WO2023110156A1

WO2023110156A1 - Electronic assembly

Info

Publication number: WO2023110156A1
Application number: PCT/EP2022/051510
Authority: WO
Inventors: Simon PFAFF; Matthias Wellens; Hubert GLEICH; Dirk Wischnewski
Original assignee: Valeo Comfort And Driving Assistance
Priority date: 2021-12-15
Filing date: 2022-01-24
Publication date: 2023-06-22

Abstract

The invention relates to an electronic assembly (1) comprising: - a printed circuit board (2), - at least one electronic module (3) fixed on a first side of the printed circuit board, said electronic module comprising a plurality of pins so as to electrically couple said electronic module and the printed circuit board, - a casing (4) having a back thermally conductive back wall (44) and side walls (42), and - at least one cooling module, placed on a second side of the printed circuit board (2), so as to be thermally coupled to both the thermally conductive back wall and the electronic module. According to the invention, at least a portion of said side walls comprises a plurality of cooling openings (45) arranged between the printed circuit board and the thermally conductive back wall, all around the cooling module.

Description

Electronic assembly

Technical field

[0001] The invention belongs to the technical field of electronic devices.

[0002] It relates specially to electronic devices used in automotive vehicles, for instance telecommunication devices used for telematics operations in cars, and also relates to means for cooling electronic devices.

[0003] More precisely the invention relates to an electronic assembly comprising:

- a printed circuit board,

- at least one electronic module fixed on a first side of the printed circuit board, said electronic module comprising a plurality of pins so as to electrically couple said electronic module and the printed circuit board,

- a casing having a thermally conductive back wall and side walls, and

- at least one cooling module, placed on a second side of the printed circuit board, so as to be thermally coupled to both the thermally conductive back wall and the electronic module.

Technological background

[0004] Telematics control units are embedded electronic systems that perform telecommunication operations, for instance operations for establishing wireless connections between a vehicle and external services (such as services provided by a vehicle manufacturer) or operations of tracking of the vehicle. In order to optimize the telecommunication performance and to associate the antennas with electronic components, telematics control units are often placed on the roof of the vehicle.

[0005] The temperature of the roof of a vehicle is subject to large variation. For instance, the temperature of the roof of a black car exposed to solar radiation during a sufficiently long period of time may reach more than 100°C. The optimal temperature for a good functioning of the telematics control unit is often below this limit. Such temperature rises may hinder the proper functioning of the telematics control unit and thus reduce the availability of the communication services. [0006] Several solutions exist to cool down the telematics control units. In particular, document US2017/0170542 describes the use of a cooler based on a Peltier element in order to cool down the telematics control unit. However, such electronic systems present drawbacks that limit the efficiency of the cooling.

Summary of the invention

[0007] The invention relates to an electronic assembly that allows improving the efficiency of the cooling.

[0008] More particularly, the invention relates to an electronic assembly as defined in the introduction and in which at least a portion of said side walls comprises a plurality of cooling openings arranged between the printed circuit board and the thermally conductive back wall, all around the cooling module.

[0009] When the electronic assembly is operating, the cooling module actively shifts the heat away from the electronic module toward the thermally conductive back wall. The temperature of this thermally conductive back wall thus increases. The heat is then transferred back from the thermally conductive back wall to the printed circuit board via the side walls. The cooling openings thus allows avoiding this direct heat transfer from the thermally conductive back wall to the printed circuit board. The cooling openings thus acts as a barrier between the thermally conductive back wall and the printed circuit board. These cooling openings thus allows improving the global cooling of the electronic module.

[0010] Other advantageous features of the electronic assembly are the following ones:

- the cooling openings extend along the printed circuit board;

- the cooling openings are arranged side by side;

- each cooling opening is rectangular;

- the largest size of each cooling opening is lower than a threshold that is equal to half of the wavelength of a signal propagating in the electronic assembly;

- the largest size of each cooling opening is lower than 2.5 centimetres;

- the largest size of each cooling opening is lower than 2.5 millimetres;

- two consecutive cooling openings are separated by a finger extending until the printed circuit board; - the casing comprises a non-thermally conductive front wall;

- the electronic assembly further comprises at least three fastening means configured to keep the printed circuit board at a distance from the thermally conductive back wall inside the casing;

- the printed circuit board comprises an alternating of electrically conductive layers and electrically insulated layers;

- each electrically conductive layer of the printed circuit board comprises a non- electrica I ly conductive area extending along at least a part of a closed outline positioned around at least one of the three fastening means;

- the non-electrically conductive area in each electrically conductive layer presents a form of a dashed outline;

- all the non-electrically conductive areas of the electrically conductive layers are aligned with each other through the printed circuit board;

- the non-electrically conductive area in each electrically conductive layer presents a form of a continuous outline; and

- the non-electrically conductive area comprises a material with fibres and a polymer.

