Analysis of Crack Formation in Germanium Substrate at AlInGaP Die Bonding Process

摘要

Cracked die is a serious failure mode in Light Emitting Diode (LED) industry – affecting the LED quality and long-term reliability performance. In this paper, an investigation has been carried out to find out a relation between die bonding force and the occurrence of die crack at Germanium (Ge) substrate due to die attach (DA) ejector pin indentation. Based on the analysis, the results show that cracks start to occur at 60 gram-force (gF) bond force and above. The crack length at the die substrate increases with respect to the bond force. These indented dies were further analyzed by using Scanning Electron Microscope (SEM). The results show plastic deformation, slip traces and material pile-up at the vicinity of ejector pin crater. Some samples were sectioned using Focus Ion Beam (FIB) and it was found the crack depth does not exceed beyond 20.5μm and it follows the (111) plane. These findings, concludes that cracks start to appear at 60gF and they are confined to surface level even indented at extreme load (140gF). These cracks are far away from the active region of LED.