Optimal Ni(P) thickness design in ultrathin-ENEPIG metallization for soldering application concerning electrical impedance and mechanical bonding strength

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 1000 h, the high-speed impact energy of ultrathin-ENEPIG with 0.31 μm Ni(P) layer deteriorated significantly. In contrast, mechanical performance maintained well for ultrathin-ENEPIG with 0.18 μm Ni(P) deposit. The loss of adhesion might be attributed to the Kirkendall voids resulting from the unbalanced diffusion for Sn and Cu in Ni3P crystalline. In ultrathin-ENEPIG with 0.18 μm Ni(P) deposit, on the other hand, the migration of Sn in Ni2Sn1+xP1−x was faster than in Ni3P. Besides, secondary-(Cu,Ni)6Sn5 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.