LAUSR

Thermocompression bonding (TCB) is an important process in electronic packaging and is widely seen as a promising technology for miniaturized electronic devices. However, this process usually yields a lower throughput compared to more conventional mass-reflow processes, mainly because the thermal distribution uniformity across the bonding plane, as required for reliable joints, is achieved with longer bonding dwell times. Higher throughputs could be achieved by reducing the dwell time and increasing the heating rates, but this comes at the cost of higher temperature variations between the center and edges of the bonded component, leading to defects such as nonwet or bridged. Reliable temperature distribution measurements are thus needed to eliminate these joint defects. We present a novel method of temperature measurements to quantify the thermal limits of the TCB process. A microfabricated sensor with high temporal and spatial resolution was designed and fabricated for in situ temperature profile measurements up to 250 °C. This work aims to evaluate the influence of different heating rates on the temperature distribution across the chip surface, as well as on the resulting bonding quality. The bonding quality was assessed by the evaluation of bonding pull strength and interfacial defect characterization. The results demonstrate that slow heating rates (50 °C/s) lead to bridge defects and high heating rates (>80 °C/s) induce nonwetting defects in the solder joints. The solder joint defects can be related to the temperature uniformity measurements performed with the RTD sensor, thus providing a mean to more efficiently optimize the TCB heating rate in industrial processes.