Au and Pd embrittlement in space-confined soldering reactions for 3D IC applications

Soldering reactions under space confinement has become increasingly important due to its application for chip stacking in three-dimensional integrated circuits (3D ICs. This study reports the effects of Au, from the dissolution of surface finishes, in such space-confined solder joints. Our results indicate that (Au,Ni)Sn₄ can form a continuous layer across the entire of the joint, even when Au is very thin. This morphology is detrimental to the joint reliability. In other words, the so-called gold embrittlement has becomes relevant in 3D IC packaging. Pd is one of the most commonly used materials for surface finishes. The effects of Pd will also be discussed. In addition, solutions to solve the Au and Pd embrittlement are presented in this work.