita tion point, the total halide ion concentration is at least 0.2 moles in excess of the maximum potential halide ion concentration and preferably, at least 0.5 moles in excess. The maximum concentration is not critical and the total halide ion concentration can be at saturation. Accordingly, the range for the total halide ion concentration is from an excess halide ion concentration of at least 0.2 moles to saturation and preferably at least 0.5 moles to saturation. The concentration of the extraneous source of halide ions is that amount necessary to increase the actual concentration of the halide ions to the total concentration of halide ions required as described above. Obviously, a greater amount of extraneous halide ions will be required when one or more of the catalyst components such as the catalytic metal salt, the stannous salt or the acid is not in the form of the halide.

With regard to catalyst formulationshaving a pH above the precipitation point (in the absence of an extraneous source of halide ions), the amount of excess halide ion is more difficult to define as it is dependent upon the pH of the catalyst and the concentration of the stannous ions. The relationship between total halide ion concentration, pH and stannous ion content is depicted in FIGS. 1 and 2 of the drawings for the system palladium chloride (1 gram per liter of solution), stannous chloride, hydrochloric acid and lithium chloride as the source of the extraneous ions. It should be understood that other systems are similar to this system though the numerical limitations defining the curves might differ.

In FIG. 1 of the drawings, there is depicted two families of curves. The first family comprises curves A, B, C and D which represent the change in the precipitation point of the catalyst (pH) as a function of total chloride ion concentration for several different stannous ion concentrations. The second family of curves, A, B, C and D represent the actual chloride ion concentration derived from the total of the catalyst components the stannous chloride, palladium chloride and hydrochloric acid, but not the lithium chloride. Curves A and A are for a stannous ion content of 0.05 moles per liter of solution, B and B for 0.13 moles per liter of solution, C and C for 0.26 moles per liter of solution and D and D for 0.39 moles per liter of solution. The precipitation point for this catalyst system in the absence of any extraneous halide ions (lithium chloride) is at a pH of about 0.9. As extraneous chloride ions are introduced into the system and the total chloride ion concentration is increased, the precipitation point (pH) is also increased, but not as rapidly for formulations having a high stannous ion concentration (Curve D) as for for mulations having a low stannous ion concentration (Curve A). Thus, it can be seen that the highest pH (about 3.5) is obtainable only with the lowest concentration of stannous ion and the highest total concentration of chloride ion. As the total chloride ion concentration decreases or the stannous ion concentration increases, the highest possible pH decreases.

The curves of FIG. 1 represent precipitation point. Therefore, the area above any given curve represents a stable catalyst while the area below the curve represents a catalyst containing a precipitate that is of no commercial value.

FIGv 1 may be used to determine the amount of extraneous halide ion required for the catalyst formulation. This is determined from the concetration difference between curves at any given pH and stannous ion concentration. For example, at a pH of 2 and a stannous ion concentration of 0.26 moles per liter of solution (Curves C and C), the concentration difference between curves C and C' is about 4.5 so that the concentration of extraneous chloride ions required to reach the precipitation point is 4.5 moles per liter of solution. Thus, 4.5 moles oflithium chloride are added to the formulation to provide a total chloride ion concentration of about moles, per liter of solution. However, this chloride ion concentration is only sufficient to reach the precipitation point of the catalyst and the total chloride ion concentrationshould be in excess of this amount to provide a stable catalyst. In general, for this catalyst system and others within the scope of the invention, the total halide ion concentration shouldbe at least sufficient to prevent formation of a precipitate and this is generally at least about 0.2 moles per. liter of solution above the halide ion concentration atthe precipitation point of the catalyst and preferably at least above 0.5 moles per. liter of solution above that required at the precipitation point. The upper limit is not critical and can be the saturation point of the halide ion in solution Applying these general guidelines to the specific formulation depicted in FIG. I, again .making. referenceto the example at a pH of 2and a stannous ion concentration of 0.26 moles per liter of solution, the total chlorideion concentration at the precipitation point is 5 moles per liter of solution, but to assure the stability, thetotal chloride ion concentration should be at least 5.2 moles per liter of solution and preferably at least 5.5 moles per liter of solution. Accordingly, the concentration of the extraneous chloride ions -the lithium chloride, added to the formulation should be more than 4.5 moles per liter ofsolution, preferably shouldbe at least.4.7 moles per liter of solution and more preferably, should be at least 50 moles perliter of solution. 7 v

