Description
Cheng-Yu Lee1, Wei-Ling Chou1, Ming-Kai Lu1, Tsai-Tung Kuo2, Cheng-En Ho1; 1Yuan Ze University, 2Taiwan Uyemura Limited Company
The effects of Pd(P) thickness (δPd(P)) on the interfacial reaction between eutectic Sn-Ag (Sn-3.5Ag) solder and Au/Pd(P)/Ni(P) (ENEPIG) surface finish and on the joint mechanical reliability were investigated. The types of intermetallic compound (IMC) species grew at the joint interface strongly depended on δPd(P). A slight increase of δPd(P) from 0 \\956;m to 0.2 \\956;m might cause an additional (Pd,Ni)Sn4 layer formed at the interface after soldering and subsequently solid-state annealing, which significantly retarded the growths of Ni3Sn4, Ni2SnP, and Ni3P, and seriously degraded the shear strength of solder joints in high-speed ball shear (HSBS) testing. This δPd(P)-dependent interfacial microstructure was distinctly different from the Cu-containing joint system, i.e., Sn-Ag-Cu/Au/Pd(P)/Ni(P) and can be rationalized using a Pd-Ni-Sn isotherm. The above observations indicated that δPd(P) is an important factor of solderability and should be appropriately reduced to a specific thickness value in terms of ENEPIG solderability.