GB2310321A

GB2310321A - Deformable heat sink

Info

Publication number: GB2310321A
Application number: GB9701856A
Authority: GB
Inventors: Helmut Nechansky
Original assignee: Electrovac AG
Current assignee: Electrovac AG
Priority date: 1996-02-13
Filing date: 1997-01-30
Publication date: 1997-08-20
Also published as: FR2744873A1; AT404532B; DE19704549A1; ITMI970270A1; IT1290293B1; ATA25096A; GB9701856D0

Description

2310321 HEAT SINK FOR ELECTRICAL OR ELEC.VRONIC COMPONENTS - 1 - The

invention relates to a heat sink for electrical or electronic components.

Hitherto known heat sinks of the generic type are made of a solid material and are fixed on the components to be cooled by screwing or adhesive bonding - if appropriate with a heat- conducting paste in between. They are produced from a material with good heat-conducting properties, usually from aluminium.

A disadvantage of such heat sinks is that they are designed for attaching only to a single component, with the result that, even for cooling components which are closely adjacent, separate heat sinks have to be used for each of them.

The greatest problem of adjacent components on is which a common heat sink is to be arranged is their differing overall height. Of course it would be possible to form a solid heat sink in such a way that it can be connected to all the components to be cooled; however, it can then only be used for the specific component con- figuration for which it was designed; for a different type of component arrangement it would be necessary again to make a purpose-built model.

The object of the invention is to avoid this disadvantage and specify a heat sink of the type mentioned at the beginning which can be fitted onto a group of adjacent component housings and at the same time can be adapted to different configurations of the components to be cooled.

According to the invention, this is achieved by a heat sink which has a deformable casing, which is filled at least partially with a heat transfer medium.

Such a heat sink can be adapted to any desired component groupings; it fits onto all the individual components, thereby ensuring good heat transfer and consequently efficient heat removal.

According to one variant of the invention it may be provided that the heat transfer medium has a pasty consistency, because this allows the heat sink to shape itself well to the components to be cooled and because it 2 retains its shape.

According to further design variant, the heat transfer medium may have a liquid consistency.

Liquid heat transfer media are particularly well suited for absorbing and carrying away heat, with the result that heat sinks designed in a way corresponding to this design variant are particularly effective.

According to an alternative design possibility of the invention, it may be provided that the heat transfer medium is f ormed by a solid material which is in the f orm of a multiplicity of individual parts and preferably has good heat-conducting properties.

On account of the good heat conductivity of solid materials, heat sinks designed in a way according to the is invention produce satisfactory results, in a way similar to previously customary rigid heat sinks likewise produced from solid material.

In this connection, it may be provided that the solid material has a powdery consistency.

Such a heat-conducting powder is particularly simple to produce, with the result that the production costs of such a heat sink can be kept low.

In this connection, it may be provided that the particles of the solid, powdery material have the f orm of small beads.

Compared with other geometrical bodies, beads have a large volume in comparison with their surface and can lie very closely together, with the result that, with this form of granular particles, a large amount of heatdissipating material can be accommodated in the casing of the heat sink. Consequently, the heat sink can be given a great heat-dissipating capacity.

It may constitute a further design of the invention f or the solid material to be in the form of flexible parts, such as for example wires, strips, foils or the like.

This produces relatively long heat transfer paths, which are free from material transitions, with the result that a higher heat conductivity can be achieved by 3 this type of design.

It is advantageous if the solid material is formed by a metal, such as for example copper, aluminium or the like, since metal can be easily brought into the necessary form - granules, strips, wires or the like has good heat conductivity and the necessary temperature resistance.

If a liquid or pasty heat transfer medium is used, it may be provided that the heat transfer medium is mixed with a solid material, in the form of a multiplicity of individual parts.

Solid heat transfer media, in particular metals, have a particularly high heat conductivity, with the result that their addition to a liquid heat transfer is medium can have the effect of increasing the heat conductivity of the latter in a simple way.

According to a preferred embodiment of the invention, it may be provided that the liquid heat transfer medium is formed. by water, paraffin, benzyl- toluene, biphenyl, terphenyl, silicone oils or the like, since these heat transfer media are particularly well suited for the temperature range occurring in the case of electronic components.

it may further be provided that the liquid heat transf er medium is f ormed by a ref rigerant, such as f ully or partially halogenated hydrocarbons, such as for example methyl chloride, di- or trichlorofluoromethane or the like; or by a halogen-free refrigerant, such as for example sulphur dioxide, carbon dioxide or the like.

