Reliability of Cu to Cu joints fabricated using SnAg capping layer for 3D applications

Abstract

Chip to Chip bonding technology using Cu bumps with solder capping layer has been widely investigated for 3D chip stacking applications. We studied the reliability of the Cu joints. Cu bumps capped with Sn-Ag solder layer were joined to bare Cu pads or Au/Ni electroplated Cu pads at 300°C for 10 sec after dispensing non-conductive paste (NCP). After joining, there were no failed joints and the contact resistance of the joints was very low in all specimens. High temperature storage (HTS) test (120°C, up to 2000 hrs) results demonstrated that the reliability was good in all specimens, while thermal cycling test (-55°C /+125°C, up to 2500 cycles) results showed that the contact resistance of the joints increased quickly after 2000 cycles which was attributed the crack formation in the joint interfaces.