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

Abstract

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

Description

Field of the InventionThe invention relates to a printed circuit board having at least one contact element, to a housing having such a printed circuit board, and to a method for producing a low-impedance electrical connection.Prior ArtFor connecting a printed circuit board to an electrical potential of a metallic housing, the printed circuit board can have a cable with a plug contact. A corresponding plug contact can be arranged on the housing. During assembly, the plug contacts are connected, the printed circuit board is connected to a housing part and the housing is closed by a further housing part. Alternatively, the printed circuit board can have a soldered-on spring contact element with a contact region with the housing which is designed in the shape of a dome or ball.Furthermore, U.S. Pat. No. 6,186,812 B1 discloses a socket for a surface-mounted integrated circuit, wherein a plurality of bent contact elements are provided, and wherein one end of the contact elements is configured in a forked manner and has sharp edges for penetrating an oxide layer of a contact surface.In addition, DE 100 53 300 A1 discloses a multipolar electrical connection connector which is provided for fastening in an opening of a housing wall, wherein a contact element in the form of a retaining spring for the penetration of paint layers or an oxide layer is formed sharp-edged and / or profiled in order to achieve a particularly secure electrical contact with the housing.Furthermore, EP 3 384 561 B1 discloses a conductor connection contact having at least one soldering connection surface for connection to a printed circuit board, wherein a insulation displacement contact connection formed from two contact fingers is arranged at one end of the conductor connection contact, and wherein inner edges of the contact fingers facing one another are sharp-edged or designed as insulation displacement contacts in order, for example, to cut open an insulating material jacket of a wire bridge or an insulated electrical conductor when it is inserted into the insulation displacement contact.Disclosure of the InventionAgainst this background, the approach presented here presents 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 refinements and improvements of the approach presented here are evident from the description and are described in the dependent claims.Advantages of the InventionA metallic case may be made of a metal material forming an oxide layer having poor electrical conductivity. The metal material may be, for example, an aluminum material. Therefore, contacting of the housing for the purpose of electric potential compensation is difficult. Hitherto, therefore, a contact element made of a metal material which forms no oxide layer or only small oxide layers is arranged on the housing. This contact element is then contacted by a matching contact element of a printed circuit board. The contact element of the printed circuit board can be arranged in particular on a cable. Alternatively, the contact element can be a spring contact soldered onto the printed circuit board and having a contact point in the form of a spherical cap. The contact element can be gold-plated, for example.In the approach 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. The contact surface may be covered by an oxide layer. The contact element has at least one non-deburred or sharp edge at a contact point for contacting the contact surface. The edge penetrates the oxide layer of the package material and reaches unoxidized metal material. This produces an electrically conductive connection between the conductor plate and the housing, which has a low contact resistance.The approach presented here makes it possible to dispense with an extra plug connection for the potential compensation or with a separate contact surface made of non-oxidizing or low-oxidizing material. This substantially simplifies the mounting of the circuit board in the housing.According to a first aspect of the invention, a printed circuit board having at least one contact element is presented, 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, said spring region defining a deflection 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 sharp edge for penetrating an oxide layer of the contact surface, wherein flanks of the sharp edge are aligned obliquely to the deflection direction.According to a second aspect of the invention, a housing having at least one inserted printed circuit board according to the first aspect is presented, wherein the contact point bears against an oxidized contact surface of the housing and the spring region is compressed in the compression direction, wherein the sharp edge is pressed against the contact surface with a resulting contact force, penetrates an oxide layer of the contact surface and establishes a low-resistance electrical connection between the printed circuit board and the contact surface.According to a third aspect of the invention, a method for producing a low-resistance electrical connection between a printed circuit board according to the first aspect and a housing is presented, wherein the sharp edge is placed on an oxidized contact surface of the housing and the spring region is compressed in the compression direction, wherein the sharp edge is pressed against the contact surface with a resulting contact force, wherein the sharp edge penetrates the oxide layer and produces the low-resistance electrical connection to non-oxidized material of the contact surface.Ideas regarding embodiments of the present invention can be considered, among