Materials science challenges in green high power density devices 1. The Ag loaded glues for die bonding

Thermal and electrical performances of two conductive adhesive materials loaded with Ag particles suitable for power die bonding have been studied. The study has been performed using dice of Power MOSFETs having an area higher than 30 mm 2 assembled in TO220 package in comparison with Pb95.5-Sn2-Ag2.5 (wt.%) soft solder as reference; the interfaces between chip backside metal, leadframe and glues have been characterized by means of X-ray Photoelectron Spectroscopy after mechanical test and their compositions have been correlated to the thermal conductivity and electrical resistivity of the die-leadframe joints. The results shows that interfaces between die backmetal, leadframe and glue in the die-leadframe joint play an important role in determining the final electrical and thermal conductivities. XPS analyses show the presence of silver depleted insulating regions inside the glues layers 9-10 nm thick, at least, and Ag particles electrically floating.