JPS6227152B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electroless copper plating solution, and more particularly to an electroless copper plating solution that provides plating copper with high tensile strength and excellent bending fatigue strength. Research and development to improve the mechanical properties of copper obtained from electroless copper plating has been actively carried out, and one of the reasons why it is still active is that this electroless copper plating This is because the application of the mounting technology to circuit formation on printed wiring boards has the potential to produce great effects. That is, the circuit density of printed wiring boards is becoming higher and higher year by year, and the diameter of through holes for conducting circuits on different surfaces is becoming smaller and smaller. Under these circumstances, electroless copper plating is expected to produce less difference in the plating thickness between the flat surface and the inner wall surface of the through-hole compared to electroplating methods. In addition, in the method of electroplating and etching away copper other than the circuit (subtract method), etching creates an undercut (in the thickness direction of the copper).
Although the dimensions of the surface portion are maintained by the etching resist film, etching progresses further near the substrate, resulting in an inverted trapezoidal cross section of the circuit. ), making it difficult to create thin wire circuits. On the other hand, in electroless copper plating (additive method), only the circuit portion is plated, so there is no undercut problem and it is advantageous for thinning the circuit. However, most electroless copper plating to date has been
The physical properties of copper (pyrocopper) obtained from pyrophosphate electroplating, which is generally used to form circuits on printed wiring boards, are inferior to the tensile strength and bending fatigue strength measured by the method described later. Because of this, the reliability of the product is not very high. That is, there is a drawback that circuits are easily broken due to heating caused by soldering after components are mounted on a printed wiring board. The tensile strength of pyro-copper is 50 to 60 Kg/mm ² , and the bending fatigue strength is 2000 to 3000 times at a thickness of 25 μm. In contrast, the tensile strength of copper obtained from electroless copper plating, which is used on an industrial level, is approximately 30 kg/mm ² , and the bending fatigue strength is 800 to 1100.
times (25 μm). Wiring boards with high-density wiring circuits also require high connection reliability, so electroless copper plating is rarely used, even though it is advantageous for increasing wiring density for the reasons mentioned above. is the current situation. Therefore, if the physical properties of copper obtained by electroless copper plating are improved and brought closer to those of pyrocopper, for example, a new path will open up. The present invention has been made in view of these points, and includes a silver ion supply source, diol, hydroxycarboxylic acid, Added at least one of dicarboxylic acid, diamine, cyanohydrin, mono- or dialkyl ether of ethylene glycol, aliphatic secondary or tertiary amine having a hydroxy group, O-methyl-ethanolamine, P-dioxane, morpholine, and piperazine. It is characterized by Silver ion sources include metallic silver, silver iodide,
Silver bromide, silver chloride, silver nitrate, silver sulfate, silver cyanide,
At least one type of silver compound such as silver acetate or silver carbonate is used. Silver ions improve the mechanical strength of the plated copper obtained, especially the tensile strength and bending fatigue strength. When metallic silver or silver iodide is used as a silver ion source, an addition amount of 1 mg/m is sufficient, but even if the amount is more than this, the plating solution will not become unstable and decompose. This is metallic silver,
This is because the solubility of silver iodide is extremely low. The solubility in water is 2.8× at 25℃ for metallic silver.
10 ^-5 g/(2.6 x 10 ^-7 mol/), in the case of silver iodide, 3.4 x 10 ^-5 g/(1.4 x 10 ^-7 mol/) at 20°C.
). On the other hand, other silver compounds (such as silver nitrate) generally have high solubility, so if more than a certain amount is added, the plating solution becomes unstable and easily decomposes. This is because the concentration of silver ions in the plating solution increases. In this case, decomposition can be suppressed to some extent by adding a large amount of stabilizer, but even in that case there is a limit. When using a highly soluble silver ion source,
These compounds have been shown to increase the silver ion concentration in the plating solution, improve the mechanical strength of the plating, that is, improve the tensile strength and bending fatigue strength, and raise the concentration so that the plating solution does not become unstable and decompose. will be supplied in sufficient quantity. Generally, the concentration of silver ions in the plating solution is 10 ^-10
-10 ^-3 mol/more preferably 10 ^-8 -10 ^-5 mol/. Diols, hydroxycarboxylic acids, dicarboxylic acids, diamines, cyanohydrins, mono- or dialkyl ethers of ethylene glycol, aliphatic secondary or tertiary amines with hydroxy groups, O
-Methyl-ethanolamine, P-diokigane,
Morpholine and piperazine improve the stability of electroless plating solutions. The general formula of each of the above substances is expressed as follows. That is, diols are HO—R ₁ —OH, hydroxycarboxylic acids are HO—R ₂ —COOH, dicarboxylic acids are HOOC—R ₂ —COOH, and diamines are H ₂ N—
R ₄ -NH ₂ , cyanohydrin is HO-R ₅ -CN, mono- or dialkyl ether of ethylene glycol is R ₆ -O-CH ₂ CH ₂ -OH or R ₇ -O-
CH ₂ CH ₂ -O-R ₈ , an aliphatic secondary or tertiary amine with a hydroxy group is R ₁₀ -NH-R ₉ -OH or R ₁₃ R ₁₂ N-R ₁₁ -OH, O-methyl-ethanolamine is H ₃ C―O―CH ₂ CH ₂ ―NH ₂ , P-dioxane is

