Abstract:
The invention relates to a contact element for connecting to a circuit board. The circuit board has at least one substrate layer, particularly an electrically insulating substrate layer. The circuit board also has at least one electrically conductive layer. The contact element is designed for connecting to the electrically conductive layer. According to the invention, the contact element is designed to be pushed onto a circuit board edge of the circuit board. The contact element is designed to reach over the circuit board edge and has at least one cutting blade with a cutting edge, the cutting edge having a harder metal in the area of a severing section than in an adjoining contact section alongside the cutting edge. The cutting edge is designed to cut through the substrate layer with the severing section when pushed onto the circuit board edge and to contact the electrically conductive layer electrically with the contact section.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a contact element for connecting to a circuit board. The circuit board has at least one substrate layer, particularly an electrically insulating substrate layer. The circuit board also has at least one electrically conductive layer, particularly an internal electrically conductive layer. The electrically conductive layer is preferably connected to the substrate layer. The contact element is designed for connecting to the electrically conductive layer. 
     In systems known from the prior art in which a contact element, which, for example, is connected to a terminal or a connecting wire, an electrically conductive inner layer of the circuit board is connected to a connecting element, for example a soldering pin or the like. The contact element can then be attached to the soldering pin in the form of a plug connector. 
     SUMMARY OF THE INVENTION 
     The invention is particularly characterized in that the contact element is designed to be pushed onto a circuit board edge of the circuit board. The contact element is preferably designed to reach over the circuit board edge. The contact element has at least one cutting blade with a cutting edge, the cutting edge having a harder metal in the area of a severing section than in an adjoining contact section alongside the cutting edge. The cutting edge is preferably designed to cut through the substrate layer with the severing section when pushed onto the circuit board edge and to contact the electrically conductive layer electrically with the contact section. 
     An electrically conductive inner layer of a circuit board can thus be advantageously contacted without exposing and thus laying bare the electrically conductive layer from the substrate at least on one surface area by, for example, milling or drilling. 
     The electrically conductive layer of the circuit board preferably forms an inner layer of the circuit board. The circuit board is preferably a multi-layered circuit board which, for example, has at least two electrically conductive layers and comprises—preferably in accordance with a sandwich construction—substrate layers which insulate the electrically conductive layers from one another and surround the same. The substrate layer is preferably an epoxy resin layer and furthermore preferably a fiber-reinforced, in particular fiberglass-reinforced epoxy resin layer. 
     The contact element can advantageously cut through the substrate layer by means of the cutting edge which is designed in the manner described above and contact the electrically conductive layer in the area of the circuit board edge with the contact section, which preferably has a better electrical conductivity than the severing section. 
     The contact element has preferably at least two cutting edges and is designed to reach over the circuit board edge and to contact the electrically conductive layers from two sides by means of the two cutting edges. The contact element has preferably two clamping jaws which are spaced apart from one another and jointly reach around an opening that extends longitudinally. The clamping jaws each have at least one cutting edge. The cutting edges preferably extend with the longitudinal extension thereof in the longitudinal direction of the opening. The blades of the cutting edges starting from the clamping jaws extend into the opening disposed between the clamping jaws. 
     In a preferred embodiment, the contact element has an opening which tapers towards one end and extends longitudinally, the cutting edge forming an opening edge of the opening. 
     A pressing effect can be achieved by means of the tapering and longitudinally extending opening; thus, when inserting the circuit board edge into the opening, enabling the previously mentioned clamping jaws to generate an increasing pressing force during insertion of the circuit board edge along the longitudinal extension of the opening. 
     In a preferred embodiment, the contact element is of U-shaped design, wherein the U-limbs are each formed by a clamping jaw. At least one of the clamping jaws of the U-shaped contact element has preferably at least one cutting edge. In a further preferable manner, both clamping jaws have at least one cutting edge. 
     The cutting edges are preferably designed in each case to extend linearly. 
     In a preferred embodiment, the at least one cutting edge runs circumferentially around a rotational axis so as to be spaced apart radially from the rotational axis. The contact element is preferably designed to cut into the circuit board edge by being rotationally moved about the rotational axis. The contact element is furthermore preferably designed to cut through the substrate layer with the severing section and to contact the electrically conductive layer electrically with the contact section. 
     The previously mentioned contact element comprising the cutting edge disposed circumferentially around the rotational axis is preferably cylindrical in design, wherein the rotational axis extends coaxially with respect to a longitudinal axis of the cylinder. The cylindrically designed contact element is at least in part designed in the shape of a hollow cylinder; thus enabling the circuit board edge to be at least in part accommodated in the hollow cylinder when the contact element is turned onto the circuit board edge. 
