Material characterization and in-situ process monitoring for a robust ACF base flip chip technology

Thermal and mechanical material properties involved in ACF base flip chip technology were carefully investigated. A process sequence was designed based on thermal and mechanical properties of ACFs and substrates determined with thermo-mechanical analysis equipment, dynamic mechanical analysis equipment and differential scanning calorimeter measurements. In-situ monitoring of contact resistance of two single interconnects, daisy chain resistance, bonding force and bonding temperature was performed. Monitoring interconnect resistance and daisy chain resistance, bonding forces of 10 or 20 kg/die were adapted. Extra force applied to junctions caused bump, pad and substrate deformation, resulting in poor junction reliability. It will be shown that in-situ process monitoring can be a powerful tool for process optimization and material selection for ACF base flip chip technology. Interconnect reliability of ACF base flip chip technology was evaluated under several accelerated stress conditions. It was found that ACF interconnect is very stable up to 2 000 h under high temperature storage life test at 125°C and temperature and humidity test at 85°C and 85% RH, regardless of bump materials, ACF materials and substrate materials examined in this work. This work demonstrated that a careful study of ACF thermal and mechanical properties and in-situ monitoring of ACF flip chip process can provide a robust ACF flip chip technology