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luxeon m assembly and handling information introduction this application brief addresses the recommended assembly and handling procedures for luxeon m emitters. luxeon m emitters are designed to deliver high luminous fux and efcacy from a compact optical source in order to enable a wide range of outdoor and industrial lighting applications. proper assembly, handling, and thermal management, as outlined in this application brief, ensure high optical output and long lumen maintenance for luxeon m emitters. scope the assembly and handling guidelines in this application brief apply to the following products with the part number designation as described below: lxra-bcde-fghj where a C designates minimum cri (7 = 70, 8 = 80, 9 = 90, 0 = royal blue) b C four led chips electrical confguration (s = all four chips are electrically connected in series, resulting in less than 12v, r = two by two chips in series-parallel with less than 6v, q = all four chips in parallel with voltage less than 3v ) c C designates color designation (w = white, r = royal blue) de C designates nominal cct (27 = 2700k, 30 = 3000k, etc and 00 = royal blue) fghj C minimum fux (optional) in the remainder of this document the term luxeon emitter refers to any product in the two luxeon product series listed above. any handling requirements that are specifc to a subset of luxeon emitters will be clearly marked. general illumination AB103 luxeon m application brief ?2015 lumileds holding b.v. all rights reserved.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 2 table of contents introduction 1 scope 1 1 component 3 1.1 description .......................................................................... 3 1.2 optical center ....................................................................... 3 1.3 handling precautions ................................................................. 4 1.4 cleaning ............................................................................ 5 1.5 electrical isolation .................................................................... 5 1.6 mechanical files ...................................................................... 5 1.7 soldering ............................................................................ 5 2 luxeon m printed circuit board design rules 5 2.1 luxeon z footprint and land pattern .................................................. 5 2.2 surface finishing ..................................................................... 6 2.3 minimum spacing .................................................................... 6 3 thermal management 6 3.1 pcb designs for luxeon m ............................................................ 7 3.2 thermal resistance results ............................................................ 8 3.3 other thermal assembly and design considerations ..................................... 8 4 thermal measurement guidelines 10 4.1 stencil design ....................................................................... 10 5 assembly process guidelines 12 5.1 stencil design ....................................................................... 12 5.2 solder paste ........................................................................ 12 5.3 pick-and-place ...................................................................... 12 5.4 solder refow profle ................................................................. 17 5.5 placement and refow accuracy ....................................................... 17 5.6 jedec moisture sensitivity levels ...................................................... 18 6 luxeon emitter drivers 18 6.1 introduction ........................................................................ 18 6.2 active control led current driver ..................................................... 19 7 packaging considerations chemical compatibility 20 about lumileds 22
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 3 1. component 1.1 description the luxeon m emitter consists of a 2x2 led chip array mounted onto a ceramic substrate. this substrate provides mechanical support and thermally connects the led chips to a thermal pad on the bottom of the substrate. an electrical interconnect layer connects the led chips to a cathode and anode on the bottom of the ceramic substrate. the ceramic substrate is surrounded by a larger ceramic frame and is overmolded with a silicone dome to enhance light extraction and to shield the chip array from the environment. each luxeon m emitter includes a transient voltage suppressor (tvs) chip under the silicone dome to protect