Abstract
ENEPIG with various thicknesses of submicron Ni(P) deposit (Ultrathin-ENEPIG) was adopted to evaluate the electrical impedance behavior, microstructural comparison, and high-speed impact resistance prior to and after isothermal aging process. The results show that when extending the aging time to 1000h, the high-speed impact energy of ultrathin-ENEPIG with 0.31μm Ni(P) layer deteriorated significantly. In contrast, mechanical performance maintained well for ultrathin-ENEPIG with 0.18μm Ni(P) deposit. The loss of adhesion might be attributed to the Kirkendall voids resulting from the unbalanced diffusion for Sn and Cu in Ni 3 P crystalline. In ultrathin-ENEPIG with 0.18μm Ni(P) deposit, on the other hand, the migration of Sn in Ni 2 Sn 1+x P 1-x was faster than in Ni 3 P. Besides, secondary-(Cu,Ni) 6 Sn 5 layer slowed down the out-diffusion of Cu. Thereby, the unbalanced diffusion can be eliminated. The optimization of the Ni(P) deposit thickness selection in ultrathin-ENEPIG would be discussed and proposed based on the observations of the electrical behavior, joint strength evolution, and interfacial thermal stability. © 2014 Elsevier B.V.