JPS5818430B2 - Electroless plating bath and plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved electroless plating bath for the automated catalytic deposition of Group IB metals on substrates.

More particularly, the present invention relates to improved electroless silver, copper and gold plating baths for automated catalytic deposition on contact surfaces, the baths providing plating properties including improved plating rates. .

More specifically, the present invention provides an I
This invention relates to improved methods for plating various substrates using electroless plating baths of Group B metals.

The use of electroless plating baths for the automated catalytic deposition of gold and other Group IB metals onto a variety of substrates has become widely known.

Compared to conventional electrolytic plating baths, such baths have the advantage that they can deposit metals on a variety of metallic or non-metallic substrates without the need for the use of electricity.

For example, in a series of papers on plating published in early September 1970, Dr. Okinaka presented an electroless analysis of gold using borohydride and dimethylamineboreine as reducing agents and alkali metal cyanide as the source of gold. It is shown that there is a clear deterioration in the bath by the increase in cyanide concentration, especially upon replenishment with additional alkaline earth metal cyanide fraction. .

In fact, he specifically demonstrated this in his November 1971 paper (see Figure 2 of that paper), and that the accumulation of free cyanide ions is known to reduce the rate of deposition (plating). It points out that there are.

After one replenishment, the author notes that some gold sank.

Dr. Okinaka discloses that his method resulted in plating rates reaching approximately 2.5 microns per hour, and that although these rates were achieved, significant bath instability occurred.

Furthermore, U.S. Patent No. 3.589 to Oni MC Cormack,
No. 916 contains, in addition to a water-soluble borohydride or amineboreine reducing agent and a stabilizing amount of a cyanide compound, a water-soluble gold salt and its complexing compound for gold;
Electroless gold plating baths are described, all of which are maintained at T)H between 10 and 14.

The disclosure thus teaches the use of complexing compounds to form gold complexes for the purpose of preventing gold precipitation during plating.

This disclosure also includes 5 micrograms per liter to 50 micrograms per liter.
It is taught that an amount of water-soluble cyanide compound of 0 milligrams is critical.

However, each of the gold sources used heretofore has not been completely satisfactory.

Thus, with the use of gold cyanide compounds, the plating bath experienced a significant deterioration as the cyanide ion concentration increased, especially upon replenishment of the bath.

Furthermore, these compounds are not water soluble to a large extent and therefore require considerable effort to remain in solution, and water soluble compounds, as described in U.S. Pat. No. 3, '589,916, In addition to the use of salt, the decomposition of the bath resulted.

Thus, one of the objects of the present invention is to provide an improved electroless plating bath for the automatic catalytic deposition of Group IB metals including silver, copper and gold.

Another object of the invention is to provide an electroless plating bath with improved plating speed and plating life.

Yet another object of the present invention is to improve adhesion, thickness,
IB with improved properties including brightness and spreadability
An object of the present invention is to provide an electroless plating bath that results in the deposition of group metal plating.

Yet another object of the present invention is to provide a method for plating a variety of metallic and non-metallic substrates using such electroless plating baths.

In accordance with the present invention, an electroless plating bath is provided for automated catalytic deposition of thick silver, copper and gold plating on a variety of substrates.

The electroless plating bath of the present invention comprises an imide complex of the Group IB metal to be plated; an alkali metal cyanide in an amount sufficient to stabilize the bath; a reducing agent selected from the group comprising;

The pH of the bath is maintained at about 11-14.

It has thus been found that the electroless plating bath exhibits excellent plating rates without concomitant bath decomposition.

More particularly, the bath provides a plating rate of greater than 2.5 microns per hour, and preferably greater than 2.7 microns per hour.

In a preferred embodiment of the invention, the required pH level is maintained by adding an alkali metal hydroxide to the bath, and preferably the alkali metal hydroxide is added to the bath to obtain a good degree of pH control. In addition to the metal hydroxide, an alkali metal buffer salt is added to the bath.

Additionally, certain organic chelating agents may be added to those electroless plating baths to form complexes with the substituting metals and inhibit their precipitation, especially if metallic substrates are to be plated by the baths. Organic chelating agents are added to prevent this.

Additionally, in accordance with the present invention, an improved method for plating a variety of substrates is provided, in which the metallic or non-metallic substrate is immersed in the improved electroless plating bath. catalytically activated.

In this way, malleable silver, copper and gold platings are provided which have strong adhesion to the substrate used and have a more uniform thickness compared to platings obtained by prior art plating baths. Ru.

It has thus been found that highly improved electroless plating baths are obtained when an imide complex of a Group IB metal to be plated is used as the source of that metal, for example gold.

