Optimized Design of Various Ag Decorated Sn-xAg-Cu0.7 Solder Bump on Cycling Fatigue Reliability for Wafer-Level Chip Scale Packaging

Effects of Ag content (0 ~ 3 wt.%) in Sn-xAgCu0.7 solders on microstructure characteristics and low cycling fatigue at different temperature conditions are overall investigated. To increase Ag content, the solidus point 228.8 ? of Sn-Cu0.7 gradually decreases to 218.5 ? and temperature range of solid-liquid coexistence phase is also decrease. The Sn-Cu0.7 matrix consisted of small particles of Cu6Sn5 within ß-Sn equiaxial grains and did not significantly influence solder hardness. Moreover, much intermetallic compound of plate-like Ag3Sn and rod-like Cu6Sn5 existed in Sn-xAgCu0.7 solders enables to enhance the hardness due to dense network of Ag3Sn precipitation and near eutectic point. As a result of plastic displacement decreases with higher Ag additions, better fatigue lifetime could be achieved at Ag content to 1.5 wt.%. Besides, crack stemmed from thicker IMC layer in Sn-3.0Ag-Cu0.7 solder interface will decrease fatigue performance especially for 80 ? and 120 ?.

Effect of Ag additions on the microstructure and phase transformations of Zn-22Al-2Cu (wt.%) alloy

The relationship between microstructure and mechanical properties is studied for eutectoid Zn-22Al (wt.%) alloys modified with Cu and Ag. Three alloys with a Cu content of 2 wt.% and varying amounts of Ag were cast and hot-extruded. Different microstructural characteristics were induced by heat treatments: natural aging, artificial aging and furnace cooling. Structural and microstructural characterizations were carried out with X-ray diffraction and scanning electron microscopy. Mechanical properties were determined by tensile testing. Dilatometry was used for determining the effects of composition on the transformation points. The addition of Ag increased the ε phase fraction and provided solid solution strengthening, improving the mechanical strength and reducing ductility. Ag additions also displaced the eutectoid reaction to higher temperatures. The microstructure of the matrix has proven to have a strong impact on mechanical properties. The naturally aged specimens presented the highest ductility and tensile strength; however, these properties are severely affected by aging. Lamellar microstructures present the lowest ductility and values of tensile strength between those of the natural and artificially-aged specimens.