LED industry in the past in order to benefit fully of white light LED light beam, has developed a large size LED chip sought to achieve the desired objectives, but in fact imposed power white light LED continuous time beam will fall more than 1W, luminous efficiency is relatively lower 20~30%, in other words white LED light brightness if several times larger than conventional LED consumer wish to rise above power characteristic fluorescent lamps, Must first overcome the following four areas: a. inhibition of temperature rise; b. ensuring life; c. improved luminescent efficiencies; d. photoluminescence of equalization.
Issues related to temperature rise concrete method is to reduce the package thermal resistance; maintenance LED the life of the specific method is to improve the chip shape, using a small chip; improving the specific method of LED luminous efficiency is improving chip architecture, the use of small chips; as for luminescent characteristics of homogenization improvement of specific methods are LED packaging methods is generally believed that 2005-2006 white-light LED this measure is expected to be adopted.
Development Jingwei increased power instead will caused package of hot impedance sharply dropped to 10K/W following, therefore abroad industry who had development resistance high temperature white light LED tried to borrowed this improve above problem, however actually high power LED of calorific value but than small power LED high dozens of times times above, and temperature rose also will makes glow efficiency substantially decreased by, even package technology allows high heat however LED chip of junction temperature but has may over allowed value, last industry who finally understanding to solve package of thermal problem is fundamental method.
About LED of using life, for example instead Silicon mass sealed material and ceramic package material, can makes LED of using life improve 10%, especially white light LED of glow spectrum contains wavelength below 450nm short wavelength light, traditional epoxy resin sealed material very easy was short wavelength light damage, high power white light LED of large light volume more accelerated sealed material of bad of, under industry who test results display continuous lighting does not to 10,000 hours, high power white light LED of brightness has reduced half above, Can not meet the basic requirements for lighting and long life.
The LED luminous efficiency, improve chip structure and packaging structure, with low power white LED can be reached the same level, mainly due to the current density increase twice above, not only are not easy to remove the light from a large chip, results will make light-emitting efficiency than the dilemma of low power white LED light, if the electrode structure to improve chip, take light of these problems can be solved in theory.
About uniformity of luminescence is generally believed that as long as improved concentration of fluorescent material uniformity of white-light LED, and the making of Phosphor technology should be able to overcome these problems.
As mentioned above while improving power imposed, must seek to reduce the thermal impedance, improved heat dissipation, specific contents are:
① reduce chip to package thermal resistance
② inhibiting packaging to printed circuit substrate thermal impedance
③ increasing chip cooling 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, then then with welding way will printed circuit plate 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 plate 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 plate temperature of effect, so comes required managed to reduced LED chip of temperature, in other words reduced LED chip to welding points of hot impedance, Can effectively reduce the burden of LED chip cooling job. Contrary even white light LED has suppression hot impedance of structure, if heat cannot from package conduction to printed circuit plate words, LED temperature rose of results glow efficiency will sharply fell, therefore Panasonic electrician development printed circuit plate and package integration technology, the company will 1mm square of Blu-ray LED to flip chip way package in ceramic base plate Shang, then then will ceramic base plate paste in copper mass printed circuit plate surface, According to the Panasonic contains module, printed circuit board as a whole about the thermal resistance is approximately 15K/W.
Due to thermal fin tablets and printed circuit plate Zhijian of key with sexual directly around hot conduction effect, therefore printed circuit plate of design became very complex, has in view of this United States Lumileds and Japan CITIZEN, lighting device, and LED package manufacturers, successively development high power LED with simple thermal technology, CITIZEN company 2004 began samples shipments of white light LED package, does not needs special junction technology also can will thick about 2~3mm thermal fin tablets of heat directly emissions to external, According to the company said although the LED chip junction thermal impedance to the heat sink fins 30K/W larger than the OSRAM 9K/W, and under the General environment at room temperature will increase the thermal impedance around 1W, but even the traditional printed circuit boards without cooling fan forced air cooling mode, or continuous lighting using the white light LED modules.
Lumileds companies in 2005 to start sample shipments of high power LED chips, junction allowed temperature is as high as +1850C, 600C higher than other companies similar products, using traditional RF4 when printed circuit board packaging, the ambient temperature within the 400C can enter 1.5W electric current (about 400mA).
