Failure analysis of (DIMM hole) solder void in lead free process used OSP coated PCB

Abstract

IPC-610D defines the degree of barrel fill in PTH (Planting through hole) into three levels, 25%, 50% and 75%. However, in PCBA stage, when using X-ray to inspect PTH, it is often the case that after wave soldering, there will be solder void. If the size of the solder void accounts the majority size of the PTH, three levels of the IPC-610D is often regarded as the standards for approximate calculation. For instance, during X-ray inspection, if the size of solder void is smaller than 50% size of the PTH, then the product passes the inspection. However, such method is only for estimation purposes instead of precise calculation. Such situation is due to that the number of solder void may be more than one. Moreover, sometimes multiple solder void distribution is possible. It is difficult to analyze the cause of each individual solder void as well as calculate the size of the solder void precisely. Under such complicated circumstances, we focus on the root cause of PTH solder void by failure analysis method. The goal of the analysis is to prevent the occurrence of solder void in advance as well as establish the manufacturing indicators as a bench mark.