A low temperature die attach technique for high temperature applications based on indium infiltrating micro-porous Ag sheet

A low-temperature die attach method based on In infiltrating micro-porous Ag sheet was proposed for high temperature power electronic applications. The bonding temperature was decreased down to 180 °C, reducing the thermal stress caused by coefficient of thermal expansion (CTE) mismatch between die and direct bonded copper (DBC). In the bonding process, the effect of In infiltrated the micro-porous Ag sheet was driven by capillary force. The high specific area of micro-porous Ag sheet accelerated the consumption of the low-melting-point In phase. The compositions evolution of the bondline was investigated. When reflowed at 200 °C for 10 min, the melting point of the bondline was increased to 660 °C due to the formation of Ag₉In₄. Moreover, after aging at 300 °C for 72 h, the melting point of the bondline was further increased to more than 695 °C, due to the formation of (Ag). Furthermore, shear tests at both room temperature (RT) and elevated temperatures were conducted. The shear strength of the samples reflowed at 200 °C for 10 min reached 40.2 MPa at RT. After aging at 300 °C for 168 h, the shear strengths reached 37.9, 26.2, 13.0 MPa at 300, 400, 500 °C, respectively. In addition, ductile features were observed in the fracture morphology of the aged samples. Vickers hardness dramatically dropped after initial aging and slowly decreased thereafter. The performance of the whole bondline turns to be more like a metal rather than intermetallic compounds (IMCs) with the aging process going on.