Patent Description:
In many areas, for example within the field of telecommunications, components may require thermal cooling. This may for example be the case for components in a network access node for a wireless communication system, such as for example a base station. Thermal cooling involves a transfer of heat from the module or component to be cooled, e.g. to the ambient or to another module or component, such as an electrical active cooling device or a passive heat sink. A passive heat sink does not require electric power to transfer heat. In general, a heat sink may be seen as a passive heat exchanger configured to transfer heat from a heat-producing component to another medium, such as air or any other fluid medium, for example a liquid. A heat sink can, for example, release the received heat partly or entirely to the ambient via cooling fins of a fin structure. Between the module or component to be cooled and an active cooling device or a heat sink, there may be structures and thermally insulating air gaps which impair the heat transfer to the active cooling device or heat sink.

<CIT> discloses a thermal-transfer assembly including a first transfer module having a plurality of first projections. The first projections are spaced apart from one another to form corresponding gaps therebetween. The thermal-transfer assembly also includes a second transfer module having a plurality of second projections. The second projections are spaced apart from one another to form corresponding gaps therebetween. The first and second transfer modules interface with each other in a mated arrangement. The first and second projections project in opposite directions along a Z-axis and intimately engage one another to transfer thermal energy therebetween. The thermal-transfer assembly also includes an assembly clip coupled to and configured to engage each of the first and second transfer modules. The assembly clip prevents the first and second transfer modules from separating along the Z-axis and/or biases the first and second transfer modules away from each other along the Z-axis.

<CIT> discloses a cooling device of a multi-chip module having micropackages that are independent of thermal deformation and easy to assembly and disassembly. The multi-chip module includes a multi-layer substrate on which the micropackages, each encasing an LSI chip, are mounted, and a housing formed integrally with a cooler. Each of the micropackages includes a first heat conduction member, having a cap portion for receiving the LSI chip and a first fin made of the same material as the cap portion to be integral therewith, and a substrate fixed to the cap portion of the first heat conduction member while being fixedly joined at the back surface thereof to an inner surface of the cap portion of the first heat conduction member. Second heat conduction members, each including a base portion and a second fin, are disposed to engage with the first fins and be pressed against the cooler by a spring, respectively.

<CIT> discloses a thermal conducting device that removes heat from a power dissipating device installed within a case, and includes a base coupled to the power dissipating device and a translational portion that is movable in a vertical dimension. The translational portion couples at an upper surface to the inner surface of the case panel. A cavity and piston in the base and the translating portion may provide complementary guide surfaces to constrain movement of the translational portion generally to a vertical dimension. A biasing element may urge the translational portion upward. The translational portion and the external panel may allow movement of their respective surfaces relative to one another. The cavity may include a port allowing air to pass into and out of the cavity. The upper surface of the translational portion may be tiltable with respect to the base. An adhesive layer may couple the base and the power dissipating device.

<CIT> discloses a variable expansion type cooling apparatus comprising: a heating element contact part contacting a heating element; a cooling element contact part contacting a cooling element; a heat transfer part, provided between the heating element contact part and the cooling element contact part, for transmitting heat of the heating element contact part to the cooling element contact part; and a shock absorbing part, provided between the heating element contact part and the cooling element contact part, for dampening an impact applied to the cooling element contact part which is transmitted to the heating element by an elastic force, wherein the heat transfer part is configured such that a plurality of heat transfer posts provide in one of the heating element contact part and the cooling element contact part is inserted into and contacts the other of the heating element contact part and the cooling element contact part to transmit heat, and the cooling element contact part is brought into contact with an inner wall of an external cooling element.

<CIT> discloses a cooling device for cooling at least one pluggable module each having a pluggable component and a frame for accommodating the pluggable component, the frame having an opening on a top wall thereof. The cooling device comprises at least one thermal conductive block, a heat radiator and a resilient thermal conductive pad. The resilient thermal conductive pad being adapted to be in a substantially released position when the pluggable component is decoupled from the frame and substantially biased when the pluggable component is inserted into the frame thus exerting a biasing force on the thermal conductive block and the heat radiator whereby the thermal conductive block is pressed through the opening of the frame into direct thermal contact with the pluggable element of the pluggable module for conducting the heat generated by the pluggable component to the heat radiator through the thermal conductive block and the resilient thermal conductive pad.

An object of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

According to a first aspect of the invention, the above-mentioned and other objects are achieved with a device for transferring heat between a first module and a second module, the device comprising:.

