Micro void growth in NiSnP layer between (Cu,Ni)(6)Sn-5 intermetallic compound and Ni3P by higher reflow temperature and multiple reflow

Abstract

This study examines the growth mechanism of micro void called "Kirkendall voids" within NiSnP nano-crystalline layer between (Cu,Ni)(6)Sn-5 intermetallic compound (IMC) and Ni3P formed during two double reflow processes. The micro voids in NiSnP layer formed at the first reflow grow faster under the elevated reflow temperature than under the standard lead-free reflow, during the second reflow process. Despite the diffusion barrier Ni(P), the inward diffusion flux of Sit from (Cu,Ni)(6)Sn-5 into NiSnP layer is much slower than the outward flux of Sn from NiSnP layer into Ni3P, consequently leaving voids as NiSnP thickness increases. Results show that the thermal activation energy through the elevated reflow temperature has a higher influence in micro void growth than the number of reflows for the inward and outward diffusion flux difference of Sn within NiSnP layer in electroless Ni(P)/immersion Au and SnAgCu reaction system.