Wednesday, January 5, 2011

【 Weak current College 】 LED separation technology 】

The human eye for color and brightness of the light of the resolution is very high, especially for color difference and change very sensitive. For different color wavelength of light the human eye's sensitivity is different. For example, for optical wavelength is 585nm, when the color changes greater than 1nm, the human eye can feel; for wavelength 650nm red light for, when the color changes in 3nm, the human eye can perceive.
In the early days, LED mainly to be used as a direction or display lamp, and generally to single dual devices appear, so for its wavelength of separation and the brightness of the control requirements are not high. However, as LED by efficiency and brightness, its application range has become an increasingly widespread. When the LED display as array and display devices, because the human eye for color wavelength and intensity of sensitivity, with no separation of LED variable will result in uneven phenomenon, affecting people's Visual effects. Wavelength and uneven brightness will give rise to an uncomfortable feeling. This is the LED display manufacturer are not willing to see, it is unacceptable. LED usually follow the dominant wavelength, luminous intensity and luminous flux bright, color temperature, voltage, reverse Breakdown voltage, and other key parameters for testing and sorting. LED by testing and sorting is LED production a necessary process. At present, it is a lot of LED chip and package manufacturers capacity bottlenecks, and also the led chip production and packaging costs.
1, LED by separation method
LED by sorting in two ways: first, to chip-based test sorting, the second is to encapsulate the good LED to test sorting.
(1) chip test sorting
LED chip sorting difficult, mainly because of the LED chip scale is generally very small, from 9mil to 14mil (0.22-0.35nm). Such a small chip need microprobe to complete testing and sorting process requires precise machinery and image recognition system, which makes the device cost becomes very high, and test the speed is limited. Now the LED chip test separator price in about 100 million Yuan; & # 92, the test speed in just about every hour 10000. If you follow the monthly 25 days calculation, each separator production 5KK per month.
Currently, chip test sorting in two ways: one way is to test sorting is completed by the same machine, it is reliable, but is very slow, low productivity; another option is to test and sorting is completed by two machines, test equipment to record the location of each chip and parameters, and then take the data passed to the sorting device for quick sorting, this advantage is fast, but the disadvantage is that reliability is relatively low, and prone to error, because in the test and the separation between two steps often have substrate thinning and chip separation process, and in this process, the wafer is likely to break-up, partial incomplete or partially torn fragments, making the actual chip distribution and storage in the separator does not match the data in, causing separation difficulties.
Fundamentally resolve the chip test sorting key bottleneck is to improve wafer uniformity. If a wafer wavelength distribution in 2nm, brightness changes in + 15%, you can set the film on the chip into a stall (Bin), as long as the test gave unqualified chip removal, will greatly increase the chip capacity and reduce the cost of the chip. In uniformity is not very good, you can use to test and put "not qualified products more" chip area used inkjet coated way disposed to quickly get to the "qualified" chip, but the cost is too high, will put a lot of rooms meet the other requirements of the chip are done for non-conformity of waste treatment, the final accounting of the chip cost may be a market cannot be accepted.
(2) LED test sorting
Package LED after you follow the wavelength, luminous intensity, wide viewing angle, as well as operational voltage for test selection. The result is the LED into many stalls (Bin) and category, and then test the sorting of the opportunity to automatically according to the set of test standards LED packing in different Bin box. As people increasingly high demands of LED, early separator is 32Bin, later increased to 64Bin, now have 72Bin commercial separator. Even so, a Bin of LED specification is still unable to meet the needs of the production and marketing.
LED test separator is in a specific table current (20mA), LED, will be a general reverse voltage value of test. Now the LED test separator price in about 40-50 million RMB/set, the test speed in just about every hour 18000. If you follow the monthly 25 days 20 hours of working time, each separator production 9KK per month.
Large screen display or other high-end application client, LED by the high quality requirements. Especially in the wavelength and brightness uniformity requirements are very strict. If the led packaging plant in chip purchase without stringent requirements, these packaging plant in large amounts of packaging will find packaged LED in only a small number of products to meet a customer's request, the majority of the remaining ones will be turned into a warehouse stock. This situation forced led packaging plant in purchasing led chip is made, particularly wavelength, brightness, and working voltage of indicators; for example, in the past on the wavelength is + 2nm and now the requirement is + 1 nm, even in some applications, has made + 0.5 nm. So for chip factory creates enormous pressure on the chip sales must be strict separation.
From the above about LED and LED chip in the selected analysis can be seen, more economical way is to test sorting LED. However, due to a variety of LED, have different forms, not now, different dimensions, different beam angle, different customer requirements, different application requirements, this right was completely through the LED test selection of products sorting becomes very difficult to exerciseMake. It is currently LED by the application are distributed in several wavelength and intensity paragraph of a packaging plant is very difficult to prepare all the customer needs of various forms and kinds of LED. So the key back to MOCVD epitaxial growth process, how to produce the desired wavelength and intensity of LED Epitaxial wafers is the key point of the reduction of costs, the problem is not solved, LED by the productivity and cost still will not be fully resolved. But in the wafer uniformity is controlled in the past, more effective approach is resolving fast low cost chip sorting issues.
2. sorting equipment
At present, the LED chip test sorting equipment mainly by the United States and Japan, which LED manufacturers to test sorting equipment mostly from Taiwan, Hong Kong, mainland China, the vendor has not yet been able to provide similar equipment manufacturers. LED chip sorter includes two major hardware components (machine hand, microprobe and optoelectronic tester) and a set of system software, and the three parts from different manufacturers to provide further integration; and LED test points select machine include LED transmit of machinery, storage and optical test in two parts.
3.LED minutes select technology development trends
(1) in the wafer uniformity is controlled in the past, research and development, rapid and low-cost chip separation technology and equipment.
(2) with the W-level power LED technology, traditional LED product parameter testing standards and testing methods can not meet the need for lighting applications, the development of new testing standards and methods, contains more and lighting-related optical elements.
(3) in the LED system life testing, research and development of LED systems of long-term performance and rapid determination of evaluation of the technical life span.
(4) lighting LED at high current drive, and that the higher reliability requirements. Traditional LED the way for screening is not appropriate lighting high-power led, must develop new screening test for early failure, rejection, guarantee product reliability.

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