Throughput Optimization of a Sintering Die Attach Process

Sintering as a means of die attach in power electronics modules shows advantages over solder connections with regards to reliability and ageing phenomena, especially at higher temperatures. Some wide-bandgap semiconductors such as silicon carbide can be operated at or above the melting point of conventional lead-free solder, making alternative bonding methods mandatory. However, the formation of sintered joints requires more complex machines compared to soldering, as mechanical pressure, in addition to heat, needs to be applied to form a satisfactory connection. As each joint is created individually and joint formation typically takes time in the range of several minutes, this would induce high machine costs or very low throughput in industrial applications. To mitigate this issue, we propose a two-step manufacturing method that requires pressure only in the beginning of joint formation, followed by a pressure-less second step to finalize the sintered connection. This time-consuming second step can be performed in conventional soldering ovens in large batches, increasing throughput compared to consecutive manufacturing in sintering presses. Shear strength of two-step manufactured samples reached above 50 MPa with a pressure-less second sintering step of two hours at $300^{\circ}\mathrm{C}$ in nitrogen atmosphere. We found the absence of oxygen during the second step to be crucial for strong joint formation, an identical process performed in air yielded a shear strength of only 20 MPa. In conclusion, two-step manufacturing can solve the issue of having to strike a balance between manufacturing throughput and joint strength.