DE102021125264A1 - electronic device - Google Patents

Abstract

The invention relates to an electronic device, comprising an electronic circuit board fitted with at least one electronic component, in particular a plurality of electronic components, and a housing in which the fitted circuit board is arranged, with cavity sections between the inner surfaces of the housing and the fitted circuit board for shielding are encapsulated with a casting compound on the assembled electronic circuit board in the housing due to environmental influences. The electronic device according to the invention is characterized in that the assembled circuit board is covered at least in sections with a compressible foam mat that is at least 0.5 mm thick in such a way that the foam mat covers surface areas of the circuit board and surface areas of the electronic components and the casting compound on the surface facing away from the circuit board against the foam mat.

Description

The invention relates to an electronic device, comprising an electronic circuit board fitted with at least one electronic component, in particular a plurality of electronic components, a housing in which the fitted circuit board is arranged, with cavity sections between the inner surfaces of the housing and the fitted circuit board for shielding against environmental influences cast on the assembled electronic circuit board in the housing with a casting compound.

Electronic devices of this type are well known in the field and are used in particular in the motor vehicle sector, since the electronic devices used there, such as aggregate controls, external electronic actuation devices, or headlights, etc., can be exposed to extreme weather fluctuations and environmental influences such as dust and moisture. A known problem with such electronic devices is that casting materials are often used in which the casting compound cast into the housing is subject to a certain amount of shrinkage when curing. Depending on the specific design, this can result in impermissibly high mechanical forces acting on the printed circuit board, the electronic components and/or connection points between the components and the printed circuit board, which can ultimately lead to the failure of the respective electronic circuit on the printed circuit board. In a similar way, different thermal expansion coefficients of the materials of the printed circuit board, components and/or potting material or relative movements of the parts to one another, caused by operational movements such as vibrations, can lead to mechanical forces occurring within the electronic device, which can lead to the failure of the electronic circuit.

In this respect, the present invention is based on the object of developing a conventional electronic device in such a way that the risk of a functional failure of the device caused by shrinkage of the casting compound during curing and/or due to high temperature differences during operation or due to relative movements of the parts of the electronic device to one another during operation is caused, can be excluded or at least significantly reduced.

The present invention solves this problem with an electronic device, comprising an electronic printed circuit board equipped with at least one electronic component, in particular with a plurality of electronic components, a housing in which the printed circuit board with components is arranged, with cavity sections between the inner surfaces of the housing and the component Printed circuit board for shielding from environmental influences are shed on the assembled electronic circuit board in the housing with a potting compound. The electronic device according to the invention is characterized in that the assembled circuit board is covered at least in sections with a compressible and/or expandable foam mat that is at least 0.5 mm thick in such a way that the foam mat covers surface areas of the circuit board and surface areas of the electronic components and the casting compound on the surface of the foam mat facing away from the printed circuit board.

The invention is based on the idea, by providing a sufficiently thick covering of the assembled printed circuit board with a compressible and/or stretchable material in the form of a foam mat for volume compensation when the potting material shrinks or when the parts within the electronic device move relative to one another, for example caused by a different temperature coefficient or by operational vibrations of the parts to one another, so that no impermissible forces occur, in particular on the electronic components of the electronic circuit board, so that a failure of an electronic component arranged on the circuit board or an electronic circuit arranged on the circuit board is avoided can be. By covering the assembled circuit board with the foam mat at least in sections, the casting compound in these sections does not lie directly against the assembled circuit board or the electrical components arranged there, but rather corresponding foam mat sections that act as a compressible and/or expandable buffer between the assembled circuit board and Potting compound work.

The term foam is to be understood broadly and includes a plastic whose structure can be formed by a large number of cells, which can represent cavities or pores enclosed by the base material. Provision can preferably be made for a fluid such as air to be arranged in these cells. The term "mat" means a flat structure in which the thickness is smaller, in particular very much smaller, in particular less than 1/10 of the respective length and width.

In principle, the invention can be applied or implemented to devices in which an electronic printed circuit board equipped with an electronic component or a plurality of electronic components is encapsulated in a housing sen is Such devices are to be understood as electronic devices within the meaning of the present application. In addition to the at least one printed circuit board, other parts can of course also be cast with the casting material in the housing, for example retaining elements, fixed sections of actuators, or other functional elements. Such electronic devices can be designed in particular for use outdoors, for example motor vehicle ancillary units, evaluation and/or control circuits arranged in a housing, electrical or electronic actuating devices arranged in a housing, headlights, etc., include or be, with the respective application such electronic devices according to the invention is not limited to the motor vehicle sector. Provision can be made for the plurality of electronic components, in particular SMD components, to be electrically connected to form an electronic circuit which is arranged on the printed circuit board. Furthermore, all known types of printed circuit boards can be used to implement the electronic device according to the invention, in particular single-sided printed circuit boards, multilayer printed circuit boards or also special technology printed circuit boards such as ultra-thin printed circuit boards or HDI (high-density interconnect) printed circuit boards.

