Al Wire Bonding Failure and Automatic Optical Inspection on Power Device Leadframe
|School||Huazhong University of Science and Technology|
|Course||Nanoscale Science and Technology|
|Keywords||power device lead frame Al wire bond failure analysis finite element analysis automatic optical inspection (AOI)|
The bond lift and heel crack failure of Al wire bond with Ni clad of power device lead frame was studied, and the interface and fracture of failure sample was analyzed with microscope and scanning electron microscopy. The finite element analysis model of wire bonding process was built by simplifying the bond tool, material and loading process on the basis of real bonding process. Then the bonding process was simulated by importing the model to ANSYS/LS-DYNA.It was found that enough deformation of the bond material (Al wire and Ni clad) was the requirement of the bonding. When the wire was bonded by low parameters, the deformation of the Ni clad and Al wire would be too small to form a bond with high strength and normal size, there would be large disbond area in the center of the bond point, so the bond lift would easily arise during the reliability test. But when the bond parameter was too high, the excessive deformation of the Al wire would lead to large size of the bond point and the deterioration of the heel strength, which caused by the extrusion and friction of the bonding tool. And the bond would be subject to heel crack during the temperature cycle test.The process window of the actual production was too narrow to control the bond quality. To improve the bondability and reliability of the bond, the method of reducing the Ni clad hardness was proposed. Simulation experiment showed that it can expand the process window, reduce the bad bond point.According to the results of failure analysis and simulation tests, improper parameter would reduce the bond quality and reliability, which also lead to abnormal deformation of the bond material. Al wire second bond on the Ni clad was bonded with different parameters, after the visual examination, peeling test, bond pull test, bond shear test, it was found that transverse deformation of the bond was sensitive to the variation of the bond parameters, it can be used as the characteristic parameter of the visual test. According to the actual situation, the automatic visual inspection of the bond point was feasible to meet the qualifications of the test speed and resolution.A method was proposed to improve the bonding yield, the automatic optical inspection equipment (AOI) was used to examine all the bond points, instead of manual sampling inspection, the AOI used in power device bond point was preliminarily designed. According to the check requirements of the high density, small size bond, in order to reduce the cost and improve the efficiency and reliability of AOI, a improved algorithm was proposed to achieve the real-time controlling of the bonding process.