GB2502148A

GB2502148A - Heatsink for a PCB with channels accepting edges of the PCB preferably in a cut-out.

Info

Publication number: GB2502148A
Application number: GB1208816.7A
Authority: GB
Inventors: Rhys Marc Owen
Original assignee: Control Techniques Ltd
Current assignee: Nidec Control Techniques Ltd
Priority date: 2012-05-18
Filing date: 2012-05-18
Publication date: 2013-11-20
Anticipated expiration: 2032-05-18
Also published as: GB201208816D0; CN203279444U; GB2502148B

Abstract

A heatsink for mounting on a printed circuit board (PCB) has a first face for mounting electronic components and a second face opposite the first face for heat dissipation via fins etc. The heatsink has at least one channel, but preferably more, for receiving parts of the PCB such a finger 409 and edges (405 fig 4). When assembled, the component mounting surface faces in substantially the same direction as a first face of the PCB that may carry components, such a s package 501, and the heat dissipating surface faces in substantially the same direction as the second opposite face of the PCB. Preferably the heatsink is positioned at least partially within a cutout of the PCB (see figure 4), and most preferably a fastener 507 can connect the component (via hole 503) and the PCB (via hole 411 in the finger) together. Figures 6 and 7 show top and bottom depictions of the assembly of component heatsink and PCB.

Description

PRINTED CIRCUIT BOARD HEATSINK MOUNTING

Field of the Invention

The present invention relates to a heatsink for mounting on a printed circuit board. The present invention further relates to a heatsink assembly.

Background of the Invention

heat is an unavoidable by-product of electronic devices and circuits. To dissipate generated heat in electronic systems, a heatsink may be provided. Heatsinks are passive components which cool a device by dissipating heat into [lie surrounding niedium, usually air. A heatsink may he used to cool an electronic component, such as a semiconductor device, mounted on a printed circuit board (PCB). The heatsink is designed to have a high surface area in contact with the air and heat is transferred by means of radiation, convection and conduction. For good dissipation of heat, there should be a high thermal gradient between the heatsink and the surrounding cooling medium.

A PCI-3 heatsink generally comprises a base, which is attached to the heat-generating electronic component (and, optionally, the PCB) plus a plurality of fins extending from the base The fins increase tile surface area and provide a conduit for conveying heat away from tile PCB and electronic component. Figure 1 is a schematic illustration of a prior art heatsink for cooling an electronic component 101 on a printed circuit board (PCB) 103. The heatsink 105 is mounted on PCB 103 and electronic component 101 is mounted on the heatsink 105. The heatsink 105 comprises a heatsink base 107 and a plurality of heatsink fins 109. Ihe electronic component 101 is mounted on a portion of base 107 which does not include fins 109. The base 107 is attached to 1-'CB 103 and fins 109 extend away from the base 107 and PCB 103, so as to provide a conduit for conveying heat away from the component 101. The device, heatsink and PCB may be attached by any suitable attachment means, for exaniple, clips, screws, brackets, thermal tape or a sprung clip.

Thus, in the prior art arrangement shown in Figure 1, the electronic component and hcatsink arc mounted together on the same face of the PCB. It is an object of the invention to provide an improved arrangement for mounting a heatsink for cooling an electronic component mounted on a PCB.

Summary of the Invention

According to a first aspect of the invention. there is provided a heatsink for mounting on a prnted circuit board (PCB) having a first face for mounting electronic components and a second face opposite the fimt face, the heatsink coniprising: a component mounting surface; a heat dissipating surface opposite the coniponent niounting surface: and at least one channel for receiving the PCI3; wherein the heatsink is arranged to he mounted on the l'Cl such that: a portion of the I'CB is received in the at least one channel, the component mounting surface faces in substantially the same direction as Ihe first face of the PCI3, and the heat dissipaling surface faces in substantially the same direction as the second lace of the PCB; and wherein, when the heatsink is mounted on the PCI-3 and an electronic component is mounted on the component mounting surface of the heatsink, heat from the electronic component is conveyed from the component mounting surface of the heatsink to the heat dissipating surface of the heatsink.

