Thermal-mechanical analysis of copper pillar pitch size during reflow soldering assembly process

This study investigates the effect of pitch sizes on the thermal and mechanical performance of the copper (Cu) pillar bumps during the reflow soldering assembly process. The simulated reflow temperature is compared with the experimental result, which is in good agreement. The simulated flow field reveals that radiation is the dominant heat transfer mode in the reflow oven. Moreover, the heat transfer is affected by airflow circulation, leading to uneven temperature distribution and temperature deviations between the bumps. The simulation results demonstrate that overall reflow temperature, the temperature difference between peak temperatures of bumps, deformation, and stress-strain distribution significantly impact Cu pillar bump reliability. Pitch size of 0.40 mm yielded minor total deformation and the lowest stress distribution. Thus, this study provides a comprehensive guide for monitoring the temperature distributions on Cu pillar bumps and their capability to resist deformation and stress strain, which are crucial criteria for achieving high-quality bonding and reliable electronic products during the reflow soldering assembly process.