A Measurement Method Using Bi-Metal Fixture for Non-Linear Property of Thin Layer Joint

Silicon Carbide Power (SiC) Devices which are operable under high temperature are focused, since the cooling system for the power modules can be miniaturized. In the conventional power devices, the thermal stress that is caused by the thermal expansion mismatch between the Si chip and the substrate can be absorbed by the deformation of solder joint. As a result, the thermal fatigue reliability of the conventional structures is secured. However, the solder materials cannot be used to mount the high temperature operable device like SiC because the operating temperature is higher than their melting temperature. In this study, a kind of Ag nanoparticle thin layer joint is proposed to the mount high temperature operable device. The feature of the Ag nanoparticle is to joint the chip on the substrate by low temperature sintering, and the melting point of the thin layer after mounting process is equal to the bulk Ag. To evaluate the reliability potential of proposed structure, the nonlinear material properties of the thin layer is required. However, it is difficult to measure these properties by the current method. Since it is considered the thin layer has different micro structure from that of the bulk Ag, and it is difficult to prepare a bulk specimen made of the Ag nanoparticle material. Therefore, it is necessary to measure the properties of Ag nanoparticle in the state of a thin layer. In this research, a new approach was proposed to measure the nonlinear properties in the state of thin layer by using a bi-metal fixture which is composed of two different materials whose CTEs are different. When the fixture is heated, micro displacement can be generated between two materials. The thin layer which is formed between the two metals in the fixture deformed in shear direction by the displacement. During the heating, the shear deformation of the thin layer is measured by a digital image correlation method. The load on the thin layer is measured by strain gauge attached at fixture. In this study, the nonlinear properties of Ag nanoparticle thin layer were measured by this method. In addition, properties of solder were measured by this method too as a reference, and the results were compared with the property of bulk solder to confirm the accuracy of the method using bi-metal fixture.