With respect to FIG. 1 described above, lithium chloridewas selected as the source of the extraneous,chloride ion because ofits very high solubility in solution. Other halide salts are not so soluble. For example, when sodium chloride is selected as a source of extraneous chloride ion. the solution becomes saturated when the total concentration is about 4.5 moles per li-.

ter. This puts a practical limitation on the maximum pH obtainable as FIG. 1 indicates that when the formulation contains 0.39 moles per liter of solution of stannous ion, the maximum obtainable pH was 4.5 moles of total chloride ion is about 1.65. when the solutionvcontains only 0.05 moles per liter of solution of stannous ion, the maximum possible pH is about 2.5 with 4.5 total moles of chloride ion. 7

With regard to the source of the extraneous halide ion, any halide salt having the requisite solubility properties issuitable provided it does not have a cation that would interfere with the functioning of the catalyst. In

Lil

stannous ion concentration at different total halide ion 4 concentrations. Again, the source of the extraneous halide concentration necessary to increase the actual halide ion concentration to the total halide ion concentration is lithium chloride. Each curve in the family of curves is numbered and the numbers proceed from 1 through 8. Each number on the curve is the total halide ion concentration for that curve. Each curve represents the precipitation point of the catalyst under consideration and it should be understood that the region to the left of any given curve represents a useable catalyst and the region to the right of any given:curve represents a catalyst .in' having a pH in excess of its precipitation point .andone wherein a precipitate has formed.

From FIG. 2, it can be seen that as the total chloride ion concentration increasesflas one progresses from Curve No. l to Curve No. 8','the'maximum possible pH also increases. It can also be seen that the concentration of the stannous ion becomes more important at the higher pH levels. For 'examplefwhere the total chloride ion concentration is 8 moles per liter of solution, the maximum pH obtainable with 0.4 moles per liter of stannousion is 2.4 whereas with only 0.5 moles per liter of stannousion, the maximum pH is in excess of 3.5. Since the curves in FIG. 2 represent precipitation points, a'slight excess of total 'chloride ion concentration beyond that represented in the curve is required to make a c'atalyst free'of a precipitate. I v

The catalyst can be formulated using the procedures of the prior'art with the extraneous halide ions dissolved in the acid solution used to dissolve the other catalyst components. A preferred method for formulating a catalyst in accordance with "the invention would comprise first preparing a catalyst concentrate and then diluting the concentrate when ready for use. In this way, the concentrate can be made fairly acidic to ensure proper dissolution of the catalyst components and then the pH can be increased to the extent desired by dilution. The concentrate would be prepared by first dissolving'the catalytic metal salt in acid solution, then adding the stannous chloride and letting the formulation age. During the ageing process, the catalyst will turn from a dark blue to green to brown coloration. Following ageing, the catalyst can be diluted with a sodium chloride solution. Where a catalyst having a pH above the precipitation point is desired, the same procedure is involved, but as a final step, some of the acid can be neutralized with a suitable neutralizing agent. preferably a weak base sodium bicarbonate.