[0011] The different characteristics, variants, and embodiments of the invention may be combined with each other in various combinations insofar as they are not incompatible or exclusive of each other.

Description of the drawings

[0012] Many other features of the invention are apparent from the following description made with reference to the drawings which illustrate embodiments of the invention, in no way limiting, and where:

- Figure 1 represents a telecommunication system in which an electronic system according to the invention is embedded in an automotive vehicle;

- Figure 2 shows a first example of an electronic assembly according to the invention, represented in cross-section from the side;

- Figure 3 represents a side view of a part of the electronic assembly according to the invention; - Figure 4 represents a partial view of a printed circuit board comprised in the electronic assembly according to the invention, represented in cross-section from the side;

- Figure 5 represents a top view of one electrically conductive layer of the printed circuit board of Figure 4; and

- Figure 6 shows a second example of an electronic assembly according to the invention, represented in cross-section from the side.

[0013] It should be noted that in these figures, the structural and/or functional elements common to the different embodiments may have the same references, even if they have slightly different features.

Description of embodiments

[0014] It should be noted that, in this description, the sign

is used to separate the references of different embodiments.

[0015] Figure 1 represents a communication system CS comprising an automotive vehicle AV, a distant network DN and an equipment manufacturer backend system EM. The automotive vehicle is able to establish a wireless communication link WL with the distant network DN. The equipment manufacturer backend system EM is linked to the distant network DN so that a communication channel may be established between the automotive vehicle AV and the equipment manufacturer backend system EM.

[0016] As represented in Figure 1, the automotive vehicle AV (for example here, a car) comprises an electronic assembly 1 according to the invention. This electronic assembly is here located on the roof of the automotive vehicle AV.

[0017] The electronic assembly 1; 10 comprises at least one electronic module 3; 3a, 3b. As represented in Figures 2, 3 and 4, the electronic assembly comprises only one electronic module 3. According to the alternative represented in Figure 6, the electronic assembly can comprise two electronic modules 3a, 3b. As another alternative, the electronic assembly can comprise more than two electronic modules.

[0018] The electronic module 3; 3a, 3b is here a telecommunication circuit, for instance a Network Access Device. The electronic module 3; 3a, 3b is configured here to establish the wireless communication link WL with the distant network DN. For this purpose, the distant network comprises an Internet network and/or a cellular network.

[0019] The automotive vehicle AV is equipped with an internal network IN comprising and linking together various electronics units (for instance, command units, displays, sensors...) of the vehicle AV, among which the electronic module 3; 3a, 3b hosted by the electronic assembly 1; 10. Therefore, the electronic module 3; 3a, 3b is able to communicate with the internal network IN of the automotive vehicle and exchange data with the equipment manufacturer backend system EM through the distant network DN.

[0020] The exchanged data comprise for example information about the location and the speed of the car, information relating to the maintenance of the vehicle, for instance alerts about a failure of equipment, and more generally to various signals from the sensors of the vehicle AV.

[0021] Figures 2 and 6 represent two examples of the electronic assembly 1; 10 according to the invention. In both examples, the electronic assembly 1; 10 comprises a casing 4, a printed circuit board 2, at least one electronic module 3; 3a, 3b and at least one cooling module 7; 7a, 7b.

[0022] The casing 4 comprises a non-electrically conductive front wall 5 and a thermally conductive back wall 44, both edged by side walls coming into contact with each other. Side walls 5a of the non-electrically conductive front wall 5 are also non-thermally conductive walls. Side walls 42 of the thermally conductive back wall 44 are thermally conductive walls. The thermally conductive back wall 44 and the corresponding side walls 42 are for example a metallic wall, for instance an aluminium wall.

