FLAT PANEL DISPLAYS
Perfect pixels
Matthew Dale explores the high-resolution imaging solutions emerging for inspecting OLEDs and other electronic displays
S
creens for consumer devices have grown in size and resolution over the past decade, to the point where
displays offering ultra-high definition (4k or 8k resolution), organic LED (OLED) or quantum dot LED (QLED) features are now commonly seen in our homes or our hands. Inspecting these high-resolution displays presents a number of challenges, the main one being that as pixels get smaller so do the size of the defects. In addition, for OLED displays in particular, which differ in composition to LCDs, new kinds of defects can occur that require new methods of inspection. At the recent UKIVA Machine Vision
Conference in Milton Keynes, UK, Wojciech Majewski, sales director for the optical imaging division of Vieworks, based in South Korea, discussed a 155-megapixel CMOS area scan camera with a wide field of view that the firm has developed to address the increasing
demands of flat panel display inspection. Known as the VC-155, the camera is able to
run at 15fps at 8 bits and 7.5fps at 12 bits with a rolling electronic shutter. Majewski explained that the camera is used to inspect FPDs once the multiple layers used to produce them – for example the filters, glass and metallic mesh – have all been combined. Te 155-megapixel resolution of the camera
is roughly five times that of modern mobile phone OLED displays, like those found on the Samsung Galaxy S8. Tis makes the camera suitable for detecting defects such as glass markings or faulty pixels. Vieworks’ annual report confirms that the firm’s customers include Samsung Electronics, in addition to other major FPD manufacturers. Te wide field of view of
before each picture is taken,’ Majewski said. ‘Time is money when you are producing 50 to 80 million mobile phones of a particular model.’ While the primary use of the VC-155 is
the VC-155 means that the entire display is captured in one image, rather than needing multiple images with lower resolution cameras. ‘Taking multiple images wastes a lot more time when inspecting mobile displays, as the camera needs to be mechanically moved
Taking multiple images wastes time when inspecting mobile displays ... Time is money when you are producing 50 to 80 million mobile phones
inspecting mobile displays, according to Majewski, the camera can also be used to inspect televisions. Here multiple images are required; however, thanks to the camera’s high frame rate it can be moved over the surface at higher speeds, compared to alternative solutions with lower resolution and frame rate. Other high-resolution
imaging solutions have emerged recently targeted at FPD inspection. For example, at the end of 2017 Teledyne Dalsa unveiled its 86-megapixel Falcon4 camera operating at up to 16fps, while towards the end of last year Gpixel announced its 65-megapixel CMOS sensor and On
Semiconductor a 50-megapixel CCD sensor. In June Canon USA also revealed a 122-megapixel CMOS sensor that can operate up to 9.4fps. ‘As past trends have shown, there will always
be a need to make larger, higher-resolution cameras,’ said Majewski. ‘For our demanding customers, even while the 155-megapixels we offer at 15fps has satisfied their demands for a period, this isn’t enough to satisfy their demands in the future. Tey are already asking for faster, bigger cameras, which I can confirm will be coming in the future – so the trend will continue.’
InZiv’s nano-optical inspection system for R&D and quality assessment integrated with an optical inspection system 16 Imaging and Machine Vision Europe • August/September 2019
Rising resolutions Te majority of high-end televisions and mobile devices are now equipped with OLED displays. According to Majewski, the biggest problem in OLED display inspection is encountered when examining how well the
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