An Accurate Experimental Determination of Effective Strain for Heterogeneous Electronic Packages with Digital Image Correlation Method

This paper presents an accurate experimental method to determine the effective strain for the advanced electronic packages with heterogeneous structure or multiple composite layers when the out-of-plane deformation has evident effects on the in-plane strain quantification. The experimental results rely on the 3-D digital image correlation (DIC) technique, a full-field optical measurement method. Several advantages make this technique a perfect choice for characterizing the effective strain for electronic packages, especially for the heterogeneously designed packages that are likely to have large warpage after reflow process. In order to generate the effective strain with the consideration of warpage and thickness effects, an improved data process algorithm for 3-D DIC is introduced to obtain the neutral plane strain. The result was validated analytically and numerically based on the Timoshenko beam theory and finite-element method. The effectiveness and necessity of this paper are demonstrated by applying the results into a practical multilayer package and forecasting the accurate behavior under thermal loading.