Effects of Silver Particle Size on Thermal Expansion Behavior of Low-Temperature-Sintered Silver Paste

Silver conductive paste is a common interconnect material in semiconductor chip electronic packaging engineering. The usage temperature of soldered silver paste generally ranges from
$200^{\circ}\mathrm{C}$
to
$350^{\circ}\mathrm{C}$
, and the main functional phase component is silver nanoparticles. The particle size of the powder significantly affects the thermal expansion coefficient of the silver paste sintered samples. In this study, five different particle sizes of silver powders with average particle sizes of
$30/60/80/100/200\text{nm}$
were selected, and low-temperature sintered silver paste was prepared using the same process. The sintered samples of the silver paste were prepared at
$400^{\circ}\mathrm{C}$
with the same process, and the density and compressive mechanical properties of the samples were analyzed. The thermal expansion characteristics of the silver sintered bodies between
$200^{\circ}\mathrm{C}$
and
$350^{\circ}\mathrm{C}$
were analyzed using Hot-Stage Microscope and Dilatometer. The results showed that all the silver powder could achieve sintering at
$400^{\circ}\mathrm{C}$
. The smaller the average particle size, the larger the thermal expansion coefficient of silver paste sintered body. Silver sintered bodies with a particle size within 100nm can maintain good mechanical and electrical properties. The sintered bodies of silver powders with an average particle size of 30nm and 60nm had high thermal expansion coefficients resulting in higher thermal stresses during high-temperature usage. By selecting the particle size of silver powder, the thermal expansion behavior of the silver paste sintered body can be effectively adjusted to meet the packaging requirements under different operating temperature conditions.