other things, to be based on the ideas and findings described below.A contact element may consist of an electrically conductive metal material. The contact element can be, for example, a stamped and bent part. A sharp edge can be produced by a non-deburring of a cut edge of the contact element. Alternatively, the cut edge can be subsequently sharpened. The sharp edge results in a high surface pressure when the edge touches a contact surface of a contact partner. The surface pressure can be so high that the sharp edge penetrates at least partially into the contact surface. During the penetration, an oxide layer on the contact surface is destroyed and unoxidized material under the oxide layer is exposed. The sharp edge can penetrate particularly well into the contact surface if the sharp edge is moved relative to the contact surface after being placed on the contact surface.The contact partner can in particular be a housing made of an oxidizing material.The sharp edge may be arranged at a free end of the contact element. The free end can be provided as a contact point of the contact element. As a result, the contact element can be elastically deformed when the contact point touches the contact surface of the contact partner. The contact element can thus compensate for manufacturing tolerances and / or assembly tolerances.At an 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, to be soldered onto the printed circuit board.A spring region may be arranged between the contact point and a fastening region for fastening to the printed circuit board. The spring portion may be bent transversely to a spring direction of the spring portion. The spring portion may reduce a rigidity of the contact member in the spring direction. The spring region can increase the rigidity transversely to the spring direction. The spring region can be used to set the contact force of the sharp-edged region against the contact surface.The spring portion may be S-shaped. The spring portion may be bent twice in opposite directions. The S-shape can reduce a bending load per bending point. Due to the S-shape, the contact element can be made compact.By the pressing force of the spring in conjunction with the sharp edge, a gas-tight connection can be produced between the contact region of the spring and the housing. Reoxidization by the oxygen contained in the air can thus be prevented.The sharp edge may extend around a protruding tip of the contact element. The sharp edge may form a point. The tip can penetrate the oxide layer even at a low contact pressure.The sharp edge can extend along an arcuate protrusion of the contact element. The sharp edge may form a blade. The blade may be convex. Thus, a partial region of the blade can always abut the contact surface even if an angle between the contact element and the contact surface changes.The tip or the projection can be oriented obliquely to the main extension plane of the printed circuit board. By means of an inclination, a distance between the spring region and the contact surface can be increased.The sharp edge can be aligned with an insertion direction of the contact element. In particular, if the sharp edge forms a blade, the sharp edge can be moved along the edge over the contact surface when the contact element is placed on the contact surface. The printed circuit board can be inserted into a receptacle of the housing. In this case, the contact element can be placed on the contact surface and moved over the contact surface in the insertion direction of the printed circuit board.The contact element can have two sharp edges. The edges may be disposed on opposite sides of the contact location. By means of two sharp edges, the contact element can make electrical contact with the contact surface at two points. By means of two sharp edges, tilting of the contact point on the contact surface can be reduced. Even if one sharp edge is damaged, the other sharp edge can ensure electrical contact.It is to be understood that some of the possible features and advantages of the invention are described herein with reference to various embodiments. A person skilled in the art recognizes that the features of the control unit and of the method can be combined, adapted or exchanged in a suitable manner in order to arrive at further embodiments of the invention.Brief Description of the DrawingsEmbodiments of the invention are described below with reference to the attached drawings, wherein neither the drawings nor the description should be interpreted as restricting the invention. FIGS. 1 to 5 show representations of contact points of contact elements according to exemplary embodiments.The figures are schematic only and not to scale. Identical reference numerals designate identical or identically acting features.Embodiments of the InventionFIG. 1 shows an illustration of a contact point 100 of a contact element 102 according to an exemplary embodiment. The contact point 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 to produce as a potential contact a low-ohmic electrically conductive connection, i.e. an electrically conductive connection with a very low contact transition resistance, between the printed circuit board and a metal housing with an electrically insulating oxide layer.The contact element 102 is a stamped and bent part made of a metal sheet. The contact point 100 is formed as a flat tip or claw. The tip points in a main extension direction of the contact element 102. At least at the contact point 100, the contact element 102 has a sharp edge 104. The sharp edge 104 is located on both sides of the tip and extends across the tip. The sharp edge 104 is a non-deburred cut edge of the die cut.When the contact pad 