US2955944A - Electroless nickel plating bath control - Google Patents

Description

United States, Patent "Ce ELECTROLESS NICKEL PLAT-ING BATH CONTROL Robert A. Spanlding, Huntington Woods, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware I No Drawing. Filed July 3, 1953, Ser. No. 366,069

1 Claims. 01. 106-1) This invention relates to improvements in the deposition of nickel from chemical reduction plating solutions and more particularly to an improved plating bath, its control and maintenance.

It is known that nickel can be deposited on certain types of metals by immersion of the metal in an aqueous solution of a nickel salt and a reducing agent such as sodium hypophosphite or potassium hypophosphite. There .will be'seen that continued operation of this type plating bath results in an undesirable lowering of the pH by 7 the accumulation of hydrochloric acid.

- Accordingly,-for continuous or extended plating operations it is necessary, in addition to replenishing the nickel and reducing agent as they are used up, to regulate the .bathpH" by additions of an alkali. In the past, this has been accomplished by additions of a water soluble nickel salt such'as nickel chloride, an alkali such as sodium hydroxide, and a reducing agent, generally sodium hypophosphitea However, prior reduction plating bath replenishment techniques, in" addition torequiringextremely accurate pH determinations, involve certain difiiculties because of the by-products formed during'the interreaction of the .added ingredients. For example, in a typical chemical reduction plating bath, utilizing nickel chloride, which has been in use forsome time there are quantities of hydrochloric acid, sodium dihydrogen phosphite and/ or phosphate, and lesser amounts of'reducing agent such as sodium hypophosphite, as well as the dissolved nickel .salt. If another water-soluble nickel salt such as nickel sulfate is used, the corresponding acid is formed as the nickelis depleted. When caustic soda is added to such a bathto adjust its pH, and awater-soluble nickel salt such as'nickel chloride is added to replenish the nickel content, there occurs an interreaction of the sodium hy- 1 d1'0Xid and nickel chloride and/ or the hydrochloric acid already present to form sodium chloride or other undesirable byproducts 'which. accumulate and necessitate dispo sal of the plating solution. t

I have now discovered that the above-mentioned difii culties can be avoided andthe operating life of a chemical reduction plating bath can be greatly extended by utilizing a water-insoluble nickel'salt as a source of nickel. More particularly, the water-insoluble nickel salts contemplated in the present invention are those adapted, when Patented Oct. 1-1, 1960 2 v dissolved in the plating solution, to regulate the bath pH, thus eliminating thenecessity of separate additions of alkali.

Examples of suitable water-insoluble nickel salts are: nickel oxy salts such as nickel monoxide, nickel peroxide, nickel sesquioxide, nickelous nickelic oxide, and nickel superoxide; hydroxy nickel salts such as nickelic hydroxide and nickelous hydroxide; and carbonates such as nickel carbonate andbasic nickel carbonate. By employing one or' more of these water-insoluble nickel salts as a source of nickel, either in replenishing a conventional chemical reduction bath or in the-original bath makeup, not only is the desired nickel content provided, but also the bath pH is regulated by 'the alkaline radical liberated in the plating solution. e 1

Typical of a nickel reduction plating bath which may be regulated in operation by the practice of the present invention is the following composition where the quantities expressed are per liter of water:

Nickel chloride "grams" 30 Sodium hypophosphite do 10 Glycollic acid milliliters; 35 Sodium hydroxide "grams" 15 K It will. be understood of course that the above bath composition is intended only as an illustration of a typical reduction plating bath and that the present invention is applicable to a wide range of bath compositions. For example, plating bathscontaining about 5 to 50 grams per liter of a Water-soluble nickel salt such as nickel chloride, nickel acetate, nickel sulfate, etc.; approximately 5 to.100 grams per liter of a reducing agent, such as hypophosphorous acid, sodium hypophosphite or other soluble hypophosphites; and about 15 to grams per liter of abulfer such as glycollic acid, sodium hydroxy acetate, sodium acetate, sodium citrate, etc. and/ or other bath. additives can vsimilarly be replenished in accordance with the present invention.

Although various chemical reactions occur during the plating processrand the bath replenishment, the exact interdependence of which is not clearly understood atpre sout, the following reactionsrillustrate generally how. the nickel salts of the present invention serve tojreplenish the nickel content andregulate the bath pH.,

Employing nickel hydroxide:

Using basic nickel carbonate; 1 V V ZNiCO 3Ni( OH) 2 4H O+ l0HCl 5NiCl +9H O+CO As shown in these reactionis,when a nickel salt of the to regulate the pH.

