Method of cooling high power PCB mounted components

Abstract

The invention relates to an electrical load cooling device comprising a printed circuit board, PCB, having a first side and a second side opposing the first side, a plurality of electrical loads mounted on the first side of the PCB. The PCB has a plurality of through holes. Each electrical load of the plurality of electrical loads has a back surface facing the PCB. The back surface is at least partly exposed to a through hole of the plurality of through holes. The electrical load cooling device further comprises a heat conductive element comprising a plurality of protrusions aligned with the plurality of through holes, wherein the heat conductive element is mounted on the second side of the PCB such that each protrusion of the plurality of protrusions is within a respective through hole of the plurality of through holes such that the heat conductive element is in thermal contact with each back surface of the plurality of electrical loads.

Description

[0001] METHOD OF COOLING HIGH POWER PCB MOUNTED COMPONENTS

[0002] FIELD OF THE INVENTION

[0003] The invention relates to an electrical load cooling device. The invention further relates to an electrical load device. The invention further relates to a lighting system.

[0004] BACKGROUND OF THE INVENTION

[0005] Electrical systems normally comprise of a printed circuit board, PCB, on which electrical components are placed. These components generate heat. Some components generate more heat than others. The heat causes thermal problem for the electrical components as an overtemperature reduces lifetime, efficiency and potential breakdown of the electrical components. To reduce the temperature at the PCB, a heatsink is provided on one side of the PCB. Thermal vias are provided through the PCB from the electrical components to the heatsink. This improves the removal of thermal energy efficiently. If more electrical components are placed closely together i.e., the electrical component density is increased on the PCB, or when the electrical components generate more heat, thermal vias may not suffice for removing the heat away from the PCB. A solution may be to use water cooling, allowing more heat to be extracted from the PCB but in some situations may still not be sufficient. This is however costly and requires additional components such as a water pump and water hoses further affecting the reliability of the entire system. It is desired to provide a solution for improved cooling of the electrical components in a reliable and cheaper way.

[0006] SUMMARY OF THE INVENTION

[0007] It is an objective of the invention to provide a cooling mechanism that allows a load with a high heat generation to be cooled properly in a simple and reliable way.

[0008] To overcome this concern, in a first aspect of the invention, an electrical load cooling device is provided. The electrical load cooling device comprises: a printed circuit board, PCB having a first side and a second side opposing the first side, a plurality of electrical loads (3) mounted on the first side of the PCB, wherein the PCB has a plurality of through holes, wherein each electrical load of the plurality of electrical loads has a back surface facing the PCB, the back surface being at least partly exposed to a through hole of the plurality of through holes, the electrical load cooling device further comprising: a heat conductive element comprising a plurality of protrusions aligned with the plurality of through holes, wherein the heat conductive element is mounted on the second side of the PCB such that each protrusion of the plurality of protrusions is within a respective through hole of the plurality of through holes such that the heat conductive element is in thermal contact with each back surface of the plurality of electrical loads.

[0009] The electrical load cooling device has a PCB on which, on a first side of the PCB, a plurality of electrical loads are mounted. The electrical loads may provide a main function e.g., generating light and thereby also generates heat. This heat needs to be transferred away from the electrical loads in the best way possible to prevent the electrical loads from overheating. An increased temperature of the electrical loads may result in accelerated degradation of the electrical loads and potentially even cause the electrical loads to break down. For this purpose, it is desired to provide a heat conductive element as close to the electrical loads as possible. This is done by providing the through holes in the PCB beneath the electrical loads. The back surfaces of the electrical loads face the holes and are therefore directly exposed to the second side of the PCB. On the second side of the PCB, a heat conductive element is provided. The heat conductive element has a plurality of protrusions that fit in and are aligned with the through holes and approach the back surfaces of the electrical loads such that the back surfaces of the electrical loads are in thermal contact with the protrusions and therefore the heat conductive element. To provide a good manufacturability of the electrical load cooling device, the heat conductive element is preferably soldered to the second side of the PCB. The PCB with soldered heat conductive element can then be provided into a pick and place machine for automatic placing additional components on the PCB e.g., the electrical load and potential additional electronic components. The entire electrical load cooling device with additional components is then sent through the reflow station and all components are soldered to the PCB. Preferably, the top of the protrusion is coplanar with the first side of the PCB. This allows the soldering via a solder paste to be applied in a simple and reliable way. In a further example, the thermal contact is realized by a thermal material placed between the back surface of the electrical load and the protrusion of the heat conductive element.

