LED product reliability verification

- Feb 21, 2019-

‘Reliability’ is a noun that uses time as the main axis, that is, the probability that the device will operate normally for a specified period of time. At present, the concept of reliability has been applied in the design and development stage of various electronic products, the purpose of which is to ensure that the quality of the design of the own products can meet the expectations and meet the needs of users.

Of course, due to the financial tsunami in the world from 2008 to 2009, the economic situation has fallen into a rare low tide in the past century. At this time, 'energy saving and carbon reduction' has become the only slogan and common pursuit goal in the world, so led (light-emitting diode - Light- Emitting Diode) has thus become a product of the era of 'energy saving and carbon reduction'. As long as it is a product related to ‘light’, each manufacturer has no need to try its best to connect with LED. For example: indicator lights, lighting, indoor atmosphere lights, advertising kanban lights, car lights, panel backlights, etc., have developed rapidly in the past two years, and even the development of these LED related peripheral products is much faster than the LEDs developed by international standard units. Test regulations have resulted in the fact that there is no one-size-fits-all code in the world that can be used by LED-related product designers. Therefore, the current LED regulations market has become a warring country with a hundred schools of thought and expression.

Therefore, the author sees this situation and judges that there should be no consensus results in a short period of time. Therefore, I would like to provide some suggestions for the majority of LED product designers. The purpose is not to call everyone to the LED regulations. Give birth, but share personal experience in the field of reliability, to outline how a product designer can do preliminary and basic verification of the LED products he designed without the precedent or international standard method. Understand the tolerance of the LED products developed, thereby improving the quality of their design, increasing market acceptance and reducing the risk of customer retreat.

The following two parts will be briefly introduced. Regardless of whether the LED is presented as a part or a finished product, the following modes can be utilized and the basic verification of the LED product can be achieved.

1, product life verification

In the electronics industry, in order to claim the life of a product, three methods are usually used.

(1) Life Prediction Method (Prediction)

Method: According to MIL HDBK 217 Part Count and Part stress principles, software is used to calculate the life of the product.

Advantages: Short time and low cost

Disadvantages: The result is very different from the actual product life

(2) Lifetime measurement method (Demonstration)

Method: Using the Acceleration model, the Acceleration factor was obtained and the actual sample was provided. The sample was measured by an environmental test simulator to obtain the product life. At present, the acceleration model adopts the highest Arrhenius model (high temperature acceleration), Coffin-Manson model (temperature cycle acceleration) and Hallberg-Peck (humidity acceleration).

Advantages: The result is more realistic than the prediction method, and the industry is highly accepted.

Disadvantages: Higher cost and time-consuming than estimated method

(3) Field return method (Field return)

Method: Recycle the use of product users on the market.

Advantages: The result is equal to the real life

Disadvantages: Time and cost are longer, market usage is difficult to obtain, usually only the brand field self-preservation

The above three methods for obtaining the life of the product are adopted by the industry at the most, because it can not only eliminate the shortcomings of the result and the actual difference, but it is obtained through actual measurement, regardless of the high acceptance of both buyers and sellers.

2, product environmental test verification

In the March 2009 issue of the component magazine, the author has proposed which projects to implement environmental testing of LED-related products and a simple definition of these projects. Therefore, the content and details of the test here are not much inked here. But this time to guide everyone how to use these environmental test projects has reached a level of quality that truly enhances product design.

First of all, be sure to analyze the life profile of the product you are designing. What is the environment that the product may be in the life cycle? What are the users? The properties of this product? Are there any other special requirements for the product? These factors may be Influencing the future is the specification of the test, and do not fall into the norm of the process in the process, because a good verification specification is definitely not completely copied from a certain specification, because even the best specification can not simulate the actual environmental requirements. That is just a loss, it will only waste more resources and costs. For example: The designer of LED lamps designed a street lamp for use in the streets of Indonesia and set a verification specification of -40 ° C. It is very happy to do it because the recommended low temperature in the IEC is -40 ° C. But please think back, Indonesia is located near the equator, it has a tropical climate. How can it encounter a climate of -40 °C when it is hot and humid all year round? Therefore, designing a product that never touches the environment will only increase the design. Cost, because the cost of LED luminaires designed to withstand -40 ° C environment must be higher than the design is designed to withstand 0 ° C environment.

Therefore, the author's intention is to invite product designers to return to the fundamentals, to carefully review the products designed by their own, in order to achieve an efficient and reliable verification of the actual requirements.

Finally, because the LED products are different from other electronic products, regardless of the reliability before and after verification, the luminescence characteristics must be measured. Generally, the calculus ball or the light distribution curve meter can measure the color of the LED products. Temperature), Luminous flux, Luminous intensity, Chromaticity coordinates, Color rendering, Wave length, etc., as the basis for reliability verification results.