Study on the Thermosonic Flip Chip Bonding of Chips with Copper Interconnect onto rigid and flex substrate

• Main Authors: Qing-An Liao, 廖慶安
• Other Authors: J. N. Aoh
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/71394271671884811093

碩士 === 國立中正大學 === 機械工程所 === 95 === In this study, thermosonic bonding was applied to flip chip bonding of Cu chip to alumina substrate. The effect of flip chip bonding parameters and high temperature storage（HTS） on the shear strength was discussed. Investigation of bonding strength variation with die shear test was conducted. It has been verified that the bonding strength beyond the standard value was achieved. The effect of flip chip parameters including ultrasonic power, bonding force and bonding time was studied. High ultrasonic power resulted in deformation of gold stud bumps and achieved greater bonding strength between chip and substrate. The bonding strength first increased with increasing bonding force then the bonding strength remained a steady value, the gold stud bumps and alumina substrate revealed a satisfactory bonding when bonding force higher than 995 gf. Too short a bonding time and insufficient ultrasonic power resulted in poor bonding between the gold stud bumps and alumina. Too long a bonding time and too high a ultrasonic power caused separation between gold stud bumps and silver layer and resulted in poor bonding strength. The bonding strength increased with increasing hold temperature after HTS test. Investigation on the bonding morphology between gold stud bump and silver layer revealed a defect free interface, thus the reliability of HTS for gold stud bumps onto the silver bonding layer was not a issue of concern. The optimal processing parameters are as following：ultrasonic power 4.52 W, bonding force 995 gf, bonding time 0.5 sec, bonding temperature 200℃. A further objective of this study was to investigate the bonding of Cu chip onto flex substrate with the addition of non-conductive paste（NCP）. The effect of flip chip bonding parameters including ultrasonic power, bonding force, curing temperature and curing time were investigated. We found that the ultrasonic power was the most relevant process parameter. The ultrasonic power play an important role in removing partly NCP on flex substrate during bonding process, so that gold stud bump could bond onto copper electrode layer to form an electrical path between the gold stud bump and the flex substrate. Too large a bonding force caused insufficient filling of NCP paste as an underfill between Cu chip and resulted in deterioration of bonding strength. Too low a curing temperature caused insufficient cure of NCP and resulted in lower bonding strength. The optimal processing parameters achieved in the study were as following：ultrasonic power 14.46 W, bonding force 500 gf, curing temperature 140 ℃, curing time 40 sec, bonding time 0.5 sec, Cu chip prior temperature 200℃. Keywords：Ultrasonic flip-chip bonding process, alumina substrate, flex substrate, non-conductive paste（NCP）.