Voidless Underfilling and Stable Micro Solder Joint Formation for Fine Pitch Applications by Innovative Slow Cure NCF

TCB (Thermal Compression Bonding) with NCF (Non Conductive Film) is expected as an effective solution to realize fine pitch interconnections, however, the actual production volume is still small due to its low productivity. Although some multiple die bonding technics represented by collective bonding are being studied to enhance the productivity, any NCF material satisfying user's requirements has not emerged yet. NCF developed in the previous study showed large potentials to be applied to the collective bonding process by demonstrating excellent solder joint formations even after long thermal exposure on a bonding stage, but some technical challenges such as underfill voiding and excessive solder creeping still existed. That is why the new NCF was developed this time. At the beginning of this study, new resin composition was designed to improve hardening behavior of NCF by adjusting melt viscosity and heat flow. TCB and the following post curing were performed with several NCFs with the new resin composition to evaluate underfill voiding and solder joint formation. As the result, it was confirmed that the NCF developed in this study obtained suitable hardening reactivity to achieve both of stable solder joint formations and void less underfilling even after long term thermal exposure on the bonding stage. Moreover the combination of the developed slow cure NCF and post curing under high pressure was successfully demonstrated.