Effect of protection atmosphere's temperature on morphology of Au-Sn IMCs in laser reflowed micro-solder joints

摘要

Formation of AuSnx IMCs in laser reflowed solder joints protected by N2 atmosphere at room temperature, 60°C, 100°C and 130°C was investigated respectively. The solder balls were Sn-2.0Ag-0.75Cu-3.0Bi, and 120µm in diameter. The surface finish of one pad in the solder joints was 4.0µmAu/0.1µmNiFe/0.01µmTa, the other pad was made of Cu plated with 3.0µm thickness of Au. The laser reflow time was within 10ms. AuSn4 IMCs and Au-riched phases formed at the interfaces of solder and pads, the AuSn4 was needle-like in morphology in the solder joints protected by N2 atmosphere at room temperature. As the temperature of N2 atmosphere was increased to higher than 100 °C, almost all of the Au-riched phases disappeared, more needle-like AuSn4 IMCs formed at the interface, and orientation of the IMCs changed obviously as compared with that in the solder joints protected by N2 atmosphere at room temperature. The results indicated that the temperature of protection atmosphere would affect the Au-Sn interfacial reaction in the solder joints fabricated by laser reflow process evidently, even the reflow time was shorter than 10ms. Therefore, by regulating the temperature of protection atmosphere, we may control the morphology of Au-Sn IMCs in the laser reflowed micro-solder joints, and achieve solder joints with good properties.