Two-phase cooling for light-emitting devices

System, method, and apparatus for two phase cooling in light-emitting devices are disclosed. In one aspect of the present disclosure, an apparatus includes a light-emitting device and a two-phase cooling apparatus coupled to the light-emitting device. The coupling of the two-phase cooling apparatus and the light-emitting device is operatively configured such that thermal coupling between the light-emitting device and the two-phase cooling apparatus enables, when, in operation, heat generated from the light-emitting device to be absorbed by a substance of a first phase in the two-phase cooling apparatus to convert the substance to a second phase.

TECHNICAL FIELD

The techniques are generally related to the field of thermal management and packaging of light-emitting devices, in particular, to two-phase cooling of light-emitting diodes.

BACKGROUND

When using white LEDs as a light source, the (ηLED) or wall efficiency is typically 20% to 30% of input power. This is the effective percentage of electricity that is converted to visible light, while the remaining 70% to 80% of input power is converted to heat that must be conducted from the LED die to the underlying heat sink, housing and finally to the surrounding air to maintain an acceptable LED junction temperature. In the United States, the goals of solid state lighting have been identified by the Department of Energy (DOE) and the Optoelectronics Industry Development Association (OIDA). The DOE would like to reproduce the spectrum of sunlight at 50% system efficiency, while the OIDA goal is to achieve an efficiency of 200 lm/W with good color rendering by 2020.

There is a feverish race to achieve LED and/or HBLED modules that can cannibalize the market for incandescent bulbs in the area of illumination. In order to achieve such a goal in moving LED's from indication applications to general illumination thermal management has become a major area in need of innovation. The thermal resistance of LED packages together with the maximum operating temperature determines the maximum power that can be dissipated in the package. At the outset of LED packaging in the 1960's the thermal resistance of a 5 mm package (still used for low power LEDs) typically would be 250 K/W.

Some LED packages utilize surface mount technology (SMT) as illustrated in the example ofFIG. 1. The key feature of SMT technology, is the onboard heat sink typically made of copper or aluminum. SMT packaging approaches can generally typically achieve 6-12 K/W thermal resistance. Some SMT packaging having a thermal resistance of 2.5 K/W and 9 W of power handling. This level of thermal resistance is typically achieved when the junction temperature reaches approximately 432K (159° C.).

Note that the LED junction temperature is directly related to the emission spectrum and the spectrum shift caused by slight variations in temperature is generally sensed by the human eye. Thus, considerable effort should be made in maintaining the junction temperature substantially constant and low to ensure robust and reliable operations of LEDs for various applications. In addition, packaging multiple LED dies in a single SMT package is a difficult task due to thermal crosstalk. Thus an incandescent bulb replacement for general illumination is currently out of reach of the majority of LED vendors.

DETAILED DESCRIPTION

Embodiments of the present disclosure include systems, apparatuses, and methods for thermal management and cooling in light emitting devices. One embodiment includes integration of a micro-loop heat pipe with discrete or indiscrete packaging for light emitting devices (e.g., LED/HBLED). The coupling of the two-phase cooling apparatus and the light-emitting device can be operatively configured such that thermal coupling between the light-emitting device and the two-phase cooling apparatus enables heat generated from the light-emitting device to be absorbed by a substance of a first phase in the two-phase cooling apparatus, the absorbed heat converting the substance to a second phase. The light emitting device can be formed on a wafer or a die. The substance may comprise substantially of water. In one embodiment, the first phase is liquid and the second phase is vapor.

The heat absorbed from the light-emitting device is typically at least a latent heat of the substance.

In one embodiment, the two-phase cooling apparatus further comprises, a vapor port that is substantially unobstructed in operation to allow exit of generated vapor and a chamber thermally coupled to the light-emitting device. When, in operation, the heat generated from the light-emitting device can be absorbed by the liquid stored in the chamber.

In one embodiment, the two phase cooling apparatus further comprises, a condensor coupled to the vapor port and/or a liquid port coupled to the condensor and the chamber suitable for storage of liquid. In addition, a heat sink may be coupled to the condenser and an air flow generator can be coupled to the heat sink.

One embodiment of an apparatus includes, a light-emitting device and a two-phase cooling apparatus coupled to the light-emitting device. One embodiment of the two-phase cooling apparatus comprises a micro-loop heat pipe. The micro-loop heat pipe can include a top cap portion and/or a layer having porous semiconductor structures thermally coupled to the top cap portion. The top cap portion may be coupled to the light-emitting device.

