Degradations in the silver-filled electrically conductive adhesive joints to a molybdenum electrode after environmental ageing

Abstract

The electrically conductive adhesives (ECAs) are the emerging materials that can provide a lot of opportunities for the electronic manufacturing. They have much lower processing temperatures comparing to soldering, that reduces the heat impact on the components. Due to their properties they can be applied for interconnecting the temperature sensitive elements in the devices, for example in liquid-crystal displays or modules of thin film solar cells. The ECA interconnections, when applied to contact the components with noble metal (Ag, Au, Pt, Pd) finishes, have low electrical contact resistance and are stable to the environment loads. But in the ECA joints to non-noble metals (Cu, Ni, Sn and its alloys, Mo) the degradations happen under specific conditions, which cause the increase of the contact resistance and decrease of the adhesion. That's why it is important to investigate a stability of such type of joints under different ageing conditions. The investigations in this field are mostly concentrated on the contacts to tin (Sn), because this non-noble metal is widely used in the electronic packaging. The Sn/ECA joints remain stable under the (120 °C) thermal ageing, but suffer from increase in the contact resistance after heat/humidity ageing (85 °C/85% RH) and accelerated thermal cycling (−40 to 125 °C). Another contact of ECAs to non-noble metal that needs investigation is ECA to molybdenum (Mo). This combination of materials take place during the interconnection of the thin-film solar cells (Mo is used as a back contact of thin film solar cells and ECAs as interconnecting material for assembling the individual cells in modules). The focus of this work is to investigate the degradations in the contact between ECAs and molybdenum films after different aging exposures.