As above introduced Lumileds and CITIZEN company take improve junction points allowed temperature, Germany OSRAM company is is will LED chip set in thermal fins 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 mention is the LED module package Shi, used and traditional method same of flip chip way, however LED module and hot fins tablets junction Shi, Closest to the LED chip emitting layer is selected as the land, take this light layer of heat conduction emission can in the shortest possible distance.
2003 Toshiba Lighting company had in 400mm square of aluminum alloy surface, laying glow efficiency for 60lm/W low heat impedance white light LED, no cooling fan, special thermal component premise Xia, try for beam for 300lm of LED module, due to Toshiba Lighting company has rich of try for experience, therefore the company said due to simulation analysis technology of progress, 2006 years zhihou over 60lm/W of white light LED, are can easily using lamps, and Frames improve thermal conductivity, or by cooling fan forced air cooling heat sink design lighting equipment, modular structure that does not require special cooling technology can also use white LED light.
Long life about LED, LED manufacturers to take countermeasures at present is change sealing material, while fluorescent material dispersed within the seal material, especially Silicon sealing material than traditional blue, epoxy sealing material over the near-UV LED chip, you can more effectively suppress material deterioration and reduced light penetration rate of speed.
Due to the absorption wavelength of epoxy resin as a percentage of 400~450nm light 45%, silicone sealing material of less than 1%, halving the luminance of less than 10,000 hours of epoxy resin, silicone sealing material can be extended up to 40,000 hours, almost the same as lighting design life, does not require replacement during this means lighting use white LED light. But Silicon resin is highly elastic, soft materials, machining required will not scratch the Silicon resin on surface technology, in addition to manufacturing Silicon resin vulnerable to attachment on cuttings, so future required developing technology to improve the surface characteristics.
Although silica sealing material can ensure that LED 40,000 hours of service life, but lighting industry who have different views, the main argument is the traditional life of incandescent and fluorescent lamps, is defined as "brightness fell below 30%", the LED brightness by half time of 40,000 hours, if converted into brightness fell below 30%, approximately only about 20,000 hours. At present there are two ways to prolong service life of the component strategies, namely:
1, contain the white light LED the overall temperature rise;
2, stop using resin package.
Generally considered if full implementation of the above two life extension strategies, brightness can be reached 30% hours of request. Inhibition of white light LED temperature cooling LED packaging method of printed circuit board can be used, mainly due to packaging resins under high temperature, coupled with strong light will execute a fast deterioration, in accordance with the rule Arenius temperature drop 100C life to be extended twice.
Stopping resin package can be used to clean the deterioration factors, because LED light reflection in the packaging resins, if you use may change the chip side resin material reflector of light direction, due to the reflective plate will absorb light, so the light of the offtake will drop sharply, which is also LED manufacturers in line with ceramic and metal packaging material mainly because of the Department.
There are two ways you can improve the luminous efficiency of white light LED chip, is a small chip area than (approximately 1mm2) 10 times times large LED chip; another way is to use multiple small high luminescence efficiency of LED chip, combined into a single module. Although large LED chip can get large beams, but increase the chip area would harm, such as chip unequal, glow, inner glow layer territories part limited, chip inside the light radiation to the external procedure is a serious attenuation, and so on. Electrodes for the above problems LED manufacturers modified the structure of, the use of flip chip package, while consolidating the chip surface processing technique has now reached 50lm/W luminous efficiency.
About chips overall parity, since 2, 3 years ago a comb-like grid (MeSH) after the p-type electrode, this way the manufacturer increasing, and the electrode is in best direction.
About flip chip package way, due to glow layer close to package end very easy emissions heat, plus glow layer of light radiation to external Shi no electrode blanked of plagued, so United States Lumileds and Japan Toyota synthesis has official used flip chip package way, 2005 began volume produced large LED of Panasonic electrical/Panasonic electrician and Toshiba also gradually followed up, past used wire bonding package way of day Asia chemical, 2004 published of 50lm/ W customers special products for LED, also uses a flip chip package.
About chip surface processing, it prevents light from inside the chip-chip external radiation in the interface reflection, according to Japan when an LED manufacturers have indicated their flip chip package, in the light removing parts set the bump-like structures on Sapphire substrates, chip external beam out can improve 30%.
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