CN114390810A

CN114390810A - Electronic module

Info

Publication number: CN114390810A
Application number: CN202111158654.3A
Authority: CN
Inventors: H·布劳恩; K·席门茨
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-10-06
Filing date: 2021-09-30
Publication date: 2022-04-22
Also published as: DE102020212585A1

Abstract

The invention relates to an electronic module (1), in particular a transmission control module for a motor vehicle transmission, having a circuit board (2), the electronic module comprises a circuit board (2) having a first side (21) and a second side (22) facing away from the first side, an electronic component (3) arranged on the first side (21) and a potting compound (7) arranged on the first side (21) of the circuit board (2) covering the electronic component (3), a cooling surface (23) arranged on the second side (22) and at least one recess (24) extending from the first side (21) through the circuit board (2) to the second side (22), wherein the electronic module (1) has at least one fixing bush (4), the fixing bush has a continuous inner receptacle (43) for receiving a screwable connecting means. It is proposed that a second end (42) of the fixing bushing, which end faces away from a first end (41) of the fixing bushing (4), is guided through a cutout (7) of the circuit board (2) and protrudes from a cooling surface (22) of the circuit board (2) at a second side (22) of the circuit board (2) by a defined dimension (A).

Description

Electronic module

Technical Field

The invention relates to an electronic module, in particular a transmission control module for a motor vehicle transmission.

Background

Known electronic modules, for example for transmission control of automatic transmissions in motor vehicles, have electrical components which are protected from the environment. The electronic module may have, for example, electronic components including control circuits and power electronics components, as well as sensors and plug parts for connection to a vehicle wiring harness and contact elements for contacting the actuators. In particular, electronic modules for transmission control are installed in relatively Aggressive Transmission Fluid (ATF) and are subjected to high temperatures of up to 150 ℃ prevailing there. To protect sensitive electronic components from aggressive fluids, the electronic components must be tightly packaged.

For example, an electronic module is known from DE 102016216739 a1, which uses a barrier filling method for protecting electronic components, in which a circumferential barrier is applied to a first side of a circuit board, which barrier is subsequently filled with a potting compound that covers the electronic components. The second side face opposite to the first side face serves as a cooling face. The casting material on the first side forms a polymer protective system for the electronic component. This configuration combines the advantages of anti-erosive transmission fluids with high temperature resistance and vibration resistance. Furthermore, the electrical components are protected from metal chips contained in the transmission fluid by the potting material.

In order to fix the electronic module mechanically firmly to the driver block, a screw connection is usually used. The fixing of the electronic module must be sufficiently strong to be able to transmit the required tightening force to the electronic module. In particular, the pretension of the bolts must be maintained during the service life. For this purpose, in the prior art, differently configured metal structures are used on the electronic module, so that a sufficiently small installation behavior is ensured. Here, a pretensioning of the screw is necessary to avoid an unintentional loosening of the screw connection.

DE 102016216739 a1 relates to a special floating bearing bush for fixing electronic modules. Different types of fixing bushes are shown in the description and the drawings. Below this, there is a fixing bush described as a fixing support bush, in which the circuit board is provided with a cut-out which passes through the circuit board from the first side to the second side. The associated fixing bush is provided with a continuous inner receptacle for receiving a screwable connecting means and has a bearing surface facing the first side of the circuit board, which is soldered to a contact surface arranged at the edge of the cutout at the first side of the circuit board. The first end of the fixing bush facing away from the first side of the circuit board is not covered by the potting compound, so that the insertion of the screw can be achieved.

In DE 102016216739 a1, the cooling surface on the second side of the circuit board facing away from the first side serves as a bearing surface for bearing on the driver block. However, it is only conditionally possible to use this bearing surface for the screw connection during the service life of the electronic module, since a high clamping force on the plastic supported via the bearing surface to the circuit board can lead to yielding or loosening of the plastic in unfavorable cases, whereby the screw connection can also loosen during operation.

Disclosure of Invention

The invention relates to an electronic module of the type mentioned at the outset, wherein a second end of the fixing bushing facing away from a first end of the fixing bushing is guided through a cutout of the circuit board and protrudes from a cooling surface of the circuit board over a second side of the circuit board by a defined dimension.

