Reliability of 20 μm pitch ncf type cof package with compliant-bump

Abstract

In this study, three kinds of nonconductive film (NCF) adhesives named as NCF I-NCF II and NCF III, were applied to COF package with compliant-bump. Firstly, to investigate bonding temperature effects, the curing rate of the NCFs and strength of interconnection under different bonding temperatures (150°C ~ 230°C) were evaluated using differential scanning calorimeter (DSC) test and a 90 degree peeling test, respectively. Then, the electrical performances of NCF joints bonded at different bonding temperatures were monitored by measuring daisy chain and insulated resistance. After that, the reliability tests of 85°C / 85% RH thermal humidity storage test (THST), and 55°C ~ 125°C thermal cycling test (TCT) were performed. Finally, the cross-section images of failure samples from SEM were observed to find the failure mode. The results showed that the resistance variation of samples with NCF III was below 3% after 1,000 hours of THST. Due to insufficient curing degree for NCF materials, resistance of samples with NCF I - II at bonding temperature of 150°C increased rapidly after 100 hours of THST. After increasing bonding temperature higher than 170°C, all the testing samples can pass the THST for 1,000 hours. However, more than 10% resistance variation can be obtained due to moisture hygro-swelling effect on the NCF materials. The main failure caused by THST is delemination at the complaint-bump / copper lead interface. Moreover, no matter which NCF material is adopted in compliant-bump bonded COF package, the contact resistance variation is within 1% in TCT. In compliant-bump bonded COF package, moisture hygro-swelling effect and curing degree for NCF materials are main factors to dominate the reliability performance. It is proved that NCF type COF package with compliant-bump structure can get stable electrical performance in reliability of THST / TCT and come to the application of ultra-fine pitch COF package.