Characterization of Printed Silver Thin Films Sintered by a Scanning Laser Technique

Direct write printing, which is part of additive manufacturing (AM) technology, offers unique capabilities that can complement traditional methods of electronics fabrication. Printing of electrical interconnects is one of the areas in AM that is very important in electronics fabrication. Post-print sintering is a critical step in printed electrical interconnects because it strongly influences the electrical resistivity of the interconnects. Interconnects require the lowest possible resistivity to achieve better performance. Thermal sintering is the most common technique employed in printed interconnects. However, it is limited to substrates that can handle the high temperature requirement of this technique. For plastics or other substrates with low thermal budget such as the ones used in wearable electronics, sintering becomes a challenge. In this work, we explored a scanning laser technique as an alternative to thermal sintering. Characterization of printed silver from different vendors and sintered by this technique has been performed. This characterization includes quantifying DC resistivity, temperature coefficient of resistance, surface morphology and porosity. The effect of different sintering parameters such as laser power and laser scan speed were also investigated. Results from this work demonstrate some advantages of this sintering technique such as being able to selectively wash off un-sintered silver, which is attractive for fabricating strain sensors.