IMC Evolution and Reliability of Lead-free Solder Bump Formed by Induction Self Heat Reflow

Induction self heat reflow (ISHR) technology, which has the advantages of 3-D selective heating and high heating speed, can solve the problems which can´t be controlled in traditional reflow technologies, such as inhomogeneous heating of ball grid array (different bumps), simultaneous heating of chip and carrier with solder ball, etc., which have been increasingly serious with the development of packaging technology. In this paper, the results of the aging experiment and bump shear experiment of Sn_3.5Ag and Sn₃Ag_0.5Cu solder bumps reflowed on the Au/Ni/Cu pad respectively are used for evaluating the reliability of the bumps manufactured through ISHR. It is shown that the bumps can supply sufficient shear strength for use. Three kinds of different shear failure behaviors controlled by different failure mechanisms are observed. During the aging time a continual pure Ni_xSn₄ layer exists at the interface of Sn_3.5Ag solder bumps, and dispersed (Au_x,Ni_1-x)Sn₄ inside solder matrix. Two quaternary Au-Ni-Cu-Sn IMC layers, (Cu,Ni,Au)₃ Sn close to Ni layer and (Cu,Ni,Au)₆Sn₅ close to solder bulk, existed at the interface of the Sn_3.0Ag _0.5Cu bump after aging. IMC thickness increased linearly with square root of aging time. The IMC growth was a diffusion controlled process