[0010] Preferably, it may be desired to bridge any air space between the protrusion and the back surface of the electrical load by using a thermal material. The thermal material may be any material placed between the protrusion and the back surface of the electrical load such as e.g., a thermal interface material, TIM, thermal paste or thermal adhesive. This provides an optimum heat transfer from the electrical load to the heat conductive element.

[0011] In a further example, the back surface of the electrical load is soldered to the protrusion of the heat conductive element.

[0012] In an example, the protrusion is soldered to the back surface of the electrical load. The back surface of the electrical load may e.g. have a solderable thermal pad that can be soldered to the protrusion. This soldering provides an improved thermal coupling between the electrical load and the heat conductive element since they are now in physical contact. This solder connection also forms an additional mechanical connection between the heat conductive element and the PCB.

[0013] In a further example, the heat conductive element is coupled to a protective earth.

[0014] Coupling the heat conductive element to the protective earth allows the heat conductive element to be touch safe. It therefore also simplifies the usage of such heat conductive element in the design as the heat conductive element is considered a safe to touch component and therefore does not require any additional shielding or protection.

[0015] In a further example, the heat conductive element comprises copper.

[0016] Preferably, the heat conductive element is made of copper. This allows good thermal conduction and also allows a simple and robust soldering to the PCB. Alternatively, the heat conductive element can be provided with copper pads or cladding at the points where the heat conductive element is soldered to the PCB. It is clear that the same applies for the protrusions.

[0017] In a further example, each protrusion is soldered to each corresponding back surface of the electrical load.

[0018] Preferably, each protrusion is soldered to the corresponding back surface of the electrical load. This a stronger mechanical fixation of the heat conductive element. In a further example, the soldering of the heat conductive element to the PCB is done by a plurality of discrete solder joints.

[0019] Providing discrete solder joints between the heat conductive element and the PCB provides a strong mechanical coupling of the heat conductive element to the PCB, while not taking too much space on the PCB allowing the placement of e.g., traces on the second side to be not impacted too much by the solder connection.

[0020] In a further example, the heat conductive element is soldered to the second side of the PCB and wherein a solder used for soldering the heat conductive element to the PCB has a melting temperature higher than a melting temperature of a reflow solder.

[0021] The heat conductive element may be mounted on the PCB before the PCB is sent through the reflow station. The solder temperature in the reflow station is below the solder temperature used for soldering the heat conductive element to the PCB. The heat conductive element connection is therefore not affected by the reflow process.

[0022] In a further example, the heat conductive element is press fitted in the PCB.

[0023] The protrusions of the heat conductive element may be aligned with the through holes in the PCB. The protrusions may then be pressed in the holes allowing a strong fixation between the heat conductive element and the PCB.

[0024] In a further example, the heat conductive element and the protrusion form a monolithic structure.

[0025] Preferably, the heat conductive element and the protrusion form a single structure, providing a strong mechanical connection between the heat conductive element and the protrusion. This also allows simpler manufacturing by e.g. extrusion.

[0026] In another example, the electrical load comprises a surface-mounted device, SMD, package, wherein the back surface of the electrical load is a back surface of the SMD package.

[0027] Preferably, the electrical load has an SMD package. An SMD package may have a thermal pad at the back surface of the SMD package. The back surface of the electrical load is therefore the back surface of the SMD package. The back surface of the SMD package is therefore in thermal contact with the protrusion.

[0028] In a further example, the heat conductive element comprises mounting positions for mounting the heat conductive element to a heatsink and wherein the electrical load cooling device comprises fastening means for fastening the heat conductive element to the heatsink. Preferably, the heat conductive element has mounting positions e.g., holes for receiving screws, that allows the heat conductive element to be fastened e.g., screwed, to the heatsink. Preferably, the PCB, the heat conductive element and the heatsink have holes. Screws or bolts and nuts can be provided through the holes, allowing the PCB, the heat conductive element and the heatsink to be fastened to each other.

[0029] In another example, the electrical load is a solid-state lighting load.

[0030] Preferably, the electrical load is a solid-state lighting load with a main function of generating light. The solid-state lighting load however also generates undesired heat that needs to be transferred away from the solid-state lighting load. This is done by the electrical load cooling device as defined in the aforementioned examples.

[0031] In another example, a lighting system comprises the electrical load cooling device according to the aforementioned examples and a driver for driving the electrical load.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0034] Fig. 1 shows an example of a schematic cut out of an electrical load device.

[0035] Fig. 2 shows an example of an electrical load cooling device.

[0036] Fig. 3 shows a circuit diagram of an electrical load cooling device.

[0037] Fig. 4 shows another circuit diagram of an electrical load cooling device.