The following example will serve to illustrate the invention in more detail. 7

EXAMPLES I TO 4 These examples illustrate the preparation of the catalyst used for the derivation of FIGS. 1 and 2 of the drawings. Four stock solutions were prepared and labelled sequentially l to 4. The solutions had compositions as follows:

Solution No. I 2 3 4 Palladium chloride (gm) 1 l l l Stannous chloride (gm) I0 25 50 Hydrochloric acid (37'7l-ml) 80.6 80.6 80.6 806 Water 'to 1 liter added to each to bringthe. total concentration to a tie-- convtinued sired Ofvthe so .QQ q y were Solution Time to Silver the n titratedwith sodium bicarbonateto neutralize the Identification Piccipil'iiw (his) Film acid to a point where a precipitate formed. This was 37 N considered, to bethe precipitation point. The chloride 5 3 1 4-4 200 NO introduced from eachofthe hydrochloric ac1d. the I 200 N0 stannous chloride and the .lithium chloride as well. as totalchlori de andprecipitation. point areset forth in the following ab w with ef r nce to tableit The catalysts having solution identification numbers Should be n li q that the chlorlde-,conccmmtlQns beginning with l were less stable than the other.cataare set forth m l per 9 ml of Solunon though m lysts because of the low stannous ion concentration. drawings has b converted 3 Only one of thecatalysts exhibited a silver film characmoles P 9 o wlthi Fegard to Q teristic of a catalyst. left exposed to air for a long period first pomt in the curve representsa knownpreclp tation Of y P for cltdlyst lief/mg d P W f To demonstrate the functional properties of the catafmm formulation havmg a i r lnmal Concentration lysts of this invention, the following plating sequence of hydrochlonc d- M V was used for the plating of an epoxy copper clad circuit solution, 1 -1,, 101...... 101...? 1 1, Piecipiwiioii Identification Point (pH) .100 .010 .090 .200 1.7 1-3 .100 .010 .190 .300 1.9 1-4 100 .010 .290 .400 2.3 1-5 .100 .010 .390 .500 2.7 1-6 .100 .010 g .490 .600 3.0 1-7 .100 .010 .590 .700 3.3 m .100 .010 .690 .800 3.5 2-1 .100 .026 i 0 .126 1.1 2-2 .100 .026 .074 .200 1.4 2-3 .100 .026 .174 .300 1.7 2-4 .100 .026 .274 .400 2.1 2-5 .100 .026 .374 .500 2.3 2-6 .100 .026 .474 .600 2.5 2-7 .100 .026 .574 .700 2.8 224 .100 .026 .674 .2400 3.1 3-1 .100 .052 v.0 .152 1.1 3-2 .100 .052 04s .200 1.3 3-3 .100 .052 .l48 .300 1.6 3-4 .100 .052 24s .400 1.0 3-5 .100 .052 .348 .500 2.0 3-6 .100 052 .448 .600 2.3 3-7 .100 .052 .548 .700 2.5 3-8 I .100 .052 .648 .x00 2.7 4-1 .100 .0724 0 .178 1.2 4-2 .100 .07x i .022 .200 1.2 4-3 .100 .07x .122 .300 1.4 4-4 100 .078 .222 .400 1.6 4-5 .100 .0724 .322 .500 1.7 4-6 .100 .078 .422 .600 1.0 4-7 .100 .078 .522 .700 2.0 4-x .100 .078 .622 .800 2.3

The curves of FIG. 1 are approximations as the precipitation point was observed visually subject to ex- 4 perimental error. The explanationof the results of this i series of experiments is set forth above and will not be repeated here.

Various of the above formulations were again prepared though the total chloride ion concentration was 50 increased by 0.] moles per 100 milliliters so thatthe total chloride ion concentration was in excess of the chloride ion concentration and the precipitation point. board base material provided with a random array of Stability of these formulations was determined by pourthrough-holes. The catalysts used were those described ing a portion of the formulation into a beaker and leav- 5; in the immediately preceding table. ing the beaker exposed to air for a prolonged period of i l. Pre-clean the copper substrate. time. In this way. the catalyst formulation had a relaa. Clean the substrate by immersion in hot alkaline tively large exposed surface area. The catalyst was left cleaner and rinse in clean water. exposed to air in this manner until such time as a preb. Pickle in an acid bath with an etchant for copper, cipitate formed. The results obtained are set forth in for example, a cupric chloridehydrochloric acid the following table: bath. and rinse.