100 is placed on a contact surface of the housing, the sharp edge 104 first contacts the contact surface. Due to the sharp-edged tip, a contact force with which the contact element 102 is pressed against the contact surface acts on a very small surface, as a result of which a high surface pressure results even in the case of a low contact force. Due to the high surface pressure, the sharp edge 104 or the tip penetrates the electrically insulating oxide layer that is very likely to be present on the contact surface even at a low contact pressure and thus ensures the low-impedance electrical connection between the contact element 102 and the housing.In one exemplary embodiment, the contact point 100 is bent obliquely out of a main extension plane of the contact element 102 in the direction of the contact surface. Here, the flat tip is oriented obliquely to the main extension plane by 45°, for example. As a result, the sharp edge 104 protrudes in the direction of the contact surface. Thus, another portion of the contact member 102 is prevented from coming into contact with the contact surface and the pressing force at the sharp edge 104 is reduced.In one exemplary embodiment, the contact point 100 is cranked by a step 106 from the main plane of extent. The sharp edge 104 protrudes from the contact element 102 in the direction of the contact surface through the step 106. Thus, another portion of the contact member 102 is prevented from coming into contact with the contact surface and the pressing force at the sharp edge 104 is reduced.The contact element 102 has a spring region 108 between the contact point 100 and the fastening point. The spring region 108 is resilient and is elastically deformed when the contact point 100 is placed on the contact surface, as a result of which the contact point 100 is pressed against the contact surface with the contact force resulting from a restoring force of the elastic deformation. Due to the spring region 108, the contact element 102 can compensate for shape and position tolerances between the printed circuit board and the housing.The spring region 108 is bent in an S-shaped manner here. As a result, the spring region 108 has a reduced spring stiffness and can ensure an approximately constant contact pressure force over a larger deformation range. In addition, the entire contact element 102 is very compact due to the doubly bent spring region 108.In one embodiment, the contact element 102 is nickel coated. This results in a small electrochemical voltage difference between the contact point 100 and the contact surface. In the case of moisture at the contact point 100, electrochemical corrosion can thus be minimized and the low-resistance electrical connection can be permanently ensured.FIG. 2 shows an illustration of a contact point 100 of a contact element 102 according to an exemplary embodiment. The contact pad 100 substantially corresponds to the contact pad in FIG. 1 In contrast, the contact pad 100 has two sharp edges 104, each of which is formed as a tip. The tips point here transversely to the main direction of extension of the contact element 102. The tips point in opposite directions. The two sharp edges 104 break open the oxide layer of the contact surface at two points and ensure the low-resistance connection at least at one of the tips if one of the tips should have an increased contact transition resistance.FIG. 3 shows an illustration of a contact point 100 of a contact element 102 according to an exemplary embodiment. The contact point 100 corresponds substantially to the contact point in FIG. 2 In contrast to this, the two tips are designed here to be angled by more than 90° with respect to the main extension plane. As a result, the tips below the contact point 100 and the sharp-edged regions 104 are arranged closer together than in FIG. 2.FIG. 4 shows an illustration of a contact point 100 of a contact element 102 according to an exemplary embodiment. The contact pad 100 substantially corresponds to the contact pad in FIG. 2 In contrast, the sharp edges 104 are disposed here on arcuate projections of the contact pad 100. As in FIG. 2, the projections are arranged transversely to the main direction of extension and obliquely to the contact surface. This enables the contact points 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 arc shape, a partial region of the sharp edge is always aligned tangentially to the contact surface at different angles between the contact element 102 and the contact surface. As a result, the sharp edges 104 can penetrate through the oxide layer in a particularly efficient manner and produce the low-resistance contact.FIG. 5 shows an illustration of a contact point 100 of a contact element 102 according to an exemplary embodiment. The contact point 100 corresponds substantially to the contact point in FIG. 4 In contrast to this, the two projections are designed here to be angled by more than 90° with respect to the main extension plane. As a result, the projections under the contact point 100 and the sharp edges 104 are arranged closer together than in FIG. 4.Possible embodiments of the invention are summarized again below or presented with a slightly different word selection.A contact element design for the penetration of metal oxide layers and a production of a reliable, low-resistance electrical connection is presented.The approach presented here makes it possible to achieve reliable electrical contacting of metals which form electrically non-conductive metal oxide layers, for example aluminum.An EPS may have high interference emissions. The ECU may be completely enclosed by an aluminum housing and may require a low impedance electrical connection