Failure characterization of BGA solder joint fracture during field application

Abstract

This paper presents a systematic failure analysis approach on a field return Ball Grid Array (BGA) solder joint crack. The lead free BGA solder ball sits on Au/ Ni metallization with Sn-37.5Pb solder paste. The field return component exhibits no form of mechanical induced damage and destructive analysis showed a brittle fracture mechanism at the intermetallic compound (IMC) interface and a thicker IMC was observed when compared to a reference unit. Experimental works were carried out to investigate the effect of repeated numbers of reflow and shear test condition on the brittle failure mode of a solder joint. It has been found out that when the sample was reflowed at the component level, the IMC layer thickness did not increase significantly with the increase of the numbers of reflow. The shear force of the solder joint did not vary much either regardless of high or low shear speed and the failure mode are almost ductile. When the sample was reflowed at the board level, the thickness of the total IMC layer increased significantly with higher numbers of reflow. Low speed shear yields mainly ductile failure mode while high speed shear observed more brittle failure mode linearly in relation to the higher numbers of reflow. The shear strength of the solder joint with brittle failure mode is about 2/3 of that with ductile failure mode. Thus, this experiment setup is able to simulate a replica of the field failure under mechanical shocking condition with the hypothesis proven of multiple reflow which result in thicker IMC that can lead to solder joint crack.