Printed circuit board having at least one contact element, housing having such printed circuit board, and method for forming low-resistance electrical connection

Abstract

To provide a printed circuit board having at least one contact element.SOLUTION: A fixed end of a contact element 102 is connected to a printed circuit board, and a free end of the contact element 102 includes a contact point 100 for contacting an oxidized contact surface. An S-shaped spring region 108 is disposed between the fixed end and the free end. The spring region 108 defines a direction of compression of the contact point 100 substantially perpendicular to a main extension plane of the printed circuit board. The contact point 100 includes at least one sharp edge for penetrating an oxide layer of the contact surface. Flanks of the sharp edge are oriented oblique to the compression direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a printed circuit board with at least one contact element, a housing with such a printed circuit board, and a method for forming a low resistance electrical connection.

[0002] Prior art To connect the printed circuit board to the electrical potential of the metal housing, the printed circuit board can have a cable with plug contacts. Corresponding plug contacts may be arranged in the housing. During assembly, the plug contacts are connected, the printed circuit board is connected to the housing part, and the housing is closed by a further housing part. Alternatively, the printed circuit board can have spring contact elements soldered to the housing with contact areas formed in a dome or sphere shape.

[0003] Disclosure of the Invention Against this background, the approach presented herein is to provide a printed circuit board with at least one contact element, a housing with such a printed circuit board, and a method for producing a low-resistance electrical connection according to the independent claims. Advantageous developments and improvements of the approach presented herein become apparent from the description and are set out in the dependent claims.

[0004] Advantages of the Invention The metallic housing may be made of a metal material that forms an oxide layer with low electrical conductivity. This metal material may be, for example, an aluminum material. Therefore, contacting the housing for potential compensation purposes is difficult. Therefore, contact elements made of metal materials that do not form any oxide layer or that only form a slight oxide layer have been arranged on the housing up to now. These contact elements are then contacted by suitable contact elements on the printed circuit board. These contact elements on the printed circuit board may, in particular, be arranged on the cable. Alternatively, the contact elements may be spring contacts soldered to the printed circuit board with spherical, dome-shaped contact points. The contact elements may, for example, be gold-plated.

[0005] In the approach presented here, contact elements are fixedly arranged on a printed circuit board. The housing has only a contact surface made of the metal material of the housing. The contact surface may be covered with an oxide layer. The contact element has at least one burr-free or pointed edge at the contact point for contacting the contact surface. This edge penetrates the oxide layer of the housing material and reaches the non-oxidized metal material. This results in a conductive connection between the printed circuit board and the housing with only low contact resistance.

[0006] The approach presented here makes it possible to dispense with additional plug-in connections for potential compensation or separate contact surfaces made of non-oxidizing or slightly oxidizing material, which significantly simplifies the installation of the printed circuit board in the housing.

[0007] According to a first aspect of the present invention, a printed circuit board is provided with at least one contact element, wherein a fixed end of the contact element is connected to the printed circuit board and a free end of the contact element has a contact point for contacting an oxidized contact surface, wherein an S-shaped spring region is arranged between the fixed end and the free end, the spring region defining a biasing direction of the contact point substantially perpendicular to a main extension plane of the printed circuit board, wherein the contact point has at least one pointed edge for penetrating the oxide layer of the contact surface, wherein the side surfaces of the pointed edge are oriented obliquely with respect to the biasing direction.

[0008] According to a second aspect of the present invention, a housing is provided with at least one inserted printed circuit board according to the first aspect, wherein the contact points abut against an oxidized contact surface of the housing and the spring areas are biased in the biasing direction, wherein the pointed edges are pressed against the contact surface with the resulting pressing force, penetrating the oxide layer of the contact surface and forming a low-resistance electrical connection between the printed circuit board and the contact surface.

[0009] According to a third aspect of the present invention, a method for forming a low resistance electrical connection between a printed circuit board according to the first aspect and a housing is provided, wherein a pointed edge is placed on an oxidized contact surface of the housing and the spring region is biased in a biasing direction, wherein the pointed edge is pressed against the contact surface with a resulting pressing force, wherein the pointed edge penetrates the oxide layer and forms a low resistance electrical connection with the non-oxidized material of the contact surface.

[0010] Discussion of embodiments of the present invention may be considered based, inter alia, on the ideas and realizations set forth below.

