The Influence of Pd Layer Thickness in ENEPIG on Solder Joint Morphology and Reliability

As electronic packaging technology advances, optimizing solder joint reliability is critical. This study examines the effect of Pd layer thickness in ENEPIG surface finishes on the formation of intermetallic compounds (IMCs) and the mechanical performance of solder joints using intense pulsed light (IPL) soldering. Pd layers of 0.05 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex>, 0.1 μm, and 0.15 μm were tested. Results show that a Pd thickness of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.1 \mu \mathrm{m}$</tex> and 0.15 μm led to the formation of discontinuous IMCs, which significantly enhanced the shear strength and hardness of the solder joints compared to those with continuous IMCs at 0.05 μm. The shear strength increased as the thickness of the Pd layer increased. TEM-EDS analysis showed that more Pd dissolved into the solder joint at higher thicknesses, which increased the hardness of the solder joint. The highest hardness was observed at 0.15 μm, with a 40% increase over the 0.05 μm sample. These findings demonstrate that optimizing Pd layer thickness can enhance solder joint reliability, while IPL soldering offers a more energy-efficient alternative to traditional reflow processes.