Microstructural evolution and mechanical reliability of transient liquid phase sintered joint during thermal aging

摘要

Solder paste of Ag and SAC0307 (Sn-0.3wt%Ag-0.7wt%Cu) mixed powders was fabricated and utilized as the interlayer to achieve a Cu/SAC0307-Ag/Cu transient liquid phase (TLP) sintered joint. The microstructural evolution and mechanical reliability of the joint during thermal aging at 350 degrees C were systematically studied. A serial transition of Ag-Sn phase occurred from Ag3Sn into Ag4Sn and eventually into Ag-Sn solid solution (Ag) until 15days, accompanied with the formation of Cu3Sn network inside the Ag-Sn phase layer. It was because that the Cu atoms diffused from the substrate into the Ag-Sn phase layer and then reacted with Ag-Sn phase, including two processes: 4Ag(3)Sn+3Cu3Ag(4)Sn+Cu3Sn and Ag4Sn+3Cu4Ag+Cu3Sn. The shear strength of the aged joint decreased from 75 to 60MPa after 15days due to the transition of Ag-Sn phases and the formation of contraction voids, and then it remained stable. The comparisons of hardness and elasticity modulus between the three Ag-Sn phases were both as follows: Ag3SnAg4SnAg-Sn solid solution. Thus, the excellent reliability of the TLP sintered joint with SAC0307-Ag powders was experimentally verified.