Mechanisms and solutions to the brittle solder joint in electroless Ni plating

Brittle solder joints in Electroless Ni electroless Pd immersion Au (ENEPIG) surface finishes are one of the key re­ liability issues in electronics assembly. Previous characterization of the reflow process has indicated that interfa­ cial voids formed after solder reflow are responsible for the decreases in solder joint strength. However, the mechanisms behind the formation of these voids in the ENEPIG process remain unclear. In this paper, the inter­ action between various aspects of the ENEPIG process and solder joint strength were investigated. Surface rough­ ness, morphology, and nano-pitting at the interface between electroless Pd and Ni-P were characterized. The size and density of nano voids inside Ni2SnP were measured after the specimens were reflowed with Sn4Ag0·5Cu sol­ der ball. Additionally, high speed shear solder joint strength measurements were made. The results indicated that anion adhesion induced nano-pitting at the interface between the Ni2SnP intermetallic and Pd, resulting in the formation of a nano void layer during reflow. These interfacial voids lead to lower solder joint strength. Based on the results, a solution to prevent the brittle solder joint failures is suggested.