An advantage of the device according to the first aspect is that the plurality of protrusions and the plurality of cavities of the first unit and the second unit, respectively, increase the surface area of the first unit and the second unit. Thereby, the thermal coupling between the first unit and the second unit can be improved such that an efficient heat transfer between the first module and the second module can be provided. When the second module is a heat-generating module, the thermal coupling between the first unit and second unit provides an efficient heat transfer from the second module to the first module and hence an efficient cooling of the second module. The biasing apparatus ensures a suitable contact pressure for good thermal transfer between the second module and the second unit. The biasing apparatus may comprise an elastic element or a resilient element (e.g. a spring) and may therefore be referred to herein also as a spring element or resilient element. An advantage of the device according to the first aspect is that the heat transfer between the second module and the first module is improved. Consequently, an improved heat dissipation is provided.

In an implementation form of a device according to the first aspect, each contact surface has a first extension which extends in the first direction. An advantage with this implementation form is that the contact surfaces of the plurality of protrusions and the contact surfaces of the plurality of cavities extend in the direction in which the second unit moves. Thus, a distance between the contact surfaces facing each other can be maintained when the second unit moves between relative to the first unit. Thereby, a good thermal coupling between the first unit and the second unit is ensured.

In an implementation form of a device according to the first aspect, each protrusion of the plurality of protrusions is shaped as a cylinder. An advantage with this implementation form is that the plurality of protrusions is easy and inexpensive to manufacture.

In an implementation form of a device according to the first aspect, the inner surface of each cavity of the plurality of cavities matches the protrusion shaped as a cylinder which engages the cavity. An advantage with this implementation form is that each cavity easily engages with its respective protrusion and that the heat transfer area between each cavity and its respective protrusion can be increased. Thereby, the thermal coupling between the first unit and the second unit can provide an efficient heat transfer between the first module and the second module.

In an implementation form of a device according to the first aspect, each cavity of the plurality of cavities is a recess. The recess may have a bottom section. An advantage with this implementation form is that the plurality of cavities is easy and inexpensive to manufacture. Alternatively, the cavity may be a through-hole.

In an implementation form of a device according to the first aspect, the plurality of protrusions comprises at least five protrusions and the plurality of cavities comprises at least five cavities. An advantage with this implementation form is that the increase of the surface area of the first unit and the second unit is such that the heat transfer between the first module and the second module can be increased.

In an implementation form of a device according to the first aspect, the first unit is configured to be fixed in relation to the first module. "Fixed in relation to the first module" in the context of this embodiment means that the first unit is stationary in relation to the first module, i.e. the first unit does not move relative to the first module. An advantage with this implementation form is that a good thermal coupling between the first unit and the first module can be provided.

In an implementation form of a device according to the first aspect, the first unit is configured to be connected the first module. The first unit may be configured to be connected to the first module by being configured to be attached to the first module or by being configured to be formed integrally with the first module, i.e. formed as a unit with the first module. An advantage with this implementation form is a flexible design of the first unit and the first module.

In an implementation form of a device according to the first aspect, there is a gap between at least a portion of the contact surface of each cavity of the plurality of cavities and at least a portion of the contact surface of the protrusion of the plurality of protrusions which engages the cavity. An advantage with this implementation form is that manufacturing variances with regard to the plurality of cavities and the engaging plurality of protrusions can be handled.

In an implementation form of a device according to the first aspect, each cavity of the plurality of cavities holds a thermally conductive grease. An advantage with this implementation form is that the thermal resistance between the first unit and the second unit can be further reduced. Thereby, the thermal coupling between the first unit and the second unit is improved and hence the heat transfer between the first module and the second module is improved.

In an implementation form of a device according to the first aspect, the biasing apparatus comprises any one from the group comprising: a spring and a gasket. An advantage with this implementation form is that the biasing apparatus can be implemented by using standard components which are reliable and inexpensive.

In an implementation form of a device according to the first aspect, the holder comprises a compartment configured to receive and hold the second module. The compartment may further be configured to receive and hold the second module detachably.

In an implementation form of a device according to the first aspect, the device comprises a housing, which houses the compartment, and a printed circuit board, to which the housing is attached, wherein the compartment has a first opening for receiving the second module, the second module being connectable to the printed circuit board, wherein the compartment has a second opening, and wherein the second unit comprises a projection/boss, the projection being configured to engage the second opening and abut against the second module placed in the compartment. The embodiments of the device according to the invention are especially advantageous for such an implementation. Conventionally, an interface comprising a metal housing is often used for connecting a signal cable to a printed circuit board via a second module, for example a transceiver module, held by a compartment in the housing. By the second opening and embodiments of the device according to the present invention, an improved heat transfer is provided between the second module and the second unit for reasons mentioned above.

