Key Factors for the Formation of Intermetallic Compound During Cu-Sn TLPB Process

Compared with Si-based power devices, wide-bandgap (WBG) semiconductor devices exhibit higher conversion efficiency, and higher operating temperature. The operating temperature of WBG power devices implies the need for novel die-attach materials with high reliability at high temperatures. Due to the wide application of Cu in electronics integration and the transient liquid phase bonding (TLPB) has been widely studied as a reliable and low-cost die-attach technology, the typical representative is Cu-Sn TLPB system, which involves two typical intermetallic compounds (IMCs): Cu
6
Sn
5
and Cu
3
Sn, where Cu
3
Sn has higher thermal stability and higher fracture toughness. Therefore, the regulation of the type of the final IMC is very crucial for the industrial application of TLPB. In this work, Cu-Sn TLPB joints were formed by optimizing the formulation and regulating the bonding process using a low-temperature TLPB technique. The key factors of IMC formation species and growth in TLPB joints were systematically investigated. We found that the Cu-Sn TLPB joints obtained by adding 150 nm Cu powders to the Sn-based solder had very low shear strength (0.68 MPa), while the Cu-Sn TLPB joints obtained by adding 2500 nm Cu powders had the highest shear strength (36.54 MPa). With the increase of bonding time, the Cu
6
Sn
5
is finally transformed into Cu
3
Sn throughout the bonding layer, and the shear strength of the joints obtained by bonding at 200°C for 30 min was increased to 38.48 MPa. In this work, the growth type and time of IMC were controlled by optimizing the formulation and regulating the bonding process to meet the practical application requirements, which laid a certain research foundation for the industrial application of TLPB.