Abstract:

Printed Wiring Board (PWB) laminates are composed of layers of plain-weave fabric reinforcement embedded in resin, a typical example being FR-4 laminates which have E-glass fabric reinforcement laminated in an epoxy (FR-4) resin system.  These composites are orthotropic with different properties along different directions.  Therefore nine independent mechanical constants and three coefficients of thermal expansion (CTE) are required to completely characterize their thermo-mechanical behavior.  In this paper, these properties are estimated by numerical simulation techniques.  A Finite Element Model (FEM) developed previously by the authors (1), is used for detailed simulationof the fabric weave micro-architecture.  Appropriate loads and boundary conditions are applied on this FEM micro-mechanical model to numerically compute the thermo-mechanical properties for the laminates.  Linear properties are presented for a wide variety of common use PWB materials.  Non-linear stress-strain behavior of FR-4 PWB laminates is then obtained by modeling the nonlinear behavior for FR-4 resin system.  The numerical properties obtained are found to agree well with available data from literature.  The difficulty of experimentally obtaining accurate estimates of all the twelve thermo-mechanical properties mentioned above makes this numerical simulation technique an attractive and powerful alternative.
 

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