the emitter against electrostatic discharges (esd). the bottom of the luxeon m emitter (figure 1) contains four metallization pads, a large thermal pad in the center, an anode, a cathode, and a small pad with a laser engraved led serial number. the pad with the serial number is not designed to be soldered onto a pcb. each luxeon m emitter contains three staircase-style fducials on the ceramic frame outside the dome (see the top view of luxeon m in figure 1). in order to identify the anode and cathode, rotate the luxeon m emitter so that the three fducials are on the top left, bottom left, and top right corner of the ceramic substrate when viewed from above as shown in figure 1. the left side, marked by the two fducials in the top and bottom corner, then corresponds to the cathode side of the luxeon m emitter. the anode side only contains one fducial in the top corner, when viewed from above. 1.2 optical center the luxeon m emitter contains three feature sets to locate the theoretical optical center (see figure 2): 1. topside fducials the fducial marks on the ceramic frame of the luxeon m emitter provide the most accurate methodology to locate the theoretical optical center. the theoretical optical center is located 3.14mm from the vertical and horizontal edges of each fducial mark. 2. backside metallization the optical center can be located using the edges of the thermal pad on the bottom of the ceramic substrate. the theoretical optical center is 1.08mm and 1.75mm from the long and short edge, respectively, of the thermal pad. 3. led outline the theoretical optical center is located 3.50mm from the edge of the luxeon m emitter. optical rayset data for luxeon m is available upon request. figure 1. top view (left) and bottom view (right) of luxeon m emitter. the pad with the laser marking should not be soldered onto a pcb.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 4 figure 2. fiducial marks on the top of the luxeon m emitter provide the most accurate method to locate the theoretical optical center. 1.3 handling precautions luxeon m is designed to maximize light output and reliability. however, improper handling of the device may damage the silicone dome and afect the overall performance and reliability. in order to minimize the risk of damage to the silicone dome during handling, luxeon m emitters should only be picked up from the side of the ceramic frame as shown in figure 3.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 5 figure 3. incorrect handling (left and middle) and correct handling (right) of luxeon m emitters. 1.4 cleaning luxeon m should not be exposed to dust and debris. excessive du st and debris may cause a drastic decrease in optical output. in the event that a luxeon m emitter requires cleaning, frst try a gentle swabbing using a lint-free swab. if needed, a lint-free swab and isopropyl alcohol (ipa) can be used to gen tly remove dirt from the lens. do not use other solvents as they may adversely react with the led assembly. for more information regarding chemical compatibility, see section 6. 1.5 electrical isolation the thermal pad of the luxeon m is electrically isolated from its cathode and anode. consequently, a high voltage diference between electrical and thermal metallization may occur in applications where multiple luxeon m emitters are connected in series. as a reference, the nominal distance between the electrical metallization and the thermal metallization of the luxeon m emitter is 0.3mm. in order to avoid any electrical shocks and/or damage to the luxeon m emitter, each design needs to comply with the appropriate standards of safety and isolation distances, known as clearance and creepage distances, respectively (e.g. iec60950, clause 2.10.4). 1.6 mechanical files mechanical drawings for luxeon m (2d and 3d) are available upon request. 1.7 soldering luxeon m emitters are designed to be soldered onto a printed circuit board (pcb). for detailed assembly instructions, see section 2. 2. luxeon m printed circuit board design rules the luxeon m emitter is designed to be soldered onto a metal core pcb (mcpcb) or a multi-layer fr4 pcb. to ensure optimal operation of the luxeon m emitter, the pcb should be designed to minimize the overall thermal resistance between the led package and the heat sink. 2.1 luxeon z footprint and land pattern the luxeon m emitter has three pads that need to be soldered onto corresponding pads on the pcb to ensure proper thermal and electrical operation. the pad with the laser engraved serial number is not designed to be soldered onto the pcb. figure 4 shows the recommended footprint design for the solder mask and the copper layout on a metal core pcb. lumileds recommends extending the thermal pad and electrodes at least 10mm from the center of the luxeon m led to maximize heat spreading into the pcb. the recommended footprint design includes special fducials near the corners of the luxeon m to facilitate visual inspection of the placement accuracy of the luxeon m emitter on the pcb board.