Bonding of Large Substrates by Silver Sintering and Characterization of the Interface Thermal Resistance

Low-temperature silver sintering technology, which has been proven to be a promising die-attach solution, was extended to bonding large substrates. Strong bonding strengths for substrates with a dimension of greater than 25 mm × 50 mm were achieved by sintering a nanosilver paste at temperatures below 270 °C under a pressure of less than 5 MPa. To characterize the thermal performance of the substrate-attach interface, we applied a transient thermal technique with cumulative structure function analysis. Using self-heating and the temperature-sensitive threshold voltage of a power device, we measured the transient thermal responses of the device placed at various locations on the bonded structures. Each transient thermal response was used to determine the cumulative structure function, which represents the relationship between cumulative thermal capacitance and cumulative thermal resistance from the device junction to the ambient environment. Two-dimensional maps corresponding to interface thermal resistance were obtained from structure function plots. We found that for well-bonded substrates, the average specific thermal resistance contributed by the sintered silver interface was between 5.20 and 5.78 mm2K/W with a variation of 4.7%-6.0%.