Microstructure Study of High Lead Bump FCBGA Bending Test

The solder bump interconnection is originated by IBM in the early 1960s and Flip chip technology became popular in packaging. Comparing with conventional wire bonding interconnection package method, flip chip interconnection can offer excellent electrical performance, very small chip size packages and high input/output handling capability. Recently, organic substrates have replaced conventional ceramic substrate. It is due to that the organic substrate can provide a minimal board area requirement, such as a reduction in weight and height profile. Therefore, the interconnection of flip chip was made of high melting solders on the chip combined with low melting solders on the organic substrates. Solder joint fatigue failure is a serious reliability concern in area technologies. Different test environment induced solder joint microstructure change and intermetallic compound growth, such as the thermal cycle test, high temperature and mechanical bending cycle. Therefore, the solder joint microstructures is the important information to find out the root cause of failure for varied test environment. In this study, the microstructure of high lead bump attached on 63Sn/37Pb solder substrate is investigated. Back scattered scanning electron microscopy (BS-SEM) and energy dispersive X-ray (EDX) were employed to examine the morphology and the composition of combination solders and intermetallic compounds layers. The solder microstructure of the change with the reflow process, high temperature storage test and mechanical 3 point bending cycle test is observed. There are three kind of loading force, as 5, 30 and 45 psi. The study results showed that the solder microstructure coarsened and intermetallic compound layers grew after solid aging condition. Most of Sn phase congregated at the substrate side and coarsening. If the solid aging time increases, the Sn phase in the solder is gradually consumed and diffuses to the interface of bump and substrate side to form the IMC formation.