Sn-Ag-Cu alloy. The Sn-Ag-Cu-Ge alloy solder ball had higher ball shear strength than the Sn-Ag-Cu alloy after an aging test at 150°C. The Sn-Ag-Cu-Ge alloy solder has better characteristics for both thermal oxidation and thermal reliability test. Therefore, it can be concluded that the Sn-Ag-Cu-Ge alloy is a good candidate to solve the oxidation problem, which is the most critical problem of the Pb-free solder. ExperimentalTwo solder ball compositions (in wt%) chosen in this study were : Sn3.0Ag0.5Cu and Sn3.0Ag0.5Cu0.05Ge, and had a diameter of 0.450 mm. The substrate used was CSP with 144 pad openings and each pad was 0.38 mm in diameter. The pads had an electroplated Ni/Au surface finish over Cu trace, with about 0.5 and 5.0 lm in thickness respectively. The solder balls from each composition were bonded to the CSP substrate using a water soluble flux under a reflow oven. The reflow condition is that preheating was done for 2 min at 150°C, the peak temperature was 235°C, and the dwell time was 60 sec.The solder balls after one were then analyzed or subjected to either multiple reflow up to 5 times or aging at 150°C for a duration up to 500 hs. XPS was utilized to check the oxide layer thickness and examine the surface chemical composition. We assumed that the oxide thickness can be defined by oxygen concentration under three atomic percent. The mechanical joint strength of the bonded balls was evaluated with Dage shear tester using a shear speed of 200 lm/s at a shear height of 10 lm.It is well known that ambient moisture and other environmental influences are detrimental to the adhesion of polymeric materials to metal surfaces. The primary reason why adhesion loss occurs is believed to be due to moisture accumulation at the polymer/metal interface. This is why adhesion loss does not generally correlate with the bulk moisture content of the polymer. In this work, we present measurements of the interfacial moisture content and adhesion for a series of polymer coatings having different surface chemistries. Measurements were made after reaching an apparent equilibrium in either a dry (0 % relative humidity) or wet (100 % relative humidity) environment. The loss of adhesion is found to correlate directly with interfacial water content. Surface treatments that resulted in a more hydrophilic surface lead to an increase in the interfacial water content and a decrease in interfacial fracture energy.Ambient moisture is well known to adversely affect the durability and performance of adhesive joints and coatings. [1] The interplay between the mechanical stress and chemical changes in the adhesive joint due to moisture adsorption is generally believed to be the root cause of failure of the adhesive application. Failure typically occurs at the polymer/metal interface, indicating that the primary mechanism for failure is not degradation of the bulk polymer. Instead, the structure of the coating near the interface is the determining factor in COMMUNICATIONS 114

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