POWER SUPPLY APPARATUS

Abstract

Power supply apparatus (10) comprising a circuit board (11) and one or more power devices (12) attached to a first surface (11a) of the circuit board (11). A plate (14a) composed of a thermally conductive plastic faces the first surface of the circuit board (11). A thermally conductive encapsulant (15) is provided between the first surfaces (11a) of the circuit board (11) and the plate (14a). The circuit board (11) comprises one or more heat-spreading layers (212*,213*) configured to enhance heat transfer in directions parallel to the first surface (11a) of the circuit board (11). The first surface (14aa) of the plate (14a) may also be irregular and comprises one or more first regions (32) and one or more second regions (31) that are further from the first surface (11a) of the circuit board (11) than the one or more first regions (32), with the one or more power devices (12) being aligned with the one or more second regions (31).

Claims

1. A power supply apparatus, comprising: a circuit board; one or more power devices attached to a first surface of the circuit board; a plate at least partly composed of a thermally conductive plastic, wherein a first surface of the plate faces the first surface of the circuit board; and a thermally conductive encapsulant between the first surfaces of the circuit board and the plate; and wherein the circuit board comprises one or more heat-spreading layers configured to enhance heat transfer in directions parallel to the first surface of the circuit board.

2. Apparatus according to claim 1 wherein the encapsulant has a thermal conductivity of between about 0.5 and 2 Wm.sup.1K.sup.1.

3. Apparatus according to claim 1 wherein the thermally conductive plastic is at least partly composed of a polymer and a thermally-conductive additive.

4. Apparatus according to claim 1 wherein the thermally conductive plastic has a thermal conductivity of between about 1 and 10 Wm.sup.1K.sup.1.

5. Apparatus according to claim 1 wherein one or more of the heat-spreading layers comprise copper.

6. Apparatus according to claim 1 wherein one or more of the heat-spreading layers are at least substantially unpatterned.

7. Apparatus according to claim 1: wherein the circuit board is a multi-layer printed circuit board comprising one or more inner layers and a first outer layer proximate to the first surface of the circuit board, wherein the one or more inner layers include the one or more heat-spreading layers.

8. Apparatus according to claim 7, wherein a separation between the first outer layer and a nearest one of the heat-spreading layers is no more than 150 micrometres.

9. Apparatus according to claim 1 wherein the circuit board comprises a first outer layer proximate to the first surface of the circuit board, wherein the first outer layer comprises one or more copper floods in a vicinity of one or more of the power devices.

10. Apparatus according to claim 1 wherein the first surface of the plate is irregular and comprises one or more first regions and one or more second regions that are further from the first surface of the circuit board than the one or more first regions, and wherein the one or more power devices are at least partly aligned with the one or more second regions.

11. Apparatus according to claim 10 wherein a distance between at least one of the one or more first regions and the first surface of the circuit board is less than a height of at least one of the one or more power devices.

12. Apparatus according to claim 10 wherein a distance between the first surface of the plate and the first surface of the circuit board is no more than 1 millimetre over substantially all of the first surface of the circuit board.

13. Apparatus according to claim 1 wherein the plate corresponds to at least part of a base of an enclosure.

14. Apparatus according to claim 13 wherein the enclosure comprises sidewalls extending from the first surface of the plate toward the first surface of the circuit board.

15. Apparatus according to claim 14, wherein the enclosure further comprises one or more sidewall formations projecting laterally inward.

16. A power supply apparatus, comprising: a circuit board; one or more power devices attached to a first surface of the circuit board; a plate at least partly composed of a thermally conductive plastic, wherein a first surface of the plate faces the first surface of the circuit board; and a thermally conductive encapsulant between the first surfaces of the circuit board and the plate; and wherein the first surface of the plate is irregular and comprises one or more first regions and one or more second regions that are further from the first surface of the circuit board than the one or more first regions, and wherein the one or more power devices are at least partly aligned with the one or more second regions.

17. Apparatus according to claim 10 wherein a distance between the first surface of the plate and a power device attached the first surface of the circuit board is no more than 1 millimetre over substantially all of the first surface of the circuit board.

