Micro void growth in NiSnP layer between (Cu,Ni)_6Sn_5 intermetallic compound and Ni3P by higher reflow temperature and multiple,reflow

摘要

This study examines the growth mechanism of micro void called "Kirkendall voids" within NiSnP nano-crystalline layer between (Cu,Ni)_6Sn_5 intermetallic compound (IMC) and Ni_3P 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 Sn from (Cu,Ni)_6Sn_5 into NiSnP layer is much slower than the outward flux of Sn from NiSnP layer into Ni_3P, 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.