The invention further relates to a method for producing such an electronic module, comprising the following method steps:

providing a circuit board having a first side and a second side facing away from the first side and at least one recess connecting the first side to the second side, wherein the circuit board is provided with a contact surface at least on the first side and with a cooling surface on the second side, wherein at least one contact surface is provided on the first side at an edge of the recess,

providing at least one fixing bushing having a continuous inner receptacle for receiving a screwable connecting means, wherein the fixing bushing has a first end and a second end facing away from the first end and a bearing surface for bearing on the circuit board,

-applying solder to the contact surface,

-mounting an electronic component on the contact surface of the first side provided with solder,

-inserting the fixing bushing into the indentation such that a bearing surface facing the first side of the circuit board bears at the edge of the indentation on the contact surface provided with solder, while the second end of the fixing bushing is guided through the indentation of the circuit board and protrudes from the cooling surface of the circuit board at the second side of the circuit board with the defined dimension, and

soldering the component and the bearing surface of the fixing bush to the associated contact surface, and

-applying a potting material onto the first side of the circuit board such that the electronic component is covered by the potting material and the fixing bush is not covered by the potting material on its first end.

The electronic module according to the invention offers the advantage that the forces required for establishing the fixing of the electronic module on, for example, a transmission block can be completely absorbed by the fixing bushing. Since the fixing bush can be made of metal, the circuit board or the potting material can be protected against compressive loads. This is achieved by the defined extension of the fastening bush on the second side of the circuit board, which extends the circuit board by a defined dimension from the cooling surface of the circuit board, so that the cooling surface is not subjected to load when the screw-on fastening means is screwed on. The interference from which the fixing bush projects as a cooling surface can advantageously be set so small that the axial distance between the second end of the fixing bush facing away from the first end of the fixing bush and the cooling surface is minimal. It is thereby possible to keep the gap between the electronic module and the transmission block connected thereto by the screw connection small, so that the thermal resistance does not become too great and sufficient cooling of the electronic components can also be ensured.

The manufacture of the electronic module with the fixing bush advantageously does not incur additional costs compared to the known solutions. Furthermore, the space requirement of the fixing bush on the circuit board can be kept very small, so that there is more space for fitting the remaining components. The fixing bush can advantageously be mounted and soldered on the circuit board as an SMD component by a subsequent reflow soldering method with an SMT method (SMT = Surface Mount Technology). The method may be performed in conjunction with the application and soldering of the electronic component. By subsequently casting the printed circuit board with the potting compound, the fixing bushing can be connected to the module in a mechanically robust and hermetically sealed manner.

Advantageous embodiments and refinements of the invention are achieved by the features contained in the dependent claims.

The fastening bush can be designed inexpensively as a cylindrical sleeve body with a continuous inner recess and a collar surrounding the sleeve body, on which collar a bearing surface is provided.

Advantageously, the defined dimensions are dimensioned in such a way that the distance between the bearing surface and the second end of the fixing bushing is dimensioned in such a way that the fixing bushing reliably projects from the cooling surface independently of manufacturing-related tolerances of the thickness of the circuit board between the first side surface and the second side surface. In other words, the distance of the bearing surface from the second end of the fixing bushing is dimensioned such that the desired tolerance with respect to the thickness of the circuit board always ensures that the second end of the fixing bushing projects from the cooling surface.

In a preferred embodiment variant, the fastening bush can protrude at least 1 micrometer and at most 500 micrometers and in particular at least 10 micrometers and at most 200 micrometers from the cooling surface of the circuit board. In the case of an expected tolerance variation of the thickness of the circuit board in the range of approximately 180 micrometers, the defined dimension a can be set in a simple manner by selecting the spacing dimension H of the fixing bushing such that the second end in any case projects out of the cooling surface of the circuit board independently of the thickness tolerance and at the same time the gap between the cooling surface and the counter surface on the driver block does not become too large, thereby not jeopardizing an adequate heat dissipation from the cooling surface.

