微米尺度铜键合丝疲劳性能研究

目前,铜键合丝广泛用于集成电路、电子封装等领域,但是铜丝在制造和键合的过程中受到的局部应力和摆动,会不可避免地产生疲劳问题。通过一套以自激振动为原理组装的微结构疲劳试验装置,对不同直径的微米级铜键合丝进行对称弯曲疲劳性能测试。试验结果表明:该试验装置能够成功地对微米级铜丝进行对称弯曲疲劳性能试验;无论是屈服强度、抗拉强度还是弹性模量,直径20μm的铜丝均高于直径30μm、40μm的铜丝,表现出明显的尺寸效应;所有铜丝的疲劳寿命集中在4.5×104~1×107;在相同应力条件下,铜丝的疲劳寿命随着铜丝直径的增加而减小;直径20μm、30μm、40μm的铜丝对应的疲劳强度(N=106)分别为147 MPa、97 MPa、70 MPa。从扫描电子显微镜的断口分析结果可以看出拉伸断口为凿峰状,断口周围表面出现许多相间的条状拉拔痕迹;疲劳断口为平齐正断,两条裂纹起源于试样表面,瞬断区为窄条状。

Research on Fatigue Properties of Micron Scale Copper Bonding Wires

At present, the copper bonding wires are widely used in integrated circuits, electronic packaging and other fields, but the fatigue problem will be inevitably produced by the local stress and the swing in the manufacturing and bonding process. The fatigue behavior of micron scale copper bonding wires with different diameter are examined by using a new device for micro-cantilevers based on self-excited vibration principle. The results show that symmetrical bending fatigue performance of micron scale copper bonding wires can be successfully measured by this device, tensile test indicate that the yield strength, ultimate tensile strength and elastic modulus of copper wire with diameter of 20μm are higher than those of the diameter of 30μm and 40μm, which significantly performs size effect. Fatigue life of copper wires is about 104-107cycles. Under the same stress condition, fatigue life of copper wire increases with the decreasing of the diameter. Fatigue strength (N=106) of copper wires (d=20μm, 30μm, 40μm) is 140 MPa, 97 MPa, 70 MPa respectively. Scanning electron microscope(SEM) images show that fracture surface of tensile sample is Chisel-shaped peak, the surface around the fracture appears many strip drawing traces, while fracture surface of fatigue sample is flat and two cracks almost simultaneously originate from the surface, final rupture region is like narrow sheet.