Discussion: How to produce high-quality LEDs

Most lighting designers believe that all LED products are of the same quality. However, there are many manufacturers and suppliers of LEDs, and Asian manufacturers supply low-cost LEDs to the world. Surprisingly, only a small number of these manufacturers can produce high-quality LEDs. For applications that are only used for simple indication, low-quality LEDs are sufficient. However, high-quality LEDs must be used in many areas that require consistency, reliability, solid-state indication or lighting, especially in harsh environments, such as on highways, military/aviation, and industrial applications.

In environments such as New York subway stations, safety requirements are very stringent and LEDs must meet high quality requirements.

What are the factors that distinguish the quality of LEDs? How to tell the difference between two LEDs? In fact, there are many factors to consider when choosing high-quality LEDs, starting from the chip to the assembly. Tier-One LED manufacturing companies are able to produce high-quality wafers with consistent specifications starting from high-quality LED manufacturing materials, which can then produce high-quality chips. Among the conditions that determine all the performance indicators of LEDs, the chemical materials used in the wafer production process are quite important factors.

A 2-inch wafer can be cut into more than 6,000 LED chips, and only the performance indicators of individual chips are different from the overall. The chips manufactured by a good chip manufacturer have very small differences in color, brightness and voltage drop. When LED chips are packaged, many of their performance indicators may vary greatly, such as viewing angle. In addition, the impact of packaging materials is also considerable. For example, silicone resin performs better than epoxy resin.

Classification ability

Excellent LED manufacturers can not only manufacture high-quality chips, but also have the ability to classify and package LEDs according to their color, brightness, voltage drop and viewing angle. High-quality LED suppliers will provide customers with products with consistent working characteristics, while low-quality LED suppliers can only provide LEDs similar to "mixed packaging".

For high-end, quality-critical applications, such as airport runway boundary lights, which must meet FAA-level color and brightness specifications, LED packaging consistency is also strictly limited to ensure performance and safety. LEDs with poor packaging grades used in demanding applications will lead to a series of non-consistency problems such as premature failure, which may lead to major accidents. In order to avoid equipment downtime and ensure that the LEDs specified in the design have reliable operating characteristics, it is very important to avoid using "mixed" products in high-end and quality-critical applications.

Product Support Capabilities

In addition to discrete LEDs, the assembly and power supply of LEDs have a very important impact on its performance, brightness, color and other indicators. Since ambient temperature, operating current, circuit structure, voltage spikes and environmental factors can affect the performance indicators of LEDs, proper circuit design and assembly are the key to protecting LEDs and ensuring performance. LED manufacturers also use a variety of technologies and different materials to design circuit structures and assemblies. In most cases, the difference in experience of LED assemblers will cause differences in the overall performance and reliability of LEDs in the same application.

As the demand for LEDs grows rapidly, the number of manufacturers and assembly plants serving the global market has also increased rapidly. Unfortunately, the surge in supporting manufacturers not only uses a large number of low-quality LEDs, but their packaging and LED design engineers are also relatively inexperienced. Therefore, in addition to accurately screening LED suppliers through existing experience, OEMs must also examine their circuit design and assembly technology to ensure that design specifications are met, and whether the design provides sufficient heat dissipation capabilities, because the main factor leading to LED failure and inconsistent performance is overheating.

To ensure that design requirements are met, OEMs must test the LED assembly and circuit structure.

Third-party testing

In order to eliminate the unfairness in testing, many companies have entrusted a third party to test the assembly and circuit structure of LEDs. An LED device may be tested or used for weeks in a harsh environment. During the test, pressure, temperature cycle, voltage fixation/variation, current fixation/variation and other tests are carried out simultaneously to determine whether the LED meets the application requirements. A large number of parameter changes before and after the test must be recorded, and the changes in the brightness, color and voltage drop of the tested LED must be monitored.

Accelerated life cycle testing is a key test to avoid failures in special applications. Testing helps to screen out those LEDs that are expected to work for at least 100,000 hours, but fail prematurely after only 1,000 hours. This situation is possible because low-quality LEDs (or high-quality LEDs that are not properly assembled) will lose brightness after 1,000 hours of operation. In fact, a low-quality LED will be brighter than a high-quality LED at the beginning of operation if it has a higher drive current. However, too high a current will cause the LED to heat up too quickly, and the end result is dimming or burning.

In addition, there are also examples where assembly technology has a greater impact on LED performance than the chip itself. Design engineers should ask LED suppliers for LED reliability specifications, and should also perform LED assembly tests to ensure that higher brightness is indeed better. Some excellent LED suppliers can guarantee that the reliability of their LED assembly technology can last for three years or more, and can further provide final LED products including high-quality LEDs and appropriate designs for special applications.

Importance of testing

Two applications in the transportation field help explain how adequate testing can prevent LED failures in applications that provide high visibility. In the early 1990s, LEDs were used in brake lights for cars and trucks. Some LED designs quickly showed inconsistent performance and burned out, either because of the quality of the LEDs or simply because of the design of the products themselves. This phenomenon was not taken seriously until recently, when LEDs became a more suitable light source for traffic lights. Companies designing 8- or 12-inch diameter printed boards filled with LEDs must consider environmental and application requirements in selecting LEDs and improving designs.

In any of the above cases, if stress testing or accelerated life cycle testing has been done, it can be considered that the high-quality LED or LED assembly is qualified and can be used in situations that require longer service life and higher reliability.

Fair Use

Not every application requires high-quality LED assembly technology. If the LED assembly does not meet the requirements of a harsh environment, the application does not necessarily present a greater safety risk, or if the repair cost of the final product is not very high, using inferior assembly technology may be more appropriate.

The most fundamental point is that LEDs must be affordable. Therefore, within the constraints of cost requirements, factors such as the packaging level of the supplier's products, experience in assembly design, and testing must be considered. Design that meets application and market needs is the most effective means of serving end users. If the application requires a high-end solution, then the choice of chip suppliers, design experience, and testing are all factors that should be considered. If the selling price of high-end products is not a consideration, other relevant factors that distinguish good from bad LEDs should be carefully considered. LED suppliers with the ability to classify packaging levels and manufacturers that can perform reliability and accelerated life cycle testing can be long-term partners, which will help manufacturers develop high-end products using more reliable LEDs.