Effect of temperature and substrate on shear strength of the joints formed by sintering of micro-sized Ag particle paste without pressure

The production of joints using micro-sized Ag particle paste without applied pressure was investigated for replacing high lead containing solder in power electronic packaging. The micro-sized Ag paste used in this study was composed of chestnut-burr-like and spherical particles whose weight ratio was 5:5. Sintering was conducted at 250–400 °C for 60 min in a nitrogen atmosphere. Electroless nickel immersion gold (ENIG) finished Cu and bare Cu were used as the joint substrates. The experimental results showed that the microstructure at all sintering temperatures had an open porous system. The shear strength increased from 10.4 to 16.1 MPa with increasing sintering temperature from 250 to 300 °C, and there was no significant improvement above 300 °C. The Ag area ratio gradually increased with increasing sintering temperature, but the bonding ratio exhibited a similar trend to the shear strength. The ENIG finished Cu showed better bonding strength than bare Cu. The Ag area ratio of both substrates was almost similar but the bonding ratio on ENIG finished Cu (64.1%) was higher than that on bare Cu (40.9%).