View AB32_9035927.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

luxeon rebel plaform assembly and handling information introduction this application brief covers recommended board designs and assembly procedures for the luxeon leds referenced below in the scope. luxeon leds are revolutionary, ultra-compact, surface mount, high-power leds. these leds ofer a compact package with high lumen output and superior thermal performance. the compact design allows close packing for maximum light output per unit area of board space while retaining high efcacy and maximum lumen maintenance. proper handling, board design, and thermal management are required in order to ensure high optical output and long led lumen maintenance times. scope the assembly and handling guidelines in this application brief apply to the following luxeon products: ? luxeon r ? luxeon rebel es ? luxeon rebel (automotive & general illumination) ? luxeon rebel plus ? luxeon rebel color the luxeon leds that belong to these product categories have very similar form factors. consequently, most handling requirements and board design recommendations in this application brief apply to all leds. any handling requirements that are specifc to a subset of luxeon leds will be clearly marked. in the remainder of this document the term luxeon led refers to any led that belongs to one of the luxeon products listed above. automotive & illumination AB32 luxeon rebel platform assembly and handling information application brief ?2016 lumileds holding b.v. all rights reserved.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?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 lens handling ...................................................................... 7 1.4 lens cleaning ...................................................................... 7 1.5 electrical isolation ................................................................... 7 2 board design rules 8 2.1 pcb requirements .................................................................. 8 2.2 luxeon led footprint and land pattern .............................................. 8 2.3 surface finishing .................................................................. 10 2.4 luxeon led close proximity placement .............................................. 10 3 fr4-based boards 10 3.1 material properties ................................................................ 10 3.2 optimal thermal design ............................................................ 10 3.3 thermal via design ................................................................ 12 3.4 component spacing ............................................................... 14 3.5 thermal resistance ................................................................ 15 3.6 fr4 board handling ................................................................ 19 4 mcpcb board design 21 5 assembly process recommendations and parameters 23 5.1 stencil design ..................................................................... 23 5.2 solder paste ...................................................................... 24 5.3 pick and place nozzle .............................................................. 24 5.4 pick and place machine optimization ................................................. 27 5.5 placement accuracy ................................................................ 30 5.6 refow profle ..................................................................... 31 5.7 refow accuracy ................................................................... 32 5.8 void inspection and solderability indicators ........................................... 33 6 jedec moisture sensitivity level 35 7 product packaging considerations chemical compatibility 36 about lumileds 38
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 3 1. component 1.1. description a luxeon led is a revolutionary, ultra-compact, surface mount, high-power led which comes in two diferent mechanical confgurations: ? confguration a: a luxeon led with this confguration has a fat surface area outside the silicone lens. this confguration is used for all luxeon rebel color and luxeon rebel white leds (datasheets ds58, ds64, and ds68). ? confguration b: a luxeon led with this confguration has a transient voltage suppressor chip in a separate pocket on the ceramic substrate. this confguration is used for all luxeon rebel es, and luxeon r leds (datasheets ds61 and ds101). cross sections for both confgurations are shown in figure 1, highlighting the main components of a luxeon led. each luxeon led contains a high brightness led chip on a ceramic substrate. the ceramic substrate provides mechanical support and thermally connects the led chip to a heat pad on the bottom of the substrate. an electrical interconnect layer connects the led chip to a cathode and anode (not visible in the cross sections) on the bottom of the substrate. a silicone lens above the led chip extracts the light that is generated inside the led chip. all ingan luxeon leds contain a transient voltage suppressor (tvs) chip which protects the led chip against electrostatic dischage (esd) events. ceramic substrate ther ma l pad (electrical ly is ol ated) metal inte rc onnect layer bond laye r led chip cathode tv s silicone lens tv s cathode figure 1. a luxeon led comes in two diferent confgurations. confguration a (left) has a planar surface outside the silicone lens while confguration b (right) has a tvs which resides inside a special pocket on the ceramic substrate outside the silicone lens (right). 