These media have a low boiling point, with the result that, at the low temperatures occurring in the case of the application in question, they can remove the heat just by evaporation and subsequent condensation.

According to another variant of the invention, it may be provided that the heat transfer medium has a gaseous consistency.

As a result, the heat sink is particularly easily deformable and can be fitted onto adjacent components which differ considerably in their overall heights.

4 - is In the case of all the design variants presented so far, it may be provided that the casing is formed by a foil.

A foil can be deformed particularly easily, with the result that the heat sink can be brought into optimum contact with the individual components, and consequently optimum heat removal can be achieved, by the weight of the heat transfer medium alone.

In a development of the invention, it may be provided that the casing is made up of a plurality of pieces of foil, which pieces of foil are connected to one another, preferably along the length of their edges.

This type of design allows a particularly simple production operation.

In this connection, it may be provided that the pieces of foil are welded to one another.

Consequently, the individual pieces of foil are connected to one another particularly reliably.

It may be advantageous if the foil or the pieces of foil are formed from a material with good heat-con- ducting properties, preferably from a metal such as copper, aluminium or the like, because in this way the heat generated in the components can be given off to the ambient atmosphere with particularly little loss. It may constitute a particularly preferred embodiment of the invention for the casing to be formed by two pieces of foil, which pieces of foil have, if appropriate, different strength properties from one another.

The use of two pieces of foil can make the production process particularly simple, in particular the operation of connecting the two pieces of foil.

In this connection, it may constitute a develop ment of the invention for the first piece of foil to be plastically deformable and the second piece of foil to be elastically deformable.

If the piece of foil facing the components to be cooled is made to be plastically deformable, the heat sink can be fitted well onto the individual housings, the - 5 elastic design of the second piece of foil having the effect that the heat sink is always kept in a specific basic shape.

If the heat trans f er medium has a solid material, in the form of flexible parts, it may be provided according to a preferred design of the invention that the flexible parts, such as for example wires, strips, foils or the like, are fixed in each case by at least one end on the inner side of the casing.

Consequently, good contact, and thus low-loss heat transfer, is ensured between casing and heat transfer medium.

A development of the invention may provide that the casing has openings, via which openings heat transfer is medium can be supplied and removed.

Consequently, a circuit in which the heat transfer medium is moved can be set up, whereby the amount of heat removed by the heat sink can be increased.

According to another variant of the invention, it may be provided that the casing has at least one tubular attachment, in which attachment evaporated heat transfer medium can condense.

This attachment, based on the principle of a "heat pipe" also has the effect that the amount of heat removed can be increased.

According to a further embodiment of the invention, it may be provided that at least one solid body is fixed on the casing.

In the case of such an arrangement, the casing filled with heat transfer medium is used only to compensate for the difference in height between the individual components; the actual heat removal takes place via the solid body which is fixed on the casing and is advantageously designed in the form of a conventional heat sink.

In this connection, in a development of the invention it may be provided that, in addition to the casing, there may be f ixed on the solid body at least one further deformable casing, filled at least partially with a heat transfer medium.

As a result, the heat sink can be fitted simultaneously onto two different groupings of electronic components - as is the case with mutually parallel plugin cards.

The invention is now explained in more detail with reference to the preferred embodiments represented in the drawings, in which:

Fig. 1 shown sectionally in elevation a circuit board populated with microchips along with an embodiment of the invention; Figs. 2a, b show in plan view and elevation the circuit board according to Fig. 1 with a preferred embodiment of the invention; Figs. 3, 4 show in elevation developments according to the invention of the heat sink according to Figs. 2a, b; Fig. 5 shows the heat sink according to Figs. 2a, b with a solid cooling element fixed on it; 20 Fig. 6 shows in plan view an embodiment of the invention for the simultaneous cooling of two component groupings, and Figs. 7a, b show sectionally in elevation heat sinks according to the invention with a solid heat transfer medium.

Electronic components which are arranged on a common circuit board generally have different shapes of housing from one another. An example of this is shown in Fig. 1, in which a grouping of microchips arranged on a common circuit board 1 is represented. There are both differences in overall height of components 2, the terminal pins of which protrude through holes in the conductor path and are soldered on the underside 10 of the circuit board 1, but in particular also a significant difference in size with respect to surface-mounted devices 3 (SMDs).

