Copper sintering with nano-structured particles and formate dissociation

• Applicants: Professor Gordon Elger, Ph.D.; Professor Dr.-Ing. Martin Schneider-Ramelow
• Subject Area: Synthesis and Properties of Functional Materials ; Materials in Sintering Processes and Generative Manufacturing Processes ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496149269

The project’s research in the field of die attach in microelectronics has two scientific foci: (1) The production and characterization of sinterable copper particles and the realization of sinter pastes by suitable binders with copper formate complex and (2) the formation of interconnects with these novel copper particles realized under (1). Models for the mechanisms and processes shall be developed.By selective etching of the surface of copper particles and by in situ production of copper nano particles via the thermal decomposition of complexed metal salts, the sintering mechanisms, in particular surface diffusion, can be accelerated, thus enabling the formation of interconnects at comparatively low temperature and pressure in a short time. It is known that the material transport necessary for sintering is enhanced if the specific surface area is increased. (1) The following two approaches define the aim of the research concerning the sinterable copper particles and binder:(a) How does the selective etching of copper and alloyed particles lead to a specific surface structure and what influence do the parameters (acid concentration, duration, size and microstructure of the particles) have on the formation of the structural features? The aim is to achieve the largest possible specific surface area.(b) Description of the thermal decomposition process of copper(II) formate under the influence of different chemical environments and the formation of copper nanoparticles as a function of sintering process parameters and properties of the sintering paste. The working hypothesis shall be validated: The decomposition of the copper-metal complex at low temperature (≤ 200 °C) leads to the formation of atomic copper, which accelerates the formation of sinter necks by depositing on to the contact points or forming copper nanoparticles (10-100 nm), which significantly increase the contact area. In this way, the process variables, specifically time and temperature can be decisively reduced (t < 15min and T < 250°C).(2) To understand the formation of connections with the novel copper particles shown in (1) by a coherent sinter structure, the effect of the influencing factors such as temperature, time, pressure and chemical environment on the novel nanostructured copper particles and on those formed in situ must be investigated. Specifically, the influence of the increase of the specific surface of the particles shown in (1) on the phases of the sintering process, as well as the development of the nanostructured surfaces, shall be modelled. The material property targets for the sintered connection are high thermal and electrical conductivity (> 50% of the copper bulk values), low porosity (< 20%), high shear strength (> 60 MPa) and high fatigue strength (> 1000 temperature cycles at -55 °C/200 °C), which should be achieved at low process parameter values (≤ 275 °C; ≤ 10 MPa; ≤ 15 min).

• DFG Programme: Research Grants