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The mechanical shear fatigue test has been performed to study the effect of silver content on the fatigue properties of Sn-xAg-0.5Cu (x ϭ 1, 2, 3, and 4) for flip-chip interconnections. The strength of the solder alloy increases with increasing silver content, preventing shear plastic deformation of the solder bump. The flip-chip joints made using higher silver content solder, such as 3%Ag and 4%Ag, exhibit longer fatigue life for all conditions. The fatigue ductility of the solder decreases with an increase in the silver content. The fatigue endurance of 1%Ag solder is superior to other solders over the plastic strain range of 3%, even though the strength of the solder is the lowest in the solders tested. Based on this study, the 3Ag solder may exhibit good fatigue performance for all conditions, and the 1Ag solder is optimum for severe strain conditions.

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In order to develop and elaborate the Weertman's thetheory of creep of solid solution alloys, the high temperature creep test was carried out with Al-Mg alloys. The results are summarized as follows: (1) In alloys containing more than 3at% Mg, the dependence of the steady-state creep rate on stress and temperature is described by the equation, where A is a numerical constant depending on the solute concentration, (2) Transmission electron microscopy showed that the dislocations distributed uniformly without forming cell structures. An alternating array of oppositely signed edge dislocations is considered as the most possible distribution. In such a case, the maximum internal stress is estimated to be less than ten percent of the applied stress and so is negligible compared with the latter. (3) The measured dislocation density was proportional approximately to the square of the stress and was independent of solute concentration. (4) The experimental relation between the dislocation density and the applied stress is explained theoretically by a model based on the balance between multiplication and annihilation of dislocations. The climb velocity which is estimated from comparison between the calculated and measured creep curves, is in good agreement with the theoretical value. (5) The high temperature creep rate of alloys is controlled by the viscous motion of dislocations and is proportional to the cube of the stress, provided that the following conditions are satisfied; a large atom misfit parameter, a rather high solute concentration, a high stacking fault energy and a uniform distribution of dislocations. It is therefore concluded that the high temperature creep rate of solid solution alloys is not always controlled by the viscous motion of dislocations.

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Micro-bulk fatigue testing developed to investigate the fatigue lives and damage mechanisms of Sn-3.0Ag-0.5Cu and Sn-37Pb solder alloys. The fatigue life of micro-bulk solder obeyed Manson-Coffin's empirical law, and the fatigue ductility exponents were about 0.5 for both Sn-Ag-Cu and Sn-Pb alloys. The fatigue life of Sn-3.0Ag-0.5Cu alloy was 10 times longer than that of Sn-37Pb alloy under symmetrical cycling at 298 K, although fatigue resistance of Sn-3.0Ag-0.5Cu alloy was not very superior under asymmetrical wave and elevated temperature condition. The fatigue crack was developed from extrusion and intrusion of slip band in Sn-3.0Ag-0.5Cu alloy, while the crack was observed at colony boundary and grain boundary in Sn-37Pb alloy. The difference in damage mechanism may affect the susceptibility to fatigue life test condition of reversibility.

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