Pressureless Sintering of Microscale Silver Paste for 300 °C Applications

High-temperature die attach is necessary to fabricate digital and analog thick film modules for 300 °C applications. Sintered Ag is a promising die attach material, but typically requires pressure during sintering for larger die. Pressureless sintering of a microscale Ag paste has been evaluated with Au and Ag die metallization on Au, Ag, and PdAg thick film metalized substrates. With Au metallization on either the die or the substrate, degradation of shear strength rapidly occurred with aging at 300 °C. Formation of a dense Ag layer and a depletion region near the Au surface was observed with 300 °C aging. This was attributed to the rapid surface diffusion of Ag on Au surfaces at 300 °C. This did not occur with Ag thin film die metallization and Ag and PdAg thick film metallization. After 8000 h at 300 °C, 8 mm × 8 mm Ag metalized die on Ag thick film substrates could not be sheared at 100 kg of applied force. The same was true for 8 mm × 8 mm Ag metalized die on PdAg thick film substrates after 2000 h at 300 °C.