[0038] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The invention will be described with reference to the Figures.

[0040] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should also be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0041] Figure 1 shows an example of a cut out of an electrical load cooling device. A printed circuit board 1, PCB, is provided. The PCB 1 has a first side and a second side. On the first side of the PCB 1, electrical components are mounted. On the first side of the PCB 1, an electrical load 3 is mounted, in the example provided, at least six electrical loads 3 can be seen. The PCB 1 has a through hole between the first side of the PCB 1 and the second side of the PCB 1. The through hole is placed at least partly under the back surface of the electrical load 3. The back surface of the electrical load 3 is therefore effectively exposed. In the example provided, three through holes are shown, exposing at least parts of the back surfaces of all six electrical loads 3. The heat conductive element 2 has a protrusion 4 that, when the heat conductive element 2 is placed at it its final position i.e., mounted to the second side of the PCB 1, is within the through hole and configured to be in thermal contact with the back surface of the electrical load 3. In this example, three protrusions 4 are shown.

[0042] Figure 2 shows an example of an electrical load cooling device. Figure 2 shows the second side of the PCB 1. The electrical load 3 is mounted on the first side of the PCB 1 and is therefore not visible. The back side of the heat conductive element 2 is shown. The protrusions 4 of the heat conductive element 2 are within the through holes of the PCB 1 and are therefore not visible. The heat conductive element 2 is soldered to the PCB 1. As can be seen in Figure 2, this may be done by e.g., discrete solder joint. Other ways of soldering are also possible, such as circumferentially soldering the heat conductive element 2 to the PCB 1. This may provide additional mechanical strength. Preferably, this soldering is done using a solder material that has a higher melting temperature that the solder material used for soldering in a reflow soldering process e.g., soldering the electrical load 3 to the PCB 1. This allows the combination of heat conductive element 2 and PCB 1 to be provided to the reflow station as a single unit without a risk of accidental desoldering the heat conductive element 2.

[0043] The heat conductive element 2 may be provided with holes, which allows a heatsink to be mounted to the heat conductive element 2.

[0044] Figure 3 shows an example of a circuit diagram of an electrical load cooling device. In this example, a driver may be arranged to provide a regulated voltage or a regulated current to the electrical load 3, shown as LEDs. The LEDs are cooled using a heat conductive element 2. The LEDs have a casing that may be used for cooling. The casing provides a parasitic capacitance between the LEDs and the heat conductive element 2, which is represented as capacitances Cpl and Cp2. The electrical load cooling device may be placed in a housing that is connected to a protective earth. Another parasitic capacitance Cp3 is present between the heat conductive element 2 and the housing. All these parasitic capacitances may cause an undesired current to flow throughout the circuit, which may result in electromagnetic interference, EMI. The heat conductive element 2 can be used to reduce the effects of EMI.

[0045] Figure 4 shows an example of how the heat conductive element 2 can be used to reduce the effects of EMI. The heat conductive element 2 is soldered to the PCB 1. The soldering may also be electrically connected to the ground potential of the circuit for driving the electrical load 3. This effectively makes the heat conductive element 2 a large solid ground plane providing a small current loop for undesired currents, resulting in reduced EMI. The driver for driving the electrical load 3 may also be mounted on the PCB 1 and the heat conductive element 2 may then also be used as the ground plane for the driver. By soldering at least one protrusion to the electrical load 3, the electrical path from the ground plane to the electrical load 3 is kept as low as possible. Optionally, the heat conductive element 2 may also be connected to protective earth, effectively connecting the ground and the protective earth together.

[0046] Figure 5 shows an example of a view of the lighting system where the mounting positions can be seen. The mounting positions extend through the PCB 1, the heat conductive element 2 and the heatsink. A fastening means 5 e.g. a screw can be used to fasten the PCB 1, heat conductive element 2 and heatsink all together such that a good thermal contact can be guaranteed. Preferably, between the heat conductive element 2 and the heatsink, a thermal conductive material is provided such as a thermal paste or a thermal pad.

[0047] In the examples provided, the electrical load 3 is shown as a lighting load e.g., LEDs. Other electrical loads can also benefit from this invention. A solid-state switching element e.g., a MOSFET may also be provided with a back surface that can be made into thermal contact with a protrusion. The cooling performance of such solid-state switching element is therefore also improved.

[0048] In the examples provided, the PCB 1 may be designed to fit the needs of the electric design of the electrical load cooling device. The PCB 1 may for example be a multicore PCB having multiple layers of traces allowing an optimized routing of the traces at the PCB 1. The PCB 1 may also be a metal core PCB, but that may not be required since the heat conductive element 2 according to the invention provides an improved cooling of the electrical load 3.

