Low stress bonding for large size die application

For 3D packages and large die application, large warpage and stress on low-k layer during bonding process are most significant problems. Therefore the bonding techniques for these applications require a low temperature bonding process to reduce stress during bonding process. In this paper, we will discuss the warpage behavior during bonding process using Sn57wt%Bi (Sn57Bi) solder and Sn3.0wt%Ag0.5wt%Cu (SAC305) with a large die (20×20 mm). We investigated stress change of bump interconnection area as a function of distance from the center of chip by Electron backscattered diffraction (EBSD) analyses. The full assembly packages were evaluated by thermal cycling (TC) test. And we also discuss the difference of warpage and the stress change between mass reflow process and thermal compression bonding (TCB). Regarding mass reflow process, by using Sn57Bi solder, the warpage after reflow was reduced more than 60 % compared with the use of SAC305. By using SAC305, large crack observed at the corner bump after TC 500 cycles. By using Sn57Bi, any voids or cracks was not observed after TC 1000 cycles. Regarding bonding process, by using SAC305 solder, the warpage after TCB process was less than 2/3 compared with the case of mass reflow process. In the case of TCB process, we will need to reduce the stress of the interface of solder / substrate pad.