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 20 μm are higher than those of the diameter of 30 μm and 40 μm, which significantly performs size effect. Fatigue life of copper wires is about 10⁴-10⁷ cycles. 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=20 μm, 30 μm, 40 μm) 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.