The principal component analysis of Cu stud bump shaping process parameters

As copper wire has excellent thermal conductivity, mechanical properties, low-cost advantages and copper stud bump process is similar the traditional wire bonding process, it makes copper stud bump technology better for medium and low I/O devices, and even in the future, it will expand into midrange I/O packages because it offers a large potential savings in packaging costs with the improved performance. However, the reliability of copper stud bump is crucial problem, and it is still hard to determine the critical process parameters which affect the reliability of copper stud bump. In this paper, by finite element method, the die chip having forty pads was used to build a model, and considering that: the first bonding joint process doesn´t affect the second boding joint, so by using of software ANSYS/LS-DYNA, only one bonding joint model was built to decrease mass computation, and then combine different bonding processing parameters to simulate the copper stud bump shaping processing. Based on this, collect the max ball shear stress during bonding as data samples, and then bonding processing parameters are analyzed by the method of principal component analysis through the software SAS software, take the ninety accumulative percentage as a boundary, extract the main characteristic factors from the bonding processing parameters to decrease the bonding processing parameters dimensions and eliminate the correlation among these bonding processing parameters. Then for the new defining main characteristic factors and original bonding processing parameters, the relative analyses are carried out to generate the main characteristic factors dates. This provides the basis with which the copper bonding reliability after bonding processing is predicted by the method of BP network.