Description

[0024] Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0025] FIG. 1 is a schematic cross-sectional view of a known power supply including a gap pad;

[0026] FIG. 2 is a schematic cross-sectional view of a first example of a power supply;

[0027] FIG. 3 is a schematic cross-sectional view of a part of a printed circuit board used in a second example of a power supply;

[0028] FIG. 4 is a schematic cross-sectional view of a third example of a power supply;

[0029] FIG. 5 is a isometric view of an enclosure for a fourth example of a power supply; and

[0030] FIG. 6 is a plan view of the enclosure shown in FIG. 6.

[0031] Referring to FIG. 2, a first example of a power supply 10 will now be described.

[0032] The power supply 10 includes a circuit board 11. The circuit board 11 may correspond to a conventional printed circuit board. For example, the circuit board 11 may have an FR-4 glass epoxy substrate. The circuit board 11 has a first major surface 11a (hereinafter referred to as a lower surface) and a second major surface 11b (hereinafter referred to as an upper surface, although it will be appreciated that the power supply 10 may have any suitable orientation).

[0033] A power device 12 is attached to the lower surface 11a of the circuit board 11. In this example, there is only one power device 12. However, there may be multiple power devices 12. The power device 12 may be a power diode, a thyristor, a power MOSFET (metal-oxide-semiconductor field-effect transistor), an IGBT (insulated-gate bipolar transistor) or any other type of power device. The power device 12 may be surface-mounted on the circuit board 11. There may also be other electronic components attached to the lower surface 11a of the circuit board 11.

[0034] Other electronic components 13 are attached to the upper surface 11b of the circuit board 11. In this example, there are two components 13, although there may be any number of components 13. The components 13 may be leaded components. The components 13 may be of any suitable typeincluding, in principle, power devices. In some examples, there may not be any components attached to the upper surface 11b of the circuit board 11.

[0035] The power supply 10 also includes an enclosure 14. The enclosure 14 may correspond to a potting box. The enclosure 14 includes a base 14a, which, in this example, is substantially rectangular. Accordingly, the enclosure includes four side walls 14b, two of which are visible in the figure. The base 14a has an interior surface 14aa (hereinafter referred to as an upper surface) and an exterior surface 14ab (hereinafter referred to as a lower surface).

[0036] The circuit board 11 is arranged relative to the enclosure 14 such that the lower surface 11a of the circuit board 11 faces the upper surface 14aa of the base 14a of the enclosure 14. The surfaces 11a, 14aa may be substantially parallel with each other and may be separated by a distance equal to a height h of the power device 12 plus a clearance d.sub.1. The clearance d.sub.1 is preferably as low as possible in view of the mechanical tolerances of, for example, the power device 12 and the enclosure 14. The clearance d.sub.1 may be, for example, between 1 and 10 millimetres.

[0037] In this example, the side walls 14b of the enclosure 14 have upper surfaces which form a rim 14c and the rim 14c supports the lower surface 11a of the circuit board 11. The power supply 10 may include suitable means for securing the circuit board 11 and the enclosure 14 to each other.

[0038] The enclosure 14 is at least partly composed of a thermally-conductive plastic. The plastic is typically at least partly composed of a polymer and a thermally-conductive additive. The plastic is electrically insulating.

[0039] The enclosure 14 may be manufactured in any suitable way, for example by injection moulding. The enclosure 14 may be a single part or may be made of several parts. In some examples, the base 14a may be made separately from, and/or from a different material from, the remainder of the enclosure 14. In such examples, only the base 14a may include the thermally-conductive plastic.

[0040] The power supply 10 also includes a thermally-conductive encapsulant 15. The encapsulant 15 is arranged between the lower surface 11a of the circuit board and the upper surface 14aa of the base 14a of the enclosure 14. The encapsulant 15 preferably fills substantially all of the empty space between the two surfaces 11a, 14aa. The encapsulant 15 is preferably in contact with substantially all of the surfaces bounding this empty space, i.e. exposed parts of the lower surface 11a of the circuit board 11, exposed surfaces of the power device 12, the upper surface 14aa of the base 14a and interior surfaces of the side walls 14b of the enclosure 14.

