研究了表面封装焊在剪切应力作用下等温低周疲劳特征，得到疲劳寿命与循环应力幅的关系曲线．分析了６２Ｓｎ─３６Ｐｂ─２Ａｇ焊点的低周疲劳失效机理。结果表明：６２Ｓｎ─３６Ｐｂ─２Ａｇ表面封装焊点在剪应力控制等温低周疲劳过程中有明显的循环蠕变行为，焊点的失效是由于疲劳与蠕变的交互作用造成的。在２５℃，低应力水平下，焊点的失效主要受疲劳过程控制，而高应力水平下，焊点的失效主要受蠕变过程控制；１００℃等温低周疲劳的失效机理与室温疲劳相似，其由疲劳机理向蠕变机理转化的应力水平τ_（＋）较室温下为低，但在相对应力水平（τ_＋／τ_ｂ和τ_＋／τ_ｂ＇）相同时，１００℃与室温时疲劳裂纹的扩展速率ｄａ／ｄＮ基本一致。
The isothermal low-cycle fatigue behaviour of 62Sn-36Pb-2Ag surface mount solder joint under shear stress has been discussed, meanwhile, the curve of shear fatigue life vs cyclic shear stress amplitude has been obtained, and the failure mechanism under different shear stress amplitude at different temperatures is analyzed. The results show that:there are obvious cyclic creep behaviour during constant stress amplitude low-cycle fatigue in 62Sn-36Pb-2Ag surface mount solder joints. The failure of solder joint is due to the interaction of fatigue and creep. At 25℃, under low shear stress amplitude, the failure is controlled mainly by fatigue mechanism, in constrast, under high shear stress amplitude, controlled mainly by creep mechanism:the failure mechanism at 100℃ is similar to that at 25℃ , only the transfer stress τ_(+) from fatigue mechanism to creep mechanism is lower than that at 25℃. Under similar relatative shear stress amplitude (τ_(+)/τ_b and τ_(+)/τ_b＇), the fatigue rack propagation rate da / dN at 100℃ is similar to that at 25℃ .Correspondent: LI Yunqing, lecturer, Department of Materials Science and Engineering, Tsinghua University,Beijing 100084
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