1.2. optical center a luxeon led contains three feature sets that locate the theoretical optical center. these features are the topside fducials, backside metallization, and led outline. fiducial marks on a luxeon led (confguration a) the fducial marks on a luxeon led (confguration a) provide the most accurate methodology to locate the theoretical optical center as shown in figure 2. to fnd the optical center of a luxeon led, use the fducials on the led package as follows: 1. draw an imaginary line between the centers of fducials f1 and f2. 2. using fducial f2 as the pivot point, rotate the line 19.66o counter clockwise. 3. the theoretical optical center lies on this line and is 2.248mm above the center of f2. once the theoretical optical center has been located, the actual optical center of a luxeon led (confguration a) is within a circular diameter of 0.29mm with respect to the theoretical optical center. note that the nominal position of the fducials on a luxeon led (confguration a) is identical for all colors. however, there is a diference in the metallization pattern between ingan and alingap luxeon leds, as indicated in figure 3.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 4 figure 2. the most accurate method to fnd the theoretical optic al center and the center of the silicone lens is by using the fducials located on the front side of a luxeon led (confguration a). all dimensions are in mm. figure 3. top views of alingap and ingan luxeon leds (confgurat ion a). the fducials on an alingap luxeon led (left) are connected to the metallization patterns while the fducials on an ingan luxeon led (right) are isolated.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 5 fiducial marks for a luxeon led (confguration b): a luxeon led (confguration b) has two fducial marks labeled f1 and f2 as shown in figure 4. an optional third fducial, f3, may be present as well. these fducial marks provide the most accurate methodology to locate the theoretical optical center, marked by the red dot in figure 4. the theoretical optical center is located 1.450mm from the vertical and horizontal edges of fducial marks f1 and f2. the theoretical optical center also lies 1.577mm above the center of fducial f3, if present, along an imaginary line drawn between the center of fducial f3 and the midpoint between fducials f1 and f2. the actual optical center of a luxeon led (confguration b) is within a circular diameter of 0.290mm with respect to the theoretical optical center. ( o p tional ) theoretical optical center ( p ) o o sulhhpdffxudhph4hhuhlfdoslfdofhhuoolphlduhlpp figure 5 shows the typical metallization pattern of a luxeon led (confguration b). figure 5. typical metallization pattern of a luxeon led (confgu ration b). hllf4xudluhlhldhsdudhsfnhhfhudplfxeudh
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 6 led outline and backside metallization while the fducial marks provide the most accurate technique to fnd the optical center of the silicone lens, one can also use the edges or the backside metallization to locate the theoretical optical center of a luxeon led. figure 2 and figure 4 illustrate the position of the optical center with respect to the edges of the ceramic substrate for the two diferent luxeon led confgurations. in both confgurations the optical center is located 1.525mm from the top and side of the luxeon led edges. the optical center can also be located using the edges of the thermal pad on the bottom of the ceramic substrate as shown in figure 6. the actual position of the center of the lens will be within a circle with a diameter of 0.350mm with respect to the theoretical optical center found using the edges of the thermal pad as a reference. figure 6. the theoretical optical center may be located using t he edges of the thermal pad on the bottom of a luxeon led. the center of the silicone lens will be within a 0.35mm radius with respect to the theoretical optical center. all dimensions are in mm.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 7 1.3 lens handling a luxeon led is designed to maximize light output and reliability. however, improper handling of a luxeon led may damage the silicone lens and afect the overall light performance and reliability. to minimize the risk of damage to the silicone lens during manual handling, only pick up luxeon leds from the sides of the ceramic substrate and never from the silicone lens itself (see figure 7). figure 7. correct handling (left) and incorrect handling (right ) of a luxeon led. due to its small size, the silicone lens of a luxeon led can only withstand a limited amount of force. in order to avoid any mechanical damage to the silicone lens of a luxeon led or to the led chip inside the luxeon led, do not apply more than 3n of shear force (300g) directly onto the lens. when utilizing a pick and place machine, always ensure that the pick and place nozzle does not place excessive pressure onto the silicone lens of a luxeon led. for more information see section 5.3 pick and place nozzle of this document. similar restrictions exist for manual handling. 1.4 lens cleaning the silicone lens of a luxeon led should not be exposed to dust and debris. excessive dust and debris may cause a drastic decrease in optical output. in the event that an 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 lens. do not use other solvents as they may adversely react with a luxeon led. for more information regarding chemical compatibility, see section 7. product packaging considerations chemical compatibility. 