An embodiment is particularly advantageous in which the printed circuit board, which is often originally designed as a multilayer circuit board, has conductor tracks on inner layers separated by insulating layers, and has conductor track layers completely surrounding the recess in the region of the recess on at least one of the inner layers and preferably on all inner layers. Due to the special layer structure of the circuit board, the thickness tolerances are significantly reduced. This advantageously results in the possibility of designing the axial distance between the cooling surface and the second end of the fixed bushing as small as possible, thereby reducing the thermal resistance between the cooling surface and the mounting surface on the transmission block. This in turn makes it possible to use components with high power consumption and heat generation, or to use electronic modules at high ambient temperatures.

Furthermore, an embodiment is advantageous in which the circumferential depression is milled into the circuit board in the edge region of the cutout on the first side of the circuit board, whereby the thickness of the circuit board is reduced at least in the region of the circuit board surrounding the cutout. The thickness tolerances can also be significantly reduced by this measure, which can be used instead of or in addition to the conductor track layer.

The fastening bushing is preferably made of metal, so that a continuous metallic fastening structure is ensured between the screwable fastening means and the mounting surface of the electronic module on, for example, the transmission block.

Drawings

Possible embodiments of the invention are explained below with reference to the drawings.

Figure 1 shows a cut-out of a schematic cross-section of an electronic module according to the invention,

figure 2 shows an embodiment of a detail in the area of the indentation of the circuit board,

fig. 3 shows a cut-out of a schematic cross-section of another embodiment of an electronic module according to the invention.

Detailed Description

Fig. 1 shows a cut-out of a schematic cross-section of an electronic module 1 according to the invention. The electronic module 1 has a circuit board 2 with a first side 21, which is provided as a mounting side, and a second side 22, which faces away from the first side. The circuit board 2 preferably has a plurality of recesses 24 which lead through from the first side 21 to the second side 22 of the circuit board 2. Only one of the recesses 24, which may be designed as a bore, for example, can be seen in fig. 1.

The printed circuit board 2 may be designed as a multilayer circuit board, in which the conductor tracks 25 made of copper are guided on inner layers separated by insulating layers, which inner layers may be electrically connected to one another and to the contact surfaces 5 on the first side 21 by means of Vias (Vias) or metallized through holes (durchkongtakierungen). On the second side 22, the circuit board 2 may be provided with a protective lacquer, the outer side of which is provided with a cooling surface 23. The protective lacquer 23 may cover, for example, the conductor tracks 25, which are in heat-conducting connection with the heat-generating electronic components on the first side 21 of the printed circuit board via the metallized through-holes. In this way, the generated heat can be transported through the circuit board to the cooling surface 23. The cooling surface 23 forms a flat surface on the lower side of the circuit board 2. In the context of the present application, "cooling surface" is understood to mean any flat surface provided on the underside of the circuit board for the purpose of heat removal. The cooling surface can be formed by a lacquer layer on top of the conductor tracks or also by a metal layer. The cooling surface 2 is intended to be placed parallel opposite a flat cooling body, for example a transmission block, with the smallest possible distance in order to transfer heat to the cooling body.

The contact surface 5 on the first side 21 also comprises a contact surface 5a in the form of a land which surrounds the edge of the recess 24 on the first side 21 of the circuit board 2. The contact surface 5 and the further contact surface 5a may be coated with solder 6 in a conventional manner. The connecting elements of the electronic component 3 are soldered to the contact surfaces 5 by means of solder 6.

Furthermore, a fastening bush 4, preferably made of metal, is provided, which has, for example, a cylindrical sleeve body 46 with a continuous inner recess 43 and a flange 45 surrounding the sleeve body 46, the side of the sleeve body facing the circuit board forming an annular bearing surface 44. The flange 25 projects radially out of the housing of the sleeve body 46 between the first axial end 41 and the second axial end 42 of the fixing bush 4, preferably so that the bearing surface 44 is oriented parallel to the contact surface 5 a. The support surface 44 is circumferentially connected to the contact surface 5a by the solder layer 6. The connection can be, but need not be, electrically conductive. The main function is to ensure tightness for the subsequent application of the potting material 7.

