Effects of heating factors on the geometry size of unrestricted lead-free joints

In this paper, the effects of heating factor on the geometry size of unrestricted lead-free joints were investigated. The morphologies of IMC formed in the joint were studied in detail by using SEM and EDX. When the Sn3.5Ag0.5Cu solder joint was formed in unrestricted condition, the width of the joint and the mean thickness of interfacial IMC increased with the increase of heating factor. The volume of the joint was larger than the volume of the Sn3.5Ag0.5Cu solder, but the effects of heating factor on the change of volume were undulate. The morphologies of the interfacial IMC were needle-like when heating factor was small, and then, grew, coarsened when heating factor increased. The tensile fractography of the joint indicated that the morphologies of IMC at fracture surface were various. Some of IMCs shaped like pyramid, and some of IMCs shaped like needle. And part of the fracture surface located in the solder, and part of the fracture surface located at the interface between the interfacial IMC and solder.