For the plastic electronics industry, organic light emitting diodes (OLEDs) used in digital displays need to be checked for quality. Specifically, the end user in the PlastronicsSpec consortium produced OLEDs by inkjet printing. This OLED inkjet printing process can result in defective pixels, resulting from cracks, chips, pin holes and misaligned layers. The objective of the developed PlastronicsSpec system is to perform rapid and high resolution inspection of printed plastic flat panels or reel-to-reel flexible electronics sheet using real-time digital radiographic imaging. This enables the automatic detection and instant rejection of defective products with minimum wastage and the elimination of human error in data interpretation.
The main features of the PlastronicsSpec system are:
a microfocus X-ray source and a 2D flat panel digital detector which generates radiographs with up to 1.2µm resolution at high magnification
prototype can accommodate a 600mm2 flat OLED panel and can be adapted to handle roll-to-roll (R2R) flexible electronic samples
novel multimode signal processing options have been used to detect the smallest possible image differences. Various image filtering techniques have been integrated to achieve optimum pattern recognition and accurately size defects. The software allows automatic sentencing of parts as good or bad.
TWI Technology Centre (Wales) developed, optimised and automated the digital X-ray inspection based techniques for both projects. TWI first simulated the radiography environment to optimise the placement of the X-ray source and detector, surveyed the market for the appropriate source and detector, and finally procured the most suitable X-ray source and detectors for the intended applications.
The two applications could not be more different in terms of radiography. For the PM samples the team identified high energy (160-200kV) to penetrate the material, whereas for the OLED inspection the energies had to be low (55kV) to avoid being destructive to the OLED panels. For the PM parts the goal was to inspect defects such as cracking to 25μm resolution, whereas with OLED display inspection the requirement was to resolve flaws down to 2-4μm.
Project co-ordinator Dr Mihai Iovea thanks TWI and states that, because of the contribution of TWI and other collaborators, he is in a very good position to commercially exploit the completed prototypes.
TWI can develop one-off automated inspection prototypes and solutions for its Members. If you think you might have an inspection requirement where digital radiography can be deployed, or you need to inspect a component using radiography, please email firstname.lastname@example.org
More information about the projects can be found at www.autoinspectproject.eu and www.plastronicsspec.eu
The PlastronicsSpec project has received funding from the European Union under grant agreement no. 286531. The AutoInspect project received funding from the European Union under grant agreement no. 286007.