A Smoothing Algorithm for Strain Measurement by Digital Image Correlation Method

Deformation measurement of solder joints under various loadings such thermal and drop/impact is important in reliability design of electronic packages. It is difficult to use traditional techniques such as strain gage method to measure the strain of solder joints because of their small sizes. Instead, the digital image correlation method (DICM) is applied to catch the deformation of the solder joints. The discrete displacement obtained by the digital image correlation method does not satisfy the deformation compatibility, as a result the error in strain which is calculated by deriving the displacement is enlarged. In order to reduce the error, an approach is proposed in which a continuous displacement field is constructed firstly to fit the discrete measure points by the technique used in the finite element method and the least square method, then the strain is calculated from the continuous displacement field. The results indicate that error in displacement and strain can be significantly reduced by the proposed approach.