Fluxless flip chip bonding processes and aerial fluxless bonding technology

New fluxless flip chip processes of Sn-rich non-eutectic Au-Sn solder bumps were developed using vacuum deposition and electroplating technique. It is believed that this is the first report that non-eutectic Au-Sn flip chip solder bonding is achieved without the use of flux. In order to make 200mum diameter and 10mum thick Au-Sn solder bump 0.03mum of Cr, 10mum of Sn and 0.3mum of Au were vacuum deposited on the Si wafer through the high carbon steal stencil mask. Nearly void-free solder bumps with small grains of AuSn4 intermetallic compound were achieved. The re-melting temperature of solder bumps was measured to be 220°C.; In the second part, first, the fluxless bonding process was performed in hydrogen environment with electroplated 4 mm x 4mm Au-Sn multi-layer chips if electroplating technique is compatible with our process. High quality and nearly void free solder joint was successfully achieved with this new process. After proving compatibility of the process, tall electroplated Sn/Au bumps (50 mum) were produced by photolithography method using Su-8 photoresist. The bumps in the chip were flip chip bonded to the borosilicate glass wafer coated with Cr (0.03 mum) and Au (0.05 mum) pads without using any flux.; Fluxless and lead-free bonding technology in air ambient based on non eutectic 5 at. % Au-95 at. % Sn and eutectic 57 at. %Sn-43 at. % Bi with Au capping layer have been developed and studied. To understand the fluxless bonding principles in air ambient, phase formation mechanism of Au-Sn intermetallics embedded in Bi matrix has been postulated. The Au-Sn intermetallic-capping layer covers most outer surface of the samples and inhibits formation of oxide layer due to the minimizing exposure of (beta-Sn) phase to the air.; In conclusion, new-lead free and fluxless bonding processes for flip chip packages were developed. In this work, Sn-rich Au-Sn flip chip solder bumps using vacuum deposition and electroplating process were successfully produced. It is believed that the processes presented in this dissertation offer additional process windows to lead-free flip chip technology and have various applications where flux cannot be used such as optoelectronic devices, biomedical devices, and MEMS (MicroElectroMechanical Systems) devices. Aerial fluxless bonding technology was also reported for the first time in my knowledge. Although conventional fluxless bonding processes has been successfully adopted in many application, the need of specific ambient gases such as forming gas or hydrogen is not compatible with pick-and-place bonding machines in the electronic industry. Thus, fluxless bonding technology in air ambient could provide a valuable and economical alternative way to the electronic and photonic packaging industries. (Abstract shortened by UMI.)...