Additional inventive features and developments of the invention are specified in the following general description, the figures, the description of the figures and the dependent claims.

It can expediently be provided that the at least one foam mat is designed and arranged to compensate for different temperature expansion coefficients of the potting material, the printed circuit board material and the electronic components of the printed circuit board and/or to compensate for a reduction in hardness of the potting material. For this purpose, it can be provided that the material of the foam mat is designed to be compressible and/or stretchable, in particular through the specified cellular structuring with a fluid arranged in the cells, in particular air, in which case the cell walls can be designed to be elastic in order to provide compressibility and stretchability of the foam mat .

Depending on the embodiment, the foam mat can have a closed-cell foam, in which the walls between the individual cells are completely closed, or a mixed-cell foam, in which the walls between the individual cells are completely closed in some of the cells and the walls between the individual cells are completely closed in another part of the cells cell walls are not closed. In one embodiment, it can also be provided that the foam is designed as an integral foam with a closed outer skin and a cellular core, in which the density decreases with distance from the outer skin.

It can expediently be provided that an adhesive layer is provided between the assembled circuit board and the at least one foam mat in order to provide a material connection between the foam mat and a respectively assigned surface area of the assembled circuit board, so that during the manufacture of the electronic device according to the invention, in particular during the step of encapsulating the in the housing arranged assembled circuit board with a casting material no relative displacement between foam mat and assembled circuit board occurs.

It can expediently be provided that at least one side of the assembled circuit board, in particular both sides, is covered with a plurality of such foam mats, in particular in such a way that individual foam mats are arranged next to one another to essentially completely cover predetermined surface areas or the entire surface of the assembled circuit board with foam mats, it is also possible to overlap adjacent foam mats to provide gap-free coverage. In one embodiment, it can also be provided that several, in particular two or three, of the foam mats are arranged one on top of the other in order to provide a predetermined thickness of the foam mat occupancy on the printed circuit board.

It can expediently be provided that the at least one foam mat has a thickness of ≦6 mm, i. H. that this thickness is between 0.5 mm and 6 mm, including the above limits. In particular, this thickness can be between 1 mm and 5 mm, preferably between 1 mm and 3 mm, particularly preferably between 1 mm and 2 mm, and in particular 1.5 mm. It can be provided that the thickness of the foam mat is adapted to the size of the respective cavity between the assembled circuit board and the boundary wall surfaces of the housing.

The at least one foam mat can expediently comprise a cellular rubber, in particular a closed-cell or mixed-cell, soft-elastic cellular rubber such as EPDM. Provision can preferably be made to use a foam mat that is self-adhesive on one side for covering the printed circuit board. In principle, the material can for the production of the at least one foam mat include in particular natural and/or synthetic rubber.

As shown, it can be provided that a closed-cell or mixed-cell cellular rubber is used as the material for the at least one foam mat, wherein the closed cells can be watertight and airtight, so that in particular with closed-cell foam, but also with mixed-cell foam with a thickness of more than 500 μm it can be ensured that such a surface section of the assembled printed circuit board covered with the at least one foam mat can be kept free of casting compound, d. H. such a surface area may not come into contact with the potting compound, but instead a compressible and/or expandable section of foam material may be placed adjacent thereto to safely avoid the problems noted above with conventional electronic devices.

As a synthetic rubber material for producing the at least one foam mat for designing the electronic device according to the invention, in addition to the already mentioned EPDM (ethylene propylene diene rubber), for example styrene butadiene rubber (SPR), butadiene acrylonitrile rubber (NBR) or chloroprene rubber (CR) can be used.

Any of the known casting materials can expediently be used in the electronic device designed according to the invention, in particular epoxy resin materials, polyurethanes and silicone materials. As a rule, these can be designed as two-component materials, for example a corresponding synthetic resin component and an associated hardener component, with the casting compound being able to be produced by mixing the two. In principle, in the design of the electronics device according to the invention, due to the covering of the printed circuit board with a foam mat, it can be provided that a casting material is used that has a comparatively large shrinkage due to hardening. Since such a material is often comparatively inexpensive, the described disadvantages of such casting compounds can be compensated for in the electronic device according to the invention.