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 6 figure 4. recommended luxeon m footprint design for metal core pcb. all dimensions in mm. 2.2 surface finishing lumileds recommends using a high temperature organic solderability preservative (osp) or electroless nickel immersion gold (enig) plating on the exposed copper pads. 2.3 minimum spacing lumileds recommends a minimum edge to edge spacing between luxeon m emitters of 13mm. placing multiple luxeon m emitters too close to each other may adversely impact the ability of the pcb to dissipate the heat from the emitters. also, the light output for each led may drop due to optical absorption by adjacent led packages. 3. thermal management the overall thermal resistance between the luxeon m emitter and the heat sink is strongly afected by the design and material of the pcb on which the luxeon m emitter is soldered. metal core pcbs have been historically used in the led industry for their low thermal resistance and rigidity. however, mcpcbs may not always ofer the most economical solution. multi-layer epoxy fr4 pcbs are commonly used in the electronics industry and can in certain led applications yield a lower cost solution. given the poor thermal conductivity of the epoxy in fr4 pcbs, it is important to include special thermal vias in the pcb design to aid the transport of heat from the led to the heat sink on which the pcb is mounted. a thermal via is a plated through hole that can be open, plugged, flled or flled and capped. open vias are typically placed outside the pads on which the leds are soldered to prevent any solder from reaching the other side during refow. a flled-and-capped via, in contrast, can be placed directly underneath the thermal pad of the led, improving the thermal performance of the pcb. lumileds conducted a simulation study to determine the typical thermal resistance for various luxeon m pcb designs. in addition, several pcb designs were manufactured and the thermal resistance was experimentally determined. the remainder of this section discusses the diferent pcb designs which were considered and compares the merits of each pcb design in terms of its overall thermal resistance between the luxeon m emitter and the heat sink.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 7 figure 5. several luxeon m pcb designs were simulated and/or experimentally measured to determine the typical thermal resistance between the thermal pad and the heat sink. 3.1 pcb designs for luxeon m the thermal resistance study for luxeon m focused on several diferent pcb designs requiring diferent pcb manufacturing technologies (see figure 5): metal core pcb the thermal simulation study focused on an mcpcb design with a 100m dielectric layer and a 70m (2oz) copper foil. the thermal conductivity of the dielectric material in the simulation study is assumed to be 1wm -1 k -1 . in addition, several mcpbcs were manufactured. each mcpcb contained an 80m thick dielectric layer with a thermal conductivity of 2.7wm -1 k -1 and a copper foil thickness of 35m (1oz) or 70m (2oz). in order to assess the impact of the metal substrate on the overall thermal resistance, both aluminum core and copper core mcpcb designs were evaluated. fr4 pcb with flled-and-capped vias the thermal simulation study included two fr4 pcb designs with flled-and-capped vias. the fr4 epoxy board in each design is assumed to be 0.8mm thick and has a glass fber content of 25%. copper foils with a thickness of 70m (2oz) copper foils are attached to both sides. the metallization patterns on top and bottom of the pcbs are assumed to be identical. the flled-and-capped vias have a diameter of 0.5mm, are plated with 25m copper, and are flled with epoxy afterwards. the pitch between the flled-and-capped vias is 0.75mm. the frst design in this category contains flled-and- capped vias in the thermal pad only. the second design has additional flled-and-capped vias on the electrodes as well. aluminum core mcpcb fr4 with capped-and-filled vias fr4 with capped - and - filled vias (vias on thermal pad only) capped and filled vias (vias on thermal pad and electrodes)