It is often necessary for all the components 2, 3 to be provided with a heat sink, in which connection it would be particularly favourable to provide just one single heat sink for the entire assembly, it being advantageous f or the said heat sink to be detachably fixed on the components 2, 3 in order that any necessary exchange of a component 2, 3 can be performed in a simple way.

A heat sink 4 according to the invention, the basic structure of which is likewise represented in Fig. 1, has a deformable casing 5, which casing 5 is at least partially filled with a heat transfer medium 6.

Consequently, the heat sink 4 according to the invention corresponds with respect to its heat -dissipating properties to a conventional, rigid heat sink.

The casing 5 could be made of a sheet-like material, which is bent in a way corresponding to the is contours of the components 2, 3 to be cooled. However, this would mean that the heat sink 4 could be adapted to another component configuration only with some effort, with the result that the casing 5 is advantageously formed by a foil.. 20 The heat transfer medium 6 accommodated by the casing 5 must be able to adapt i toelf to the shape of the casing 5, for which purpose it has a pasty or liquid consistency. As an alternative to this, it is equally possible to use a solid material which is in the form of a multi plicity of individual parts and preferably has good heatconducting properties. The individual parts may in this case be relatively small, with the result that a powdery consistency of the solid heat transfer medium 6 is obtained, or else they have the f orm of f lexible parts 7, such as f or example wires, strips, foils or the like.

This produces a felt-like structure of the heat transfer medium, the main advantage of which is that the individual elements form elongated dissipation paths with good heat-conducting properties.

To ensure adequate deformability of the casing 5 even in the case of such heat transfer media, the casing 5 must not be filled right up but only partially with the 8 transfer medium in powdery, strip, foil or wire form.

To achieve good heat dissipation, it is favourable in this connection to use a material with good heat-conducting properties. Preferably, the heat transfer medium in powder, strip, foil or wire form is therefore formed from a metal, such as for example copper, aluminium or the like.

Furthermore, a combination of the two heat transfer media described is conceivable, i.e. the heat transfer medium 6 has liquid or pasty consistency and is mixed with a solid material in one of the forms described.

The individual particles of the powdery material do not have to have any specific geometrical shape, since is this is of secondary importance for the heat-dissipating properties. Preferably, the solid material has very small particle sizes, such as are produced, for example, by abrasion of the material. However, it is equally possible to use the heat -dissipating material as granules, the particles of which have a specific geometrical shape, for example a spherical shape.

Suitable as the material for a liquid heat transfer medium 6 are, inter alia, water, paraffin, benzy1toluene, biphenyl, terphenyl, silicone oils or the like, but also refrigerants, such as fully or partially halogenated hydrocarbons, such as for example methyl chloride, di- or trichlorofluoromethane or the like; or by a halogen-free refrigerant, such as for example sulphur dioxide, carbon dioxide or the like.

It may also be provided for a liquid or pasty heat transfer medium 6, which has thixotropic properties, to be used. This has the advantage that the heat sink 4 can be deformed very easily under the effect of mechanical forces and consequently be adapted to component groupings; in the state of rest, however, in other words while resting on components, it is to some extent fixed and consequently also protected against detachment from the components even when there are movements of the structural unit.

9 - Finally, it is also possible to use a gaseous heat transfer medium.

In the case of all the design variants described, there is obtained a "cushion- like" heat sink 4, which can easily be designed for a wide variety of component groupings. The foil may be produced from any desired materials; with a view to achieving good heat transfer from the components to be cooled to the heat transfer medium 6, it is favourable to use a material with good heat-conducting properties. Since the housings of electronic components 2, 3 generally consist of insulating plastic, it is quite possible to use a metal, such as for example copper or aluminium.

Figures 2a, b show a particularly preferred is embodiment of the invention. In this case, the casing 5 of the heat sink 4 according to the invention is made up of a plurality of, in this specific case two, pieces of foil 50, 51. The two pieces of foil 50, 51 have a rectangular shape, are cut such that they are congruent with respect to each other and are placed congruently one on top of the other. Along the length of their edges, they are connected in a sealed manner to one another. In the hollow space enclosed by the two pieces of foil 50, 51 there is, in analogy with the embodiment according to Fig. 1, a liquid, pasty, powder-, strip-, wire- or foilform solid or gaseous heat transfer medium 6.