[0041] The encapsulant 15 may be a thermally-enhanced silicone encapsulant with a thermal conductivity of about 0.8 Wm.sup.1K.sup.1. The encapsulant 15 is electrically insulating.

[0042] In use, the power supply 10 is typically arranged such that the lower surface 14ab of the base 14a of the enclosure 14 is in thermal contact with a surface of a heat sink, cold plate or the like (hereinafter assumed to be a heat sink). Accordingly, heat generated by the power device may be conducted from the power device 12 via the encapsulant 15 and the base 14 to the heat sink. Heat is conducted from the power device 12 directly to the encapsulant 15 and indirectly via the circuit board 11 to the encapsulant 15. Heat generated by any other electronic devices attached to the circuit board 11 may be conducted to the heat sink in a similar way.

[0043] Thus, the power supply 10 can conductively cool the power device 12 in an effective way with relatively low-cost componentsfor example, the circuit board 11, the enclosure 14 and/or the encapsulant 15.

[0044] Referring to FIGS. 2 and 3, a second example of a power supply 10 will now be described.

[0045] The power supply 10 is the same as the first example of the power supply 10 (as illustrated in FIG. 2) but with a specifically designed circuit board 11 (a part of which is illustrated in FIG. 3).

[0046] Similarly to the first example, the circuit board 11 has a lower surface 11a (to which the power device 12 is attached) and an upper surface 11b (to which the components 13 are attached).

[0047] In this example, the circuit board 11 is a multi-layer printed circuit board and includes several conductive layers 21. The conductive layers 21 are typically composed of copper. In this example, there are four conductive layers 21.sub.1-21.sub.4, although there may be any suitable number of conductive layers 21. The two outermost conductive layers 21.sub.1, 21.sub.4 are hereinafter referred to as outer layers. The other conductive layers 21.sub.2*, 21.sub.3* are hereinafter referred to as inner layers. The circuit board 11 includes a substrate layer 22 between each pair of conductive layers 21 and a coating layer 23 on the outermost surface of each of the outer layers 21. The substrate layers 22 may be composed of FR-4 glass epoxy.

[0048] One or more inner layers 21.sub.2*, 21.sub.3* (hereinafter referred to as heat-spreading layers) are adapted to enhance heat transfer in directions parallel to the lower surface 11a of the circuit board 11. In this example, all of the inner layers 21.sub.2*, 21.sub.3* correspond to heat-spreading layers, although this need not be the case.

[0049] The inner layers 21.sub.2*, 21.sub.3*, particularly the inner layer(s) 21.sub.2* closer to the lower surface 11a, are configured to include no (or relatively few) patterns or circuit tracks, thus forming a (substantially) solid copper sheet, which can maximise the heat spreading effect.

[0050] The conductive layers 21 need not all have the same thickness. The heat-spreading layers 21.sub.2*, 21.sub.3* can be conveniently adapted to be thicker than the outer layers 21.sub.1, 21.sub.4 to enhance the heat spreading effect. Each of the heat spreading layers 21.sub.2*, 21.sub.3* may have a thickness of, for example, between about 35 m (1 oz copper) and 210 m (6 oz copper).

[0051] As will be appreciated, the circuit board 11 may be made using conventional techniques, except with thicker foils being used to form the heat-spreading layers 21.sub.2*, 21.sub.3*. Hence the additional costs are relatively low.

[0052] The heat-spreading layers 21.sub.2*, 21.sub.3* are preferably relatively close to the lowermost outer layer 21.sub.1. This allows heat to be more effectively transferred from the power device 12 via the substrate layers 22.sub.1, 22.sub.2 to the heat-spreading layers 21.sub.2*, 21.sub.3*. In this example, a separation s between the lowermost heat-spreading layer 21.sub.2* and the lowermost outer layer 21.sub.1 is about 150 micrometres. In other examples, the separation s may be different.

[0053] Thus, due to the heat-spreading layers 21.sub.2*, 21.sub.3*, heat generated by the power device 12 is more effectively distributed through the circuit board 11, thereby increasing an effective contact area with the encapsulant 15 and hence increasing a thermal conductance between the circuit board 11 and the encapsulant 15.

