WO2000048439A1

WO2000048439A1 - Mechanical arrangement for heattransfer from an electric device

Info

Publication number: WO2000048439A1
Application number: PCT/SE2000/000068
Authority: WO
Inventors: Ödgärd ANDERSSON
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 1999-02-09
Filing date: 2000-01-14
Publication date: 2000-08-17
Also published as: SE515449C2; JP2002537638A; AU2835900A; SE9900428D0; SE9900428L

Abstract

The present invention relates to cooling of components within a housing of an electric apparatus (200). A housing for an insert card comprises a first and a second rectangular housing part (203, 204) with a number of resilient tongues (214-217) formed as part of the respective first and second housing part. The resilient tongues (214-217) abut corresponding components (222a-d, 223a-b) in the electric apparatus (200) so that a thermal path is achieved between the components and the housing. Heat generated by the components (222a-d, 223a-b) is distributed to the housing by the resilient tongues (214-217) so that the components are cooled.

Description

MECHANICAL ARRANGEMENT FOR HEATTRANSFER FROM AN ELECTRIC DEVICE

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field φf cooling and, in particular, to arrangements for heat transfer from an electric device arranged in a housing of an electric apparatus .

DESCRIPTION OF RELATED ART

An electric apparatus can as an example comprise a housing in which an electric device with components is arranged. It is common that one or more of these components, e.g. digital circuits, resistors, coils, and transformers, in the electric apparatus become warm and even hot during operation. This heat often has a negative influence on the performance of the components e.g. by component stress, by deformation of materials in the circuits and by deterioration of solder.

A known solution to this problem is to arrange some kind of heat sink.

The space inside a housing of an electric apparatus is often limited. Sometimes very limited such as in insert cards (also called plug-in cards, PCMCIA cards, PC cards or Compact Flash Cards) where e.g. the height of the components is limited by the insert cards standards, e.g. PCMCIA or JEIDA which are PC cards and/or Compact Flash standards. Another example of an electric apparatus where the space and the height of the components is limited is a power supply, e.g. a power supply module for mounting on a printed wiring board. This reduces the number of possible heat-sink arrangements that can be used in e.g. an insert card.

Insert cards are commonly used in portable PCs, electronic notebooks, mobile phones, FAX modems, LAN cards etc. An insert card can as an example comprise a radio unit, an IC memory, a radio modem or data processing equipment. Generally insert cards are removable interconnected with the electric equipment with which it is used so as to be inserted when needed and extracted when not needed.

A known solution for cooling components in insert cards is to distribute the heat to the printed wiring board on which the components are arranged. This can as an example be done by letting the casing of the component abut a copper area arranged on the printed wiring board. The heat is then distributed from the casing of the component out to the copper area arranged on the printed wiring board. This reduces the hot spot temperature on the component. The copper area is preferably bigger than the foot-print of the component. Furthermore, the legs on the component can also be used to distribute the heat from the component to the printed wiring board. There is however a great risk that the printed wiring board becomes to hot if one or more components are generating a lot of heat. The printed wiring board then has to be cooled.

Another known solution is to apply a metallic cooling element to the casing of the component to reduce the hot spot temperature on the component. Such a metallic device designed for higher hot spot temperature is often too big to be arranged inside an insert card.

Yet another solution is to use a built-in fan that can cool the components, if there is room in the electric apparatus.

A further solution for an insert card is to use the connector in the insert card to transport the heat from the printed wiring board to the apparatus into which it is connected. SUMMARY

The present invention meets some problems related to cooling elements, e.g. components or conductors, on an electric device arranged in a housing of an electric apparatus.

One problem is to provide a heat sink for an element in an electric apparatus.

Another problem is to provide a low-cost and easy to assemble heat sink in an electric apparatus.

A further problem is to provide a heat sink that does not limit the component height in the electric apparatus.

In light of the foregoing, a primary object of the present invention is to provide a heat sink for components and/or conductors on an electric device arranged in a housing of an electric apparatus.

Other objects of the present invention are to provide a heat sink that is cheap and easy to manufacture and makes the assembly and disassembly of the electric apparatus fast and easy.

Yet another object of the present invention is to provide a heat sink that does not affect the component height in the electric apparatus.

In a housing according to the present invention, accommodating an electric device, at least one tongue is arranged to create a thermal contact with one or several elements in the electric device that has a need to be cooled. The tongue establishes a thermal path between the element to be cooled and the housing.

According to one embodiment of the invention the housing comprises a first and a second part. Resilient tongues are integrated in the first and second part and are arranged to abut against components to be cooled on the electric device in the housing. The heat generated in the components is distributed from the components via the tongues to the housing whereby the components are cooled.

The inventive arrangement is therewith characterised according to claim 1.

An advantage with the present invention is that it is possible to arrange a heat sink within an electric apparatus with limited space inside the electric apparatus .