Such imide compounds thus form unexpectedly strong complexes with the Group IB metals to be plated, thereby preventing precipitation of the Group IB metals during plating and at the same time allowing the metals to They completely dissolve in the plating solution and become sufficiently stable that they do not react with the reducing agent before they are deposited.

The imides of the present invention which are capable of forming particularly strong complexes with Group IB metals to be plated, such as gold, have the general formula: where R is alkylene, substituted alkylene, arylene,
a radical selected from the group containing substituted arylene)
has.

Preferably, R is sulfonyl-D-phenylene,
-802-C6H4-1 substituted arylene group, and specifically sulfobenzoic imide, C6H4(SO2)
(CO)NH.

In this way, complexes of these imides and gold, such as alkaline earth metal sulfobenzoic imides, are prepared for the preparation of electroless gold plating baths.

Preferably, the imide with which the Group IB metal to be complexed has the general formula: where R is a radical selected from the group comprising alkylene, substituted alkylene, arylene, or substituted arylene. be).

Preferably R is alkylene.

For example, if R is ethylene, -CH2CH2-, the imide will be succinimide, and if R is D-phenylene, C6H14=, the imide will be phthalimide.

These two compounds, namely succinimide and phthalimide, are particularly preferred when an electroless gold plating bath is desired, thus alkaline earth metal succinimide, specifically potassium gold succinimide and alkaline earth metal phthalimide, Specifically, a complex with gold is formed in the form of potassium gold phthalimide.

It is also essential that the electroless plating bath of the present invention contains a critical amount of soluble cyanide compounds in order to maintain the stability of the bath.

These water-soluble cyanide compounds include alkali metal cyanides such as sodium, potassium and lysium cyanide.

Among them, sodium and potassium cyanide are particularly preferred.

However, other such compounds may be used, such as nitriles, including alpha hydroxynitriles, such as those described in U.S. Pat. No. 3,589,916, which are incorporated herein by reference. It shall be integrated into the specification.

However, these water-soluble cyanide compounds are present in specific amounts, generally about 2 to 20 grams per liter.
It is critical that it is used and preferably in an amount of about 5 to 15 grams per liter.

Thus, below about 2 grams per liter, the electroless Metuki bath of the present invention is relatively unstable such that the metal to be plated precipitates from the bath and the concentration of cyanide compounds decreases. It has been found that as the plating rate is increased to about 20 grams per bath, the plating rate achieved by the bath decreases rapidly.

Therefore, the amount of water-soluble cyanide compound described in U.S. Pat. Plating baths are highly unstable.

Reducing agents used in connection with the electroless plating solution of the present invention include any soluble and aqueous stable borohydride or amine boreine.

In this way, alkali metal borohydrides are used, preferably sodium and:potassium borohydrides, but also various substituted borohydrides, such as sodium or potassium, trimethoxyborohydride, NaCK)B(OCHs)sHl. can be used.

Also mono- and di-lower alkyl (e.g. C6 or
Aminebonins such as alkyl)-amineboreines are used, with isoprobylamineboreine and dimethylamineboreine being particularly preferred.

Additionally, formaldehyde is also an excellent reducing agent for use in these baths, and is particularly suitable for copper and silver precipitation.

It is also essential that the electroless plating bath of the present invention should be maintained at a pH of about 11 to 14 primarily to prevent its spontaneous decomposition.

Preferably, an alkali metal hydroxide, such as sodium or potassium hydroxide, is used to maintain the pH at this level in this way.

However, it has been found that adjusting the pH is considerably easier when an alkali metal buffer salt is used in addition to the alkali metal hydroxide.

Thus, in order to maintain the electroless plating bath of the present invention at the required pH level during plating, an alkali metal hydroxide is necessary as the pH tends to decrease; Ease of control is considerably facilitated by the addition of such alkali metal buffer salts.

Thus, these alkali metal buffer salts include alkali metal phosphates, citrates, tartrates, mechborates, and the like.

In particular, these alkali metal buffer salts include sodium or potassium phosphate, potassium pyrophosphate, sodium or potassium citrate, sodium or potassium tartrate, sodium or potassium borate, sodium or potassium meborate, and the like.

Preferred alkali metal buffer salts are sodium or potassium citrate and sodium or potassium tartrate.

To further improve the electroless plating bath of the present invention, it is preferred to add an organic chelating agent to the bath.

Such chelating agents bind to displacing surface metal ions and thus interfere with the plating process of those metals, as well as the resulting color properties of the deposited layer as well as other properties such as adhesion and thickness. Deterioration of plating properties is prevented.

Thus, these organic chelating agents include the di-, trisodium and tetra-sodium and potassium salts of ethylenediaminetetraacetic acid, di-ethylenetriaminepentaacetic acid, nitrilotriacetic acid.