In an implementation form of a device according to the first aspect, the second unit covers the second opening. A second opening in the compartment could increase the risk of electromagnetic interference, EMI, leakage from the second module, for example the transceiver module, and from a connector electrically connecting the transceiver module to the printed circuit board. The electromagnetic interference leakage could for example influence an antenna nearby. Further, a second opening in the compartment could increase the risk of interference caused by signals from an antenna nearby or from other electrical components. However, when the second unit covers the second opening, electromagnetic interference shielding is provided. Thus, an improved heat transfer can be provided between the second module and the first module without an increased risk of electromagnetic interference leakage.

In an implementation form of a device according to the first aspect, the holder is configured to hold a second module which is a transceiver module to which a signal cable is connectable. The transceiver module is mechanically connectable to the signal cable. When the signal cable is connected to the transceiver module, a signal connection is provided between the transceiver module and signal cable, i.e. a connection through which signal transmission is possible. The transceiver module may in turn be electrically connectable or connected to a printed circuit board, PCB. The transceiver module may be an optical transceiver module and the signal cable may be an optical signal cable, for example an optical fibre cable. When in use, an optical transceiver module produces a substantial amount of heat which should be dissipated or transferred away from the optical transceiver module, and also away from a printed circuit board located close to the transceiver module. The heat is produced when the optical transceiver module converts optical signals to electrical signals. The electrical signals are then transmitted to the printed circuit board. Thus, for applications where the second module is a transceiver module, for example an optical transceiver module, the embodiments of the device according to the invention are especially advantageous.

In an implementation form of a device according to the first aspect, the holder is configured to receive and hold a second module which is any module from the group comprising: a small form-factor pluggable, SFP, module and a quad small form-factor pluggable, QSFP, module. An advantage with this implementation form is that a flexible mechanical connection for the second module is provided involving the known concepts SFP and QSFP.

According to a second aspect of the invention, the above mentioned and other objects are achieved with an arrangement for cooling a second module, the arrangement comprises the device according to any one of the appended claims <NUM> to <NUM> and the first module which comprises a heat sink.

An advantage of the arrangement according to the second aspect is that an improved heat transfer between a second module placed in the holder of the device and the first module in the form of a heat sink is provided. Further advantages correspond to the advantages of the device and its embodiments mentioned above or below.

In an implementation form of an arrangement according to the second aspect, the arrangement comprises the second module.

According to a third aspect of the invention, the above mentioned and other objects are achieved with a network access node, which may comprise a base station, for a wireless communication system, wherein the network access node comprises a device or an arrangement according to any of the above- or below-mentioned embodiments. Advantages of the network access node correspond to the advantages of the device and the arrangement and their embodiments mentioned above or below. The network access node may comprise a base station.

In order to cool a module, for example an electrical component, an electrical active cooling device or a passive heat sink may be used. The use of an electrical active cooling device to cool the module has the disadvantage that the electrical active cooling device consumes power to lower the temperature. This leads to high costs and to the generation of heat load in other parts or components close to the module.

Another disadvantage with conventional cooling is that air gaps may be present between the module to be cooled and the electrical active cooling device or the passive heat sink. Air gaps introduces high thermal resistance and makes it more difficult to cool the module. In order to avoid air gaps a thermally conductive filling material, which provide and facilitate the heat transfer, may be placed between the module to be cooled and the active cooling device or the passive heat sink. Conventional thermal interface materials are resilient to a certain extent to be able to expand and fill the air gaps but may lose their resilient character completely or to some degree after some time in a compressed state. Thus, the thermal interface material may for example not properly expand and fill the air gaps when the module is removed and replaced or reintroduced after inspection. This leads to thermally insulating air gaps which reduces the heat transfer between the module and the electrical active cooling device or the passive heat sink. There may hence be a temperature increase in the module, which results in an increased risk of overheating and a shortened lifetime of the module.

According to embodiments of the invention, a device for transferring or conducting heat between a first module and a second module is disclosed. The device improves the heat transfer between the first module and the second module and can address manufacturing variances with regard to the first module and the second module. The device further maintains its flexibility over time.

