Ultrafine dendritic Cu particles for extremely fast pressure-assisted sintering under air and pore-free bond lines

To overcome the bottleneck of the die-attach process in the manufacture of power modules based utilizing band gap semiconductors, an extremely fast pressure-assisted sinter-bonding method employing a low-cost Cu paste was developed. Ultrafine dendritic Cu particles with maximized surface areas were synthesized via a wet process using a catalyst, mixed with a high-performance reducing solvent, and prepared as a paste to evaluate their sinter-bonding properties. The synthesized ultrafine dendrites exhibited slightly larger d50 values than their original counterparts; however, as aggregates of smaller nanoparticles, they demonstrated significantly finer morphologies and more than two-fold larger surface area per unit weight. These morphological changes in the dendrites directly affected the thermal behavior of the paste and the sintering behavior of the dendrites. As a result, the bond line formed using the ultrafine Cu dendrite paste exhibited an exceptional shear strength of 42.8 MPa after only 10 s of bonding under 10 MPa compression at 300 °C in air. Furthermore, the formation of a near-full-density bond line microstructure without dendritic particle shapes or coarse voids was achieved. The finer stems and branches facilitated bending deformation during sinter-bonding, and the expanded surface area increased the contact area between the dendrites and the in situ reduction-generated Cu nanoparticles. These factors collectively led to near-complete sinter-bonding within 10 s. Furthermore, freeze-dried ultrafine Cu dendrites exhibited improved dispersion, resulting in a bond line shear strength exceeding 50 MPa (50.6 MPa) and the densest observed bulk microstructure after 10 s of bonding.