Another advantage with the present invention is that the heat sink is integrated in the housing, i.e. no extra devices for cooling have to be bought and assembled in the apparatus .

Yet another advantage is that the heat sink makes the housing very easy to assemble and disassemble.

Still another advantage is that the heat sink can be made in the same processing step as when the housing is made, i.e. the heat sink does not introduce any extra manufacturing steps .

Another advantage is that the heat sink does not affect the component height in the electric apparatus.

A further advantage is that the arrangement used for cooling can also be used to position the electric device in a predetermined position inside the electric apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a perspective view of an insert card.

Figure 2 illustrates an exploded view of a first insert card according to the present invention.

Figure 3a illustrates a view of a first housing part according to the present invention. Figure 3b illustrates a view of a cut-out section from figure 3a.

Figure 3c illustrates a cross sectional view of a resilient tongue according to the present invention.

Figure 4 illustrates an exploded view of a second insert card according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention relates to cooling elements, e.g. components or conductors, on an electric device arranged in a housing of an electric apparatus, e.g. an insert card or a power supply.

Figure 1 illustrates an insert card 100 with a connector 101 arranged in a housing 102 that encloses the interior of the insert card 100. A label 103 is attached on the housing 102. The insert card can as an example comprise a transceiver, an IC memory, a radio modem or data processing equipment. The insert card 100 is an example of an electric apparatus comprising a housing in which an electric device with components is arranged. A power supply module (not illustrated in any figures) can be designed in a similar way as the insert card 100 with a housing that encloses an electric device, in this case e.g. DC/DC or AC/DC converters .

Figure 2 is an exploded view illustrating a first insert card 200 according to a first embodiment of the present invention. The insert card 200 includes two labels 201, 202 respectively, a first and a second rectangular housing part 203, 204 respectively and a rectangular printed wiring board 205 with components. The first and second housing parts 203, 204 respectively, preferably consisting of plates, are made of metal, e.g. steel or aluminium, and form two halves of a housing. Each one of the housing parts 203, 204 respectively shows two parallel longitudinal narrow sides 206-209 respectively, an inner surface 210, 211 respectively facing towards the interior of the insert card and an outer surface 212, 213 respectively facing outwards. The narrow side 207 and the inner surface 210 of the first housing part 203 and the outer surface 213 of the second housing part 204 are hidden in figure 2.

The first housing part 203 has a first and a second resilient tongue 214, 215 respectively. The second housing part 204 has a third and a fourth resilient tongue 216, 217 respectively. The resilient tongues 214-217 are formed as part of the respective first and second housing part. A detailed description of these tongues is made in connection with figures 3a-c below.

The labels 201 and 202 are adhered on the outer surface 212, 213 respectively of the first and second housing parts. The labels are used for product marking and to cover openings in each housing part. A description of these openings is made in connection with figure 3c below.

The rectangular printed wiring board 205 is arranged between the first and second housing part 203, 204 respectively. The rectangular printed wiring board 205 comprises a first side 218 facing the first housing part 203, a second side 219 (hidden) facing the second housing part 204, a connector 220, at least one ground plane (not illustrated) and a number of components, whereby two components 222a-b on the first side 218 and two components 223a-b on the second side 218 are illustrated in figure 2. The components 223a-b on the second side 219 are illustrated with dashed lines in figure 2. The connector 220 is attached at one of two parallel short sides of the rectangular printed wiring board 205. The connector 220 is used for connecting the insert card 200 to the electric equipment into which it is inserted. The printed wiring board 205 with components and the connector 220 is also referred to as the electric device .

The components 222a, 222b, 223a and 223b respectively are components that generate heat when the insert card is in operation. These components have a casing, e.g. of metal or ceramic, which becomes hot when heat is generated in the components .

Figure 3a illustrates the first housing part 203 with the first and second resilient tongue 214, 215 respectively. The tongues are each partially stamped-out of the housing part 203 to form outstretched and resilient parts of the housing. This means that the tongues are a homogeneous part of the housing. The first and second tongues 214, 215 respectively are arranged across the inner surface 210 of the first housing part 203 in such a way that the tip of the tongues 214, 215 respectively abut the corresponding component 222a, 222b respectively on the first side of the printed wiring board 205 when the first insert card 200 is assembled. The tongues 214, 215 respectively create a "thermal path" between the respective component and the housing of the insert card 200. Hence, each tongue works as a heat sink for the respective component on the printed wiring board 205.

Figure 3b illustrates a cut-out section C from figure 3a of the first housing part 203 with the first resilient tongue 214.