The porous semiconductor structures generally form through-holes across the layer. The through-holes have first and second ends where the first ends of the through-holes can be proximal to the top cap portion and the second ends of the through-holes can be proximal to the chamber. In one embodiment, the top cap portion is coupled to the layer having porous semiconductor structures such that the first ends of the through-holes are substantially unobstructed to liquid or vapor flow.

The micro-loop heat pipe can further include a chamber suitable for storage of liquid coupled to the layer having porous semiconductor structures. In one embodiment, the chamber is coupled to the layer having porous semiconductor structures such that, when in operation, the liquid in the chamber travels through the through-holes. The heat generated from the light-emitting device causes the liquid stored in the chamber to travel through the through-holes and convert into vapor. In one embodiment, the top cap portion has formed within or is coupled to a vapor port.

One embodiment of the apparatus further includes an electrostatic discharge circuitry electrically coupled to the light emitting device. The electrostatic discharge circuitry can include a first diode connected to the light-emitting diode in parallel. The electrostatic discharge circuitry can further include, a second diode electrically connected to the first diode. In one embodiment, the first diode is a zener diode having a lower breakdown voltage than the light-emitting diode.

FIG. 1illustrates a cross sectional view of an LED package100of the surface mount type.

One common package type for a LED packaging or HBLED packaging is that of the surface mount type. An example of surface mount packaging is shown inFIG. 1. The LED package100has a light-emitting diode (LED) or LED die104. The LED device or LED die104can be bonded to a carrier wafer106(e.g., silicon, germanium, or other semiconductor-based carrier wafer). The carrier wafer typically contains patterned diodes which can provide protection from Electrostatic Discharge (ESD). The carrier wafer106can be further mounted to a heat sink110via a bonding layer108(e.g., solder bond). In general, the heat sink110can be any type of heat spreader or heat slug that is made from material with high thermal conductivity including but not limited to aluminum and copper.

The bias that drives the LED diode104can be applied by wires112(e.g., gold or copper wires). The wires112can be further connected to the external leads of the copper electrodes of the SMT package. The LED104, in some instances, emits UV or ultra-violet light that can be converted to white light, for example, using a phosphor coating of the LED104. The phosphor coating can be embedded in silicone carrier102that surrounds the LED104. The phosphor coating may further be sealed in by a polymeric lens114. The heat that is generated by the LED104typically conducts through the wafer106and then into the heat sink110.

FIG. 2illustrates a cross sectional view of a surface mount LED package200integrated with a two-phase cooling apparatus in a surface mount package, according to one embodiment.

In one embodiment, one or more LED devices or dies202can be integrated with a two-phase cooling apparatus to facilitate cooling of the one or more LED devices or dies202. The two-phase cooling apparatus can be a micro-loop heat pipe that is packaged with the LEDs202in the LED package200.

For example, the integration can be implemented by coupling the LEDs202with the evaporator210of the micro-loop heat pipe. The evaporator210can further be integrated with the SMT LED package200thus allowing the liquid flow below the LED devices or dies202to absorb heat generated from operation and to prevent the junction temperature from substantially rising. Improved thermal management through integration of a two-phase cooling apparatus can substantially prevent increase in junction temperature and maintain the temperature within certain ranges can facilitate increased LED packing density to obtain the desired illumination according to the lighting application.

During operation, the heat generated by the LEDs202at least partially conduct through a layer204, also referred to as a top cap. The top cap204, in one embodiment, channels vapor to a vapor exit path (not shown). The vapor is generated from liquid stored in the chamber208. The top cap204typically comprises substantially of any material that has a low or high thermal conductivity depending on the embodied design.

In one embodiment, the material of the top cap204has a coefficient of thermal expansion (CTE) that is suitable for reduced cyclic thermal stress. In general, the material of the top cap204is selected taking into consideration thermal expansion (e.g., as measured by coefficient of thermal expansion, linear thermal expansion, area thermal expansion and/or volumetric thermal expansion) and/or the thermal conductivity. Materials that are generally thermal conductive or thermally conductive during specified/predetermined operating conditions having a suitable degree of thermal expansion can, in one embodiment, be ideal for top cap204material. For example, the top cap204can comprise, one or more of, silicon, germanium, diamond, SiC, AlN, Al2O3, and/or CMOS-grade silicon. In addition, the top cap204can also be formed out of Kovar, Kovar with silver, Cu, CuW (e.g., copper tungsten alloy), Al and/or anodized Al.

