Electronic device with improved cooling

Abstract

An electronic device comprising at least one printed circuit board (1), a power electronic component (3) embedded in the printed circuit board, characterized in that the printed circuit board (1) comprises at least one electrically insulating layer (11, 12.1, 12.2, 15.1, 15.2) having a thermal conductivity of at least 1 W / mK to form a thermally conductive electrically insulating layer and arranged to participate in heat transfer by conduction between the power electronic component (3) and the outer face of the printed circuit board (1). Figure 1

Description

Title of the invention: Electronic device with improved cooling

[0001] The present invention relates to the field of electronics and in particular the cooling of electronic power components. The power components are, for example, inverters, converters, circuit breakers, transistors or any other component of a power circuit...

[0002] BACKGROUND OF THE INVENTION

[0003] Electronic cards are known comprising a printed circuit board or plate (commonly called PCB), rigid or flexible, comprising conductive tracks and electronic components which are fixed on the printed circuit board and which have pads electrically connected to the conductive tracks. The printed circuit boards most commonly used today comprise electrically conductive layers and electrically insulating layers extending alternately with each other. When one of the electronic components is a power component, it is often necessary to provide cooling means such as a radiator arranged on the external face of the printed circuit board opposite the power component and thermal vias and / or metal drains passing through the printed circuit board to connect the radiator to the power electronic component.It is generally necessary to provide electrically insulating thermal interfaces in these arrangements between, on the one hand, the thermal vias and metal drains and, on the other hand, the power electronic component and the conductive tracks. The thermal interfaces must retain their properties throughout the lifetime of the electronic device. The implementation of these thermal interfaces generates design and manufacturing constraints.

[0004] Furthermore, the reduction in the size of electronic boxes, necessary in many applications, has led to an increase in the densities of electronic components and the burying of some of these components in the printed circuit board.

[0005] SUBJECT OF THE INVENTION

[0006] The invention aims in particular to improve the cooling of electronic circuits. Summary of the invention

[0007] For this purpose, according to the invention, there is provided an electronic device comprising at least one printed circuit board, an electronic power component buried in the printed circuit board. The printed circuit board comprises at least an electrically insulating layer which has a thermal conductivity at least equal to IW / mK to form an electrically insulating thermal conduction layer and which is arranged to participate in a heat transfer by conduction between the electronic power component and the external face of the printed circuit board.

[0008] Thus, at least one of the electrically insulating layers of the printed circuit board provides a dual function: an electrical insulation function and a thermal conduction function. It will be noted that the larger the surface area of ​​the electrically insulating thermal conduction layer, the more it will be able to conduct heat. By exploiting the entire surface area of ​​the electrically insulating layer, it is possible to ensure greater thermal conduction than that provided by heat drains whose overall section is smaller.The printed circuit board itself therefore participates in the heat dissipation function by ensuring a thermal conduction function for the heat produced by the power electronic component. This also makes it possible to limit the use of thermal vias and ensure better electrical insulation towards the outside. It is therefore possible to use thin materials and / or materials containing electrically conductive particles as thermal interfaces (electrically conductive materials are generally better thermal conductors than electrically insulating materials).

[0009] Other characteristics and advantages of the invention will emerge from reading the following description of a particular and non-limiting embodiment of the invention. Brief description of the drawings

[0010] Reference will be made to the accompanying drawings, among which:

[0011] [Fig.l] [Fig.l] is a schematic cross-sectional view of an electronic device electronics according to a first embodiment;

[0012] [Fig.2] [Fig.2] is a schematic cross-sectional view of an electronic device electronics according to a second embodiment;

[0013] [Fig.3] [Fig.3] is a schematic cross-sectional view of an electronic device electronics according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] With reference to the figures, the invention relates to an electronic card comprising at least one printed circuit board generally designated 1, electronic components 2, 3 and a heat sink in the form of a radiator 4. It will be noted that the hatching used in the drawings does not give any information on the nature of the materials used.

