Roll-to-roll functional testing of printed conductors and organic light emitting devices

Printing technologies enable manufacturing of large-area electronics on flexible substrates. Especially roll-to-roll (R2R) printing is utilized for high-volume manufacturing of components and applications in printed electronics. A main characteristic in R2R printing is high number of functional samples in a single printing run. Thus, a systematic approach is required for verifying the quality and electrical functionality of R2R printed units. This paper presents an automated electrical test equipment for R2R testing purposes by means of stop and go bed-of-nails test method. The functional tester comprises reeling equipment, general-purpose test and measurement instruments and utilizes test automation software to quantify the quality of printed electronics devices in roll form. In this study, the automated test system is utilized to perform electrical measurements for printed conductors and to verify the functionality of organic light emitting devices (OLEDs) on a roll. The conductors with variable width and orientation are rotary screen printed on over a 60 m long polyethylene terephthalate (PET) foil by using a conductive silver ink. The electrical response of each line is evaluated by resistance measurements to verify their quality and performance. The OLED modules under test are single devices attached on a separate PET roll. Their functionality is tested by configuring the R2R tester to measure the IV-curves for all the devices and by including a photo diode to the test setup to verify the light output for each test sample. The test results show that the R2R test equipment is capable of measuring resistances for conductors repeatedly through the roll. Another implication is that the response of conductors varies along the roll, giving significant feedback for the R2R printing process. For testing of OLEDs, the measured characteristics show correct electrical responses for the test samples and verified their functionality. To conclude, the obtained test results prove that the automated test system has the capacity and capability for systematic functional testing of printed electronics structures and applications as a R2R process.