c Dip in a l() per cent by volume hydrochloric acid Solution Time t6 Silver to remove residues, and rinse. Identification Precipitatc (hrs) Film 2 C l i H 154 Immerse the clean substrate for 30 seconds or more (at: in the catalyst described above to catalyze both the 34 N0 copper surface and the plastic surface both on the :0 back side of the circuit board base material and in 244 11 i 1 3-1 200 "N0 1 through'holes- 3-4 14s NO 3. Accelerate:

1 1 Immerse in an acidic accelerating solution, for examplc. a 10 per cent by weight perchloric acid solution, for one minute or more. and rinse. 4. Metal Deposition:

12 through 4. Moreover, each of the catalysts set forth in the immediately preceding table were highly effective in catalyzing a substrate in the metallization process described above.

Immerse the catalyzed surface in the desired metal In the aforesaid Examples 5 through 8, the maximum deposition solution, for example. a copper bath concentration of extraneous chloride ion is about 4.5 such as that of Example 1 Of US. Pat. No. moles per liter of solution because of the limited solu- 3,329,512 included herein by reference, for asuffibility of sodium chloride. Accordingly, using sodium cient time to build up the desired thickness of the chloride, the maximum possible pH obtainable with metallic coating. Rinse thoroughly and dry. 10 grams of stannous chloride per liter of solution is about 5. Electroplate: 2.5.

Immerse the metal coated substrate in a IO per cent The following are examples of formulations within solution of hydrochloric acid to assure a clean copthe scope ofthe invention. All are capable of catalyzing per coating, rinse and electroplate copper over the a substrate following the procedure described above. electroless copper coating until a desired thickness is obtained.

With the above process, each of the tested catalyst Example 9 formulations provided a strong uniform coating of con Palladium nitrate (gm) I duetive metal on the plastic surface exposed in the E (gm) 2O Nitric acid (ml) through-holes and on the back side of the circuit board Calcium chloride base material well as on the copper clad. There is no Water in 1 liter necessit for removal of the metal coatin over the co Example m y g p Palladium sulfate (gm) I per clad material prior to electroplating the bond be- Stannous Sulfate (gm) l c Sulfuric acid (rnl) 2O tween the copper clad and the e cctroless copper dc 95 Calcium bromide (gm) )0 posit is quite strong. Water to 1 liter Example I l EXAMPLES 5 THROUGH 8 Palladium chloride (gm) 0.5

Stannous fluohorate (gm) 5U Fluoroboric acid (ml) 5() Solution No. 5 (i 7 8 Calcium chloride (gm) 200 20 Water to 1 liter Palladium chloride (gm) 3 3 3 3 Example l2 Stannous chloride (gm) 3O 75 I50 225 Palladium bromide (gm) 0.50 Hydrochloric Acid IZN (nil) 24.2 24.2 24.2 24.2 Stannous bromide (gm) 25 Sodium chloride (gm) I74 I74 I74 I74 H \drohroinic acid (JXJI-ml) I00 Water to 3 liters Sodium bromide (gm) 150 Water to 1 liter Example I3 Palladium bromide (gm) 0.50 The above formulations were prepared by dissolving f s p (tim) I I 3 4 itric aci (m) It) the palladium chloride and sodium chloride in one half Magnesium hmmik 250 of the volume of water. The stannous chloride was then water to i liter added in an initial amount such that there is an excess i (.mld chloride (gm) I and the balance added slowly with stirring. The solu- Smmmus chimidc (gm) 35 tions were then permitted to age until a brown colorl' ll) I b d Th l h rt t Sodium chloride (gm) 200 ation was 0 taint. c so utions were t en spi in o wmcr m I Mr three equal 1 liter portions and additional sodium chlo- Ex mpl 15 t Platinum Chloride (gm) 1 ride in a given amount was then added to each of the Summus Chlmidg (gm) 25 separate solutions. The catalysts were then titrated with Hydrochloric acid (37/-ml) l0 sodium bicarbonate to increase the pH and determine g chlmdc (gm) 3"? 1 e 0 ICT the precipitation point of the catalyst. The following Example 16 table sets forth solution identification, chloride content ghvdium i I a v x I 1 tannous su ate (gm) 25 from each of thc hydrochloric acid, stannous chloride Sun-uric Add ml) 3 and sodium chloride, the total chloride content and the Sodium chloride (gm) 200 n Water to 1 liter precipitation points of the catalyst. Example [7 Solution 1, |(l IMF, [Cl [CI' Precipitation Identification Point (pH) 5-I .I .i0 i.00 r20 1.3 5-2 .I .I() i.s0 2.00 L? 5.1 .1 .i0 3.240 4.00 2.3 6-] .l .26 L00 l.3t'i l.2 0-2 .I .20 L64 200 1.5 0.1 .l .20 3.04 4.00 10 7-] .l .52 L00 L0: 1.2 7-2 .I .52 L38 200 L3 7-1 .I .52 ms 400 is 24-1 .1 .7x L00 Iss 1.: 8-2 .I .7x Li: 2.00 1.: sn .1 .7s 3.I2 4.00 is I x A Palladium chloride (gm) 0.5 From the above results, it can be seen that the results Platinum Chlmidc (gm ()5 obtained are similar to those obtained in Examples 1 Stannous chloride (gm) 25 EXAMPLES 18 TO 20 The following examples illustrate a catalyst with a very low stannous ion concentration:

