Discussing the test solution of COB packaging

In recent years, LED devices packaged in COB (Chip On Board) have developed rapidly with their unique advantages. This integrated packaging process has been expanded to include MCOB, MLCOB, COF, COMMB and other forms. Both the light efficiency and heat dissipation performance indicators have been greatly improved. It has been widely used in various LED lighting devices and has become one of the mainstream forms of LED packaging.

　　The optical, color and electrical parameter testing of COB devices brings some special requirements to their laboratory testing and production line testing due to their high power, high price per unit and various appearances. The author would like to share some of his experiences here for communication.

　　About COB laboratory testing program

　　Due to the high power of COB, the junction temperature changes very quickly after power is turned on during the test process. Different test methods and conditions have a great impact on the test results. The length of the test time and the heat dissipation of the test fixture directly affect the test results. Under the same test conditions, the change in junction temperature can change the important indicators of LED luminous flux, color temperature, and light efficiency by more than 8%. Therefore, the junction temperature problem must be considered in the COB test process. At present, most laboratory tests use the scheme of starting the test after the heat sink reaches thermal equilibrium. This scheme is simple and convenient to use, but the disadvantage is that it is time-consuming. When testing similar products, if the thermal resistance of the device has a large deviation, it will cause test errors. The optional test scheme provided by Xingpu Company is to test the light, color, and electrical parameters under the set junction temperature conditions. The advantages of this scheme are that no specific temperature control fixture is required, the test speed is fast, the consistency of the same batch of samples is good, and the test repeatability is good. The disadvantage is that special equipment is required (such as Xingpu Optoelectronics' SSP8810-S series products).

　　The increase in the configuration of the test fixture due to the variety of appearances also brings inconvenience to the test. Different fixtures will cause deviations in the light color parameter test. The solution is generally to calibrate and correct each fixture.

　　Solutions for COB production line testing

　　The following problems bring inconvenience to the production line testing of COB. First, there is no unified specification and standard for the appearance and other specifications of COB products. Most of them are set by manufacturers according to their own needs. Therefore, there are many types of COB on the market, and the output of a single variety is difficult to achieve large-scale production. This is unfavorable for the development of fully automatic COB testing and sorting equipment. Second, the cost of a single COB is relatively high, and the production process according to order requirements requires a very high yield rate, so the powder replenishment link in the production process is necessary, and because COB has many specifications and varieties, the testing link needs to provide personalized services. Third, the method of installing the COB on the radiator and testing it after the temperature reaches equilibrium takes too long and cannot meet the production requirements of production line testing.

　　At present, there are many methods for COB production line testing. Generally, suitable fixtures are designed to meet the test and loading requirements of COBs of different specifications. The test methods mostly use transient tests, fixed delay tests, etc. However, the results of these test methods are sometimes quite different, and there will be situations where the requirements for direct comparison cannot be met. Production line test equipment not only requires accurate testing of COB's relevant performance indicators, but also requires meeting certain process and timeliness requirements, and needs to be perfectly connected with the existing production process of the manufacturer.

　　The fundamental reason for the deviation of COB test results due to different test methods is the different junction temperatures during the test. Some companies have also designed different test methods based on their own understanding. For example, Philips once commissioned Star Spectrum Optoelectronics to customize COB and its module production line test equipment, which took the junction temperature factor into consideration. The requirement for comprehensive testing of COB in terms of light, color, heat and electricity at a specific substrate temperature was proposed. The advantages of this test method are very obvious. The junction temperature during the test is close to the junction temperature during actual use, which makes the test results closer to the actual use status. For manufacturers of LED application products, they are very concerned about the junction temperature data of LED devices after lighting under normal ambient temperature conditions. Because it can provide an intuitive basis for the reliability and life evaluation of the product, and can also provide a basis for the rationality evaluation of the product in the thermal structure design. Because the unified and recognized methods and standards for accelerated aging testing are still in the research stage, the junction temperature of the product under normal working conditions can reflect whether the product is working safely, which is also one of the main bases for life evaluation. In terms of COB junction temperature testing, the voltage method commonly used internationally has been used to measure COB junction temperature. COB is regarded as a PN junction, and its comprehensive junction temperature is tested using the voltage method, which has achieved relatively good results.

　　As the market demand for COB continues to increase and specifications are unified, the design concept of COB detection and sorting equipment will change, and fully automatic equipment will become the mainstream to meet its production needs.

　　In view of the current situation of diversified specifications and parameters in the COB market and small output of a single specification, the matching testing equipment must provide customized tooling services. Xingpu Optoelectronics provides excellent modular design solutions in this regard, so that one device can be conveniently used for COB testing, sorting and powder replenishment of various specifications, meeting the production needs of COB manufacturers and reducing the actual cost of equipment. At the same time, the SSP8810-S series equipment for thermal performance testing and the SSP3190-JCH test and powder replenishment equipment have reserved test design space for high-voltage chips, which can meet various needs.

　　At present, Xingpu Optoelectronics has launched the SSP8810-SLED light, color, electricity, and heat comprehensive test system, SSP3190-JCH COB array test and powder replenishing machine, and 3112-JC COB production line test system in response to various needs of COB thermal characteristics testing and production line testing. Among them, the company's latest developed 3112-HP COB lamp production line comprehensive performance test system has successfully passed the Philips Lighting test acceptance, and the company has also become a designated qualified supplier of Philips Lighting. At the same time, the SSP3190-IPCOB automatic spectrometer with an hourly production capacity of more than 3k is now on the market.

　　SSP3190-JCH COB row test powder filling machine;

　　SSP8810-SLED light, color, electricity and heat comprehensive test system.

　　In order to ensure the accuracy of the junction temperature test, Starspect Optoelectronics' test system not only has an ingenious design, but also uses high-end imported chips and is equipped with a 3112 light color test system, enabling the system to simultaneously detect the light, heat, electricity, and color characteristic parameters of various LEDs and lamps and their interrelationships.

　　Its function of continuously testing the change of light color characteristics under different junction temperatures can continuously express the relationship between the change of luminous flux, luminous efficiency, wavelength, color temperature, color rendering index, color coordinates and other parameters of LED and LED lamps with junction temperature. There are currently no similar products at home and abroad with this functional design.

　　SSP3112-HP Integrated Package (COB) LED Production Line Comprehensive Test System: This is a device that can perform comprehensive light, color, heat, and electricity tests on COB and COB finished modules at a specific TC temperature. It is the first of its kind in the industry and has passed the test acceptance of Philips Lighting. The advantages of this test method are obvious: the junction temperature during the test is close to the junction temperature during the actual application, and the test results are closer to the actual use status, objectively considering the factor of junction temperature. This product can also provide multiple functions such as resistance detection and low current dead light detection according to the customer's product characteristics. It can be used for large-scale incoming material inspection and quality inspection of finished modules. There is also SSP3190-IPCOB automatic spectrometer, etc.