In many prior art heatsink assemblies, the arrangement needs to allow the electronic component to he cooled and the heatsink, particularly the heat dissipating surface, to he on the same sidc of the PCB. In thc arrangement of the prcscnt invcntion, however, the heatsink extcnds between thc facc of thc PCB on which electronic components arc mounted (that is, topsidc) and the opposite lace (that is, underside) of the I'CB. Ihis allows the heat dissipating surface of the heatsink to he in contact with a cooling medium at the underside of the I'CIL while still allowing the electronic component to be located on the topside of die PCB. This is particularly advantageous if the environment is dirty or corrosive. Preferably, the cooling medium is air. The heat dissipating surface of the heatsink may be located in the blown air chamber of an electronic device. The electronic component may he mounted on the heatsink by any suitable attachment mechanism. A simple attachment process may be used to attach the electronic component to the heatsink and the heatsink to the PCB.

Moreover, in prior art heatsink assemblies, the legs of the l'CR mounted electronic component may he stressed if the heatsink moves during vibration. However, the arrangement of the present invention permits only minimal movement of the heatsink both parallel to the plane of the PCI-3 and perpendicular to the plane of the ICR. Ihis minimises stress to the legs of the electronic component during vibration. In addition, the heatsink arrangement of the invention may save PCB space, since no holes may he required outside the footprint of the electronic component.

The heatsink may have the general shape of a cuboid. In that case, one surface of the cuhoid may comprise the component mounting surface and the opposite surface ol the cuhoid may conipnsc the heat dissipating surface. The particular dimensions of the heatsink will depend on the PCB on which it is to be mounted, the elcctronic component to be cooled and other design parameters.

In one embodiment, the heat dissipating surface comprises a plurality of fins for dissipating heat. Ihe fins increase the surface area of the heat dissipating surface and enhance the heat dissipation properties of the heatsink. Any suitable number of fins niay be provided, for example, two, three, four, five, six, seven, eight, nine or ten fins. Ihe particular shape and configuration of the fins may be chosen as desired and will affect the thermal properties of the heatsink. For example. the fins may comprise pin shaped fins. For example, the fins may comprise elongate blade shaped fins.

In that case, the fins niay extend generally parallel to each other. The tins niay extend generally parallel to one dimension of the heatsink. Not all the fins need have the same shape.

In a particularly preferred embodiment, the plurality ci fins comprises a plurality ci elongate blades extending generally parallel to each other, and at least one of the fins is configured to form the at least one channel br receiving the PCl-3.

The plurality of blades may have any suitable blade shape. For example. the fins may comprise slats, plates or sheets..'l'le particular shape and configuration of the fins may he chosen as desired, depending on the desired thermal properties of the heatsink, In one arrangement, the elongate blades extend generally parallel to an edge of the heatsink.

The at least one fin which is configured to form the at least one channel may he a fin or fins at the outer edge of the heatsink. In one embodiment, the two outer fins are in the form of clongate blades configured to form channels at two opposite edges of the heatsinlc. Ihe channels are in the form of grooves or runners which may extend along the length of the blades. Preferably. the heatsink is mounted on the PCB by sliding a portion of the PCB into the channel or channels.

Preferably. the channel or channels have substantially the same height as the thickness of the PCB.

so as to produce a smooth sliding movement. Alternatively the channels may be formed in another portion oi the heatsink.

The particular shape and configuration of the heatsink will affect the thermal properties of the heatsink. For example, the heatsink niay comprise any suitable material which has suitable thermal impedance. I or example. the heatsink may comprise aluminium or aluminium alloy, which has high thermal conductivity hut is also relatively light and mechanically malleable. The heatsink may comprise extruded aluminium or aluminium alloy, or another extruded material. Alternatively.

the heatsink may he machined from a solid piece oi material. Alternatively, the heat dissipating fins may comprise a different material from the body of the heatsink, and be inserted into the body of the heatsink for manufacture. In that case, the heat dissipating fins may comprise any suitable material, for example, copper. For example, the heatsink may have any suitable surface colour. The surface colour of the heatsink may affect the thermal properties oi the heatsink because it will affect the rate of heat dissipation from the heatsink. For example, a matt black surface niay dissipate more heat than a bare metal surfaec.