Palladium chloride (gm) 0.25 0.25 0.25 Stannous chloride 3.2 3.2 3.2 Hydrochloric acid (37% ml) 2.0 80 Sodium chloride (gm) 200 200 200 Water to 1 liter All of the above were made according to the process of Example 1. The formulation of Example 18 was stable in a petri dish exposed to air for a period of 87 hours while the formulations of Examples 19 and were stable for a period of 87 hours.

We claim:

1. A catalyst formulation for catalyzing a substrate prior to electroless metal deposition, said formulation comprising the product of admixture of (1) catalytic precious metal ions, (2) stannous ions in an amount in molar excess of said catalytic metal ions, the ratio of said stannous ions to said precious metal ions varying between 2:] and 100:1, (3) hydrogen ions in an amount sufficient to provide a formulation having a pH less than about 3.5 and (4) extraneous halide ions other than iodide ions. the concentration of said extraneous halide ions at a pH below the precipitation point of the catalyst being sufficicnt to make the total halide ion concentration at least 0.2 moles per liter in excess of the concentration of halide ions provided by all other catalyst components and at a pH at or above the pre' cipitation point being at least sufficient to prevent the formation of a precipitate.

2. The formulation of claim 1 where the pH is below the precipitation point.

3. The formulation of claim 2 where the total halide ion concentration is from 0.2 moles in excess of the concentration of halide ions provided by all other catalyst components to saturation.

4. The formulation of claim 2 where the total halide ion concentration is from 05 moles in excess of the concentration of halide ions provided from all other catalyst components to saturation.

5. The formulation of claim 1 where the pH is at or above the precipitation point.

6. The formulation of claim 5 where the total halide ion concentration varies from at least 0.2 moles in excess of that required to prevent formation of a precipitate to saturation.

7. The formulation of claim 5 where the total halide ion concentration varies from at least 0.5 moles in excess of that required to prevent formation of a precipitate to saturation.

8. The formulation of claim 1 where all halide ions in the catalyst formulation are chloride ions.

9. The formulation ofclaim 8 where the pH varies between about 0.9 and about 3.5.

10. The formulation of claim 8 where the pH varies between about 0.9 and 2.5.

11. A catalyst formulation for catalyzing a substrate prior to electroless metal deposition, said formulation comprising the product of admixture of l a catalytic metal salt selected from the group of gold. silver. and platinum family salts, the concentration of said catalytic metal salt not exceeding 5 grams per liter of solution, (2) a stannous salt in an amount such that the stannous ion concentration is in molar excess of the catalytic metal ion concentration, the molar ratio of said stannous ions to catalytic metal ions varying between about 2:1 and :1, (3) hydrogen ions in an amount sufficient to provide a formulation having a pH less than about 3.5, and (4) a halide salt other than an iodine salt in an amount such that the total halide ion concentration at a pH below the precipitation point of the catalyst is at least 0.2 moles per liter in excess of the concentration of halide ions provided by all other catalyst components and at a pH at or above the precipitation point is at least sufficient to prevent the formation of a precipitate.