between the metal housing and the circuit boards. If the contact junction resistances are significantly higher than specified, the EMC filter efficiency may be too low. As a result, the EMC interference emissions may be significantly out of specification.The resilient electrical contacting of electrical assemblies to a complete or partial metal housing around the electronics assemblies is realized by spring elements fixed on printed circuit boards. These spring elements have the task of producing a low-impedance electrical connection between a metallic housing component and an electrical potential of an electronic assembly, e.g. a printed circuit board.Typically, the contact points of spring elements in the direction of the metal housing parts to be contacted have a spherical or spherical geometry. Such a geometry is suitable for establishing a low-impedance electrical connection with electrically well-conductive surfaces of contact partners.However, if the metals of the contact partners form poorly or non-conductive (insulating) surfaces, a spherical or ball-shaped contact point geometry is not suitable. Poorly or non-conductive surfaces form, for example, aluminum or aluminum alloys by the formation of aluminum oxides. A spherical or spherical contact geometry can penetrate such an oxide layer only with difficulty and produce a reliable contact.The spring-elastic contact elements available on the market with their spherical or ball-shaped contact point geometry are not suitable for producing a reliable and low-resistance electrical connection between housing and e.g. printed circuit boards with the metal housings used in EPS, made e.g. of aluminum or aluminum alloys without an additional surface treatment such as a passivation. The contact geometry is not able to reliably penetrate an insulating oxide layer with the contact force typically present and to produce a more secure and low-resistance electrical connection. However, such a compound is of fundamental importance for the effectiveness and efficiency of EMC filter assemblies in the EPS.A further problem, in particular of S-shaped or double-S-shaped spring geometries, is that, when the spring element springs in, the contact point "migrates" lying in the plane of the contact surface of the contact partner. This movement of the contact point leads, in the case of a ball-shaped or dome-shaped contact geometry and a corresponding contact pressure, to scraping of the natural oxide layer of the aluminum component. However, the removed oxide can be forced as a wedge between the contact dome and the contact surface. The electrical contact resistance is unstable and can increase significantly.For an efficient filtering effect of the EMC filters, a contact transition resistance of less than 160 mΩ for (3 σ) or less than 200 mΩ for (6 σ) is advantageous. The available contact spring designs do not meet this requirement. Therefore, an optimized design is urgent.The approach presented here makes it possible to significantly increase the filter efficiency of EMC filter elements by means of lower contact-making or transition resistances. EMC emissions can be reduced by more than 20 dB, which corresponds to a factor of 0.1, by the approach presented here. EMC requirements can be met without large and heavy inductive EMC filter components and using fewer or smaller filter elements.The contact geometry presented here makes it possible to realize a very low-ohmic contact transition resistance between a contact spring and a metal surface with a natural insulating oxide layer. The contact geometry is capable of penetrating a natural metal oxide layer by high point contact forces. The contact geometry prevents metal oxides which are not or are poorly electrically conductive and which have been removed when the contact point is displaced between the contact partners from accumulating between the contact surfaces and as a result in turn an increase and / or instability of the contact transition resistance is brought about.An alternative contact region geometry for electrical contact-making elements is presented, which allows significantly higher contact pressures (force per area) with the same spring force and thus allows easier penetration of insulating oxide layers onto metals with simultaneously reduced contact resistance. The contact area geometry also reduces the accumulation of insulating metal oxide between the spring contact geometry and the contact area to such an extent in certain forms of the contact geometry and when the contact point slides over the contact area that there is no longer any adverse influence on the contact transition resistance. In certain forms of contact geometry, sliding of the contact point and accumulation of insulating oxides between contact element and contact surface is avoided. In certain forms of the contact geometry, a deep penetration of the contact geometry into the metal to be contacted is made possible with simultaneous displacement of the oxide layers and in this case a gas-tight electrically low-ohmic connection is made possible which prevents oxidation of the contact point of an aluminum material by atmospheric oxygen. Certain forms of the contact geometry avoid chip formation to the greatest extent when the contact point slides over the contact surface. The contact region geometry enables a significantly lower electrical contact contact contact contact contact contact contact resistance in the case of the present contact forces. The contact region geometry allows for a significantly lower variance in contact transition resistance in the present contact forces.The surface coating of the contact geometry is selected such that the electrochemical voltage difference