A SOLUTION USING UNDERFILL MATERIAL TO PROVIDE A STANDOFF FOR EUTECTIC BUMPED FLIP CHIP DEVICES
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Aug-02
The attachment of flip chip die with eutectic sol- der bumps onto organic printed wiring boards hav- ing metal landing pads results in smaller die-to- board "gap" distances (typically 50 - 70 microns depending on the wettable area of the board die site) as compared to those obtained with the high-lead, non-reflowing C4 bump on eutectic solder cladded boards (-100 microns). The wettable area of the board die site is determined by the openings in the solder mask layer. Boards having larger openings would have a larger wettable area for each bump, thereby resulting in more area for the eutectic solder to wet (i.e., greater collapse of the bump).