[Formula] Morpholine is

[Formula] Piperazine is

[Formula]. Examples of diols include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, 1,10-decanediol,
1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 2,5-hexanediol, etc. are used. Examples of hydroxycarboxylic acids include glycolic acid, β-hydroxypropionic acid, and 3-hydroxycarboxylic acid.
Hydroxybutyric acid and the like are used. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, methylsuccinic acid,
Maleic acid, fumaric acid, etc. are used. Examples of the diamine include ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5
-Pentanediamine, 1,6-hexanediamine, etc. are used. Examples of cyanohydrin include ethylene cyanohydrin. Examples of ethylene glycol mono- or dialol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether,
Cotylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-iso-butyl ether, ethylene glycol mono-n-hexyl ether, ethylene glycol monophenyl ether or ethylene glycol dimethyl ether, ethylene glycol diethyl ether are used. Ru. As the aliphatic secondary or tertiary amine having a hydroxy group, for example, N-methylethanolamine, N-ethylethanolamine, N,N-dimethylethanolamine or N,N-diethylethanolamine is used. Diols, hydroxycarboxylic acids, dicarboxylic acids, diamines, dianhydrins, mono- or dialkyl ethers of ethylene glycol, aliphatic secondary or tertiary amines with hydroxy groups, O
-Methyl-ethanolamine, P-dioxane,
The amount of morpholine and piperazine added is 0.001g/
Above, preferably 0.01 to 10 g/, most preferably 0.5 to 5 g/. If the amount added is less than 0.001 g/l, the stability of the plating solution decreases, and the physical properties of the plated copper, ie, tensile strength and bending fatigue strength, decrease. Even if the amount added is large, there will be no adverse effect, but addition of more than 10 g/l is generally unnecessary. 0.001g/amyl alcohol, preferably
It is also possible to further add 0.01-10g/most preferably 0.5-5g/. The electroless copper plating solution that is the base of the present invention is not particularly formulated. A general electroless copper plating solution consisting of a copper salt, a complexing agent, a reducing agent and a PH adjuster is used. Copper salts include copper sulfate, copper halides, copper nitrate, copper acetate, etc. Complexing agents include ethylenediaminetetraacetic acid, Rothsiel's salt, etc. Reducing agents include formalin, paraformaldehyde, etc., and pH adjusters include Sodium hydroxide etc. are used. Typical electroless plating solutions include 3 to 20 g of copper sulfate, ethylenediaminetetraacetic acid, 1.2 to 3 times the molar concentration of the copper salt, 2 to 25 ml of a 37% formalin aqueous solution, and a pH of 11.5 to 13.0. Preferably. It is best to keep the temperature below 90℃. As explained above, by using the electroless copper plating solution of the present invention, a matted copper having excellent tensile strength and bending fatigue strength was obtained. Examples 1 to 9 Copper sulfate 0.04 mol/ethylenediaminetetraacetic acid
0.05 mol/, formaldehyde 0.03 mol/,
An electroless copper plating solution was prepared by adding the additives listed in the table below to a solution with a pH of 11.8. An activated stainless steel plate was immersed in these plating solutions and subjected to electroless plating at 70°C to obtain a copper foil having a plated film thickness of 25 to 35 μm. The plating precipitation rate, tensile strength and bending fatigue strength of the resulting copper foil are as shown in the following table. The tensile strength was measured using a 10 mm x 70 mm test piece using a Tensilon type universal testing machine manufactured by Toyo Sokki at a gripping interval of 15 mm and a tensile speed of 1 mm/min. In addition, the bending fatigue strength was measured using a bending fatigue tester conforming to JIS P8115. The radius of curvature of the bending point was 2 mm. According to this tester, the bending fatigue strength is indicated by the number of times the sample is bent until it breaks.

[Table] Comparative Examples 1 to 3 Copper sulfate 0.04 mol/, ethylenediaminetetraacetic acid
0.05 mol/, formaldehyde 0.03 mol/,
An electroless copper plating solution was prepared by adding the additives listed in the following table to a solution with a pH of 11.8, and its properties were measured in the same manner as in the examples.

【table】

Claims (1)

[Scope of Claims] 1. An electroless copper plating solution containing a copper salt, a complexing agent, a reducing agent, and a PH adjuster, a silver ion source, and a diol, hydroxycarboxylic acid, dicarboxylic acid, diamine, cyanohydrin, and ethylene. An electroless copper plating solution containing at least one of glycol mono- or dialkyl ether, aliphatic secondary or tertiary amine having a hydroxyl group, O-methyl-ethanolamine, P-dioxane, morpholine, and piperazine. 2 Add the silver ion source to the electroless plating solution so that the concentration of silver ions is such that the tensile strength and bending fatigue strength of the resulting matted copper are improved and the plating solution does not decompose. At the same time,
Diols, hydroxycarboxylic acids, dicarboxylic acids, diamines, cyanohydrins, mono- or dialkyl ethers of ethylene glycol, aliphatic secondary or tertiary amines with hydroxy groups, O
-Methyl-ethanolamine, P-dioxane,
At least one of morpholine and piperazine
The electroless copper plating solution according to claim 1, in which 0.001 g/or more is added. 3. The electroless copper plating solution according to claim 1 or 2, wherein the silver ion source is metallic silver or silver iodide.