Prediction and verification of process induced warpage of electronic packages

Abstract

During the manufacturing, testing and service, thermally induced deformations and stresses will occur in IC devices and packages, which may cause various kinds of product failures. FEM techniques are widely used to predict the thermal deformations and stresses and their evolutions. However, due to the complexity of the real engineering problems, various assumptions and simplifications have to be made in conducting FEM modelling. Therefore, the applicability of the predicted results depend strongly on the reliability and accuracy of the developed FEM-based prediction models which should be verified before applications. In this paper, FEM models are developed to predict the thermal deformations of certain electronic packages and naked die samples under packaging and testing loading. For all the package constituents, appropriate material properties and models are used, including temperature-dependent visco-elasticity, anisotropy, and temperature-dependent elasticity and plasticity. To verify the developed FE models, a series of optical metrology tests are performed. A compact 3D interferometry testing system that can measure simultaneously out-of plane and in-plane deformations has been developed. Thermal deformation measurements are performed on samples of both real electronic packages and naked dies attached on a leadframe. Identical deformation patterns were found for the measured fringe patterns in the U-, V-, and W-fields and the simulated ones. Also, quantitatively, the maximum deformation mismatch between the predicted and tested results is within 15%. It is concluded that the thermally induced deformations predicted by the non-linear FEM models match well with measured deformations for both the naked die and the real packages.