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

Abstract

The invention relates to a printed circuit board having at least one contact element (102), a fixed end of the contact element (102) being connected to the printed circuit board and a free end of the contact element (102) having a contact point (100) for contacting an oxidized contact surface, an S-shaped spring region (108) being arranged between the fixed end and the free end, the contact point (100) has a spring region which defines a direction of springing of the contact point (100) substantially perpendicular to a main plane of extension of the printed circuit board, the contact point (100) having at least one sharp edge (104) for penetrating an oxide layer of the contact surface, the side of the sharp edge (104) being oriented obliquely to the direction of springing.

Description

Technical Field

[0001] The invention relates to a printed circuit board having at least one contact element, a housing having such a printed circuit board, and a method for producing a low-impedance electrical connection. Background Art

[0002] To connect the printed circuit board to the potential of the metal housing, the printed circuit board can have a cable with plug-in contacts. Corresponding plug-in contacts can be arranged on the housing. During assembly, the plug-in contacts are connected, the printed circuit board is connected to the housing part, and the housing is closed with further housing parts. Alternatively, the circuit card can have soldered-on spring contact elements with a spherical or spherical contact area for the housing. Summary of the Invention

[0003] Against this background, the solution presented here describes a printed circuit board having at least one contact element, a housing having such a printed circuit board, and a method for producing a low-impedance electrical connection according to the independent claims. Advantageous developments and improvements of the solution presented here are derived from the description and are described in the dependent claims.

[0004] Advantages of the present invention.

[0005] The metal housing can be made of a metal material that forms an oxide layer with poor conductivity. The metal material can be aluminum, for example. Therefore, contacting the housing for potential compensation is difficult. Therefore, contact elements made of a metal material that forms no or only a small oxide layer have been placed on the housing. These contact elements are then contacted via matching contact elements on the printed circuit board. The printed circuit board contact elements can be placed, in particular, on the cable. Alternatively, the contact elements can be spring contacts with hemispherical contact points soldered to the circuit card. The contact elements can be gold-plated, for example.

[0006] In the solution presented here, a contact element is fixedly arranged on the printed circuit board. The housing has only one contact surface made of the metal material of the housing. This contact surface can be covered by an oxide layer. At the contact point for contacting the contact surface, the contact element has at least one unburred or sharp edge. This edge penetrates the oxide layer of the housing material and reaches the unoxidized metal material. This creates an electrically conductive connection with low transition resistance between the printed circuit board and the housing.

[0007] The solution presented here makes it possible to dispense with additional plug connections for potential equalization or separate contact surfaces made of non-oxidizing or less-oxidizing material, thereby significantly simplifying the assembly of the printed circuit board in the housing.

[0008] According to a first aspect of the present invention, a printed circuit board having at least one contact element is described, 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 portion for contacting an oxidized contact surface, wherein an S-shaped spring region is arranged between the fixed end and the free end, which spring region defines a spring direction of the contact portion essentially perpendicular to a main extension plane of the printed circuit board, wherein the contact portion has at least one sharp edge for penetrating an oxide layer of the contact surface, wherein side surfaces of the sharp edge are oriented obliquely to the spring direction.

[0009] According to a second aspect of the present invention, a housing is described, which has at least one inserted printed circuit board according to the first aspect, wherein the contact point abuts against an oxidized contact surface of the housing and the spring region springs in a springing direction, wherein the sharp edge presses against the contact surface with the resulting contact force, penetrates the oxide layer of the contact surface, and establishes a low-impedance electrical connection between the printed circuit board and the contact surface.

[0010] According to a third aspect of the present invention, a method for producing a low-resistance electrical connection between a printed circuit board according to the first aspect and a housing is described, wherein a sharp edge is placed on an oxidized contact surface of the housing, and a spring region is spring-loaded in a spring direction, wherein the sharp edge is pressed against the contact surface with the resulting contact force, wherein the sharp edge penetrates the oxide layer and produces a low-resistance electrical connection to the non-oxidized material of the contact surface.

[0011] The concept of the embodiments of the present invention can be considered to be based in particular on the ideas and findings described below.