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 8 table 1. r values between luxeon m thermal pad and heat sink for various pcb designs. pcb technology details cu-foil r pad-heat sink [k/w] ofruh pglhohfwulfp k ) pr 1.8 ofruh03 pglhohfwulfp k ) pr 2.9 ofruh03 pglhohfwulfp k ) pr 3.3 xfruh03 pglhohfwulfp k ) pr 2.3 xfruh03 pglhohfwulfp k ) pr 3.2 )54oohgdqgfdhgldv vias on thermal pad only pr 5.3 )54oohgdqgfdhgldv vias on thermal pad and electrodes pr 3.7 7kh4oohgdqgfdhgldvlqwkhvh)5ghvlqvfuhdwhdqhohfwulfdodwkehwzhhqwkhwrdqgerwwrpphwdooldwlrqodhuv riwkh37khuhiruhdqdgglwlrqdo7khupdoCqwhuidfh0dwhuldo7C0lvuhtxluhgehwzhhqwkh)53dqgkhdwvlqn wrhqvxuhvxflhqwhohfwulfdovklhoglqehwzhhqwkhwudfhvrqwkh)53dqgwkhkhdwvlqnCqrughuwrurlghdidlu frpdulvrqehwzhhqwkhglhuhqwerdugghvlqvlqwklvvwxgdpp7C0odhuzlwkdwkhupdofrqgxfwllwp k is lqfoxghglqdoowkhupdovlpxodwlrqvriwkh4oohgdqgfdhg)5ghvlqv 3.2 thermal resistance results 7deohvxppdulhvkhkhupdouhvlvdfhydoxhvehzhhkhkhdvlndgkh/8(210khupdosdgirukhydulrxv pcb designs considered in this study. these results suggest that the typical thermal resistance of a properly designed 03lvvrphzkhuhehwzhhq.dqg.ghhqglqrqwkhtxdolwdqgwklfnqhvvriwkhpdwhuldovxvhgCq frqwudvwdq)53zlwk4oohgdqgfdhgwkhupdoldvlhogvdwkhupdouhvlvwdqfhehwzhhq.dqg. )rufrpohwhqhvvvhhudo)53ghvlqvzlwkrhqldvzhuhdovrfrqvlghuhglqwklvvwxg+rzhhuerwkhhulphqwdo dqgvlpxodwlrquhvxowvlqglfdwhwkdwwkhwlfdowkhupdouhvlvwdqfhiruwkhvhghvlqvlvderh. 6lpxodwlrqdqghhulphqwdouhvxowvlqglfdwhwkdwwkhwkhupdouhvlvwdqfhridq03fdqehuhgxfhgwrzhooehorz. liwkhglhohfwulfpdwhuldoehwzhhqwkh8(210wkhupdodgdqgwkhfruhriwkh03lvholplqdwhg7klvdurdfkfdq ehduwlfxoduoxvhixolqfhuwdlqklkghqvlwdolfdwlrqvzkhuhpxowloh8(210(vduhodfhglqforvhurlplwwr each other. 3.3 other thermal assembly and design considerations thermal interface materials (tim) selection once the suitable pcb board material and design has been made, the choice of tim material selection should be made zlwkwkhiroorzlqfrqvlghudwlrqv ? 3xprxw6rph7C0vzlooprhrxwriwkhwkhupdodwkgxulqhwuhphwhphudwxuhhfxuvlrqvdqgfuhdwhrlgvlqwkh thermal path. these materials should not be used. ? 7C0wklfnqhvv(fhvvlhwklfnqhvvrivrph7C0vzloouhvhqwdqxqdffhwdeohwkhupdouhvlvwdqfhhhqwkrxkwkh thermal conductivity of the material may be high. ? 6xuidfhurxkqhvvCqrughuwr4oowkhdludvehwzhhqdgmdfhqwvxuidfhvfkrrvhwkhduruldwh7C0wkdwplqlplhv the interfacial contact resistance. ? 2hudwlqwhphudwxuh6rph7C0vhuiruprruodwhohdwhgwhphudwxuhvduhvkrxogehhhuflvhgwrvhohfwd7C0 wkdwzloohuirupzhooxqghuwkhdqwlfldwhgrhudwlqfrqglwlrqv ? 2xwdvvlq2xwdvvlqrivrph7C0vdwghvlqwhphudwxuhvpdurgxfhxqghvludeohrwlfdorudhdudqfhtxdolwlhv hirlqlqdvhdohgvvwhp6hfldofrqvlghudwlrqpxvwehlhqwrolplwwklvhhfw ? odplqirufh7C0vvxfkdvwkhupdowdhrudgvhuirupehwwhuzkhqwkhulkwuhvvxuhlvdolhg
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 9 led component spacing (density) as more leds are packed closely together, thermal crowding efect becomes more important and will afect the ability of the pcb to dissipate heat. electrical power distribution pcb electrical (copper) trace width and length (routing) can afect thermal performance. if the copper trace is too narrow and long, there is more voltage drop across the copper trace (power dissipation = current x voltage) and more heat is generated. in led array confguration, the pcb area where the trace is generating more heat will lead to increase operating junction temperature of the neighboring leds. this will cause poor light output uniformity. as a general rule of thumb, layout the copper trace frst such that the most optimum thermal performance can be achieved and then fgure out how to route the electrical traces. in some network topology, it may be necessary to make the luxeon m thermal pad electrically active. figure 6 and figure 7 illustrate the impact of copper trace length and width on overall system thermal performance. figure 6. top left shows long copper trace length (red lines) with narrower trace width. top right shows the same layout as th e left drawing but with wider trace width. the latter minimizes heat generated in the copper trace. bottom left and right shows optimize trace route (shortest). depending on the operating drive current of the led system and the electrical layout of the /(vsdudoohovhulhvkhfrsshuudfhzlgkpdhhgrehd gmxvhgghshgljrkhdprxrifxuuh5rzljkurxjk each section of the trace. see figure 7 for this example.