CTE measurements for 3D package substrates using Digital Image Correlation

Thermo-mechanical stresses are often induced during processing of IC-packages. This is mainly due the Coefficient of Thermal Expansion (CTE) mismatch between the materials used to make these packages. Therefore, accurate CTE measurements is of great importance. In this study in-plane CTE measurements were conducted for thin film samples using Digital Image Correlation (DIC). The methodology was validated using copper test samples. Two different package substrates were characterized. DIC technique was compared to Thermal Mechanical Analysis (TMA) technique. The CTE measured by DIC is about 25-33% higher than TMA. Finally, some experimental and numerical tests were conducted to assess errors related to DIC technique. Both numerical and experimental tests, based on rigid-body motion were conducted. They allow to assess the errors related to lighting, the optical lens distortion, the noise due to CCD sensor and heat radiation, the out-of-plane displacement and the correlation algorithm.