I. Introduction

        Fromthe point of view of practical applications: simple installation in mostlighting applications, the relatively small volume of high-power LED deviceswill replace the traditional low-power LED devices. Its benefits are veryobvious, low-power LED lighting in order to achieve the lighting needs, we mustconcentrate many LED light energy in order to meet the design requirements.Bring the drawback is that the line is very complex, poor heat dissipation,necessary for the design of complex power supply circuit in order to balancethe current-voltage relationship between each LED. In contrast, the power ofhigh-power LED monomer is much larger than a single LED is equal to the sum ofthe number of small power LED, power lines are relatively simple, perfect heatdissipation structure, physical properties and stability. So, the high-powerLED devices instead of small power LED devices become mainstream semiconductorlighting devices is inevitable. But encapsulation method for high-power LEDdevices, we can not simply apply the traditional package of small power LEDdevices and packaging materials. Large power dissipation, the large amount ofheat, high light efficiency to our packaging process packaging equipment andpackaging materials proposed new and higher requirements.

        Second,the high-power LED chips

        Inorder to get a high-power LED devices must prepare a suitable high-power LEDchips. The usual manufacturing method are summarized as follows:

        2.1oversize Act:

        Theuniform distribution of the special design of the electrode structure(typically a comb-shaped electrodes) is changed in order to achieve the desiredluminous flux by increasing the effective luminescence area of a single LED, and the current increases the size after promptedthrough Tcl layer. However, simply increasing the light-emitting area can notsolve the fundamental problem of the heat and the light problem, and notachieve the desired effect of luminous flux and the practical application of.

        2.2silicon backplane the flip-law:

        Firstpreparing a large-size LED chips having suitable eutectic soldering electrodes(Flip

        ChipLED). Simultaneously prepare the corresponding size of the silicon substrate,and fabricated on the gold for eutectic soldering conductive layer and leads tothe electrically conductive layer (Ultrasonic gold ball joints). Then, the LEDchip and the silicon substrate of the large-size equipment will be weldedtogether by eutectic soldering. (This structure is more reasonable to considerthe light problem, taking into account the heat problem, which is the currentmainstream High Output Power Chip LED mode of production.)

        Thethe United States LumiLeds 2001 developed a AlGaInN power flip-chip (FCLED)structure, the specific approach: the first step, at the the epitaxial waferstop of the P-type GaN: Mg deposition thickness greater than 500A NiAu layer for ohmic contact and backreflector; second step, using a mask to select the P-type layer andmulti-quantum well active layer is etched away, exposing the N-type layer;third step, deposition, etching to form the N-type ohmic contact layer, thechip size 1 × 1mm2, P-typeohmic contact is square, the to N ohmic contact in order to comb insertedtherein, which can shorten the distance to the current spreading, the spreadingresistance is minimized; fourth step, the metal bumps AlGaInN flip chipsoldering silicon carrier with anti-static protection diode (ESD).

        2.3Ceramic floor the flip-law:

        Thefirst use of the generic device of the LED chip plant prepared by the LED chipand the corresponding ceramic substrate having a large light exit area of the electrode structure suitable for eutectic soldering, andfabricated on the eutectic soldering the conductive layer and the extractionconductive layer. After eutectic soldering equipment to the large size LED chipand the ceramic substrate are welded together. (The structure of this Idemitsualso take into account the heat problem for high thermal conductivity ceramicplates and ceramic plate, the cooling effect is ideal, the price is relativelylow for more suitable substrate material, and may in the future integratedcircuits integrated package servo circuit set aside under the installationspace)

        2.4sapphire substrate transition law:

        Chipmanufacturing method in accordance with the traditional InGaN grown on asapphire substrate, the PN junction after resecting sapphire substrate and thenconnect the traditional four-membered, material and manufacture of the largesize of the blue LED chip of the upper and lower electrode structures.

        2.5AlGaInN/ silicon carbide (SiC) on the back light method:

        CreeInc. is the world's only manufacturer of ultra-high brightness LED manufacturingAlGaInN SiC substrate, the past few years AlGaInN / SiCa chip structurecontinue to improve brightness continuously improve. Since the P-type andN-type electrode, respectively, after the bottom and top of the chip, thesingle wire bonding, better compatibility, ease of use, and thus become themainstream of another of the the AlGaInN LED development.