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 10 figure 8. a real life example of an application design concept as described in figure 11. left and right pictures are thermal images of the same board. the narrow pcb copper trace as indicated in the left picture carries very high current to feed several leds connected in parallel. right picture with green ar rows shows a modifed electrical trace routing (in this case, soldering the right wire size to each node of the leds). notice that the right picture shows more uniform temperature distribution than the left picture after adjusting the electrical power distribution to each led. 4. thermal measurement guidelines 4.1 stencil design the typical thermal resistance r (j-thermal pad) between the junction and thermal pad for luxeon m is 1.25k/w. with this information, the junction temperature t j can be easily determined according to the following equation: t j = t thermal pad + r j-thermal pad ? p electrical in this equation t thermal pad is the temperature at the bottom of the luxeon m thermal pad and p electrical is the electrical power going into the luxeon m emitter. figure 7. top and bottom drawing each show four leds connected in parallel. each led is assumed to have the same forward voltage and same current fowing. t 1 to t 8 sections represent copper trace width. thicker line means wider copper trace width. top drawing has poor electrical layout since more heat is generated in t 1 than t 2 , etc due to higher current fowing in t 1 than t 2 , etc. temperature in t 1 > t 2 > t 3 > t 4 . bottom drawing represents good electrical layout. since more current fows in t 5 than t 6 , the trace width in t 5 is made correspondingly larger than t 6 and so on. much easier will be to make the trace width the same (larger) for all of t 5 to t 8 . note that as the copper trace area is increased, this may lead to increase pcb board capacitance and may interact with other transient tests such as electrical surge immunity test.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 11 in typical applications it may be difcult, though, to measure the thermal pad temperature t thermal pad directly. therefore, a practical way to determine the luxeon m junction temperature is by measuring the temperature t s of a predetermined sensor pad on the pcb right next to the luxeon m emitter with a thermocouple (see figure 9). the recommended location of the sensor pad is 0.5mm from the edge of the luxeon m emitter, on the center line between anode and cathode. the thermocouple must make direct contact with the copper of the pcb onto which the luxeon m thermal pad is soldered, i.e. any solder mask must be frst removed before mounting the thermocouple onto the pcb. the thermal resistance r j-s between the sensor pad and the luxeon m junction was experimentally determined to be approximately 3.0k/w on a mcpcb. the junction temperature can then be calculated as follows: t j = t s + 3.0 ? p electrical figure 9. the recommended temperature measurement point t s is located next to the luxeon m emitter on the thermal pad of the pcb.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 12 5. assembly process guidelines 5.1 stencil design figure 10 shows the recommended stencil design for luxeon m. the recommended stencil thickness is 125m. 5.2 solder paste lumileds recommends lead-free solder for the luxeon m emitter. lumileds has successfully tested sac305-om338 from alpha metals with satisfactory results. however, since application environments vary widely, lumileds recommends that customers always perform their own solder paste evaluation in order to ensure it is suitable for the targeted application and operating conditions. 5.3 pick-and-place automated pick and place equipment provides the best placement accuracy for luxeon m emitters. figure 11 C figure 14 show various pick and place nozzle designs and corresponding machine settings which were successfully used for luxeon m emitters with pick and place equipment from panasonic, yamaha, juki and samsung. each nozzle is designed to pick the luxeon m emitter up from the fat area around the dome without making any contact with the silicone dome. note that pick and place nozzles are customer specifc and are typically machined to ft specifc pick and place tools. figure 10. recommended stencil design for luxeon m. all dimensions in mm.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 13 pick and mount information vision information pick timer 0.3 s alignment group chip mount timer 0.3 s alignment type std.chip pick height 2.5mm alignment module fore & back & las mount height -1.0mm light selection main + coax mount action qfp lighting level 5/8 mount speed 50% comp. threshold 30 pickup speed 50% comp. tolerance 30 vacuum check normal chk search area 0.8mm pick vacuum 30% comp. intensity 116 wmount vacuum 50% auto threshold use figure 11. pick and place nozzle design and machine settings for yamaha yv100x. all dimensions in mm. nozzle drawing courtesy of ching yi technology pte ltd (part #: ymh-0078/12).
