Because BGA (Ball Grid Array) solder balls are hidden under the body, it’s quite difficult to inspect their performance. Up to now, Automated X-ray Inspection is applied to help exposing the defects of BGA solder balls including void, displacement, bridging, cold solder etc. Once defects are found out, rework has to be implemented. However, rework always costs a lot, which is absolutely NOT called for by OEMs. Therefore, it is first and foremost to guarantee the quality of BGA solder balls by effectively stopping solder defects from being generated. So, this article will discuss the key elements to be captured in the process of SMT assembly.