Environmental ageing effects on the electrical resistance of silver-epoxy electrically conductive adhesive joints to a molybdenum electrode

The electrically conductive adhesives (ECAs) provide a large amount of opportunities for the electronic manufacturing. They have much lower processing temperatures, so the heat impact on the electronic components can be reduced. It makes them suitable for interconnecting the temperature sensitive elements in the devices, for example in liquid-crystal displays or modules of flexible thin film solar cells. However, this type of interconnections has to overcome some challenges. As the contact to noble metals has relatively low electrical resistance and is stable to the environment loads, in the ECA joints to non-noble metals the degradation happens (increase of contact resistance, decrease of adhesion). That's why it is important to investigate such type of joints for stability under different ageing conditions. Most of the latest investigations in this field are concentrated on the ECA joints to Sn, because this non-noble metal is widely used in the electronic packaging. This system of contacted materials remains stable under the (120°C) thermal ageing, but suffer from increase of the contact resistance after heat/humidity ageing (85 °C/85% relative humidity) and accelerated thermal cycling (-40 to 125°C). Another contact of non-noble metal to ECA that needs to be investigated is Mo to ECA. Molybdenum is used as a back contact in thin film solar cell manufacturing and the ECAs are used for interconnection and assembling the individual cells in modules. The focus of this work is to investigate the contact behavior between ECAs and non-noble, molybdenum films under different ageing conditions. The experiments are focused on the electrical conductivity. The goal of the work is to investigate the degradation behavior of non-noble metal - ECA joints and to predict the reliability of this type of an electrical contact.