[0015] In Figures 1 and 2 showing the first and second embodiments of the invention, the printed circuit board 1 comprises at least a first set of outer layers 10.1 and a second set of outer layers 10.2 extending on either side of at least a first electrically insulating layer 11.

[0016] Each set of outer layers 10.1, 10.2 comprises a second electrically insulating layer, a first electrically conductive layer disposed between the second electrically insulating layer and the first electrically insulating layer 11, a second electrically conductive layer disposed opposite the first electrically insulating layer, and a third electrically insulating layer covering the second electrically conductive layer and the portions of the second electrically insulating layer left uncovered by the second electrically conductive layer.

[0017] Thus, for the first set of external layers 10.1: - the second electrically insulating layer 12.1 extends between the first electrically conductive layer 13.1 and the second electrically conductive layer 14.1, the first electrically conductive layer 13.1 being arranged on the side of the first electrically insulating layer 11, - the third electrically insulating layer 15.1 covers the second electrically conductive layer 14.1 and the portions of the second electrically insulating layer 12.1 left uncovered by the second electrically conductive layer 14.1,

[0018] The first set of outer layers 10.1 further comprises a third electrically conductive layer 16.1 which extends over the third electrically insulating layer 15.1.

[0019] For the second set of external layers 10.2: - the second electrically insulating layer 12.2 extends between the first electrically conductive layer 13.2 and the second electrically conductive layer 14.2, the first electrically conductive layer 13.2 being arranged on the side of the first electrically insulating layer 11, - the third electrically insulating layer 15.2 covers the second electrically conductive layer 14.2 and the portions of the second electrically insulating layer 12.2 left uncovered by the second electrically conductive layer 14.2.

[0020] The second set of outer layers 10.2 further comprises a third layer electrically conductive layer 16.2 which extends over the third electrically insulating layer 15.2.

[0021] It is understood that the sets of external layers are symmetrical in terms of number of layers and thickness of the layers.

[0022] The electronic component 2 is mounted outside the printed circuit board 1 and has pads connected by a solder 17 to areas of the third electronic layer. trically conductive 16.

[0023] The electronic component 3 is buried in the first electrically insulating layer 11 and has pads 3' connected by a solder 18 to pads of the first electrically conductive layer 13.1 of the first set of external layers 10.1. The electronic component 3 is here a power electronic component such as a transistor. As an example, a component implementing a GaN (gallium nitride semiconductor) type technology will be used.

[0024] The radiator 4 is fixed to the third electrically insulating layer 15.1 of the first set of external layers 10.1 by means of a thermal interface 19 covering the third electrically conductive layer 16.1 extending over the third electrically insulating layer 15.1. The thermal interface 19 is here produced in the form of a film of electrically and thermally conductive material such as an adhesive or a solder, or a sheet of electrically and thermally conductive material such as a metal strip.

[0025] In the first embodiment, the first electrically insulating layer 11 is for example formed from a plurality of pre-impregnated sub-layers (commonly called “prepreg”) comprising a composite material, with an epoxy matrix and glass fibers, of the type conventionally used for producing printed circuit boards, that is to say that the composite material has a thermal conductivity of between 0.3 and 0.4 W / mK.

[0026] Each set of external layers 10.1, 10.2 is here produced in the form of a laminate or laminate. The second electrically insulating layer 12.1, 12.2 is a sheet of the composite material of the above type having opposite faces on which copper sheets have been deposited forming the first and second electrically conductive layers 13.1, 13.2, 14.1, 14.2. The third electrically conductive layer 16 which extends over the third electrically insulating layer 15.2 is a copper sheet like the first and second electrically conductive layers 13.2, 14.2.