     In a preferred embodiment, the severing section of the cutting edge is designed to cut through fibers integrated into the substrate layer when pushed onto, or in the case of the cylindrical contact element: when turned onto, the circuit board edge. The fibers are, for example, glass fibers. 
     The material of the cutting edge preferably comprises steel or ceramics in the severing section and copper in the contact section. The contact section preferably consists at least in part of copper, preferably pure copper. Advantageous embodiments for the copper in the region of the contact section are copper alloys, for example an alloy of copper and tin, in particular CuSn4, CuSn6, or a copper alloy that complies with the US standard: Unified Numbering System (UNS) C18018. In another embodiment, the copper alloy comprises 0.8 to 1.8 percent nickel, 0.15 to 0.35 percent silicon and 0.01 percent phosphorus. The copper alloy is preferably an alloy that complies with the UNS-C-19010 standard. 
     The copper alloy preferably comprises an admixture consisting of chrome, silver, iron, titanium, silicon and for the most part copper. 
     The contents of the admixture are in each case preferably 0.5% chrome, 0.1% silver, 0.08% iron, 0.06% titanium and 0.03% silicon. An electrical conductivity of the contact section is preferably at least 30, preferably 46, megasiemens per meter. 
     The cutting edge preferably has a coating comprising tin, bismuth, silver, gold, lead or a combination thereof in the region of the contact section. 
     The invention also relates to a contact system comprising at least a contact element according to the type described above. The contact system comprises a circuit board having at least one substrate layer and at least one electrically conductive layer. The material of the cutting edge of the contact element is preferably designed harder in the area of the contact section than the material of the electrically conductive layer. The material of the electrically conductive layer of the circuit board is, for example, formed from a pure copper which is of softer design than the material of the cutting edge, in particular in the area of the contact section. The harder or, respectively, softer embodiment preferably relates to a Shore hardness and/or to a modulus of elasticity of the electrically conductive material. 
     As a result of the harder design of the cutting edge in the area of the contact section, a plastic deformation of the electrically conductive layer of the circuit board can preferably be achieved by the opening which tapers and extends longitudinally. In a further preferred manner, the contact element of the contact system is designed to produce a cold weld between the contact section of the cutting edge and the electrically conductive layer in the area of the circuit board edge when pushed onto or turned onto said circuit board edge. 
     A substrate layer to be severed by the cutting edge, in particular by a cutting edge of the cutting edges, has preferably a thickness that is between five percent and thirty percent of the thickness of the circuit board, further preferably of at least one tenth the thickness of the circuit board. 
     A thickness of the substrate layer to be severed is preferably at least 100 micrometers. 
     The electrically conductive layer can, for example, be produced by means of stamping prior to being laminated to the substrate layers. The electrically conductive layer has, for example, a layer thickness between 0.1 and 2 millimeters. 
     The invention also relates to a method for connecting a circuit board to a contact element. 
     The circuit board has at least one electrically conductive layer and at least one electrically insulating substrate layer connected to the electrically conductive layer. In the method, the substrate layer is severed—preferably by means of a severing section of a cutting blade—when pushing the contact element onto a circuit board edge of the circuit board; and the electrically conductive layer is electrically contacted—preferably by means of a contact section of the cutting blade—in the area of the severed substrate section. 
     The substrate layer preferably comprises fibers, in particular glass fibers, and is severed together with the fibers. 
     The invention is now described below with the aid of the drawings and further exemplary embodiments. Further advantageous embodiments ensue from the features of the dependent claims and the features of the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  shows an exemplary embodiment for a contact system comprising a multi-layered circuit board having an internal copper thick-layer and two contact elements which contact the copper thick-layers in a longitudinal cross section; 
         FIG. 2  shows the contact element depicted in  FIG. 1  in a top view of the cutting blade; 
         FIG. 3  shows a cylindrically designed contact element which can be turned onto a circuit board edge; 
         FIG. 4  shows the contact element depicted in  FIG. 3  in a sectional view; 
         FIG. 5  shows a variant for a cutting blade comprising a cutting edge which has teeth in the severing section thereof. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows—schematically—an exemplary embodiment for a contact system  1 . The contact system  1  has a circuit board  3 . The circuit board  3  comprises a substrate layer  4  and a substrate layer  4   a , which are formed in each case by fiber-reinforced epoxy resin in this exemplary embodiment. The circuit board  1  also comprises three electrically conductive layers which lie in said circuit board  1 , namely the electrically conductive layer  5 , the electrically conductive layer  6  and the electrically conductive layer  7 . The electrically conductive layers  6  and  7  extend parallel to one another and are spaced apart from one another and are insulated from one another by a further substrate layer. In this exemplary embodiment, the electrically conductive layer  5  has a thickness dimension which is three times as large as a thickness dimension of the substrate layers  4  and  4   a , between which the electrically conductive layer  5  is enclosed—in a sandwich-like manner. 