The pieces of foil 50, 51 may be connected in various ways, such as for example by adhesive bonding; however, it is preferred for the pieces of foil 50, 51 to be welded to one another, because in this way the connection can be made particularly durable and sealed.

If the casing 5 is made up of a plurality of pieces of foil 50, 51, they may be produced from one and the same material and with the same strength properties, but it is also possible to use different materials or, by making the pieces of foil 50, 51 in different thicknesses, to give the individual pieces of foil 50, 51 different strength and deformation properties.

In this connection, the piece of foil 50 facing - the components 2, 3 could be made to be plastically deformable, in order to ensure that the heat sink 4 rests flat on the individual components 2, 3, whereas the piece of foil 51 is made to be elastically deformable, in other words resilient.

To increase the performance of the heat sink 4 according to the invention, i.e. the amount of heat removed by it per unit of time, various measures are conceivable, the most important of which are represented in Figs. 3-5 and are explained below.

According to the embodiment shown in Fig. 3, the casing 4 is provided with openings 41, 42, via which openings heat transfer medium 6 can be supplied and removed. In this case, there can expediently be set up a heat transfer medium circuit, in which the'heat transfer medium 6 heated by the components 2, 3 is removed via one opening 42, cooled and then returned to the heat sink 4 via the other opening 41.

The casing 4 of the embodiment according to Fig.

4 is made to be fluid-tight, but has a tubular attachment 43 and is filled only partially with a liquid heat transfer medium 6. In the case of this embodiment, the heat transfer medium 6 of the heat sink 4 is evaporated by the heat of the components 2, 3. This vapour rises into the tubular attachment 43, at the upper end of which it condenses - on account of the lower temperature prevailing there - and consequently gives off thermal energy.

Finally, a design of the invention corresponding to Fig. 5 is also conceivable, in which there is fixed on the casing 4 a solid body 44, possibly even a plurality of such bodies. These bodies 44, preferably made of a material with good heat-conducting properties, correspond in their action to the conventional rigid heat sinks, in other words on the one hand they store the heat supplied to them and on the other hand they also give it of f to the ambient atmosphere.

Even if not represented in separate drawings, any desired combinations of the measures last described for - 11 improving the heat removal are also possible. For example, a heat sink 4 provided with a solid body 44 could have openings 41, 42 for setting up a heat transfer medium circuit or be provided with a tubular attachment 43 which corresponds in its function to a "heat pipe".

It is often the case that an electronic device, such as for example computers, control equipment such as programmable controllers or the like, have to be made up of a multiplicity of electronic components. As represented in Fig. 6, in order to obtain a modular structure which is easy to maintain, in such cases it is often so that each of the assemblies is constructed on a separate circuit carrier 11, 12. The individual circuit carriers 11, 12 - so-called plug-in cards - are plugged onto a common breadboard 13 which bears the necessary connection lines between the assemblies, to be precise in such a way that they are mutually parallel. If it is necessary to cool the components 2, 3 of two neighbouring plug-in cards 11, 12, it is likewise possible to use for this a heat sink 4 according to the invention, as has been described up to now.

In connection with this area of use, however, the heat sink may also be designed in a way corresponding to Fig. 6 and be formed by a solid body 44 which is in plate form and has a first casing 5 and a further casing 51. Both casings 5, 51 are deformable and filled at least partially with a heat transfer medium 6 of the composition already described.

The body 44 in plate form may in this case serve as a separating layer between the two casings 5, 5', with the result that the heat transfer media 6 contained in the latter do not come into contact with each other. The said body may equally well be designed such that it is permeable to the heat transfer medium 6, and if appro- priate it may have openings for the supply and removal of heat transfer medium 6 or a central heat-pipe construction (tubular attachment 43).

If a solid material, in the form of flexible parts 7, is used as the heat transfer medium 6 - if appropriate in combination with a liquid -, the individual parts 7, in other words wires, strips, foils or the like, may be fixed in the way represented in Fig. 7a, b in the interior of the casing 5.

According to Fig. 7a, they are connected to the casing 5 by in each case one end 70, while their other end 71 is free and is supported resiliently on the section of the casing lying opposite their fixing point. In principle, the parts 7 may be fixed at any desired points of the casing 5, in other words either on the section of the casing resting on the components 2, 3 or else on the section of the casing at a distance away from the components 2, 3.

