The doped Pd on the crystal calculation and intermetallic property of low-temperature soldered ENEPIG substrates

Abstract

The preparation of new solder joint materials for chip packaging by designing a variety of brazing material mixes has become one of the future research directions for solder joints. They added low melting point elements to traditional solder materials to prepare low-temperature hybrid solder to meet the low-temperature packaging trend. To improve the performance of low-temperature solder, adding some alloying elements can refine the grain, change the IMC morphology and size, and improve the joint strength to a certain extent. The design of the hybrid solder joint system needs to be based on different metal pads. There are various failure modes of interconnected solder joints on different metal pads. Therefore, the interfacial response, microstructure, and mechanical properties between different hybrid solder and different metal pads need to be studied to optimize the design of the hybrid solder joint system. This paper investigated hybrid low-temperature Sn–3Ag-0.5Cu/Sn–58Bi solder joints on Au/Ni/Cu (ENIG) and Au/Pd/Ni/Cu (ENEPIG) substrates. The addition of Pd elements can change the IMC morphology of hybrid solder joints and affect the fracture failure mode of the joints under shear, with a higher average shear strength at different process parameters than ENIG welded joints. Finally, the presence form of Pd elements in the solder joints was observed under TEM and the fracture mechanism was analyzed. The results showed that Pd atoms on ENEPIG pads can replace some Cu atoms to form (Cu, Pd)6Sn5 intermetallic compounds, distorting the lattice stripe to produce distortions. And compared to ENIG pads, the IMC morphology is pin-rod-like and finer, with more complex grain boundary paths between the grains of the hybrid solder.