In such embodiments, in which the assembled circuit board includes an electronic component with high heat loss, it can expediently be provided that such a predetermined electronic component is exempt from being covered with the at least one foam mat, so that the potting material rests on the surface of this electronic component, in particular for heat dissipation via the casting material or the casting compound. It can expediently be provided, in particular for this purpose, to use a thermally conductive casting compound such as a silicone elastomer as the casting material in the electronic device according to the invention.

In particular when using a mixed-cell foam mat, to ensure a sufficient, compressible and/or stretchable layer of the plastic mat, it can be provided that the potting material has a penetration depth into the at least one foam mat that is less than about 30%, in particular less than about 20% of the thickness of the foam mat.

A large number of materials are possible for designing the housing of the electronic device designed according to the invention, for example metals, but also plastics, in particular plastic materials which are usually used for designing housings for electronic printed circuit boards. The shape of the housing can be adapted to the respective application, e.g. cuboid or cylindrical. In the case of a closed housing, this can have, for example, one or more small pouring openings and possibly one or more small air outlet openings. However, it is also possible for the housing for the electronic device according to the invention itself to be designed to be open, e.g. as a hollow-cylindrical housing with an open end face, or as a cuboid housing that is open on one side surface. In such embodiments, the potting compound can be introduced into the housing via the side opening, possibly in such a way that the potting compound closes the side opening of the housing.

The electronic device designed according to the invention can also have more than one individual electrical circuit board equipped with electronic components, encapsulated in a housing, which are arranged inside the housing and each covered at least in sections with a compressible foam mat that is at least 0.5 mm thick in such a way that the foam mat covers surface areas of the respective printed circuit board and surface areas of the electronic components and the casting compound lies against the surface of the foam mat facing away from the printed circuit board.

• - Bereitstellen einer mit zumindest einem elektronischen Bauteil, insbesondere einer Mehrzahl von elektronischen Bauteilen bestückten Leiterplatte;
• - Bereitstellen zumindest einer komprimierbaren und/oder dehnbaren Schaumstoffmatte;
• - zumindest einseitiges Belegen der bestückten Leiterplatte mit wenigstens einer, zumindest 0,5 mm dicken Schaumstoffmatte, sodass die zumindest eine Schaumstoffmatte Oberflächenbereiche der Leiterplatte und Oberflächenbereiche des zumindest einen elektronischen Bauteils zumindest abschnittsweise abdeckt;
• - Bereitstellen eines Gehäuses;
• - Anordnen der bestückten Leiterplatte in dem Gehäuse;
• - Vergießen der mit zumindest einer Schaumstoffmatte belegten, bestückten Leiterplatte in dem Gehäuse mit einer Vergussmasse, sodass die Vergussmasse an der der Leiterplatte abgewandten Oberfläche der Schaumstoffmatte anliegt.

The above-specified object of the present invention is achieved in terms of method by a method for producing an electronic device, comprising one with at least one Electronic component, in particular an electronic printed circuit board fitted with a plurality of electronic components, a housing in which the fitted printed circuit board is arranged, with cavity sections between the inner surfaces of the housing and the fitted printed circuit board being encapsulated with a casting compound to shield the fitted electronic printed circuit board against environmental influences in the housing be, in particular for the production of an electronic device according to one of claims 1-7. The method according to the invention comprises the steps:

• - providing a printed circuit board fitted with at least one electronic component, in particular a plurality of electronic components;
• - Providing at least one compressible and/or stretchable foam mat;
• - at least one-sided covering of the assembled printed circuit board with at least one foam mat that is at least 0.5 mm thick, so that the at least one foam mat covers surface areas of the printed circuit board and surface areas of the at least one electronic component at least in sections;
• - providing a housing;
• - Arranging the assembled circuit board in the housing;
• - Potting the at least one foam mat covered, populated printed circuit board in the housing with a potting compound, so that the potting compound rests against the surface of the foam mat facing away from the circuit board.

It should be noted that the method steps specified above can also be carried out in a different order according to the invention, for example the printed circuit board equipped with at least one electronic component can also first be arranged in the housing and only then be covered with the at least one foam mat.

In order to avoid a relative displacement of the at least one foam mat on the assembled circuit board during the casting process for casting the circuit board in the housing, it can expediently be provided that the at least one foam mat provided is fixed to the circuit board before the casting process, for example by clamping or screwing. However, it can also be provided that the at least one foam mat has an adhesive layer on at least one side and when covering the assembled circuit board with the at least one foam mat, this is glued onto the assembled circuit board. Provision can also be made to apply a double-sided adhesive film to the assembled circuit board before the at least one foam mat is placed on the assembled circuit board and then to apply the at least one foam mat, so that the at least one foam mat is fixed to the assembled circuit board before the casting process is carried out .