<FIG> schematically illustrates a device <NUM> for transferring or conducting heat between a first module <NUM> and a second module <NUM> according to an embodiment of the invention. In the embodiment shown in <FIG>, the second module <NUM> is a heat-generating module and the device <NUM> hence transfers heat from the second module <NUM> to the first module <NUM>. The device <NUM> comprises a holder <NUM> for holding the second module <NUM>. Further, the device <NUM> includes a first unit <NUM> configured to be thermally coupled to the first module <NUM>. By thermal coupling is meant that there is a heat transfer between the first unit <NUM> and the first module <NUM>, or in other words, that there is a heat-conducting communication between the first unit <NUM> and the first module <NUM>. The first unit <NUM> may be thermally coupled to the first module <NUM>, for example through direct physical abutment or via additional thermally conductive material.

In embodiments of the device <NUM>, the first unit <NUM> is configured to be fixed, i.e. stationary, in relation to the first module <NUM> such that the first unit <NUM> does not move relative to the first module <NUM>. The first unit <NUM> may further be configured to be connected to the first module <NUM>. The first unit <NUM> may be connected/attached to the first module <NUM> by using for example a mechanical fastening means or an adhesive. Alternatively, the first unit <NUM> may be integral with the first module <NUM>, i.e. formed as a unit with the first module <NUM>. When the first unit <NUM> is attached to the first module <NUM>, a thermal interface material, TIM, may be arranged between the first unit <NUM> and the first module <NUM> to further reduce thermal resistance between them.

The device <NUM> further comprises a second unit <NUM>. The first unit <NUM> and the second unit <NUM> are thermally coupled to one another, i.e. there is a heat transfer between the first unit <NUM> and the second unit <NUM>. The second unit <NUM> is movable in a first direction D1 in relation to the first unit <NUM> and the holder <NUM>, and also in relation to the first module <NUM>. With reference to <FIG>, the second unit <NUM> may be arranged between the first unit <NUM> and the holder <NUM> such that the second unit <NUM> moves in the first direction D1 between the first unit <NUM> and the holder <NUM>. Thus, the second unit <NUM> may move in the first direction D1 both towards the first unit <NUM> and towards the holder <NUM>.

In the embodiment shown in <FIG>, a fastening means <NUM> is configured to connect/attach the first unit <NUM> and the second unit <NUM> to each other. The connection provided by the fastening means <NUM> is such that it allows the second unit <NUM> to move in the first direction D1 in relation to the first unit <NUM> and the holder <NUM>. However, in alternative embodiments, the first unit <NUM> and the second unit <NUM> may instead be thermally coupled without being connected/attached with a fastening means.

With reference to <FIG>, the device <NUM> further comprises a biasing apparatus <NUM> for urging the second unit <NUM> away from the first unit <NUM>, thereby urging the second unit <NUM> against the second module <NUM> placed in the holder <NUM>. When the biasing apparatus <NUM> urges the second unit <NUM> away from the first unit <NUM>, the second unit <NUM> is moved in the first direction D1 towards the second module <NUM> placed in the holder <NUM> such that the second unit <NUM> abuts the second module <NUM>. The second unit <NUM> is hence thermally coupled to the second module <NUM>, when the second module <NUM> is held in the holder <NUM>. The second unit <NUM> may be thermally coupled to the second module <NUM> through direct physical abutment or via additional thermally conductive material.

One of the first and second units <NUM>, <NUM> comprises a plurality of protrusions <NUM> and the other one of the first and second units <NUM>, <NUM> comprises a plurality of cavities <NUM>. In the embodiment shown in <FIG>, the first unit <NUM> comprises the plurality of cavities <NUM>, and the second unit <NUM> comprises the plurality of protrusions <NUM>. However, in alternative embodiments, the second unit <NUM> may include the plurality of cavities <NUM>, and the first unit <NUM> may include the plurality of protrusions <NUM>. Furthermore, each of the first unit <NUM> and the second unit <NUM>, may in alternative embodiments comprise both a plurality of protrusions <NUM> and a plurality of cavities <NUM>.

