Surprisingly, only a few of these manufacturers are able to make high-quality LEDs. For simple indication applications, low-quality LEDs are sufficient. But high-quality LEDs must be used in many areas that require consistency, reliability, solid-state indication or lighting, especially in harsh environments such as highways, military/aviation, and industrial applications.
In environments such as New York subway stations, where safety requirements are very demanding, LEDs must meet the fundamental factors of high quality.
What are the factors that distinguish the quality of LEDs? How can we tell the difference between the two LEDs? In fact, there are many factors that need to be considered from the start of the chip until the assembly is complete. The chemical material used in the wafer production process is a very important factor in determining all the performance indicators of LEDs.
A 2-inch wafer can be cut into more than 6,000 LED chips, and only the performance indicators of individual chips will be different from the whole. A good chip maker makes chips with very little variation in color, brightness, and voltage drop. But when LEDs are complete, many of their performance metrics can vary widely. In addition, the effect of the encapsulation material is considerable, for example, silicone resins perform better than epoxy resins.
THE ABILITY TO CATEGORIZE
A good LED manufacturer not only makes high-quality chips, but also has the ability to sort and package LEDs based on their color, brightness, voltage drop, and viewing angle. High-quality LED suppliers will provide customers with products with the same characteristics, while lower-quality LED suppliers can only provide LEDs with “mixed characteristics”.
For high-end, quality-critical applications, such as boundary lights for airport runways, the LEDs used must meet FAA-level specifications for color and brightness. The consistency of LED packaging is also strictly limited to ensure performance and safety. LEDs with poor packaging grades used in demanding applications can lead to a series of inconsistencies such as premature failure, which is likely to lead to major accidents. In order to avoid equipment downtime and to ensure that the LEDs specified in the design have reliable operating characteristics, it is important to avoid the use of "mixed" products in high-end and quality-critical applications.
PRODUCT SUPPORTING CAPABILITY
In addition to discrete LEDs, LED assembly and power supply have a very important impact on its performance, brightness and color. Due to the ambient temperature, operating current, circuit structure, voltage spikes and environmental factors can affect the performance of the LED. Proper assembly is the key to protecting LEDs and guaranteeing performance. LED manufacturers also use a variety of techniques and different materials to design circuit structures and assemblies. In most cases, differences in the experience of LED assemblers can cause differences in the overall performance and reliability of LEDs in the same application.
As demand for LEDs has grown rapidly, so has the number of manufacturers and assembly plants serving the global market. Regrettably, however, the proliferation of support manufacturers not only mass adoption of low-quality LEDs, but also relatively inexperienced packaging and LED design engineers. Therefore, in addition to screening LED suppliers through established criteria, OEMs must also examine circuit design and assembly techniques. To ensure design requirements are met, OEMs must inspect the LED assembly and circuit structure.
THIRD PARTY TESTING
In order to eliminate the injustice in testing, many companies entrust third parties to test the LED assembly and circuit structure. An LED device may be tested or used in harsh environments for weeks. During the test, tests such as pressure, temperature cycling, voltage fixation/variation, and current fixation/variation are performed simultaneously. Numerous parameter changes that occur before and after testing are recorded, and changes in brightness, color, and voltage drop of the LEDs under test are monitored.
Accelerated life cycle testing is a key test to avoid failures in specific application areas. This test helps ensure that LEDs that are expected to operate for at least 100,000 hours are screened out, but fail prematurely after only 1,000 hours of operation. This is possible because low-quality LEDs (and possibly high-quality LEDs that are poorly assembled and designed) lose brightness after 1000 hours of operation. In fact, a low-quality LED with a higher drive current will be brighter than a high-quality LED initially. However, too much current will heat up the LED too quickly, and the end result will be dimmed or burned out.
In addition, there are also examples where assembly technology has a greater impact on LED performance than the chip itself. The design engineer should ask the LED supplier for the reliability specification of the LED, and should also conduct assembly testing of the LED to ensure that the brighter one is indeed better. Some good LED suppliers can guarantee the reliability of their LED assembly technology for three years or more, and can further provide final LED products that include high quality LEDs and proper designs for specific applications.
IMPORTANCE OF TESTING
Two applications within the transportation sector help explain how adequate testing can prevent LED failure in applications that provide high visibility. In the early 1990s, LEDs were used for brake lights on cars and trucks. Some LED designs quickly show inconsistencies in performance metrics and burn out quickly. The reason may be the quality of the LED, or it may be completely the design of the product itself. This phenomenon was not taken seriously until recently, when LEDs became a more suitable light source when it comes to traffic lights. Companies designing 8-inch or 12-inch diameter printed boards filled with LEDs must consider environmental and application needs when selecting LEDs and improving their designs.
In any of the above cases, if stress testing or accelerated life cycle testing has been done, it can be considered that a high quality LED or LED assembly is qualified.
FAIR USE
Not every application requires high-quality LED assembly technology. If the LED assembly does not meet the requirements of harsh environments, it may be more appropriate to use a lesser assembly technique.
The bottom line is that LEDs must be affordable. Therefore, within the constraints of cost requirements, factors such as the packaging grade of the supplier's product, the experience and testing of the assembly design, etc. must be considered. Designing to meet application and market needs is the most effective means of serving end users. If the application requires a high-end solution, the choice of chip supplier, design experience, and testing are all factors that should be considered.
Long-term cooperation is possible between LED suppliers with the ability to classify packaging grades, and manufacturers who can conduct reliability and accelerated life cycle testing, which helps manufacturers develop high-end products with more reliable LEDs.
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