[0023] The non-thermally conductive front wall 5 and the corresponding side walls 5a form an upper housing. The thermally conductive back wall 44 and the corresponding side walls 42 form a lower housing. Each housing is made in a monobloc piece

[0024] In the meaning of the invention, a material is qualified as thermally conductive when it allows a sufficient exchange of heat with its environment, i.e. here when it has a heat transfer coefficient greater than 5 W.M ^-1.K ^-1.

[0025] The non-thermally conductive walls (front and side walls) comprise a material that does not interfere with the radio frequency waves, so as to allow the establishment of the wireless communication link WL. For example here, the non-thermally conductive walls of the casing 4 are made of polymer material.

[0026] On the contrary, the thermally conductive back wall 44 and the corresponding side walls 42 present a shielding function in order to enable the damping of the electromagnetic waves.

[0027] As represented in Figures 2 and 6, the electronic assembly 1; 10 comprises at least one electronic module 3; 3a, 3b. Each electronic module 3; 3a, 3b is fixed on a first side 2a of the printed circuit board 2. The electronic module 3; 3a, 3b comprises a plurality of pins (signal and ground pins) so as to electrically couple the concerned electronic module 3; 3a, 3b and the printed circuit board 2. Most of ground pins of the plurality of pins (not represented) goes through the whole thickness of the printed circuit board in order to allow the heat transfer from the electronic module 3; 3a, 3b through the printed circuit board 2 to a cooling module 7; 7a, 7b. The signal pins can end in an intermediate layer of the printed circuit board.

[0028] The electronic assembly 1; 10 also comprises at least one cooling module 7; 7a, 7b. In the main embodiment shown in Figure 2, it comprises only one cooling module 7. In a variant represented in Figure 6, each electronic module 3a, 3b is associated with one corresponding cooling module 7a, 7b. As a variant (not represented), one single cooling module can be used for several electronic modules.

[0029] Each cooling module 7; 7a, 7b is placed between the printed circuit board 2, on a second side 2b of the printed circuit board 2, and the thermally conductive back wall 44 of the casing 4.

[0030] In practice, the cooling module 7; 7a, 7b is thermally coupled to the thermally conductive back wall 6 and to the electronic module 3; 3a, 3b via thermal pads, thermal paste or thermal foam (not represented). In the meaning of the invention, the wording "thermally coupled" implies a thermal transfer with or without physical contact.

[0031] Thermal pads, thermal foam or thermal paste increase the heat transfer (by thermal conduction) between the cooling module 7; 7a, 7b, the thermally conductive back wall 44 and the electronic module 3; 3a, 3b. Moreover, the thermal pads, the thermal foam or the thermal paste also act as mechanical stress absorbers. The cooling module 7; 7a, 7b is thus arranged to reduce the temperature of the electronic module 3; 3a, 3b by coupling it to the thermally conductive back wall 6. This thermally conductive back wall 44 thus acts as a heatsink.

[0032] The cooling module 7; 7a, 7b comprises at least one active part 8. Each active part 8 is surrounded by a plate 9 that is placed on each side of the active part 8. In other words, one plate 9 is placed between the printed circuit board 2 and the active part 8 and another plate 9 is placed between the active part 9 and the thermally conductive back wall 6.

[0033] The plate 9 is for example made of ceramic.

[0034] Each plate 9 comprises, on its inner side (i.e. the side facing the active part 8), a electrically conductive material in order to make the connection between the thermoelectric elements that represents the active part 8.

[0035] The thermally conductive back wall 6 comprises fastening means (not represented) in order to keep the cooling module at the right position.

[0036] The active part 8 of the cooling module 7; 7a, 7b is here a Peltier cooler, or thermoelectric cooler. The active part 8 is therefore powered with electricity to transfer heat (by thermal conduction) from a first surface 8a of the active part 8 to a second surface 8b of the active part. A heat transfer that relies on an external source of energy is qualified as "active". Therefore, a Peltier cooler, which consumes electricity, is an active cooling device. On the contrary, a heat transfer that does not rely on any external energy source is qualified as passive.

[0037] The printed circuit board 2 is located in the casing 4. As visible in Figures 2 and 6, the contour of the printed circuit board is clamped between the side walls 5a of the upper housing and the side walls 42 of the lower housing.

