Optimization of Compression Bonding processing temperature for fine pitch Cu-column flip chip devices

For the demand of high density input/output (I/O), fine-pitch, and low-k materials in copper column bump flip chip packages, Thermal Compression Bonding (TCB) with pre-applied Non Conductive Paste (NCP) has been developed in order to ensure manufacturing reliability. The narrow bonding process window of pre-applied NCP, short bonding time, and high bonding head temperature can cause low yield issues such as NCP voiding in solder and no solder wetting on substrate. For this reason, the bonding parameters, such as bonding temperature profiles and dwell times, have to be controlled and optimized to achieve good solder wettability. In this paper, the optimized maximum bonding temperatures and timing of the TCB process for fine pitch copper column flip chip package are examined. A thermal simulation is also conducted to correlate with experimental data. In the experiment, the bump temperature is measured with a thermocouple while the bonding head temperature and time are controlled with a heat controller. In the thermal simulation, a transient approach is used to consider the bonding temperature profiles and boundary conditions. The paper concludes with an approach and methodology to obtain optimized bonding temperature profiles which is crucial for the development of next generation fine pitch flip chip devices.