Effects of bond temperature and pressure on microstructures of tape automated bonding (TAB) inner lead bonds (ILB) with thin tape metallization

In view of the advantages of low cost, simple manufacturing process and significant miniaturization in size, Tape Automated Bonding (TAB) technology is important to the future development of consumer electronic products. Inner lead bonding (ILB) process is especially crucial for the production of high quality TAB packages and components. In this investigation, the effects of two critical bonding parameters: bond temperature and bond pressure on the final ILBs integrity and microstructures have been studied. The possibility of gang bonding 0.4 μm Sn-plated Cu lead beams with straight wall gold bumps to form reliable TAB inner lead bonds is demonstrated in this study. The variations in microstructure of ILB joints have been studied by microsectioning, metallography, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) Spectroscopy. The gold rich Au/Sn(30/20 wt.%) eutectic structure and ζ phase have been observed, However, it was found that the Au/Sn eutectic exhibit different structures as the bond temperature and pressure were changed. Binary Au/Sn and ternary Au/Sn/Cu intermetallic compounds have also been detected. The adhesion of the bonded interface has been studied by mechanical pull test. Lead pull values and the failure modes obtained are discussed with the result of microstructural evaluations