Characterization of Printed Components Under Space Conditions

As required by the NSTRF Grant, a goal was developed for the research being performed: “The goal of this project is to characterize the electrical and mechanical property evolution of conductive traces printed with silver and carbon inks on a variety of relevant substrates when subjected to the following three simulated space environmental conditions: 1) hard vacuum, 2) extreme thermal cycling [<-120 °C to +100 °C], and 3) radiation. From this information, the reliability in the harsh environment of space of electrical components printed using these techniques and materials may be inferred.” A variety of research delays and difficulties forced some alterations in scope from this stated goal. Carbon ink was removed from the research project because of printing problems, several planned substrates did not prove readily adaptable to the printing process, and the temperature range for extreme thermal cycling was shifted somewhat, but the core goal of the project (helping to enable the use of printed electronics in space by understanding the effects of space environments on the materials unique to printed electronics) was still accomplished. In the end, the scope of the project became: “…to characterize the electrical and mechanical property evolution of conductive traces inkjet printed with silver ink on Kapton and Willow Glass substrates when subjected to the following three simulated space environmental conditions: 1) hard vacuum (<2x10-6 torr for up to 7 days), 2) extreme thermal cycling [<-170 °C to +60 °C], and 3) gamma radiation (up to 25.6 kGy).” This research highlighted the surprising natural durability and space environmental stability of inkjetable silver ink and Kapton and Willow Glass substrates. In the end, it seems safe to say that the future of printed electronics in space is a promising one, at least from a materials standpoint. Both the ink and the substrates it was paired with showed no negative effects (or really any effects whatsoever) from extended vacuum exposure. The slight off gassing of the Kapton substrate did not appear to induce any blistering in the silver ink while the Willow Glass samples were completely unaffected. Extreme thermal cycling did appear to weaken the adhesion between the silver ink and its Willow Glass substrate, likely because of damage slowly accumulated as a result of coefficient of thermal expansion mismatches between the two materials. However, the Kapton samples once again showed no noticeable damage or degradation as a result of this environmental exposure. Even the large doses of gamma radiation to which the samples were exposed seemed insufficient to produce any significant negative effects in either ink/substrate combination. The Willow Glass samples may have experienced a very slight increase in resistance after testing, but this claim would require more statistical exploration to give it any real weight.