[0027] The third electrically insulating layer 15.1, 15.2 of the sets of external layers 10.1, 10.2 is here formed from a plurality of pre-impregnated sub-layers (commonly called “prepreg”) comprising a composite material, here with an epoxy matrix and glass fibers, having a glass transition temperature (commonly noted Tg) at least equal to 150°C and a thermal conductivity at least equal to 1 W / mK and here at least equal to 2W / mK or even 3W / mK. The material used in the present example is that produced under the brand name 92ML by the company Rogers Corporation, which has a glass transition temperature of 160°C and has a thermal conductivity of approximately 2.3W / mK in the plane. Alternatively, it is also possible to use the VT-5A2 material produced by the company VENTEC having a glass transition temperature of 190°C. and a thermal conductivity of 2.2 to 3.4 W / mK. The third electrically insulating layer 15.1, 15.2 of the sets of external layers 10.1, 10.2 is thus arranged to form an electrically insulating thermal conduction layer arranged to participate in a heat transfer by conduction from the electronic components 2,3.

[0028] The printed circuit board 1 further comprises means for thermal conduction in a direction transverse to the printed circuit board 1 (i.e. in the direction of the thickness).

[0029] The second electrically insulating layer 12.1 of the first set of external layers 10.1 is thus crossed by at least one and here thermal drains 20 ensuring thermal conduction between the first electrically conductive layer 13.1 and the second electrically conductive layer 14.1 of the first set of external layers 10.1. The thermal drains 20 are formed by copper filling microvias which are arranged in the second electrically insulating layer 12.1 between the two electrically conductive layers 13.1, 14.1. The third electrically insulating layer 15.1 of the first set of external layers 10.1, the electrically conductive layers 13.1, 14.1, the solders 18, the heat sinks 20, the third electrically conductive layer 16.1 and the thermal interface 19 ensure heat transfer by conduction between the electronic component 3 and the radiator 4.

[0030] The third electrically insulating layer 15.2 of the second set of external layers 10.2 is crossed by at least one and here electrical conductors 21 ensuring electrical conduction and thermal conduction between the third electrically conductive layer 16.2 and the second electrically conductive layer 14.2 of the second set of external layers 10.2. The electrical conductors 21 are formed by copper filling microvias which are arranged in the third electrically insulating layer 15.2 between the two electrically conductive layers 16.2, 14.2.

[0031] At least one electrical conductor 22 further extends in the printed circuit board 1 between the second electrically conductive layer 14.1 of the first set of outer layers 10.1 and the second electrically conductive layer 14.2 of the second set of outer layers 10.2. The electrical conductor 22 provides electrical conduction and thermal conduction between the layers 14.1 and 14.2. Preferably, the electrical conductor 22 is also connected to the first electrically conductive layer 13.1 of the first set of outer layers 10.1.

[0032] The third electrically insulating layer 15.2 of the second set of external layers 10.2, the solders 17, the electrically conductive layers 13.2, 14.2, the electrical conductors 21, the electrical conductor 22, the electrically conductive layers 13.1, 14.1, the heat sinks 20, the third electrically insulating layer 15.1 of the first set of external layers 10.1, the third electrically conductive layer 16.1 and the thermal interface 19 ensure heat transfer by conduction between the electronic component 2 and the radiator 4.

[0033] The third electrically insulating layer 15.1 of the set of external layers 10.1 is thus arranged to form an electrically insulating thermal conduction layer arranged to participate in a heat transfer by conduction from the electronic component 3 to the radiator 4. The electronic component 2 does not need to be specifically cooled. The presence of the second set of external layers aims to create a symmetry of the printed circuit board 1 in order to avoid deformations of the printed circuit board under the effect of differential thermal expansions.

[0034] It will be noted that this arrangement promotes cooling of the component 3 from below.

[0035] It will also be noted that, preferably, the ends of the heat drains do not open into the open air, in order to ensure an electrical insulation function in the PCB. If the two external surfaces of the printed circuit board 1 are formed by the third electrically insulating layers 15.1, 15.2, the circuit of the printed circuit board 1 is electrically insulated from the outside while allowing dissipation of the heat produced by the components. The mounting of the radiator 4 is also facilitated.

[0036] Elements identical or analogous to those previously described will bear numerical references identical to the latter, in the following description of the two embodiments of figures 2 and 3.

