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Publication numberUS3415666 A
Publication typeGrant
Publication dateDec 10, 1968
Filing dateJun 16, 1966
Priority dateJun 19, 1965
Also published asDE1521120B1
Publication numberUS 3415666 A, US 3415666A, US-A-3415666, US3415666 A, US3415666A
InventorsHisae Moriya, Koji Furumoto, Sakae Akimoto, Satoshi Nagai
Original AssigneeAsahi Dow Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electroless copper plating bath
US 3415666 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 3,415,666 ELECTROLESS COPPER PLATING BATH Satoshi Nagai, Tokyo, Koji Furumoto, Yokohama, Hisae Moriya, Urawa-shi, and Sakae Akimoto, Kawasaki-ski, Japan, assignors to Asahi Dow Limited, Tokyo, Japan, a corporation of Japan No Drawing. Filed June 16, 1966, Ser. No. 557,893 Claims priority, application Japan, June 19, 1965,

0/36,245 2 Claims. (Cl. 106--1) The present invention relates to an electroless copper plating bath. Heretofore, an electroless plating process has been used in order to impart electroconductivity to a surface of an insulating material, e.g. a material made of wood, paper or plastics. Electroless copper plating is to use copper mirror reaction. The electroless copper plating is practiced by dipping an electrically insulated material in a plating bath to reduce and deposit copper on the surface of the material. The plating bath is made by adding a reductive aqueous solution containing alkalis to an aqueous solution of Formalin, hydrazine, hydroxylamines, hydroquinone of acid metal salts such as sodium hypophosphite. The Forma-lin is most familiar as the base of the plating bath because it is the cheapest. However, the

Formalin base plating bath has fault that reduction of Formalin proceeds, once prepared and even before and after plating, to deposit copper in the bath and copper ion substantially disappears only after 2 or 3 hours, with the result that the plating bath does not work at all. Hereinafter, the time required from which copper begins to deposit in the electroless plating bath is referred to as holding time.

From a practical point of view, as above-mentioned the holding time is so short that a great trouble is caused in the operation, and that the characteristic of copper film produced is not so good.

An object of the invention is to provide an improved plating bath. Another object of the present invention is to provide an electroless copper plating bath of good stability and having extended holding time. The other object is to provide an electroless copper plating bath which can deposit a copper film enabling to electroplate a pretreated body to be plated in a short time (1-2 minutes). Further object is to provide an electroless copper plating bath in which a compact and lustrous electroless copper film is deposited on a body to be plated.

According to the present invention, an aqueous solution of acid salt of copper mentioned above and a reducing aqueous solution are mixed or small amounts of sodium thiosulfate and lower alcohol are added to the reducing aqueous solution, thereby effectively depositing copper on the pretreated body to be plated in a short period of time. The deposition of copper, however, ceases in the bath for a prolonged period of time when the plating of body to be plated is not carried out therewith. Accordingly, the holding time of the bath is remark-ably extended before plating, thereby providing a good working efiiciency and depositing on the body to be plated the copper film having excellent characteristic features. Thus, the present invention is advantageous from the industrial point of view.

Thus, the present invention is to provide an electroless copper plating bath prepared by adding 0.000001- 0.100000 part by weight of sodium thiosulfate and 0.00080-2.400000 parts by weight of lower alcohol to 100 parts by weight of an electroless copper plating solution consisting of 35-70 parts by weight of copper sulfate, 20-200 parts by weight of Formalin, 17-340 parts by weight of Rochelle salt, 5-100 parts by weight of sodium hydroxide, 8-160 parts by weight of sodium carbonate and 1,000 parts by volume of water. It is, however, preferable to add sodium thiosulfate and lower alcohol to 3,415,666 Patented Dec. 10, 1968 add to a mixture when prepared by mixing an aqueous solution of acid metal salt containing copper sulfate and Formalin and a reducing aqueous solution containing sodium hydroxide, Rochelle salt and sodium carbonate, are previously added to the reducing aqueous solution.

