Fabrication and Bonding Strength of Sn-Decorated MWCNT-Reinforced Sn-3.0Ag-0.5Cu Composite Solder Joints: Reflow vs. IPL Soldering

The rapid advancement of microelectronic packaging has created a critical need for lead-free solder joints with enhanced mechanical and thermal reliability. This study introduces a novel approach to improve Sn-3.0Ag-0.5Cu (SAC 305) solder joints by incorporating Sn-decorated multiwalled carbon nanotubes (MWCNTs). To address the poor wettability and agglomeration of carbon nanotubes in molten solder, MWCNTs were functionalized and uniformly coated with ~70 nm Sn nanoparticles via electroless plating. Soldering was conducted using intense pulsed light (IPL), a rapid, energy-efficient heat source, and was compared with conventional reflow soldering. The study systematically investigated the influence of MWCNT content (0, 0.05, 0.1, and 0.2 wt.%) and IPL soldering conditions with pulse numbers: 27–36 for shear tests, and 30–42 for drop impact tests. IPL processing produced thinner Cu6Sn5 IMC layers than reflow soldering due to its shorter duration. The composite solder with 0.1 wt.% Sn-decorated MWCNTs achieved the highest density, superior thermal dissipation in LED packages, and maximum shear strength and drop impact resistance. These results demonstrate that optimizing Sn-MWCNT content, especially at 0.1 wt.%, and precisely controlling IPL energy can yield highly reliable, mechanically robust, and thermally efficient lead-free solder joints for advanced electronic packaging.