OPTIMIZATION OF PROCESS PARAMETERS IN LASER TRANSMISSION BONDING TO INCREASE THE SHEAR STRENGTH OF AU-SN (IMCS) JOINT

Abstract Au-Sn solder has been currently used for soldering the laser diode silicon chip on the slider surface which is alumina (Al2O3) titanium carbide (TiC) in hard disk drive (HDD). However, intermetallic compounds (IMCs) form at the interface during the bonding process and result in cracks within these interfacial IMCs. As a consequence, the bonded joint failure occurs for Au-Sn (IMCs) joints with low shear stress. The shear stress is considered a major contributor to the quality and reliability of HDD. At present, the average shear strength of the Au-Sn (IMCs) joint is approximately 2.716 MPa. In this work, 4,572 Au-Sn bonded samples using the laser transmission bonding process were analysed to find suitable bonding factors to improve the shear stress of Au-Sn (IMCs). The analyse phase utilizes heat map correlation to determine 5 key process input variables (KPIVs) including (1) Temperature, (2) Stage Cross-Track (CT), (3) Stage Down-Track (DT), (4) Z-height (5) Laser power. The key process output variable (KPOV) is the shear strength of the IMCs layer between the laser diode silicon chip and the Alumina Titanium Carbide (AlTiC) substrate. Then, a response surface methodology (RSM) is performed to provide the significant factors that generate a reliable mathematical relationship between the process parameters and the desired response. The confirmation experiment performed illustrates that the new process setting of the IMCs shear strength layer is increased from 2.716 MPa to 5.050 MPa which accounts for 85.94% which is a significant improvement.