CA1232104A

CA1232104A - Electroless nickel initiator solution and process for rejuvenation

Info

Publication number: CA1232104A
Application number: CA000468840A
Authority: CA
Inventors: Roy W. Klein; Donald A. Arcilesi
Original assignee: OMI International Corp
Current assignee: OMI International Corp
Priority date: 1983-12-02
Filing date: 1984-11-28
Publication date: 1988-02-02
Also published as: GB8430429D0; GB2150601B; JPS60138075A; DE3443471C2; DE3443471A1; JPH0148349B2; GB2150601A

Abstract

Abstract of the Disclosure An aqueous initiator solution and process for rejuvenating such initiator solutions and for prolonging the useful operating life thereof by which copper and copper alloy substrates are treated therein to render them receptive to a subsequent electroless nickel plating step. The detrimental effects of progressive contamination of such aqueous initiator solutions with metal ion complexing agents during commercial use and/or precipitation of the noble metal ions which progressively impairs the operativeness of such activator solutions is overcome in accordance with the present invention by the addition of controlled amounts of ferric ions effective to maintain at least a sufficient portion of the noble metal ions in solution in a noncomplexed condition whereby the initiator solution is effective to pretreat the copper substrate prior to electroless nickel plating.

Description

~3~34 Case No . Pull ,135 EIECTROLESS NICKEL INSHORE S~LUlloN
AND PROCESS FOX REJUVENArICN

Background of the Invention The present invention is broadly applicable to the deposition of a metallic plating on polymeric plastic substrates, and more particle lye to an improved initiator solution and process for treating copper and copper alloy substrates to render them receptive to the electroless deposition of nickel on copper and copper alloy substrates.
An electroless copper plating followed by an electroless nickel plating has be found to be a very useful composite metallic coating on polymeric substrates such as electrical component housings because of the excellent electromagnetic interference (EM) shielding which is provided by such coating.
; The deposition of about 20 to about 40 micro inches of electroless copper on such a polymeric substrate provides the requisite EM
shielding and the subsequent electroless nickel over plate provides for improved corrosion resistance and decorative appearance of the cc~osite plate.
A continuing problem has been encc~ntered in effecting a uniform electroless nickel deposit on copper or copper alloy substrates in that the electroless nickel process is somewhat unpredictable depending upon the specific type of electroless nickel process employed. Generally, electroless nickel processes can be categorized as being of the high temperature ~175 to 212F) acid process and the low temperature (75 to 160F) 1~3~

alkaline pro ox so. Initiation of a nickel deposit will occur much faster from hot acid electroless nickel processes than in fewer temperature alkaline electroless nickel pro ox sues in which the initiation time may exceed 30 minutes which is commercially unsatisfactory. The initiation time as herein used is defined as the period commencing when a copter substrate is immersed into the bath and ending when the nickel plating common ox s. In order to reduce the initiation time, three general methods are currently in use to effect fairly rapid initiation of an electroless nickel plate on copper and copper alloy Of fax ox s which include the electrolytic deposition of an initial nickel strike, the direct reduction method in which the copper substrate is contacted with a reducing agent, and, finally, the cathodic ox if method employing an aqueous solution containing noble metal ions such as gold or palladium to deposit catalytic reduction sites on the copper substrate by chemical displacement. Of the foregoing, the cathodic ox if method is considered technically superior and is better adapted for high volume production installations.
In accordant ox with prior cathodic ox if initiator techniques, a noble metal, particularly palladium is employed in the aqueous solution in which a previously electroless copper plated substrate is immersed for a controlled time period. It has been found, however, that after only several days of heavy production use, certain such palladium containing initiator solutions become ineffective no ox ssitating disposal and replacement. Because of the relatively few own ox nitration of palladium in the initiator solution, it is not presently ~321~'~

economical to subject such waste initiator solutions to recovery of the valuable palladium constituents therein. In addition to the cost and waste disposal problems associated with the discarding of such spent initiator solutions, the progressive degradation of such solutions during use also causes erratic and unpredictable behavior of the substrates being treated in the electroless nickel plating solution detracting from the attainment of uniform nickel deposits thereon.
he present invention overcomes the problems and cost disadvantages associated with prior art noble metal initiator solutions by providing a composition which provides for a stabilization and prolonged effective operating life of such initiator solutions as well as a process for rejuvenating such initiator solutions which have been rendered ineffective or impaired due to the progressive contamination thereof particularly by organic metal ion completing agents.

