TECHNICAL FIELD

The present invention relates to a casing for electronics equipment comprising a base arranged for receiving at least one printed circuit board with at least one electronics component in a component housing which is to be cooled, and a cover, which is to be fastened to the base over the printed circuit board, the base comprising a heat sink for cooling of the component housing on the printed circuit board.

BACKGROUND OF THE INVENTION

Heat sinks are used for cooling purposes in different applications such as, e.g., in cooling of electronics components arranged in component housings mounted onto printed circuit boards (PCB) lodged inside a casing. The printed circuit board is usually arranged flatly against a bottom of a base of the casing, the heat sink in the form of cooling fins being integral with the base, and a cover is then screwed onto the base.

The base of the casing is arranged to conduct heat to the cooling fins, a thermally conductive gap filler usually having been applied between the base and a lower side of the PCB onto which the housings with all the electronics components are mounted, and heat generated by the electronics components are dissipated to the cooling fins via the base and the filler. In order to provide a sufficient thermal contact the PCB has to be pressed firmly against the base.

As stated above the PCB has to be held pressed against the base in order to get a sufficient thermal contact. The cover and possibly also the base usually comprise side walls. The cover is arranged to be screwed onto the base so that a peripheral wall on the cover comes into contact with the base, to provide for water tightness and proper electromagnetic shielding while at the same time the PCB is thereby pressed against the base. The total height of the PCB, the component housings on the PCB and the thermally conductive gap filler should be slightly greater than the distance between the base and the cover to provide a suitable compression of the thermally conductive gap filler. However, due to the tolerances in manufacture of the base and the cover and due to the tolerances in the mounting of the PCB on the base it is difficult to achieve the appropriate relationship between the heights. This may result in the breakage of the component housing when the height of the walls of the cover and/or the base plate are too low in relation to the total height of the PCB, the component housing and the thermally conductive gap filler. Alternatively it may result in inferior thermal contact between the base and the component casing when the walls of the cover and/or the base plate are too high in relation to the total height of the PCB, the component casing and the thermally conductive gap filler.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a casing with a heat sink, which casing is an alternative to the casings of the prior art. In particular, the invention allows for tolerances without compromising the required electromagnetic shielding in relation to the outside of the casing, whilst at the same time accumulation of condensed water in the outside air is prevented or limited, making the casing highly suitable in environments at sea, such as for off-shore wind turbines. This is achieved through a casing for electronics equipment and with an integrated heat sink, comprising a base, a cover and at least one printed circuit board having electronics components mounted thereon, the base including raised portions, such as plateaus, supporting sectors or areas of the printed circuit board and configured for dissipating heat energy to the heat sink. Preferably, at least one clamping element is arranged between the base and the cover and applies a pressure against the raised portions via the printed circuit board, to fix the latter and to ensure reliable heat conduction between the printed circuit board and the heat sink. This is of particular advantage when the printed circuit board has a first side and a second, opposite side, with electronics components being mounted onto both sides, the bottom of the base defining together with a peripheral wall of the base a compartment for receiving the electronics components mounted on the second side, wherein electronics components mounted onto the first side and presenting a relatively high cooling requirement are located on the printed circuit board opposite or near the raised portions. The cover includes a peripheral wall, with a peripheral tortuous or labyrinthic ventilating gap, i.e. a gap presenting turns, such as a zig-zag course, running between edges of the peripheral walls of the base and the cover. This involves advantages in principle achievable independently of the use of the aforementioned clamping device and/or compartment in allowing for ventilation of the interior of the casing to prevent build-up of any condensed water in the air, while at the same time being so narrow that water that may splash onto the casing, as might happen when used in off-shore installations, will not readily flow into the interior of the casing. Even so, due to the edge portions overlapping, a sufficient electromagnetic shielding is provided.

An advantage of the invention is that the combination of the raised portions of the base or cover and the labyrinth gap, allows for few points with high tolerances, i.e. only the raised portions have be at a very specific height in respect of where the PCB is arranged in the casing. The distance between the labyrinth gap is defined by the tolerance of the metal casting process.

Solutions of the prior art requires rubber seals or very fine tooling of the contact edges of the walls to ensure good contact. Especially in respect of EMC compli- ance.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following an embodiment of the invention will be described in more detail with reference to the drawings, wherein :

FIG. 1 is a view showing two parts of a heat sink casing of the present invention for electronics components,

FIG. 2 shows a top view of the base of the casing,

FIG. 3 shows a bottom view of the base of the casing, FIG. 4 shows a clamping device for fixing PCB's inside the casing, as seen from the side,

FIG. 5 is a cross-sectional view of the assembled casing, and

FIG. 6, is an enlarged detailed view of FIG. 5, in the area of the joint between the base and the cover along one side of the casing.