1.5 electrical isolation the ceramic substrate of a luxeon led electrically isolates the thermal pad from the led cathode and anode (see the cross sections in figure 1). consequently, a high voltage diference between the electrical and thermal metallization may occur in applications where multiple luxeon leds are connected in series. as a reference, the minimum distance between the top electrical metallization and the bottom thermal metallization of a luxeon led, considering x, y and z dimensions, is > 0.35mm. in order to avoid any electrical shocks and/or damage to luxeon leds, each design needs to comply with the appropriate standards of safety and isolation distances, known as clearance and creepage distances, respectively. compliance with appropriate standards is application and design specifc. examples of standards are iec 60065 for audio/video equipment and iec 60598 for general lighting applications. with proper use of electrical isolation and circuitry (e.g. short-circuits protection) the length of a series of luxeon leds can be many tens of units long.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 8 2. board design rules 2.1 pcb requirements a luxeon led is designed to be mounted on a two-layer fr4 pcb (printed circuit board), a multi-layer fr4 pcb or an mcpcb (metal core printed circuit board). to ensure optimal operation of a luxeon led, the thermal path between the led package and the heat sink should have a thermal resistance as low as feasible. historically, mcpcb has been used for its low thermal resistance and rigidity. however, mcpcb is not always the most economical solution for certain applications. a two layer fr4 board (with open vias or flled and capped vias), in contrast, often ofers a much lower cost solution for a thermally efcient package. by following the guidelines outlined below, one can achieve a thermal resistance for fr4 pcb that is equivalent to or lower than a mcpcb equivalent design with lower cost than that of mcpcb. for reference, here are the applicable ipc standards when designing pcb boards. ? general pcb design: C ipc a-610d: acceptability of electronic assemblies ? filled and capped via boards: C ipc 4761: design guide for protection of printed board via structures C ipc 2315: design guide for high density interconnects and micro vias C ipc 2226: design standard for high density interconnect printed boards 2.2 luxeon led footprint and land pattern lumileds has conducted an investigation to determine the optimal land pattern design for a luxeon led on a pcb. the goal of this study was to create a board with low thermal resistance, high placement accuracy, a minimum number of solder voids, and solderability indicators. figure 8 shows the individual layers of the suggested layout with solderability indicators for an open via plated through hole (pth) board design. the green solder mask is a photolithographic mask, which ofers a highly accurate alignment to the copper layer. the white mask labeled white text is a printed layer consisting of a double printed layers of for instance, tamura usi-210wp ink (ul e38152). this white layer enhances light refectivity, but is optional. the solderability indicators, shown as the diagonally extended copper areas on the thermal and electrical land patterns, provide visual proof of efective solder refow on all pads. in addition to acting as solderability indicators, the extended area can also be electrically probed during quality control tests. refow placement accuracy and thermal resistance will not be afected by the removal of the solderability indicators in the layout. in this discussion, the term land pattern refers to the pattern on the pcb for the pads of a luxeon led. the land pattern designs are available as .dxf fle on the lumileds website at lumileds.com .
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 9 figure 8. recommended layout for a luxeon led with open via pth board. figure 9. recommended layout for a luxeon led with flled and capped vias. thermal vias solderability indicators filled and capped via
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 10 2.3 surface finishing lumileds recommends using a high temperature organic solderability preservative (osp) on the copper layer. 2.4 luxeon led close proximity placement lumileds recommends a minimal edge to edge spacing of 0.3mm between luxeon leds. if the edge to edge spacing is less, the components may drift together during the solder step. also, the light output for each luxeon led may drop due to optical absorption by adjacent led packages. for open via pth design, close spacing of luxeon leds may require the removal of the solderability indicators shown in figure 8. removal of the solderability indicators does not afect the placement accuracy. 3. fr4-based boards 3.1 material properties fr4 is an industry standard pcb technology. depending on the led application, drive condition and the number of leds on the board, the choice for tg (glass transition temperature) and cti (comparative tracking index) value of the base material needs to be set. most common fr4 material has tg=130c and cti=175v. for high voltage applications, the trace clearances and cti values may be increased accordingly. 