Improvement of the Bonding Reliability of Electroless Thin-film Ni/Au Plating Using Co Activation

We developed Co activation using reduction reaction and the bonding reliability when making thinner of the electroless Ni- P plating film was improved. Co activation was uniformly formed by reduction reaction, directly above the electroless Ni- P plating film also was uniformly deposited, and the plating film covering was improved. As a result, we considered that superior solder wettability and solder joint strength were obtained even with electroless Ni- P plating film thickness of 0.5μm and that Cu diffusion wasn't occurred in the solder when the solder was bonded.

I. Introduction

In recent years, as electronic devices have become smaller, Cu wiring on circuit boards has become finer. Therefore, bonding reliability in limited area is important. To improve the joint reliability of solder and wire bonding, electroless Ni-PI Au(5.0/ 0.05 μm) plating or electroless Ni-P/Pd/ Au(5.01 0.11 0.05 μm) plating is used as the metal finishing on Cu wiring [1]–[3]. However, with this method, when the Cu wiring is further miniaturized, there is concern about shorts between wirings due to thick electroless Ni-P film. To solve this problem, it must be reduced thickness of the electroless Ni-P plating film. However, if the electroless Ni-P plating film is made thinner, there are concerns that it is susceptible to occurrence of voids due to excessive dissolution of the Cu, and deterioration of plating film coatability due to the formation of non-uniform Pd activation.