Computed-Tomography-Based Analysis of Voids in SnBi57Ag1 Solder Joints and their Influence on the Reliability

The first area of research in this article focuses on the characterization of solder joints that contain voids by means of computed tomography (CT). This non-destructive test method made it possible to detect both cracks and voids in solder joints, to define their precise positions, and to capture the void volume of each void. In addition to CT, we carried out metallographic examinations so that we could demonstrate the interaction of both methods. In the process, CT was used to localize the defect and metallography to display the defect in high resolution. The article goes on to discuss the question of whether voids have an effect on the thermo-mechanical reliability of SnBi57Ag1 solder joints. For this purpose, the solder joints were first classified by their void area ratio using radioscopy. In order to analyze the effect of the void area ratio on the reliability of the joint, the assembly underwent an accelerated aging process through thermal shock testing according to IPC 9701. Subsequently, the shocked assemblies were sheared. With the shear values after 1000 cycles, we were able to show that the voids affect the reliability of the SnBi57Ag1 solder joints only slightly and that the joints were hardly damaged. By means of CT examinations performed prior to the thermal shocks, cracks starting from the meniscus tip could be attributed to the temperature changes. These cracks may be crucial when they occur with cracks found on macrovoids inside the meniscus.