Suitable lower alcohol to be used in the present invention includes such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol and the like. In the electroless copper plating bath according to the present invention, when the amount of sodium thiosulfate added thereto is less than 0.00001 part by weight based on 100 parts by weight. of an electroless copper plating solution, the velocity of reaction of the electroless copper plating solution becomes so fast and the holding time of said bath is so shortened that an effeet and advantage cannot be obtained as desired similarly to the conventional electroless copper plating bath. Furthermore, when more than 0.100000 part by Weight of sodium thiosulfate is added thereto, the deposition of copper does not take place at all on the surface of body to be plated and the function as the electroless copper platin solution is lost.

Furthermore, in the electroless copper plating bath of this invention, when the amount of lower alcohol added thereto is less than 0.000080 part by Weight the copper deposited on the surface of body to be plated has no luster at all and when it is more than 2.400000 parts by weight, sodium thiosulfate does not completely dissolve, and c0nsequently the holding time of the electroless copper plating solution cannot be extended. The holding time of the electroless copper plating bath according to this invention has more than about forty times that of the conventional electroless copper plating solution. Accordingly, in a process for the industrial scale operation the conventional bath type method can be altered to an automatic continuous method, thereby accomplishing a drastic curtailment of production cost. When the electroless copper plating bath is used, furthermore, the film of copper deposited on the surface of body to be plated had good luster and subsequent process such as electro plating of copper, nickel, chrome or the like can be smoothly carried out with ease, thereby obtaining good luster on a deposited metal. Still more, one of the great advantages of the process of this invention is that bufling which is extremely hazardous for a body having low thermal resistance is not required at all.

The present invention will be further explained fully by referring to the following examples.

EXAMPLE 1 First, an aqueous solution of acid metal salt and a reducing aqueous solution were prepared respectively according to the formulations set forth hereinbelow.

A. Aqueous solution of acid metal salt:

Copper sulfate g 18 Formalin g 100 Water cc 500 B. Reducing aqueous solution:

Rochelle salt g Sodium hydroxide g 25 Sodium carbonate g 40 Water cc 500 Next, the electroless copper plating bath was prepared by mixing the above-mentioned two solutions with each other and adding as additives 0.019 g. of sodium thiosulfate and 3.2 g. of ethyl alcohol thereto with mixing.

3 EXAMPLE 2 By the same manner as in Example 1, an electroless copper plating bath was prepared according to the following formulations.

A. Aqueous solution of acid metal salt:

An electroless copper plating bath was prepared according to the following formulations by the same manner as in Example 1.

A. Aqueous solution of acid metal salt:

Copper sulfate g- 5 Formalin g 29 Water cc 500 B. Reducing aqueous solution:

Rochelle salt g 25 Sodium hydroxide g 6 Sodium carbonate g- 11 Water cc 500 C. Additive:

Sodium thiosulfate g 0.0048

Butyl alcohol Mg 2.4

Comparative Example 1 For comparison, an electroless copper plating solution was prepared by an aqueous solution of acid metal salt and a reducing aqueous solution previously prepared respectively by the following formulations.

A. Aqueous solution of acid metal salt:

Copper sulfate g 18 Formalin g 100 Water cc 500 B. Reducing aqueous solution:

Rochelle salt g 85 Sodium hydroxide g 25 Sodium carbonate g 40 Water cc 500 The electroless copper plating baths and the electroless copper solution illustrated respectively in the above-mentioned Examples 1-3 and Comparative Example 1 were allowed to stand, as they are. The holding times thereof were measured with the result as denoted in the following table. The holding time was determined by the visual observation at the moment when the foam of hydrogen gas just begins to generate.

TABLE Example No: Holding time (hr.) 1 80 3 100 Comparative Example 1 2 As is clear from the above results, the holding time of the electroless copper plating bath distinctively extends over for a long space of time, compared with that of the conventional electroless copper plating solution.

Next, the samples of ABS resin (acrylonitrile-butadienestyrene copolymer) subjected to pretreatment, i.e. (1) surface roughing, (2) degrease-washing with water, (3) surface cleaning, (4) washing with water, (5) sensitization, (6) washing with water, (7) activation and (8) washing with water, were respectively immersed in the electroless copper plating baths of Examples 1-3 and the electroless copper plating solution of Comparative Example 1, so that the time required for depositing a copper film of 0.3g in thickness capable of enabling subsequent electro plating, can be measured. As a result, in each case of Examples 1-3 it took one minute 30 seconds and in case of Comparative Example 1, 12 minutes. Furthermore, the luster of copper film attained in Examples 1-3 using the electroless copper plating bath of this invention was precise and good, compared with that attained in Comparative Example 1 using the conventional electroless copper plating solution.

