Deviceand Method Study For The Stress Test In TSV-Cu Structure

The TSV structure is getting it’s superiority in3-D electrical packaging because it’s low power consumption and small size. But it faces very serious reliability problems during the service process due to the characteristic of the TSV structure and the material properties. These reliability problems are obstacles for the application of TSV structure in3D electrical packaging. So more and more companies and scholars focus on the reliability of the TSV structure.This paper focus on the TSV interposer with electroplated copper as the conductive material and has passivation layer and insulation between copper and silicon. The thermal stress caused by the differential of the CTE(Coefficient of Thermal Expansion) between copper and silicon is an important factor that effects the reliability of the packages during the service process. The shear stress and tensile stress on the interface caused by thermal load will lead to the interface failure。In order to improve the reliability of TSV structure, we can improve the interfacial properties by improve the processing technology. The main work of this paper is finding a method to measure the interfacial fracture toughness to provide the basis for improving processing technology.Because the TSV interposer with no RDL layer and the composite sample for single fiber push out test have similar structure, so try to use single fiber push out test to measure the fracture toughness and use nano-indenter to conduct the experiment. Design a special holder to guarantee the support end of copper pillar free and prevent the silicon matrix gets crack.In experiment process, the berkovich indenter has already touch the matrix before the fiber has been push out. After reduce the thickness of the TSV interposer to34μm, the copper pillar can be push out before the indenter touches the matrix. Based on the displacement/load curve, using modified energy method to calculate the critical energy release rate of the interface which is38.30J/m, using shear lag theory to calculate the critical shear stress of the interface which is108MPa, getting the force of friction by pushing back the fiber which has already been push out, the value of the force of friction is31mN, the shear stress on the interface when the interface sliding is14.5MPa, the residual stress in copper pillar is-11.56MPa.