Influence of Electroless Ni-P Film Condition on Wire Bondability

With increasing thickness of electroless gold films (greater than 0.5 μm) as a top layer, Au/Ni film shows good wire bondability. However, we confirmed that the deposited nickel structure influences wire bondability for thinner (less than 0.5 μm) electroless gold plating after heat treatment because of the different diffusion behavior of gold on the deposited nickel used as an underlayer. In this study, two types of electroless nickel plating structure with columnar and layered structure were observed and bondability was evaluated. Auto-catalytic gold of 0.2 μm thickness on the layered nickel deposits shows good wire bondability after heat treatment because the gold was deposited uniformly. In contrast, for a columnar structure, the gold on the Ni films shows poor wire bondability after heat treatment because of local corrosion occurring at the initial stage of gold immersion and because the subsequent auto-catalytic gold is not evenly distributed.