The second end 42 of the fixing bush 4 facing away from the first end 41 is guided through the recess 7 of the circuit board 2 and protrudes at the second side 22 of the circuit board 2 with a defined dimension a from the cooling surface 22 of the circuit board 2. The continuous inner receptacle 43 of the fixing bush 4 is preferably arranged coaxially with the cutout 24 of the circuit board.

The defined dimension a is preferably dimensioned such that the distance H between the bearing surface 44 and the second end 42 of the fixing bush 4 has a value in which the fixing bush 4 reliably projects from the cooling surface 23 independently of manufacturing-related tolerances of the circuit board thickness D between the first side 21 and the second side 22 of the circuit board 2. D in fig. 1 denotes the thickness of the circuit board between the cooling surface 23 forming the lower outer side and the contact surface 5a on the first side 21 of the circuit board 2. The circuit board thickness D, denoted by D', increases the thickness of the solder layer 6 arranged on the contact face 5 a. Reference H indicates the spacing between the bearing surface 44 and the second end 42 of the fixed bushing. As can be seen in fig. 1, the sum of D' and a equals H.

In the case of different tolerances in the thickness D of the circuit boards, it is important that the second end 42 of the fixing bush 4 is still always secured from the projection a of the cooling surface 23. This can be taken into account when designing the fixing bush. The spacing H of the fixing bushes 4 should therefore be designed such that, in the event of expected tolerance fluctuations in the thickness of the circuit board, an excess of the cooling surface 23 is always ensured. However, the spacing dimension H should not be selected too large in order to ensure that the gap between the cooling surface 23 and the mounting surface, for example on the drive block, on which the fixing bush 4 bears directly with the second end 42, is not too large.

For example, the defined dimension a can be set very simply by selecting the spacing dimension H such that the second end 42 projects at least 1 micrometer and at most 500 micrometers from the circuit board. If tolerance fluctuations are based on a circuit board thickness of 180 micrometers, the defined dimension a can advantageously be set by selecting the spacing dimension H of the fixing bushing such that the second end 42 projects at least 10 micrometers and at most 200 micrometers from the cooling surface 23 of the circuit board.

It follows from the above illustration that, if the thickness tolerance of the circuit board 2 can be reduced at least in the region of the recess 24, the spacing dimension a can then be reduced (and the gap between the cooling surface 23 and the second end 42 of the fixing bush 4 can advantageously be selected as small as possible). This can be achieved, for example, in that at least one and preferably all of the inner layers of the circuit board 2 have a conductor track layer 26 in the region of the recess 24, which completely surrounds the recess. In normal multilayer circuit boards, tolerance fluctuations in the circuit board thickness D are also produced by the fact that, in the production of the multilayer circuit board, the conductor track structures which are arranged irregularly on the inner layer must be filled with resin of a circuit board prepreg which serves as an insulating interlayer. The intermediate spaces of different thickness between the two conductor track layers, which are caused by the position of the conductor tracks, can lead to depressions at the first and second side of the circuit board and ultimately to thickness fluctuations.

As shown in fig. 2, if, in the region of the recess 24, as far as possible, all inner layers of the printed circuit board 2 now each have a ring-shaped conductor track layer 26 which completely surrounds the recess 24, it can be ensured that in this region the intermediate space between the conductor track layers 26 is filled uniformly with an insulating intermediate layer with an outer diameter d3 and an inner diameter d2, wherein the value of the inner diameter d2 can advantageously approach the value of the inner diameter d1 of the recess 24 and the value of the outer diameter d3 can advantageously approach the value of the outer diameter of the contact surface 5 a. As a result, fluctuations in the thickness D of the circuit board can be reduced at least in the region around the recess 24, in which the fixing bush 4 bears (autoflies) on the circuit board 2. In this way, the interference a can be selected to be smaller. The annular conductor track layer 26 surrounding the recess 24 need not have an electrical function and can serve only for reducing fluctuations in the circuit board thickness D or for reducing tolerance fluctuations in the circuit board thickness D.

