2018 Best Paper Honorable Mention

Derivation of Equation on Thermal Life Prediction of Plated Through Hole for Printed Wiring Board

Derivation of Equation on Thermal Life Prediction of
Plated Through Hole for Printed Wiring Board

Yoshiyuki Hiroshima, Shunichi Kikuchi, Akiko Matsui, Yoshiharu Kariya, Kazuki Watanabe, Hiroshi Shimizu, Jack Tan - Fujitsu Advanced Technologies Limited, Kanagawa, Japan Department of Materials Science and Engineering, Shibaura Institute of Technology, Tokyo, Japan Graduate School of Shibaura Institute of Technology, Tokyo, Japan Hitachi Chemical Company, Ltd., Ibaraki, Japan HDP User Group International, Inc., AZ, USA

Abstract

Printed wiring boards(PWBs) have recently been experiencing higher thermal stress in car electronics and high current equipment, etc.  In this study, the effects of structural factors and material properties on thermal fatigue life of plated through hole (PTH) in multilayer PWB have been investigated by finite element method (FEM) based on Box-Behnken experimental design.  This methodology showed the effects of single factor and interactions of multiple factors of PWB on the strain causing an occurrence of cracks in copper (Cu) plating of PTH.  The simulation was conducted with obtained properties of thin Cu plating in previous research and a model of a simplified glass cloth equivalent to a cross section of a PWB.  It became clear that the effects of Cu plating thickness of PTH, CTE (coefficient of thermal expansion) and elastic modulus of PWB material were significant on inelastic strain range (⊿εin) in PTH during thermal fatigue.  PTH pitch, though, did not have a measurable impact.  The influence of PWB material Tg was found to be so overwhelmingly strong in the experimental design that behaviours of other factors became too muted to be analysed, which means Tmax should be below Tg.  A formula of the ⊿εin, in consideration of the significant factors and its temperature-scaling factor related to ⊿T, was proposed.  In addition, the ⊿εin became large in accordance with shape and size of roughness of PTH.  When the Cu plating of PTH obeys Manson-Coffin rule, the thermal fatigue life of PTH in consideration of the structural and material factors, can be predicted by the proposed formula on ⊿εin and the low-cycle fatigue life prediction law of Cu plating obtained by previous research.  The acceleration factor (AF) equation was established and validated by test data using various PWBs and temperature conditions in temperature cycling test (TCT).  The calculated AF roughly agreed with the ratios of Weibull average of TCT results.

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