In order to avoid heat build-up and the resulting failure of an electronic component arranged on the printed circuit board, it can be provided, particularly in the case of electronic components that have a high level of heat loss, that a section of the assembled printed circuit board in which such a given electronic component is arranged Occupancy with the at least one foam mat is excluded, so that the potting material or potting compound is applied to the surface of the electronic component facing away from the printed circuit board in order to dissipate the waste heat generated by the electronic component. In this embodiment, the casting compound can preferably have a comparatively high heat conduction.

In order to secure at least all sensitive surface sections on the assembled printed circuit board, it can expediently be provided that the step of covering the assembled printed circuit board with the at least one foam mat that is at least 0.5 mm thick involves the application of a plurality of foam mats arranged next to one another on the assembled printed circuit board includes, such that a predominant portion of the surface or at least one main surface of the assembled circuit board is covered with the foam mats. Depending on the embodiment, it can also be provided that adjacent foam mats or foam mats placed next to one another are arranged in an overlapping manner to ensure that at least in this area no casting compound gets onto the underlying surface sections of the circuit board and/or electronic components and that the foam mats therefore cover the respective surface section of the fully cover the assembled printed circuit board.

• 1 in einer perspektivischen Ansicht die Belegung einer bestückten Leiterplatte an einer ihrer Hauptflächen mit zwei Schaumstoffmatten zur Gestaltung einer erfindungsgemäßen Elektronikeinrichtung,
• 2 die Belegung der in 1 gezeigten bestückten elektronischen Leiterplatte auf ihrer Rückseite mit einer weiteren Schaumstoffmatte, und
• 3 ein Gehäuse zur Aufnahme der in den 1, 2 dargestellten bestückten, und mit Schaumstoffmatten belegten Leiterplatte und zum Vergießen der Leiterplatte in dem Gehäuse mit einer Vergussmasse

zeigt.The invention is explained below by describing an embodiment together with modifications of an electronic device according to the invention with reference to the attached drawings, wherein

• 1 in a perspective view the occupancy of an assembled printed circuit board on one of its main surfaces with two foam mats for the design of an electronic device according to the invention,
• 2 the occupancy of the in 1 shown assembled electronic circuit board on its back with another foam mat, and
• 3 a housing for receiving in the 1 , 2 illustrated assembled circuit board covered with foam mats and for casting the circuit board in the housing with a casting compound

shows.

The production of an embodiment of an electronic device according to the invention, which is designed as a headlight, is described below. 1 shows an assembled printed circuit board 2, comprising an in 1 horizontally arranged printed circuit board section 3a and two spaced apart and arranged and fastened on respective end faces of the printed circuit board section 3a, vertically running printed circuit board sections 3b, 3c.

In the embodiment described, the printed circuit board section 3a fitted with electronic components comprises a driver circuit or supply circuit for two different light sources, e.g. different LEDs, which are each arranged separately on the printed circuit board sections 3b, c.

To simplify the illustration, the electronic components are not shown, in particular on the horizontally running printed circuit board section 3a. Two foam mats 4a, 4b are assigned to the horizontally running printed circuit board section 3a, aligned in the horizontal plane and covered with an adhesive on the side facing the printed circuit board section 3a. A relative movement of the two foam mats 4a, 4b and the horizontally running printed circuit board section 3a towards one another in the specified vertical direction leads to the two foam mats 4a, 4b being fixed at the in 1a visible main surface of the occupied with electronic components printed circuit board section 3a. In the embodiment described, the foam mats 4a, b, c have a thickness of 1.5 mm and comprise a closed-cell cellular rubber made of EPDM.

Since in the embodiment described the printed circuit board section 3a, which is arranged horizontally in the figures, is fitted on its two main surfaces with respective electronic SMD components, the illustration of FIG 2 the back of the circuit board section 3a with a plastic mat 4c in the same way as with reference to FIG 1 indicated, occupied, wherein the foam mat 4c is in turn glued to the printed circuit board section 3a.

The printed circuit board 2 covered on both sides in the region of the printed circuit board section 3a with foam mats 4a, b, c is then inserted into a cylindrical housing in the embodiment described, see FIG 3 . Connection cables, not shown, are soldered to the printed circuit board section 3a of the printed circuit board 2 to supply the driver circuit or feed circuit with power. The cylindrical housing 6 has an optical cover (not shown) on one end face 60a, which rests sealingly against the cylindrical wall of the housing 6 at the end face and through which the light generated by the lamps arranged on the printed circuit board sections 3b, 3c leaves the device. On the opposite end face of the cylindrical housing 6, the connection cables (not shown) for supplying the electronic circuit of the printed circuit board 2 are routed out of the housing 6 for connection to a supply source such as a power source.

