Effect of rapid thermal cycles on the microstructure of single solder joint

Lead-free solder joints in electronic packages experience the thermal cycles as the electronic packaging products encounter the temperature fluctuations. This study provides some prospectives into the microstructural changes of the solder joints interconnection by rapid thermal cycles. The influence of the different heating temperatures on the interfacial microstructure between single Sn-3.0Ag-0.5Cu (SAC) solder joints and Cu substrate was also investigated. The single solder joint was prepared by reflowing ball grid array (BGA) and then was cut separately. According to the testing temperature and time the specimen is rapidly heated and cooled by the designed experiment apparatus. The microstructures and compositions of solder joints are observed and analyzed by scanning electron microscopy (SEM). It was found that the rapid thermal cycles has a significant influence on the microstructure of single SAC lead-free solder joint. The thickness of intermetallic compound (IMC) increases gradually with the elevated heating temperature portion of rapid thermal cycles. In addition, the intermetallic compound (IMC) Cu₃Sn layer is observed except for Cu₆Sn₅ layer, the heterogeneously coarsened region occur between the IMC and Cu substrate, the coarsening is not associated with the SAC/Cu solder interface. The strain and stress of single solder joint were affected after rapid thermal cycles as well.