[0011] The contact element can consist of a conductive metallic material. The contact element can be, for example, a stamped and bent part. The sharp edge can be formed by an undeburred cut edge of the contact element. Alternatively, the cut edge can be subsequently ground. The sharp edge generates a high surface pressure when it touches the contact surface of the contacting partner. This surface pressure can become very high if the sharp edge penetrates at least partially into the contacting surface. During this penetration, the oxide layer on the contacting surface is broken down, exposing the unoxidized material underneath. The sharp edge can penetrate into the contacting surface particularly well if it is placed on the contacting surface and then moved relative to it.

[0012] The contact partner may in particular be a housing made of an oxidizing material.

[0013] The pointed edge may be arranged at a free end of the contact element, which may be provided as a contact point of the contact element, so that the contact element can be elastically deformed when the contact point comes into contact with a contact surface of a contact partner, thereby allowing the contact element to compensate for forming and / or mounting tolerances.

[0014] At the opposite end, the contact element can have a fixing area for fixing to a printed circuit board, which fixing area may in particular be configured to be soldered to the printed circuit board.

[0015] The spring region may be arranged between the contact location and a fixing region for fixing to a printed circuit board. The spring region may be bent in a direction transverse to the biasing direction of the spring region. This spring region can reduce the stiffness of the contact element in the biasing direction. The spring region can increase the stiffness in the direction transverse to the biasing direction. The spring region can set the pressing force of the tip edge region against the contact surface.

[0016] The spring region may be S-shaped. The spring region may be bent twice in opposite directions. The S-shape may reduce the bending load per bend. The S-shape may also allow for a compact implementation of the contact element.

[0017] The pressure of the spring in combination with the pointed edge allows a gas-tight connection to be formed between the contact area of ​​the spring and the housing, thus preventing further oxidation due to the oxygen contained in the air.

[0018] The pointed edge can extend around the protruding tip of the contact element. The pointed edge can form a tip that can penetrate the oxide layer under low pressure.

[0019] The sharp edge can extend along the arcuate projection of the contact element and form a cutting edge, which can be convex, so that even if the angle between the contact element and the contact surface changes, a portion of the cutting edge can always abut against the contact surface.

[0020] The tips or protrusions may be oriented obliquely relative to the main extension plane of the printed circuit board, which allows the distance between the spring region and the contact surface to be increased.

[0021] The pointed edge may be oriented in the insertion direction of the contact element. In particular, if the pointed edge forms a cutting edge, the pointed edge can move along an edge on the contacting surface when the contact element is placed on the contacting surface. The printed circuit board can be inserted into the receiving part of the housing. In this case, the contact element is placed on the contacting surface and can move on the contacting surface in the insertion direction of the printed circuit board.

[0022] The contact element can have two pointed edges, which can be arranged on opposite sides of the contact location. The two pointed edges allow the contact element to establish an electrical contact with the contacting surface at two points. The two pointed edges reduce the tilt of the contact location on the contacting surface. If one pointed edge is damaged, the other pointed edge can still ensure the electrical contact.

[0023] It should be noted that some of the possible features and advantages of the present invention have been described herein with reference to different embodiments, and those skilled in the art will recognize that the features of the control devices and methods can be combined, adapted, or interchanged in any suitable manner to arrive at further embodiments of the present invention.

[0024] Embodiments of the present invention will now be described with reference to the accompanying drawings, but neither the drawings nor the description should be construed as limiting the invention. [Brief explanation of the drawings]

[0025] [Figure 1] 1A and 1B show depictions of contact points of contact elements according to an embodiment. [Figure 2] 1A and 1B show depictions of contact points of contact elements according to an embodiment. [Figure 3] 1A and 1B show depictions of contact points of contact elements according to an embodiment. [Figure 4] 1A and 1B show depictions of contact points of contact elements according to an embodiment. [Figure 5] 1A and 1B show depictions of contact points of contact elements according to an embodiment.

[0026] The drawings are only schematic and are not to scale, and the same reference numbers represent the same or equivalent features.

[0027] Embodiments of the invention 1 shows a representation of a contact location 100 of a contact element 102 according to an embodiment. The contact location 100 is arranged at a free end of the contact element 102. At a fixed end (not shown here), the contact element 102 is connected to a printed circuit board. The contact element 102 is configured as a potential contact connection to form a low-resistance conductive connection between the printed circuit board and a metal housing with an electrically insulating oxide layer, i.e., a conductive connection with very little contact resistance.

[0028] The contact element 102 is a stamped and formed part from sheet metal. The contact location 100 is formed as a flat tip or claw. The tip faces in the main direction of extension of the contact element 102. At least at the contact location 100, the contact element 102 has pointed edges 104. The pointed edges 104 are located on either side of the tip and extend beyond the tip. The pointed edges 104 are undeburred cut edges of the stamped and formed part.

