Advanced Bonding Process based on Intense Pulsed Light Irradiation for Solder Bump in Flip-Chip Package

Abstract

In this study, the Intense pulsed light (IPL) bonding process was investigated for applying the flip-chip package compared with conventional reflow bonding process. This study was focused on optimizing this IPL irradiation energy to achieve a reduced thickness of intermetallic compounds (IMCs) while enhancing the shear force of the soldered joints. A comprehensive transient thermal analysis utilizing finite-element analysis facilitated the fine-tuning of IPL parameters, such as the pulse number, pulse width, etc. This optimization result was clearly validated by the in-situ resistance and temperature monitoring of IPL bonding process. This study determined that an optimized IPL condition, characterized by a pulse number of 40, was ideal for the flip-chip packaging bonding process. Microstructural analysis of the IMCs formed between the solder bump and the Cu pad on the PCB was conducted using optical microscopy and scanning electron microscopy. This analysis revealed that the IPL bonding method, by applying only the necessary energy for bonding, resulted in the formation of a significantly thinner layer of IMCs compared to that formed by conventional convection reflow bonding. Consequently, the shear force, as measured by the die shear test, exhibited a 30% improvement, emphasizing the potential of IPL bonding as a more efficient and effective method for flip-chip packaging.