12. The formulation of claim 11 where the pH is below the precipitation point and the total halide ion concentration is from 0.2 moles in excess of the concentration of halide ions provided by all other catalyst components to saturation.

13. The formulation of claim 12 where the total halide ion concentration is from 0.5 moles in excess of the concentration of halide ions from all other catalyst components to saturation.

14. The formulation ofclaim 11 where the pH is at or above the precipitation point and the total halide ion concentration varies from at least 0.2 moles in excess of that required to prevent formation of a precipitate to saturation.

15. The formulation of claim 14 where the total halide ion concentration varies from at least 0.5 moles in excess of that required to prevent formation of a precipitate to saturation.

16. The formulation of claim 11 where all halide ions are chloride ions.

17. The formulation of claim 16 where the pH varies between about 0.9 and 3.5.

18. The formulation of claim 16 where the pH varies between about 0.9 and 2.5.

19. The formulation of claim 11 where the ratio of the stannous ion from the stannous salt to the catalytic metal ion from the salt of the catalytic metal varies between about 1011 and 40:1.

20. The formulation of claim 19 where the catalytic metal salt is palladium chloride.

21. A catalyst formulation for catalyzing a substrate prior to electroless metal deposition, said formulation comprising the product of admixture of( 1 a catalytic metal halide selected from the group of gold halide, silver halide and platinum family halides. the concentration of said catalytic metal halide not exceeding about 5 grams per liter of solution. (2) a stannous halide in an amount such that the stannous ion concentration is in molar excess of the catalytic metal ion concentration. the molar ratio of said stannous ion to catalytic metal ion varying between 2:1 and 100:]. (3) a hydrohalide acid in an amount sufficient to provide a formulation having a pH less than about 3.5 and (4) a halide salt in an amount such that the total halide ion concentration at a pH below the precipitation point of the catalyst isat least 0.2 moles per liter in excess of the concentration of halide ions provided by all other catalyst components and at a pH at or above the precipitation point of the catalyst is at least sufficient to prevent the formation of a precipitatepsaid formulation being substantially free of iodide ions.

22. The formulation 'of claim 21 where the pH is below the precipitation point and the total halide ion concentration is from 0.2 moles in excess of the concentration of halide ions provided by all other catalyst components to saturation. I

23. The formulation of claim 22 where the total halide ion concentration is from 0.5 moles in excess of the concentration of halide ions provided from all other catalyst components to saturation. I I

24. The formulation of claim 21 where the pH is at or above the precipitation point of the catalyst and the total halide ion concentration varies from at least 0.2 moles in excess of that required to prevent formation of a precipitate to saturation.

25. The formulation of claim 24 where the total halide ion concentration varies from at least 0.5 moles in excess of that required to prevent formation of a pre cipitate to saturation. I

26. The formulation of claim 21 where all halide ions are chloride ions. i I I I 27. The formulation of claim 26 where the pH varies between about 0.9 and 3.5. g

28. The formulation of claim 26 where the pH varies between about 0.9 and 2.5.

29. The formulation of claim 21 where the ratio of the stannous ions from the stannous halide to the catalytic metal ions from the halide of the catalytic metal varies between about :1 and 40:1. 7

30. The formulation of claim 29 where the catalytic metal salt is palladium chloride.

31. A catalyst formulation for catalyzing a substrate prior to electroless metal deposition, saidformulation comprising the product of admixture of palladium chloride in an amount not exceeding 5 grams per liter of solution, stannous chloride in an amount such thatthe stannous ion concentration is in molar excess of the palladium ion concentration, the molar ratio of said stannous ions to palladium ions varying between 211' and 100: l, hydrochloric acid in an amountsufficient to provide a formulation having a pH less than about 3.5 and a chloride salt in an amount such that the total chloride ion concentration at'a pH below the precipitation point of the catalyst is at least.0.2 moles per liter in excess of the concentration of the chloride ions provided by all other catalyst components and at a pH at or above the precipitation point, is at least sufficient to prevent formation of a precipitate.