Fig. 3 shows a further method for reducing the thickness tolerance of the circuit board 2 in the region of the recess 24. The side of the fixing bush 4 to the right of the axis corresponds to the illustration in fig. 1, while the side of the fixing bush 4 to the left of the axis shows a further embodiment for comparison, in which a circumferential depression 27 is milled into the circuit board 2 in the edge region of the recess 24 on the first side 21 of the circuit board 2. As can be seen in fig. 3, the circuit board thickness D ″ is thereby reduced relative to the thickness D at least in the region of the circuit board 2 surrounding the recess 24. The milling of the circuit board 2 can be performed with a higher precision than in the pressing of the layers. Thereby reducing the tolerance of the thickness of the circuit board and possibly reducing the defined dimension a of the excess.

The manufacture of the circuit board may be performed as follows. First, a printed circuit board 2 is provided, which has a first side 21 and a second side 22 facing away from the first side, and at least one recess 24 connecting the first side 21 to the second side 22, and which is provided with a contact surface 5 at least on the first side 21 and a cooling surface 23 on the second side 22. The contact surface 5a is arranged on the first side 21 at the edge of the recess 24. Furthermore, a fixing bush 4 associated with the recess 24 is provided, which has a continuous inner receptacle 43 for receiving a screwable connecting means, wherein the fixing bush 4 has a first end 41, a second end 42 facing away from the first end 41, which is spaced apart from the first end 41 by an axial length L of the fixing bush 4, and a bearing surface 44 for bearing on the circuit board 2. In a further manufacturing step, solder 6 is applied to the contact surfaces 5, for example in a soldering station. In a mounting Device, for example, in the form of an SMD mounting Device (SMD = Surface Mount Device), the electronic component 3 is placed (aufsetzen) on the contact Surface 5 of the first side 21, which contact Surface is provided with solder 6. Parallel to this, the fixing bush 4 can be inserted into the recess 24 such that the bearing surface 44 facing the first side 21 bears (autoflies) at the edge of the recess 24 on the contact surface 5a provided with the solder 6, while the second end 42 of the fixing bush 4 is guided through the recess 24 of the circuit board 2 and projects from the cooling surface 23 of the circuit board 2 at the second side 22 of the circuit board 2 by the defined dimension a. This can also be done with SMD mounters. In a further production step, the bearing surfaces 44 of the component 3 and of the fastening bush 4 are soldered to the associated

contact surfaces

5 and 5a, which can be carried out, for example, in a reflow soldering station.

Finally, the potting compound 7 is applied to the first side 21 of the circuit board 2, so that the electronic component 3 is covered by the potting compound 7 and the fixing bush 4 is not covered by the potting compound 7 at its first end 41. The potting compound 7 may comprise a polymer protective system, in particular an epoxy resin, which is applied to the first side 21 of the circuit board 2 in liquid form within the enclosure 8 previously applied from the first side 21 and then hardens.

When the electronic module 1 is fixed to a mating body, for example a drive block, the electronic module 1 is supported with the second end 42 of the fixing bush 4 on the mating body, so that the cooling surface 23 is opposite the mating body via a narrow gap, which is defined by the spacing dimension a. The screw-on fastening means can be screwed into the counterpart via the inner receptacle 43 of the fastening bush 4. The clamping force of the bolt transmitted to the first end 41 of the fixing bush 4 is completely absorbed by the fixing bush.

Claims

1. An electronic module (1), in particular a transmission control module for a motor vehicle transmission, having a circuit board (2) with a first side (21) and a second side (22) facing away from the first side, having an electronic component (3) arranged on the first side (21) and having a potting compound (7) arranged on the first side (21) of the circuit board (2) covering the electronic component (3), having a cooling surface (23) arranged on the second side (22) and having at least one recess (24) extending from the first side (21) through the circuit board (2) to the second side (22), wherein the electronic module (1) has at least one fastening bush (4) with a continuous inner receptacle (43) for receiving a screw-on connection means, wherein the fixing bushing (4) has a bearing surface (44) facing the first side (21), which is soldered to a circumferential contact surface (5 a) arranged at the edge of the cutout (24) at the first side (21) of the circuit board, wherein the fixing bushing (4) is not covered by the potting compound (7) with its first end (41) facing away from the first side (21) of the circuit board (2), characterized in that a second end (42) of the fixing bushing facing away from the first end (41) of the fixing bushing (4) is guided through the cutout (7) of the circuit board (2) and protrudes from the cooling surface (22) of the circuit board (2) at the second side (22) of the circuit board (2) with a defined dimension (A).

