Early on, the LED street lighting is mainly used as an indication or display lamps , and generally appear to single devices , so for the wavelength of sorting and brightness control requirements are not high . But with the efficiency and brightness of the LED continuously improve its increasingly wide range of applications . When the LED display and the display device as an array , because the human eye for color and brightness wavelength sensitivity , with no sorting through the LED turns will produce uneven phenomenon , thereby affecting people's visual effects. Wavelength and brightness unevenness will give an uncomfortable feeling. This is the LED display manufacturers are not willing to see, is that people can not accept.
LED generally in accordance with the dominant wavelength, luminous intensity , luminous flux , color temperature , voltage, reverse breakdown voltage , and several other key parameters for testing and sorting . LED testing and sorting LED production process is a necessary step . Currently, it is the number of LED chips and packaging manufacturers capacity bottlenecks , but also the LED chip manufacturing and packaging costs an important part .
Method of selection of LED
LED sorting of two ways: First, the chip -based test separator , the second is for testing packaged LED sorting .
( 1 ) test of the chip sorting
LED chip sorting is very difficult, mainly due to the LED chip size is generally very small, from 9mil to 14mil (0.22-0.35nm). Such small microprobe chip needs to be able to complete the test , the process of sorting machines and require precise image recognition system , which makes the cost of the device becomes high , and the test speed is limited . Now the LED chip testing sorter price of about one million yuan \ Taiwan , and its test speed of about 10,000 per hour . If the calculation of the monthly 25 days , each sorter 's monthly capacity 5KK.
At present , the test chip sorting in two ways:
One way is to test the sorting completed by the same machine , it has the advantage to be reliable , but the speed is very slow, low productivity ;
Another method is to test and sorting done by the two machines , testing equipment, record the location and parameters of each chip , and then pass the data to the sorting device, for quick sorting, so the advantage is fast, but the drawback is relatively low reliability , error-prone , because in testing and sorting usually has between two steps separating the substrate and chip thinning process , and in this process , the wafer may be broken , local incomplete or partially incomplete fragmentation , making the actual distribution and stored in the chip sorting machine where the data does not match , resulting in separation difficult.
From the fundamental solution to the bottleneck problem of sorting chip testing is the key to improving wafer uniformity. If a wafer within 2nm wavelength distribution in brightness changes within +15 % , it can be all the chips on this film into one file (Bin), as long as the failure to pass the test chip removal can will greatly increase the capacity and reduce the chip cost of the chip . Uniformity is not very good in the case can also be used to test and put " more substandard products ," the chip area coated inkjet manner disposed of, to quickly get the desired "qualified" chip , but doing so the cost is too high , other rooms will meet the requirements of many chips as substandard waste disposal permit , the final accounting of the cost of the chip market may be an unacceptable level .
(2) LED sorting tests
The LED can be packaged according to wavelength , light intensity , light angle and the operating voltage testing sorting . As a result, the LED into many files (Bin) and categories , and then test the sorting opportunities automatically according to the setting of the LED test standards in different Bin packing box. As people increasingly high demand for the LED , the early sorter is 32Bin, later increased 64Bin, now has 72Bin commercial sorter . Even so, the sub- Bin LED technology indicators are still unable to meet production and market demand.
LED test separator working in a specific TPC flow ( eg 20mA), the LED test , the general will do a reverse voltage value of the test . Now LED test sorter price of about 40 to 500,000 yuan / Taiwan, its test speed of about 18,000 per hour . If you follow a monthly 25 days , 20 hours per day working time calculation , each sorter 's monthly capacity 9KK.
Large display applications , or other high-end customers, high quality requirements of the LED . Especially in the wavelength and brightness consistency requirements are very strict . If the LED packaging factory in chip purchases not made strict requirements , these packaging factory in a large number of packages will be found , packaged LED , only a small number of products to meet a customer's requirements , most of the rest will become into the warehouse inventory. This situation forces the LED packaging plant in the LED chip purchases made strict requirements , in particular the wavelength , brightness, and the voltage indicator table ; for example , a wavelength of the last requirement is +2 nm, and now requires the +1 nm, and even in some these applications have been proposed +0.5 nm requirements. For chip factory to produce such enormous pressure , before selling the chip must be strict separation .
From the above the LED chips on the LED of the selected points can be seen , more economical approach is to test the LED street lighting sorting . However, a wide range of the LED , different forms , but now the shape of different sizes , different light angles, different customer requirements, different application requirements, which have completely the right to use the LED products selected for the test of the sub- select become difficult to operate. And the current LED applications are mainly distributed in several wavelengths, and brightness range segment , a packaging factory is difficult to prepare all the customer needs in various forms and types of the LED. So the key issue back MOCVD epitaxial process , how to grow a desired wavelength and brightness of the LED epitaxial wafers is to reduce the cost of key points , this problem is not resolved , LED production capacity and costs will not be fully resolved. But the uniformity of the epitaxial film is controlled ago, relatively effective method is to solve the fast low-cost chip sorting problem .
Sorting equipment
Currently, LED chip testing sorting equipment mainly by the United States and Japan, vendors , and LED test sorting equipment mostly by Taiwan, Hong Kong manufacturers in mainland China is not able to provide similar equipment manufacturers. LED chip sorter includes two hardware components ( robot , micro- probe and optical tester ) and a set of system software, which is three parts by different manufacturers to provide further integrate ; while the LED test points selected machine includes LED mechanical transmission , storage and optical testing in two parts.
LED technology trends of selected
( 1 ) the uniformity of the epitaxial film be controlled before the rapid development of low-cost chip sorting processes and equipment.
( 2 ) With the class W power LED technology, the traditional parameters of LED product testing standards and testing methods can not meet the lighting needs of the application , shall develop new test standards and methods , contains more optical and lighting related content.
( 3 ) in the LED system life testing, research and development of LED systems rapid determination of long-term performance and lifetime assessment techniques .
( 4 ) LED lighting is in working under high current drive , which raised its higher reliability requirements. Filter by inappropriate traditional LED lighting with high-power LED. Must develop new screening test approach , excluding early failures goods, to ensure product reliability.
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