[0037] In the second embodiment shown in [Fig.2], the following are identical to those of the first embodiment: the stacking of layers 15.1, 14.1, 12.1, 13.1, 11, 13.2, 12.2, 14.2, 15.2, 16.1, 16.2; the positioning of electronic components 2, 3 and radiator 4; and the arrangement of drains 20 and electrical conductors 21, 22.

[0038] The second embodiment differs from the first embodiment in that, in the second embodiment, all the electrically insulating layers (11, 12.1 and 12.2) are also thermally conductive. Thus, the electrically insulating layers 11, 12.1, 12.2 are - like the electrically insulating layers 15.1 and 15.2 - made of a composite material, here with an epoxy matrix and glass fibers, having a glass transition temperature (commonly noted Tg) at least equal to 150°C and a thermal conductivity at least equal to 1W / mK and here at least equal to 2W / mK or even 3W / mK. The material used in the present example is that produced under the brand name 92ML by the company Rogers Corporation, which has a glass transition temperature of 160°C and has a thermal conductivity of approximately 2.3W / mK in the plane.Alternatively, VT-5A2 material produced by VENTEC with a glass transition temperature of 190°C can also be used. and a thermal conductivity of 2.2 to 3.4 W / mK. The electrically insulating layers 11, 12.1, 15.1, 12.2, 15.2 are thus arranged to form electrically insulating layers known as “thermal conduction” layers, i.e. having a thermal conductivity optimized to participate in a heat transfer by conduction from the electronic components 2, 3.

[0039] By favoring electrically insulating layers over thermal drains to ensure thermal conduction, electrical insulation is improved.

[0040] In the third embodiment of [Fig. 3], an arrangement is illustrated allowing cooling of the electronic component 3 from above.

[0041] The printed circuit board comprises, as previously, a first electrically insulating layer 11 and two sets of external layers 10.1, 10.2 each comprising a second electrically insulating layer, a first electrically conductive layer arranged between the second electrically insulating layer and the first electrically insulating layer, and a second electrically conductive layer arranged opposite the first electrically insulating layer.

[0042] Thus, for the first set of external layers 10.1, the second electrically insulating layer 12.1 extends between the first electrically conductive layer 13.1 and the second electrically conductive layer 14.1, the first electrically conductive layer 13.1 being arranged on the side of the first electrically insulating layer 11.

[0043] For the second set of outer layers 10.2, the second electrically insulating layer 12.2 extends between the first electrically conductive layer 13.2 and the second electrically conductive layer 14.2, the first electrically conductive layer 13.2 being arranged on the side of the first electrically insulating layer 11.

[0044] A thermal interface 19 covers the second electrically conductive layer 14.2 and the portions of the second electrically insulating layer 12.2 left uncovered by the second electrically conductive layer 14.2.

[0045] The electronic component 2 is mounted outside the printed circuit board 1 and has pads connected by a solder 17 to areas of the second electrically conductive layer 14.1 of the first set of external layers 10.1.

[0046] The electronic component 3 is buried in the first electrically insulating layer 11 and has pads 3' soldered onto pads of the first electrically conductive layer 13.1 of the first set of external layers 10.1. The component here is of the LGA or BGA type but other types of component are possible.

[0047] The radiator 4 is fixed via the thermal interface 19 on the second electrically conductive layer 14.2 of the second set of external layers 10.2.

[0048] As previously, thermal drains 20 and conductors are provided electrical 22.

[0049] The second electrically insulating layer 12.2 of the second set of external layers 10.2 is crossed by thermal drains 23 ensuring thermal conduction between the first electrically conductive layer 13.2 and the second electrically conductive layer 14.2 of the second set of external layers 10.2. The thermal drains 23 are formed by copper filling microvias which are arranged in the second electrically insulating layer 12.2 between the two electrically conductive layers 13.2, 14.2.

