Solder Extrusions and Underfill Delaminations: A remarkable Flip Chip Qualification Experience

摘要

The last years have witnessed an explosive growing demand for all those electronic products, which can be jointly referred to as "mobile electronics". To fulfill such a development rate in the worldwide market, the smaller, cheaper and faster philosophy in the microelectronics packaging industry needs to be pursued with ever increasing efforts. The most suitable packaging solution from this standpoint is mostly identified as the flip chip connection technology. In this environment, the Celestica Italia Packaging & Technology Development Group performed a qualification run on Multi-Chip Module Laminates (MCM-Ls). Two flip chip attach concepts, different in the die passivation, the under bump metallurgy and the array geometry, were evaluated on the same Sequential Build-up (SBU) substrate, with the devices reliability being the most important monitored property. It has been reported that the most detrimental effects on reliability come from the underfill delamination and from a problem related to the eutectic SnPb solder alloys after multiple reflows: the solder extrusion, otherwise called "Amoeba" phenomenon. The solution to these problems is vital for the flip chip technology: the successful actions have regarded the fluxes, the reflow profiles, the surfaces cleanliness but especially the underfill. The latter represents the most influential aspect, even for the future flip chip evolution steps: the reworkability and the no-flow fluxing capability.