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 14 pick and mount information vision information pick height -3.5mm camera no fly cam5 mount height 1mm side 11 delay C pick up 300msec outer 8 delay - place 100msec delay - vac of 0 delay C blow on 100msec speed C xy 2 speed C z pick down 2 speed C z pick up 2 speed C r 2 speed C z place down 2 speed C z place up 2 z align speed 2 2 soft touch pick & mount mount method normal figure 12. pick and place nozzle design and machine settings for samsung sm421. all dimensions in mm. nozzle drawing courtesy of ching yi technology pte ltd. (part #: sam-1313/11).
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 15 pick and mount information vision information xy speed 1 camera 2d large fov theta speed 1 upper l 0 nozzle movement C pickup 1: middle l 1 descend 1 stroke lower l 3 ascend 1 stroke nozzle movement C mount 1: descend 1 stroke ascend 1 stroke pickup C height 0.6mm pickup C thickness 0.6mm pickup C depth 0mm pickup C height allowance 0mm pickup C height ofset -3.0mm mount height 1.0mm figure 13. pick and place nozzle design and machine settings for panasonic bm221. all dimensions in mm. nozzle drawing courtesy of micro-mechanics pte ltd (drawing #: 19-mt-10053-01).
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 16 pick and mount information placing stroke 1.0mm picking stroke 2.5mm xy speed fast picking z down fast picking z up fast placing z down fast placing z up fast laser position -0.11 figure 14. pick and place nozzle design and machine settings for juki ke750. all dimensions in mm. nozzle drawing courtesy of micro-mechanics pte ltd (drawing #: 19-mt-10043-01). a production pick and place machine will typically include a vision camera system to recognize the bottom pads of the package. however, the juki ke750 pick and place machine used in this study is a dedicated test machine and did not include any vision camera system. consequently, no detailed vision information is available for this machine.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 17 5.4 solder refow profle the luxeon m emitter is compatible with standard surface-mount and lead-free refow technologies. this greatly simplifes the manufacturing process by eliminating the need for adhesives and epoxies. the refow step itself is the most critical step in the refow soldering process and occurs when the boards move through the oven and the solder paste melts, forming the solder joints. to form good solder joints, the time and temperature profle throughout the refow process must be well maintained. a temperature profle consists of three primary phases: 1. preheat: the board enters the refow oven and is warmed up to a temperature lower than the melting point of the solder alloy. 2. refow: the board is heated to a peak temperature above the melting point of the solder, but below the temperature that would damage the components or the board. 3. cool down: the board is cooled down, allowing the solder to freeze, before the board exits the oven. as a point of reference, the melting temperature for sac 305 is 217c, and the minimum peak refow temperature is 235c. for detailed information on the recommended refow profle, refer to the ipc/jedec j-std-020c refow profle in the luxeon m datasheet. 5.5 placement and refow accuracy in order to achieve the highest placement accuracy lumileds recommends using an automated pick and place tool with a vision system that can recognize the bottom metallization of the luxeon m emitter. global fducials on a pcb panel can be used to calculate the refow accuracy of the luxeon m emitter with respect to its theoretical board position. lumileds has determined that the typical placement accuracy of a luxeon m emitter after refow is well within 100m in the x- and y-direction for the footprint in figure 4. figure 15. alignment crosses on the pcb (a) help estimate the placement accuracy of the luxeon m emitter on the pcb before and/or after refow. the outer corner of the stai rcase style fducials on the luxeon m ceramic substrate align with the inner corner of the alignment crosses on the pcb for a properly placed luxeon m emitter (b). placement errors in x- and y-direction (c). rotation errors in additions to placement errors in x- and y-direction (d).
