LCD Quality
Quality Control
Most LCD panels have imperfect transistors, resulting in permanently unlit or lit pixels which are typically considered dead pixels or stuck pixels respectively. LCD panels that come with imperfect pixels are normally rather usable, unlike ICs (integrated circuits). It is an economical prohibition in dismissing a panel with a small amount of defective pixels as LCD panels are far bigger than ICs. Manufacturers have various standards for choosing a maximum number of defective pixels which are acceptable. At one point, Samsung set a policy of a
zero tolerance for LCD monitors which are sold in Korea. At present, although Samsung sticks to the less restrictive ISO 13406-2 standard. Other manufactures have been reported in tolerating 11 dead pixels in the policies which have been controversial issue between customers and manufactures. To manipulate the acceptable defects and to protect the end user, ISO launched the ISO 13406-2 standard. Nonetheless, not every LCD manufacture tries to adapt to the ISO standard which is rather interpreted in various ways.
LCD panels tend to have defects than most ICs because of the bigger size. For instance, eight defects are found in a 300 mm SVGA LCD and three found in a 150 mm wafer. However, 134 out of 137 dues on the water will be quite acceptable while rejection of the LCD panel will be a 0% yield. The standard gets higher these days because of the high competition between manufactures and the improvement of quality control. Customers are allowed to exchange a new SVGA LCD panel which is quite defective due to its four defective pixels. A display with only a small amount of defective pixels might be unacceptable if they are near each other. The replacement criteria might be relaxed when defective pixels are put in the centre of the viewing area.