On the second end face 60b of the housing 6, which is open, a potting compound, here a silicone-based potting compound, is then introduced in a manufacturing step, so that gaps between the inner wall of the housing 6 and the assembled electrical circuit board 2 are filled with potting compound, whereby the housing is also closed in the area of its second end face 60b. After the casting compound has hardened, the electronic device designed here as a headlight can be attached to a vehicle, for example via the fastening rod 61, and connected to a supply source.

Reference List

1

electronic device

2

Assembled electrical circuit board

3a,b,c

circuit board section

4a,b,c

foam mat

6

Housing

60a, b

face

61

mounting rod

Claims (11)

Electronic device (1), comprising - an electronic printed circuit board (2) fitted with at least one electronic component, in particular with a plurality of electronic components, - a housing (6) in which the fitted printed circuit board (2) is arranged, with cavity sections between Inner surfaces of the housing and the assembled circuit board (2) for shielding the assembled electronic circuit board in the housing from environmental influences with a casting compound are encapsulated, characterized in that the printed circuit board (2) with components is covered at least in sections with a compressible, at least 0.5 mm thick foam mat (4a,b,c) in such a way that the foam mat surface areas of the circuit board (2) and surface areas of the electronic Covering components and the potting compound rests against the surface of the foam mat facing away from the circuit board. Electronic device (1) after claim 1 , characterized in that the at least one foam mat (4a,b,c) is designed and arranged as a closed-cell or mixed-cell foam mat to compensate for different temperature expansion coefficients of the potting material, the printed circuit board material and the electronic components of the printed circuit board (2) and/or to compensate for curing shrinkage of the potting material. Electronic device (1) after claim 1 or 2 , characterized in that the at least one foam mat (4a, b, c) has a thickness between 0.5 mm - 6 mm, in particular between 1 mm - 3 mm, preferably a thickness of about 1.5 mm. Electronic device (1) after claim 1 , 2 or 3 , characterized in that the material of the at least one foam mat (4a, b, c) comprises a cellular rubber such as EPDM, in particular is made from a cellular rubber such as EPDM. Electronic device (1) according to one of Claims 1 until 4 , characterized in that the material of the at least one foam mat (4a, b, c) has a Shore A hardness value between 60 and 100, in particular from about 70. Electronic device (1) according to one of Claims 1 until 5 , characterized in that the potting material comprises a silicone potting material, an epoxy resin potting material, or a polyurethane potting material. Electronic device (1) according to one of Claims 1 until 6 , characterized in that the potting material has a penetration depth into the foam mat (4a, b, c) which is less than about 30%, in particular less than about 20% of the thickness of the foam mat. Method for producing an electronic device (1), comprising an electronic printed circuit board (2) equipped with at least one electronic component, in particular with a plurality of electronic components, a housing (6) in which the printed circuit board is arranged, with cavity sections between inner surfaces of the housing (6) and the assembled printed circuit board (2) are cast on the assembled electronic printed circuit board (2) in the housing with a casting material to shield against environmental influences, in particular for the production of an electronic device according to one of Claims 1 until 7 , comprising the steps of: - providing an assembled printed circuit board (2); - Providing at least one compressible, at least 0.5 mm thick foam mat (4a,b,c); - at least one-sided covering of the printed circuit board (2) with the at least one foam mat (4a, b, c), so that the foam mat covers surface areas of the circuit board (2) and surface areas of the at least one electronic component at least in sections; - Providing a housing (6); - arranging the printed circuit board (2) equipped with at least one electronic component in the housing (6); - Potting the at least one foam mat (4a,b,c) occupied, populated circuit board (2) in the housing with a potting compound, so that the potting compound rests against the surface of the foam mat facing away from the circuit board. procedure after claim 8 , characterized in that an adhesive layer is applied to at least one side of the at least one foam mat (4a, b, c) provided and when covering the assembled circuit board (2) with the at least one foam mat, this is glued to the assembled circuit board. procedure after claim 8 or 9 , characterized in that a section of the assembled printed circuit board (2), in which a given electronic component is arranged, is excluded from the occupancy of the at least one foam mat (4a, b, c), so that when the printed circuit board (2) is cast the potting compound is applied to the surface of the electronic component facing away from the printed circuit board. procedure after claim 8 , 9 or 10 , characterized in that the step of covering the assembled circuit board (2) with the at least one foam mat (4a, b, c) comprises the application of a plurality of foam mats arranged next to one another on the assembled circuit board in such a way that a predominant portion of the surface at least one main surface of the assembled circuit board (2) is covered with the foam mats (4a,b,c).

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