Each cavity <NUM> of the plurality of cavities <NUM> is complementary to one of the plurality of protrusions <NUM> and each protrusion <NUM> of the plurality of protrusions <NUM> engages one of the plurality of cavities <NUM>. This allows each protrusion <NUM> to fit into a complementary cavity <NUM>, as illustrated in <FIG>. Furthermore, each protrusion <NUM> of the plurality of protrusions <NUM> has a contact surface, and each cavity <NUM> of the plurality of cavities <NUM> has a contact surface. The contact surface of each protrusion <NUM> of the plurality of protrusions <NUM> faces the contact surface of one the plurality of cavities <NUM>. Each contact surface has a first extension which extends in the first direction D1. Thus, when the second unit <NUM> moves in the first direction D1 between the first unit <NUM> and the holder <NUM>, the plurality of protrusions <NUM> may move within their respective cavity <NUM> with the contact surface of each protrusion <NUM> still facing the contact surface of the engaged cavity <NUM>.

The plurality of protrusions <NUM> and the plurality of cavities <NUM> increases the surface area of the first unit <NUM> and the second unit <NUM>, respectively, making it possible to increase a thermal interface area between the first unit <NUM> and the second unit <NUM>. The thermal interface area comprises the area where the first unit <NUM> and the second unit <NUM> essentially abut or are in contact with each other, i.e. comprises the contact surfaces of the plurality of protrusions <NUM> facing the contact surfaces of the plurality of cavities <NUM>. Hence, the size of the thermal interface area depends on the circumference of the protrusions <NUM>, the length of the contact surfaces and the number of engaging protrusion <NUM> and cavity <NUM> pairs. The thermal interface area can thus be adjusted by adapting the shape and number of protrusions <NUM> and cavities <NUM>. Since the heat transfer between the first unit <NUM> and the second unit <NUM> depends on the thermal interface area, the shape and number of protrusions <NUM> and cavities <NUM> affect the heat transfer capability of the device <NUM>. Thus, by adjusting the shape and number of protrusions <NUM> and cavities <NUM>, the heat transfer capability of the device <NUM> can be adapted to different applications and heat loads to be transferred.

In embodiments, the plurality of protrusions <NUM> comprises at least five protrusions <NUM>, and the plurality of cavities <NUM> comprises at least five cavities <NUM>. The plurality of protrusions <NUM> and the plurality of cavities <NUM> may however in some embodiments comprise any one of at least ten, at least twenty, at least fifty, at least one hundred, at least two hundred or more protrusions <NUM> and cavities <NUM>, respectively.

According to embodiments of the invention, each protrusion <NUM> of the plurality of protrusions <NUM> may be shaped as a cylinder. With reference to <FIG>, each protrusion <NUM> may for example be a pin/finger with a right circular cylinder shape. In other words, each protrusion <NUM> may have the same circular cross-section over the height of the protrusion <NUM> and extend essentially perpendicular from the first or second unit <NUM>, <NUM>. Each protrusion <NUM> may further be solid or hollow. The plurality of protrusions <NUM> may be arranged in rows, where the rows may comprise the same or a different number of protrusions <NUM>, or in other formations.

The shape of each cavity <NUM> matches the shape of the protrusion <NUM> with which the cavity <NUM> engages such that the protrusion <NUM> can fit into the cavity <NUM>. Each cavity <NUM> of the plurality of cavities <NUM> may be a recess arranged to receive the engaging protrusion <NUM>. The recess may have a bottom section. Alternatively, each cavity <NUM> of the plurality of cavities <NUM> may be a through-hole. In embodiments where each protrusion <NUM> of the plurality of protrusions <NUM> is shaped as a cylinder, the inner surface of each cavity <NUM> of the plurality of cavities <NUM> matches the protrusion <NUM> shaped as a cylinder which engages the cavity <NUM>. The plurality of cavities <NUM> may hence be recesses/holes with an inner shape of a cylinder. For example, each cavity <NUM> may have a right circular cylinder shape dimensioned to engage with a protrusion <NUM> with a right circular cylinder shape, such as the one shown in <FIG>. The diameter of the cavity <NUM> may be slightly larger than the diameter of the protrusion <NUM> so that the protrusion <NUM> can move within the engaged cavity <NUM>. For example, this allows the protrusion <NUM> to move in the first direction D1 and take different positions in the engaged cavity <NUM>.

The increased surface area of the first unit <NUM> and the second unit <NUM> can also be achieved with protrusions <NUM> and cavities <NUM> of other shapes than the above described. The protrusions <NUM> and cavities <NUM> may for example have a cylinder shape with a triangular, rectangular, or polygonal cross-section. Alternatively, the protrusions <NUM> and cavities <NUM> may have a conical shape with a circular, triangular, rectangular or polygonal base. Furthermore, each of the protrusions <NUM> may have an extended flat shape, for example be a longitudinal fin extending over at least a part of the length of the first or second unit <NUM>, <NUM>. Each cavity <NUM> may in this case comprise the recess between two longitudinal fins extending over at least a part of the length of the other of the first or second unit <NUM>, <NUM>. The fins may be formed with different geometrical shapes, for example be rectangular or have a rounded form.

