Past led industry who to profit full of white light LED beam, had development large size LED flood lights chip tries to by this way reached expected target, but actually white light LED of imposed power continued over 1W above time beam instead will fell, glow efficiency is relative reduced 2030%, in other words white light LED of brightness if to than traditional LED large number times, consumption power characteristics hope beyond Firefly light lamp words, on required first overcome following of four topics, including, suppression temperature rose, and ensure using life, and Improvement of luminous efficiency and photoluminescence of equalization.
The problem of temperature rise of the specific method is to reduce the thermal resistance of the package; maintenance of Blue LED strip the life of a specific method, is the improvement of chip shape, small chip; improving the LED luminous efficiency of specific measures is to improve the structure, a small chip chip; improvement of luminescent characteristics of uniform methods is LED packaging methods, and in the development of these methods have come to be.
Thermal problem is the fundamental way to solve package
Due to increased power instead will caused package of hot impedance sharply fell to 10K/W following, so abroad industry who had development resistance high temperature white light LED tries to by this improve above problem, however actually power LED panel of heat is than small power LED high dozens of times times above, and temperature rose also will makes glow efficiency sharply fell, even package technology allows high heat, but LED chip of junction temperature is has may over allowed value
Finally finally learned to solve thermal problems is the root of the package.
About LED of using life, such as instead Silicon mass package material and ceramic package material, can makes LED of using life improve one number, especially white light LED of glow spectrum contains wavelength below 450nm short wavelength light, traditional epoxy resin package material very easy is short wavelength light damage, high power white light LED of large light volume more accelerated package material of bad of, under industry who test results displayed continuous light does not to 10,000 hours, high power white light LED of brightness has reduced half above, Does not meet the basic requirements for lighting and long life.
About LED of glow efficiency, improve chip structure and package structure, are can reached and low power white light LED same level, main causes is current density improve twice times above Shi, not only does not easy from large chip out light, results instead will caused glow efficiency than low power white light LED of dilemma, if improve chip of electrode constructed, theory on can solution above take light problem.
Seeks to reduce the thermal resistance, improve the heat sink problem
About luminescent characteristics of uniform, General believes that improving the concentration of fluorescent white light LED material uniformity and fluorescent technology, should be able to overcome these problems. As mentioned above while improving power imposed, must try to minimize thermal impedance, improved heat dissipation, and specific content in the report are: reducing the chip to the thermal resistance of the package, contain the package thermal resistance, improve the chip to printed circuit substrate heat sink of smooth.
To to reduced hot impedance, many abroad LED manufacturers will LED chip set in copper and ceramic material made of thermal fin tablets (heat sink) surface, received s then with welding way will printed circuit board Shang thermal with wire, connection to using cooling fan forced empty cold of thermal fin tablets Shang, under Germany OSRAM Opto Semiconductors Gmb experimental results confirmed, above structure of LED chip to welding points of hot impedance can reduced 9K/W, about is traditional LED of One-sixth around, package Hou of LED imposed 2W of power Shi, LED chip of junction temperature than welding points high 18K, even printed circuit board temperature rose to 500C, junction temperature at most only 700C around; phase than Xia past hot impedance once reduced words, LED chip of junction temperature on will was printed circuit board temperature of effect, so then required managed to reduced LED chip of temperature, in other words reduced LED chip to welding points of hot impedance, can effective reduce LED Chip cooling burden of the job. Contrary even white light LED has suppression hot impedance of structure, if heat cannot from package conduction to printed circuit board words, LED temperature rose of results glow efficiency will sharply fell, so Panasonic electrical development printed circuit board and package integration technology, the company will 1mm square of Blu-ray LED to flip chip way package in ceramic base board Shang, received s then will ceramic base board paste in copper mass printed circuit board surface, under Panasonic said contains printed circuit board zainei module overall of hot impedance about is About 15K/W.
Show thermal design power
Due to thermal fin tablets and printed circuit board Zhijian of key s sexual directly around hot conduction effect, so printed circuit board of design became very complex, has prison Yu this United States Lumileds and Japan CITIZEN, lighting device, and LED package manufacturers, have development high power LED with simple thermal technology, CITIZEN in 2004 began samples shipments of white light LED package, does not needs special junction technology also to will thick about 23mm thermal fin tablets of heat directly emissions to external, under the CITIZEN said although the LED chip junction to heat thermal impedance than the OSRAM 9K/W fin 30K/W, and in general the environment around room temperature will increase the thermal resistance under 1W, however even traditional printed circuit boards without the cooling fan under forced air cooling, the white light LED modules can also use continuous lighting.
Lumileds high power LED chip began sample shipments in 2005, junction allowed temperature is as high as +1850C, 600C higher than similar products of other companies, when using traditional RF4 printed circuit board packaging, the ambient temperature can enter 400C range 1.5W electric current (about 400mA). So Lumileds and CITIZEN makes take improve junction points allowed temperature, Germany OSRAM company is is will LED chip set in thermal fin tablets surface, reached 9K/W super low heat impedance records, the records than OSRAM past development sibling products of hot impedance reduced 40%, worth a to is the LED module package Shi, used and traditional method same of flip chip way, but LED module and hot fin tablets junction Shi, is select most near LED Chip layer as the land, take the light layer to provide short-distance transmission of heat emission.
LED flood lightsBlue LED stripLED panel
Article Source: Improve the thermal structure of white light LED life
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