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A previously published analytical model for thermal stress and strain in idealized plated-through-vias (PTVs) has been adapted to conduct elastic-plastic analyses of vias with geometric defects using elastic stress concentration factors calculated earlier. The von Mises stress amplitude, at the mid-plane of the perfect via and at the defect (Δσ0 and Δσ, respectively), and the cumulative plastic von Mises strain, also at the mid-plane of a perfect via and at a defect (ε0pl and εpl, respectively), compared well with results of finite element analyses (FEAs). Four types of PTV defects were evaluated: barrel thickness reduction, occasional waviness, continuous waviness, and wicking. This model provides a relatively simple alternative to FEA to calculate stresses and strains in vias with defects as well as in perfect vias subjected to multiple thermal cycles. This model provides a tool to investigate quickly the influence of possible PTV design dimensions and defects under thermal cycling conditions (i.e., which are particularly damaging in a given situation). It is much easier than FEA for parametric studies like this. It also provides a means for calculating damage metrics, such as the cumulative von Mises strain, which can then be empirically correlated with the cycles to failure data from thermal cycling tests of PTVs.
Components, Packaging and Manufacturing Technology, IEEE Transactions on (Volume:1 , Issue: 5 )
Date of Publication: May 2011