     The contact system also comprises a contact element  8  and a contact element  9 . The contact element  8  is U-shaped in this exemplary embodiment, the U-limbs forming in each case a clamping jaw  19  and a clamping jaw  20 . The clamping jaws  19  and  20  jointly enclose an opening  13 . 
     In this exemplary embodiment, the contact element  8  has a cutting blade which is connected to the clamping jaw  20  and forms the previously mentioned cutting edge. The cutting blade has a cutting edge  10  and comprises two materials which are different from each other along a longitudinal extension thereof, namely a harder material  24 , in this embodiment steel, and a material  21  which is softer in comparison thereto, in this exemplary embodiment copper. The copper is formed in this exemplary embodiment by the previously mentioned copper alloy C18018. The contact section  21  extends through one connecting section  27  that connects the clamping jaws  19  and  20 , wherein a terminal  16  is formed in the region of an end which protrudes from the connecting section  27 . The terminal  16  is connected to an electrical connecting wire  25  in this exemplary embodiment. 
     The clamping jaw  19  has a cutting blade which has a severing section  23  and a contact section  22  along the longitudinal extension thereof. The severing section  23  is formed from steel in this exemplary embodiment; and the contact element  22  is formed from the previously mentioned copper alloy. The contact section  22  is, similarly to the contact section  21 , guided through the connecting section  27  and protrudes with an end section out of the connecting section  27  and forms a contact  17  there. The contact  17  is connected to an electrical connecting cable  26 . 
     If the contact element  8  is pushed along the direction of the arrow  18  onto an end section of the circuit board  3 , the cutting edge  10  then cuts in the area of severing section  24  into the substrate layer  4   a . If the contact element  8  is pushed further in the direction of the arrow  18  onto the end section of the circuit board  3 , the cutting edge  10  then contacts the electrically conductive layer  5  on one side in the area of the contact section  21  and cuts in there. The cutting edge  12  has cut into the substrate layer  4  with the severing section  23  on the side opposite to that on which the cutting edge  10  has cut into the substrate layer  4   a  and said cutting edge  12  contacts the electrically conductive layer  5 . When the contact element  8  is pushed further onto the end section of the circuit board  3 , the contact section  22  contacts the electrically conductive layer  5  on the opposite side. The cutting edges  10  and  12  are spaced apart at a distance from one another in the area of the severing section  23  or, respectively,  24 , the distance corresponding to the thickness dimension  14  of the electrically conductive layer  5 . The cutting edges  10  and  12  are spaced apart at a distance from one another in the area of the contact section  21  or, respectively,  22 , the distance being equal to or smaller than the thickness dimension of the electrically conductive layer  5 . In this exemplary embodiment, the cutting edges  10  and  12  enclose an angle  15  between themselves, so that the opening  13  between the limbs in the area of the cutting edges  10  and  12  is designed to taper towards the connecting section that connects the clamping jaws  19  and  20 . In this way, the cutting edges  10  and  12  can also cut into the electrically conductive layer and can be respectively cold welded to the same. 
     A contact element  9  is also depicted which is designed like the contact element  8 . The elements of the contact element  9  having the same reference sign correspond in characteristic and function to those of the contact element  8  having the same reference sign. The contact element  9  has already been pushed onto an end section of the circuit board  3  which lies opposite the end section comprising the electrically conductive layer  5 . The electrically conductive layer is thereby contacted by the severing section  23  and by the contact section  22 . The electrical terminal  17  is therefore in electrical operative connection with the electrically conductive layer  7 . 
     The severing section  24  has severed, in particular cut through or milled through, the substrate layer  4   a  which covers the electrically conductive layer  6  towards the outside; thus enabling the severing section  24  and the contact section  21  to contact the electrically conductive layer  6  by means of the cutting edge  10  in a plastically deforming manner. In so doing, a cold weld is formed, so that the contact section  21  is connected to the electrically conductive layer  6  by means of a particularly good and gastight electrically conductive connection. The electrical terminal  16  therefore contacts the electrically conductive layer  6  via the contact section  21  in the area of the incision or, respectively, in the area of the plastic deformation of the electrically conductive layer  6  by means of said contact section  21  and additionally in the area of the severing section  24 . 
