The effects of Au film thickness on the reliability of Sn-Pb solder joints

Ceramic ball grid array (CBGA) modules are high density, high-performance surface mount (SMT) packages. With miniaturization of solder joints in electronic packaging, the intermetallic compound (IMC) which formed at the interface between the solder ball and under bump metallization (UBM) have considerable effects on the reliability of solder joints. In this paper, the effects of Au film thickness on the growth of IMC were studied, including with the type, the composition and the thickness of IMC. And the mechanical properties of IMC were studied using ball shear tests and ball pull tests. Based on the growth of IMC under different aging time, the effects of IMC on Board-Level reliability of solder joints under thermal store load conditions were researched. Finally, the effects of IMC thickness on the thermal fatigue reliability of solder joints under thermal cycling load were analyzed by the electric on-off tests of the daisy chain. The result demonstrate that, the thickness of IMC increase rapidly due to the augment of Au film thickness, which might lead to "black pad" and the strength of solder joints reduce radically, as while as the shorten of the fatigue life.