Reliability of electrically conductive adhesive interconnections in printed flex-to-flex system integration

Electrically conductive adhesives (ECA) facilitate low processing temperatures for interconnecting printed and flexible electronic components into a complete system. This study investigates the reliability of adhesive interconnections when attaching a functional large-area device and a system-level back-plane circuitry. The test samples to be studied are prepared by interconnecting roll-to-roll (R2R) printed organic light emitting diodes (OLEDs) and flexible conductors by using an automated R2R pick-and-place machine. The critical process parameters such as curing time and temperature are varied after dispensing the adhesive to obtain the optimal process recipe for the interconnection procedure. Especially, ensuring proper galvanic connection between the conductors and large-area contacts at the bottom of vias in an OLED element, and the capability to withstand current levels required for OLED powering is under interest. The experimental observations are supported by means of modeling. The reliability of electrically conductive interconnections is assessed by utilizing accelerated lifetime tests, namely temperature cycling, steady state humidity bias and dynamic bending tests. The electrical performance of test samples is monitored with resistance measurements as the increase in resistance indicates the interconnection malfunction. After conducting the tests, the measurement data is examined with Weibull analysis resulting in a cumulative failure rate over time for each test sample population. The results achieved by the study provide guidelines to design the interconnections and the process set-up with reliable output. The results are essential also from the productivity perspective as the curing conditions of adhesive interconnections play an important role in throughput of automated production lines.