Designed fatigue experiments to improve the reliability of liquidcrystal displays

摘要

The objective of this paper is to show how reliability improvementmay be achieved using statistically designed experiments. Environmentalstress testing has been performed on liquid crystal displays (LCDs) toidentify the parameter settings that allow an increase in theirlifetime. During their operating life, the LCDs are connected toelectronic devices and are inserted into cases. They are used to displaymeasurements to aircraft pilots during commercial flights. Typically thefailure time was 4000 hours of flight which was considered not to belong enough. The design of experiments provided an opportunity to checkwhether the most likely hypothesis was correct. During the tests,degradation rates were used as a response. The effects of three factorswere studied using two overlapped 22 orthogonal designs. Apowerful spotlight located at 2.5 meters from the tested LCDs, was usedto model the degradation rate. One of the factors was found to reducedramatically the degradation rate, allowing a very substantial increasein the product lifetimes. More generally, we propose to use the slope ofthe degradation function as a response in designs of experiments forreliability. The advantages of doing this are that the responses arenormally distributed and when the data are right censored, it does notcause as many problems as when failure times are recorded. The drawbackis that the product degradation needs to be periodically monitored untilan accurate estimate of the degradation rate is available, moreover thedegradation function may not be linear so that a data transformation isrequired