Comparison of Laser and Reflow Soldering in Sn-3.0Ag-0.5Cu/ENEPIG Joints

In this study, the laser soldering process was compared with the conventional reflow soldering process using a Sn- 3.0Ag-0.5Cu solder and an ENEPIG (Electroless Nickel-Electroless Palladium-Immersion Gold) surface-finished substrate. Laser soldering enables localized heating and shorter bonding time compared to reflow soldering, which reduces thermal damage to both the chip and the substrate. To evaluate the long-term thermal reliability, aging tests were conducted at 150 °C for up to 2000 h. Immediately after reflow soldering, (Cu, Ni)<sub>6</sub>Sn<sub>5</sub> and (Ni, Cu)<sub>3</sub>Sn intermetallic compounds (IMCs) were formed at the joint interface, and the IMC layer thickness increased with aging time. In the case of laser-soldered joints, a very thin (Cu, Ni)<sub>6</sub>Sn<sub>5</sub> layer was observed at the interface, and although its thickness increased with aging, (Ni, Cu)<sub>3</sub>Sn was not detected even after 2000 h of aging. After 2000 h, IMC spalling was observed at the interface. For both soldering processes, the shear strength decreased with increasing aging time, while the laser-soldered joints consistently showed higher values than those obtained by reflow soldering. All samples exhibited ductile fracture behavior.