Summary of the Invention .
It his now been discovered that the rapid degradation and loss of effectiveness of such initiator solutions is at least in part attributable to the progressive contamination thereof by drag-in of residual solutions employed in the pretreatment and electroless copper plating of polymeric substrates including organic completing agents present in the electroless copper plating bath. In view of the complex configuration of many such polymeric substrates including housings for electronic components, it is virtually impossible from a commercial standpoint to eliminate such detrimental drag-in. Experimental tests conducted have shown that as little as 0.3 percent by volume of a typical electroless copper plating solution can render a palladium initiator solution ineffective for initiating nickel deposition in a subsequent electroless nickel plating bath within commercially acceptable times.
It has been further discovered that the degradation and loss of effectiveness of such initiator solutions such as palladium initiator solutions is in part attributable due to a precipitation of palladium compounds including palladium metal rendering the solution less effective or totally inoperative for initiating nickel deposition in a subsequent electroless nickel plating bath.
Accordingly, the benefits and advantages of the present invention in accordant ox with the process aspects thereof include the rejuvenation of an aqueous initiator solution containing noble metal ions which has become ineffective due to a contamination with organic completing agents from a prior electroless copper plating solution rendering it incapable of treating topper plated substrates to make them receptive to a subsequent electroless nickel plating step. In accordance with the process, bath soluble and compatible ferris metal ions are introduced into the impaired initiator solution in an amount sufficient to restore the initiator solution to effective operation and generally, are employed in amounts of about 10 Mel to about 5 g/l.
In accordance with a further process aspect of the present invention, a stabilization and substantial prolongation of the useful operating life of such aqueous initiator solutions is achieved by adding controlled effective amounts of ferris ions to the initiator solution in anticipation of progressive contamination thereof with organic metal ion complex m g agents and precipitation of the noble metal ions thereby maintaining the noble metal ions present in the initiator solution available for reaction with the copper and copper alloy substrates immersed therein assuring rapid and predictable uniform deposition of nickel in a subsequent electroless nickel plating step.
In accordance with the composition aspects of the present invention, an improved aqueous initiator solution is provided containing a controlled effective amount of noble metal ions present to effect rapid initiation of an electroless nickel deposit on the substrate following the pretreatment thereof in further combination with contaminating organic metal ion chelating agents and an effective amount of ferris ions. Preferably, the ferris ions are present in amounts of about 40 to about 500 Mel Additional benefits and advantages of the present invention will become apparent upon a reading of the Description of the Preferred EhhxIlunents taken in conjunction with the specific examples provided.

description of the Preferred Ehtx~diments he composition and process of the present invention is particularly applicable for providing a composite topper and nickel electroless plating on polymeric substrates including playable plastics and polymeric plastics including acrylonitrile-~23~

butadiene-styrene (AS), polyaryl ethers, polyphenylene oxide, polystyrene, ply carbonate nylon or the like. Such electroless plating processes conventionally comprise a plurality of sequential pretreatment steps to render the polymeric substrate no ox ptive to the application of the electroless copper plating.
Conventionally, the pretreatment steps employed include a cleaning or series of cleaning steps, if no ox scary, to rewove surface films or contaminating substances followed thereafter by an aqueous acidic etching step employing a hexavalent chromium solution to achieve a desired Æ fax ox roughness or texture which enhances the mechanical interlock between the substrate surface and the metallic plating to be applied there over. The etched substrate is subjected to one or a plurality of rinse treaters to extract and rove any residual hexavalent chromium ions on the surf ox s of the substrate which may also include a neutralization step incorporating reducing agents to substantially convert any residual he~avalent chromium to the trivalent state. m e rinsed etched substrate is thereafter subjected to activation treatment in an aqueous acidic solution containing a tin-palladium complex to form active sites on the surf ox of the substrate followed by one or more rinsing steps after which the activated surf ox is subjected to an a ox berating treatment in an aqueous solution to extract any residual tin constituents or compounds on the surface thereof. The accelerated plastic part is again rinsed and thereafter subjected to an electroless plating operation to effect the deposition ox a Shapiro plate thereon over all or selected sections of the surface thereof thereafter the topper plated 1~3~