[0038] The electronic assembly 1; 10 comprises at least three fastening means 10 that are configured to fix the printed circuit board 2 to the casing 4. More particularly, the printed circuit board 2 is fixed here to the thermally conductive back wall 44.

[0039] These fastening means are also configured to keep the printed circuit board 2 at a distance from the thermally conductive back wall 44, inside the casing 4. In other words, the second side 2b of the printed circuit board 2 faces the thermally conductive back wall 44.

[0040] The fastening means 10 also allows keeping the printed circuit board 2 in a predetermined position in the casing 4 and tying the upper housing and the lower housing with each other. The fastening means thus allow maintaining the printed circuit board 2 between the side walls 5a of the upper housing and the side walls 42 of the lower housing.

[0041] The fastening means are for example screws. The screws 10 are thermally conductive, for example made of metal.

[0042] As represented in Figure 4, the printed circuit board 2 comprises an alternating of at least partially electrically conductive layers 23 and insulated layers 24. The expression "at least partially electrically conductive" means here that the concerned layer is not completely formed by an electrically conductive material but comprises some parts with non-electrically conductive material. Here, an electrically conductive layer 22; 23 comprises more than 50% of an electrically conductive material.

[0043] In particular, an external electrically conductive layer 23A is defined as the electrically conductive layer 23 of the printed circuit board 2 that is the closest to the electronic module 3. Symmetrically, an internal layer 23B is defined as the electrically conductive layer 23 of the printed circuit board 2 that is the closest to the cooling module 7.

[0044] As represented in Figure 4, two consecutive electrically conductive layers 23 are always separated by one insulated layer 24. Symmetrically, two consecutive insulated layers 24 are always separated by one electrically conductive layer 23.

[0045] In order to ensure electrical conductivity of the printed circuit board 2, the latter comprises through-hole vias 40 which extends from the first side 2a to the second side 2b of the printed circuit board 2.

[0046] These through-holes 40 are filled with an electrically conductive material in order to guarantee the electrical conductivity through all the layers of the printed circuit board 2. The electrically conductive material is here a metal, for example copper. [0047] Advantageously, thanks to the electrical connection provided by the through-hole vias 40 from the first side 2a to the second side 2b of the printed circuit board 2, these through-hole vias 40 also contribute to the heat transfer from the electronic module 3 to the cooling module 7 through the printed circuit board 2.

[0048] Each electrically conductive layers 23 comprises a non-electrically conductive area 26. This non-electrically conductive area 26 extends along at least a part of a closed outline positioned around at least one of the three fastening means 10.

[0049] This non-electrically conductive area 26 are free from electrically conductive material. For example, the non-electrically conductive area 26 comprise a material with fibres and a polymer (also commonly named "prepreg").

[0050] The electrical conductivity is here guaranteed despite the presence of these non- electrically conductive areas in the electrically conductive layers thanks to the through- hole 40 vias previously described.

[0051] As fastening means 10 are thermally conductive, they may reduce the efficiency of the cooling of the electronic assembly 1. Indeed, when the electronic assembly 1; 10 is operating, the cooling module 7; 7a, 7b actively shifts the heat away from the electronic module 3; 3a, 3b toward the thermally conductive back wall 44. The temperature of this thermally conductive back wall 44 thus increases. As the side walls 42 of the lower housing comprise the thermally conductive fastening means 10, the heat is transferred back from the thermally conductive back wall 44 to the printed circuit board 2 via the side walls 42. The non-electrically conductive area 26 thus allows reducing significantly the thermal conductivity of the printed circuit board and thus improving the global cooling of the electronic assembly.

[0052] By the expression "at least a part of closed outline", it should be here understood that the non-electrically conductive area 26 extends along at least 80% of the closed outline. Furthermore, the closed outline here reaches the edges of the printed circuit board 2.

[0053] As visible in Figure 4, all the non-electrically conductive areas 26 of the electrically conductive layers 23 are here aligned with each other through the printed circuit board 2. [0054] According to a first embodiment (Figure 5), the non-electrically conductive area 26 in each electrically conductive layer 23 presents a form of a dashed outline. More particularly, this dashed outline is a part of a dashed rectangle extending between the edges of the printed circuit board. As an alternative, the dashed outline can be of any other dashed shape.

