파워 소자의 고속 다이 접합을 위한 5 μm Cu@Sn 입자 기반 프리폼의 천이액상 소결접합 특성

To ensure the high-temperature stability of a bondline under next-generation power devices suchas SiC semiconductors, a die bonding test was performed by transient liquid-phase (TLP) sinter-bonding usinga Sn-coated Cu (Cu@Sn) particle-based preform. Compared to the existing 20 min-bonding result using a 30μm Cu@Sn particle-based preform, a 5 μm Cu@Sn particle-based preform was used to significantly reducethe bonding time to 5 min, and the optimal levels of the amount of Sn in the Cu@Sn particles, the thicknessesof Sn surface finish layers on the chip and substrate, and compression pressure during the bonding wereinvestigated. The Sn content in the Cu@Sn particles significantly changed the microstructure, including theporosity of the prepared preform. The preform porosity of 0.01% was confirmed after the formation of sufficientSn shells with an average thickness of about 602 nm at Sn 30 wt%. In addition, in the preform with Sn 30wt% content, the Sn phase was almost depleted after 3 min after annealing at 250 °C. The Sn finish layerwas evaluated in the thickness range of 0.63−4.12 μm, and it was observed that the shear strength of theformed bondline tended to increase with increasing pressure for all Sn layer thicknesses. In particular, whenthe bonding was carried out at a pressure of 2 MPa using a dummy Cu chip and substrate coated with a 1.53μm thick Sn layer, the best shear strength value of 36.89 MPa was achieved. In this case, all the Sn phasestransformed into intermetallic compound phases of Cu6Sn5 and Cu3Sn, and all the phases formed within thebondline, including Cu, exhibited high melting-point characteristics. Therefore, it was determined that therewould be no remelting of the bondline or a drastic decrease in mechanical properties in a high-temperatureenvironment below 300 oC, as initially intended. By increasing the content of the Sn shell up to 30 wt%, itwas possible to achieve a nearly full density (porosity: 0.3%) bondline structure, due to the rearrangementbehavior of particles, by maintaining liquid Sn for a long time during the bonding process. In conclusion, theoptimal Sn finish thickness was determined to be at the level of 1.5 μm, and the optimal pressure was at thelevel of 2 MPa. The short bonding time of 5 min represents a significant advance in TLP bonding processes,and it is expected to contribute to a substantial improvement in the die bonding of future SiC power devices.