3.2 optimal thermal design thermal vias are the primary method of heat transportation to the heat sink at the pcb bottom. a thermal via is a plated through hole that can be open, plugged, flled or flled and capped. lumileds conducted a study on two thermal via designs aimed at reducing the thermal resistance. they are (a) open via pth and (b) flled and capped via. open via pth design a cross section of this design is shown in figure 10. the fnal thermal resistance is determined by the number and density of vias, the copper plating thickness and pth thickness. figure 11 shows a design with a standard two layer board. here the total copper plating is 70m with the pth plating thickness of 35um. in total, 33 vias are placed outside the thermal landing pad. the placement of the two smaller thermal vias is to minimize voiding in the solder joint. for the recommended design, the measured thermal resistance for a 0.8mm thick fr4 pcb with these design features approaches 7k/w. ink copper (70m) so lder mask epoxy plated through hole via ( 35 m ) copper (70m) figure 10. cross section of fr4 based pcb with thermal vias to decrease the thermal resistance.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 11 figure 11. outline of the recommended pad layout for a luxeon l ed (top view). see figure 8 for more illustrations. there is 0.5mm spacing between the thermal and electrical pads. filled and capped via design a cross section of this design for a standard two layers board is shown in figure 12. the fnal thermal resistance is determined by the number and density of vias, the copper plating thickness, pth thickness and the plugging material used to fll the vias. figure 13 shows the recommended layout for a two layer board. the thermal resistance for a 0.8mm thick fr4 pcb with these design features approaches 3k/w. ink copper (85m) so lder mask epoxy plated through hole via ( 35 m ) plugging material 25um plang on top of ?lled vias copper (85m) figure 12. cross section of fr4 based pcb with flled and capped thermal via for two layer board. green solder mask pth thermal via white text copper traces etched copper for isolation solder stencil 13
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 12 figure 13. outline of the recommended pad layout for a luxeon l ed on a pcb with flled and capped vias. see figure 9 for alternate views. a multilayer fr4 board with flled and capped via may be considered. see figure 14 for a cross section of the multilayer board design. i n k c o p p e r so l d e r m a s k ep o x y p l u g g i n g m a t e r i a l c o p p e r p l a t i n g o n t o p o f f i l l e d v i a s c o p p e r c o p p e r l a s e r v i a i n k c o p p e r so l d e r m a s k ep o x y p l u g g i n g m a t e r i a l p l u g g i n g m a t e r i a l c o p p e r p l a t i n g o n t o p o f f i l l e d v i a s c o p p e r c o p p e r l a s e r v i a figure 14. cross section of flled and capped via multilayer board. 3.3 thermal via design for both the open via pth and flled and capped via design, the fnished hole diameter is 0.5mm. a smaller diameter will lead to an increased thermal resistance. the recommended distance between two holes is 0.4mm. this results in a minimal pitch of 0.9mm between the vias. figure 15 indicates the typical dimensions. the position of the vias may difer from the preferred layout of figure 11 and figure 13, without signifcantly changing thermal properties. for open via pth design, the drill hole for the two smaller vias with a 35m plating thickness is 0.32mm. the solder mask area around the vias is needed to avoid solder to fow through the vias to the backside. this would lead to a reduced heat sink contact of the pcb bottom surface. an opening in the solder mask of 0.05mm surrounds each via. the total minimal width of the solder mask around the via is 0.25mm. figure 16 shows the resulting solder mask design of the thermal pad. for flled and capped via design, each via is flled or plugged with an epoxy material. standard industry practices recommend using a plugging material with a cte (coefcient of thermal expansion) and tg to match the thermal characteristics of the pcb. recommendations on qualifcation criteria for the plugging process are documented in ipc- 4761 design guide for protection of printed board via structures. use of thermally improved plugging material can further reduce the board thermal resistance, although the absolute improvement will be small. c o p p e r t r a ce s e t ch e d co p p e r f o r i so l a t i o n fi l l e d a n d ca p p e d t h e r m a l v i a g r e e n s o l d e r m a sk w h i t e t e x t s o l d e r st e n ci l c o p p e r t r a ce s c o p p e r t r a ce s e t ch e d co p p e r f o r i so l a t i o n fi l l e d a n d ca p p e d t h e r m a l v i a g r e e n s o l d e r m a sk w h i t e t e x t s o l d e r st e n ci l
