The Analysis Of Thermal Reliability And Heat Dissipation Of QFN Device

The Epoxy Molding Compound (EMC) has extensively used as an encapsulant for electronic packages to protect the IC chips from mechanical and chemical hazards. It is well known that molding compounds show not only strong temperature dependent but also time dependent behavior. Only by correctly characterize visco-elastic properties of EMC, then more accurate simulation results be obtain in finite element analysis. The research in this thesis is supported by the National Natural Science Foundation Project. The structure and dimension parameters of Quad Flat no-lead package (QFN) devices has been optimized and analyzed. The heat could be generated inevitably when the electronic devices and circuits are working. To improve the reliability of electronic products and electrical properties, the heat dissipation of devices must be improved. The heat dissipation of quad flat no-lead device was analyzed in this paper, because this is very important to investigate the heat dissipation of the components.In this thesis, the Dynamic Mechanical Analyzer in the Micronano-electronics Packaging Technology Center was employed to test the parameters of storage modulus E′, loss modulus E″and the loss tangent tanδof EMC. And the Thermal Mechanical Analyzer was used to determine the thermal propreties of the samples. The necessary parameters of visco-elastic material which the finite element software needs were obtained by fitting the data. For the reason of simplicity, many researchers often take the property of EMC as onlyconstant elastic or temperature-dependent elastic, but the real property of EMC is visco-elastic. To illustrate the differences of EMC based on three different material models (visco-elastic, only temperature-dependent elastic and elastic), in this paper, the maximum equivalent stress and warpage of QFN device models were simulated using finite element software MSC.Marc in the temperature cycle. And the affections of the thermal expansion coefficient for maximum equivalent stress and the warpage were studied.Eight structure and dimension parameters of QFN device were selected and statistical analysis software MINITAB was employed. Based on the factorial experimental design, the significant factors which affecting the maximum equivalent stress and warpage were obtained. The widely used engineering software, Design-Expert 7.1, was conducted to obtain the regression equations of maximum equivalent stress and warpage. And based on the response surface methodology, the interactions on the maximum equivalent stress and warpage were analyzed.The electronic system cooling simulation software FLOTHERM was employed to analyze the cooling ways of QFN device under natural convection and study the influence on maximum junction temperature under forced convection.