Understanding LCD Failures - A Case Study in Reliability Testing:
At CMH Met Labs, we specialize in identifying the root causes of material and electronic component failures. Recently, we worked with our prestigious client to investigate two malfunctioning liquid crystal displays (LCDs) compared to a functional unit of the same model (ER-TFT070A2-4). This case study highlights the importance of environmental conditions, material integrity, and proper manufacturing processes in ensuring display reliability.
Figure 1: Stereomicroscope images taken from the display board, (a) a composite image of the board with special illumination, (b), and (c) higher magnification images showing oxidation mostly around or on solder joints pointed by arrows at some of the affected areas.
Background of the Case
– Samples Received: Two malfunctioning LCDs (dated March 2022) and one functional LCD (dated August 2024).
– Associated Hardware: Display board (CE16260H01) and IO board (CE16260H02).
– Reported Issue: Two units displayed a permanent white screen, while one operated normally.
Figure 2: (a) through (d) are images of the FCB ribbon connection to the backlight in a malfunctioning LCD, (a) and (b) are at 7x magnification under a normal and a special illumination, respectively, showing oxidation of the solder joints and tearing of the flex ribbon at different locations, (c) is one side of the connection at 20x magnification and, (d) is the other side of the connection at 30x magnification. Oxidation of the solder alloy is evident. The areas of the FCB showing signs of tearing or stress are shown by arrows.
3. Key Findings
1. Board and Connector Analysis
– Oxidation was observed around solder joints on the display and FCB (flexible circuit board).
– Despite oxidation, the boards still transmitted signals effectively to the working display.
2. Stress on Flexible Circuits
– Tearing of FCB ribbons near the backlight connections indicated mechanical stress during service.
– These stress marks suggest handling, vibration, or bending during operation.
Figure 3:Images (a) and (b) are stereomicroscope images of the malfunctioning LCD near the FCB and COG showing evidence for oxidation as shown by the arrows, both images are at 20x magnification, (c) shows ACF that is used on this LCD assembly at 15x magnification under a special illumination, (d) through (f) are images taken near the FCB and COG and ACF while instead of focusing on the surface of the LCD, focusing gradually changed to have a focused images from the layers below the surface revealing a massive amount of tiny spot like constituent that are likely very minute bubbles formed inside the multi-layer LCD, (d), (e), and (f) are all at 30x magnification and a special illumination was used for images (e) and (f).
3. LCD Internal Examination
– No major disconnections were found in the circuits.
– Evidence of oxidation was detected near the Chip-on-Glass (COG) region.
– Most critically, bubbles were discovered between LCD layers, especially near COG-ACF (anisotropic conductive film) bonds.
• These bubbles disrupted the signal path, leaving only the backlight visible (white screen).
Root Causes of Failure
The failures were traced to service-related environmental stresses, not immediate manufacturing defects:
– Humidity Ingress: Weak seals allowed moisture to penetrate, leading to vapor bubble formation.
– Thermal Cycling: Repeated heating/cooling caused expansion and contraction, weakening ACF bonds.
– Oxidation: Solder joints and bonding areas degraded under exposure to air and stress.
– Adhesive Degradation: Possible under-cured or low-grade ACF/adhesives accelerated bubble formation.
Recommendations for Improved Reliability
To mitigate such failures in LCDs and similar components, we recommend:
1. Use High-Reliability ACF: Select materials with proven resistance to degradation.
2. Add Moisture Protection: Apply conformal coatings and ensure robust sealing.
3. Control Storage Conditions: Store units with desiccants to prevent moisture absorption.
4. Select Low Out-Gassing Materials: Ensure adhesives and coatings remain stable under heat and UV exposure.
5. Account for Service Conditions: Design displays for environments with high humidity, vibration, or temperature fluctuations.
Conclusion
This investigation reinforces that LCD reliability is closely tied to environmental stresses and material durability. By proactively addressing humidity, oxidation, and adhesive stability, manufacturers and end-users can significantly extend the service life of electronic displays.
At CMH Met Labs, we combine advanced microscopy, failure analysis, and materials testing expertise to help clients uncover hidden failure modes and enhance product performance.