In one embodiment, the at least one channel for receiving the PCB comprises two channels at opposite edges of the heatsink, and the channels are arranged to receive portions of PCB at opposite edges oi a cutout in the PCIL By mounting (preferably by sliding) the heatsink onto a cutout or notch or indent in the PCI-3, the heatsink is securely positioned and movement of the heatsinlc relative to the PCI-3 is minimised. The cutout may he at the edge of the PCB. Preferably. the channel or channels have generally the same height as the thickness of the PUB so that the heatsink slides smoothly onto the PCB with minimal movement in a direction perpendicular to the PCB plane.

In a preferred embodiment, the cutout is in the edge of the PUB and has generally the same width as the dimension of the heatsink which extends between the two channels. Thus, the channels a opposfte edges of the healsink may slide onto the cu1ou in the PCI3 thereby securing the heasink to the PCB. The direction of sliding is generally parallel to the longitudinal axes of the channels.

Once the heatsink is in posilion, movement of' Lhe heatsink in a direction parallel lo the width of the cutout is restricted. In a preferred embodiment, the cutout in the PCB has generally the same depth as another dimension of the heatsink. Ihus, the heatsink may slide into the cutout and abut the inner edge of the cutout. Once the heatsink is in position, movement of the heatsink in a direction parallel to the depth of the cutout is resiricted. Allernatively, or additionally, Lhe heatsink may slide onto the PCB in a direction gencrally perpendicular to the longitudinal axis of the channel or channels.

The cutout may have any suitable shape to accommodate thc hcatsink. If the cutout is at the edge of the PCl-3, Ihe cuiou may he generally U-shaped.

In that embodiment, the heat dissipating surface of the heatsink is arranged to engage with a finger of PCB extending from the cutout. Preferably. the cutout in the PCB includes a finger extending from the cutout. When the heatsink is mounted onto the PCB, the channels in the heatsink engaging with the edges of the cutout, the finger of PCB may extend across the heat dissipating surface of Ihe heatsink and he in contact with the heat dissipating surface of the heatsink.

Preferably, the heatsink, PCIJ and electronic component are secured to one another by a fixing means. The fixing means may comprise any suitable fixing means, for example, a screw. The fixing means may he used to ensure close coniact hdween the heatsink, l'C13 and electronic component. This provides good thermal transfer, and also restricts movement of the heatsink relative tothePcB.

One or more of the healsink, PCI-3 and componeni may include holes for receiving the fixing means. the fixing means may extend through one or more of the holes. If a Pd finger is provided to engage with the heat dissipating surface, a hole may be provided in the PCB finger, and the fixing means may extend through the hole in the PCB finger.

Ihis provides a low cost solution, because a single fastener is needed to secure all the components of the heatsink assembly. The attachment mechanism for the heatsink also provides the attachment mechanism for the electronic component. In addition, this arrangement saves PCB space since no holes are required outside the footprint of the electronic component. Heatsink movement is minimised, both parallel to the plane of the PCB and perpendicular to the plane of the PCB.

According o a second aspect of the invenlion, there is provided a heatsink assenihly eonipnsing: a printed circuit board (PCB) having a first face for mounting electronic components and a second face opposile the first lace: a heatsink having a component mounling surface, a hear dissipating surface opposite the component mounting surface, and at least one channel for receiving the PCB, the heatsink being mounted on the PCB such that: a portion of the PCB is received in the at least one channel, the eoniponent mounting surface faces in substantially the same direction as the first lace of the PC13, and the heat dissipating surface faces in suhslantially the same direction as the second face of the PCB: and an electronic component mounted on the component mounting surface of the heatsink such that heat from the electronic conlpOneflt is conveyed from the component mounting surface of the heatsink to the heat dissipating surface of the heatsink.

In the heatsink assembly of the second aspect of the invention, the heatsink extends between the face of the PCB on which electronic components are mounted (that is. topside) and the opposite face (that is, underside) of the PCl3. Ibis allows the heat dissipating surface of the heatsinlc to he in contact with a cooling medium at the underside of the PCB, while still allowing the component to be located on the topside of the I'CIL I further, a siniple attachment process may he used to attach the componcnt to thc hcatsink and the hcatsink to thc PCB. Becausc only minimal movement of the hcatsink is pcrrnittcd in thc hcatsink asscmbly of the sceond aspect of the invention, there is minhnal stress to the legs of the electronic component during vibration. Ihe heatsink assembly also saves PCB space, since no holes may be required outside the electronic component's footprint The heat dissipating surface of thc heatsink may comprise a plurality of fins for dissipating hcat. Thc fins increase thc surface area of the heat dissipating surface and enhance the hcat dissipation properties of the heatsink.

l'he plurality of fins may comprise a plurality of elongate blades extending generally parallel to each other, and at least one of the fins may he configured to form the at least one channel for receiving the PCB.