        Third,the basic package structure

        Thereare two main issues to be considered in the high-power LED packaging: heat andIdemitsu.

        No.Material Thermal conductivity / λW (m.K)

        01carbon steel (C = 0.5-1.5) 39.2-36.7

        02nickel steel (Ni = 1% -50%) 45.5-19.6

        03brass (70Cu-30Zn) 109

        04aluminum alloy (60Cu-40Ni) 22.2

        05aluminum alloy (87Al-13Si) 162

        06aluminum bronze (90Cu-10Al) 56

        07Mg 156

        08Mo 138

        No.Material Thermal conductivity / λW (m.K)

        09Platinum 71.4

        10Silver 427

        11tin 67

        12Zinc 121

        13pure copper 398

        14Gold 315

        15pure aluminum 236

        16pure iron 81.1

        17glass 0.65-0.71

        Thediagram may be learned from the current / temperature / flux, cooling for thepower type LED device is critical. If not timely dissipate the heat generatedby the current, to maintain the junction temperature of the PN junction iswithin the allowable range, would not be able to obtain a stable light outputand maintenance of the normal lifetime of the devices.

        Onecan be learned from the table, the best the silver thermal conductivity coolingmaterial, but the higher cost of silver conduction cooling plate is unfit foruniversal radiator. And the thermal conductivity of copper is relatively closeto the silver, and its cost is lower than silver. Although the thermalconductivity of aluminum is lower than copper, but wins in the lowest overallcosts favor large-scale manufacturing.

        Aftera two-year experimental comparison we found a more appropriate approach is:connect the chip part of the copper-based or silver-based heat sink, and thenthe heat sink connected to the thermal conductivity of ladder-type structure,the use of copper or silver aluminum radiator high The thermal conductivity ofthe efficient delivery of heat generated by the chip to the aluminum radiator,aluminum radiator to dissipate the heat (shed by air cooling or heatconduction).

        Theadvantage of this approach is: give full consideration to the the radiator costperformance, and together the different characteristics of the radiator toachieve efficient heat dissipation, and the rationalization of cost control.

        Notethat: the connection between the copper-based heat sink with the chip ofmaterial selection is very important, the LED used in the chip-connectingmaterial is silver glue. However, after a study found that high thermalresistance of the silver plastic :10-25W / (mK), silver plastic as connectingmaterial, is equivalent to the human in between the chip and the heat sink witha thermal resistance. In addition the basic the silver glue curing the internalstructure is: the epoxy skeleton + silver-filled thermal conductive structure,so the structure of the thermal resistance high TG point is lower, stable toheat and physical properties of the devices extremely unfavorable. Our approachto resolve this issue: welding tin sheet as the material of the connectionbetween the die and the heat sink (thermal conductivity of tin 67W/mK) can beobtained the ideal thermal effects (thermal resistance of about 16 ° C / W),tin thermal effects and physical properties far superior to the silver plastic.

        3.2light

        Wefound that the conventional LED device package can only use about 50% of thechip emits light, due to the refractive index of the semiconductor and closedepoxy larger difference, resulting in the internal total reflection criticalangle is small, the light generated by the active layer only a small portion isremoved, most of the multiple reflections inside the chip is absorbed, become theroot cause of the high brightness LED chip light extraction efficiency is verylow. Between different materials of the internal refraction, reflectionconsumed 50% of the light to be utilized, is the design of an optical systemkey.

        Canbe more effective than conventional LED chip packaging technology light exitthrough the chip's flip (Flip Chip) technology. However, if the increase in thebottom of the off-chip light-emitting electrode layer to the reflective layerto reflect a wasted light energy will result in the loss of about 8% of thelight. Therefore, the reflective layer must be increased in the floor material.Chip side surface of the light must also use a heat sink mirror machiningmethod to be reflected, to increase the device to the light-receiving rate.With epoxy resin light guide, and in the part of the sapphire substrate offlip-chip (Sapphire) surface should be coupled with a layer of siliconematerials in order to improve the chip out of the refractive index of thelight.

