Numerical analysis of laser thermal compression bonding for flip chip package

In recent flip chip technology, Copper (Cu) pillar bump has replaced the conventional solder ball because of its higher input/output density, higher reliability, finer pitch. However, as size of Cu pillar bump and pitch decreasing, Cu pillar bump technology face some problems such as interconnect shorting, higher low-k stress when the conventional mass reflow process is used. To solve this problem, several new bonding processes has been developed such as the thermal compression bonding (TCB) and laser assisted bonding, New bonding processes has been developed to meet the requirements of fine pitch and higher reliability of Cu pillar bump technology. During TCB process or laser assisted bonding process, the substrate has a lower temperature than the chip, which reduces the coefficient of thermal expansion (CTE) mismatch-induced stresses and package warpage. In this study, the absorptivity, reflectivity and transmittivity of Si chips were measured by using spectrometer and halogen lamp. The obtained absorptivity was applied to numerical analysis to optimize laser assisted bonding conditions. We performed laser reflow and laser thermal compression bonding warpage simulation using finite element analysis. Similar warpage results were obtained compared with the real samples and the validity of the numerical analysis was verified.