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 13 figure 15. recommended fnished diameter and spacing dimensions for both open via pth and flled and capped via design. all dimensions are in mm. figure 16. solder mask design of thermal pad for open via pth. all dimensions are in mm.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 14 3.4 component spacing for the open via pth design, the minimal edge to edge spacing is 4mm to maintain the thermal properties, see figure 17. spacing below 4mm results in fewer vias between the components, thus increasing thermal resistance. 4.00 figure 17. illustration of edge to edge spacing. the thermal re sistance will increase dramatically if the spacing is less than 4mm edge to edge. for flled and capped vias with the above recommended design, the minimal edge to edge spacing is 0.3mm, see figure 18. this board design yields higher component density while still achieving a low thermal resistance.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 15 0.30 figure 18. illustration of edge to edge spacing for a flled and capped via design. 3.5 thermal resistance the thermal resistance between the component case (body) and the back of the board/heatsink (r c-hs ) of the pcb depends on the size of cu area around the thermal pad, the number of vias, the placement of vias, the cu plating thicknesses, and the pcb thickness. efect of pcb thickness and plating thickness figure 19 shows simulated r c-hs values for open pth and flled and capped via as a function of pcb thickness. a double layer fr4 board with various through hole plating thicknesses (20m and 35m) and total surface plating (50m and 70m for open pth, 70m and 85m for flled and capped via) are studied. the open pth via board design uses 33 vias and the flled and capped design uses 27 vias. data is for a single luxeon led. the thicker the pcb board, the higher is the thermal resistance. thicker plating thickness for the thermal via will reduce the thermal resistance and vice versa. 0 2 4 6 8 10 12 14 16 0. 50 .6 0. 70 .8 0. 91 1. 11 .2 1. 31 .4 1. 51 .6 1. 7 pc b th ic kn ess ( mm) boar d th er ma l re sist an ce rt h c-hs (k /w ) op en vi a pt h cu pl at in g 70 / 35 op en vi a pt h cu pl at in g 50/ 20 fi lled and ca pped vi a cu pl ati ng 85 / 35 fi lled and ca pped vi a cu pl ati ng 70 / 20 figure 19. r c-hs values as function of pcb thickness for two layers fr4 board with diferent plating thicknesses.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 16 impact of the thermal via count for an open via pth board, removal of the 14 outer vias increases the thermal resistance by approximately 1k/w. the 14 outer vias are labeled in figure 11. eliminating the two smaller vias in the thermal landing pad increases the r c-hs value by 1 k/w as well since the copper area around the thermal landing pad has a large contribution to the thermal spreading. the optimal copper area extends 3mm beyond the thermal pad. any extension beyond 3mm will not signifcantly lower the thermal resistance. elimination of both the outer vias and the copper area outside the thermal pad increases the thermal resistance to above 30k/w. with flled and capped vias, the thermal resistance decreases from 4k/w to 3k/w when adding the additional vias around the 11 vias in the thermal landing pad as shown in figure 18. 0 1 2 3 4 5 6 01 02 03 04 05 0 # of vi as pe r luxeon le d rt h c- hs (k /w ) )ljxuh6lpxodwlrqriwkhwkhupdouhvlvwdqfhdvdixqfwlrqriqxpehuriyldv4oohgdqgfdsshgyld efect of component density for an open via pth, bringing the components closer together than 4mm will lead to elimination of vias and decreases the copper area around the thermal pad. if the spacing is less than 2mm, the thermal resistance will increase dramatically. figure 21 shows the simulated thermal resistance as a function of spacing. figure 22 shows the reduction of vias when the spacing decreases from 4mm to 2mm. these simulation results correspond to a 0.8mm fr4 board thickness with 70m of total copper plating and 35m copper plating via.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 17 90 v ias 124 v ias luxeon led spacing 2mm 4mm r per led 7k/w 6.8k/w (simulation estimate) c-hs figure 22. when the edge to edge spacing is reduced from 4 to 2 mm, the number of vias decreases from 124 to 90. thermal resistance values are simulated. 0 2 4 6 8 10 12 14 01 23 45 sp acing (m m) board th ermal r esi st an ce rt h c-hs (k /w) rt h (c -h s) 4l ed cl us te r figure 21. simulated r c-hs values for close spacing of leds for a two layer fr4 pcb.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 18 for flled and capped via, a low thermal resistance can be achieved with a minimum component spacing of 0.3mm for a 35m/70m (through-hole/total surface) copper plating thickness as shown in figure 23 (blue line). figure 23. r c-hs values of the pcb for diferent led spacing and diferent via plating thicknesses. figure 24 shows a comparison of the thermal resistance of various board technologies. mcpcb uses 35m plating, open pth via board uses 70/35m copper and flled and capped via board uses 85/35m copper. note that the default number of vias is 33 for open pth and 27 for flled and capped via for 8mm led spacing. fewer vias are employed when the led spacing is reduced which increases the thermal resistance. figure 24. comparison r c-hs of various board technologies as a function of led spacing.