Thermal stability of low-temperature sintered joint using Sn-coated Cu particles during isothermal aging at 250 °C

Abstract

In this paper, we investigate the microstructural stability of a Cu–Cu joint sintered with microscale Cu particles and Sn-coated Cu (Cu@Sn) particles during an isothermal aging. Using Cu particles and Cu@Sn particles as die attach materials, pure Cu discs were bonded at 200 °C for 20 min with an applied pressure of 10 MPa in a formic acid atmosphere. After the bonding, the Cu sintered joint showed a loosely sintered structure, while the Cu@Sn sintered joint exhibited a microstructure comprised of a Cu3Sn network with a dispersion of Cu particles. The isothermal aging test was conducted at 250 °C in an air atmosphere. Debonding of the Cu sintered joint happened after the aging for only 100 h, due to a severe oxidation of the sintered Cu layer and Cu substrate. On the other hand, the Cu@Sn sintered joints showed better thermal stability. The joint presented nearly 20 MPa shear strength after the aging for 1000 h. The Cu3Sn IMC network suppressed the oxidation of Cu both in the sintered layer and on the substrate, thereby maintaining the microstructural integrity of the Cu@Sn sintered joint.