No Clean Flux technology for large die flip chip packages

A new No Clean Flux (NCFx) material for large die packages was formulated, which has good wettability for area array lead-free solder bumps of 20 × 20 mm dies, and which doesn't leave any liquid residues under the die. In a reliability study on large die modules with a copper lid as a heat spreader, we confirmed no failures of electrical insulation during thermal and humidity tests. However, significant chip sidewall delamination was found at the early stage of a thermal cycle test. XPS analysis of the chip sidewall showed that an enhanced plasma treatment is necessary to make the sidewall clean compared with a typical water-cleaned reference sample. A CantiLever Beam (CLB) test to measure adhesion strength on chip sidewall also suggested that the SiO2 surface (assumed to be the chip sidewall) treated with the enhanced plasma has stronger adhesion than the reference sample.