Evaluation of UBM Prepared by Electroless Ni Plating Method.

The advantage of forming under barrier metal using the electroless plating method, compared to electro-plating method, is that the electroless plating method requires less process steps, which means less time will be required. Normally, when applying solder to electroless nickel plated surface in phosphoric acid bath, a fragile layer of enriched phosphorus is formed between the two metals. It is also a fact that this enriched phosphorus layer is easily destroyed by external stress such as thermal stress.In this paper, we have formed a solder bump (pad) onto the surface of the under barrier metal formed using the electroless nickel plating process, controlling the phosphorus density. As a result of analyzing the movements of the phosphorus density of the joining layers before and after the several acceleration tests, we were able to see a trend that by controlling the electroless nickel plating process, we are able to regulate the phosphorus within the plating layer.