A comprehensive study on 40-mil PBGA

Abstract

The 40-mil PBGA is an effective application for higher I/O density. In regular consideration, the pad size and the solder sphere should be smaller due to decreasing the bump pitch from 50 or 60 mils to 40-mil PBGA. Until now, we could not find any standard product or paper which refers to pad size and solder sphere diameter. So we setup this experiment to find out the results and hope it will be useful to build-up the optimal bumping process of 40-mil PBGA. In this study, we considered many different factors such as substrate pad size and solder sphere diameter. In order to find out the best combination of all these factors to achieve the highest manufacturing yield, we applied the thermocouple technology to measure the thermal distribution of the entire substrate in reflow furnace. After bumping the solder ball onto the substrate, we use ball shear test to analyze the force difference between the balls caused by different temperature profile. The shear height and shear speed variables of the ball shear testing are also investigated in this study. The x-section technology was applied in this experiment for examining the bump shape after finishing the bumping process. In this study, we also utilize the noncontact laser technology to examine the bump height after solder bumping process. In order to understand data about SMT application of 40-mil PBGA, the solder joint height with different solder ball diameter and the reliability test data were both included in this experiment. Of course, we design a test board with daisy chain and utilize the x-section technology to achieve the jobs.