Solid–Solid Reaction Between Sn-3Ag-0.5Cu Alloy and Au/Pd(P)/Ni(P) Metallization Pad with Various Pd(P) Thicknesses

Abstract

The effect of Pd(P) thickness on the solid-solid reaction between Sn-3Ag-0.5Cu and Au/Pd(P)/Ni(P) at 180°C was investigated in this study. The reaction was conducted after reflow, thereby removing the Au/Pd finish before the solidstate reaction. The reaction products included (Cu,Ni) 6 Sn 5 , Ni 2 SnP, and Ni 3 P, and their growth strongly depended on the Pd(P) thickness, especially for the former phases [i.e., (Cu,Ni) 6 Sn 5 and Ni 2 SnP]. As the Pd(P) thickness increased from 0 lm, to 0.1 lm, to 0.22 lm, the (Cu,Ni) 6 Sn 5 exhibited a needle-like dense layer, chunk-like morphology, and discontinuous morphology, respectively. The alternative phase (Ni 2 SnP) behaved in a manner opposite to that of (Cu,Ni) 6 Sn 5 , growing with a discontinuous morphology to a dense layer with increasing Pd(P) thickness. However, this strong dependence disappeared when the solder joints were subsequently subjected to solid-state aging. The (Cu,Ni) 6 Sn 5 and Ni 2 SnP both became layered structures for all cases examined. A high-speed ball shear (HSBS) test was conducted to quantify the mechanical response of the interfacial microstructures. The HSBS test results showed that any initial difference in shear strength caused by the various Pd(P) thicknesses could be reduced after the solid-state aging, which is consistent with the microstructural evolution observed. The mechanical strength of the solder joints was decreased due to the presence of a bi-intermetallic structure of (Cu,Ni) 6 Sn 5 /Ni 2 SnP at the interface. Detailed analysis of the growth of (Cu,Ni) 6 Sn 5 and Ni 2 SnP is also provided.

Effect of Interfacial Microstructures on the Bonding Strength of Sn–3.0Ag–0.5Cu Pb-Free Solder Bump

“…Many studies have been conducted to evaluate the reliability of Pb-free solder joints with respect to solder alloy types and surface finishes. [11][12][13][14][15][16][17][18][19][20][21][22][23] Recently, various studies on the mechanical reliability of Sn-3.0Ag-0.5Cu solder joints have been reported by other researchers, including the effects of high-speed shear test conditions on the failure behaviors and the bonding force of BGA Sn-3.0Ag-0.5Cu solder joints, 13) the effects of shear speed and tip height on the high-speed shear test of Sn-3.0Ag-0.5Cu ball joints, 15) the interfacial reactions and joint reliability of Sn-3.0Ag-0.5Cu solder with ENIG and electroless nickelelectroless palladium-immersion gold (ENEPIG) finishes during a reflow process, 24) the effect of Pd(P) thickness on the solid-solid reaction between Sn-3.0Ag-0.5Cu and Au/ Pd(P)/Ni(P), 25) and the interfacial reaction between Ni and Sn-3.0Ag-0.5Cu-xPd alloys at 250 C and the mechanical reliability of the solder joints. 26) As mentioned above, Sn-3.0Ag-0.5Cu solder alloys and surface finishes such as ENIG, immersion Sn, and OSP have been widely used in industry.…”