Interfacial TEM Analysis of Sintered Silver in Air and N<inf>2</inf>-5%H<inf>2</inf> Gases Environment

Abstract

Sintered silver (Ag) is being used as a Pb-free die-attach material for selected high-temperature application. Reliable sintered Ag joint depends on sintering pressure, time, temperature, paste formulation, bonding area and environment to achieve the desired density and bonding to the substrates. Interfacial region determines the bonding strength as much as the densification of the sintered Ag joint. Air atmosphere sintering of micron-Ag paste oxidized the Cu substrate to prevent any inter-diffusion of Ag atoms which were observable under HR-TEM. Yet, these copper oxides acted as adhesive to produce higher die shear strength than those sintered in the forming gas (N 2 -5%H 2 ). The N 2 -5%H 2 environment assisted the densification and sintering of micron-Ag to the pristine Cu substrate; increasing the bonding quality and die-shear strength, compared to the total absence of bonding for the micron-Ag paste sintered in N2 environment. This result highlights the importance of using high resolution TEM to understand the strengthening mechanism of micron-Ag joints at Cu substrates in air and forming (N 2 -5%H 2 ) gases environment.