Among these, ethylenediaminetetraacetic acid and its di-, tri-, and tetra-sodium salts are preferred chelating agents, especially its di-, tri-, and tetra-sodium salts.

Particular preference is given to the tetra-sodium salt.

In order to autocatalytically deposit a Group IB metal plating, such as gold plating, in accordance with the present invention, it is necessary to contact such an electroless plating solution with a catalytically active substrate surface.

Thus, if a metallic substrate is used, such surface includes all metals that are accessible to the reduction of dissolved metal cations in the bath.

It is therefore preferable to make the substrate more susceptible to metals such as nickel, cobalt, iron, copper, palladium, platinum, copper, brass, manganese, etc., by treatments known to those skilled in the art. , chromium, molybdenum, tungsten, titanium, tin, silver, etc. can be used as a metal substrate onto which metals such as Group IB metals, such as gold, can be plated.

However, with non-metallic substrates, their surfaces must be made catalytically active by forming a film of catalytic material particles thereon.

This can be done on surfaces such as glass, ceramics, various plastics, etc. in the manner described in US Pat. No. 3,589,91.6.

Preferably, if a plastic substrate is to be plated according to the invention, it is first etched, preferably in a solution of chromic acid and sulfuric acid.

The substrate is poured and rinsed, then immersed in an acidic solution of stannous chloride, such as stannous chloride and hydrochloric acid, rinsed with water, and then soaked in an acidic solution of precious metals, such as palladium chloride and hydrochloric acid. It comes into contact with a solution such as

Subsequently, the now catalytically active non-metallic substrate can be contacted with the electroless plating solution of the present invention to autocatalytically deposit a plate of Group IB metal thereon.

In highly preferred embodiments of the invention, where a metal substrate is to be plated, a pre-plating step is used.

Thus, when the catalytically active metallic substrates of the present invention are used directly in the electroless plating baths herein, the substrate metal is replaced by the Group IB metal being plated thereon. It has been discovered that contamination of the plating bath occurs, thereby affecting the purity of the deposit obtained and the stability of the electroless plating solution.

Therefore, in such situations it is preferable to carry out a pre-plating step to prepare a thin layer of gold.

This is explained in US Pat. No. 3,230,098.
tO-mex'' method, in which the metallic substrate is a soluble gold salt selected from the group comprising alkaline earth metal cyanides, and the pH of the bath is adjusted to about 5. It is immersed in an aqueous gilding bath containing an ammonium buffer that can be maintained at a temperature between 5 and 14, and an organic chelating agent that can chelate with the metal ions of the substrate used.

After a thin layer of gold, approximately 2 to 10 microinches, preferably 5 to 10 microinches, has been plated in the manner described above, the plated substrate exhibits the improved properties obtained in accordance with the present invention. can be immersed in the electroless plating bath of the present invention to obtain a thick, malleable plated layer of Group IB metal having a .

A typical plating bath prepared according to the present invention is shown below.

Example 1 Potassium gold succinimide dissolved in water has a concentration of about 70 to 95
A total solution is obtained by heating to °C.

Potassium cyanide, tripotassium citrate, potassium hydroxide and ethylenediaminetetraacetic acid were added to the solution and the pH was maintained at about 13 and the temperature at about 80°C.

Next, dimethylamine boron was dissolved in water and added to the above solution.

To continue the gold plating, gold was replenished with an aqueous solution containing gold as potassium gold succinimide.

Additional amount of dimethylamineborein and also suitable p
Addition of potassium hydroxide to maintain H may be required.

The initial plating bath thus prepared had the following composition.

Gold, potassium gold as succinimide 3.0
? /l Potassium cyanide ・・・・・・・・・
5.0 f/1 EDTA (tetrasodium salt)...
・2.0! /l tripotassium citrate...
...25.0'? / potassium hydroxide ・
...Song 1 o, og/l dimethylamine borein...
...River...10.0? /1 Example 2 A silver solution was prepared by dissolving sodium silver phthalimide in water with sodium potassium tartrate, potassium silver succinimide, and potassium hydroxide.

The solution was then heated to about 55°C and a 37% formaldehyde solution was added to it.

The silver plating bath prepared in this way had the following composition: Silver, sodium silver fume...2. Off
Potassium cyanide as /l limide ・・・・・・・・・IOP/ is sodium potassium tartrate ・・・・・・・・・259/ is potassium hydroxide ・・・・・・・・・ 5 ? /l
Formaldehyde (37%)...50711Vt Example 3 A copper solution was prepared by dissolving potassium copper sulfobenzoicimide in an aqueous solution of potassium sodium tartrate, potassium cyanide, and potassium hydroxide.

