Patent Publication Number: US-2013250585-A1

Title: Led packages for an led bulb

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. 119(e) of prior copending U.S. Provisional Patent Application No. 61/535,356, filed Sep. 15, 2011; U.S. Provisional Patent Application No. 61/569,191, filed Dec. 9, 2011; U.S. Provisional Patent Application No. 61/579,626, filed Dec. 22, 2011; U.S. Provisional Patent Application No. 61/585,231, filed Jan. 10, 2012; U.S. Provisional Patent Application No. 61/585,226 filed Jan. 10, 2012; and U.S. Provisional Patent Application No. 61/682,163 filed Aug. 10, 2012, each of which is hereby incorporated by reference in the present disclosure in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates generally to light-emitting diode (LED) bulbs, and more specifically to structures for mounting an LED die within a liquid-filled shell of an LED bulb. 
     2. Description of Related Art 
     Traditionally, lighting has been generated using fluorescent and incandescent light bulbs. While both types of light bulbs have been reliably used, each suffers from certain drawbacks. For instance, incandescent bulbs tend to be inefficient, using only 2-3% of their power to produce light, while the remaining 97-98% of their power is lost as heat. Fluorescent bulbs, while more efficient than incandescent bulbs, do not produce the same warm light as that generated by incandescent bulbs. Additionally, there are health and environmental concerns regarding the mercury contained in fluorescent bulbs. 
     Thus, an alternative light source is desired. One such alternative is a bulb utilizing an LED. An LED comprises a semiconductor junction that emits light due to an electrical current flowing through the junction. Compared to a traditional incandescent bulb, an LED bulb is capable of producing more light using the same amount of power. Additionally, the operational life of an LED bulb is orders of magnitude longer than that of an incandescent bulb, for example, 10,000-100,000 hours as opposed to 1,000-2,000 hours. 
     While there are many advantages to using an LED bulb rather than an incandescent or fluorescent bulb, LEDs have a number of drawbacks that have prevented them from being as widely adopted as incandescent and fluorescent replacements. One drawback is that an LED, being a semiconductor, generally cannot be allowed to get hotter than approximately 120° C. As an example, A-type LED bulbs have been limited to very low power (i.e., less than approximately 8 W), producing insufficient illumination for incandescent or fluorescent replacements. 
     One approach to alleviating the heat problem of LED bulbs is to attach the LED to a conductive heat sink. To facilitate thermal conduction, it may be advantageous to thermally couple the LED to the heat sink in a way that minimizes thermal resistance. However, traditional LED mounting techniques require multiple layers and interfaces that increase the thermal resistance between the LED and the heat sink. 
     As shown in one example depicted in  FIG. 1 , there are several layers between an LED die  102  and a heat sink  110 . In this example, LED die  102  is mounted to a package substrate  103 . The package substrate  103  may be an Al 2 O 3  or AlN lead frame used as an electrical interface to the LED die  102 . The package substrate  103  also serves as the physical mount for the LED die  102 . The package substrate  103  is bonded to a flexible circuit  106 . In some cases, another type of direct chip attachment (DCA) substrate (e.g., glass or printed circuit board) is used in place of the flexible circuit  106 . The package substrate  103  may be attached to the flexible circuit  106  using an adhesive layer, such as a polyimide adhesive having suitable properties. In some cases, the adhesive may be an insulator or a conductor depending on whether an electrical connection is to be made between the package substrate  103  and the flexible circuit  106 . 
     In this example, the flexible circuit  106  is attached to a coupon  108 . In some cases, the coupon  108  stabilizes the flexible circuit  106  and package substrate  103  during the assembly process. The flexible circuit may be attached to the coupon  108  using an adhesive layer. The coupon  108  is typically an aluminum metal plate having a thickness of approximately 1 mm to 2 mm. One face of the coupon  108  is mounted to heat sink  110  using another adhesive layer. The heat sink  110  is typically a thermally conductive material that is thick enough to conduct heat produced by the LED die  102 . 
     As shown in  FIG. 1 , a typical implementation may include multiple layers and multiple interfaces between the LED die  102  and the heat sink  110 . Each layer and interface increases the thermal resistance at least some amount. 
     Another drawback to using an LED is that light may be reflected back into the LED at the interface between the emitting face of the LED die and the surrounding medium. Typically, an LED has an index of refraction of approximately 2.2. If an LED die is mounted in air (having an index of refraction of approximately 1.0), as much as 20% of the light produced by the LED die may be reflected back at the interface between the LED die and the air. 
     As shown in  FIG. 1 , one solution to this problem is to embed the LED die  102  in a lens  105  having an index of refraction somewhere between the LED die (2.2) and the air (1.0) to reduce the back reflection and improve efficiency. However, as shown in  FIG. 1 , using traditional lens mounting techniques requires additional components (e.g., package substrate  103  and lens  105 ) that may impair the optical properties and/or the ability to conduct heat away from the LED die  102 . In some cases, the LED die  102 , package substrate  103 , and lens  105  are manufactured as a single component sometimes referred to as an LED package  107 . 
     The embodiments described herein can be used to improve thermal conduction and optical performance by mounting an LED die in an LED bulb that is filled with a thermally conductive liquid. 
     SUMMARY 
     In one exemplary embodiment, a light-emitting diode bulb includes a base, a shell connected to the base, a thermally conductive liquid held within the shell, and one or more support structures disposed within the shell. One or more LEDs are mounted to the one or more support structures and are immersed in the thermally conductive liquid. The one or more LEDs each comprise a semiconductor die having at least one light-emitting interface and the one or more LEDs configured to emit light from the at least one light-emitting interface directly into the thermally conductive liquid. 
     In one exemplary embodiment, the LED bulb omits a lens disposed between the at least one light-emitting interface and the thermally conductive liquid. In one exemplary embodiment, the semiconductor die of each of the one or more LEDs is directly mounted to the one or more support structures. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts an LED die mounted to a package substrate with a lens. 
         FIG. 2  depicts a liquid-filled LED bulb. 
         FIG. 3  depicts an exemplary mounting for an LED die. 
         FIG. 4  depicts an exemplary mounting for an LED die. 
         FIG. 5  depicts an exemplary mounting for an LED die. 
         FIGS. 6A and 6B  depict a liquid-filled LED bulb. 
         FIG. 7  depicts an exemplary mounting for an LED die. 
         FIG. 8  depicts an exemplary mounting for an LED die. 
         FIG. 9  depicts an exemplary mounting for an LED die. 
         FIG. 10  depicts a liquid-filled LED bulb. 
         FIG. 11  depicts an exemplary mounting for an LED die. 
         FIG. 12  depicts an exemplary mounting for an LED die. 
         FIG. 13  depicts an exemplary mounting for an LED die. 
         FIGS. 14A and 14B  depict an exemplary flexible circuit for mounting an LED die. 
         FIG. 15  depicts an exemplary mounting for an LED with a phosphor. 
         FIGS. 16A and 16B  depict exemplary results of an LED die emitting light directly into a thermally conductive liquid. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown, but are to be accorded the scope consistent with the claims. 
     Various embodiments are described below relating to LED bulbs. As used herein, an “LED bulb” refers to any light-generating device (e.g., a lamp) in which at least one LED is used to generate light. Thus, as used herein, an “LED bulb” does not include a light-generating device in which a filament is used to generate the light, such as a conventional incandescent light bulb. It should be recognized that the LED bulb may have various shapes in addition to the bulb-like A-type shape of a conventional incandescent light bulb. For example, the bulb may have a tubular shape, a globe shape, or the like. The LED bulb of the present disclosure may further include any type of connector; for example, a screw-in base, a dual-prong connector, a standard two- or three-prong wall outlet plug, bayonet base, Edison Screw base, single-pin base, multiple-pin base, recessed base, flanged base, grooved base, side base, or the like. 
       FIG. 2  depicts an exemplary LED bulb  200 . For convenience, all examples provided in the present disclosure describe and show LED bulb  200  being a standard A-type form factor bulb. However, as mentioned above, it should be appreciated that the present disclosure may be applied to LED bulbs having any shape, such as a tubular bulb, a globe-shaped bulb, or the like. 
     In some embodiments, LED bulb  200  may use 6 W or more of electrical power to produce light equivalent to a 40 W incandescent bulb. In some embodiments, LED bulb  200  may use 20 W or more to produce light equivalent to or greater than a 75 W incandescent bulb. Depending on the efficiency of the LED bulb  200 , between 4 W and 16 W of heat energy may be produced when the LED bulb  200  is illuminated. 
     LED bulb  200  includes a shell  222  and base  224 , which interact to form an enclosed volume  220  over one or more LED dies  202 . The enclosed volume  220  is filled with a thermally conductive liquid. As shown in  FIG. 2 , the base  224  includes an adaptor for connecting the bulb to a lighting fixture. In some cases, the shell  222  and base  224  have a form factor similar to an A-type shape of a conventional incandescent light bulb. 
     Shell  222  may be made from any transparent or translucent material such as plastic, glass, polycarbonate, or the like. Shell  222  may include dispersion material spread throughout the shell to disperse light generated by LED dies  202 . The dispersion material prevents LED bulb  200  from appearing to have one or more point sources of light. The shell  222  may also be coated or treated to diffuse the light produced by the LED dies  202 . 
     LED bulb  200  includes a plurality of LED dies  202  mounted in a radial pattern within the shell  222 . Each of the LED dies  202  includes at least one semiconductor die having at least one light-emitting interface. Each of the plurality of LED dies  202  is attached to a support structure  208  of a heat sink  210  and is immersed in the thermally conductive liquid. The support structures  208  and heat sink  210  may be made of any thermally conductive material, such as aluminum, copper, brass, magnesium, zinc, or the like. Since the support structures  208  and heat sink  210  are formed from a thermally conductive material, heat generated by LED dies  202  may be conductively transferred to the support structures  208  and heat sink  210 . The support structures  208  and heat sink  210  are at least partially immersed in the thermally conductive liquid and, therefore, are able to dissipate heat to the thermally conductive liquid. The support structures  208  are adapted to mount LED dies  202  on a side mounting face, as shown in  FIG. 2 . The support structures  208  have channels or openings between each support structure  208  to allow the passage of liquid. Example support structures  208  may include, but are not limited to, finger-shaped protrusions or posts. In another embodiment, LED dies  202  may be mounted on a top mounting face of the support structures  208 . 
     The LED dies  202  can be mounted to the support structures  208  of the heat sink  210  using a variety of techniques that reduce the number of thermal interfaces, as compared to the example discussed with respect to  FIG. 1 , above. The mounting technique illustrated in  FIG. 2  most closely correlates to the LED die mounting shown in  FIG. 3 , discussed in more detail below.  FIGS. 4 and 5 , also discussed in more detail below, depict alternative LED die mounting techniques. Generally, the LED die mounting techniques shown in  FIGS. 3 ,  4 , and  5  reduce the number of thermal barriers as compared to the LED die mounting shown in  FIG. 1 . The reduction in thermal barriers may increase the cooling efficiency of the support structures  208  and heat sink  210  and allow for a smaller and more economical heat sink  210  and support structures  208 . Additionally, increasing the thermal efficiency of the support structures  208  and heat sink  210  may allow the LED dies  202  to be driven at a higher current and produce more light. 
     As discussed above, shell  222  and base  224  of LED bulb  200  interact to define an enclosed volume  220  filled with a thermally conductive liquid. As used herein, the term “liquid” refers to a substance capable of flowing. Also, the substance used as the thermally conductive liquid is a liquid or at the liquid state within, at least, the operating, ambient-temperature range of the bulb. An exemplary temperature range includes temperatures between −40° C. to +40° C. The thermally conductive liquid may be mineral oil, silicone oil, glycols (PAGs), fluorocarbons, or other material capable of flowing. In the examples discussed below, 20 cSt viscosity polydimethylsiloxane (PDMS) liquid sold by Clearco is used as a thermally conductive liquid. It may be desirable to have the liquid chosen be a non-corrosive dielectric. Selecting such a liquid can reduce the likelihood that the liquid will cause electrical shorts and reduce damage done to the components of LED bulb  200 . 
     As described above, the thermally conductive liquid is able to transfer heat away from the LED dies  202 , the support structures  208 , and heat sink  210 . Typically, the thermally conductive liquid transfers the heat via conduction and passive convection to other components of the LED bulb  200 , including the shell  222  and base  224 . When the thermally conductive liquid is used in combination with the LED die mounting techniques described herein, heat can be removed from the LED dies  202  more efficiently, as compared to the multilayered configuration shown in  FIG. 1 . Specifically, by reducing the number of thermal barriers between the LED dies  202  and the support structures  208 , and immersing the LED dies  202  and support structures  208  in a thermally conductive liquid and allowing for conductive and passive convective cooling, the overall heat transfer may be significantly improved when compared to the LED die mounting technique shown in  FIG. 1 . This is particularly true as compared to the LED die mounting technique shown in  FIG. 1 , which is typically implemented in an open air configuration (without a thermally conductive liquid). 
     As a result of the heat transfer, the temperature of portions of the thermally conductive liquid is typically above the ambient or room temperature. The increase in temperature depends on the number of LED dies  202 , the total wattage of the LED bulb  200  and the physical configuration of components of the LED bulb  200 . The elevated temperatures of the thermally conductive liquid near the LED dies  202  may facilitate passive convective flow within the thermally conductive liquid. Generally, increases in passive convective flow increase the heat transfer capacity of the LED bulb  200 . 
     Also, as described above, the thermally conductive liquid acts as an optical medium by transmitting the light emitted from the LED dies  202  to the translucent shell  222 . By using a thermally conductive liquid, as shown in  FIG. 2 , an LED die  202  can be used without using a lens  105  or equivalent structures (as shown in, for example,  FIG. 1 ). In this example, LED dies  202  may emit light directly into the thermally conductive liquid. 
     For purposes of the description of the embodiments herein, a lens is considered to be any component made from a solid translucent material that is capable of directing or focusing rays of light. A lens may be formed from a glass or plastic material having at least two refracting surfaces. Either or both of the refracting surfaces may be curved to form either a convex or concave shape such that light entering one of the refracting surfaces is directed or focused in a prescribed direction. In some cases, the lens may be tinted, colored, or include a dispersion material. For purposes of this discussion, a phosphor coating or other photoluminescent material, by itself, is not considered a lens. 
     With reference to  FIG. 1 , the lens  105  can be omitted if, for example, the LED die  202  is configured to emit light directly into a thermally conductive liquid having an index of refraction somewhere between the index of refraction of the LED dies  202  and the surrounding medium. In one example, an LED die  202  has an index of refraction of approximately 2.2. The bulb  200  may be surrounded by an air medium having an index of refraction of approximately 1.0. In this case, the thermally conductive liquid is selected to have an index of refraction between 2.2 and 1.0. In some implementations, the index of refraction of the thermally conductive liquid is approximately 1.4. The shell  222  is also selected to have an index of refraction between 2.2 and 1.0. In some cases, the shell  222  has an index of refraction lower than the index of refraction of the thermally conductive liquid but greater than air. 
     Another benefit of an LED die emitting light directly into the thermally conductive liquid is that the light&#39;s transition to air (with an index of refraction of 1.0) is moved further away from the LED die. The further away the transition to air occurs, the higher the chance that reflected light will be reflected back to a surface that will not absorb the light but will instead reflect the light out of the bulb. For example, reflected light hitting support structures  208  and/or heat sink  210  has a higher chance of being reflected back out of the bulb as compared to light reflecting back on the LED dies  202 . By moving transitions from one index of refraction to another index of refraction further away from LED dies  202 , reflected light may have a lower chance of being absorbed by LED dies  202 . 
     In general, an LED die can be configured to emit light directly into the thermally conductive liquid and also be coated with a phosphor or photoluminescent material used to produce a particular color light emission. By using a thermally conductive liquid having an index of refraction between the index of refraction of a coated LED die and the shell, the back reflection at the interface between the surface of the coated LED die and the thermally conductive liquid can be reduced (as compared to an LED die-to-air or an LED die-to-lens interface). In other words, less of the light produced by the LED and phosphor combination will be reflected back and absorbed by the LED die. 
     One exemplary configuration of a phosphor-coated LED  1500  is depicted in  FIG. 15 . As shown in  FIG. 15 , an LED die  1502  is mounted to an encapsulant  1504  and coated with a phosphor  1506 . The encapsulant  1504  may be made from a variety of materials including, for example, a liquid crystal polymer (LCP) or a hybrid material including a silicone-epoxy polymer. As shown in  FIG. 15 , the encapsulant  1504  is open on at least one side and does not include a lens or equivalent structure. As a result, the phosphor-coated LED  1500  may emit light directly into the thermally conductive liquid. 
     In general, the phosphor-coated LED  1500  shown in  FIG. 15  can be used in place of the LED die (e.g.,  202  or  1002 ) depicted in any of the embodiments described herein. In some cases, a phosphor-coated LED includes more than one LED die mounted within the same encapsulant. In some cases, the phosphor-coated LED is configured with electrical leads to facilitate the electrical connection between one or more LED dies and a flexible circuit. 
     One advantage to implementing a phosphor-coated LED that is configured to emit light directly into the thermally conductive liquid is that the color of the emitted light is shifted, as compared to a phosphor-coated LED configured to emit light into an air medium or through a lens mounted to the face of the LED. As discussed above, emitting light directly into a thermally conductive liquid reduces back reflection into the LED die. In some cases, a color shift may be due, in part, to the LED die absorbing a disproportionate amount of blue light. By reducing the back reflection into the LED die, the amount of blue light that is emitted may be increased and result in a color shift of the emitted light. 
     The resulting color shift may allow for the use of alternative phosphor combinations. For example, the resulting color shift may expand the range of alternative phosphor combinations that may have been considered unacceptable for traditional lighting applications (when configured to emit light into an air medium or through a lens). These alternative phosphor combinations may be less expensive or have improved availability, as compared to phosphor-coated LEDs that are used in traditional lighting applications. 
       FIGS. 16A and 16B  depict predicted exemplary color emissions for a phosphor-coated LED emitting light directly into a thermally conductive liquid as compared to an emission directly into an air medium. The predicted color emission directly into an air medium may also roughly correspond to the color emission through a lens attached to the light-emitting face of the phosphor-coated LED. The predicted light emission colors depicted in  FIGS. 16A and 16B  are mapped to an Ccx-Ccy color space with respect to a black-body temperature measured in degrees Kelvin. 
       FIG. 16A  depicts a phosphor-coated LED (Nichia NSL2757) configured to emit light having a black-body color temperature of approximately 2,700 degrees Kelvin when emitting directly into an air medium. The predicted color emission is designated by point  1602 . When the same phosphor-coated LED emits light directly into a thermally conductive liquid (without an intermediate lens or equivalent structure), the emitted light has a predicted black-body color temperature of approximately 3,400 degrees Kelvin, designated by point  1604 . Thus, a color shift of approximately 700 degrees Kelvin can be achieved by emitting light directly into a thermally conductive liquid. 
       FIG. 16B  depicts another phosphor-coated LED (Nichia NFSL157AT-H3) configured to emit light having a black-body color temperature of approximately 2,580 degrees Kelvin when emitting directly into an air medium. The predicted color emission is designated by point  1606 . When the same phosphor-coated LED emits light directly into a thermally conductive liquid (without an intermediate lens or equivalent structure), the emitted light has a black-body color temperature of approximately 3,070 degrees Kelvin, designated by point  1608 . Thus, a color shift of approximately 490 degrees Kelvin can be achieved by emitting light directly into a thermally conductive liquid. 
     1. LED Die Mounting 
       FIG. 3  depicts an LED die mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 3 , the LED die  202  is mounted directly to a flexible circuit  206 . The LED die  202  is bonded to the flexible circuit  206  using either an electrically insulating or conductive adhesive. Electrical connections are made to the flexible circuit  206  by reflowing a metal alloy that is electrically connected to the LED die  202  and to connections on a surface of the flexible circuit  206 . Additionally or alternatively, the LED die  202  can be electrically connected to the flexible circuit  206  using wire bonding techniques. In  FIG. 3 , the flexible circuit  206  is attached to the support structure  208 . The flexible circuit  206  may be attached to the support structure  208  using an adhesive or mechanical-bonding technique. 
     In the example shown in  FIG. 3 , only two thermal interfaces are required: a first between the LED die  202  and the flexible circuit  206  and a second between the flexible circuit  206  and the support structure  208 . The reduction in the number of thermal interfaces (as compared to  FIG. 1 ) provides improved heat transfer from LED die  202  to support structure  208 . The reduced number of parts may also reduce cost and simplify manufacturing. 
     For example, the LED mounting technique of  FIG. 3  may result in a thermal resistance from the LED die to the heat sink of approximately 5-6° C./W. This is a significant improvement over the mounting technique shown in  FIG. 1 , which may result in a thermal resistance from the LED die to the heat sink of approximately 12-15° C./W. 
     The mounting technique shown in  FIG. 3  also omits the lens  105  shown in  FIG. 1 . As explained above, because the LED die  202  is immersed in the thermally conductive liquid when installed in a liquid-filled LED bulb, a traditional lens  105 , acting as an intermediate medium between the LED die and the air, is not necessary. As a result, LED dies  202  may emit light directly into the thermally conductive liquid. 
       FIG. 4  depicts an alternative LED die mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 4 , the LED die  202  is mounted directly to a support structure  208 . If the support structure  208  is made from an electrically conductive material, such as aluminum or copper, an insulating dielectric layer  404  may be attached or applied to the surface of the support structure  208 . The LED die  202  is bonded to the support structure  208  and/or dielectric layer  404  using either an electrically insulating or conductive adhesive. Electrical connections are made to the LED die  202  using traces embedded in the support structure  208 . 
       FIG. 5  depicts an alternative LED die mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 5 , the LED die  202  is mounted to a conductive layer  502 . The conductive layer  502  is mounted to a dielectric or insulating layer  504 . The dielectric layer is attached to a surface of the support structure  208 . The components shown in  FIG. 5  can be bonded using one or more adhesives. 
     For many of the same reasons discussed above with respect to  FIG. 3 , the heat transfer and optical properties of the alternative mounting technique shown in  FIGS. 4 and 5  may also be advantageous as compared to the LED mounting shown in  FIG. 1 . 
     2. LED Die Mounting Using Thermally Conductive Structures 
       FIGS. 6A and 6B  depict a side view and a top view of a liquid-filled LED bulb  600  having conducting support structures  608  instead of support structures  208  of a heat sink  210  (as shown in  FIG. 2 ). Similar to the LED bulb  200  of  FIG. 2 , the LED bulb  600  has a base  624  connected to a shell  622  that surrounds the LED dies  602 . The support structures  608  of the LED bulb  600  are mechanically and thermally connected to the base  624 . The shell  622  and base  624  interact to form an enclosed volume  620 . The enclosed volume  620  is filled with a thermally conductive liquid. The thermally conductive liquid removes heat from the LED dies  602  and support structures  608  via conduction and convection. 
     In some embodiments, the LED dies  602  are electrically connected together with a single flexible circuit. In an exemplary embodiment, a single flexible circuit is bonded to the support structures  608  and is used to mount the individual LED dies  602 . 
       FIGS. 7 ,  8 , and  9  depict alternative embodiments of LED die mounting techniques with thermally conductive support structures. 
       FIG. 7  depicts an exemplary LED die mounting technique for mounting an LED die in a liquid-filled LED bulb, such as the liquid-filled LED bulb  600  shown in  FIGS. 6A and 6B . In  FIG. 7 , the LED die  602  is mounted directly to a support structure  608 . If the support structure  608  is made from an electrically conductive material, such as aluminum or copper, an insulating dielectric layer  704  may be attached or applied to the surface of the support structure  608 . The LED die  602  is bonded to the support structure  608  and/or dielectric layer  704  using either an electrically insulating or conductive adhesive. Electrical connections are made to the LED die  602  with a reflowed metal alloy or wire bonds electrically contacting traces embedded in the support structure  608 . 
       FIG. 8  depicts an LED die mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 8 , the LED die  602  is mounted directly to a flexible circuit  806 . The LED die  602  is bonded to the flexible circuit  806  using either an electrically insulating or conductive adhesive. Electrical connections are made to the flexible circuit  806  by reflowing a metal alloy that is electrically connected to the LED die  602  and to connections on a surface of the flexible circuit  806 . Additionally or alternatively, the LED die  602  can be electrically connected to the flexible circuit  806  using wire bonding techniques. In  FIG. 8 , the flexible circuit  806  is attached to the support structure  608 . The flexible circuit  806  may be attached to the support structure  608  using an adhesive or mechanical bonding technique. 
       FIG. 9  depicts an alternative LED die mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 9 , the LED die  602  is mounted to a conductive layer  902 . The conductive layer  902  is mounted to a dielectric or insulating layer  904 . The dielectric layer  904  is attached to a surface of the support structure  608 . The components shown in  FIG. 9  can be bonded using one or more adhesives. 
     The exemplary mounting techniques for the LEDs discussed above with respect to  FIGS. 7 ,  8 , and  9  may occur prior to attaching the support structures  608  to base  624  ( FIG. 6A ). For example, LED dies  602  may be mounted to support structures  608 . Then, each support structure  608  with a mounted LED die  602  may be attached to base  624  using, for example, a screw, an adhesive or a spot weld. In other cases, support structures  608  may be clamped in place to base  624 . 
     For many of the same reasons discussed above with respect to  FIG. 3 , the heat transfer and optical properties of the alternative mounting techniques shown in  FIGS. 7 ,  8 , and  9  may also be advantageous as compared to the LED mounting shown in  FIG. 1 . 
     3. LED Die Mounting Using Thermally Conductive Structures 
       FIG. 10  depicts a liquid-filled LED bulb  1000  having a cylindrical support structure  1008  for mounting LEDs  1002 . Similar to the LED bulb  200  of  FIG. 2 , the LED bulb  1000  has a base  1024  connected to a shell  1022  that surrounds the LEDs  1002 . The support structures  1008  of the LED bulb  1000  are mechanically and thermally connected to the base  1024 . The shell  1022  and base  1024  interact to form an enclosed volume  1020 . The enclosed volume  1020  is filled with a thermally conductive liquid. The thermally conductive liquid removes heat from the LEDs  1002  and support structures  1008  via conduction and convection. 
     In the present embodiment, the support structure  1008  is a composite laminate structure including a flexible circuit laminated to a thermally conductive support material. As discussed in more detail below with respect to  FIGS. 14A and 14B , the composite laminate structure may include any thermally conductive structural material, such as aluminum, copper, brass, magnesium, zinc, or the like. The support structure  1008  includes multiple flange portions, each flange portion having an electrical connection for an LED  1002 . The LEDs  1002  are electrically connected together with a single flexible circuit that is incorporated into the support structure  1008 . 
     As shown in  FIG. 10 , the support structure  1008  is attached to a chassis  1030 . In some cases, the support structures  1008  are attached to the chassis  1030  to form a mechanical and thermal bond between the two components. The chassis  1030  is attached to the base  1024  and may also be made from a thermally conductive material. The chassis  1030  includes multiple slotted portions  1032  to allow the passage of the thermally conductive liquid. 
       FIGS. 11 ,  12 , and  13  depict alternative embodiments of LED die mounting techniques with thermally conductive support structures. 
       FIG. 11  depicts an LED mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 11 , the LED die  1002  is mounted directly to a flexible circuit  1106 . The LED die  2002  is bonded to the flexible circuit  1106  using either an electrically insulating or conductive adhesive. Electrical connections are made to the flexible circuit  1106  by reflowing a metal alloy that is electrically connected to the LED die  1002  and to connections on a surface of the flexible circuit  1106 . Additionally or alternatively, the LED die  2002  can be electrically connected to the flexible circuit  1106  using wire-bonding techniques. In  FIG. 11 , the flexible circuit  1106  is incorporated into the support structure  1108 , which is formed from a composite laminate structure. 
       FIG. 12  depicts an exemplary LED mounting technique for mounting an LED  1002  in a liquid-filled LED bulb, such as the liquid-filled LED bulb  1000  shown in  FIG. 10 . In  FIG. 12 , the LED  1002  is mounted directly to a support structure  1208 . If the support structure  1208  is made from an electrically conductive material, such as aluminum or copper, an insulating dielectric layer  1204  may be attached or applied to the surface of the support structure  1208 . The LED  1002  is bonded to the support structure  1208  and/or dielectric layer  1204  using either an electrically insulating or conductive adhesive. Electrical connections are made to the LED die  1002  with a reflowed metal alloy or wire bonds electrically contacting traces embedded in the support structure  1208 . 
       FIG. 13  depicts an alternative LED die mounting technique for mounting an LED die in a liquid-filled LED bulb. In  FIG. 13 , the LED die  1002  is mounted to a conductive layer  1302 . The conductive layer  1302  is mounted to a dielectric or insulating layer  1304 . The dielectric layer  1304  is attached to a surface of a mechanical support layer  1306 . Layers  1302 ,  1304 , and  1306  are incorporated into the support structure  1308 , which is formed from a composite laminate structure. 
     For many of the same reasons discussed above with respect to  FIG. 3 , the heat transfer and optical properties of the alternative mounting techniques shown in  FIGS. 11 ,  12 , and  13  may also be advantageous as compared to the LED mounting shown in  FIG. 1 . 
     4. Electrical Interconnects Used as a Heat Spreader 
     In some variations of the embodiments described above with respect to  FIGS. 2-13 , the electrical interconnects (e.g., the flexible circuit, conductive layer, embedded traces, wire bonds, or the like) that deliver electrical current to the LEDs may be constructed using thermally conductive materials, such as copper, silver, aluminum, other metals, or other thermally and electrically conductive materials, for spreading heat from the LEDs and transferring the heat to the surrounding liquid. For example, electrical interconnects, such as embedded traces, a thermal bonding copper solder pad, or a backing layer of copper or aluminum, can be arranged to transfer heat from their surfaces directly into the liquid or can be arranged to transfer heat from their surfaces into the liquid through a covering of solder mask or a protective cover layer for electrical isolation of the underlying conductor. In this way, the heated electrical interconnects act as a direct heat transfer surface to the liquid (utilizing convection and conduction into the liquid). 
       FIGS. 14A and 14B  depict an exemplary flexible circuit  1406  used as an electrical interconnect for mounting LED dies. The flexible circuit  1406  includes mounting pads  1430  for electrically connecting multiple LED dies. The mounting pads  1430  are electrically connected by conductive traces  1412 , which terminate at bonding pads  1414 . The bonding pads  1414  can be used to attach electrical lead wires or another type conductive element to receive power for the LED dies. 
     The materials used to construct the flexible circuit may also be thermally conductive. In some cases, the electrical conductors of the flexible circuit  1406  are configured to also conduct heat away from the LED dies. The thermally conductive materials may facilitate heat spreading from the LED dies to the surrounding liquid and to other components of the LED bulb. 
     Flexible circuit  1406  can be printed and cut using a flat sheet of flexible circuit material to form multiple flange portions  1416 . LED dies can also be installed on the flexible circuit  1406  while the flexible circuit  1406  is flat. The flexible circuit  1406  can be formed into a cylindrical or conical shape. When the flexible circuit  1406  is formed into a cylindrical or conical shape, the LED dies are arranged in a radial pattern. The flange portions  1416  of the flexible circuit  1406  may also be attached to supports of a cylindrical or conical heat sink. (See, e.g.,  FIG. 2  depicting a cylindrical heat sink  210  with support structures  208  arranged in a radial pattern.) 
     The flexible circuit  1406  may also be incorporated into a composite laminate structure. In one example, the flexible circuit  1406  is laminated to a thermally conductive structural material that provides structural rigidity to the flexible circuit  1406 . The composite laminate structure may include any thermally conductive structural material, such as aluminum, copper, brass, magnesium, zinc, or the like. The composite laminate structure may be formed as a laminate plate and then cut into the profile shape shown in  FIGS. 14A and 14B . The composite laminate structure may then be formed into a cylindrical or conical shape and attached to another component of the LED bulb. Because the composite laminate structure may have structural rigidity, it may include relief portions and may be formed using a mandrel or other metal-forming tool. 
       FIGS. 14A and 14B  depict one exemplary embodiment of a flexible circuit used as an electrical interconnect. As mentioned above, other types of electrical interconnects could also be used including conductive layers, embedded traces, wire bonds, or the like. In general, the surface area of the electrical interconnects near the LEDs (e.g., mounting pads  1430 , electrical traces  1412 ) can be increased. For example, the width of the electrical interconnects can be increased, the surface of the electrical interconnects can be curved or textured, fin protrusions can be attached to the electrical interconnects, or other arrangements may be used to increase the surface area of the electrical interconnects near the LEDs. 
     Typically, the temperature of the electrical interconnects is higher in regions closer to the LED die. One advantage to increasing the surface area near the LED dies is that heat transfer between a heat sink and a thermally conductive liquid can be more efficient at higher temperatures. Thus, in order to increase the efficiency of heat transfer between the LED, electrical interconnects, and the thermally conductive liquid, the surface area of the electrical interconnects can be increased in areas having higher temperatures. 
     In some embodiments, the electrical interconnects can include metal layers laminated to flexible or rigid underlying dielectric materials (e.g., a composite laminate structure discussed above). The dielectric materials can also be laminated to additional metal layers or constructions. In these embodiments, the first metal layer acts as an efficient surface to spread heat and to transfer heat from its heated surface to the surrounding liquid. The metal backing layer behind the dielectric insulating layer also acts as a surface for spreading heat and for transferring heat from its heater surface to the surrounding liquid. In some embodiments, the LEDs can be packaged or can be placed directly as chips onto the metal interconnect layers that serve to spread and transfer the heat to the thermally conductive liquid. The heat spreading and transfer layers can include the electrical interconnect traces, a thermal interface pad soldered to the associated thermal pad on the LED, or both. 
     in some embodiments, an alternate heat transfer path may be created that transfers heat from the LED through solder material into a thermal pad, through a dielectric layer, and an underlying mechanical structure that then allows heat spread and transfer to the thermally conductive liquid. While this arrangement creates a higher thermal resistance between the LED and the thermally conductive liquid, it can have a lower thermal resistance than alternative arrangements relying on heat spreading using only a heat sink. 
     Although a feature may appear to be described in connection with a particular embodiment, one skilled in the art would recognize that various features of the described embodiments may be combined. Moreover, aspects described in connection with an embodiment may stand alone.