Micro-Compression of Freestanding Electroplated Copper Through-Glass Vias

In this study, the micro-compression of freestanding copper (Cu) through-glass vias (TGVs) is presented. An innovative approach was developed to obtain freestanding Cu TGVs where the Cu overburden was used as a bottom platen for the micro-compression test, allowing the mechanical responses of individual TGVs to be directly obtained. From the measured mechanical responses, the average yield strength of the Cu TGVs was determined as 123 MPa with a standard deviation of 7.85MPa. The yield strength values of the six tested TGVs were in good agreement, indicating a reliable and repeatable test procedure. This value was found to be slightly lower than the yield stress values of Cu TSVs, but within the range reported for electroplated Cu. Factors that affect the mechanical properties of the Cu TGVs, including electroplating parameters and microstructure variation, were discussed. The sample preparation and the micro-compression test methods demonstrated in this study can be readily adopted for TGVs subjected to various fabrication and annealing conditions, which will enable the fine-tuning of the processing parameters to produce Cu TGVs with desirable properties for a specific application. Results from this test will also provide valuable input for predictive thermo-mechanical models to enable the development of reliable glass interposers.