There's more to displays than meets the eye
The majority of LCDs in use are colour displays (computer screens, TV sets, multimedia devices, etc.), which are based on an active matrix structure, in which a matrix of TFTs (thin-film transistors) is added to the polarizing and colour filters.
Transistors activate and deactivate each row of pixels. Active matrix displays are bright, sharp and usually have a quick response time.
Passive matrix displays are still needed, produced and used today in monochrome displays. They can be found in personal organizers, in low-cost devices that need showing limited information only, and when low-power consumption is required (no backlight needed).
Certain types of passive matrix displays retain their state and show information without the need to have a steady electric charge.
Standards are still needed for monochrome displays
As passive matrix displays are still produced and used in many applications, it is necessary to have Standards to assess their quality and in particular to detect possible flaws in their components such as cells and modules.
If mechanical and other technical tests are essential visual inspection remains important.
IEC TC 110 has issued two publications concerning the visual inspection of such components.
IEC 61747-20-1:2015, Liquid crystal display devices – Part 20-1: Visual inspection – Monochrome liquid crystal display cells (excluding all active matrix liquid crystal display cells), sets out the methods and criteria for the visual inspection of LCD cells. LCD cells are used to modulate light to present information. The Standard contains figures that show different types of defects in the viewing area, within segments, deviations of dimensions and shapes, defects within the sealing area and of the contact pad areas.
IEC 61747-20-2, Liquid crystal display devices – Part 20-2: Visual inspection – Monochrome matrix liquid crystal display modules (excluding all active matrix liquid crystal display modules), was published as an FDIS (Final Draft International Standard) in December 2014.
This publication sets out the methods and criteria for the visual inspection of LCD modules. LCD modules are display units that combine an LCD cell with drive electronics. Like IEC 61747-20-1:2015 this publication contains figures showing different types of defects.
Both publications list the types of areas that need inspecting for defects as well as the criteria to be observed to reject imperfect cells and modules.
The eyes have it!
Both publications are important to ensure the production of flawless monochrome LCD devices and are proof that technical testing cannot always replace human intervention to assess the quality of industrial products.