In one embodiment, the I-'CB includes a cutout, the at least one channel in the heatsink for receiving thc PCB comprises two channels at opposite edges of the heatsink. and the channels arc arranged to receive portions of the PCB at opposite edges of the cutout. By mounting (preferably by sliding) the heatsink onto a cutout in the PCI-3, the heatsinlc is securely positioned, and movement of the heatsink relative to the PCIJ is minimised.

In that embodiment, thc PCB may include a PCB finger extending from the cutout, and the heat dissipating surface of the heatsink may be arranged to engage with tile PCB finger.

I'he heatsink assembly may further comprise a fixing means for securing together the heatsink. PCB and electronic component. The fixing means may comprise any suitable fixing means, for example, a screw. The fixing means may be used to ensure close contact between the heatsink. PUB and electronic component. This ensures good thermal transfer, and also restricts movement of the heatsink relative to the PUB. One or more of the heatsink. PUB and component may include holes for receiving the fixing means. I'he fixing means may extend through one or niore of the holes. This provides a low cost solution, because a single fastener is needed to secure all the components of the heatsinlc assembly. In addition, this arrangement saves PUB space since no holes are required outside the footprint of the electronic component.

Features described in relation to one aspect of the invention may also be applicable to the other aspect of die invention.

Brief Description of the Drawings

A prior art arrangement has already been described with reference to accompanying Figure 1. l'he invention will now' he lurther described, by way of example only, with reference to accompanying Figures 2 to 7. of which: Figure 2 is a first perspective view of a heatsink according to one embodiment of the invention; Figure 3 is a second perspective view' oF the heatsink of'ligure 2; Figure 4 is a perspective view of a portion of printed circuit board (PCB) for receiving the hcatsink shown in Figures 2 and 3; Figure 5 show's a method of assembling a heatsink assembly according to one embodiment of the invention; Figure 6 is a first perspective view of a heatsink assembly according to onc embodiment of the invention; and Figure 7 is a second perspective view of the heatsink assembly of Figure 6.

Detailed Description

Figures 2 and 3 show a heatsink according to one embodiment of the invention. Figure 2 is a perspective view' of the topside of the healsink and Figure 3 is a perspective view of' the underside of the heatsink. Referring to Figures 2 and 3. heatsink 201 comprises a component mounting surface 203 on the topside of the heatsink, and a heat dissipating surface 205 on the underside of the heatsink. Component mounting surface 203 is for receiving an electronic component to he cooled, as will he described further with reference to l'igure 5' heat dissipating surface 205 comprises a plurality of heat dissipating fins 207 which extend away from the hcatsink and allow heat to be conveyed from the eleconic component when the component is mounted on the heatsink. In the illustrated embodiment, the heatsink 201 is generally rectangular in crs section and eight heat dissipating fins 207 are provided. The fins 207 extend generally parallel to each other and to one edge of the rectangular hcatsink 201. However, any suitable fin number and configuration may be provided, as desired for optimal thermal performance.

In the embodiment shown in Figures 2 and 3, the two outer heat dissipating fins 207 (that is, those fins which are at the outer edges of the heatsink and furthest from each other) are shaped and configured so as to form two channels 209, one at each edge of the heatsink 201. The channels 209 are for receiving an edge of a printed circuit hoard (PCI-3) when the heatsink slides onto the I'CI-3, as will be described further with reference to Figures 4 and 5. In the illustrated embodiment, two channels are formed by two of the heat dissipating fins 207. However, this does not need to he the ease and the channel or channels may be formed in another portion of the heatsink. Any number of channels may he provided, and this will depend on the configuration of the PCB onto which the hcatsink is to be mounted.

