JPH0369191B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an improvement in a method of copper plating on an alumina substrate. With the increasing density of printed circuit boards, polyimide, alumina, metal, and the like are being considered and put into practical use as substitutes for epoxy resin for the base material of printed circuit boards. (Prior art and its problems) By the way, in order to form a circuit on an alumina substrate,
Conventionally, paste, dry plating, wet plating, etc. have been used, but since the adhesion between copper and alumina substrate is poor in wet plating, various pretreatment methods are being investigated. However, no pretreatment method that can improve adhesion has yet been developed. (Objective of the Invention) The present invention was made in view of the above circumstances, and it is an object of the present invention to improve the copper plating process without improving the pretreatment method, and to provide a method for copper plating on an alumina substrate with excellent adhesion. It was developed. (Means for Solving the Problems) In the method of copper plating on an alumina substrate according to the present invention, first, a normal pretreatment for applying electroless copper plating to an alumina substrate is performed, and then electroless copper plating is applied to the alumina substrate by 0.5%. ~
After applying 2μ coating, washing with water and drying, heat treatment at 300 to 900℃ in an oxidizing atmosphere, further treatment at 200 to 900℃ in a reducing atmosphere, and then electroless copper plating.
It is characterized by applying copper plating of 0.5 to 2μ and then electrolytic copper plating to obtain a predetermined copper plating thickness. (Function) In the copper plating method of the present invention, the thickness of the initial electroless copper plating on the alumina substrate is set to 0.5~
The reason for setting the value to 2μ is to ensure that the copper and alumina are sufficiently wetted during the heat treatment in the post-process, and to obtain the necessary film thickness to cover the alumina surface.If it is less than 0.5μ, sufficient adhesion cannot be obtained, and if it exceeds 2μ. Although there is no problem with the adhesion between the copper and the alumina, the copper plating itself will peel off. The heat treatment temperature was set at 300 to 900°C because if it is less than 300°C, the reaction between copper and alumina is insufficient, and if it exceeds 900°C, the reaction is too active and a brittle phase is produced. The reason why the heat treatment atmosphere is an oxidizing atmosphere is because the reaction between copper and alumina is essentially a reaction between copper oxide and alumina, and it is particularly preferable to use the atmosphere because it is most easily obtained. The reason why the heat treatment is further performed in a reducing atmosphere is to reduce CuO in the surface layer and improve adhesion to electroless Cu plating performed in the next step. Here the temperature is 200~900℃
This is because reduction is insufficient below 200℃.
Furthermore, at temperatures above 900°C, the reaction between Cu and Al ₂ O ₃ becomes active and a brittle phase is formed. Furthermore, electroless copper plating of 0.5 to 2 μm is applied after heat treatment to ensure that the final electrolytic copper plating is performed reliably. This is because problems such as cracks occur and a uniform surface cannot be obtained. This second electroless copper plating results in plating of a composite oxide film of Cu and AL, and the adhesion is sufficient. Next, a specific example of the method of copper plating on an alumina substrate according to the present invention will be compared with a conventional wet plating method. [Example] After performing the usual pretreatment for applying electroless copper plating to an alumina substrate, 1μ of electroless copper plating was applied,
Next, it was washed with water, dried, and then heat-treated at 500°C for 30 minutes in a heating furnace open to the atmosphere, and further heat-treated at 500°C in a H ₂ stream for 30 minutes. Next, 1μ electroless copper plating was applied.
Thereafter, electrolytic copper plating of 20 μm was applied to form a copper plating with a total thickness of 21 μm. [Conventional example] After performing the usual pretreatment for wet plating on an alumina substrate, it was deposited in a copper plating bath at 30℃ for 30 minutes, electroless Cu plating was applied to 1μ, and immediately after washing with water. , electrolytic copper plating was applied to 20μ to form a 21μ thick copper plating. However, when the adhesion of the copper-plated circuits on these alumina substrates was measured by a peel test, the results shown in the table below were obtained.

[Table] As is clear from the table above, the copper plating on the alumina substrate obtained by the copper plating method of the example is compared to the copper plating on the alumina substrate obtained by the conventional wet plating method. It can be seen that the degree of adhesion is extremely high. (Effects of the Invention) As can be seen from the above explanation, according to the method of copper plating on an alumina substrate of the present invention, highly adhesive copper plating can be performed on an alumina substrate without special pretreatment. It has the excellent effect of being able to

Claims (1)

[Claims] 1 After pre-treating the alumina substrate for electroless copper plating, apply 0.5 to 2μ of electroless copper plating, then wash with water,
After drying, it is heat treated in an oxidizing atmosphere at 300-900℃, further treated at 200-900℃ in a reducing atmosphere, then electroless copper plating is applied to 0.5-2μ, and then electrolytic copper plating is applied. A method for plating copper on an alumina substrate, the method comprising: applying copper plating to obtain a predetermined copper plating thickness.