Integrated RTD Sensors for Maintaining Thermal Uniformity During TCB Process

Thermocompression bonding (TCB) is an advantageous method adapted for system miniaturization, for instance to assemble microelectronic devices in 3D stacks. Low throughput and yield are the main drawbacks of TCB, which consequently can lead to higher production costs. Throughput can be improved by reducing the process cycle time using faster heating rates, generally at the cost of reducing the temperature uniformity of the assembly and therefore inducing more assembly defects and incurring higher yield losses. A rapid heating rate allows solder joints to achieve their melting point faster, but can cause large temperature variations between the edge and the center of the die. This significantly affects the quality of bonds and leads to the formation of non-wet (open) and bridge (short) defects. These defects are a barrier to achieving a high-quality product at low cost. We report a novel methodology to quantify the thermal limits of the TCB process in terms of achievable temperature uniformity across the chip area, as a function of heating rate. We investigate the effect of the heating rate on the surface temperature uniformity using a specially designed temperature sensor with high spatial and temporal resolutions, and which further minimally perturbs the TCB process when it is inserted into industrial TCB equipment for testing.