Solder ball joint reliability with electroless Ni/Pd/Au plating -influence of electroless Pd deposition reaction process and electroless Pd film thickness

On the solder ball joint reliability, the influence of electroless Pd deposition reaction process and Pd film thickness in electroless Ni/Pd/Au plating was examined. The solder ball joint reliability was evaluated by a high-speed solder ball shear test. Sn-3.0Ag-0.5Cu (SAC305) was used as the solder ball in this study. In the electroless Pd deposition on the electroless Ni film, deposition reaction processes involve replacement reaction and following reduction reaction. We considered that the solder joint reliability was influenced by Pd replacement reaction time and was excellent when replacement reaction time was short. On the basis of the solder joint reliability obtained after multiple reflow cycles and thermal aging, the optimum thickness of the Pd film was found to be 0.05-0.2 μm. The covering property of electroless Pd plating film on the electroless Ni plating film was also investigated. We found that an electroless Pd plating film with a thickness of 0.02 μm or more covered the electroless Ni plating film adequately, and the solder ball joint reliability in this case was better than that with electroless Ni/Au plating. We consider that the shape of the intermetallic compounds (IMCs) is one of the factors that influence the solder joint reliability after multiple reflow cycles. Consequently, we inferred that the high adhesion at the dendrite layers of IMCs/solder interface resulted in excellent solder ball joint reliability after the reflow cycles. We consider that the thickness of the IMCs is one of the factors that influence the solder joint reliability after thermal aging. In (Cu, Ni, Pd)
₆
Sn
₅
IMCs that contained trace amounts of Pd, the growth of the IMCs is prevented by Pd, resulting in excellent solder ball joint reliability after thermal aging.