In this connection, a design according to Fig. 7b is also conceivable, in which the individual heat transfer media parts 7 are fixed on both sides on the inner wall of the casing. The flexibility of the individual parts 7 has the ef f ect that the heat sink 4 also remains deformable as a whole. of particular advan- tage in the case of this type of design is that there are continuous heat -dissipating paths through the entire heat sink 4.

Also in the case of a heat sink 4 designed according to Fig. 7 there may be provided a solid body 44 fixed on the casing 5; provision of a tubular attachment, or openings for the supply and removal of the heat transfer medium 6, is possible, as is a combination of a number of these measures.

Claims

PATENT CLAIMS

Heat sink for electrical or electronic components, characterized by a deformable casing (5), which is filled at least partially with a heat transfer medium (6).
2. Heat sink according to Claim 1, characterized in that the heat transfer medium (6) has a pasty consistency.
3. Heat sink according to Claim 1, characterized in that the heat transfer medium (6) has a liquid consistency.
4. Heat sink according to Claim 1, characterized in that the heat transfer medium (6) is formed by a solid material which is in the form of a multiplicity of is individual parts and preferably has good heat-conducting p roperties.
5. Heat sink according to Claim 4, characterized in that the solid material has a powdery consistency.
6. Heat sink according to Claim 5, characterized in that the particles of the solid, powdery material have the form of small beads.
7. Heat sink according to Claim 4, characterized in that the solid material is in the form of flexible parts 7, such as for example wires, strips, foils or the like.
8. Heat sink according to one of Claims 4 to 7, characterized in that the solid material is formed by a metal, such as for example copper, aluminium or the like.
9. Heat sink according to Claim 2 or 3, charac terized in that the liquid or pasty heat transfer medium (6) is mixed with a solid material in the form of a multiplicity of individual parts.
10. Heat sink according to one of Claims 2, 3 or 9, characterized in that the liquid heat transfer medium (6) is formed by water, paraffin, benzy1toluene, biphenyl, terphenyl, silicone oils or the like.
11. Heat sink according to one of Claims 2, 3 or 9, characterized in that the liquid heat transfer medium (6) is formed by a refrigerant, such as fully or partially halogenated hydrocarbons, such as for example methyl is chloride, di- or trichlorofluoromethane or the like; or by a halogen-free refrigerant, such as for example sulphur dioxide, carbon dioxide or the like.
12. Heat sink according to Claim 1, characterized in that the heat transfer medium (6) has a gaseous consistency.
13. Heat sink according to one of Claims 1 to 12, characterized in that the casing (5) is formed by a foil.
14. Heat sink according to Claim 13, characterized in that the casing (5) is made up of a plurality of pieces of foil (50, 51), which pieces of foil (50, 51) are connected to one another, preferably along the length of their edges.
15. Heat sink according to Claim 14, characterized in that the pieces of foil (50, 51) are welded to one another.
16. Heat sink according to Claim 13, 14 or 15, characterized in that the foil or the pieces of foil (50, 51) are formed fr ' om a material with good heat-conducting properties, preferably from a metal such as copper, aluminium or the like.
17. Heat sink according to one of Claims 13 to 16, characterized in that the casing (5) is formed by two pieces of foil (50, 51), which pieces of foil (50, 51) have, if appropriate, different strength properties from one another.
18. Heat sink according to Claim 17, characterized in that the first piece of foil (50) is plastically deformable and the second piece of foil (51) is elastically deformable.
19. Heat sink according to one of Claims 4 to 18, the heat transfer medium (6) having solid material in the form of flexible parts (7), characterized in that the flexible parts (7), such as for example wires, strips, foils or the like, are fixed in each case by at least one end (70) on the inner side of the casing (5).
20. Heat sink according to one of Claims 1 to 19, characterized in that the casing (5) has openings (41, 42), via which openings (41, 42) heat transfer medium (6) - is can be supplied and removed.
21. Heat sink according to one of Claims 3, 9, 10, 11 or 13-19, characterized in that the casing (5) has at least one tubular attachment (43), in which attachment (43) evaporated heat transfer medium (6) can condense.
22. Heat sink according to one of Claims 1 to 21, characterized in that at least one solid body (44) is fixed on the casing (5).
23. Heat sink according to Claim 22, characterized in that, in addition to the casing (5), there is fixed on the solid body (44) at least one further deformable casing W), filled at least partially with a heat transfer medium (6).