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 18 the pcb design in figure 4 contains three alignment crosses, which correspond to the location of the three staircase style fducials on the ceramic substrate of the luxeon m emitter (see figure 1). these alignment features enable visual verifcation of the proper orientation of the luxeon m on the pcb. in addition, these features help approximate the placement accuracy of the luxeon m before and/or after refow, see figure 15. 5.6 jedec moisture sensitivity levels luxeon m emitters have a jedec moisture sensitivity level of 1. this is the highest level ofered in the industry and highest level within the jedec standard. this ensures ease of use since the user no longer needs to be concerned about bake out times and foor life. 6. luxeon emitter drivers 6.1 introduction led is best driven with current source. this mode of operation provides the best control of the amount of current fowing through the leds at any operating temperature. a voltage source does not provide a predetermined current, may vary signifcantly and depends on the forward voltage and the operating temperature of the leds. however a voltage source can be assembled with few passive components such resistor, capacitor and bridge rectifer, assuming incoming ac power supply. such confguration is cheap and compact but has poor power efciency and poor current control. this section discusses led current drivers via active controls (more common) incorporating transistors and linear ics such as constant current regulators (ccrs). figure 16. typical transistor operation regions. ohmic or linear region is shaded in yellow while the saturation or switching region is shaded green.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 19 6.2 active control led current driver there are two types of active control led current drivers: a. linear regulated power supply b. switch mode power supply the main diference is how the power supply is being regulated. in linear regulated power supply, the transistor connected to a load is used to control the output voltage or current. in order to do this, the transistor must operate in the ohmic or linear region as shown in figure 16. since there is current fowing through the transistor (operating in ohmic region), the transistor behaves like a variable resistor and generates heat. in a switched mode power supply, as the name implies, the transistor is used as a switch to either switch in or out electrical storage elements such as inductor (current source) or capacitor (voltage source) to a load. in order to achieve this, the transistor must be operating in the saturation region as shown in figure 16. in the on or close switch, there is hardly any resistance through the transistor and hence does not generate any heat when a current fows through it. in off or open switch, no current is fowing through the transistor. this type of power supply has high power efciency than the linear regulated power supply. however due to the switching of the circuit, it generates electromagnetic interference (emi) which must be taken into account and minimized during the design stage. there are several switch mode power supply confgurations such as buck, boost and buck-boost convertor. a summary of the major diferences between these two active control led current drivers is given in table 2 below. table 2. comparison of a typical linear regulated versus switch mode power supply. linear switch mode cost cheap expensive emc none potential circuitry simple complicated power efciency low (~50...~70%) high (~75%... 95%) size & weight big and heavy* small and light *: if magnetics are used to step down the voltage before the regulator. a typical example of an ac-dc led system block circuit may consist of a bridge rectifer, transient circuit protection (e.g. varistor), dimming circuit (triac) and a control circuit (either passive or active control) with ficker-free, over-voltage protection, flters and/or feedback loop circuits. figure 17 shows an example of a system block diagram of a typical led driver circuit. lumileds maintains a list of various linear ic driver manufacturers.examples of various driver circuit designs are provided by each manufacturer. to access this information, go to lumileds website at lumileds.com . go to the support tab and select design tools. click on the eco-system and then the drivers tab. registration is required to access this list.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 20 figure 17. a typical system block diagram of one example of a led driver circuit. 