Warpage Of BGA Product And Test Process Optimization

The objective of this paper is to study the warpage transformation of BGA product, and the optimization of related test process. BGA is a typical assembly type of IC, such as CPU. Compare to other kinds of assembly type like PGA and LGA, it is thinner and lighter. As the market trend become pursue higher mobility, BGA and thinner BGA component is getting more and more popular. Compare to PGA and LGA, the final assembly process is solder reflow which is to mount the device on the PCB to finalize joint connection. In order to ensure product reliability, how BGA become warp and transformed needs to be understand. And during practical manufacturing experience, there is a case of 40% to 50% yield loss due to after test warpage excess limit. Before test, the units are good. This is key to considerate the relationship of warpage and testing process in semiconductor manufacturing environment.Using product for experiment, could achieve the conclusion, but there are 2 disadvantages, 1st is the product resource is limited, each product unit is cost raw material and pre-process cost. 2nd is using physical goods for experiment also cost a lot of time, which might extend or delay the whole progress. So the main experiment job handled by simulation tool – ANSYS, a creative way for process characterization and practical. For ANSYS, it’s a simulation platform, it’s good at visualization the result under particular situation, mostly hard expected situation. It mixed the material science and practical product and test condition together. Based on the simulator, could save a lot resources by just replicate input parameter getting various output we expected. And based on the simulation result, the final physical optimization could be achieved with low cost.The study process is mainly as below. Based on material science and BGA product specification to simulate the warpage output based on different product design change. like, 1, thinner substrate, 2, thinner die, 3, enlarged die surface area, 4, multiple die situation, etc. And based on experience of test engineer, consider if below change could result less warpage: 1, different time of force apply. 2, contact area optimize of substrate.The final output of the paper is detail understand how BGA warpage be impacted by different design factor, and what is the way to minimize the warpage result by testing process, delivery high yield product. Finally reduced the test process yield loss from 40%~50% to 0%.