DESCRIPTION OF EMBODIMENTS

In fig. 1 reference numeral 1 generally designates a casing for electronic equipment, comprising a base 20 and a cover 30. The base 20 is shaped as a tray and is adapted for receiving at least one printed circuit board (PCB) 2 supporting a variety of electronic components 4.

In fig. 1 a first, upper side of a first PCB 2 received in the base 20 is visible; a first plurality of electronics components 4 are mounted onto this first side while a sec- ond plurality of electronics components 4' are mounted onto the opposite second side of the PCB 2. The shown PCB 2 has dimensions corresponding essentially to the length and width of the base 20; the electronics components 4 generally are contained in housings and project to some extent from the surface of the PCB 2. The cover 30 generally has a peripheral wall 31 and may in a first embodiment shown in fig. 1 have a multiplicity of cooling fins 33. Adjoining the peripheral wall 31 of the cover 30 are corner portions 6, 6', each with a through-going threaded bore for receiving a respective screw cooperating with similar corner portions 5, 5' adjoining a first peripheral wall 24 of the base 20. The base 20 also have another, second peripheral wall 28. In the shown embodiment base 20 corner portions referred to by numeral 5' will bear against corner portions 6' of the cover 30 when the cover 30 is secured in place on top of the base 30 to enclose the PCB 2 within the casing 1.

Fig. 1 shows a surface identified by numerals 3 and 32. It will be understood that the cover 30 has a bottom 32 integrally connected with the peripheral wall 31 and optionally carrying the aforementioned cooling fins 33. In some embodiments of the invention the cover 30 provided with such cooling fins 33 may include features as described below in relation to the base 20, in which case the surface visible in fig. 1 would represent a further, second PCB 3 positioned essentially parallel with the bottom 32 of the cover 30, thus hiding the aforementioned features of the base 20 to be discussed below.

Turning now to fig. 2 the inside of the base 20 is shown more clearly in that the first PCB 2 has not yet been put into place. Shown is the bottom 22 of the base 20, the first peripheral wall 24, the second peripheral wall 28 and a peripheral plateau 25 between the first wall 24 and the second wall 28. The first and second walls 24, 28 extend in a direction generally upwards from the bottom 22 while the plateau 25 has a face generally parallel with the bottom 22 but located at a height above the bottom 22. It will be understood that the base 20, and normally also the cover 30, are made of a thermally conductive material, to allow the casing 1 to act as a heat sink to dissipate, by direct contact between the PCB 2 and the base 20, heat generated by the electronics components 4, 4' during operation of the electronics equipment.

As mentioned above, the PCB 2 generally has electronics components 4, 4' mounted onto its first and opposite second side. With the invention the PCB 2 will normally not bear against the bottom 22 of the base 20 for the purpose of dissipating heat through direct contact. Rather, with the invention the base 20 has raised contact faces, arranged raised above the level of the bottom 22, and defining a recess or compartment C (see fig. 5).

Preferably, electronics components 4 generating little or relatively low heat and, hence, presenting a relatively low cooling requirement, are mounted onto the sec- ond, lower side of the PCB 2, and are received in this compartment C. On the other hand, electronics components generating relatively much heat energy and consequently presenting a relatively large cooling requirement are mounted onto the opposite side of the PCB 2.

The contact faces referred to above are in the shown embodiment comprised by the aforementioned peripheral plateau 25 as well as a further plateau 29 defined by a raised structure integral with the bottom 22. Additional such further plateaus 29 may be included as required. The raised contact faces, represented by the plateaus 25, 29, contact or touch areas or sectors of the second, lower side of the PCB 2 for direct heat transfer from the PCB 2 to a series of cooling fins 23 that are integral with the bottom 22 of the base 20 and that extend on the outside of the casing 1, see fig. 3. In this way the compartment C delimited by the second peripheral wall 28 receives those electronics components that are mounted onto the second, lower side of the PCB, the extension or height of the second peripheral 28 above the bottom 22 preferably being selected such that there is a gap between those electronics components and the face of the bottom 22, to avoid damage to those electronics components when the casing 1 is assembled in the manner discussed further below.

The PCB 2 and/or the base 20 is/are designed such that aforementioned areas or sectors include, mounted onto the first, upper side of the PCB 2, the aforemen- tioned electronics components presenting a high cooling requirement. Since in the shown embodiment direct heat transfer may take place to the peripheral plateau 25 running along the first peripheral wall 24, electronics components 4 requiring efficient cooling may advantageously be mounted onto the PCB 2 along the periphery thereof, which periphery contacts the aforementioned peripheral plateau 25. Where, for circuitry reasons, such heat generating electronics components 4 need to be located at other places on the PCB 2 the latter components may either be arranged on the PCB 2 where the further plateaus 29 are located, or the base 20 may be designed such that the further plateaus 29 is/are located in accordance with the location of such heat generating components. It will be understood that the base 20 preferably is a one piece item, molded or cast of a thermally conductive material, such as metal, with the aforementioned plateaus 25, 29 for direct heat transfer with the PCB 2; it may sometimes be de- sirable to additionally include a thermally conductive, but electrically non- conductive, gap filler between the PCB 2 and the plateaus 25, 29.

