The Cu[sbnd]Cu self-propagating reaction joining with different thickness of tin

Abstract

As a transient and localized heating joining process, the self-propagating reaction joining (SPRJ) method can confine the heat at the joint itself formed by adjacent materials. By proper joint design and heat control from SPRJ, this advantage can be utilized to develop a kind of low-temperature joining approach, which is greatly required by thermal-sensitive device packaging. In this paper, the SPRJ process based on the Al/Ni multilayer film was investigated to join copper substrates electroplated with thin tin solder layers of different thicknesses under the pressure of 5 MPa at room temperature. It showed that the thickness of tin solder layer was a very critical parameter for forming high-quality joints. It was found that the thickness of Cu6Sn5 intermetallic compound (IMC) layer at Cu/Sn interface increased greatly along with tin solder layer thickening from 1 to 4 μm, and then tended to be stabilized with the further increase of tin layer thickness. Meanwhile, the change of the shear strength of the CuCu joints showed the same trend with the variation of Cu6Sn5 layer thickness. The defects were easily formed when the tin layer was too thin, while too thick tin layer may not be further beneficial for the reduce of defects and the formation of IMC due to the limited heat release of the Al/Ni multilayer film and the rapid cool process.