substrate is rinsed and subject to the activator treat-mint prior to the electroless nickel plating step.
Typical of plating processes for pretreatment of polymeric substrates are those described in United States Patent Nos. 3,622,370: 3,961,109, 3,962,497 and 4,204,013. US. Patent No . 3,962,497 discloses a typical neutralization treatment while US. Patent No. 3,011,920 and 3,532,518 disclose typical one-step activation treat-mints. US. Patent No. 4,204,013 teaches typical come positions for etching, neutralizing, activating and electroless copper plating of polymeric substrates. Such electroless copper plating solutions contain organic come flexing agents in an amount sufficient to maintain the copper ions in solution. Typical of such completing agents are ethylene Dunn twitter acetic acid, gluco-heptonate, NUN tetrakis (2-hydroxy propel) ethylene Damon or the like.
The aqueous acidic solution in accordance with the composition aspects of the present invention contains hydrogen ions in an amount to provide an acidic pi and usually, a pi of less than about 1. Acidification of the solution can be achieved by employing a variety of acidic substances of which mineral acids are generally preferred and among which hydrochloric acid is particularly sails-factory. The activator solution further i~3210~1 obtains noble metal ions such as gold, platinum, palladium and mixtures thereof of which palladium itself constitutes a preferred material. The concentration of the noble metal ions can generally range from as low as about I Mel to concentrations up to about 100 Mel and higher. Generally higher concentrations are undesirable for economic considerations and in view of the fact that such concentrations above about 100 Mel do not provide for any appreciable benefits aver those obtained at relatively lower concentrations. Particularly satisfactory results are obtained I the noble metal ion concentration is controlled within a range of about up to about ED nil m e copper or copper alloy substrate is contacted such as by inversion with the aqueous activator solution which is usually controlled at a temperature of about room temperature (60F) up to about 100F for periods of time of about 10 seconds up to about 5 minutes or longer. Typically, in high volume commercial operation, immersion times of about 15 seconds up to about 2 m m vies have provided satisfactory pretreatment for the subsequent electroless nickel plating step. Pretreatment of the copper or copper alloy substrate in the activator solution is preferably done in the preset ox of bath agitation such as mechanical agitation, cathode rod agitation, and preferably air agitation itch has further been surprisingly found to effect a redissolving of any noble metal precipitates formed in the activator bath in the presence of the ferris ions in the solution.
In addition to the foregoing constituents, the aqueous acidic initiator solution further contains controlled effective LIZ

amounts of ferris ions present in an amount effective to stabilize and maintain the operating efficiency of the initiator solution aver prolonged time periods as well as to rejuvenate an initiator solution the effectiveness of which has become impaired due to the preset ox of con tam m cling completing agents and/or the precipitation of the noble metal ions present. It has been discovered that concentrations of the ferris ions as low as about 10 mgtl are effective while concentrations substantially higher than that can key employed up to a level below that at which excessive etching of the copper or copper alloy substrate occurs as a result of excessive oxidation attack by the ferris ions causing the copper substrate to deplete. The particular maximum concentration of ferris ions will vary in consideration of the duration of the initiation cycle, the temperature of the initiator solution and the acidity thereof. m e higher the temperature, the longer the treatment time and the lower the pi of the initiator solution will necessitate a corresponding reduction in the permissible ferris ion concentration. Generally, the concentration of ferris ions is controlled within a range of about 10 Mel up to stout 5 g/l with concentrations of about 40 Mel to about 500 Mel being preferred.
The ferris ions are included in the initiator solution by the addition of bath soluble and compatible ferris salts or con be formed in situ by the addition of iron particles and/or ferrous salts or compounds which are subsequently oxidized to the ferris state such as by the use of various oxidizing agents, and I

preferably, by the bubbling of air or oxygen through the bath as conventionally performed during air agitation thereof.
In the preparation of a fresh initiator solution, the ferris ion concentration can be controlled within the foregoing ranges with the concentration preferably increasing from the lower concentration toward the upper concentration during use of the solution to maintain stability and effectiveness thereof. I the process of rejuvenating an initiator solution which has become impaired due to the presence of contaminating vexing agents therein and/or the precipitation of the noble metal constituent, it is preferred to intrude ox the ferris ions by gradual addition in the presence of agitation to restore activity of the solution within a period of about one to about two hours. When an initiator solution has been impaired primarily due to precipitation of the noble metal ions therein, it is preferred to intrude ox the ferris ions in the preset ox of air agitation providing an oxidizing medium for redissolving the noble metal ions such as palladium in the solution in which they are effective to pretreat the copper substrate prior to the subsequent electroless nickel plating.
In order to further illustrate the composition and pro ox so of the present invention, the following specific examples are provided. It will be understood that the examples are provided for illustrative purposes and are not intended to be limiting of the scope of the invention as herein disclosed and as set forth in the subjoined claims.