[0055] According to a second embodiment (not represented), the non-electrically conductive area in each electrically conductive layer presents a form of a continuous outline. More particularly, the continuous outline is a part of a continuous rectangle extending between the edges of the printed circuit board. As an alternative, the continuous outline can be of any other continuous shape.

[0056] As described previously, the invention aims at improving the cooling efficiency of the electronic assembly.

[0057] The thermal resistance R_th of an area is generally defined by the following expression:

[°⁰⁵⁸l

[0059] with d the typical length of the concerned area, A the surface of this area and A the specific thermal conductivity associated with the concerned area.

[0060] According to this expression, there are three possibilities to increase the thermal resistance. First, the typical length of the concerned area can be increased. This first solution is not adapted to the electronic assembly as the mounting space is limited.

[0061] Second, it is possible to reduce the specific thermal conductivity A. However, in order to guarantee an efficient heat transfer from the cooling module, the specific thermal conductivity of the lower housing cannot be too low.

[0062] Third, the surface A can be reduced. This can be performed by reducing the thickness of the concerned area but mechanical limitations should be taken into account. Another possibility is to perform cutouts in the concerned area, i.e. introducing openings in the concerned area.

[0063] According to the invention, at least a portion of side walls 42 of the lower housing thus comprises a plurality of cooling openings 45 (Figure 3). These cooling openings 45 are arranged between the printed circuit board 2 and the cooling module 7. They are arranged around the cooling module 7 on the side walls 42 of the lower housing.

[0064] As visible in Figure 3, the cooling openings 45 are preferably arranged side by side. The cooling openings 45 are evenly distributed on the side walls 42 of the lower housing.

[0065] Preferably, the cooling openings 45 preferably extend along the printed circuit board 2. As a variant, the cooling opening could extend along the thermally conductive back wall. As another variant, the cooling opening could extend in the side walls of the lower housing away from the printed circuit board and away from the thermally conductive back wall.

[0066] Therefore, the lower housing present three advantageous functions. First, the lower housing acts as a protection for the electronic components. Then, the lower housing acts as a heatsink and enables the heat transfer from the cooling module to the external environment of the electronic assembly. Finally, the lower housing acts as a shielding to reduce the emission of electromagnetic waves from the electronic components of the electronic assembly to the external environment. Advantageously here, the cooling openings 45 maintain a good shielding performance of the lower housing.

[0067] The cooling openings allows increasing the thermal resistance between the printed circuit board 2 and the thermally conductive back wall 44. More particularly, these cooling openings are configured in order to avoid direct heat transfer from the thermally conductive back wall 44 to the printed circuit board 2. In other words, the cooling openings correspond to a heat barrier between the thermally conductive back wall and the printed circuit board that avoid direct heat transfer from the thermally conductive back wall 44 (that acts as a heatsink) to the printed circuit board 2. Thanks to their specific dimensions (discussed in the following), these cooling openings simultaneously allows maintaining a good shielding performance of the lower housing.

[0068] The cooling openings 45 present here a rectangular shape. As a variant, the cooling openings can be in any other shape.

[0069] Each cooling opening is defined by a largest size I. In the case of rectangular cooling openings 45 (Figure 3), the largest size I is the diagonal of the rectangle of side of length L by a side of height h. Here, the length L of the cooling opening is higher than the height h.

[0070] This largest size I is here lower than a threshold that is equal to half of the wavelength of the signal propagating in the electronic assembly. This feature allows maintaining a good shielding performance of the lower housing while reducing the heat transfer from the back wall 44 to the printed circuit board 2 via the side walls 42. Preferably, the largest size I is lower than one tenth of the wavelength. More preferably, the largest size I is lower than one twentieth of the wavelength.

[0071] As an example, for an electromagnetic signal presenting a frequency of 6 Giga Hertz (GHz), the largest size of each cooling opening 45 is lower than 2.5 centimetres (cm). Preferably in this case, the largest size of each cooling opening 45 is lower than 2.5 millimetres (mm).

[0072] As represented in Figure 3, the cooling openings extend from the printed circuit board 2. In particular, two consecutive cooling openings 45 are separated by a finger 40 extending from the printed circuit board 2 until another end of the cooling openings 45.

