|Budget Amount *help
¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1996 : ¥1,000,000 (Direct Cost : ¥1,000,000)
The effect of thermal cycles on the degradation process of lead free solder, Sn-3.5%Ag eutectic, which is regarded as one of the most possible candidates, has been investigated in comparison with that observed in conventional lead bearing alloy (Sn-37%Pb eutectic). Thermal cycles were applied by the use of thermoelectric modules, with which both heating and cooling programs are precisely controlled over the temperature range from subzero to above 373K.Thereafter the thermal fatigue resistance was evaluated through the peeling strength. It is found that Sn-Ag eutectic is superior in the thermal fatigue resistance to conventional Sn-Pb eutectic alloy, though the former is weaker than the latter if not subjected to the thermal faigue. The degradation of Sn-Pb eutectic during thermal cycling can be ascribed to the microstructural coarsening, which in turn is enhanced by the stress concentration occurring at and around the solder joint. It is also found that the peeling strength of solder joint depends on the deformation speed, meaning that the deformation speed must be identified in order to evaluate the strength of joint.