[0012] The contact element can be made of an electrically conductive metal material. The contact element can be, for example, a stamped and bent part. The sharp edge can be produced by not deburring the cut edge of the contact element. Alternatively, the cut edge can be sharpened subsequently. When the edge strikes the contact surface of the contact counterpart, a high surface contact pressure is generated by the sharp edge. The surface contact pressure can be so high that the sharp edge at least partially penetrates into the contact surface. During penetration, the oxide layer on the contact surface is destroyed and the unoxidized material beneath the oxide layer is exposed. The sharp edge can penetrate into the contact surface particularly well if, after being placed on the contact surface, it is moved relative to the contact surface.

[0013] The contact partner can, in particular, be a housing composed of an oxidic material.

[0014] The sharp edge can be arranged at the free end of the contact element. The free end can be provided as the contact point of the contact element. This allows the contact element to elastically deform when the contact point strikes the contact surface of the contact counterpart. This allows the contact element to compensate for manufacturing and / or assembly tolerances.

[0015] At the opposite end, the contact element can have a fastening region for fastening to a printed circuit board. The fastening region can be designed in particular for soldering to the printed circuit board.

[0016] The spring region can be arranged between the contact point and the fastening region for fastening to the printed circuit board. The spring region can be bent transversely to the spring direction of the spring region. The spring region can reduce the stiffness of the contact element in the spring direction. The spring region can increase the stiffness transversely to the spring direction. The spring region can adjust the contact force of the sharp-edged region against the contact surface.

[0017] The spring region can be S-shaped. The spring region can be bent twice in opposite directions. The S-shape can reduce the bending load at each bending point. The S-shape allows the contact element to be designed compactly.

[0018] By the compression force of the spring in combination with the sharp edge, a gas-tight connection can be established between the contact area of the spring and the housing, thereby preventing reoxidation due to oxygen contained in the air.

[0019] The sharp edge can extend around the protruding tip of the contact element. The sharp edge can form a tip. The tip can penetrate the oxide layer even with a low pressing force.

[0020] The sharp edge can extend along the arc-shaped protrusion of the contact element. The sharp edge can form a knife edge. The knife edge can be convex. Thus, even if the angle between the contact element and the contact surface changes, a partial area of the knife edge can always abut the contact surface.

[0021] The tip or protrusion can be oriented obliquely to the main extension plane of the printed circuit board. The distance between the spring area and the contact surface can be increased by the oblique position.

[0022] The sharp edge can be aligned in the direction of insertion of the contact element. In particular, if the sharp edge is designed as a knife edge, the sharp edge can move along the edge on the contact surface when the contact element is placed on the contact surface. The printed circuit board can be inserted into the receptacle of the housing. In this case, the contact element can be placed on the contact surface and moved on the contact surface in the direction of insertion of the printed circuit board.

[0023] The contact element can have two sharp edges. These edges can be arranged on opposite sides of the contact point. The two sharp edges allow the contact element to establish electrical contact with the contact surface at two locations. The two sharp edges can reduce the risk of the contact point tilting on the contact surface. Even if one sharp edge is damaged, the other sharp edge can still ensure electrical contact.

[0024] It is noted that some of the possible features and advantages of the present invention are described herein with reference to different embodiments. Those skilled in the art recognize that the features of the controller and the method can be combined, adapted or interchanged in a suitable manner to achieve further embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the present invention are described below with reference to the accompanying drawings, wherein neither the accompanying drawings nor the description is intended to limit the present invention.

[0026] Figures 1 to 5 The diagram shows a contact point of a contact element according to an exemplary embodiment.

[0027] The figures are schematic and not true to scale. Identical reference numerals denote identical or identically acting features. DETAILED DESCRIPTION

[0028] Figure 1 A diagram shows a contact region 100 of a contact element 102 according to one exemplary embodiment. The contact region 100 is arranged at the 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 to establish a low-impedance electrically conductive connection, i.e., an electrically conductive connection with very low contact transition resistance, as a potential contact between the printed circuit board and a metal housing having an electrically insulating oxide layer.

[0029] Contact element 102 is a stamped and bent part made of sheet metal. Contact portion 100 is configured as a flat tip or claw. The tip points in the main extension direction of contact element 102. At least at contact portion 100, contact element 102 has sharp edges 104. Sharp edges 104 are arranged on both sides of the tip and extend over the tip. Sharp edges 104 represent the unburred, cut edges of the stamped and bent part.