By employing water-insoluble nickel salts, the necessity of making frequent bath analyses for nickel content is eliminated. Moreover, the plating solution is not contaminated with by-product sodium chloride or other compounds, and since no foreign alkali need be added to the bath" to regulate its pH, accurate pH determinations are no longer necessary.

While 'tlie'pre'sent invention has thus faribeen described in some detail as being applicable for the replenishment and pH control of conventional reductionplating baths, it is to be understood that the present invention also contemplates the formation o f animproved chemical reduction plating bath utilizing awater-insoluble nickel-salt as an initial ingredient. Such a bath comprisesan aqueous mixture of a reducing agent and a water-insoluble nickel salt selected from the group consisting of oxy nickel salts, hydroxynickel salts and nickel carbonates. In most intanc s i e i b eto ad i io a y emp y. a. buffer rgagent, ,A preferred bath of this 'type comprisesnickel car *bonate,"sdium hypophosphite, and "gl'ycollic acid.

A bath of the above-mentioned 'type can be produced 'acetate,'sodium citrate or sodium hydroxy acetate, the mckel salt may first be dissolved in hypophosphorus or phosphorus acid, enough acid being U ed to obtain the desiredinitial bath pH.

The following is an example of one reduction plating bath utilizing a water-insoluble nickel salt as'an initial ingredient The quantities expressed are per liter of water.

n A satisfactory range of ingredients comprises a mixture of about 5 to 100 grams per liter of a water-insoluble nickel salt, approximately '15 to 100 g n the bath consisting ofa mixture of. insoluble nickel compound, a hypophosphite reducing agent and'bulfer, if desired, may be used. The practice of the present invention providesconvenient means :for prolonging the operating life of a conventional type electroless nickel plating solution. Moreover, the invention also provides an improved plating solution in which an undesirable foreign ion need 7 p dissolving the desired water-insoluble. nickel salt or salts in glycollie acid and thereafter adding thereducing agent. If another type buffer is used, for example, sodium not beintroduced and in which the production of an undesirable lay-product is eliminated..., j 1.

It is to be understood-that, although the invention has been-described with specific reference to particular em- 'bodiments' thereof, it is not to be'so limited since changes per liter of "a bufier such as glycollic acid, sodium hydroxy' acetate, 7

sodium acetate, sodium citrate, etc., and about 5 'to 100 phosphite, hypophosphorons'acid, or other hypophosphites.

7 Since the nickels'alts of the present inventionare e x-. tremely insoluble. in water,-eve n at elevated temperatures, 7

' the use of. these salts in the replenishment of conventional reduction nickel plating baths involves certain difficulties grams per liter of reducing agent such assodium hypoand alterations therein maybe made which are within'the full intendedscope of this invention as. defined by the appended claims. 1T

Whatisclaimed isr p p 7 1. In a chemical reduction plating process utilizing a plating bath comprising an aqueous solution of a watersoluble nickel .saltand' a hypophosphite reducing agent, the improvement which consists in maintaining the desired nickel concentration in the bath by aclditions' of a waterinsoluble nickel compound ,which'is' adapted to-increase the pH of thefplating bath. v

2. In a chemical reduction nickel plating-process of the type utilizing ajplat'ing bath comprising an aqueous solu- "tion of a water-soluble nickel salt and a soluble hypophos phite reducing agent, the improvement which consists-of adding to the bath at least one water-insoluble nickel compoundselected. f om the group consisting of nickel oxide, nickel hydroxide'nickel' carbonate and basic nickel carbonate. H V v 3. A method of maintaining the pH'and desired nickel concentration in a chemical reduction nickelplating-bath containing a soluble nickel salt and. a soluble hypophoswhich I have succeeded, iii-overcoming by the following .form of a slurry by stirring thefinely divided nickel salt divided water-insoluble nickel salt as by introducing the slurry intothe filter intake. The'used plating solution is then passed. through-the same filter-whereby a quantity 'of the insoluble nickel salt is dissolved into the plating fbath, In practice, "the amount dissolved from the filter method:.A water-insoluble nickel salt is employed in the.

phite reducing .agenbeaid method comprising the steps of preparing a water slurry of a water-insoluble nickel compound, depositing a coating of said slurry on a filter,

' and thereafter passing said nickel-plating bath'through I into water. The filter conventionally employed. in chemical reduction plating systems is then coated with the finely inedia will be approximatelyequivalent to the amount of a nickel consumed in the plating. Hence,'the plating bath {will constantly replenish itself until the charge of the insoluble nickel salt hasrbeen consumed -Moreover, since I j the amount of nickel consumed in vthe reduction plating 7 operation correspondsto "theamount of acid produced,

, V the'alkalineradical liberated in solutionby the gradual dissolving of the nickel saltwill neutralize an equivalent ainountofflacid. Thus the pH will remain relatively constant.