EXAMPLE 4 An electroless copper plating bath Was prepared according to the following formulations.

A. Aqueous solution of acid metal salt:

Copper sulfate g 17.5

Formalin g Water cc 500 B. Reducing aqueous solution:

Rochelle salt g 42 Sodium hydroxide g 22.5

Sodium carbonate g 10 Water cc 500 C. Additive:

Sodium thiosulfate g 0.005

Propyl alcohol g 3 The resultant electroless copper plating bath was allowed to stand for measuring its holding time. As a result, the holding time was hours. Furthermore, the sample of ABS resin pretreated by the same manner as in the aforementioned example was immersed in said bath to measure the depositing time for obtaining a copper film of 0.3; in thickness. As a result, it was 1 minute 30 seconds.

EXAMPLE 5 An electroless copper plating bath was prepared according to the following formulations in the same manner as in Example 1.

A. Aqueous solution of acid metal salt:

Copper sulfate g 15 Formalin g 100 Water cc 500 B. Reducing aqueous solution:

Rochelle salt 42 Sodium hydroxide g 22.5

Sodium carbonate g 10 Water cc 500 C. Additive:

Sodium thiosulfate g 0.001

Isopropyl alcohol g 1 The resultant electroless copper plating bath was al lowed to stand for measuring its holding time. As a result, it was 90 hours. Furthermore, the sample of ABS resin pretreated by the same manner as in the aforementioned example was immersed in said bath to measure the depositing time for obtaining a copper film of 0.3;1. in thickness. As a result, it was 1 minute 30 seconds.

As above, besides that the holding time of the electroless plating bath of the present invention extends over a long space of time, as compared with the conventional electroless solution, its velocity of the deposition of copper on a body to be plated is fast, its copper film has a precise luster and its working efficiency is improved. Thus, the present invention is to make a distinctive contribution to the industries concerned.

5 6 What is claimed is: propyl alcohol, isopropyl alcohol, butyl alcohol and iso- 1. An electroless copper plating bath comprising butyl alcohol. 0.000001-100000 part by weight of sodium thiosulfate, References Cited 100 parts by welght of an electroless copper platlng solu- 5 tion consisting of 35-70 parts by weight of copper sulfate, 3,307,972 3/1967 Ehrhardt 1061 XR 20-200 parts by weight of Formalin, 17-340 parts by 3,370,974 2/1968 Hepfer 7 XR Weight of Rochelle salt, 5-100 parts by weight of sodium hydroxide, 8-160 parts by weight of sodium carbonate JULIUS FROMEPr'mary Exammer' and 1000 parts by volume of water. 10 L. HAYES, Assistant Examiner.

2. An electroless copper plating bath of claim 1, U S C1 XR wherein lower alcohol is one kind or more selected from the group consisting of methyl alcohol, ethyl alcohol, 160

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3307972 *Mar 11, 1963Mar 7, 1967Bell Telephone Labor IncElectroless copper deposition
US3370974 *Oct 20, 1965Feb 27, 1968Ivan C. HepferElectroless plating on non-conductive materials
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3475186 *Jan 5, 1968Oct 28, 1969Shipley CoElectroless copper plating
US3622367 *Mar 24, 1970Nov 23, 1971Mobil Oil CorpContact deposition of platinum and other metals
US3635761 *May 5, 1970Jan 18, 1972Mobil Oil CorpElectroless deposition of metals
US3649350 *Jun 29, 1970Mar 14, 1972Gen ElectricElectroless copper plating
US4082898 *Jun 23, 1975Apr 4, 1978Ppg Industries, Inc.Reducing copper salt with alkali metal borohydride in presence of complexing agent
US4158716 *Dec 12, 1977Jun 19, 1979Ppg Industries, Inc.Electrically nonconductive copper-boron coatings on nonmetallic substrates
Classifications
U.S. Classification106/1.26
International ClassificationC23C18/20, C23C18/40, C23C18/31, C23C18/28
Cooperative ClassificationC23C18/28, C23C18/405
European ClassificationC23C18/28, C23C18/40B