[0030] When contact point 100 is placed on the contact surface of the housing, sharp edge 104 first contacts the contact surface. The sharp, angular tip applies a contact force to a very small surface area, with which contact element 102 is pressed against the contact surface. This generates a high surface contact pressure even with low contact forces. This high surface contact pressure allows sharp edge 104 or tip to penetrate the electrically insulating oxide layer that is likely to be present on the contact surface, even with low contact forces, and thus ensures a low-impedance electrical connection between contact element 102 and the housing.

[0031] In one embodiment, the contact portion 100 is bent obliquely outward from the main extension plane of the contact element 102 toward the contact surface. Here, the flat tip is oriented, for example, at a 45° angle to the main extension plane. This causes the sharp edge 104 to project toward the contact surface. This prevents other areas of the contact element 102 from contacting the contact surface and reduces the contact force at the sharp edge 104.

[0032] In one embodiment, the contact portion 100 is designed to be bent away from the main extension plane to form a step 106. The step 106 causes the sharp edge 104 to project from the contact element 102 toward the contact surface. This prevents other areas of the contact element 102 from contacting the contact surface and reduces the contact force at the sharp edge 104.

[0033] Contact element 102 has a spring region 108 between contact portion 100 and the fastening portion. Spring region 108 is spring-elastic and elastically deforms when contact portion 100 is placed on a contact surface. As a result, contact portion 100 is pressed against the contact surface with a pressing force generated by the restoring force of the elastic deformation. Spring region 108 enables contact element 102 to compensate for shape and position tolerances between the printed circuit board and the housing.

[0034] The spring region 108 is here bent in an S-shape. Thus, the spring region 108 has a reduced spring stiffness and can ensure a nearly constant pressing force within a larger deformation range. Additionally, the entire contact element 102 is very compact due to the doubly bent spring region 108.

[0035] In one embodiment, the contact element 102 is nickel-coated. This produces a low electrochemical voltage difference between the contact point 100 and the contact surface. In the presence of moisture at the contact point 100, electrochemical corrosion can be minimized and a low-resistance electrical connection can be permanently ensured.

[0036] Figure 2 FIG. 1 shows a diagram of a contact region 100 of a contact element 102 according to an exemplary embodiment. The contact region 100 corresponds substantially to Figure 1In contrast, contact point 100 has two sharp edges 104, each designed as a tip. The tips point transversely to the main extension direction of contact element 102. The tips point in opposite directions. The two sharp edges 104 destroy the oxide layer of the contact surface at two locations, and if one of the tips is to have an increased contact transition resistance, a low-impedance connection is ensured at at least one of the tips.

[0037] Figure 3 FIG. 1 shows a diagram of a contact region 100 of a contact element 102 according to an exemplary embodiment. The contact region 100 corresponds substantially to Figure 2 In contrast, the two tips are bent at more than 90° relative to the main extension plane. As a result, the tip and the sharp edge-shaped area 104 below the contact part 100 are arranged more closely than Figure 2 Closer in.

[0038] Figure 4 FIG. 1 shows a diagram of a contact region 100 of a contact element 102 according to an exemplary embodiment. The contact region 100 corresponds substantially to Figure 2 In contrast, the sharp edge 104 is arranged here at an arc-shaped protrusion of the contact portion 100. Figure 2 As in [1], the contact point 104 is arranged transversely to the main extension direction and obliquely to the contact surface. This allows the contact point to slide on the contact surface of the housing along the extension direction of the contact spring with a low risk of chip formation. Due to the curved shape, a portion of the sharp edge is always oriented tangentially to the contact surface, regardless of the angle between the contact element 102 and the contact surface. As a result, the sharp edge 104 can penetrate the oxide layer particularly efficiently and establish low-impedance contact.

[0039] Figure 5 FIG. 1 shows a diagram of a contact region 100 of a contact element 102 according to an exemplary embodiment. The contact region 100 corresponds substantially to Figure 4 In contrast, the two projections are bent at more than 90° relative to the main extension plane. As a result, the projections and sharp edges 104 below the contact portion 100 are arranged closer together. Figure 4 Closer in.

[0040] Possible embodiments of the invention are described again in summary below or in slightly different wording.

[0041] A contact element design is described for penetrating a metal oxide layer and establishing a reliable, low-resistance electrical connection.

[0042] The approach presented here makes it possible to reliably achieve electrical contacting of metals, such as aluminum, which form a non-conductive metal oxide layer.

