Printed electronic technology continues to garner significant interest across multiple product applications for both embedding devices within existing standard products and producing novel flexible devices. Compared to traditional copper foil based flexible printed circuit board (F-PCB) technologies, printed electronic circuits can accept a wider range of flexible substrate materials, can be readily integrated with other printed device functions and can exploit roll-to-roll manufacturing for extremely low cost.
On the other hand, most printed electronic offerings are based on silver inks for their conductor circuits, which are more expensive and more susceptible to electromigration issues than copper. Moreover, copper is the material of choice for component assembly, as it can create reliable intermetallic compounds with the solder alloys used for interconnection. As such, in order to transition printed electronics to the flexible device market, a copper ink based technology is favored but must demonstrate sufficient reliability in industry recognized application conditions. Considering the distinct morphology and surface of a printed copper circuit as compared to its copper foil counterpart, such reliability is not a given.
This presentation will therefore report on preliminary reliability data for a copper circuit printed on flexible polyimide with comparison to a copper foil based F-PCB. Here, the JEDEC JES022-A110 testing protocol is selected. This highly-accelerated temperature and humidity stress test subjects devices to 85°C temperature and 85% relative humidity for 1000h with continuous bias and is widely accepted in industry as an early analysis of potential field failures linked with corrosion or electromigration.
After a brief review of the key manufacturing and assembly steps for each type of flexible circuit, functionality and electrical performances of the two flexible device configurations before and after the JEDEC JES022-A110 testing are presented. Results are related to visual observations and relative performance of the two circuits are discussed with respect to potential application spaces. Finally, future reliability investigations are proposed.
