Nanoindentation of Porous Die Attach Materials as a Means of Determining Mechanical Attributes

Abstract

A die attach nanopaste for high temperature use on silicon carbide (SiC) based power semiconductor devices was developed utilizing silver (Ag) and aluminium (Al) nanoparticles as well as organic additives. Total nanoparticle content was varied at 84.7, 85.5, 86.2 and 87 wt%, while the Ag to Al ratio was fixed to 80:20. The die attach nanopaste was sintered in open air at 380 °C for 30 minutes to create an Ag-Al inter-metallic compound between the SiC die and substrate. To determine the mechanical attributes of the post-sintered die attach interlayer, nanoindentation was performed on the samples. It was found that, a low Young modulus of elasticity, E, between 9.3-9.8 GPa was obtained. This was followed by a reduction in hardness as well as stiffness for the post-sintered Ag80-Al20 die attach material when compared against that of solder alloys or bulk metals. The formation of pores in the die attach material as it underwent sintering is believed to have contributed to this decrease in mechanical properties. The findings of this research enables the possibility of introducing a much cheaper die attach material for high temperature devices, which also has excellent mechanical properties to alleviate thermal mismatch issues between the semiconductor die and substrate.