Infoplaner 1-2007 - Cadfem

CADFEM INFOPLANER 1/2007Drop Test Simulation of Electronic ProductsEfficient Combination of Explicit and Implicit Solution SchemesDescription of the performed taskThe so called drop test is one of the most severe load casesfor testing the structural integrity of electronic handheldstructures. Typical failure modes can be:• Loss of connection between plastic cover parts• Cracks within the plastic cover parts• Damage within electronic parts at the PCB• Failure at the solder joints between electronic partsand PCBThe simulation of such a test scenario by means of FEM iswidely accepted and established in industry. LS-DYNA andANSYS are approved software packages for simulations inthis field. Typically different mathematical algorithms for thetransient solution of an impact loading are implemented inthose codes. Normally highly transient analyses are solvedefficiently by explicit codes like LS-DYNA. However, due tothe time step criterion and the related mesh size requirementsfor explicit methods, ANSYS as an implicit code is necessaryto resolve local stress fields.Detailed discretization of electronic components(here BGA at the PCB)The typical failure modes shown above can be classified intodifferent scales – the macro scale considering global structuralparts and the micro scale with possible failure mechanismswithin the electronic parts. Because of the differentconstraints for the different integration methods it isn’t eitherreasonable to use a pure explicit nor to use a pure implicitsolver to calculate the structural response both for the globalmodel and the very detailed electronic components. Thesolution of this contradiction is a combination of both theexplicit method for simulation of the global structure witha very coarse description of the critical parts and the implicitmethod for simulation of a submodel with the specificcomponents. In this case the load time histories of the globalanalysis are used simply as the boundary condition for thesubmodel.This coupling allows the combination of the advantages ofexplicit and implicit time integration without caring aboutnon convergence or too small time steps. Short simulationtimes and very detailed results for further assessment of thestructure are possible.Drop test simulation of a fully equipped mobile phone by means of FEM(Courtesy of Motorola, Italy)Author and ContactThomas Iberer, CADFEM GmbH GrafingTel. +49 (0)8092-7005-50E-Mail tiberer@cadfem.deStresses and strains for assessment of the solder joint29Applications & Technology