by Jack Goho
Gideon Analytical Laboratories received several liquid-crystal displays (LCDs) that had fading issues; there were five failing LCDs and a good LCD for comparison. An LCD is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals. LCDs are extremely common in electronic devices such as laptops, digital clocks,
Failure analysis ensued. FTIR and SEM-EDS were initially chosen to determine whether there was some contamination with the liquid crystal. Contamination was not distinguishable using FTIR. The Zyglo moisture ingress testing followed FTIR. One of the faded LCDs had black spots where the LC had lost the interfacial wetting. A testing board was supplied to view the fading on the LCDs. The displays are constructed with a reflector on the back, a polarizer, glass with electrodes on the inside, a seal with liquid crystal, glass, and top polarizer. The seal integrity is the first thing to be checked on this device to determine whether the cause for the fading is inherently inside the liquid crystal or ingressing through the seal over time. Zyglo moisture ingress testing revealed no noticeable difference between the good and bad seals. No ingress was occurring.
The seals were cut to open the sandwiched LCDs, and SEM-EDS analysis was performed. The black spots occurred in the LC which had lost contact with the interface of the glass. It is most likely that moisture in very low quantities was the cause of the problem. Water vapor, however, will not show in SEM-EDS or FTIR in a single digit ppm level. There was definitely a contamination or moisture issue inside the LCD, which could be analyzed with mass spectrometry. The company which sent the LCDs, however, lacked the resources to have this performed.
Gideon Analytical Laboratories has the experience, expertise, and research equipment to tackle difficult failure analysis problems. Knowing how and why failures occur can be of invaluable importance when planning for future business for a variety of companies within the electronics industry.