Method for Obtaining Predetermined Heights in Solder/Braze Seals and Joints
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
During a soldering step mono-sized glass beads are used as permanent stand-offs between the semiconductor chip and the substrate in the Controlled Collapse Chip Connection (C4 or flip-chip) area to control gap and C4 dimension. This results in a 50-100% improvement in fatigue life. The high silica glass beads with a diameter of approximately 3 mils are mixed with the flux. The solder mounds of approximately 4 mils normally collapse to 2-2.5 mils after reflow. The glass beads prevent a collapse of this extent by acting as prop-up bumps. The beads are easily and uniformly dispersed by suspending them in the rosin flux, which has a specific gravity of 2.5, similar to that of the beads.