A comprehensive investigation of the galvanic corrosion induced Ag-Al bond degradation in microelectronic packaging using Argon Ion Milling, SEM, Dual Beam FIB-SEM, STEM-EDS and TOF-SIMS

摘要

It is known that Ag-Al bonds have strong tendency to degrade due to excessive interdiffusion and to oxidize in the presence of contaminants such as the moisture and corrosive ions, hence form a risk for both the bonding quality and the reliability of microelectronic devices [1]. However, people seldom carry out an in-depth analysis of the microstructural and the chemical information in the degraded Ag-Al bond and investigate the bond degradation mechanism in a packaging module. In this study, a comprehensive investigation of the Ag-Al bond degradation mechanism in an electrically failed module using the Argon Ion Milling, Scanning Electron Microscopy (SEM), Dual Beam Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (STEM-EDS) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is reported. It is found that the bond degradation is due to the galvanic corrosion in the Ag-Al bonding area. Specific attention is given to the information of microstructures, elements and corrosive ions in the degraded bond. Moreover, since obvious micro-delaminations were observed between the moulding compound and the Ag plated lead frames at the edge of the fresh module without any bond degradation, it is suspected that the micro-delamination acts as a potential path allowing the moisture and the corrosive ion Cl~- to seep in and attack the bonding area, leading to the galvanic corrosion in the Ag-Al bonding area. Eventually, the bond was detached due to the Cl~- accelerated galvanic corrosion. Comparing the analytical results at two lead locations in the same packaging module, it is believed that the bond degradation is highly related to the packaging designs.