Modified silver and copper nanopastes for pressureless nanojoining

• Applicant: Dr.-Ing. Susann Hausner
• Subject Area: Joining and Separation Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496163747

The project is built on the unique properties of nanoscale materials, which can be exploited to technical advantage in a joining process known as nanojoining. Nanoparticles (NPs) are used for this purpose, typically with external dimensions of less than 100 nm. NPs are of interest for joining processes due to their lower sintering and melting temperatures compared to macroscopic bulk material, which is physically is caused by the large proportion of surface atoms compared to bulk atoms. This effect offers the possibility of using metallic nanoparticles as filler material (usually in the form of a paste) for joining processes at comparatively low temperatures. With the densification and unification of the NPs during the joining process, their properties are changed back to those of the bulk material, forming a joint seam that has the melting temperature of the original material. This combination of low process temperatures and simultaneously high operating temperatures of the resulting joints represents a significant advantage over similar processes, such as soldering. Due to these advantages, nanojoining has become established, particularly in the power and microelectronics sectors, where silver nanoparticles and copper nanoparticles are already in use as alternatives to conventional solders. In contrast to conventional soldering, however, a disadvantage of nanojoining is that to achieve the desired properties, so reliable thermal-electrical conductivity and sufficient joint strength, a joining pressure must be applied and maintained throughout the joining process. Only pressing the nanoparticles leads to a dense sintered joint seam and a good bonding to the base material parts, which can withstand the stresses encountered during operation. However, the need for joining pressure leads to several disadvantages, such as more complex process technology and control, limitations in component geometries, and mechanical stress on the components during the joining process, which can even lead to breakage of the thin silicon chip dies. This is where the project approaches a solution, building on findings from the previous project. The idea involves modifying the nanopastes with a low-melting component to enable a pressureless joining process. This concept is applied to the silver and copper nanopastes used in the electronics sector for joining chip components. A pure, commercial Ag and Cu nanopaste is used as a starting point and modified accordingly. Samples are joined and extensively investigated and characterized, for example, through thermal cycling tests, determining their microstructure and the thermal and mechanical properties of the joints.

• DFG Programme: Research Grants