Figure 3c illustrates a cross sectional view taken along line A-A of figure 3b of the resilient tongue 214. The resilient tongue 214 consists of a narrow and flat outstretched arm 301 extending from the inner surface 210 of the housing part 203 towards the interior of the insert card 200. The top of the arm is slanted to form a flat tip 302 in parallel with the inner surface 210 of the housing part 203. The flat tip 302 is arranged to make good thermal contact with the component 222a on the printed wiring board 205. The size of the flat tip 302 and the arm 301 are mainly determined by the amount of heat they should transport from the component and the space available in the insert card. The tip 302 is flat in this embodiment but can easily be formed in another way, e.g. slightly bent, to achieve a good contact with e.g. an unflat part of a component casing. It is also possible to design the area of the tip 302 to be as wide as the component casing, against which it abuts, so as to cover the whole top area of a component casing. None of these two designs of the tip are shown in any figure. There is an opening 303 under the resilient tongue 214 that is created when the resilient tongue is stamped out from the housing part. The arm 301 forms a first angle 304 of e.g. 45 degrees against an imaginary surface over the opening 303. The first angle 304 is determined dependent on the distance between the housing parts and the component when the insert card is assembled and also dependent on the desired size of the opening 305. If the first angle 304 is to big the tongues will be bent when the insert card is assembled and if the first angle 304 is to small no contact against the components will be achieved.

The description of the first resilient tongue 214 in the first housing part 203 according to figure 3a-c applies equally to all the resilient tongues in the first and second housing part 203,204 respectively. The third and fourth tongue 216, 217 respectively are arranged across the inner surface 211 of the second housing part 204 in such a way that the tip of the tongues 216, 217 respectively abut the corresponding component 223a, 223b respectively when the first insert card 200 is assembled.

The resilient tongues in the first insert card 200 constitutes an effective cooling arrangement (a heat sink) by connecting components on the printed wiring board that becomes hot to the first and second housing part so that the heat can be distributed from the components to the housing.

Figure 4 is an exploded view illustrating a second insert card 400 according to a second embodiment of the present invention. The second insert card 400 has two labels 401, 402 respectively, a first and a second rectangular housing part 403, 404 respectively and a rectangular printed wiring board 405. The first and second housing parts 403, 404 respectively, preferably consisting of plates, are made of metal, e.g. steel or aluminium, and form two halves of a housing. Each one of the first and the second housing part shows two longitudinal narrow sides 406-409 respectively, an inner surface 410, 411 respectively facing towards the interior of the insert card 400 and an outer surface 412, 413 respectively facing outwards. The narrow side 407 and the inner surface 410 of the first housing part 403 and the outer surface 413 of the second housing part 404 are hidden in figure 4.

The first housing part 403 has first group of resilient tongues 414 formed as a rectangle and a first row of resilient tongues 415. The second housing part 404 has a first tongue 417. The resilient tongues 414, 415 and 417 respectively are of the same design as in the first embodiment according to figure 3a-c, but the first angle 304 for the resilient tongues 414 and 415 is determined dependent on the distance between the first housing part and the printed wiring board in this embodiment.

The labels 401 and 402 are adhered on the outer surface 412, 413 respectively of the first and second housing parts. The labels are used for product marking and to cover openings in each housing part as in the first embodiment according to figure 2.

The rectangular printed wiring board 405 arranged between the first and second housing part 403, 404 respectively comprises a first side 418 facing the first housing part 403, a second side 419 (hidden in figure 4) facing the second housing part 404, a connector 420, a number of components and at least one ground plane. For simplicity the ground plane is omitted in the figure. A first, second and third component 422a-c respectively on the first side 418 and a fourth component 422d on the second side 419 are illustrated in figure 2. The fourth component 422d on the second side 419 is illustrated with dashed lines. The connector 420 is attached at one of the two parallel short sides of the printed wiring board 405. The printed wiring board 405 with components and the connector 420 is also referred to as the electric device.

The components 422a-422d respectively are components that generate heat when the insert card 400 is in operation. These components have a casing, e.g. of metal or ceramic, which becomes hot when heat is generated in the components.

The first side 418 of the printed wiring board 405 comprises a rectangular formed thermal conductor area 421a on which the first component 422a is arranged and a T- formed thermal conductor 421b to which the second and third component 421b-c respectively are arranged. The rectangular thermal conductor area 421a is bigger than the foot-print of the first component 422a. The thermal conductors 421a-b respectively are made of copper but can as an alternative be made of tin, gold or any other electrically and thermally conductive material suitable for printed wiring boards. The thermal conductors 421a-b respectively are in this embodiment connected with the ground plane in the printed wiring board 405 so that they can be used as ground conductors .

The first group of tongues 414 in the first housing part is arranged in such a way that the tip of each tongue in the group 414 abut the rectangular area 421a on the first side of the printed wiring board when the second insert card 400 is assembled. This creates a thermal path from the first component via the rectangular area 421a and the group of tongues 414 to the housing. The rectangular area 421a should preferably be large enough to allow the tongues 414 to abut the area 421a without touching the first component 422a. This means that component 422a becomes surrounded by the tongues in the first group of tongues 414. The first row of tongues 415 in the first housing part is arranged in such a way that the tip of each tongue in the row 415 abut the thermal conductor 421b on the first side of the printed wiring board when the second insert card 400 is assembled. This creates a thermal path from the second and third component via the thermal conductor 421b and the row of tongues 414 to the housing.