[0043] EPS can have high interference emissions. The ECU can be completely enclosed in an aluminum housing, and a low-impedance electrical connection is required between the metal housing and the circuit card. If the contact-transition resistance is significantly higher than the specified value, the EMC filter efficiency may be too low. Consequently, EMC interference emissions may be significantly outside of the specified value.

[0044] The spring-elastic electrical contact between the electrical component and the complete or partial metal housing surrounding the electronic component is achieved by spring elements attached to the circuit card. These spring elements have the task of establishing a low-impedance electrical connection between the metal housing components and the potential of the electronic component (e.g., the circuit card).

[0045] Typically, the contact point of the spring element has a spherical or spherical geometry in the direction of the metal housing part to be contacted. Such a geometry is suitable for establishing a low-impedance electrical connection with a well-conducting surface of a contact partner.

[0046] However, if the metal of the contact partner has a poorly or non-conductive (insulating) surface, then a spherical or spherical contact point geometry is not suitable. For example, aluminum or aluminum alloys have a poorly or non-conductive surface due to the presence of aluminum oxide. A spherical or spherical contact geometry would have difficulty penetrating such an oxide layer and establishing reliable contact.

[0047] Commercially available spring-elastic contact elements with their spherical or spherical contact point geometry are not suitable for establishing a reliable, low-impedance electrical connection between a metal housing used in EPS (made, for example, of aluminum or an aluminum alloy and lacking additional surface treatment, such as passivation) and, for example, a circuit card. The contact geometry cannot reliably penetrate the insulating oxide layer with the typical contact forces and establish a reliable, low-impedance electrical connection. However, such a connection is crucial for the effectiveness and efficiency of the EMC filter assembly in EPS.

[0048] Another problem, particularly with S-shaped or double-S-shaped spring geometries, is that the contact point can "move" in the plane of the contact surface of the contact partner when the spring element springs. With spherical or spherical segment contact geometries and corresponding contact forces, this movement of the contact point scrapes off the natural oxide layer of the aluminum component. However, the removed oxide can become compressed as a wedge between the contact segment and the contact surface. This results in unstable transition resistance and can significantly increase.

[0049] For an efficient filtering effect of an EMC filter, a contact transition resistance of less than 160 mΩ for (3σ) or less than 200 mΩ for (6σ) is advantageous. Available contact spring designs do not meet this requirement. Therefore, an optimized design is urgently needed.

[0050] The approach presented here makes it possible to significantly improve the filter efficiency of EMC filter elements through lower contact resistance or transition resistance. EMC radiation can be reduced by more than 20 dB using the approach presented here, which corresponds to a factor of 0.1. EMC requirements can be met without large and heavy inductive EMC filter components and using fewer or smaller filter elements.

[0051] The contact geometry presented here makes it possible to achieve a very low-impedance contact transition resistance between the contact spring and the metal surface with a naturally insulating oxide layer. The contact geometry enables the penetration of the natural metal oxide layer by means of high local contact forces. The contact geometry prevents the accumulation of non-conductive or poorly conductive metal oxide removed during the movement of the contact point between the contact partners, thereby again leading to an increase in the contact transition resistance and / or instability.

[0052] An alternative contact region geometry for an electrical contact element is described. This contact region geometry enables significantly higher contact pressure (force per unit area) for the same spring force and, therefore, easier penetration of insulating oxide layers on metals while simultaneously reducing contact resistance. Furthermore, given a specific shape of the contact geometry and when the contact point slides on the contact surface, the contact region geometry reduces the accumulation of insulating metal oxides between the spring contact geometry and the contact surface, eliminating any negative impact on the contact transition resistance. The specific shape of the contact geometry prevents sliding of the contact point and the accumulation of insulating oxides between the contact element and the contact surface. The specific shape of the contact geometry allows for deeper penetration of the contact geometry into the metal to be contacted while simultaneously displacing the oxide layer, thereby achieving a gas-tight, low-resistance connection that prevents oxidation of the aluminum contact point due to oxygen in the air. The specific shape of the contact geometry largely minimizes chip formation when the contact point slides on the contact surface. The contact region geometry enables significantly lower electrical contact transition resistance under existing contact forces. The contact region geometry enables significantly smaller differences in the contact transition resistance under existing contact forces.

[0053] The surface coating of the contact geometry is selected to minimize the electrochemical voltage difference relative to the contact material. This minimizes electrochemical corrosion of less precious materials under the influence of moisture. The coating has high surface conductivity. For example, a nickel coating is used. Gold coatings are disadvantageous due to the high voltage difference when contacting aluminum.

