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luxeon 3535l line assembly and handling information introduction this application brief addresses the recommended assembly and handling guidelines for luxeon 3535l, luxeon 3535l colors, luxeon 3535l he and luxeon 3535ls emitters. these emitters deliver high efcacy and quality of light for distributed light source applications in a compact 3.5mm x 3.5mm package. proper assembly, handling and thermal management, as outlined in this application brief, ensure high optical output and reliability of these emitters. scope the assembly and handling guidelines in this application brief apply to the following luxeon product(s): products luxeon 3535l luxeon 3535l colors luxeon 3535l he luxeon 3535ls in the remainder of this document the term luxeon emitter refers to any product in the luxeon 3535l line listed above. illumination AB203 luxeon 3535l line application brief ?2016 lumileds holding b.v. all rights reserved.
AB203 luxeon 3535l line application brief 20160706 ?2016 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 ................................................................. 3 1.4 cleaning ............................................................................ 3 1.5 electrical isolation .................................................................... 3 1.6 mechanical files ...................................................................... 4 2 pcb design guidelines for the luxeon emitter 4 2.1 pcb footprint and land pattern ....................................................... 4 2.2 surface finishing ..................................................................... 4 2.3 minimum spacing .................................................................... 4 3 thermal management 5 4 thermal measurement guidelines 6 5 assembly process guidelines 7 5.1 stencil design ........................................................................ 7 5.2 solder paste ......................................................................... 7 5.3 solder refow profle .................................................................. 7 5.4 pick and place ....................................................................... 7 5.5 electrostatic discharge protection ...................................................... 8 6 luxeon emitter drivers 8 6.1 introduction ......................................................................... 8 6.2 active control led current driver ...................................................... 9 7 packaging considerationschemical compatibility 11 about lumileds 13
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 3 1. component 1.1 description luxeon 3535l, luxeon 3535l colors, luxeon 3535l he and luxeon 3535ls emitters (figure 1) consist of a 3535 lead- frame package with an anode and a cathode. a small notch on the corner of the package marks the cathode side of the emitter package. the anode and cathode both serve as thermal pads for the emitter, with the majority of the heat being dissipated through the larger pad, corresponding to the cathode. the luxeon emitter does not include any transient voltage suppressor (tvs) chip to protect the emitter against electrostatic discharges (esd) appropriate precautions should therefore be taken when handling this device (see section 5.5). 1.2 optical center the optical center coincides with the mechanical center of the luxeon emitter. optical rayset data for the luxeon emitter are available on the lumileds website at lumileds.com . 1.3 handling precautions the luxeon emitter is designed to maximize light output and reliability. however, improper handling of the device may damage the silicone coating and afect the overall performance and reliability. in order to minimize the risk of damage to the silicone coating during handling, the luxeon emitter should only be picked up from the side of the package. 1.4 cleaning the luxeon emitter should not be exposed to dust and debris. excessive dust and debris may cause a drastic decrease in optical output. in the event that a luxeon 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 gently remove dirt from the silicone coating. do not use other solvents as they may adversely react with the package of the luxeon emitter. for more information regarding chemical compatibility, see section 6. 1.5 electrical isolation the luxeon emitter has two electrodes, with a nominal spacing of 0.65mm, at the bottom of the package. in addition, the luxeon emitter contains two tabs on the side of the package. these tabs are cut-of remnants of the lead-frame and are electrically connected to the anode and cathode, respectively. so it is important to keep sufcient distance between the luxeon emitter package and any other objects or neighboring luxeon emitters to prevent any accidental shorts. in order to avoid any electrical shocks and/or damage to the luxeon 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). figure 1. package rendering of a representative luxeon emitter.
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 4 0.82 1.02 1.93 2.13 0.65 0.25 0.30 0.50 0.50 2.40 2.60 1.80 solder mask stencil t op copper package geometric center package and pad outlines figure 2. recommended pcb footprint design for the luxeon emitter. in order to ensure proper heat dissipation from the package electrodes to the pcb, it is best to extend the top copper layer at least 3 mm beyond the package of the luxeon emitter. all dimensions are in mm. 1.6 mechanical files mechanical drawings for the luxeon emitter are available on the lumileds website at lumileds.com . 2. pcb design guidelines for the luxeon emitter the luxeon emitter is designed to be soldered onto a printed circuit board (pcb). to ensure optimal operation, the pcb should be designed to minimize the overall thermal resistance between the led package and the heat sink. 2.1 pcb footprint and land pattern the recommended pcb footprint design for the luxeon emitter is shown in figure 2. in order to ensure proper heat dissipation from the emitter electrodes to the pcb, it is best to extend the top copper layer of the pcb beyond the perimeter of the luxeon emitter by at least 3 mm (see section 3). 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 emitters of 0.5mm. placing multiple luxeon emitters too close to each other may adversely impact the ability of the pcb to dissipate the heat from the emitters and may cause accidental shorts between the metal stubs on the side of neighboring luxeon emitters.