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 19 3.6 fr4 board handling the substrate of a luxeon led is made of ceramic, a relatively brittle material. even though this product has a small form factor and is unlikely to cause any problems, forces on the package should be kept to a minimum. in particular, excessive bending forces on the package may crack the ceramic substrate or break the solder joints. figure 25. excessive bending force on the pcb may crack the ceramic substrate of a luxeon led and/or damage the solder joints. figure 25 shows what forces may, inadvertently, be applied to a luxeon led when a fat assembled board is bent. this can happen, for example, when punching-of or breaking-of led strips of a pcb panel (figure 26). led strips board panel figure 26. pcb panel consisting of several strips of leds. a printed circuit board may warp after refow when layers with diferent cte (coefcient of thermal expansion) are applied to the top and bottom of the boards. if the pcb is subsequently secured to a fat surface, a vertical force is applied to the ceramic package (see figure 27). if this force is large enough, the ceramic substrate package may break. to minimize the chance of cracking the ceramic package, orientate the package such that the long side of the package is perpendicular to the dominant warpage direction. figure 27. securing a warped board to fat surface may cause excessive stress on the ceramic substrate.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 20 board warpage can be minimized by understanding how diferent cte materials are stacked up. for example, when an fr4 board is sandwiched between two full copper sheets, adding thin isolation lines in the copper sheet to create copper islands can minimize board warpage as shown in figure 28. copper isolaon copper isolation figure 28. copper islands can help reduce board warpage.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 21 4. mcpcb board design the layout for the mcpcb design is similar to the fr4 layout in figure 8 but without all the vias, see figure 29. copper solder ? mask epoxy white ? ink solder figure 29. recommended layout for a luxeon led on mcpcb. note t hat this layout is similar to the fr4 layout in figure 8 but without all the vias. in order to minimize thermal resistance the area of copper connected to the thermal pad of a luxeon led must be maximized. lumileds recommends extending the copper area for the thermal pad 3mm beyond the outline of a luxeon led. a cross section of the mcpcb is shown below. ink solde r ma sk c oppe r epox y a lum inum mc pc b figure 30. cross section of mcpcb.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 22 table 1 summarizes thermal resistance values for typical and high thermal conductivity epoxies. standard mcpcb design rules yield a board with 10k/w thermal resistance. increasing the copper thickness and using a thinner dielectric with higher thermal conductivity lowers the thermal resistance dramatically. in both cases the copper area extending outside the thermal pad is at least 3mm. table 1. mcpcb design parameters dielectric typical epoxy high conductivity epoxy dielectric thermal conductivity [w/mk] 0.8 4 al thickness [mm] 1.5 1.5 copper thickness [m] 30 70 dielectric thickness [m] 100 85 total mcpcb thermal resistance for low density design [k/w] 10 5 the diference between the coefcients of thermal expansion (cte) of a luxeon led and a mcpcb is larger than the diference between the cte of a luxeon led and an fr4 pcb. therefore, there is greater stress on the solder joint for a luxeon led on mcpcb. studies by lumileds suggest that dielectric epoxy materials have a strong impact on the solder joint reliability. lumileds, therefore, recommends that customers contact their mcpcb vendors for suitable dielectric materials.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 23 5. assembly process recommendations and parameters 5.1 stencil design the recommended solder stencil thickness is 125m. the area coverage of the solder paste is greater than 90%. this yields a solder joint thickness of approximately 50m, using the lead-free solder. figure 31 shows the recommended stencil design for the footprint with two small thermal vias and solderability indicators for open via pth board. figure 32 shows the recommended stencil design for flled and capped via board. figure 31. solder stencil for footprint with two thermal vias and four solder ability indicators. )ljxuh6roghuvwhqfloiru4oohgdqgfdsshgyld
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 24 5.2 solder paste lumileds recommends lead-free solder for a luxeon led. lumileds successfully 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 pick and place nozzle automated pick and place equipment provides the best placement accuracy for luxeon leds. since luxeon leds come in two diferent mechanical confgurations (as explained in section 1.1), lumileds recommends diferent pick and place nozzles for each confguration. note that pick and place nozzles are customer specifc and are typically machined to ft specifc pick and place tools. lumileds has successfully worked with micro-mechanics ( http://www.micro-mechanics.com/ ) in the past to obtain dedicated pick-up nozzles. pick and place for luxeon leds (confguration a) a generic nozzle for 0603 components with a pick-up area of 0.95mm x 1.75mm, or a lumileds specifc nozzle can be used for pick and place of luxeon leds (confguration a). neither nozzle makes any contact with the silicone lens of a luxeon led. figure 33 shows the typical pick-up area for a 0603 pick-up nozzle overlaid with the footprint of a luxeon led (confguration a). since the outer dimension of 0603 pick-up nozzles may vary between tools and vendors, its important to verify that the 0603 nozzle does not touch the silicone lens. using the pattern recognition system of pick and place equipment, the position of the nozzle during pick up is manually programmed. for guidance, the bottom fducial within the 0603 pick-up area can be used, as shown in figure 33. figure 33. the typical pick up area of a 0603 nozzle, overlaid with the footprint of a luxeon led (confguration a).
