The next generation of quick turn method for interfacial strength testing: High Speed Ball Shear

Abstract

In High Volume Manufacturing (HVM) environment, maintaining assembly process stability is the outmost priority to meet quality and reliability requirement. In recent years of transitioning to Lead Free (LF) solder alloy, tighter ball pitch and increasing hostile use condition, thus the expectation of better and tighter control in Solder Joint Reliability (SJR) is increasing. The SJR concern is not a new phenomenon, numerous research works are published to share the learning and options to resolve SJR issues including introduction of new solder alloy, Stress Compensation Layer (SCL), alternate surface finish and etc. The implementations of LF solder alloy have been found to be more at risk to brittle failure in the intermetallic layers. In view of the Flip Chip (FC) design requirement expands and evolves, it is important that the test metrology should likewise continue to evolve. The High Speed Ball Shear (HSBS) and conventional Cold Ball Pull (CBP) results are compared and discussed in term of the ability to predict susceptibility to interfacial failures due to assembly process changes for Flip Chip Ball Grid Array (FCBGA) packages. Examples of assembly process studies are Ball Attach (BA) reflow profile, effect of multiple reflows on the growth of intermetallic that affects the strength of solder joint performance, substrate plating process skew and etc. In additional, detailed microscopic analysis on post HSBS was executed to study the distribution and thickness of Intermetallic compound (IMC) layer on solder pad for FCBGA packages. The result showed that a higher sensitivity was demonstrated by HSBS as compare to CBP in assembly process shifts detection. This paper also covers the course of the development of fracture energy metric and implementations of HSBS metrology into HVM environment as an in line BA process monitoring system. Lastly, a comparison of the facture energy between ENIG and improve surface plating is provided to show the margin gained by improve surface plating technologies.