        Afterthe improvement of the above-mentioned optical packaging technology, cangreatly improve the power LED devices out of the light-receiving rate (flux).

        Thelens of the optical design of the top of the high-power LED devices is alsovery important, is our usual practice: and during optical lens design shouldtake full account of the the final lighting fixtures optical designrequirements, as far as possible with the application of optical lightingequipment requirements for the design.

        Commonlens shape:

        Convexlens, a concave cone lens, spherical lens, a Fresnel lens, modular lens. Lenswith high-power LED devices ideal method of assembly, hermetic package shouldbe taken, if the lens shape can also be taken semi-hermetic package. The lensmaterials should be selected high transmittance glass or acrylic and othersynthetic materials. The conventional epoxy module package can also be used,plus secondary basic thermal design can achieve the effect of increased lightrate.

        Fourth,the electrical protection

        Wemeasured SiC as a backing InGaN anti-ESD Human Body Model (HBM) more than1100V. Generally like sapphire Al2O3 underlay the InGaN anti ESD only about 400~ 500V (the consolidated results of the different brands), so low ESD immunityto the LED LAMP packaging manufacturers and the downstream electronicapplication vendors brought great inconvenience. Information learned from theinterbank annual electronic component manufacturers is very alarming problem oflosses due to ESD static protection, assembly and consumers use has a certainloss. We know, high ESD resistant SiC silicon carbide than sapphire Al2O3 theunderlay material antistatic advantage, but can not fundamentally solve the ESDproblem.

        Informalstatistics from different levels of electronics manufacturers have thefollowing table of estimated loss report

        ESDaverage loss of electronics manufacturers ESD Informal Summary of Static Lossesby Level

        StaticLosses Reported, ESD electrostatic loss

        Layersmanufacturers Min. Loss Max. Loss Est Avg. Loss

        Componentsupplier Component Manufacturer 4% 97% 16-22%

        ContractorsSubcontractors 3% 70% 9-15%

        Sub-contractorsContractors 2% 35% 8-14%

        UserUser 5% 70% 27-33%

        Source:Stephen Halperin, "Guidelines for Static Control Management,"Eurostat, 1990

        Sourcesof the different levels of the ESD

        TheESD source of 10-25% RH 65-90% RH

        Walkingon the carpet Walking across carpet 35,000 V 1,500 V

        Walkingin the vinyl floor Walking across vinyl tile 12,000 V 250V

        Workersworkbench Worker at the bench 6,000 V 100V

        Pickedup the plastic bag Poly bag matches both picked up form bench 20,000 V 1,200 V

        Styrofoamchair the Chair with urethane foam 18,000 V 1,500 V

        Wefound that If it is added in the high-power LED device package structure of thechip periphery against ESD diode, may be to improve the capacity of the ESDimmunity to more than 8500V. Basically solved the different levels of ESD lossproblems for electronics manufacturers, and the practical application of goodresults.

        Fifth,the development trend and Conclusion

        Weknow that the external quantum efficiency of the LED chip, depending on the internalquantum efficiency and light extraction efficiency of the chip of the epitaxialmaterial. Currently used by the high-power LED epitaxial material MOCVDepitaxial growth techniques and multiple quantum well structure, although nowthe internal quantum efficiency is not the highest, there is further room forimprovement. However, we found that the biggest obstacle to obtain a highluminous flux of the LED device is still a light extraction of the chip with ahigher optical efficiency of the design of the structure of a package.

        Beable to tell from the LED1970 years to 2003, thirty years of developmentexperience: LED luminous flux of approximately every 16-20 months to beincreased by 2.2 times. So to speak, can be expected within five years time,lighting-class power LED devices, optical efficiency 100Lm / W will be possiblething. However, we can not wait for the high-power LED chips to packagingtechnology development and application of this light efficiency. We believethat lighting-class power LED devices improve light efficiency depends on thechip optical efficiency improvements and package cooling technology improvelight extraction carried out simultaneously in order to do. LED manufacturingequipment manufacturers should also be carried out simultaneously to thedevelopment of such devices.

        Maythe LED can contribute to early lighting technology mainstream products for thenational economy and the people's livelihood.