[0054] Instead of the typically used spherical or spherical contact point geometry, an alternative geometry is used. Contacting of oxide-forming (electrically insulating) metal surfaces is achieved by means of a geometry in the form of an edge (also of curved design) or a tip, which, by suitably selecting the hardness of the contact element, is able to penetrate the metal oxide layer and establish a low-resistance, reliable electrical contact. The contact area of the spring penetrates into the aluminum material to be contacted, creating a gas-tight connection that largely prevents oxide formation in the area of the contact point due to oxygen in the air.

[0055] One embodiment of the contact geometry uses an edge designed as a circular arc as the contact geometry to achieve high surface contact pressure in the contact region and thus penetrate the insulating metal oxide layer. During sliding contact, the accumulation of insulating oxide between the contact geometry and the contact surface is minimized, thus preventing a negative impact on the contact transition resistance. The dual contact point improves contact reliability. Alternatively, an embodiment with only one bent contact region is also possible.

[0056] In one embodiment, the two contact points are arranged closer relative to each other.

[0057] Alternatively, an embodiment with only one bent contact region is also possible.

[0058] In one embodiment, an even higher local surface contact pressure is achieved in the contact region. The oxide layer is more easily penetrated, and the contact geometry ensures electrical contact with the metallic contact partner even with thicker oxide layers, enabling very low transition resistance. In particular, contact point shifting is avoided with S-shaped or double-S-shaped spring elements. This also reduces the effects of oxide accumulation during contact. Alternatively, an embodiment with only one bent contact region is also feasible.

[0059] One embodiment has fewer bending processes and can be manufactured more easily.

[0060] The contact geometry of the spring element was modified so that the edge, rather than the spherical segment, was formed as the contact point. All measurements showed results that were within specifications and had a clear distance from the limit.

[0061] Finally, it is pointed out that terms such as "having", "comprising", 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 limitations.

Claims

1. A printed circuit board having at least one contact element (102), wherein: The fixed end of the contact element (102) is connected to the printed circuit board, and the free end of the contact element (102) has a contact portion (100) for contacting an oxidized contact surface, wherein an S-shaped spring area (108) is arranged between the fixed end and the free end, which spring area defines a spring direction of the contact portion (100) substantially perpendicular to a main extension plane of the printed circuit board, wherein the contact portion (100) has at least one sharp edge (104) for penetrating an oxide layer of the contact surface, wherein a side surface of the sharp edge (104) is oriented obliquely to the spring direction.

2. The printed circuit board according to claim 1, wherein The sharp edge (104) extends around the protruding tip of the contact portion (100).

3. A printed circuit board according to any one of the preceding claims, wherein The sharp edge (104) extends along the arc-shaped protrusion of the contact portion (100).

4. The printed circuit board according to any one of claims 2 to 3, wherein: The tip and / or the projection are oriented obliquely to a main extension plane of the printed circuit board (102).

5. A printed circuit board according to any one of the preceding claims, wherein The contact element (102) is embodied as a stamped and bent part, wherein the sharp edge (104) is formed by an unburred edge of the stamped and bent part.

6. A printed circuit board according to any one of the preceding claims, wherein The sharp edge (104) is aligned along a direction (400) of pushing the printed circuit board into the housing.

7. A printed circuit board according to any one of the preceding claims, wherein The contact point (100) has two sharp edges (104), wherein the edges (104) are arranged on opposite sides of the contact point (100).

8. A housing having at least one inserted printed circuit board according to any one of claims 1 to 7, wherein: The contact portion (100) abuts against the oxidized contact surface of the housing, and the spring region (108) springs in a springing direction, wherein the sharp edge (104) presses against the contact surface with the generated pressing force, penetrates the oxide layer of the contact surface, and establishes a low-impedance electrical connection between the printed circuit board and the contact surface.

9. A method for establishing a low-impedance electrical connection between a printed circuit board and a housing according to any one of claims 1 to 7, wherein: The sharp edge (104) is placed on the oxidized contact surface of the housing, and the spring region (108) is spring-loaded in a springing direction, wherein the sharp edge (104) is pressed against the contact surface with the resulting contact force, wherein the sharp edge (104) penetrates the oxide layer and establishes a low-resistance electrical connection with the non-oxidized material of the contact surface.

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