This solution was then heated to about 30° C. and a 37% formaldehyde solution was added thereto.

The copper bath thus obtained had the following composition: copper, potassium as copper sulfobenzoic imide...3?
/l Potassium cyanide ・・・・・・・・・2
? / Sodium Potassium Tartrate 30
9/ potassium hydroxide ・・・・・・10
? /l formaldehyde (37%)...2om
tvt The embodiments of the present invention are shown below.

(1) An electroless plating bath according to claim 1, characterized in that the Group IB metal to be plated is selected from the group containing gold, silver and copper.

(2) 4? An electroless plating bath according to claim 1, wherein the alkali metal cyanide is present in an amount of about 2 to 20 grams per liter.

(3) An electroless plating bath according to claim 1, characterized in that the bath is maintained at a pH of about 11 to 14 by adding an alkali metal hydroxide to the bath. Electroless plating bath.

(4) The electroless plating bath according to item 3 above, wherein the bath contains an alkali metal selected from the group comprising alkali metal phosphates, citrates, tartrates, borates, metaborates, and mixtures thereof. An electroless plating bath characterized by containing a buffer salt.

(5) In the electroless plating bath according to claim 1, the imide complex of the Group IB metal to be plated has the formula RNHCOC, where R is a group containing alkylene, substituted alkylene, arylene, or substituted arylene group. An electroless plating bath characterized in that it contains an imide having a composition selected from the following.

(6) In the electroless plating bath according to claim 1, the imide complex of the IB group metal to be plated is of the formula [Seise SOC], where R is alkylene, substituted alkylene, arylene, or substituted arylene. 1. An electroless plating bath characterized in that it contains a cyclic imide having a cyclic imide selected from the group consisting of:

(7) The electroless plating bath according to item (6), wherein the imide is selected from the group containing succinimide and phthalimide.

(8) A method for plating a metallic substrate according to claim 3, wherein the layer plated with gold in the sono step (a) has a thickness of about 2 to 10 microns.

(9) A method according to claim 3, wherein the alkali metal cyanide is about 2 to 20% per liter.
A method of plating a metallic substrate characterized in that it is present in an amount of grams.

(10) A method according to claim 3, characterized in that the electroless plating bath is maintained at a pH of about 11 to 14 by adding an alkali metal hydroxide to the bath. Method of plating metallic substrates.

0υ A method for plating a metal plaster substrate according to item QO), characterized in that the electroless plating bath contains an alkali metal buffer salt.

(12) A method for plating a metallic substrate according to claim 2, wherein the electroless plating bath contains an organic chelating agent capable of forming a chelate with the metal of the substrate. .

α3) In the method according to claim 2, the group IB metal imide complex is selected from the group consisting of alkylene, substituted alkylene, arylene, or substituted arylene group. 1. A method for plating a metallic substrate, characterized by containing an imide having the following properties:

04) A method for plating a metallic substrate according to item (13), wherein the imide is sulfobenzoic imide.

The method according to claim 2, wherein the group IB metal imide complex has the formula RCONHCO
1. A method for plating a metallic substrate, characterized in that it contains an imide having the formula C, in which R is selected from the group consisting of alkylene, substituted alkylene, arylene, or substituted arylene groups.

(16) Part a! 20. A method for plating a metallic substrate according to item 19, wherein the imide is an imide selected from the group comprising succinimide and phthalimide.

17) Metal according to claim 2, characterized in that the Group IB metal consists of gold.

Claims (1)

[Claims] 1. In an electroless plating bath for automatic catalytic deposition of group IB metals on a substrate, the IB metal to be plated
an aqueous solution of a group metal imide complex; an alkali metal cyanide in an amount sufficient to stabilize the bath; and a reducing agent selected from the group comprising water-soluble alkali metal borohydrides, water-soluble amineboranes, and formaldehyde. An electroless plating bath characterized in that the bath is maintained at a pH of 11 to 14. 2 When plating a metallic substrate with a group IB metal, (
/r) the above substrate is treated with a soluble gold salt selected from the group comprising alkaline earth metal cyanides;
immersing the substrate in an aqueous gold plating bath consisting of an ammonium buffer capable of maintaining the pH of the substrate at a pH of . , and (b) the partially gold-plated metal substrate described above is
a group metal imide complex; an alkali metal cyanide in an amount sufficient to stabilize the bath; and a reducing agent selected from the group comprising water-soluble alkali metal borohydrides, water-soluble amineboranes, and formaldehyde; A method for plating a metallic substrate, comprising: subsequent immersion in an electroless plating bath maintained at a pH of ~14.