JPH01230785A - Electroless copper plating bath - Google Patents

Abstract

PURPOSE:To prevent the occurrence of the precipitation of iron and also to smooth the surface of a copper-plated plane by adding and incorporating a specific complexing agent for iron and iron cyanide to an electroless copper plating bath containing copper salt, complexing agent for copper, alkali hydrox ide, and reductant for copper ions. CONSTITUTION:Hydroxy ethyl ethylene diamine triacetate (HEDTA) as a complexing agent for iron in an amount of 0.1-5.0g/l and iron cyanide, such as yellow prussiate of potash and red prussiate are added to an electroless copper plating bath of pH11.5-13.0 containing copper salt, such as copper sulfate and copper nitrate, as a copper ion source by 0.007-0.15mole/l, a complexing agent for copper, such as tartaric acid and EDTA, by the amount 5-6times copper content, a pH regulator, such as NaOH, and formaldehyde, etc., as a reductant for copper ions by 0.03-0.75mole/l so that the amount of HEDTA is regulated to a value not more than the equivalent to iron in iron cyanide. By this method, the electroless copper plating bath free from the occurrence of Fe precipitation and having smooth Cu-plated surface can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field The present invention provides a function to obtain smooth deposited copper and to prevent precipitation of iron compounds, which are decomposition products of additives, in the plating solution. The present invention relates to an electroless copper plating solution having the following properties.

BACKGROUND OF THE INVENTION In recent years, electroless copper plating solutions have been widely used in the production of printed wiring boards and in the field of plastic metallization.

The electroless copper plating solution consists of an aqueous solution containing a copper salt, a copper complexing agent, an alkali hydroxide, and a reducing agent such as formaldehyde, a derivative thereof, or hydrogen fluoride.

Deposited copper obtained from such known plating solutions generally exhibits a dark red color and has inferior mechanical strength compared to electrolytic copper. As a method for improving the appearance and mechanical strength of such deposited copper, Japanese Patent Publication No. 60-37875 describes
Addition of iron cyanide is mentioned.

Problems to be Solved by the Invention However, in the above method, when yellow salt and red blood salt, which are typical examples of cyanide compounds of iron, are added to the plating solution, these salts may be added to the plating solution at temperatures above 60°C. At a plating temperature of , natural decomposition occurs during plating, and as a result of this decomposition, fine particles of iron hydroxide and oxide that are generated float in the plating solution, and as a result, they also precipitate in a composite manner in the precipitated copper. This method has the problem of generating many small protrusions on the surface of the deposited copper. In view of the above problems, the present invention provides an electroless copper plating solution that prevents iron precipitation from occurring during plating and prevents copper surface roughening due to complex precipitation of precipitation. It is.

Means for Solving the Problems The present invention is intended to provide an electroless copper plating solution that does not have the above-mentioned drawbacks, and which contains a copper salt and its complexing agent, alkali hydroxide, formaldehyde, etc. This is an electroless copper plating solution characterized by containing an iron complexing agent and an iron cyanide compound simultaneously in a conventional plating solution consisting of an aqueous solution of a copper reducing agent.

Function: The electroless copper plating solution of the present invention containing the above-mentioned additives has the following properties:
Even if the iron cyanide complex salt spontaneously decomposes during the plating reaction, it is immediately captured by the iron complexing agent in the solution and forms a soluble complex, eliminating the formation of iron precipitate. The mixing of fine particles of iron compounds no longer occurs, the surface roughening phenomenon of the precipitated copper disappears, and the precipitated copper becomes
It becomes extremely smooth.

Example An embodiment of the present invention will be described below.

Copper ion sources such as copper sulfate and copper nitrate can be used as the copper salt in the electroless copper plating solution, and the concentration range is O.
, OO7 to 0.15 mol/l is effective. As the copper complexing agent, tartaric acid or its salt, ethylenediaminetetraacetic acid (EDTA) or its salt, etc. are used.
It is extremely superior in that it can be effectively used in a relatively wide 1 m degree range around 00°C. The amount of copper complexing agent used may be at least an amount sufficient to complex copper ions, but in some cases, it may be used in an amount about 5 to 6 times the amount of copper. Alkali hydroxide is used to adjust the pH of the plating solution, and its pH range is suitably 11.5 to 13.0. Formaldehyde or the like is used as the reducing agent, preferably in a concentration range of 0.03 to 0.75 mol/1. In the present invention, the iron cyanide compound used as an additive is 0.01 to 5.0 g#! It can be used in a concentration range of 0.05 to 3.5 g/l, but a range of 0.05 to 3.5 g/l is preferable. Also, among the iron complexing agents, hydroxyethylethylenediaminetriacetic acid is extremely effective in trapping iron;
0.1~5.0g#! can be used over a concentration range of 0.6 to 3.5 g/l, preferably in the range 0.6 to 3.5 g/l, and only enough is needed to trap all of the iron in the iron cyanide, i.e. a maximum of iron equivalents; Since iron cyanide is unlikely to completely decompose and liberate iron during plating, it may actually be less than % equivalent of iron. Also, H
Adding an unnecessarily large amount of EDTA not only causes material loss but also impairs the luster of the deposited copper.

It was experimentally confirmed that the copper plating solution of the present invention has the characteristics shown in the following table. The composition of the basic plating bath used in the same table is copper sulfate 0.064 mol/CEDT
Ao, 075 mol/l.

Caustic soda 0.065 mol/l, formaldehyde 0.
It is 12 mol/2. The temperature of the bath was 75°C.

(Left below) In the above table, Examples 1 and 2 are examples of the electroless copper plating solution of the present invention using the additive of the present invention.

Comparative Examples 1 and 2 are conventional copper plating solutions that lack the iron complexing agent of the present invention.

Effects of the Invention Compared to conventional copper plating solutions, the electroless copper plating solution of the present invention does not cause precipitation of iron in the solution during plating, and as a result, no iron compounds are formed in the deposit shell. Since complex precipitation does not occur, the deposited surface is extremely smooth, making it possible to obtain a plating that is extremely suitable for the production of plates, plates, and metallization of plastics.

Claims (2)

[Claims] (1) Hydroxylethylethylenediaminetetratriacetic acid (HEDTA) and iron cyanide are simultaneously included in an aqueous solution consisting of a copper salt, its complexing agent, an alkali hydroxide, and a copper ion reducing agent. Electroless copper plating solution. (2) The electroless copper plating solution according to claim (1), wherein the amount of hydroxyethylethylenediaminetetratriacetic acid (HEDTA) is equal to or less than the equivalent amount of iron in the cyanide of iron.