[0050] The first electrically insulating layer 11 forms an electrically insulating thermal conduction layer. For this purpose, it is made of a composite material, here with an epoxy matrix and glass fibers, having a glass transition temperature (commonly noted Tg) at least equal to 150°C and a thermal conductivity at least equal to 1W / mK and here at least equal to 2W / mK or even 3W / mK. The material used in the present example is that produced under the brand name 92ML by the company Rogers Corporation, which has a glass transition temperature of 160°C and has a thermal conductivity of approximately 2.3W / mK in the plane. The electrically insulating thermal conduction layer is here made in the form of a plurality of pre-impregnated sub-layers stacked on top of each other.

[0051] The other electrically insulating layers are here made from traditional materials.

[0052] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0053] In particular, the structure of the device may be different from that described.

[0054] The device may for example comprise a different number of power or control components. The electronic components may be of different types: they may be analog, they may comprise one or more integrated circuits, one or more active or passive elements, etc. They may implement another technology such as that of silicon carbide (SiC), silicon (Si) or gallium nitride (GaN) semiconductors, or any other element emitting heat and which must be cooled.

[0055] The printed circuit board may comprise a different number of electrically conductive layers, electrically insulating layers and electrically insulating thermal conduction layers. For example, only the first electrically insulating layer could be arranged to provide thermal conduction. The printed circuit board may alternatively comprise one or more electrically insulating thermal conduction layers, but on only one side of the first electrically insulating layer. The printed circuit board may consist of a single laminate including one or more electrically insulating layers are arranged to ensure thermal conduction.

[0056] The material used to form the electrically insulating thermal conduction layers may be the one indicated or any other material having specifications similar to or in accordance with those mentioned. It may be a composite material or not. It may incorporate fillers improving its thermal conductivity.

[0057] The printed circuit board 1 comprises at least a first set of external layers 10.1 and a second set of external layers 10.2 extending on either side of at least a first electrically insulating layer 11 in which the power electronic component 3 is buried; the first and second sets of external layers each comprising: a second electrically insulating layer 12.1, 12.2, a first electrically conductive layer 13.1, 13.2 arranged between the second electrically insulating layer 12.1, 12.2 and the first electrically insulating layer 11, and a second electrically conductive layer 14.1, 14.2 arranged opposite the first electrically insulating layer 11; the power electronic component 3 having pads 3' connected to the first electrically conductive layer 13.1 of the first set of external layers 10.1. The second electrically insulating layer 12.1, 12.2 of at least one of the sets of outer layers 10.1, 10.2 forms the electrically insulating layer of thermal conduction.

[0058] The printed circuit board 1 comprises at least a first set of external layers 10.1 and a second set of external layers 10.2 extending on either side of at least a first electrically insulating layer 11 in which the power electronic component 3 is buried; the first and second sets of external layers each comprising: a second electrically insulating layer 12.1, 12.2, a first electrically conductive layer 13.1, 13.2 arranged between the second electrically insulating layer 12.1, 12.2 and the first electrically insulating layer 11, and a second electrically conductive layer 14.1, 14.2 arranged opposite the first electrically insulating layer 11; the power electronic component 3 having pads 3' connected to the first electrically conductive layer 13.1 of the first set of external layers 10.1. The device comprises a heat sink 4 fixed on the second electrically conductive layer 14.2 of the second set of outer layers 10.2 via a thermal interface 19. .

[0059] The heat sink may be a heat pipe or any active or passive device providing cooling.

[0060] The heat sink 4 can be fixed on the third electrically insulating layer 15.1, 15.2 via a thermal interface to promote heat dissipation of the bare circuit, which can be electrically conductive or not, or soldered on a copper layer covering the third electrically insulating layer 15.1, 15.2 (the soldering has the advantage of ensuring good thermal conduction).

[0061] The electrical conductors 21, 22 can be replaced by heat sinks if electrical conduction is not necessary.

[0062] It has been indicated that if the two external surfaces of the printed circuit board 1 are formed by the third electrically insulating layers 15.1, 15.2, the circuit of the printed circuit board 1 is electrically isolated from the outside while allowing dissipation of the heat produced by the components. It is also possible to be electrically isolated by not making laser vias in the layer 15.1 during the manufacture of the printed circuit board. The copper of the third electrically conductive surface 16.2 allows the transfer of components and the copper of the third electrically conductive surface 16.1 is favorable to heat dissipation.