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 25 to prevent the led from sticking to the nozzle after placement, lumileds uses the mold release spray sr3-500b from solent maintenance. figure 34. dedicated pick-up nozzle design for a luxeon led (co nfguration a). the nozzle tolerances must account for the led dimensions. all dimensions are in mm.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 26 pick and place for luxeon leds (confguration b) a lumileds specifc nozzle can be used for pick and place of luxeon leds (confguration b), see figure 35. this nozzle picks up from the fat area around the silicone lens and does not make any contact with the silicone lens of a luxeon led. figure 35. dedicated pick-up nozzle design for a luxeon led (co nfguration b). this nozzle design, which clears the silicone lens of the luxeon led, picks up from the fat area around the silicone lens (see the middle drawing in the right column). all dimensions are in mm.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 27 5.4 pick and place machine optimization table 2 below summarizes key pick and place parameters for the dedicated luxeon led nozzles based on lumileds internal test results. since pick and place settings vary between pick and place tools and vendors, lumileds recommends that these parameters are used as a reference only. table 2. luxeon led (configuration a) luxeon led (configuration b) pick up location referenced to top of the reel as shown in figure 36 [mm] -0.2 -1.6 vacuum [kpa] -20 -20 stencil thickness [micrometer] 125 125 over travel spring force during placement [n] 2 2 material black anodized aluminum stainless steel top of th e re el figure 36. with the top of the reel being 0mm, the nozzle will over travel into the reel by 0.2mm and 1.6mm, respectively, for confguration a and b of the luxeon led. unlike other smd electronic components, which generally have cubic shapes, a luxeon led has a silicone lens protrusion to enhance light extraction. when the cover tape of the reel is removed, there is a possibility for the silicone lens to touch a part of the sliding/guiding metal plate or the shutter of the feeder during indexing. this can lead to scratched or damaged lenses, see figure 37.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 28 shutte r after t he cover t ape is removed, t he shutter guides t he component t hrough t he feeder for pick up. during indexing, the shutter moves back and forth and the component may vibrate. this may cause the silicone lens to come into contact with the shutter. shutter ? s lides back and f ort h during indexing pick up nozzle is located here figure 37. the silicone lens of a luxeon led may be damaged by the cover plate of the pick and place feeder.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 29 in some pick and place machines a simple modifcation can be made to the pick and place feeder to achieve optimum yield. one recommendation to reduce damage to the silicone lens is to remove the shutter completely and shift the cover tape removal close to the pick-up nozzle. figure 38 illustrates this recommendation. shutter moving back & forth before modification after modification ? removing shutter and shifting the cover tape removal close to the pick-up nozzle figure 38. minor modifcations to the pick and place machine min imize the chance of damage to the silicone lens of the luxeon led. in addition to making the above change, lumileds recommends an electrical (motorized) feeder rather than a mechanical/ pneumatic feeder because units can fall out of the tape pocket or become misaligned due to abrupt movements of the tape.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 30 5.5 placement 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 a luxeon led (3 pads). if available use the sot32 profle from the component library, and modify the lead dimensions and pitch according to the dimensions in figure 39. the recognition tolerance can be set to 30%. a lower percentage improves placement accuracy but may reduce recognition yield. for high density placement (e.g. spacing between components below 0.5mm) lumileds recommends using the outline dimensions of a luxeon led (see figure 39) for recognition. reducing the tolerance on the outline dimensions to 5% eliminates the risk of staggering components. lumileds recommends a minimal spacing of 0.3 mm between luxeon leds. this avoids the risk of neighboring components touching each other after refow. note, though, that the light output for each led may drop due to optical absorption between led packages. for manual placement, the fducials on the top side assist in locating the optical center. figure 2 serves as a guideline to fnd the optical center on the top side. figure 39. mechanical dimensions of the luxeon led. all dimensions are in mm.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 31 5.6 refow profle luxeon leds are compatible with surface mount technology and lead-free refow. this greatly simplifes the manufacturing process by eliminating the need for adhesives and epoxies. it has been said that the most important step in refow soldering is the refow itself. this 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 (an example refow profle is shown in figure 40): 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. cooling 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. lumileds successfully utilized the refow profle in figure 40 for luxeon leds on pcb. figure 40. refow profle of luxeon leds using sac-305 solder paste.