Functional display testing

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By Bob Christensen | Mar 25, 2021
A display being tested for function

In our previous blog on optical characterization testing, we discussed the various tools and testing methods that ensure a display meets its optical performance requirements. Today, we’ll be focusing on the next step in display testing: functional tests.

What is functional display testing? 

While optical display testing focuses on visual requirements, functional display testing focuses on the performance requirements of a display once it is in use. Most of these tests are performed to calibrate and verify the functionality of touchscreen technology used in the assembly. 

Types of functional display testing

The types of functional display testing fall into two broad categories: automated and manual testing. 

1) Automated display testing

GMN has several automated functional testers that can provide computerized inspection services. These testing devices are capable of vision inspection to subpixel resolution, and are also equipped with electrical testing for thermistor resistance, touchscreen resistance, and touchscreen capacitance. 

Custom testing programs are employed for different displays depending on the touchscreen technology used. For resistive touchscreens, a 9-point touch test is implemented to assess input registration across all areas of the display. For projected capacitive touchscreens, shapes may be drawn across different parts of the screen to identify any breaks or areas where inputs are not registered correctly.

Automated testing is typically used for large production runs as it requires a more involved custom testing program, fixturing, and cable set-up. However, automated testing is more consistent than manual testing as it removes variability and the potential for human error. It also allows for more specific tests and measurements to collect data, whereas manual testing is generally performed on a 'pass or fail’ basis.

2) Manual display testing

Instead of using automated testing equipment, manual testing uses human inspectors to look for any display irregularities. A manual tester may visually examine a display for pixel defects or lint and bubbles trapped within the stack-up. Alternatively, they may test for touchscreen calibration by drawing simple shapes or pressing specific parts of the display to verify that inputs are received accurately.

Manual testing is more common than automatic testing since it requires simpler fixtures and a less involved testing set-up. It’s ideal for lower-volume programs or programs where specific electrical testing may not be necessary. 

Ultimately, the tests used depend on the required functionality of a display. GMN’s technical experts can help develop custom testing programs to ensure that your user interface display meets your project needs. To learn more about GMN’s in-house testing capabilities, schedule a consultation with our experts.