A series of molded AS plastic panels of a nominal size of about 3 inches by about 4 inches by about one-tenth inch thick comprised of a plastic commercially available under the designation PUG 298 from Monsanto Chemical Ccmpa~y were subjected to a conventional replating cycle including cleaning followed by a water rinse and an etch treatment in an aqueous acid solution cannoning 356 g/l chronic acid, 412 g/l sulfuric acid and 0.2 g/l of a per fluorinated proprietary wetting agent commercially available under the designation FC-98 from Minnesota Mining Ox Manufacturing Company for a period of 5 m mutes at 140F. The etched panels were thereafter cold water rinsed for 1 minutes at 70F followed by a neutralization treatment for a period of 5 minutes at 120F employing an aqueous solution containing 18 g/l hydrochloric acid and 3 g/l hydroxyl Anne sulfate. the neutralized test panels were thereafter water rinsed for 1 minute at 70F and subjected to an activation treatment for a period of 5 minutes at 110F employing an aqueous acid solution containing 0.77 g/l palladium, 9 g/l stuns chloride, 35.2 g/l hydrochloric acid and 192 g/l sodium chloride. Following activation, the test panels were water rinsed for 1 Nat at 70~F and thereafter subjected to an aloe aeration treatment for a period of 1 minute at 75F in a 5 percent by volume aqueous solution of fluoboric acid followed by a water rinse for 1 minute at 70F.
Ike pretreated test panels were thereafter subjected to an electroless copper plating step for a period of 10 minutes at a temperature of 140F containing 40 g/l EDNA tetrasodium salt, 4.2 1~2~

g/l cupric chloride, 3 g/l formaldehyde and sodium hydroxide to provide a pi of about 12.3. A copper deposit of about 45 micro inches was produced.
m e copper plated test panels were thereafter water rinsed for 1 minute at 70F and immersed m an initiator solution for a perked of 3 minutes containing 50 Mel palladium chloride and 1 percent by volume hydrochloric acid. The panels were thereafter water rinsed for period of 1 minute at 70F.
The resultant test panels were thereafter subject to an electroless nickel plating step for a period of 2 minutes at 85F
containing 12 g/l nickel chloride hexahydrate, 18 g/l sodium hypophosphite and 23 g/l citric acid.
The initiation time was about 15 to 20 seconds after the test panels were immersed in the electrDless nickel plating solution before a deposition of nickel on the test panels occurred. Following an electroless nickel plating for 2 minutes at 85F, about 2 micro inches of nickel deposit was obtained.

A second series of test panels were subjected to a replating treatment and electroless copper and nickel plating sequin ox in accordance with the pro ox dune as described in Example 1 except that 130 Mel of ETA tetrasodium salt was intentionally added to the palladium initiator solution to simulate a contamination thereof as may occur in conventional commercial practice . me test panels upon inversion in the electroless Lowe a nickel solution had an initiation time of about 25 seconds before a nickel deposit kimono ox d.

A third series of test panels were processed m accordance with the replating and electroless copper and nickel plating sequence as previously described in Example 1 with the exception that 170 my/l of Eta tetrasodium salt was intentionally added to the aqueous palladium initiator solution. m e test panels were subsequently immersed in the electroless nickel plating bath and after a period of 2 aunts immersion time, the test panels were still totally devoid of any nickel plate. Iris example demonstrates the detrimental effect of contaminating ccmplexing agents present in the palladium initiator solution.

A fourth series of test panels were processed in accordance with the procedure as described in Example 3 with the exception that in addition to the 170 Mel of ETA tetrasodium salt, 170 m3/1 of ferris chloride hexahydrate was added to the initiator solution. The AS test panels upon immersion in the electroless nickel plating solution had an initiation time of about 25 seconds before the nickel plating of the surf ox s thereof ccronenced. This example illustrates the rejuvenation of an initiator solution by the addition of a metal ion which had become impaired due to the preset ox of excessive amounts of oomplexing agents.

A fifth series of test panels were processed in accordance with the procedure and employing the solutions as described in Example 4 with the exception that the concentration of the ETA tetrasodi~rm salt corplexing agent in the initiator solution was increased from 170 Mel to 510 Mel in the preset ox of 170 mg/1 of ferris chloride hexahydrate. Upon immersion of the test panels in the electroless nickel plating solution, an initiation period of about 35 seconds was required to effect an initiation of the nickel deposit on the panels.

