Paper Title
Continuous-Wave Laser Thermography for in-Line Inspection of Micro-Cracks in Flexible OLEDS

Abstract
This study proposes a continuous-wave (CW) laser thermography (CLT) system for an instantaneous detection of micro-cracks in flexible organic light emitting diodes (OLED). The proposed CLT system consists of CW laser, a super-resolution infrared (IR) camera with a close-up lens, a control stage, and a control computer. For the operating principle of the CLT system, the CW laser generates thermal waves on the inspecting area of flexible OLEDs while a control stage directs the position of the flexible OLEDs. At the same time, the infrared (IR) camera records the thermal waves within the inspection area. Then, a novel micro-crack detection algorithm is proposed to automatically visualize micro-cracks through extracting the abnormal thermal response induced by the micro-cracks. The proposed system provides the following advantages over the existing inspection techniques: (1) rapid inspection is feasible in a noncontact and nondestructive manner; (2) micro-cracks can be detected under the manufacturing processes through the super-resolution IR camera with a close-up lens; and (3) the proposed system can reliably detect micro-cracks without false-positive alarms caused by surface scratches. The validation tests for the CLT system were performed using 46 flexible OLEDs with micro-cracks that have width of 3.0-6.0μm. The test results demonstrate that the proposed system can successfully visualize micro-cracks in all flexible OLEDs without false-positive alarms. Index Terms - Laser thermography, In-line inspection, Flexible OLED, Active thermography, crack detection