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 32 5.7 refow accuracy global fducials on the pcb board (see figure 41) can help calculate the refow accuracy between the centers of the component to the nominal board position. section 1.2 optical center explains how to fnd the theoretical optical center of the luxeon led. lumileds has determined the placement accuracy after refow to be well within 90m in the x and y directions for the footprint of figure 11. the placement accuracy is determined as follows: the pcb onto which the luxeon led is assembled must have fducials to determine the origin. the position of the luxeon led is determined using the component fducials. the diference between this measured value and the nominal placement position is the placement accuracy. board fiduc ia l board fiduci al component fiducials figure 41. the board fducials provide the origin of the board. the fducials on a luxeon led determine the optical center of th e led. the diference between the measured coordinates of the optical center and the nominal position is the placement accuracy.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 33 5.8 void inspection and solderability indicators an in-line x-ray machine can inspect for voids after refow. lumileds has determined that the two small thermal vias in the thermal pad footprint minimizes voiding by serving as an air vent during refow. a large percentage of voids in the thermal pad will increase of the thermal resistance. figure 42 and figure 43 show the impact of solder voiding on board thermal resistance (r c-hs ) based on modeled data. figure 42. impact of voiding in thermal land on thermal resistance for open via design. figure 43. impact of voiding in thermal land on thermal resistance for flled and capped via design. for visual inspection of solder wetting, solderability indicators have been designed in the footprint, see figure 44.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 34 1 2 3 4 figure 44. a luxeon led refowed onto an fr4 pcb with four solderability indicators.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 35 6. jedec moisture sensitivity level luxeon leds 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 provides the customer with ease of assembly. the customer no longer needs to be concerned about bake out times and foor life. no bake out time is required for a moisture sensitivity level of 1. moisture sensitivity level 1 allows the device to be refowed three times under the specifcations as described in the respective luxeon led datasheets. jedec has defned eight levels for moisture sensitivity, as shown in table 3. table 3. jedec moisture sensitivity levels level floor life soak requirements standard accelerated equivalent 1 time conditions time (hours) conditions time (hours) conditions 1 unlimited 30c / 85% rh 168 +5/-0 85c / 85% rh 2 1 year 30c / 60% rh 168 +5/-0 85c / 60% rh 2a 4 weeks 30c / 60% rh 696 2 +5/-0 30c / 60% rh 120 +1/-0 60c / 60% rh 3 168 hours 30c / 60% rh 192 2 +5/-0 30c / 60% rh 40 +1/-0 60c / 60% rh 4 72 hours 30c / 60% rh 96 2 +2/-0 30c / 60% rh 20 +0.5/-0 60c / 60% rh 5 48 hours 30c / 60% rh 72 2 +2/-0 30c / 60% rh 15 +0.5/-0 60c / 60% rh 5a 24 hours 30c / 60% rh 48 2 +2/-0 30c / 60% rh 10 +0.5/-0 60c / 60% rh 6 time on label (tol) 30c / 60% rh tol 30c / 60% rh
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 36 7. product packaging considerations chemical compatibility luxeon leds contain a silicone overcoat and silicone lens 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 in the luxeon led 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 leds 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 lens. under heat and blue light, the vocs inside the silicone lens 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 lens 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 which may afect the performance of luxeon leds.
AB32 luxeon rebel platform assembly and handling information application brief 20160711 ?2016 lumileds holding b.v. all rights reserved. 37 table 4. list of commonly used chemicals that will damage the silicone lens of a luxeon led. avoid using any of these chemicals in the housing that contains the led package. chemical name normally used as hydrochloric acid acid hulfuric 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 the chemicals in table 4 are typically not directly used in the fnal products that are built around luxeon 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 as pcbs. lumileds, therefore, recommends the following precautions when designing your application: ? when designing secondary lenses to be used over a single 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.
?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. AB32 luxeon rebel platform assembly and handling information application brief 20160711

▲Up To Search▲

Price & Availability of AB32

	To Download AB32 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .