Patent Application
20110180819
The present invention relates to a light-emitting arrangement comprising a light-emitting diode (LED) and a heat release member for dissipating heat generated by the LED.
Light emitting diode (LED) based light-emitting devices are today increasingly used for a wide variety of lighting applications. One problem with LEDs is that they produce heat which must be removed from the device in order to avoid damage of the LED and the device. Overheating may also reduce the performance and/or the efficiency of the LED.
Conventionally, a heatsink placed on the backside (opposite side to the LED) of a printed circuit board (PCB) onto which the LED has been arranged has been used for removing heat, thus requiring the heat to be transported through the PCB. In order to improve the heat transfer, metal core PCBs (MCPCBs) have been used, however having drawbacks as they are expensive. In contrast, glass-epoxy is a low-cost, easily processed material conventionally used for PCBs, however having poor thermal conductivity which provides a major challenge to manufacturers of LED based lighting devices.
U.S. Pat. No. 7,078,728 discloses a surface-mounted LED including a base having heat conductivity, an insulative wiring board fixed to the base and including a conductive pattern and a mounting hole, a light-emitting element chip mounted on a mounting area exposed by the mounting hole, and a reflective frame having heat conductivity and fixed to the base and thermally coupled therewith, to surround the light-emitting element chip, heat generation from the light-emitting element chip being released through both the base and the reflective frame, or either one thereof. However, this arrangement does not provide adequate heat removal from a high-power LED without the use of additional heatsinks attached either to the base or to the reflective frame.
Thus, there is a need in the art for LED arrangements having improved heat removal properties.
It is an object of the invention to at least partly overcome the above-mentioned drawbacks of the prior art. In one aspect, the invention relates to a light-emitting arrangement comprising a printed circuit board, PCB, having at least one electrically and thermally conductive portion, a light-emitting diode, LED, for emitting light, the LED being thermally connected to the at least one electrically and thermally conductive portion by at least one contact of the LED, and a heat release member for dissipating heat generated by the LED, the heat release member being thermally connected to the at least one electrically and thermally conductive portion, wherein the heat generated by the LED is transferred along a heat transfer path extending from the LED via the at least one contact and the at least one electrically and thermally conductive portion to the heat release member.
The light-emitting arrangement of the invention provides greatly improved heat removal from the LED, while using of low-cost glass-epoxy materials for the PCB. As a result it is possible to achieve a lower working temperature of the LED and thus better performance, together with reduced production cost. The invention is particularly useful when using high power LED modules.
The arrangement is uncomplicated and also mechanically robust, since the heat release member is attached to the PCB and not to the LED package.
Moreover, since the PCB may have multiple electrically and thermally conductive portions of various shapes and sizes, there is a wide range of alternatives for arranging the heat release member. Thus, the light-emitting arrangement according to the invention allows many different designs.
The contact of the LED may be an electric contact electrically connecting the LED to the at least one electrically and thermally conductive portion. The electric contacts of the LED may thus participate in the transfer of heat from the LED to the heat release member, thus reducing the need for a separate heat transfer member and/or improving the transfer of heat away from the LED.
In embodiments of the invention, the contact is a heat transfer member. Alternatively, the LED may comprise a plurality of contacts including at least one electric contact and at least one heat transfer member. The heat transfer member provides good heat transfer from the LED to the at least one electrically and thermally conductive portion. In particular, the use of a separate heat transfer member in addition to using the electric contacts of the LED for heat transfer may provide improved transfer of heat away from the LED.
The LED and the heat release member may be mounted on one side of the PCB. Additionally, the at least one electrically and thermally conductive portion may be provided on the same side of the PCB. By mounting the heat release member on the front side of the PCB, heat does not have to be transported through or around the PCB. Hence, both low thermal resistance and a less complicated assembly are achieved. Furthermore, the back side of the PCB may be used for purposes other than holding a heat release member, such as for example additional control circuitry. By using the back side of the PCB for mounting control circuitry, the circuitry may be easily protected from damage. Also, separation of heat from the LED and heat from the control circuitry may be achieved.
Furthermore, the control circuitry may at least be partly embedded in a protective material, such as a resin or similar protective material.
In embodiments of the invention, the heat release member is adapted to receive an optical element, for example used for purposes such as collimating and/or redistributing light from the LED. Using the heat release member as a holder for an optical element saves space by evading the need for a separate holder and, by reducing the number of structural elements mounted of the PCB, simplifies the manufacturing process. Furthermore, since the heat release member/optical element holder may be rather large, good heat dissipation may be obtained.
The heat release member may be mounted on the at least one electrically and thermally conductive portion using at least one, or a combination of a solder and conductive glue.
Furthermore, the heat release member may be mounted at a position such that the control circuitry is electromagnetically shielded from the LED. By using the heat release member for electromagnetic shielding, the need for a separate shielding structure is reduced, thus saving space and also simplifying the manufacturing process, which will reduce cost.
