The project investigated environmentally friendly metal pastes for additive manufacturing of integrated circuit traces, focusing on silver‑ and copper‑based formulations that can be sintered at low temperatures. The research was carried out jointly by the Leibniz Institute for New Materials (INM) and GSB Wahl GmbH. INM produced simple paste formulations that enabled fundamental studies of particle behaviour, while GSB Wahl supplied industrial‑grade pastes containing additives that improve printability and substrate adhesion. The collaboration spanned the full project duration, with each partner contributing complementary expertise in powder selection, paste formulation, screen‑printing, sintering, and post‑treatment.
Technical results began with a systematic comparison of silver particles produced by precipitation versus atomisation. The precipitated particles exhibited a lower sintering temperature than their atomised counterparts, a finding confirmed by in‑situ and ex‑situ conductivity measurements. Conductivity rose sharply as the temperature approached the minimum sintering temperature (TR,min), with the resistance dropping from 3 mΩ / sq g at 160 °C to 1.5 mΩ / sq g at 200–250 °C. Above 250 °C the resistance increased again, indicating the onset of oxidation. Scanning electron microscopy revealed the formation of silver necks between particles, which accounted for the conductivity improvement at moderate temperatures. The study also compared flake‑shaped and spherical particles. Flake‑based prints were more conductive before sintering because of the larger contact area, but this advantage vanished once sintering began, as neck formation equalised the contact.
Silver‑coated copper particles were examined to assess their stability against oxidation. Energy‑dispersive X‑ray spectroscopy showed that the silver shell began to degrade at 200 °C, with a pronounced rise in the O Kα to Cu Lα ratio at 250 °C, coinciding with the appearance of crystalline copper oxide in X‑ray diffraction patterns. In‑situ conductivity tests of prints made from 3 µm silver‑coated copper particles revealed a resistance plateau of 3 mΩ / sq g between 90 and 250 °C, followed by a linear increase at higher temperatures. SEM cross‑sections after 90 min at 200 °C confirmed the presence of silver necks, while the silver shell remained intact up to 250 °C. Above this temperature the copper core oxidised, leading to a measurable rise in sheet resistance.
Post‑treatment experiments demonstrated that a brief anneal at 200–250 °C could optimise conductivity without exceeding the temperature that triggers significant oxidation. Recycling trials of printed traces were also conducted, showing that the metal powders could be recovered with minimal loss of particle integrity, thereby supporting the project’s environmental objectives.
Overall, the study established that low‑temperature sintering of silver‑based pastes is feasible when using precipitated particles, and that silver‑coated copper offers a compromise between conductivity and oxidation resistance up to 250 °C. The collaboration between INM and GSB Wahl combined fundamental powder science with industrial paste formulation, enabling the development of printable, recyclable metal pastes suitable for additive manufacturing of integrated circuit traces.