2. The electronic module according to claim 1, characterized in that the fixing bushing (4) has a cylindrical sleeve body (46) and a flange (45) surrounding the sleeve body (46), the sleeve body having a continuous inner recess (43), the bearing surface (44) being configured on the flange.

3. The electronic module according to one of the preceding claims, characterized in that the defined dimension (A) is dimensioned such that a distance (H) of the bearing surface (44) from the second end (42) of the fixing bushing (4) is dimensioned such that the fixing bushing (4) reliably protrudes from the cooling surface (23) independently of manufacturing-induced tolerances of the circuit board thickness (D) between the first side surface (21) and the second side surface (22).

4. The electronic module according to any of the preceding claims, characterized in that the fixing bush (4) projects at least 1 micrometer and at most 500 micrometers and in particular at least 10 micrometers and at most 200 micrometers from the cooling surface (23) of the circuit board.

5. An electronic module according to any one of the preceding claims, characterised in that the circuit board (4) is a multilayer circuit board in which the conductor tracks (25) are also guided on inner layers of the circuit board (2) separated by insulating layers, and in that at least one and preferably all of the inner layers of the circuit board (2) have a conductor track layer (26) completely surrounding the gap in the region of the gap (24).

6. The electronic module according to one of the preceding claims, characterized in that a circumferential depression (27) is milled into the circuit board (2) on the first side (21) of the circuit board (2) in the edge region of the cutout (24), whereby the circuit board thickness (D) is reduced at least in the region of the circuit board (2) surrounding the cutout (24).

7. The electronic module according to any of the preceding claims, characterized in that the fixing bush (4) is made of metal.

8. Method for manufacturing an electronic module according to any of claims 1 to 7, characterized by the steps of:

-providing a circuit board (2) having a first side (21) and a second side (22) facing away from the first side and at least one recess (24) connecting the first side (21) to the second side (22), wherein the circuit board (2) is provided with a contact surface (5) at least on the first side (21) and with a cooling surface (23) on the second side, wherein at least one contact surface (5 a) is provided on the first side (21) at an edge of the recess (24),

-providing at least one fixing bushing (4) having a continuous inner receptacle (43) for accommodating a screwable connecting means, wherein the fixing bushing (4) has a first end (41) and a second end (42) facing away from the first end (41) and a bearing surface (44) for bearing on the circuit board (2),

-applying solder (6) onto the contact face (5),

-mounting an electronic component (3) on a contact face (5) of the first side face (21) provided with solder (6),

-inserting the fixing bushing (4) into the indentation (24) such that a bearing surface (44) facing the first side surface (21) bears on a contact surface (5 a) provided with solder (6) at the edge of the indentation (24), while a second end (42) of the fixing bushing (4) is guided through the indentation (24) of the circuit board (2) and protrudes from a cooling surface (23) of the circuit board (2) at the second side surface (22) of the circuit board (2) with a defined dimension (a), and

-brazing the bearing surfaces (44) of the component (3) and the fixing bush (4) to the associated contact surface (5), and

-applying a potting material (7) onto the first side (21) of the circuit board (2) such that the electronic component (3) is covered by the potting material (7) and the fixing bush (4) is not covered by the potting material (7) on its first end (41).

9. Method according to claim 8, characterized in that in the step of providing the circuit board (2) a circumferential depression (27) is milled into the circuit board (2) on the first side (21) of the circuit board (2) in the edge region of the cutout (24), whereby the circuit board thickness (D) is reduced at least in the region of the circuit board (2) surrounding the cutout (24), and in that the at least one contact surface (5 a) is arranged at the bottom of the milling at the edge of the cutout (24).