Wire bonding performance and solder joint reliability investigation on ENEPIG finish substrate

ENEPIG (Electroless Ni Electroless Pd Immersion Au) finish is a new surface finish candidate in substrate fabrication for IC packages. It can miniaturize component size, increase routing density and make substrate design flexible. It is also competitive in cost as typical Au thickness of ENEPIG finish can be reduced to 0.20 μm below. ENEPIG has been used in wafer bump and solder ball pad surface in a few CSP or FCBGA packages already. However, applying ENEPIG to wire bonding finger is still a new technology because wire bonding process is sensitive to coatings properties. In this paper, characteristics of deposit from different vendors are inspected and went with feasibility studying of assembly process. The influence of Pd/Au thickness combination on bondability, solderability and solder joint reliability are investigated particularly. Results found that ENEPIG finish has a similar assembly process capability compared with Ni/Au finish. A board level drop and bending test indicates a better mechanical reliability performance of ENEPIG finish than that of Ni/Au finish. ENEPIG finish is advisable for both soldering and wire bonding applications.