In one embodiment, the underlying structure214is retrofit to form the chamber208that when filled with liquid acts as a compensation chamber. The structure214in the example ofFIG. 2typically functions as a heat sink or other type heat spreaders comprising one or more materials with high thermal conductivity, including but not limited to aluminum or copper, for example. Additionally, non-metallic material can also be used in the structure214since thermal conduction is not the primary mechanism for heat dissipation. For example, the underlying structure214can also be formed from glass, silicon, AlN, Al2O3and/or ceramics. The manifold of liquid and vapor allows for heat to be carried away from the LEDs202and out of the SMT LED package200to an externally coupled surface area heat sink (not shown).

FIG. 3Aillustrates an LED die304packaged on the evaporator306of the micro-loop heat pipe, according to one embodiment.

Heat generated from LED die304can flow through electrical and thermal joint320and then conduct to the top cap310of the micro-loop heat pipe306. The heat is then thermally conducted through the top cap310substrate to a layer312with porous structures314coupled to the top cap310.

In one embodiment, the porous structures314are micron sized capillaries coated by an oxide. For example, the coating may be substantially silicon dioxide when the layer312is comprised of silicon. The top cap310can transfer heat to liquid menisci causing the liquid menisci to evaporation in the porous structure314of the layer312. As the liquid heats up and evaporates into vapor316, the vapor316is routed along the cavities between the top cap310and the layer312.

Note the porous structures314generally form through-holes in the layer312. Thus, the heat can cause the liquid to travel through the porous structures312and vaporize in conjunction with removing heat from the LEDs304. The heat removal can cause the LEDs to cool or to maintain temperature within a certain range. In addition, the porous structure314hydraulically connects the underlying liquid supply318. The porous structures312can generally be formed from semiconductor materials that have crystal structures of diamond or zinc blend. In one embodiment, the porous structure312comprises coherent silicon pores that are substantially uniform in spatial distribution and have a high length to diameter aspect ratio (e.g., approximately or greater than 60 to 205).

The LED die302can be coupled to the top cap304such that electrical and thermal coupling occurs at joint320. In one embodiment, the LED die304and evaporator306is protected from electrostatic discharge (ESD). Therefore, the thermal management and electrostatic discharge protection can be achieved to allow for multiple LED dies to be placed together to obtain the desired luminance. In one embodiment, ESD protection is achieved via a diode that is coupled to the LED die302. For example, areas322aand322bcan be lithographically patterned on the top cap310and subsequently doped n-type. An additional area324is doped p-type. The doped regions322a/band324form an N—P—N diode that can be biased in parallel with LED diode304.

FIG. 3Billustrates the equivalent circuit of an example of an electrostatic discharge circuitry having diodes360/370coupled to an LED350, according to one embodiment.

In one embodiment, an electrostatic discharge circuitry is optionally coupled to the LED350that is coupled to two-phase cooling apparatus. In one embodiment the electrostatic discharge circuitry comprises at least one diode360connected to the LED350in parallel. The diode360typically has a breakdown voltage that is lower than that of the LED350for ESD protection. Thus, the diode360is generally made from materials with lower bandgaps than the materials of the LED350. In one embodiment, the electrostatic circuitry composes two back to back diodes360and370connected in series to each other and further in parallel to the LED350.

The electrostatic discharge circuitry can be useful for LEDs based on materials having wide bandgaps since wide bandgap diodes such as AluInvGa1-u-vN (u,v≧0:0≦u+v≦1) can be prone to electrostatic failure due to low reverse saturation currents and high breakdown voltages.

When a forward bias is applied to a diode or LED (e.g., LED350), substantial forward current does not flow until the applied exceeds a threshold voltage (e.g., turn on voltage ˜2V). Above this voltage, the current through the LED350increases dramatically (e.g., exponentially) with the increase in voltage due to a low internal series resistance of the LED350during forward bias.

Contrastingly, when operating in the reverse bias direction the series resistance is significantly higher than when in the forward bias direction and reverse current is relatively low. However, if the reverse bias exceeds the breakdown voltage, the reverse current will increase dramatically. Since the breakdown voltage of the LED diode350is generally greater than that of the diode360(e.g., silicon zener diode), the current will flow through360as opposed to LED350thus protecting the LED350from electrostatic discharge.