[0029] When the contact point 100 is placed on a contact surface of a housing, the pointed edge 104 first comes into contact with the contact surface. Due to the tip of the pointed edge, the pressure with which the contact element 102 is pressed against the contact surface acts over a very small area, resulting in a high surface pressure even with a small pressure. The high surface pressure allows the pointed edge 104 or tip to penetrate the electrically insulating oxide layer that is likely to be present on the contact surface, even with a small pressure, thereby ensuring a low-resistance electrical connection between the contact element 102 and the housing.

[0030] In one embodiment, the contact point 100 is bent obliquely from the main extension plane of the contact element 102 in the direction of the contact surface. Here, the flat tip is oriented obliquely, for example at an angle of 45°, to the main extension plane. This causes the pointed edge 104 to protrude in the direction of the contact surface. This prevents other areas of the contact element 102 from coming into contact with the contact surface, and reduces the pressure on the pointed edge 104.

[0031] In one embodiment, the contact location 100 is offset from the main extension plane by a step 106. This step 106 causes the tip 104 to protrude from the contact element 102 in the direction of the contact surface, thereby preventing other areas of the contact element 102 from coming into contact with the contact surface and reducing the pressure on the tip 104.

[0032] The contact element 102 has a spring region 108 between the contact location 100 and the fixing location. The spring region 108 is spring-elastic and elastically deforms when the contact location 100 is placed on the contact surface, so that the contact location 100 is pressed against the contact surface by a pressing force resulting from the restoring force of the elastic deformation. The spring region 108 enables the contact element 102 to compensate for shape and position tolerances between the printed circuit board and the housing.

[0033] The spring region 108 is now bent in an S-shape, which allows the spring region 108 to have a reduced spring stiffness and to guarantee a substantially constant pressing force over a larger deformation area. Additionally, the entire contact element 102 is very compact due to the double-curved spring region 108.

[0034] In one embodiment, the contact elements 102 are nickel-coated, which results in a small electrochemical voltage difference between the contact locations 100 and the contact surface, thereby minimizing electrochemical corrosion in the presence of moisture at the contact locations 100 and ensuring a permanently low-resistance electrical connection.

[0035] FIG. 2 shows a representation of a contact location 100 of a contact element 102 according to an embodiment. This contact location 100 substantially corresponds to the contact location of FIG. 1. In contrast to the contact location of FIG. 1, this contact location 100 has two pointed edges 104, each formed as a tip. The tips here point transversely to the main extension direction of the contact element 102. The tips here point in opposite directions. The two pointed edges 104 open the oxide layer of the contact surface in two places, ensuring a low-resistance connection at at least one of the tips, even if one of the tips should have a high contact resistance.

[0036] Figure 3 shows a representation of a contact point 100 of a contact element 102 according to one embodiment. This contact point 100 substantially corresponds to the contact point of Figure 2. In contrast to the contact point of Figure 2, the two tips are now embodied at an angle of more than 90° to the main extension plane. This causes the lower tips and the pointed edge region 104 of the contact point 100 to be located closer together than in Figure 2.

[0037] FIG. 4 shows a representation of a contact location 100 of a contact element 102 according to one embodiment. This contact location 100 substantially corresponds to the contact location of FIG. 2. In contrast to the contact location of FIG. 2, the pointed edges 104 are arranged on arcuate projections of the contact location 100. These projections, as in FIG. 2, are arranged obliquely with respect to the contact surface in a direction transverse to the main extension direction. This allows the contact to slide on the contact surface of the housing along the extension direction of the contact spring with minimal risk of chip formation. Due to the arcuate shape, a portion of the pointed edge is always oriented tangentially with respect to the contact surface under various angles between the contact element 102 and the contact surface. This allows the pointed edges 104 to penetrate oxide layers particularly efficiently and form low-resistance contacts.

[0038] 5 shows a representation of a contact point 100 of a contact element 102 according to one embodiment. The contact point 100 substantially corresponds to the contact point of FIG. 4. In contrast to this contact connection point of FIG. 4, the two protrusions are here oriented at an angle of more than 90° to the main extension plane. This causes the lower protrusion and the pointed edge 104 of the contact point 100 to be located closer together than in FIG. 4.

[0039] In the following, possible embodiments of the invention are summarized again or presented in slightly different terms.

[0040] Contact element designs are presented for penetrating metal oxide layers and forming reliable, low resistance electrical connections.