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 5 figure 3. top copper trace patterns showing the maximum (optimized and standard) and minimum top side metallization. for the maximum copper design, one can optimize the copper trace pattern to take into account that the heat is mainly dissipated from the cathode pad. there is no need to have large copper area around the anode. 3. thermal management the overall thermal resistance between a luxeon emitter and the heat sink is strongly afected by the design and material of the pcb on which the emitter is soldered. on fr4 based pcb, the following general guidelines will yield optimum thermal performance: C thicker top copper layer, for e.g. 2 oz versus 1 oz copper C at least 3mm of top copper layer extending outside the led package. table 1 shows the result of the thermal resistance from junction to heat sink using two boards with diferent copper areas surrounding the led package (figure 3) C top copper trace pattern layout. figure 3 shows the optimized max copper (optimized) layout versus standard max copper (standard) layout. the former will yield lower board thermal resistance note that using double sided fr4 board will not yield noticeable improvement in the board thermal resistance. on al-mcpcb, the following additional guidelines on top of the fr4 guidelines can improve the thermal performance: C thinner dielectric layer. trade-of between thinner dielectric and pcb electrical insulation barrier must be considered C dielectric with high thermal conductivity property. on a system level, high density led packing (small led to led spacing) will increase the overall led thermal resistance when compare to low density led packing. table 1. typical junction-to-heat sink thermal resistance values for fr4 board with minimum and maximum copper (standard) top side metallization. top side metallization pattern (figure 3) r j-heat sink [k/w] minimum copper 100 maximum copper (standard) 58
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 6 figure 4. the recommended temperature measurement point t s is located right next to the cathode of the luxeon emitter on the pcb. 4. thermal measurement guidelines the typical thermal resistance r j-case between the junction and the solder pads of the luxeon emitter is provided in the datasheet. with this information, the junction temperature t j can be determined according to the following equation: t j = t case + r j-case ? p electrical in this equation t case is the temperature at the bottom of the solder pads of the luxeon emitter and p electrical is the electrical power going into the emitter. in typical applications it may be difcult, though, to measure the temperature t case directly. therefore, a practical way to determine the junction temperature of the luxeon emitter is by measuring the temperature t s of a predetermined sensor pad on the pcb with a thermocouple. the recommended location of the sensor pad is right next to the cathode of the luxeon emitter on the pcb, as shown in figure 4. to ensure accurate readings, the thermocouple must make direct contact with the copper of the pcb onto which the luxeon emitter pads are soldered, i.e. any solder mask or other masking layer must be frst removed before mounting the thermocouple onto the pcb. the thermal resistance r j-s between the sensor pad and the luxeon emitter junction was experimentally determined on various pcbs as shown in table 2. the junction temperature can then be calculated as follows: t j = t s + r j-s ? p electrical table 2. typical junction-to-t s thermal resistance values for various devices with diferent pcb constructions. device top side metallization pattern (figure 3) pcb specification typical r j-s (k/w) luxeon 3535l maximum copper (standard) 1oz copper, 1mm thick fr4 single sided 32 luxeon 3535l colors: blue maximum copper (optimized) 1oz copper, 1mm thick al-mcpcb with 2w/(mk), 100m dielectric 35 luxeon 3535l colors: green maximum copper (optimized) 1oz copper, 1mm thick al-mcpcb with 2w/(mk), 100m dielectric 47 luxeon 3535l colors: pc amber and lime maximum copper (optimized) 1oz copper, 1mm thick al-mcpcb with 2w/(mk), 100m dielectric 27 luxeon 3535l colors: red and red-orange maximum copper (optimized) 1oz copper, 1mm thick al-mcpcb with 2w/(mk), 100m dielectric 21 luxeon 3535l he maximum copper (standard) 1 oz copper, 1mm thick fr4 single sided 32 luxeon 3535ls maximum copper (standard) 1 oz copper, 1mm thick fr4 single sided 36
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 7 5. assembly process guidelines 5.1 stencil design the recommended solder stencil thickness is 125m. 5.2 solder paste lumileds recommends lead-free solder for the luxeon emitter. lumileds tested sac 305 solder paste from alpha metals (om338 grade 3 and om 325 grade 4) with satisfactory results. however, since application environments vary widely, lumileds recommends that customers perform their own solder paste evaluation in order to ensure it is suitable for the targeted application. 5.3 solder refow profle the luxeon 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 rapidly, 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. 5.4 pick and place the luxeon emitter is packaged and shipped in tape-and-reel which is compatible with standard automated pick-and- place equipment to ensure the best placement accuracy. note that pick and place nozzles are customer specifc and are typically machined to ft specifc pick and place tools. in selecting a suitable nozzle size for picking up these luxeon emitters, there are two important factors to consider: 1. the nozzle outer diameter should not be larger than the opening of the reel pocket tape otherwise it may interfere with the pocket tape cavity during the pick-up process. see respective datasheets for tape and reel dimensions. 2. the nozzle outer diameter should also not be smaller than the light emitting surface (les) diameter (figure 1) otherwise this may allow the nozzle tip to be in full contact with the silicone-flled les area and may cause damage to the surface or cause pick-up/release issues. recommended outer diameter is 3.5mm. there are two les diameters for luxeon emitters; 2.6mm and 3.0mm. see respective datasheets for mechanical package dimensions. one nozzle that meets the above criteria and suitable for picking up the luxeon emitters is shown in figure 5.
