Bonding strength in flexible electronics

Flexible electronics comprises several manufacturing techniques and material choices for assembling electronic circuits on plastic substrates. A fundamental characteristic in such assemblies is the performance and mechanical stability of bonding between rigid surface-mounted devices and flexible circuitry. This study quantifies bonding strength of 0402' sized chip resistors by a pull-off test measuring the needed perpendicular force to detach a component from a substrate. The test structures include screen-printed conductors and adhesive bonding technology prepared at roll-to-roll pilot manufacturing lines of VTT Technical Research Centre of Finland, as well as commercially available counterparts based on etched wiring and soldering process for bonding. The pull-off testing results indicate higher forces in average for solder-based samples denoting enhanced bonding strength in comparison to printed specimens with adhesive bonding. The observations are founded on higher mechanical integrity of etched wiring and differences in nature between soldering and adhesive bonding methods. However, additive printing and adhesive bonding technology provide sufficient mechanical stability for flexible electronics with low-cost substrates at lower processing temperatures. These manufacturing techniques and proven materials favor sustainability, and enable together with elastic substrates improved skin-contact in future wearable electronic applications.