[0041] The approach presented here makes it possible to ensure electrical contact connections of metals that form non-conductive metal oxide layers, such as aluminum.

[0042] The EPS can have high interference emissions. The ECU may be completely enclosed in an aluminum housing, and a low-resistance electrical connection is required between the metal housing and the printed circuit board. If the contact resistance of the contacts is significantly higher than the specification, the efficiency of the EMC filter may be too low. As a result, the EMC interference emissions may deviate significantly from the specification.

[0043] The spring-like electrical contact connection of the electrical assembly to the entire or part of the metal housing surrounding the electronic assembly is realized by spring elements fixed on the printed circuit board, which have the task of creating a low-resistance electrical connection between the metal housing parts and the potential of the electronic assembly (e.g., printed circuit board).

[0044] Typically, the contact points of the spring elements in the direction of the metallic housing part to be contacted have a dome-shaped or spherical geometry that is suitable for forming a low-resistance electrical connection with the well-conducting surface of the contact partner.

[0045] However, dome- or spherical-shaped contact geometries are not suitable if the metal of the contact partner forms a poorly or non-conductive (insulating) surface, for example, aluminum or aluminum alloys due to the formation of aluminum oxide. With dome- or spherical-shaped contact geometries, it is difficult to penetrate such oxide layers and form a reliable contact.

[0046] Commercially available spring-loaded contact elements with dome- or spherical-shaped contact geometries are not suitable for forming a reliable, low-resistance electrical connection between a housing and, for example, a printed circuit board, using a metal housing, such as aluminum or an aluminum alloy, without additional surface treatment such as passivation, as used in EPSs. The contact geometries are not capable of reliably penetrating insulating oxide layers with the contact forces typically present to form a more reliable, low-resistance electrical connection. However, such a connection is fundamental to the effectiveness and efficiency of EMC filter assemblies within EPSs.

[0047] A further problem, particularly with S-shaped or double S-shaped spring geometries, is that when the spring element is spring loaded, the contacts may "wander" within the plane of the mating contact surface. This contact movement, with spherical or dome-shaped contact geometries and the corresponding pressure, can lead to the removal of the native oxide layer, particularly on aluminum components. However, the removed oxide can act as a wedge between the contact dome and the contact surface. The electrical contact resistance can become unstable and increase significantly.

[0048] For an efficient filtering effect of the EMC filter, the contact resistance of the contact connection is advantageously less than 160 mΩ for (3σ) and less than 200 mΩ for (6σ). Available contact connection spring embodiments do not meet this requirement. Therefore, an optimized design is urgently needed.

[0049] The approach presented herein makes it possible to significantly increase the filtering efficiency of EMC filter elements due to lower contact connection or contact resistance. EMC emissions can be reduced by more than 20 dB with the approach presented herein, which corresponds to a factor of 0.1. EMC requirements can be met using fewer or smaller filter elements without large and heavy inductive EMC filter components.

[0050] The contact connection geometry proposed herein allows for very low contact resistance between the contact connection spring and a metal surface having a natural insulating oxide layer. This contact connection geometry is capable of penetrating the natural metal oxide layer with a high point contact force. This contact connection geometry avoids the deposition of non-conductive or low-conductive metal oxides between the contact connection surfaces that are scraped off when the contacts are shifted between the contact connection partners, which would also increase and / or destabilize the contact resistance of the contact connection.

[0051] An alternative contacting region geometry for the electrical contact element is presented, which allows a significantly higher pressing force (force per unit area) under the same spring force and thus allows easier penetration of the insulating oxide layer on the metal with simultaneously reduced contact resistance. Furthermore, with certain configurations of the contacting region geometry, the deposition of insulating metal oxide between the geometry of the spring contact and the contacting surface during sliding of the contact on the contacting surface is reduced to the extent that it no longer adversely affects the contact resistance of the contact. With certain configurations of the contacting geometry, sliding of the contact and the deposition of insulating oxide between the contact element and the contacting surface are avoided. With certain configurations of the contacting geometry, deep penetration of the contacting geometry into the metal to be contacted is possible simultaneously with the displacement of the oxide layer, thereby allowing a gas-tight, electrically low-resistance connection that prevents oxidation of the aluminum material contact site by oxygen in the air. The specific configuration of the contacting geometry substantially prevents the formation of chips when the contact slides over the contacting surface. The geometry of the contacting area allows for a significantly reduced contact resistance of the electrical contact under a given contacting force. The geometry of the contacting area allows for a significantly smaller fluctuation in the contact resistance of the contact under a given contacting force.