The plurality of protrusions <NUM> and the plurality of cavities <NUM> of the first and second units <NUM>, <NUM> may be manufactured by using any one of: cold forging, casting, machining, drilling, 3D-printing, extruding, and press fitting. The plurality of protrusions <NUM> and the plurality of cavities <NUM> may for example be made of aluminum, copper, zinc, graphite or other conductive materials.

The dimension of the plurality of protrusions <NUM> and the plurality of cavities <NUM> may vary depending on for example the application of the device <NUM> and the heat load generated by the second module <NUM>. The height of the protrusions <NUM> and the depth of the cavities <NUM> may be selected such that at least a part of each protrusion <NUM> stays inside the cavity <NUM> with which it engages, when the second unit <NUM> moves in the first direction D1 towards the holder <NUM>. In this way, the plurality of protrusions <NUM> and the plurality of cavities <NUM> can ensure the thermal coupling between the first unit <NUM> and the second unit <NUM>. In a nonlimiting example, the diameter of each protrusion <NUM> may be approximately <NUM>-<NUM> and the height of each protrusion <NUM> may be approximately <NUM>-<NUM>. The diameter and depth of the cavities <NUM> may match the dimensions of the protrusions <NUM> but may be slightly larger.

The plurality of protrusions <NUM> and the complementary plurality of cavities <NUM> ensures a large contact surface and thereby a good thermal coupling between the first unit <NUM> and the second units <NUM>. To further increase the heat transfer between the first unit <NUM> and the second units <NUM>, each cavity <NUM> of the plurality of cavities <NUM> may hold a thermally conductive medium, for example a grease, an oil, or a liquid. The thermally conductive medium further reduces the thermal resistance between the protrusions <NUM> and the cavities <NUM>, by filling a space between each protrusion <NUM> and its engaged cavity <NUM> arising for example from manufacturing variances allowing the protrusions <NUM> to move within in the cavities <NUM>.

In embodiments, there is a gap between at least a portion of the contact surface of each cavity <NUM> of the plurality of cavities <NUM> and at least a portion of the contact surface of the protrusion <NUM> of the plurality of protrusions <NUM> which engages the cavity <NUM>. In such embodiments, the thermally conductive medium grease may be arranged to fill the gaps. The gap ensures a smooth engagement between the plurality of cavity <NUM> and the plurality of protrusions <NUM> such that each protrusion <NUM> can move easily within its engaging cavity <NUM>. Thereby, manufacturing variances with regard to the plurality of cavities <NUM> and the engaging plurality of protrusions <NUM> are addressed.

As illustrated in <FIG>, the biasing apparatus <NUM>, which also may be called a resilient element or a spring element, may be located between the first unit <NUM> and the second unit <NUM>. The biasing apparatus <NUM> is configured to urge (or force or bias) the second unit <NUM> away from the first unit <NUM>. The biasing apparatus <NUM> may further be configured to urge (or force or bias) the first unit <NUM> away from the second unit <NUM>. In other words, the biasing apparatus <NUM> is configured to push (or impel) the second unit <NUM> in relation to the first unit <NUM> in a direction away from the first unit <NUM> and to push (or impel) the first unit <NUM> in relation to the second unit <NUM> in direction away from the second unit <NUM>. With reference to <FIG>, the biasing apparatus <NUM> hence urges the second unit <NUM> against the second module <NUM> placed in the holder <NUM>. Thus, urging the second unit <NUM> towards physical contact with the second module <NUM> such that a good thermal coupling is achieved between the second unit <NUM> and the second module <NUM>. Furthermore, the biasing apparatus <NUM> may be arranged such that the entire area of a first surface of the second unit <NUM> is urged against the second module <NUM>. In this way an even pressure over the entire contact surface between the second unit <NUM> and the second module <NUM> can be achieved.