FIG. 3Cillustrates a cross section of an example of the evaporator coupled to the LED350showing the topology of a back to back zener diode for electrostatic discharge protection, according to one embodiment.

In one embodiment, the LED or LED die350is bonded to a bond pad on the top cap310. The bond352may be a solder alloy such as but is not limited to a gold-tin bond. In addition, a metallic layer354(e.g., typically thin film) can be deposited for adhesion and wetting of the bond352(e.g., gold-tin). The metallic layer354typically comprises of adhesion metal including but not limited to, Ti, TiW, and/or Cr. The metallic layer352may further include a barrier metal including but not limited to Ni, Pt and a wetting layer (e.g., gold). Underlying this metallization is a n-doped silicon layer356alayer.

In one embodiment, additional regions/wells are formed in the top cap310. For example, the regions356a/bcan be doped n-type and the region358can be doped p-type. The electrical connections to the p-type region358and n-type region356a/bof the diode can be wire bonded together, for example, by ribbon stitching. In general, the zener diodes can be formed from any suitable material system (e.g., silicon, germanium, GaN, GaAs, etc.) by thin film fabrication. In one embodiment, the active region of the LED350comprises material with wide band gaps, including but not limited to, GaN, GaInN, InP, AlGaN, AluInvGa1-u-vN (u,v≧0:0≦u+v≦1).

FIG. 3Dillustrates an example of an LED350where the initial growth substrate has been removed to promote improved thermal design, according to one embodiment.

In one embodiment, the LED350is formed by thin film epitaxial growth. Thin film LEDs are advantageous in that they improve radiation decoupling and heat removal/dissipation. The active layer can be grown epitaxially on a substrate such as silicon carbide or sapphire. The substrate can be removed after growth grinding the silicon carbide or sapphire substrate away. Thus, thin film LEDs that are ˜30-50 micrometers thick can be fabricated thus further improving the dissipation and removal of generated heat.

In one embodiment, the active region of the LED or LED die350can have one quantum well or a plurality of quantum wells that have multiple doped or un-doped layer(s). In the example LED350ofFIG. 3D, the first layer350aof nitrides based n-doped layers electrically coupled to layer350bof nitrides-based p-doped layer forms the active region of the LED350.

The LED350may further include layer350chaving a reflective surface. For example, the layer350cmay include a layer of metal film (e.g., Ag). Under the reflection layer350c, a metal conductor350dthat is transparent (e.g., indium tin oxide or zinc oxide) can be used to enhance current spreading with low radiation absorption. The LED350may further include a diffusion barrier layer350esuch as a metallic layer (e.g., Pt or Ni). Underlying layer350ean adhesion layer350f(e.g., TiW or Cr) can be used to promote adhesion of the final wetting layer350g(e.g., gold).

FIG. 4illustrates a cross sectional view of a discrete LED package400integrated with a two-phase cooling apparatus402, according to one embodiment.

One embodiment of a system having a discrete LED package400includes, a die404mounted on a substrate406, the die404having formed thereon a light-emitting device (e.g., light emitting diode, laser, organic light emitting diode, etc.). The substrate406may be physically configured to thermally couple heat generated from the light-emitting device to a chamber418suitable for liquid storage. The chamber418may be formed within the substrate406or coupled to the substrate406. In one embodiment, the system further includes, a layer420having through-holes formed from porous structures422where the layer420has a first side and a second side. The porous structures422can be coherent silicon pores of a high length to diameter ratio.

One side of the layer420can be in contact with the chamber418suitable for liquid storage. In addition, the system includes a vapor collection layer424disposed over the second side of the layer420having through-holes such that the through-holes are substantially unobstructed to substance flow or movement. The vapor collection layer424may be further coupled to a manifold layer426having formed therein or is coupled to a vapor port428though which vapor exits.

In one embodiment, the discrete LED package400further includes an insulating substrate410that surrounds the die404, a lens414attached to the insulating substrate410that encapsulates the die404, and/or phosphor material416disposed within a region between the die404and the lens414.

The LED package assembly400is, in one embodiment, discretely packaged with one or more LED dies404. In one embodiment, by way of the two-phase cooling apparatus402the dies can be packaged in close proximity to one another. The LED dies404can include LEDs based on any materials system including but not limited wide bandgap diodes including but not limited to GaAs, GaN, GaInN, and/or AlGaN (e.g., AluInvGa1-u-vN (u,v≧0:0≦u+v≦1)). The LED die404may be mounted to a substrate406(e.g., copper, Cu—), for example, via solder408(e.g., fluxless solder such as gold tin).