Furthermore, in embodiments of the invention, the light-emitting arrangement comprises a plurality of LEDs, each LED being thermally connected to the at least one electrically and thermally conductive portion by at least one contact; and a heat release member for dissipating heat of the plurality of LEDs. Thus, a plurality of LEDs may be used with a single heat release member, hence simplifying the production of systems comprising multiple LEDs and also allowing many different designs of the light-emitting arrangement and/or a lighting system comprising the light-emitting arrangement.
Alternatively, the light-emitting arrangement may comprise a plurality of LEDs, each LED being thermally connected to the at least one electrically and thermally conductive portion by at least one contact, and a plurality of heat release members for dissipating heat generated by the plurality of LEDs, wherein heat of at least one of the plurality of LEDs is transferred along a heat transfer path extending from the at least one of the plurality of LEDs to at least one of the plurality of heat release members. By allowing high variation in the numbers of LEDs and heat release members, and in the ways of connection there between, the light-emitting arrangement according to embodiments of the invention enables many different designs.
These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention, in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.
The PCB 6 may be made of any material conventionally used in the art. The material used for the PCB 6 may have poor thermal conductivity. Typically, the PCB 6 is made of glass-epoxy.
The PCB 6 has at least one electrically and thermally conductive portion 4 formed by electrically and thermally conducting material, such as a metal or a conductive polymer. For example, the at least one electrically and thermally conductive portion 4 may be at least partly made of copper. The at least one electrically and thermally conductive portion 4 is typically a layer covering a part of the PCB 6. The at least one electrically and thermally conductive portion 4 may comprise multiple portions, such as multiple layers each covering a part of the PCB 6. The at least one electrically and thermally conductive portion 4 may have various shapes, and different electrically and thermally conductive portions may have different shapes. Typically, each of the electric contacts 31, 32 is electrically and thermally connected to a separate electrically and thermally conductive portion of the PCB 6.
Furthermore, in the embodiment shown in
Heat may be transferred from the LED 2 to the electrically and thermally conductive portion 4 and subsequently to the heat release member 5 by various routes. In embodiments of the invention, heat generated by the LED 2 is transferred along a heat transfer path extending from the LED 2 via the electric contacts 31, 32 and the at least one electrically and thermally conductive portion 4 to the heat release member 5. Alternatively, in other embodiments of the invention, the electric contacts 31, 32 are not thermally connected to the heat release member 5. Instead, heat may be transferred along a heat transfer path extending from the LED 2 via the heat transfer member 33 and the at least one electrically and thermally conductive portion 4 to the heat release member 5. In other embodiments of the invention, heat may be transferred from the LED 2 both via the electric contacts 31, 32 and via the heat transfer member 33 to the at least one electrically and thermally conductive portion 4 and subsequently to the heat release member 5.
The electric contacts 31, 32 may be of any conventional material, such as a metal. Other suitable materials for the electric contacts are known to those skilled in the art.
The heat transfer member 33 may be of any conventional thermally conductive material used in the art. Examples of suitable materials for the heat transfer member 33 include metals such as copper and aluminum, thermally conductive polymers, polymers having metal insert, and Thermal Interface Materials (TIM).
The heat release member 5 may be comprised of any material or combination of materials conventionally used for heat sinks, such as metal. Typically, the heat release member is made of a metal, e.g. aluminum, copper, or magnesium, or of a ceramic material.
In the embodiment shown in
In a further embodiment of the invention illustrated in
In order to receive the optical element 11, a side of the heat release member 5 facing the LED 2 may be provided with a shoulder. The one or more optical elements may be mountable for example by gluing, spring-loading or friction fit.
Turning now to
In the embodiment shown in
The heat release member 5 of the embodiment shown in
In other possible embodiments of the invention, the heat release member 5 may be mounted at a position such that the control circuitry 7 is electromagnetically shielded from the LED 2 by the heat release member 5. Electromagnetic shielding of the control circuitry from the LED 2 using the heat release member 5 is particularly useful when the control circuitry 7 and the LED 2 are mounted on the same side of the PCB 6.
The skilled person realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the light emitting arrangement 1 may comprise a plurality of heat release members, so that the LED 2 may be thermally connected to several heat release members. In such embodiments, at least one heat release member may be adapted to receive an optical element.
Additionally, the light-emitting arrangement 1 may comprise a plurality of LEDs. In such embodiments, two or more LEDs may be thermally connected as described above to one and the same heat release member 5. For example, a plurality of LEDs may be mounted on a PCB 6 and thermally connected as described above to a heat release member 5 which also may be mounted on the PCB, so that heat from each LED 2 is transferred via the electrically and thermally conductive portion 4 of the PCB 6 to the heat release member 5. Alternatively, in embodiments of the invention, a plurality of LEDs may be thermally connected as described above to a plurality of heat release members, each LED 2 being thermally connected to at least one heat release member 5 and each heat release member being thermally connected to a least one LED 2. For example, two or more LEDs may be thermally connected to each heat release member 5 of a plurality of heat release members.
Thus, the light-emitting arrangement according to the invention provides greatly improved heat removal from the LED while using low-cost materials for the PCB, such as glass-epoxy. As a result, much improved thermal performance together with reduced production cost may be achieved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08164417.1 | Sep 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB09/53947 | 9/9/2009 | WO | 00 | 3/11/2011 |