In general, electroless nickel reduction plating:baths of I the type contemplated herein operate most satisfactorily at a pH within the range from about 3.5 ton pH at which nickel hydroxide is precipitated. A preferred'pH range is from 5.0 to 5.5..

Plating baths embodying the'present invention generally I should be operated at a relatively high temperature for" optimum results. I have 'found'that the bath tempera; 'ture'in most instances "should'be. at least 160? F. although a temperature Within the range from about i190.:F.- -210 .Fis'preferredf said filter to dissolve it erenefi an; waterinsoluble nickel compound equivalent to the nickel consume'd in plating.

4: In a chemicalreduction nickelaplating processiofl the type utiliiing an aqueous plating solution comprising about 5 to 50 grams per liter ofa water soluble nickel salt, approximately 5 to 1 00 gramsper literof ahypophosphite reducing agent,- and about 1'5 to 100 grams per liter'of a butter, the improvement consists et replenishing the nickelcontent of said plating solution as it is depleted during plating ;by addition of atleastone water-insoluble nickel compound selected fromthe group consisting of nickel oxide, nickel hydroxidegniekel carbonate, and basic nickel carbonate. 7 1

5. A chemical reduction type n1 kel plating bath-com prising an aqueoussolutionofanickei salt, a hypophosphite reducing agen't and aQbufferQsaid solution being in contact with a water-insoluble nickebcoinpou' ndi so ihatf acid generated in said bath during plating will react therewith to increase the-pl-I and replenish the soluble nickel salt.

6; A chemical reduction type nickeliplat ng bath comprising an aqueous solution of. a 'solublegmckel salt, a

. hypophosphite reducing agent and'abufier, saidsolution being in contact witha nickel compound selected from the 7 group consisting or nickel oxide, nickel'hydroxide, nickel .Fromthe,foregoing description it will'now be understood'that'I have provided a new and different type chmical reduction nickel plating operation which the nickel #saltis replenished'and the pH LregulatedbY'adEiing to'the 7 group consisting of nickel oxide-nickel hydroxide; nic'kl' carbonate, andbasic nickel carbonate. -Alsti, ini-accordanee withthe inventiom-an additiyef replenish or bath atperiodic intervals; or'continuously in certain appli-- 1 cations, -a wateninsoluble nickel; salti selected from the IQarb'onateTand the basic nickel nbe ate;

a 7 7. In a chemical reduction nickel plating proe'ess'ofthe *type utilizing 'aplating bath comprising an'faqueous soln- *tion" ofa "water soluble nickel"salt,"a'ireduc1ng agent 7 'selected'fror'n the group consisting of s'odiumliypophosphitefand potassiumhypophosphite, and a3butler,+sa1d bath being'maintairied at'ia pHiof about ,trom-3 .5 to- 6,4)'fand; at a temperature of at least- F5, the improvement which I consists of regulating the 'pH and the desired nickel content of the bath during operation'thereof bygtheaddition Qf?": .iikl"compound selected from the; groupconsisting an. n. I

of nickel oxide, nickel hydroxide, nickel carbonate, and basic nickel carbonate.

References Cited in the file of this patent UNITED STATES PATENTS 5 Dow et a1. Sept. 12, 1911 Roehl et a1. Feb. 13, 1951 Talmey et a1 Nov. 10, 1953 Gutzeit et a1 Nov. 10, 1953 10 6 Gutzeit et a1 Nov. 10, 1953 Spaulding Dec. 13, 1955 OTHER REFERENCES Blum et 211.: Principles of Electroplating and Electroforming, 3rd edition, 1949, pages 363-364.

Hodgman et al.: Handbook of Chemistry and Physics," Chemical Rubber Publishing Co., Cleveland, 26th ed. 1942), p. 416.

Claims (1)

1. IN A CHEMICAL REDUCTION PLATING PROCESS UTILIZING A PLATING BATH COMPRISING AN AQUEOUS SOLUTION OF A WATERSOLUBLE NICKEL SALT AND A HYPOPHOSPHITE REDUCING AGENT, THE IMPROVEMENT WHICH COMSISTS IN MAINTAINING THE DESIRED NICKEL CONCENTRATION IN THE BATH BY ADDITIONS OF A WATERINSOLUBLE NICKEL COMPOUND WHICH IS ADAPTED TO INCREASE THE PH OF THE PLATING BATH.