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 8 figure 5. an example of nozzle 505 for juki ke2080l pick and place machine suitable for picking up luxeon emitters. it has an outer diameter of 3.5mm and inner diameter of 1.7mm. 5.5 electrostatic discharge protection the luxeon emitter does not include any transient voltage suppressor (tvs) chip to protect against electrostatic discharges (esd). therefore, lumileds recommends observing the following precautions when handling the luxeon emitter: ? during manual handling always use a conductive wrist band or ankle straps when positioned on a grounded conductive mat. ? all equipment, machinery, work tables and storage racks that may get in contact with the luxeon emitter should be properly grounded. ? use an ion blower to neutralize the static discharge that may build up on the surface and lens of the plastic housing of the luxeon emitter during storage and handling. luxeon emitters which are damaged by esd may not light up at low currents and/or may exhibit abnormal performance characteristics such as a high reverse leakage current and a low forward voltage. to determine whether any device is damage by esd, measure the light output and forward voltage of the emitter which is suspect. a forward voltage above 2.0v for a drive current of 0.1ma typically indicates that the led is not damaged. 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).
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 9 6.2 active control led current driver there are two types of active control led current drivers: C linear regulated power supply C 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 6. 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 6. 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. figure 6. typical transistor operation regions. ohmic or linear region is shaded in yellow while the saturation or switching region is shaded green. a summary of the major diferences between these two active control led current drivers is given in table 3 below. table 3. 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 and weight big and heavy 1 small and light notes for table 3: 1. if magnetics are used to step down the voltage before the regulator.
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 10 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 7 shows an example of a system block diagram of a typical led driver circuit. lumileds maintain 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 . navigate to the design tools section and click on login (figure 8). follow the login process or the instructions to create an account. within the lumileds design tools, click on eco-system to access the drivers tab. figure 7. a typical system block diagram of one example of a led driver circuit. figure 8. screenshots on how to navigate to the led drivers eco-system.
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 11 7. packaging considerationschemical compatibility the luxeon emitter package contains a silicone overcoat to protect the led chip 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 used in the luxeon emitter 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 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. under heat and blue light, vocs captured inside the silicone 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 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 4 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. the chemicals in table 4 are typically not directly used in the fnal products that are built around luxeon emitters. 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: C 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. C 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.
AB203 luxeon 3535l line application brief 20160706 ?2016 lumileds holding b.v. all rights reserved. 12 rohs compliant table 4. list of commonly used chemicals that will damage the silicone of the luxeon emitter. avoid using any of these chemicals in the housing that contains the led package. chemical name normally used as hydrochloric acid acid sulfuric acid acid nitric acid acid acetic acid acid sodium hydroxide alkali potassium hydroxide alkali ammonia alkali mek (methyl ethyl ketone) solvent mibk (methyl isobutyl ketone) solvent toluene solvent xylene solvent benzene solvent gasoline solvent mineral spirits solvent dichloromethane solvent tetracholorometane 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
?2016 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 global leader in light engine technology. the company develops, manufactures and distributes groundbreaking leds and automotive lighting products that shatter the status quo and help customers gain and maintain a competitive edge. with a rich history of industry frsts, lumileds is uniquely positioned to deliver lighting advancements well into the future by maintaining an unwavering focus on quality, innovation and reliability. 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. AB203 luxeon 3535l line application brief 20160706

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