to the material to be contacted is minimized. As a result, electrochemical corrosion of the less noble material under the influence of moisture is minimized. The coating has a high surface conductivity. For example, a nickel coating is used. A gold coating is not advantageous with regard to the high electrical voltage difference when contacting aluminum materials.Instead of the dome-shaped or spherical contact point geometry typically used, alternative geometries are used here. The contacting of oxide-forming (electrically insulating) metallic surfaces takes place by geometries in the form of edges (also formed in a curved manner) or tips which, by a suitable selection of the hardness of the contacting element, are capable of penetrating a metal oxide layer and of producing a low-resistance and reliable electrical contact, wherein the penetration of the contact regions of the spring into the aluminum material to be contacted produces a gas-tight connection which substantially prevents oxide formation in the region of the contact point by atmospheric oxygen.An exemplary embodiment of the contact geometry makes possible, by using an edge as a contact geometry, embodied as a circular arc, a high surface pressure in the contact region and thus the penetration of an insulating metal oxide layer. During a sliding of the contact point, an accumulation of insulating oxide between contact geometry and contact surface is minimized, so that no negative effects on the contact transition resistance arise. A double contact point increases contact safety. Alternatively, an embodiment with only one angled contact region is also possible.In one embodiment, the two contact points are arranged closer to each other.Alternatively, an embodiment with only one angled contact region is also possible.In one exemplary embodiment, an even higher point surface pressure is achieved in the contact region. Oxide layers are more easily penetrated and the contact geometry is also given electrical contact with the metal contact partner in the case of thicker oxide layers and enables very low transition resistances. A contact point displacement is avoided in particular in the case of S- or double-S-shaped spring elements. This also reduces the effect of the accumulation of oxides under the contact. Alternatively, an embodiment with only one angled contact region is also possible.An embodiment has fewer bending processes and is easier to produce.The contact geometry of the spring element has been modified in such a way that an edge and no spherical cap is formed as a contact point. Measurements all show results within the specification and with significant distance to the limit.Finally, it should be noted 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 should not be regarded as limiting.

Claims

Printed circuit board having at least one contact element (102), wherein a fixed end of the contact element (102) is connected to the printed circuit board and a free end of the contact element (102) has a contact point (100) for contacting an oxidized contact surface, wherein an S-shaped spring region (108) is arranged between the fixed end and the free end, said spring region defining a deflection direction of the contact point (100) substantially perpendicular to a main extension plane of the printed circuit board, wherein the contact point (100) has at least one sharp edge (104) for penetrating an oxide layer of the contact surface, wherein flanks of the sharp edge (104) are aligned obliquely to the deflection direction.The circuit board of claim 1, wherein the sharp edge (104) extends around a protruding tip of the contact pad (100).The circuit board according to any one of the preceding claims, wherein the sharp edge (104) extends along an arc-shaped protrusion of the contact pad (100).Printed circuit board according to one of Claims 2 to 3, in which the tip and / or the projection is aligned obliquely with respect to the main plane of extent of the printed circuit board (102).Printed circuit board according to one of the preceding claims, in which the contact element (102) is designed as a stamped bent part, wherein the sharp edge (104) is formed by an unburred edge of the stamped bent part.The circuit board according to any one of the preceding claims, wherein the sharp edge (104) is aligned with a direction (400) of insertion of the circuit board into a housing.The circuit board according to any of the preceding claims, wherein the contact pad (100) comprises two sharp edges (104), the edges (104) being arranged on opposite sides of the contact pad (100).Housing with at least one inserted printed circuit board according to one of Claims 1 to 7, wherein the contact point (100) bears against an oxidized contact surface of the housing and the spring region (108) is compressed in the compression direction, wherein the sharp edge (104) is pressed against the contact surface with a resulting contact force, penetrates an oxide layer of the contact surface and establishes a low-resistance electrical connection between the printed circuit board and the contact surface.Method for producing a low-resistance electrical connection between a printed circuit board according to one of Claims 1 to 7 and a housing, wherein the sharp edge (104) is placed on an oxidized contact surface of the housing and the spring region (108) is compressed in the compression direction, wherein the sharp edge (104) is pressed against the contact surface with a resulting contact force, wherein the sharp edge (104) penetrates the oxide layer and produces the low-resistance electrical connection to non-oxidized material of the contact surface.

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