Issue link: https://resources.mouser.com/i/1437744
During manufacture, so-called threading dislocations occur—minute discontinuities in the otherwise regular crystal structure. These vertical micro cracks are caused by a mismatch in InGaN and Sapphire or SiC crystal lattices. The micro cracks multiply over time—more quickly when the LED is exposed to high temperatures, increasing the number of sites where the chip's charge carriers can recombine without producing light. A less-than- high-quality device might lose 30 percent of its light output in 15,000 hours. That's fewer than two years of continuous operation. But, as mentioned, high-quality lamps can give you up to five times that amount of time. Specifying the lowest-cost lamp might not be a good idea. Most automotive LEDs are white, but red and amber are also used, and all come in different sizes and light intensities. Light guides, lenses, and diffusers make taillights appear as though it comes from a single source. In recent years, organic light-emitting diode (OLED) designs for taillights have been very popular with consumers. High-reliability LEDs used in instrument clusters have suffered degradation because of packaging materials. The instrument lighting must deal with just as broad a range of temperatures as external lighting. The epoxy or silicone resins for molding typical white chip LEDs could not provide a proper seal to prevent loss of luminosity and provide enough package strength for mounting on circuit boards. The recent adoption of a new material that combines epoxy and silicone resins made it possible to achieve truly high reliability in white chip LEDs in a very small package. LED also exhibits a color (chromaticity) shift with both time and temperature. Each lamp is a little different in this regard. The key to automotive LED lighting system reliability is both mechanical and circuit design. • Mechanical design to get the heat out and reduce LED junction temperature. • Circuit design to reduce power loss and ensure the current to the LED does not over-stress that junction. LEDs don't radiate a lot of heat like a filament bulb. They keep it to themselves. So even though they are efficient, the heat they generate tends to stay near their semiconductor junction. Letting that heat get out via mechanical bits is imperative. Headlights, with their high power, need a lot of thermal attention. Figure 1: Automotive LED packages provide choices. (Source: Mouser Electronics) 15 mAke it ReliAble The key to automotive LED lighting system reliability is both mechanical and circuit design.