[0049] In the examples provided, the thermal contact between the back surface of the electrical load 3 and the protrusion 4 can be achieved in several ways. The back surface of the electrical load 3 and the protrusion 4 may be soldered together to provide an optimum thermal contact. Alternatively, thermal material may be placed between the back surface of the electrical load 3 and the protrusion 4. Such thermal material may be a thermal interface material, TIM.

[0050] In the examples provided, the heat conductive element 2, also conventionally called a heat spreader, is designed to distribute the heat from the electrical loads 3 is generated at multiple small areas and spread the total generated heat over a single large area, which is larger than the sum of multiple areas of the electrical loads 3. The heat conductive element 2 is however not designed for a good heat sinking i.e., at steady state, the temperature of the conductive element 2 is close to the temperature of the electrical loads 3. For sinking the heat to e.g. the environment, a heatsink is used. This heatsink is specifically designed to distribute the heat from the heatsink to the environment. This can be done by e.g., using fins, water cooling or a vapor chamber.

[0051] In the examples provided, the plurality of electrical loads may be more than 20, even more preferably more than 100.

[0052] In the examples provided, the heat conductive element has the shape of a plate with the plurality of protrusion on the plate. Preferably the thickness of the plate is less than 2 mm, even more preferred less than 1 mm. this prevents the heat conductive element to interfere too much with the reflow process of the electrical loads since the overall thermal capacity is then still acceptable.

[0053] Preferably, the heat conductive element 2 and protrusion 4 are at least partly comprised of copper. This allows the solderability of the heat conductive element 2 and protrusion 4 to be very simple.

[0054] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An electrical load cooling device comprising: a printed circuit board (1), PCB, having a first side and a second side opposing the first side, a plurality of electrical loads (3) mounted on the first side of the PCB (1), wherein the PCB (1) has a plurality of through holes, wherein each electrical load (3) of the plurality of electrical loads (3) has a back surface facing the PCB (1), the back surface being at least partly exposed to a through hole of the plurality of through holes, the electrical load cooling device further comprising: a heat conductive element (2) comprising a plurality of protrusions (4) aligned with the plurality of through holes, wherein the heat conductive element (2) is mounted on the second side of the PCB (1) such that each protrusion (4) of the plurality of protrusions (4) is within a respective through hole of the plurality of through holes such that the heat conductive element (2) is in thermal contact with each back surface of the plurality of electrical loads (3).

2. The electrical load cooling device of claim 1, wherein the thermal contact is realized by a thermal material placed between the back surface of the electrical load (3) and the protrusion (4) of the heat conductive element (2).

3. The electrical load cooling device according to any of the preceding claims, wherein the heat conductive element (2) is coupled to a protective earth.

4. The electrical load cooling device according to any of the preceding claims, wherein the heat conductive element (2) comprises copper.

5. The electrical load cooling device according to claim 5 wherein each protrusion (4) is soldered to at least a portion of each corresponding back surface of the electrical load (3).

6. The electrical load cooling device according to any of the preceding claims, wherein the heat conductive element (2) is soldered to the second side of the PCB (1) wherein the soldering of the heat conductive element (2) to the PCB (1) is done by a plurality of discrete solder joints.

7. The electrical load cooling device according to any of the preceding claims, wherein the heat conductive element (2) is soldered to the second side of the PCB (1) and wherein a solder used for soldering the heat conductive element (2) to the PCB (1) has a melting temperature higher than a melting temperature of a reflow solder.

8. The electrical load according to any of the claims 1 to 6, wherein the heat conductive element (2) is press fitted in the PCB (1).

9. The electrical load cooling device according to any of the preceding claims, wherein the heat conductive element (2) and the protrusion (4) form a monolithic structure.

10. The electrical load cooling device according to say of the preceding claims, wherein the electrical load (3) comprises a surface-mounted device, SMD, package, wherein the back surface of the electrical load (3) is a back surface of the SMD package.

11. The electrical load cooling device according to any of the preceding claims, wherein the heat conductive element (2) comprises mounting positions for mounting the heat conductive element (2) to a heatsink and wherein the electrical load cooling device comprises fastening means (5) for fastening the heat conductive element (2) to the heatsink.

12. The electrical load cooling device according to any of the preceding claims, wherein the electrical load (3) is a solid-state lighting load.

13. A lighting system comprising an electrical load cooling device according to claim 12, a heatsink and a driver for driving the electrical load (3).

Images