Determination of interfacial thermal resistivity by finite element modeling of the flash measurements

The flash technique is widely used to determine thermophysical properties of materials and it can be used to determine interfacial thermal resistivity in multilayer composites. However, the existing data analysis tool for calculating the interfacial thermal resistivity from the flash measurements can only deal with a simple bi-layer structure. Thermophysical properties of the middle layer material in a sandwiched structure would be overlooked during the calculation. The abstract mathematical calculation, complicated expressions, and tedious software coding limit the usefulness of the technique and prevent its application to more complex composite structures, such as those commonly seen in electronic packages. In this paper, we introduce the use of finite element modeling (FEM) for determining interfacial thermal resistivity from flash measurements of multilayer composite structures. The methodology was firstly applied to Cu/Sn-37Pb/Cu sandwiched specimens to determine the Cu/Sn-37Pb interfacial thermal resistivity. Making use of half temperature rise times obtained from the flash experiment, the sample structures were recreated in I-deas™ and transient thermal FEM was performed for determining the Cu/Sn-37Pb interfacial thermal resistivity. Compared with the existing data analysis tool, the FEM method is more accurate for dealing with the multilayer structures because it takes into account thermophysical properties of the middle layer solder.