Interfacial reaction between the electroless nickel immersion gold substrate and Sn-based solders

The electroless nickel immersion gold (ENIG) surface finish is widely used in electronic packaging. The ENIG induced Au embrittlement has been investigated in SnPb/ENIG/Cu solder joint since several years ago. However, in Sn-based lead-free solder joint, discrepancies still exist about the influence of Au finish on the reliability of the solder joint. This study investigated the effects of ENIG surface finish on the interfacial reaction and thus the mechanical property of Sn-based solder joints. Experimentally, two types of ENIG with different thickness of Au layer were fabricated. The results indicated that the Au layer dissolved into the solder matrix readily in the soldering stage, and then affected the shear strength of the solder joint significantly. The Au migration occurred in the solder joint during isothermal aging. The Au migration is more apparent when the Cu6Sn5 type compound formed at the interface. The embrittlement caused by the weak interface between the (Au1-xNix)Sn-4 and Ni3Sn4 layers cannot be observed in this study. (C) 2009 Elsevier Ltd. All rights reserved.