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Research on the relationship between time-dependent strains and delamination of plastic packaged devices at polymer/copper interface under thermal-hygro environments

Delamination of polymer/metal interfaces has a destructive effect on plastic packaged devices containing thin layered structures. The physics mechanisms of the delamination inside the microstructure devices are not well understood and difficult to reveal. In order to get a deeper understanding of strain variations at the interface between the viscoelastic polymer and other elastic metal bases under a thermal-hygro environment, the following researches are conducted. Firstly, by combining the generalized Maxwell model and the hygro-mechanical strain equation of bi-layer plate, the equation set for hygro-mechanical strain at the interface of bi-layer plate is established considering the viscoelasticity of epoxy resins. Secondly, two bi-layer plate test pieces are made using elastic copper plates and two different types of viscoelastic epoxy resins (diglycidyl ether of bisphenol F (DGEBF) and Cycloaliphatic epoxy resins), and the normal strains at the interface of the two bi-layer plates under a thermal-hygro environment are measured by strain gauges sealed between the epoxy resin layer and the copper plate. Thirdly, by substituting the thermal strain results into the polynomial equations for thermo-mechanical strain at the bi-layer plate interface, the coefficients of thermal expansion of the two epoxy resins at different temperatures are obtained. Finally, multi-parameter fitting of the interface hygro-mechanical strain curves are drawn through programming in MATLAB software based on the genetic algorithm, and the shear modulus and relaxation time of the two viscoelastic epoxy resins are obtained. This paper’s experiment and calculation results reveal the relationship between time-dependent strain and delamination of plastic packaged devices at polymer/copper interface under a thermal-hygro environment, and provide a valuable reference to improve the reliability of plastic packaged devices.