The resilient tongue 417 in the second housing part 404 is arranged so that the tip of the tongue abut the casing of the fourth component 422d on the second side of the printed wiring board 405 when the second insert card 200 is assembled. This creates a thermal path from the fourth component via the resilient tongue 417 to the housing.

The resilient tongues in the second insert card 400 constitutes an effective cooling arrangement (a heat sink) by connecting the hot printed wiring board (heated by components on the printed wiring board) to the first and second housing part so that the heat can be distributed from the printed wiring board to the housing.

The thermal conductors and the components in the present invention are examples of elements on the printed wiring board that can be cooled by a resilient tongue used as a heat-sink.

The resilient tongues in the present invention are partly pushed against the respective housing part (making the first angle 304 decrease) when the housing is assembled around the printed wiring board of the insert card. This means that the tongues will exert a pressure against the printed wiring board or components which ensures a good thermal contact between the tongues and the printed wiring board and/or the components .

The surface of the tongues can be surface treated, e.g. by applying Ni, Sn or Cr, to optimise the thermal contact between the tip of the tongues and the component or printed wiring board.

The resilient tongues can also be used to position the printed wiring board in a predetermined position inside the housing of the insert card 200, 400 and 500. This means that the resilient tongues can replace frames, screws, rivets gaskets or similar fastening means which is used to fixate the circuit board in the insert card 200 and 400.

The printed wiring boards in the insert cards of this invention may comprise components on both sides, on one of these sides and/or inside the printed wiring board in an intermediate layer.

Locking means is arranged on/in the insert cards 200 and 400 to keep the first and second housing parts together. For simplicity the locking means are omitted in the figures. This type of locking means is well known in the art e.g. snap-locking, gluing or welding.

The resilient tongues are stamped and formed in the same procedure as the housing parts. This means that no extra processing step is needed to manufacture the resilient tongues in the housing parts.

The housing of the insert cards 200, 400 respectively have been described to include two housing parts but the housing may also be designed as one single housing, that e.g. is folded around the electric device inside the housing, or be designed to include more than two housing parts. It should be understood that the insert cards 200, 400 respectively comprise other components and electrical conductors for the performance of the insert card than those described. These components and electrical conductors are for simplicity omitted in the figures and the corresponding text .

The inventive arrangement with the resilient tongues can be used in a number of different boxes, covers, housings or similar which encloses electric devices. These boxes, covers, housings or similar can be made by or partially by any material suitable for heat transfer e.g. steel, aluminium or metalized plastic.

Claims

1. A housing accommodating an electric device in which electronic components are mounted, c h a r a c t e r i s e d in that said housing has at least one tongue (214-217,414,415,417), which is arranged to create a thermal contact with at least one element (222a- b, 223a-b, 421a-b, 22a-d) on said electric device in order to distribute heat from said element to said housing.

2. The housing as claimed in claim 1, wherein said tongue (214-217,414,415,417) is resilient.

3. The housing as claimed in claim 1 or 2, wherein said tongue (214-217,414,415,417) is formed as a part of said housing (203-204, 403-404).

4. The housing as claimed in any one of claims 1-3, wherein said electrical device includes at least one printed wiring board (205,405) on which said element (222a-b, 223a-b, 421a-b, 422a-d) is arranged.

5. The housing as claimed in any one of claims 1-4, wherein said element is a component (222a-b, 223a-b, 422a-d) .

6. The housing as claimed in any one of claims 1-4, wherein said element is a thermal conductor (421a-b) .

7. The housing as claimed in any one of claims 1-6, wherein said housing includes at least one housing part (203-204, 403-404) .

8. The housing as claimed in any one of claims 1-6, wherein said housing includes a first (203,403) and a second (204,404) housing part, where at least one of said first and second housing parts is provided with said tongue (214- 217,414,415,417) .

9. The housing as claimed in any one of claims 1-8, wherein said tongue (214-21,414,415,417) has been stamped out from said housing.

10. The housing as claimed in any one of claims 1-9, wherein a first number of said tongue (214-217,414,415,417) are arranged in at least one group in said housing.

11. The housing as claimed in any one of claims 1-10, wherein a second number of said tongue are arranged to position said electric device in said housing in a predetermined position.

12. The housing as claimed in any one of claims 1-11, c h a r a c t e r i s e d in that said housing accommodating said electric device is an insert card.

13. The housing as claimed in any one of claims 1-11, c h a r a c t e r i s e d in that said housing accommodating said electric device is a power supply.