       FIG. 2  shows the clamping jaw  20 , which has already been depicted in  FIG. 1 , in a top view of the opening  13  onto the cutting blade. In this exemplary embodiment, the clamping jaw  20  has four cutting blades, wherein the cutting blade already depicted in  FIG. 1  comprises the severing section  24  in the area of the inlet of the opening  13  and the contact section  21  along a longitudinal direction of the cutting edge. A cutting blade which extends parallel to and spaced apart from the cutting blade comprising the severing section  24  and the contact section  21  comprises a severing section  30  and a contact section  31 . A third cutting blade, which extends parallel to and spaced apart from the cutting blade comprising the contact section  31 , comprises a severing section  31  and a contact section  33 . A fourth cutting blade comprises a severing section  34  and a contact section  35 . When pushing the contact element comprising the clamping jaw  20  onto the circuit board edge, the severing sections  24 ,  30 ,  32  and  34  consequently jointly cut into a substrate, in particular a substrate layer covering an electrically conductive layer, of a circuit board. When said contact element is pushed further along the longitudinal direction of the cutting edges, the contact sections  21 ,  31 ,  33  and  35  then cut jointly and pressingly into the electrically conductive layer which is disposed under the substrate layer and thus contact said electrically conductive layer in a plastically deforming manner and electrically by means of cold welding. The terminal  16  is also shown, which has previously been depicted and via which the contact element comprising the clamping jaw  20  can be contacted towards the outside. The terminal  16  can be electrically connected to corresponding terminals of the contact sections  31 ,  33 , and  35 . The connecting cable  25  is therefore in electrical operative connection with the contact sections  21 ,  31 ,  33  and  35 . 
       FIG. 3  shows an embodiment for a contact element which can contact an end section of a circuit board on the basis of the same operating principle as the contact element  8  described above; however, not by means of a translatory motion but by means of a rotational motion about a rotational axis  50 . To this end, the contact element is designed cylindrically and has two cutting edges  44  and  42  that are spaced apart from one another and enclose an opening  55  between one another. The cutting edges  42  and  44  are each spaced apart in a radially circumferential manner about the rotational axis  50  which also forms a cylinder vertical axis of the contact element  40  in this exemplary embodiment. The cutting edge  42  is a constituent part of a cutting blade which comprises a severing section  46  in the area of an inlet region of the opening  55  and a contact section  45  further along a longitudinal extension of the cutting edge  42 . The severing section  46  is formed from steel in this exemplary embodiment and the contact section  45  from copper. The cutting edge  44  is a constituent part of a further cutting blade, comprising the severing section  48  and the contact section  47 , the severing section  48  being formed from steel and the contact section  47  from copper. 
     If the contact element  40  comprising the opening  55  is placed in the area of the severing sections  46  and  48  onto an edge of an end section of the circuit board  3 , the circuit board end section can thus be inserted into the opening  55  by means of a rotational movement of the contact element  40  about the rotational axis  50 . The severing section  46  cuts thereby into the substrate layer  4   a , and the severing section  48  into the substrate layer  4 . The electrically conductive layer  5  is—in a sandwich-like manner—enclosed between the substrate layers  4  and  4   a . If the contact element  40  is further rotated about the rotational axis  50 , the cutting edge  42  can then follow the cutting track which has been carved out in the substrate layer  4   a  by means of the severing section  46  and, while moving in said cutting track of said substrate layer  4   a , contact the electrically conductive layer  5  and pressingly cut into the same. To this end, the cutting edges  42  and  44  run together towards one end of the opening  55 , so that the opening  55  is formed so as to be tapered towards the end. 
       FIG. 4  shows the contact element  40  depicted in  FIG. 3  in a sectional view along the section  51  depicted in  FIG. 3 . The sectional plane of the sectional view depicted in  FIG. 4  runs perpendicularly to the rotational axis  50 . 
     The contact element  40  comprises a center column  53  which—like in  FIG. 3 —opens out into a terminal  58 . The contact element  40  can thus be connected by means of the terminal  58  to an electrical connecting cable—for example via a plug connection. The contact element  40  is—as depicted in  FIG. 4 —designed partially hollow and thus has a hollow space  56  to meet this end, in which the end section of the circuit board  3  can be received when turning the contact element  40  onto the circuit board edge. The cutting edge  42  has thereby cut through the substrate layer  4   a  into the electrically conductive layer  5 . 
       FIG. 5  shows a variant for a cutting blade, comprising a longitudinal section  67  in which the severing section  64  is formed. The cutting edge  61  has teeth  65  in the area of the severing section  64 . The cutting edge  61  can easily cut through fibers, in particular glass fibers of an epoxy resin substrate layer, using the teeth  65 . In this exemplary embodiment, the teeth  65  are formed from hardened steel and are designed to cut through a substrate layer comprising epoxy resin and glass fibers. The cutting blade  60  comprises a contact section  62  in the area of a longitudinal section  66 . The contact section  62  is made of copper, in particular a copper alloy, for example an alloy formed in accordance with the US standard C18018 or the standard UNS C-19010. The cutting blade  60  can be formed as a cutting blade on the contact element  8  depicted in  FIG. 1  and/or on the contact element  40  depicted in  FIG. 3 .