Cu–Fe–P系合金のはんだ耐候性に及ぼす析出物・加工ひずみの影響

抄録

Copper alloys used in lead frames are required to have high electrical conductivity and strength, as well as good solder heat resistance; however, the degradation mechanism of solder heat resistance has not been clarified. In this study, we examined the solder/substrate interface of Cu–Fe–P alloy after the solder heat resistance test and investigated the effects of processing strain and aging temperature. Fe–precipitates originating from the alloy were agglomerated near the solder/substrate interface due to the Kirkendall effect. The formation of the voids was observed when there were large processing strain and fine precipitates, resulting in poor solder heat resistance. By contrast, when there was almost no processing strain, no voids were found, resulting in good solder heat resistance. Good solder heat resistance was also obtained when the aging temperature was high. Coarse precipitates were observed near the interface and are likely to cause uniform interdiffusion of Cu and Sn atoms compared to the case where fine precipitates existed, resulting in improved solder heat resistance. These findings suggest that processing strain and precipitate size are dominant factors in solder heat resistance for precipitate hardening alloys.