The biasing apparatus <NUM> may comprise any one from the group comprising: a spring and a gasket. The biasing apparatus <NUM> may for example be at least one of a coil spring, a spring plate, a helical spring and an O-ring. The biasing apparatus <NUM> may be arranged either between the first unit <NUM> and the second unit <NUM> or on the outside of the first unit <NUM> and/or the second unit <NUM>. In embodiments where the biasing apparatus <NUM> is located in between the first unit <NUM> and the second unit <NUM>, the biasing apparatus <NUM> may be arranged around one or more of the protrusions <NUM> of the first or second unit <NUM>, <NUM> and/or in one or more of the cavities <NUM> of the first or second unit <NUM>, <NUM>.

In the embodiment shown in <FIG>, the biasing apparatus <NUM> comprises two springs, each spring being arranged around one protrusion <NUM> at opposite sides of the second unit <NUM>. Thereby, the biasing apparatus <NUM> urges the entire surface of the second unit <NUM> facing the second module <NUM> against the second module <NUM>.

<FIG> shows two alternative implementations of the biasing apparatus <NUM>. In a first alternative, the biasing apparatus <NUM> comprises a gasket 114a arranged between the first unit <NUM> and the second unit <NUM>, for example around a circumference of the second unit <NUM>. In a second alternative, the biasing apparatus <NUM> comprises a gasket 114b arranged in one of the cavities <NUM> positioned in the middle of the second unit <NUM>.

According to embodiments of the invention, the holder <NUM> may comprise a compartment <NUM> configured to receive and hold the second module <NUM>. In the embodiment shown in <FIG>, the holder <NUM> comprises two compartments <NUM>, where each compartment <NUM> can receive and hold one second module <NUM>. However, the holder <NUM> may have fewer or more compartments <NUM>. In <FIG>, the compartment <NUM> to the right is illustrated without a second module <NUM>, and the compartment <NUM> to the left is illustrated with a second module <NUM> received and held therein. The compartment <NUM> may be configured to detachably secure the second module <NUM> such that the second module <NUM> can be replaced or removed and re-inserted into the compartment <NUM>.

In some embodiments, the holder <NUM> may correspond to a housing <NUM> as schematically illustrated in <FIG>. Thus, the device <NUM> may in some embodiments comprise a housing <NUM>. The housing <NUM> houses the compartment <NUM> and is configured to be attached to a printed circuit board (not shown in the figures). The housing <NUM> may also be referred to as a case or casing and may for example be a metal casing. The housing <NUM> illustrated in <FIG> comprises two compartments <NUM>, each compartment <NUM> having a first opening <NUM> for receiving the second module <NUM>, the second module <NUM> being connectable to the printed circuit board. Each compartment <NUM> further has a second opening <NUM> which exposes at least a part of the second module <NUM> when held in the compartment <NUM>.

With reference to <FIG>, the second opening <NUM> of the compartment <NUM> may face the second unit <NUM> and the second unit <NUM> may comprise a projection/boss <NUM> configured to engage the second opening <NUM> and abut against the second module <NUM> placed in the compartment <NUM>. The second unit <NUM> is thus brought into physical and thermal contact with the second module <NUM> held in the compartment <NUM>. The physical and thermal contact between the second unit <NUM> and the second module <NUM> may in some embodiments be provided via additional thermally conductive material. The projection <NUM> of the second unit <NUM> together with the biasing apparatus <NUM> urging the second unit <NUM> away from the first unit <NUM> in the first direction ensure a good thermal connection between the second unit <NUM> and the second module <NUM> held in the compartment <NUM> of the housing <NUM>. To allow the second module <NUM> to easily be inserted and removed from the compartment <NUM>, the projection <NUM> of the second unit <NUM> may have tampered edges, as indicated in <FIG>. This provides sliding surfaces between the projection <NUM> and the second module <NUM> and hence prevents the second module <NUM> to be caught by an edge of the projection <NUM> during insertion and removal of the second module <NUM>.

The second unit <NUM> may cover the second opening <NUM>. When the second unit <NUM> covers the second opening <NUM>, shielding against electromagnetic interference can be provided. This reduces the risk of electromagnetic interference, EMI, leakage to and/or from the second module <NUM> through the second opening <NUM>. Thereby, the risk that the second module <NUM> causes interference to an antenna or other electrical components nearby is reduced, as well as the risk of interference in the second module <NUM> caused by signals from an antenna or from other electrical components nearby. Thus, an improved heat transfer can be provided between the second module <NUM> and the first module <NUM> without an increased risk of electromagnetic interference leakage.