The LED dies404can be bound by a glass substrate410(e.g., pyrex glass) for insulation between the upper412electrodes and the mounting substrate406. In one embodiment, a lens414encapsulates the LED404. The lens414can be fabricated from polymers including but not limited to PMMA. The polymer lens may be used for dispersing the generated light from the LED dies404and is typically selected based on the refractive index. In one embodiment, the lens414is grated.

Phosphor material416can be molded into the interior surface of the lens414between the LED404and the lens414. The phosphor material typically includes a garnet material such as Yttrium aluminum garnet (YAG). Dopants that are optically active (e.g., a rare earth element such as Cerium (Ce)) can be used to convert blue, UV or other light emitted from the LED dies404to white light or substantially white light. The phosphor material416YAG:CE can also be deposited on the inner surface of the lens414in a silicone complex or other material. In general, the material silicone/phosphor complex is resistant to UV light due to long potentially prolonged exposure to UV light during operation.

The lower part of the package400represents the hybrid integration of the evaporator402into the LED packaging400. Heat generated by the LED dies404initially conducts through the solder layer408(e.g., the gold tin solder layer). The heat can subsequently be conducted through another conductive layer406(e.g., copper and/or aluminum) and coupled to the liquid (e.g., water or other liquids) in a liquid reservoir418(e.g., or liquid chamber, chamber, etc.).

The heat generated from the LED dies404can be absorbed by the liquid in reservoir418. The heat generated from the LED can heat the liquid to a state of a temperature and pressure approaching or matching that of the vapor line on the phase diagram for the liquid. Despite the liquid having being in a state close to the vaporization state (e.g., a fully saturated condition) the phase change is predominantly subdued until the liquid is moves through the layer420with the porous structures422. Once the liquid moves through the pores422in the layer420, a vapor chamber480provides a open volume to allow the liquid to pass through in phase transition to vapor.

The approach in which the heat passes through the liquid to reach the evaporating interface is also referred to as the “wet wall approach”. The liquid reservoir418can be bound on one side by the electrically and thermally conductive layer406and on the opposing side by porous structures420which, in one embodiment, act as a membrane separating the liquid from vapor. The vapor is typically created due to absorption of the heat generated by the LEDs404and transported away from the die in the form of latent heat of vaporization. The vapor can be, in one embodiment, collected in the open space of layer424and subsequently combined in manifold layer426and exits the evaporator402through vapor port428.

The LED package404is, in one embodiment, fabricated in the following manner. The LED dies404typically come from a separately fabricated wafer in the form of singulated die. A series of photolithographically patterned direct bonded copper (e.g., “DBC”) sheets can be brazed together to form the conductive layer406(e.g., copper). The copper is typically also made available by companies such as Curamik. A glass wafer can be patterned lithographically with electrodes (e.g., gold), machined with cavities by ultrasonic impact grinding and then bonded to the conductive layer406via the solder408(e.g., gold-tin).

The LED dies404typically come in the form of a reel and can be picked and placed on the conductive layer406and soldered, for example, with gold tin solder. The porous structures420(e.g., porous silicon, porous germanium, Gallium Arsenide) can be fabricated from semiconductor wafers (e.g., silicon wafers) through a series of micro-patterning and electrochemical etching processes.

The layer420with the porous structures422can then be attached to the conductive layer406. The connection may be implemented via bonding (e.g., glass frit). The vapor chamber424, and manifold layer426can be fabricated from metals such as Kovar or Invar alloy that are brazed together. In one embodiment, the vapor port428can include materials that are robust against corrosion, readily bent to route vapor to its condensation location, and can include by way of example but not limitation, stainless steel, copper and/or nickel. The connection of the vapor port428may be formed by brazing.

In general, the light-emitting device can be a light emitting diode, a laser, or any other light emitting units.

FIG. 5Aillustrates an example of a canister type LED lighting apparatus500comprising a two-phase cooling apparatus, according to one embodiment.

The canister type LED lighting apparatus500can include an LED or an array of LEDs512coupled to the two-phase cooling apparatus. The two-phase cooling apparatus can include an evaporator502, a vapor line504, a heat sink506, and/or a liquid line510. The vapor line504can transport vapor to a condenser embedded in the heat sink506.

