The use of acid copper plating process for via-filling effectively forms interlayer connection in build-up PWBs with high-density interconnections. However, in the case of copper film deposited in a bath, which is greatly dependent on the effects of additives like via-filling technique, the drop in mechanical properties and the increase in stress in electro-deposits due to co-deposition of the additives are likely weaknesses. In view of such weaknesses, we concentrated our study on the mechanical properties of the copper films plated in two types of conformal acid copper plating baths that have been in use for some time and two types of acid copper plating baths for via-filling. As a result, selection of suitable additives was confirmed to be of great importance for the acid copper plating bath for via-filling. The use of the additives that easily deposit with copper was likely to cause drop in mechanical properties of the film. On the other hand, the fact that the acid copper plating process for via-filling nevertheless deposits a film comparable to that out of the recognized conformal type acid copper plating bath in the use of the most suitable additives was confirmed.
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