[0052] The surface coating of the contact geometry is selected to minimize the electrochemical voltage difference across the material to be contacted. This minimizes electrochemical corrosion of base metals under the influence of moisture. The coating has a high surface conductivity. For example, a nickel coating is used. A gold coating is not advantageous due to the high voltage difference that occurs when contacting aluminum materials.

[0053] Instead of the typically used dome-shaped or spherical contact geometries, alternative geometries are used here: Contacting of oxide-forming (electrically insulating) metal surfaces is effected by geometries in the form of edges or tips (which may also be curved) that, by appropriate selection of the hardness of the contact elements, are capable of penetrating the metal oxide layer and forming a low-resistance, reliable electrical contact connection; in this case, penetration of the contact area of ​​the spring into the aluminum material to be contacted results in a gas-tight connection, which largely prevents oxide formation in the contact area due to atmospheric oxygen.

[0054] One example of a contacting geometry uses an edge implemented as a circular arc, allowing for high surface pressure in the contacting region and thus penetration of the insulating metal oxide layer. During sliding of the contact, the buildup of insulating oxide between the contacting geometry and the contacting surface is minimized, so that the contact resistance of the contacting region is not adversely affected. The double contact increases the reliability of the contacting. Alternatively, an embodiment with only one angled contacting region is also possible.

[0055] In one embodiment, the two contacts are positioned closer to each other.

[0056] Alternatively, an embodiment with only one angled contact connection area is also possible.

[0057] In one embodiment, even higher point pressures are achieved in the contact area. The oxide layer is more easily penetrated, and the contact geometry allows for electrical contact with the metallic contact partner even through thicker oxide layers, resulting in very low contact resistance. Contact misalignment is avoided, particularly with S-shaped or double S-shaped spring elements. This also reduces the effects of oxide buildup under the contact. Alternatively, an embodiment with only one angled contact area is also possible.

[0058] One embodiment has fewer bending steps and is easier to form.

[0059] The contact geometry of the spring elements was changed to form edges rather than domes as contact points. Measurements show results that are all within specification and significantly outside the limits.

[0060] Finally, it should be noted that the terms "comprises", "includes", etc. do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Reference signs in the claims are not to be considered as limiting.

Claims

1. A printed circuit board having at least one contact element (102), a fixed end of the contact element (102) connected to the printed circuit board, and a free end of the contact element (102) having a contact point (100) for contacting with an oxidized contact surface; an S-shaped spring region (108) is arranged between the fixed end and the free end, the spring region (108) defining a biasing direction of the contact location (100) substantially perpendicular to a main extension plane of the printed circuit board; the contact point (100) has at least one sharp edge (104) for penetrating an oxide layer of the contacting surface, A printed circuit board, wherein the side of the pointed edge (104) is oriented obliquely relative to the biasing direction.

2. The printed circuit board of claim 1, wherein the pointed edge (104) extends around a protruding tip of the contact location (100).

3. 3. The printed circuit board of claim 1, wherein the pointed edge (104) extends along an arcuate projection of the contact location (100).

4. 4. The printed circuit board according to claim 2 or 3, wherein the tips and / or the protrusions are oriented obliquely with respect to a main extension plane of the printed circuit board (102).

5. 5. The printed circuit board according to claim 1, wherein the contact location (102) is implemented as a stamped and bent part, and the pointed edge (104) is formed by an unburred edge of the stamped and bent part.

6. The printed circuit board of any one of claims 1 to 5, wherein the pointed edge (104) is oriented in a direction of insertion (400) of the printed circuit board into a housing.

7. 7. The printed circuit board according to claim 1, wherein the contact location (100) has two pointed edges (104), the edges (104) being located on opposite sides of the contact location (100).

8. A housing with at least one inserted printed circuit board according to any one of claims 1 to 7, The contact point (100) abuts against the oxidized contact surface of the housing, and the spring area (108) is biased in the biasing direction; The pointed edge (104) is pressed against the contact-connection surface with the resulting pressing force, a housing that penetrates the oxide layer of the contacting surface and forms a low resistance electrical connection between the printed circuit board and the contacting surface;

9. 8. A method for forming a low resistance electrical connection between a printed circuit board according to any one of claims 1 to 7 and a housing, comprising the steps of: The pointed edge (104) rests on the oxidized contact surface of the housing, and the spring area (108) is biased in a biasing direction; The resulting pressure forces the pointed edge (104) against the contact surface, The pointed edge (104) penetrates the oxide layer and forms a low resistance electrical connection with the non-oxidized material of the contacting surface.

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