In one embodiment, the LED or array of LEDs512are integrated with the evaporator502of the two-phase cooling apparatus. The LED or array of LEDs512can be integrated with the evaporator502. The efficiency of condensation of the vapor can be enhanced by the heat sink506. One embodiment includes an optional air flow generator508(e.g., fan) coupled to the heat sink506. The air flow generator508can be a low velocity fan or in one embodiment a synthetic jet module but in the majority of cases it is anticipated the heat will be removed by natural convection. After the vapor has experienced phase change to fluid, the fluid is delivered back to the evaporator package via a liquid line510.

FIG. 5Billustrates the cross sectional view of the canister type LED lighting apparatus500utilizing a two-phase cooling apparatus, according to one embodiment.

In the cross sectional view, the LED dies512can be seen to be directly packaged on/integrated with the evaporator502. In the micro loop heat pipe approach, the heat generated by the LED die512conducts through a top cap layer558to a layer560having porous structures. The vapor is mostly generated from absorption of heat emitted from the LED dies512by the liquid supplied by the chamber570. The generated vapor can then exit the evaporator502through the spaces562formed in the top cap558. The vapor moves along the top cap558layer and can manifold to the vapor line504where the vapor can be transported to the condenser566.

Within the condenser566, the vapor acts to spread heat along the heat sink surface to make it nearly isothermal as it condensed on the interior surface. In one embodiment, a series of spiraling fins568within the condenser566act to increase the vapor path length ensuring condensation and utilizes gravity to cause the condensed liquid to flow down toward the evaporator. The heat from the interior of the condenser566can subsequently transfer to the fins568of the heat sink where it can be dissipated to the ambient air.

FIG. 6illustrates an example of an LED package600integrated with a two-phase cooling apparatus using an alternative air flow generator630, according to one embodiment.

In this design the LED or LED die602module is co-packaged with the evaporator610where the heat is transported to a heat sink620(e.g., a radiator style) with thin corrugated fins. In this cubic luminary design, a corona discharge device630can be integrated with the two-phase cooling apparatus to facilitate air flow to stimulate convection heat flow from the radiator fins of the heat sink620.

Compact LED luminaries with bright white light and of a small form factor can be useful as accent lights for display purposes. Also the small form factor and cubic repeat unit design the lights can be daisy chained for display or track lighting.

FIG. 7illustrates an example process flow for forming an LED packaged with a two-phase cooling apparatus, according to one embodiment.

In process702, porous structures are formed in a semiconductor layer. The porous structure may be formed via one or more convenient and/or known methods. In one embodiment, the porous structures are, for example, formed via methods as described in co-pending U.S. patent application entitled “Method of Fabricating Semiconductor-based Porous Structure”, application Ser. No. 11/933,000 filed Oct. 31, 2007, the contents of which are incorporated by reference herein.

In process704a metallic substrate is formed. The metallic substrate is formed by patterning metal foil and brazing them together. Alternatively, the metal foils can be attached by particle injection molding or additive stereo lithography.

In process706, the metallic substrate and the porous semiconductor are coupled. The coupling may be achieved via bonding (e.g., bonding using solder alloy).

In process708, an insulating layer is formed. The insulating layer can be formed by spinning on glass or sputtering directly on top of the metallic substrate via patterning and etching. Alternatively, the insulator layer can be formed of thin glass sheet. In process710, cavities are formed by etching or grinding (e.g., ultrasonic impact grinding) cavities in the insulating layer (e.g., glass).

In process712, electrodes are formed on the insulating layer. The electrodes (e.g., glass electrodes) can be formed by any known or convenient method including but not limited to, evaporation, sputtering or electroplating. If the insulating layer is not joined to the porous semiconductor/metallic substrate stack then it can be performed in process714. A liquid distribution network or header can be formed in process716. The liquid distribution network can be formed by brazing metallic layers (e.g., the metallic layers424,426,428ofFIG. 4).

In process718, the liquid distribution network (e.g., header) can be attached to the earlier mentioned layers. In process720, a light emitting die is attached to the metallic substrate. The die is wire bonded for electrical connection in process722. Then in process724, the die is encapsulated by a lens attachment. The lens can be coated with phosphor on its concave side. A vapor chamber may subsequently be formed from metallic material. Furthermore, a vapor port may be formed and brazed to the vapor chamber to form a connection.