Micro Bending Test on Double Cantilever Beams: A specimen-centred approach to accurate determination of the visco-plastic properties of Sintered Silver for Power Electronics applications

Abstract

The increased attention for sintered silver as die attach attracts also interest in its reliability assessment. Since the porous joint material shows rate-dependent behaviour at elevated temperature, its visco-plastic behaviour needs to be quantified. Though tensile tests are frequently used for that task is still a challenge to manufacture homogeneous specimens large enough to be safely handled and tensile tested. In this paper the we have presented a comprehensive technology for manufacturing sintered silver specimen for micro bending test. The sample length is about 10 mm but can still be tested with nanoindenter equipment. These specimens were bent at 25 °C at different strain rates. The corresponding stress-strain curves were obtained with transformation functions computed by a FE model. Tensile specimens of sintered silver were manufactured and tensile tested at 25, 100 and 175 °C for investigation of rate dependency and relaxation behaviour. For 25 °C no rate dependency was observed. At 100 °C and 175 °C significant reduction of tensile strength and increase of tensile strain was observed at smaller strain rates. The creep was caused by thermal activation of inner surface diffusion.