A sixth series of test panels were processed in accordant ox with the same procedure employing the same compositions as set forth in Example 5 with the exception that the con ox nitration of ferris chloride hexahydrate was increased in the initiator solution from 170 Mel to 300 Mel in the preset ox of 510 Mel of the ETA tetrasodium salt ocmplexing agent. Upon immersion of the test panels in the electroless nickel plating solution, an initiation period of only about 20 seconds was required to effect initiation of the nickel deposit on the test panels.

While it will be apparent that the preferred elite ens of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is sup ox tubule to modification, variation and change without ho departing Fran the proper scope or fair naming of the subjoined clowns.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for rejuvenating an aqueous acidic initiator solution containing noble metal ions which has become ineffective due to contamination with complexing agents from a prior electroless copper plating solution to render copper plated substrates contacted therewith receptive to a subsequent electroless nickel plating step, the improvement comprising introducing into the contaminated said initiator solution ferric ions in an amount sufficient to restore said initiator solution to effective operation, said ferric ions being bath soluble and compatible.

2. m e process as defined in claim 1 in which said ferric ions are present in an amount of at least about 10 mg/l.

3. The process as defined in claim 1 in which said ferric ions are present in an amount below that at which excessive etching of the copper substrate occurs.

4. The process as defined in claim 1 in which said ferric ions are present in an amount up to about 5 g/l.

5. The process as defined in claim 1 in which said ferric ions are present in an amount of about 40 to about 500 mg/l.

6. The process as defined in claim 1 in which the step of introducing ferric ions into said initiator solution is performed by adding a bath soluble and compatible ferric compound thereto.

7. The process as defined in claim 6 in which said compound comprises ferric chloride.

8. In a process for rejuvenating an aqueous initiator solution containing noble metal ions which has become ineffective due to precipitation of said noble metal ions from the solution, the improvement comprising introducing into said initiator solution ferric ions in an amount sufficient to effect dissolution of at least a portion of the precipitate to restore the effective operation of said initiator solution in the presence of an oxidizing medium.

9. The process as defined in claim 8 in which said ferric ions are present in an amount of at least about 10 mg/l.

10. The process as defined in claim 8 in which said ferric ions are present in an amount below that at which excessive oxidation attack of the copper substrate to be plated occurs.

11. The process as defined in claim 8 in which said ferric ions are present in an amount up to about 5 g/l.

12. The process as defined in claim 8 in which said ferric ions are present in an amount of about 40 to about 500 mg/l.

13. The process as defined in claim 8 in which said oxidizing medium is performed by bubbling an oxygen-containing gas through initiator solution for a period of tine sufficient in combination with said ferric ions present to effect a redissolution of at least a portion of said precipitate therein thereby restoring effective operation of said solution.

14. In a process for prolonging the useful operating life of an aqueous initiator solution containing noble metal ions employed for pretreating copper substrates to render such substrates receptive to a subsequent electroless nickel plating step, the improvement comprising including ferric ions into said initiator solution in an amount to maintain at least a portion of the noble metal ions in solution in a noncomplexed state effective to render the copper-plated substrated receptive to a subsequent electroless nickel plating step.

15. The process as defined in claim 14 in which said ferric ions are present in an amount of at least about 10 mg/l.

16. The process as defined in claim 14 in which said ferric ions are present in an amount below that at which undesirable etching of the copper substrate occurs.

17. The process as defined in claim 14 in which said ferric ions are present in an amount up to about 5 g/l.

18. The process as defined in claim 14 in which said ferric ions are present in an amount of about 40 to about 500 mg/l.

19. An aqueous acidic initiator solution containing noble metal ions suitable for pretreating copper substrates to render them receptive to a subsequent electroless nickel plating step comprising an aqueous solution containing noble metal ions present in an amount effective to treat the copper substrate to initiate nickel immersion plating in a subsequent electroless nickel bath, and ferric ions present in an amount sufficient to maintain at least a portion of the noble metal ions in solution in a noncomplexed state effective to render the copper substrates receptive to a subsequent electroless nickel plating step, said ferric ions being bath soluble and compatible.

20. The initiator solution as defined in claim 19 in which said ferric ions are present in an amount of about 10 mg/l up to a concentration below that at which undesirable etching of the copper substrate occurs.