Fluxless Bonding of Large Area (≥ 900 mm2) Dies-Opportunities and Challenges

In this manuscript, we are demonstrating a flux-less thermal compression bonding (TCB) process for large area (≥ 900 mm
²
) die-to-wafer assemblies in ambient as well as nitrogen environment using an in-situ formic acid (FA) vapor treatment method. A localized mini-environment is created by using a custom-designed shroud, which is mounted on the bondhead and allows delivery of FA vapors in very close proximity of the bonding surfaces. The shroud design ensures uniform distribution of reducing vapors over the entire bonding area e.g. 900 mm
²
. We show that our flux-less TCB approach results in excellent interfacial bonds, which are equally comparable to the conventional flux-based TCB processes. The most distinct feature of this flux-less process is total avoidance of post-TCB clean-up step.