Comparison of AuSnx IMCs’s Morphology, Distribution in Lead-free Solder Joints Fabricated by Laser and Hot Air Reflow Process

The morphology and distribution of Intermetallic Compounds (IMCs) in solder joints are determined by reflow process, and will definitely affect the property of solder joints. To investigate AuSnx IMCs’ morphology and distribution in the solder joints fabricated by different reflow processes, laser and hot air relow processes were utilized to fabricate the right-angled solder joints with different thickness of Au surface finish on pads. We found that in the solder joints fabricated by laser reflow process, most of AuSnx IMCs formed at the interface of solder and pads and in needle-like or dendritic shapes, and no large AuSnx IMCs formed at the interface of solder and vertical pad with 0.1 µm Au surface finish. Whereas, for solder joints fabricated by hot air reflow process, AuSnx IMCs were in big block or short stick shapes, and distributed all over the solder joints, the difference of IMCs’ morphology and distribution in solder joints is caused by the difference of reaction mechanism in the reflow processes and cooling speed of solder joints.