7. packaging considerations chemical compatibility the luxeon m package contains a silicone overcoat and dome to protect the led chips and extract the maximum amount of light. as with most silicones used in led optics, care must be taken to prevent any incompatible chemicals from directly or indirectly reacting with the silicone. the silicone overcoat in luxeon m is gas permeable. consequently, oxygen and volatile organic compound (voc) gas molecules can difuse into the silicone overcoat. vocs may originate from adhesives, solder fuxes, conformal coating materials, potting materials and even some of the inks that are used to print the pcbs. some vocs and chemicals react with silicone and produce discoloration and surface damage. other vocs do not chemically react with the silicone material directly but difuse into the silicone and oxidize during the presence of heat or light. regardless of the physical mechanism, both cases may afect the total led light output. since silicone permeability increases with temperature, more vocs may difuse into and/or evaporate out from the silicone. careful consideration must be given to whether luxeon m emitters are enclosed in an air tight environment or not. in an air tight environment, some vocs that were introduced during assembly may permeate and remain in the silicone dome. under heat and blue light, the vocs inside the dome may partially oxidize and create a silicone discoloration, particularly on the surface of the led where the fux energy is the highest. in an air rich or open air environment, vocs have a chance to leave the area (driven by the normal air fow). transferring the devices which were discolored in the enclosed environment back to open air may allow the oxidized vocs to difuse out of the silicone dome and may restore the original optical properties of the led. determining suitable threshold limits for the presence of vocs is very difcult since these limits depend on the type of enclosure used to house the leds and the operating temperatures. also, some vocs can photo-degrade over time. table 3 provides a list of commonly used chemicals that should be avoided as they may react with the silicone material. note that lumileds does not warrant that this list is exhaustive since it is impossible to determine all chemicals that may afect led performance.
AB103 luxeon m application brief 20150330 ?2015 lumileds holding b.v. all rights reserved. 21 rohs compliant the chemicals in table 3 are typically not directly used in the fnal products that are built around luxeon m leds. however, some of these chemicals may be used in intermediate manufacturing steps (e.g. cleaning agents). consequently, trace amounts of these chemicals may remain on (sub)components, such heat sinks. lumileds, therefore, recommends the following precautions when designing your application: ? when designing secondary lenses to be used over an led, provide a sufciently large air-pocket and allow for ventilation of this air away from the immediate vicinity of the led. ? use mechanical means of attaching lenses and circuit boards as much as possible. when using adhesives, potting compounds and coatings, carefully analyze its material composition and do thorough testing of the entire fxture under high temperature over life (htol) conditions. table 3. list of commonly used chemicals that will damage the silicone overcoat of luxeon m. avoid using any of these chemicals in the housing that contains the led package. chemical name normally used as acetic acid acid hydrochloric acid acid nitric acid acid sulfuric acid acid ammonia alkali potassium hydroxide alkali sodium hydroxide alkali acetone solvent benzene solvent dichloromethane solvent gasoline solvent mek (methyl ethly ketone) solvent mibk (methyl isobutyl ketone) solvent mineral spirits (turpentine) solvent tetracholorometane solvent toluene solvent xylene solvent castor oil oil lard oil linseed oil oil petroleum oil silicone oil oil halogenated hydrocarbons (containing f, cl, br elements) misc rosin fux solder fux acrylic tape adhesive cyanoacrylate (super glue) adhesive
?2015 lumileds holding b.v. all rights reserved. luxeon is a registered trademark of the lumileds holding b.v. in the united states and other countries. lumileds.com about lumileds lumileds is the light engine leader, delivering innovation, quality, and reliability. for 100 years, lumileds commitment to innovation has helped customers pioneer breakthrough products in the automotive, consumer and illumination markets. lumileds is shaping the future of light with our leds and automotive lamps, and helping our customers illuminate how people see the world around them. to learn more about our portfolio of light engines visit lumileds.com . neither lumileds holding b.v. nor its afliates shall be liable for any kind of loss of data or any other damages, direct, indirect or consequential, resulting from the use of the provided information and data. although lumileds holding b.v. and/or its afliates have attempted to provide the most accurate information and data, the materials and services information and data are provided as is, and neither lumileds holding b.v. nor its afliates warrants or guarantees the contents and correctness of the provided information and data. lumileds holding b.v. and its afliates reserve the right to make changes without notice. you as user agree to this disclaimer and user agreement with the download or use of the provided materials, information and data. AB103 luxeon m application brief 20150330

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