I'he!iealsink also includes a hole 211, which hay he threaded, extending through the heatsink. The hole 211 is for receiving a fixing means, as will be described further with reference to Figure.I'he heatsin! 201 may comprise any malerial or malerials which have suitable Ihermal resistance. For example, the heatsink may comprise extruded aluminium or aluminium alloy.

ligure 4 is a perspective view of a portion of I-'CU for receiving the heatsink shown in Figures 2 and 3. PCB 401 (shown only partially in Figure 4) includes a generally TI-shaped cutout 403, having Iwo side edges 405 and one hack edge 407. A I'C13 linger 409 extends From the hack cdgc 407 into thc U-shaped cutout 403. Thc PCB finger 409 includes a holc 411, which may bc threaded, cxtcnding through the PCB finger. The hole 411 is for rccciving a fixing means, as will bc descrihed further with reference to Figure 5. In the embodiment illustraled in Figure 4. the eutoul is provided at the edge of the I-'CU 401, hut this need not he the case.

Figure 5 shows a method of assembling the heatsink 201 of Figures 2 and 3 with the PCB 401 of Figure 4 to form a heatsink assembly. In this embodiment, each side edge 405 of the U-shaped cutout 403 in the PCB 401 is received in a channel 209 of the heatsink 201. The channels 209 have generally the same height as the thickness of the PCH 401 so thaI the healsink 201 slides smoothly onto the PCIJ 401, in a direction generally parallel to the length of the channels 209, with minimal movement in a direction perpendicular to the plane of the PCB. The heatsink 201 slides onlo the I'CU 401 until one edge of the heatsink 201 ahuts the hack edge 407 of the ti-shaped cutout 403. The U-shaped cutout 403 and heatsink 201 have generally the same dimensions such that, when the edge of the heatsink abuts the back edge 407 of the cutout 403, movement of the heatsink relative to the PCI-3 is conslrained in directions parallel to the plane of the FCI-3.

The heatsink 201 slides into the U-shaped cutout 403 of the 1-CU 401 such that the component moundng surface 203 of the heatsink 201 faces the samc direction as the topside of the PCB 401 (that is, the face of the PCB on which electronic components are to be niounted) and the heat dissipaling surface 205 of the heatsink 201 faces the same direction as the underside olthe [CR 401. (In Figure 5, the view is from the underside.) In this embodiment, the PCB finger 409 extends across the heat dissipating surface 205 of the heatsink 201, between heat dissipating fins 207. The hole 411 in the PCB finger 409 aligns with hole 211 in heatsink 201.

An electronic component 501 to be cooled may then be mounted on the component mounting surface 203 of the heatsink 201. Ihe component 501 may he mounted on the componenl mounting surface 203 by any suitable means which ensures heat conduction from the component to the healsink, for example, by gluing. A hole 503, which may he threaded, in the electronic component 501 aligns with the hole 211 in the heatsink 201 and the hole 411 in the PCB finger 409.

Electrical connections 505 for the electronic component 501 are made to the topside or underside of the PCB 401 (tbr example, by soldering). The component 501. heatsink 201 and PCB 401 niay be secured together hy means of screw 507, or other fixing means, passing through hole 503 in the component 501. hole 211 in the heatsink 201 and hole 411 in the PCB finger 409. If the holes 503.

211, 411 are threaded, the screw preferably engages with the thread. Preferably, only one of the three holes is threaded. Preferably, only hole 411 is threaded, so that the screw 507 tightens the componenl 501, heatsink 201 and PCI-3 401 together. Ihe screw 507 preferably has a length such that, when it is screwed into the holes 503. 211. 411 it is at least flush with the topside of the PCB finger 409.

Figures 6 and 7 show a heatsink assembly 601 according to one embodiment of the invention. Ihe assembly is lonned by the method illustrated in Figure 5. lgure 6 is a perspective view of the topside of the heatsink assembly 601 and Figure 7 is a perspective view of the underside of the heatsink assembly 601. Referring to Figures 6 and 7, the assembly comprises electronic componenl 501, heatsink 201 and ICR 401 secured logether by screw SOT In the heatsink assembly shown in Figures 6 and 7, the healsink 201 extends between the face of the PCB 401 on which electronic conipnents are mounted and the opposite face of the PCB 401. This allows the heat dissipating surface 205 of the heatsink 201 to he in contact with a cooling medium (most likely, air) at the underside of the PCB, while still allowing the component 501 to be located at the topside of the PCI-3. Further, a simple process may he used to atlach Ihe component 501 to the heatsink 201 and the heatsink to the PCB 40L Moreover, the heatsink assembly shown in Figures 6 and 7 allows only minimal movement of the heatsink, which reduces stress on the eleclrical connections 505 (legs) of Ihe electn)nic component 501. Movement of the heatsink 201 in directions parallel to the plane of the PCB 401 is restricted because the heatsink 201 is restrained within the cutout 403 in the PCB and is also secured with the screw 507. Movement of the healsink 201 in a direction perpendicular 1o the plane of the PCIJ 401 is restricted by the screw 507 and is also prevented because the width of the heatsink channels matches the thickness of the PCB 401. In addition, the hcatsink assembly 601 saves PCB space since no holes are required outside tile footprint of the electronic component 501. Further, only a single fastener 507 is required to secure the heatsink 201, component 501 and ICR 401.