[0063] The printed circuit board 1 comprises five electrically insulating layers 11, 12.1, 12.2, 15.1, 15.2 arranged to form the electrically insulating thermal conduction layers.

Claims

Claims

1. Electronic device comprising at least one printed circuit board (1), a power electronic component (3) buried in the printed circuit board, characterized in that the printed circuit board (1) comprises at least one electrically insulating layer (11, 12.1, 12.2, 15.1, 15.2) which has a thermal conductivity at least equal to IW / mK to form an electrically insulating thermal conduction layer and which is arranged to participate in a heat transfer by conduction between the power electronic component (3) and the external face of the printed circuit board (1).

2. Device according to claim 1, in which the thermal conductivity of the electrically insulating thermal conduction layer (11, 12.1, 12.2, 15.1, 15.2) is at least equal to 2W / mK or even 3W / mK

3. Device according to claim 1 or 2, wherein the printed circuit board (1) comprises at least a first set of external layers (10.1) and a second set of external layers (10.2) extending on either side of at least a first electrically insulating layer (11) in which the power electronic component (3) is buried; the first and second sets of external layers each comprising: a second electrically insulating layer (12.1, 12.2), a first electrically conductive layer (13.1, 13.2) arranged between the second electrically insulating layer (12.1, 12.2) and the first electrically insulating layer (11), and a second electrically conductive layer (14.1, 14.2) arranged opposite the first electrically insulating layer (11); the power electronic component (3) having pads (3') connected to the first electrically conductive layer (13.1) of the first set of external layers (10.1).

4. A device according to claim 3, wherein each set of outer layers (10.1, 10.2) comprises a third electrically insulating layer (15.1, 15.2) covering the second electrically conductive layer (14.1, 14.2), at least one of the third electrically insulating layers (15.1, 15.2) being arranged to form the thermal conduction electrically insulating layer.

5. A device according to claim 4, wherein each set of outer layers (10.1, 10.2) comprises a third electrically conductive layer (16.1, 16.2) covering the third electrically conductive layer insulating (15.1, 15.2) and the device comprises a heat sink (4) fixed on the third electrically conductive layer (16.1) of the first set of external layers via a thermal interface (19).

6. Device according to claim 5, in which the third electrically insulating layer (15.2) of the second set of external layers (10.2) is crossed by at least one electrical conductor (21) extending between the third and second electrically conductive layers of the second set of external layers (10.2).

7. Device according to claim 5 or 6, in which the second electrically insulating layer (12.1) of the first set of external layers (10.1) is crossed by at least one thermal drain (20) ensuring thermal conduction between the first and second electrically conductive layers of the first set of external layers (10.1).

8. A device according to any one of claims 3 to 7, wherein the second electrically insulating layer (12.1, 12.2) of at least one of the sets of outer layers (10.1, 10.2) forms the electrically insulating thermal conduction layer.

9. Device according to claim 3, comprising a heat sink (4) fixed on the second electrically conductive layer (14.2) of the second set of external layers (10.2) via a thermal interface (19).

10. A device according to any one of claims 3 to 9, wherein the first electrically insulating layer (11) forms the thermal conduction electrically insulating layer.

11. A device according to any one of claims 3 to 10, wherein at least one electrical conductor (22) extends in the printed circuit board (1) between the second electrically conductive layer (14.1) of the first set of outer layers (10.1) and the second electrically conductive layer (14.2) of the second set of outer layers (10.2).

12. Device according to claim 11, wherein at least the electrical conductor (22) is also connected to the first electrically conductive layer (13.1) of the first set of outer layers (10.1).

13. A device according to claim 1 or 2, wherein the printed circuit board (1) comprises five electrically insulating layers (11, 12.1, 12.2, 15.1, 15.2) arranged to form the electrically insulating thermal conduction layers.

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