According to embodiments of the invention, the holder <NUM> may be configured to hold a second module <NUM> which is a transceiver module to which a signal cable is connectable. The second module <NUM> may for example be an optical transceiver module to which an optical signal cable, for example an optical fibre cable, is connected. However, the transceiver module may also be configured to be connectable to an electrical signal cable. The device <NUM> according to the embodiments of the present invention may be especially advantageous for applications where the second module <NUM> is an optical transceiver module, since when converting optical signals from the optical signal cable to electrical signals for transmission to the printed circuit board, the optical transceiver module generates a substantial amount of heat, which should be dissipated or transferred away from the optical transceiver module, to protect the optical transceiver module from heat, since the optical transceiver module is sensitive to high temperatures. The reliability and lifetime of a transceiver module is related to the module temperature. Typical allowed maximum temperatures for the optical transceiver module is <NUM> or <NUM>. The temperature of the optical transceiver module can be reduced by <NUM>-<NUM>, but also by more, for example by <NUM>-<NUM>, if a thermally insulating air gap or air pocket is avoided by the use of the device <NUM>.

The holder <NUM> may further be configured to receive and hold a second module <NUM> which is any module from the group comprising: a small form-factor pluggable (SFP) module and a quad small form-factor pluggable (QSFP) module. The holder <NUM> may hence be an SFP or QSFP housing configured to receive the SFP module or the QSFP module, respectively. The signal cable, which may be an optical fibre cable, may be connectable to the SFP or QSFP module. SFP and QSFP per se are known to the person skilled in the art and are thus not further described in this disclosure.

The embodiments of the present invention also include an arrangement <NUM> for cooling a second module <NUM>. <FIG> shows the arrangement <NUM> according to an embodiment of the invention. The arrangement <NUM> comprises a device <NUM> according to any one of the embodiments disclosed above, and a first module <NUM> which comprises a heat sink. With reference to <FIG>, the first module <NUM> may be in the form of a heat sink having cooling fins <NUM> for heat dissipation. The arrangement <NUM> may further comprise the second module <NUM> held in the device <NUM>. The arrangement <NUM> improves the heat transfer from the second module <NUM> to the first module <NUM> by means of embodiments of the device <NUM>. Consequently, the arrangement <NUM> can provide an improved heat dissipation.

The embodiments of the present invention also include a network access node for a wireless communication system. The network access node comprises any one of the device <NUM> and the arrangement <NUM> according to the embodiments disclosed above. The network access node may comprise a base station, for example a base radio station. The network access node may include one or more antennas. The base station may have a housing which houses the antenna. Alternatively, the antenna is mounted outside the housing of the base station, for example with a distance to the housing of the base station. The antenna may in embodiments be connectable to the printed circuit board comprised in the device <NUM> via a suitable cable. By means of embodiments of the device <NUM> and/or embodiments of the arrangement <NUM> an improved heat dissipation can be provided in the network access node.

Claim 1:
A device (<NUM>) for transferring heat between a first module (<NUM>) and a second module (<NUM>), the device (<NUM>) comprising:
a first unit (<NUM>) configured to be thermally coupled to the first module (<NUM>);
characterized in that:
the first unit (<NUM>) is fixed in relation to the first module (<NUM>) such that the first unit (<NUM>) does not move relative to the first module (<NUM>); and
the device further comprises:
a holder (<NUM>) for holding the second module (<NUM>),
a second unit (<NUM>) movable in a first direction in relation to the first unit (<NUM>) and the holder (<NUM>), and
a biasing apparatus (<NUM>) for urging the second unit (<NUM>) away from the first unit (<NUM>), thereby urging the second unit (<NUM>) against the second module (<NUM>) when the second module is held in the holder (<NUM>),
wherein the first unit (<NUM>) and the second unit (<NUM>) are thermally coupled to one another,
wherein one of the first and second units (<NUM>, <NUM>) comprises a plurality of protrusions (<NUM>) and the other one of the first and second units (<NUM>, <NUM>) comprises a plurality of cavities (<NUM>), each cavity (<NUM>) of the plurality of cavities (<NUM>) being complementary to one of the plurality of protrusions (<NUM>),
wherein each protrusion (<NUM>) of the plurality of protrusions (<NUM>) engages one of the plurality of cavities (<NUM>),
wherein each protrusion (<NUM>) of the plurality of protrusions (<NUM>) has a contact surface, and each cavity (<NUM>) of the plurality of cavities (<NUM>) has a contact surface, the contact surface of each protrusion (<NUM>) of the plurality of protrusions (<NUM>) facing the contact surface of one of the plurality of cavities (<NUM>).