32. The formulation of claim 31 where the pH is below the precipitation point and the total chloride ion concentration is from 0.2 moles in excess of the concentration of chloride ions provided by all other catalyst components to saturation.

33. The formulation of claim 32 where the total chloride ion concentration is from 05 moles in excess of the concentration of the chloride ions from all other catalyst components to saturation.

34. The formulation of claim 31 where the pH is at or above the precipitation point and the total chloride ion concentration varies from at least 0.2 moles in excess of that required to prevent formation of a precipitate to saturation. I I

35. The formulation of claim 34 where the total chloride ion concentration varies from at least 0.5 moles in excess of that required to prevent formation of a precipitatc to saturation.

36. The formulation of claim 31 where the pH varies between about 0.9 and 3.5.

37. The formulation of claim 31 Where the pH varies between about 0.9 and 2.5. I

38. The formulation of claim 31 where the ratio of the stannous ion from the stannous chloride to the palladium ions from the palladium chloride varies between about l0:l and 40:1. I

39. The formulation of claim 31 where the chloride salt is' selected from the group consisting of aluminum chloride, magnesium chloride, sodium chloride, potassium chloride, calcium chloride and lithium chloride.

40. The formulation of claim 39 where the chloride salt is sodium chloride.

41. A method of catalyzing a substratefor electroless metal deposition comprising contacting said substrate with the formulation of claim 1 for a time sufficient to catalyze said substrate.

42. The process of claim 41 including the steps of acceleration and electroless metal plating. I i

43. A method of catalyzing a substrate for electroless metal deposition comprising contacting said substrate with the formulation of claim 11 for a time sufficient to catalyze said substrate. l

44. The process of claim 43 including the steps of acceleration and electroless metal plating.

45. A method of catalyzing a substrate for electroles: metal deposition comprising contacting said substrate with the formulation of claim 21 for a time sufficient to catalyze said substrate.

46. The process of claim 45 including the steps of acceleration and electroless metal plating.

47. A method of catalyzing a substrate for electroless metal deposition comprising contactingCaid substrate with the formulation of claim 31 for a time sufficient to catalyze said substrate.

48. The process 'of claim 47 including the steps of acceleration and electroless metal plating.

49. A process for stabilizing and retarding the precipitation point of a catalyst for catalyzing a substrate prior to electroless metal deposition, said catalyst comprising the product of admixture ,of l catalytic precious metal ions, (2) stannous ions in an amount in molar excess of said catalytic metal ions, the ratio of stannous ions to precious metal ions varying between 2:1 and :1, and (3) hydrogen ions in an amount sufficient to provide a formulation having a pH less than being sufficient to make the total halide ion concentration at least 0.2 moles per liter in excess of the concentration of halide ions provided by all other catalyst components and at a pH at or above the normal precipitation point, being at least sufficient to prevent the formation of a precipitate.

50. The process of claim 49 where the catalytic metal ions are palladium ions in a concentration not exceeding 5 grams per liter.

51. The process of claim 50 where the stannous ions are derived from stannous chloride.

52. The process of claim 51 where the ratio varies between 10:] and 40:1.

53. The process of claim 51 where the hydrogen ions are derived from hydrochloric acid.

18 concentration of chloride ions provided by all other catalyst components to saturation.

58. The process of claim 55 where the total chloride ion concentration is at least 0.2 moles in excess of that required to prevent formation of a precipitate to saturation.

59. The process of claim 55 where the total chloride ion concentration is at least 0.5 moles in excess of that required to prevent formation of a precipitate to saturation.

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Classifications
U.S. Classification427/304, 106/1.11
International ClassificationC23C18/28, C23C18/20
Cooperative ClassificationC23C18/28
European ClassificationC23C18/28