The Effect of the Thermal Mechanical Properties of Nonconductive Films on the Thermal Cycle Reliability of 40-mu m Fine Pitch Cu-Pillar/Ni/SnAg Microbump Flip-Chip Assembly

Abstract

Nonconductive films (NCFs) have been introduced for 3-D through-silicon via chip stacking interconnection using reliable fine pitch Cu-pillar/Ni/SnAg microbumps. In this paper, four NCF materials with various elastic modulus and coefficient of thermal expansion (CTE) values were used to investigate the effect of the thermomechanical properties of the NCFs on the thermal cycle reliability of fine pitch Cu-pillar/Ni/SnAg/Cu-pad interconnections. The NCFs' materials properties were adjusted by changing the ratio of epoxy resins and the curing accelerators. Compared with the borate curing accelerator, the use of the imidazole curing accelerator resulted in better thermomechanical properties on NCFs. And, NCFs containing higher ratio of solid epoxy resins showed higher elastic modulus and higher Tg values when using imidazole curing accelerator. After thermocompression bonding using four different types of NCFs, a thermal cycle reliability test (-40 degrees C-125 degrees C) was performed to investigate the effects of the NCFs' thermomechanical properties on the reliability of Cu-pillar/Ni/SnAg/Cu-pad joints. Due to the CTE mismatch of chips and printed circuit board (PCB) substrates, the SnAg solder joint interconnections were damaged during the thermal cycling. Compared with the four types of NCFs, NCFs with higher elastic modulus at 30 degrees C showed better thermal cycle reliability. And among the NCFs with similar CTE values, those with higher Tg and higher elastic modulus at 30 degrees C value showed better thermal cycle reliability. In summary, the NCFs with lower CTE and higher elastic modulus at 30 degrees C were suitable for highly thermal cycle reliable Cu-pillar/Ni/SnAg/Cu-pad bump joints.