[0073] The smaller the width of each finger 40, the better the prevention of heat transfer from the thermally conductive back wall 44 and the printed circuit board 2. However, the width of the finger 40 cannot be so small in order to provide a robust casing 4.

[0074] As an example, each finger 40 has a width between 1 and 2 millimetres. Preferably, each finger 40 has a width equal to 1.5 millimetres (mm).

[0075] Considering an orthogonal system defining three directions x, y and z (see 3), a height h of the fingers 40 is defined as the dimension extending in a perpendicular direction of the first and second sides of the printed circuit board, i.e. along the z direction. Here, the height h of each finger 45 corresponds to the dimension of a side of the rectangular cooling opening 45.

[0076] Preferably, all the fingers 40 present the same height. The height of each finger 40 is lower than the height of the side walls 42. This height is for example comprised between 0.5 and 1 mm. Preferably, the height of each finger 40 is equal to 0.7 mm. [0077] As a variant, the height of the fingers can be different. For example, a couple of adjacent fingers can have the same height whereas another couple can have a height slightly different from the first couple.

[0078] As another variant, the finger can extend along the whole height of the side walls of the lower housing (the height of the finger is thus equal to the height of the side walls of the lower housing).

[0079] A thickness of the fingers 40 is defined as the dimension extending along the y direction. The thickness of the fingers is equal to the thickness of the side walls of the lower housing. The thickness is for example comprised between 1.5 and 2.5 mm. Preferably, the thickness of the finger 40 is equal to 2 mm.

Claims

1. Electronic assembly (1) comprising:

- a printed circuit board (2),

- at least one electronic module (3) fixed on a first side of the printed circuit board, said electronic module comprising a plurality of pins so as to electrically couple said electronic module (3) and the printed circuit board (2),

- a casing (4) having a thermally conductive back wall (44) and side walls (42), and

- at least one cooling module (7), placed on a second side of the printed circuit board (2), so as to be thermally coupled to both the thermally conductive back wall (44) and the electronic module (3), characterized in that at least a portion of said side walls (42) comprises a plurality of cooling openings (45) arranged between the printed circuit board (2) and the thermally conductive back wall (44), all around the cooling module (7).

2. Electronic assembly (1) according to claim 1, wherein the cooling openings (45) extend along the printed circuit board (2).

3. Electronic assembly (1) according to any of claims 1 or 2, wherein each cooling opening is rectangular.

4. Electronic assembly (1) according to any of claims 1 to 3, wherein the largest size (I) of each cooling opening (45) is lower than a threshold that is equal to half of the wavelength of a signal propagating in the electronic assembly (1).

5. Electronic assembly (1) according to any of claims 1 to 4, wherein the largest size of each cooling opening (45) is lower than 2.5 centimetres.

6. Electronic assembly (1) according to any of claims 1 to 5, wherein the largest size of each cooling opening (45) is lower than 2.5 millimetres.

7. Electronic assembly (1) according to any of claims 1 to 6, wherein two consecutive cooling openings (45) are separated by a finger (40) extending until the printed circuit board (2).

8. Electronic assembly (1) according to any of claims 1 to 7, wherein the casing (4) comprises a non-thermally conductive front wall (5).

9. Electronic assembly (1) according to any of claims 1 to 8, further comprising at least three fastening means (10) configured to keep the printed circuit board (2) at a distance from the thermally conductive back wall (44) inside the casing (4).

10. Electronic assembly (1) according to claim 9, wherein, the printed circuit board (2) comprising an alternating of electrically conductive layers (23) and electrically insulated layers (24), each electrically conductive layer (23) of the printed circuit board (2) comprises a non-electrically conductive area (26) extending along at least a part of a closed outline positioned around at least one of the three fastening means.

11. Electronic assembly (1) according to claim 10, wherein the non-electrically conductive area (26) in each electrically conductive layer (23) presents a form of a dashed outline.

12. Electronic assembly (1) according to any of claims 10 or 11, wherein all the non- electrically conductive areas (26) of the electrically conductive layers (24) are aligned with each other through the printed circuit board (2).

13. Electronic assembly (1) according to claim 10, wherein the non-electrically conductive area (26) in each electrically conductive layer (23) presents a form of a continuous outline.

14. Electronic assembly (1) according to any of claims 8 to 12, wherein the non-electrically conductive area (26) comprises a material with fibres and a polymer.