Claims

Claims 1. A heatsin! br mounting on a printed circuit board (PCI-3) having a birsl lace for mounting electronic components and a second face opposite the first face, the heatsink comprising: a component mounting surface; a heat dissipating surface opposite the component mounting surface; and at least one cliannel for receiving the l'Ci3: whcrcin thc hcatsink is arrangcd to bc mountcd on thc PCB such that: a portion of thc PCB is rcccivcd in thc at icast onc channel, thc couiponcnt mounting surfacc faccs in substantially thc same direclion as Ihe firsl lace of the PC13, and the heal dissipaling surbace faces in substantially lhe same direction as the second face of the l'CB; and whcrcin. whcn the hcatsink is mountcd on thc PCB and an clectronic componcnt is mountcd on thc componcnt mounting surfacc of thc hcatsink, hcat from thc clcctronic componcnt is convcycd from thc component mounting surfacc of thc hcatsink to thc hcat dissipating surfacc of thc hcatsink.
2. A hcatsink according to claim 1, whcrcin thc hcat dissipating surfacc couipriscs a plurality of fins for dissipating heat.
3. A hcatsink according to claim 2. whcrcin thc plurality of fins compriscs a plurality of elongate blades extending generally parallel to each other, and at least one of the fins is configured to borm heal least one channel br receiving the PCI-3.
4. A hcatsink according to any prcccding claim, whcrcin: the at least one channel for receiving the PCB comprises two channels at opposite edges of the healsink, and thc channels arc arrangcd to rcccivc portions of PCB at oppositc cdgcs of a cutout in thc PCB.
5. A heatsink according to claim 4, wherein the heat dissipating surface of the heatsink is arranged lo engage with a linger of PCU exlending from the cutout.
A heatsink according to any preceding claim, wherein the heatsink, PCh3 and electronic component are secured to one another by a fixing means.
7. A hcatsink asscmbly coniprising: a printed circuit hoard (h'CU) having a birsl lace br mounling electronic components and a sccond facc oppositc thc first face; a heatsink having a component mounting surface, a heal dissipaling surface opposite the component mounting surface, and at least one channel for receiving the PCB, the heatsink being mounted on the PCI-3 such thaI: a portion of the PCI-3 is received in Ihe at leasl one channel, the component mounting surface faces in substantially the same direction as the first face of the PCB, and the heat dissipating surface faces in substantially the same direction as the second face of the PCB; and an elecftonic componenl mounled on the coniponent mounting surface of the healsink such that heat from the electronic component is convcycd from the component mounting surface of the hcatsink to the heat dissipating surface of the heatsink.
8-A heatsink assembly according to claim 7, wherein the heat dissipating surface of the heatsink comprises a plurality of fins for dissipating heat.
9. A hcatsink assembly according to claim 8, wherein the plurality of fins comprises a plurality of elongate blades extending generally parallel to each other, and at least one of the fins is configured to form the at least one channel for receiving the Pd.
Ift A heatsink assembly according to any of claims 7 to 9. wherein: the PCB includes a cutout, the at least one channel in the heatsink for receiving the PCB comprises two channels at opposite edges of the healsink, and the channels are arranged to receive portions of the P03 at opposite edges of the cutout.
11. A heatsink assembly according to claim 10, wherein tile PCB includes a PCB finger extending from the cutout, and the heat dissipating surface of the heatsink is arranged to engage with the PCB finger.
12. A hcatsink assembly according to any one of claims 7 to 11, further comprising a fixing means for securing together the heatsink, PCB and electronic component.