[0054] Referring to FIG. 4, a third example of a power supply 10 will now be described.

[0055] The power supply 10 is the same as the first example of the power supply 10 or the second example of the power supply 10, but has an enclosure 14 with a base 14a with an irregular upper surface 14aa.

[0056] The upper surface 14aa has a shape which may broadly match the shape (profile) of the combination of the lower surface 11a of the circuit board 11, the power device 12, and any other electronic components attached to the lower surface 11a of the circuit board 11.

[0057] In this example, the upper surface 14aa has several regions, each of which is parallel to the lower surface 11a of the circuit board 11 and is separated therefrom by a particular distance. In other examples, the surfaces 11a, 14aa need not be parallel.

[0058] For example, the upper surface 14aa has a region 31 (hereinafter referred to as a lowered region) which is relatively far from the lower surface 11a of the circuit board 11 and which is at least partly aligned with the power device 12. The upper surface 14aa has another region 32 (hereinafter referred to as a raised region) which is relatively close to the lower surface 11a of the circuit board 11 and is at least partly aligned with a region of the lower surface 11a of the circuit board 11 to which no electronic components are attached. It can be seen from the figure that, in the raised region 32, the distance d2 between the two surfaces 11a, 14aa is less than the height h of the power device 12.

[0059] In this example, the distance between the upper surface 14aa of the base 14a of the enclosure 14 and the lower surface 11a of the circuit board 11 or, if present, the power device 12 or another electronic component is 1 mm over substantially all (e.g. 90%) of the lower surface 11a of the circuit board 11.

[0060] The plastic used for the enclosure 14 may have a considerably higher thermal conductivity than the encapsulant (e.g. 5 Wm.sup.1K.sup.1 compared with 1 Wm.sup.1K.sup.1). Thus, by increasing the volume of plastic relative to the volume of encapsulant 15, the thermal conductance between the circuit board 11 and, for example, the lower surface 14ab of the base 14a of the enclosure 14 can be considerably increased. Moreover, the cost per unit mass of the plastic is generally lower than the encapsulant 15, and so increasing the amount of plastic relative to the amount of encapsulant 15 can help reduce overall costs.

[0061] FIGS. 5 and 6 respectively show isometric and plan views of an enclosure 14 used in a power supply apparatus according to a fourth embodiment of the invention. The electronic circuitry is the same as the first, second and third examples above, but the enclosure 14 is provided with a plurality of sidewall formations 16 which project internally from the sidewalls 14b to minimise the effective surface area or footprint of the upper surface 14aa of the base.

[0062] The sidewall formations 16 function as dams for localising the position of the encapsulant 15 which fills the space between the upper surface 14aa of the enclosure 14 and the lower surface 11a of the circuit board 11. That is, the sidewall formations 16 have a lateral profile which may substantially correspond to the lateral profile of any electronic components, including the power device 12, fitted to the lower surface 11a of the circuit board 11. As such, the sidewall formations 16 act to reduce the volume of encapsulant 15 required to fill the space between the enclosure 14 and the circuit board, and thereby minimise costs associated with the encapsulant material. At the same time, encapsulant material is still provided in regions surrounding the electronic components to optimise heat dissipation.

[0063] It will be appreciated that there may be many other variations of the above described examples.

[0064] The circuit board 11 may have a lowermost outer layer 21.sub.1 having one or more copper floods in a vicinity of the power device 12, thereby enhancing heat transfer from the power device 12 to the encapsulant 15.

[0065] The apparatus described above need not be a power supply. Instead of a power device, the apparatus may include a different type of electronic component.

[0066] Instead of a printed circuit board, the power supply may include a different type of support or substrate.

[0067] The enclosure may have a different shape.

[0068] Instead of an enclosure, the power supply may include a plate. The plate may correspond to the base of the enclosure of any of the abovedescribed examples. In other words, the side walls may be omitted. The plate may form part of another element of the power supply such as a chassis.

[0069] The power supply may include other cooling mechanisms such as a forced-air cooling mechanism.