Considerations for LCD in long life and harsh environments

This TFE has been realized in TRI T DIGITAL DISPLAY Shenzhen, Guangdong province, China through Line One Sales company based in the United Kingdom. In the 3 and a half months of my stay I was commissioned to make the report 'Considerations for LCD in long life and harsh environments', written in English at the request of the company. The report tries to conduct a study in which the conclusions must be reached of what critical points on an LCD screen can cause premature failure. The structure of this report should be that of an 'application note' that is a type of document rather typical of the electronics sector. This type of document should be: concise, easy to read and easy to understand by all the public that has been focused without being too technical. To carry out the task, I had the help of a mentor within the factory who provided me with all the knowledge to make this report. The basic construction of an LCD screen consists of two pieces of flat glass glued together by the larger surface. These parts are glued only by the perimeter so between them a cavity is created due to the thickness of the adhesive. This cavity is filled with liquid crystal due to an interruption in the application of the perimeter adhesive that is subsequently sealed. Finally the light polarizing sheets adhere, one in front and one in the back. Due to a conductive surface previously applied to the glass, applying voltage on these surfaces creates an electric field between the liquid crystal that will cause its internal crystals to twist and thus rotate the beam of light that passes through it. If the polarizers are placed with a difference of 90 degrees between them, we create the black or the white by applying voltage or not applying it. The method used to reach the conclusions of this report was through an experiment conducted in a chamber with controlled temperature and humidity. In this chamber we can artificially accelerate the passage of time controlling the aforementioned parameters. After choosing several samples at random and submitting them to this test, I analyzed the results under a microscope to determine which components had caused the sample to fail. The final conclusions of this report were that for screens equipped with FPC (flexible printed circuitboard) the most critical point is the union between the glass and the FPC, this is done with a double-sided tape called ACF. A reduction in humidity also reduced the number of fault units and samples that still showed good performance also showed signs of fatigue at the same point. For screens equipped with pin, the most critical point was also the union between the glass substrate and the component. The cause of the failure is an increase in the electrical resistance of the connection. The humidity does not affect this type of connection and the samples that still had a correct functioning also showed symptoms of a resistance higher than normal.Outgoin