Properties of Sn-3.0Ag-0.5Cu solder joints under various soldering conditions: Reflow vs. Laser vs. Intense Pulsed Light soldering

In this study, the properties of solder joints were compared after bonding process using different energy sources. Various soldering methods were employed, including reflow, laser, and Intense Pulsed Light (IPL) soldering. When reflow soldering was performed for a relatively long time, coarse solder microstructures and interfacial intermetallic compound (IMC) grains were formed. Laser and IPL soldering, which have rapid heating/cooling times, formed fine solder microstructure and thin interfacial IMCs. Then, it was confirmed that Cu₆Sn₅ and Cu₃Sn IMCs were formed at the SAC305/OSP (organic solderability preservative) interface and (Cu,Ni)₆Sn₅, Ni–Sn–P, and Ni₃P were formed at the SAC305/ENEPIG (electroless nickel electroless palladium immersion gold) interface. An observation of the IMC grain morphology under various soldering conditions revealed that (Cu,Ni)₆Sn₅ was formed on the ENEPIG substrate, which was polygonal and smaller than on the OSP substrate. The shear strength of the joint increased in the order of reflow, laser, and IPL soldering. Additionally, ductile fractures occurred under all conditions. The IPL soldering joint had a thinner IMC compared to reflow soldering, and moderate interface roughness and bonding area compared to laser soldering. Based on the obtained results, a next-generation IPL soldering method is proposed to improve the properties of Sn-3.0Ag-0.5Cu solder joints.