In an embodiment the contact surface of the plateaus 25, 29 are prepared with a mechanical tool after the metal casting. The reason for the tooling can be to en- sure a smooth contact surface to ensure high thermal conductivity to the electronics components 4 and/or to adjust the height of the plateaus 25, 29 in order to maintain the tolerances of the labyrinth ventilating gap (9).

An advantage of the above mentioned embodiment is that the same base and cover can be used for different PCB layouts, as a variation in the component height is compensated by the tooling of the height of the plateaus 25, 29. In order to secure the PCB 2 in position pressed tightly against the plateaus 25, 29, a number of clamping devices 40 may be used, acting to clamp the PCB 2 against the plateaus 25, 29. In the preferred embodiment the clamping device 40, shown in fig. 4, is an elongated metal strip 41 with bent flanges 43 having cut out raised and spaced apart legs 45 that will yield and bend towards the metal strip 41 when a force is applied onto the raised portion 45 in a direction parallel with the plane of the metal strip 41 and perpendicular to its length. The clamping device 40 is placed with its legs 45 bearing against predetermined areas of the PCB 2, such as along the periphery of the PCB 2, between or adjacent any electronics compo- nents mounted along the periphery of the PCB 2. Another such clamping device 40 may be arranged to contact central areas of the PCB 2, such as where electronics components are located that require cooling by contact with the central plateau 29.

It is foreseen that the clamping device(s) 40 may be guided by guides (not shown), such as slits, in the first peripheral wall 25 receiving the ends of the clamping device(s) 40. Establishing the clamping force on the PCB 2 holding it firmly against the plateaus 25, 29 follows when the cover 30 is applied on top of the base 20, with the clamping device 40, eg. the legs 45 as the case may be, contacting also the bottom 32 thereof, or contacting any other, second PBC 3 re- ceived in the cover 30 if designed to receive such a further PCB 3. The clamping device(s) 40 thus effectively are sandwiched between the PCB 2 and the bottom 32 of the cover 30 or any second PCB 3 received in the cover 30, such as in a case where the cover 30 is designed in accordance with the principles discussed above in relation to the base 20. The clamping force is maintained as the base 20 and the cover 30 are connected by screws applied to the respective corner portions 5, 5', 6, 6'.

Fig. 5 shows a cross-sectional view of the casing 1 with the base 20 and cover 30 joined. The drawings shows also clearly the compartment C that receives those electronics components 4 generating little or less heat energy being mounted onto the second or lower side L of the PCB 2. Other electronics components 4" that generate large amounts of energy that needs to be dissipated by the cooling fins 23 are mounted on the first, upper side of the PCB 2. As can be seen the latter electronics components 4" are mounted onto the first upper side of the PCB 2 in or adjoining those areas of the PCB 2 that contact the raised plateaus 25, 29, directly or via a thermally conductive filler, including areas along the periphery of the PCB 2 between those regions where the spaced apart legs 45 of the clamping device 40 contact the peripheral edge of the PCB 2 for the purpose of pressing the PCB 2 against the plateau 25. Pressing the second lower side L of the PCB 2 against the plateau 25 results from the legs 45 being compressed or deflected inside the casing 1 on assembling the cover 30 and base 20. Other types of clamping elements 40, such as spiral springs, may also be envisaged.

Fig. 5 also shows a peripheral labyrinth gap, i.e. a gap presenting turns, prefera- bly being defined between the edges of the peripheral walls 24, 31 of the base 20 and the cover 30, respectively, that remains when the cover 30 and the base 20 have been assembled by means of the aforementioned screws, i.e. with the respective corner portions 5, 5', 6, 6' bearing tightly against each other. The gap 9 is shown in better details in fig. 6 which shows how the peripherals walls 24, 31 conveniently have offset edge portions 31', 24' overlapping in the direction from the inside to the ouside of the casing 1, such that the labyrinth gap 9 will appear; the peripheral gap 9 preferably has a minimum width W in the order of about 0.45 mm, preferably in the range of 0.45 - 1.00 mm.

The labyrinth gap 9 allows for ventilation of the interior of the casing to prevent build-up of any condensed water in the air, and at the same time - by not being direct, i.e. by presenting turns, - reduces the risk that water that may splash onto the casing 1, as might happen when used in off-shore installations, will readily flow into the interior of the casing. Even so, due to the edge portions 24', 31' overlapping a sufficient electromagnetic shielding is provided. The skilled person will understand that the gap 9 does not need to run along the entire periphery of the base 20.

Throughout this application it is understood that the wordings tortuous gap and labyrinth gap have the same meaning and are thus interchangeable.