conductor track contact point

Abstract

Contact point (15) of a conductor track (13) on a circuit carrier (11), wherein an electrically conductive plate (16) is glued onto the contact point (15), which is cut from a flattened wire.

Description

The invention relates to the electromechanical contacting of conductor tracks on circuit carriers.It has been known for a long time, for example from DE 1 987 753 U or DE 73 32 639 U, to contact the end faces of laminated-on conductor tracks terminating at the edge of a plate-shaped circuit carrier in a spring-loaded manner. For this purpose, contacts configured in a U-like manner in longitudinal section are arranged next to one another along movable or stationary plug strips which are accessible, if appropriate, at the rear, in the outer region of their U yoke, for solder connections of cable strands.However, the two legs of such contacts do not have to be connected via a yoke to form a one-piece U-structure; they can also each be held separately in a U-shaped insulating profile into which the edge of the printed circuit board with the conductor tracks ending there and to be contacted is inserted.When such a contact leg under spring prestress is pushed over the edge of the printed circuit board onto the end face of a conductor track, the opposite support leg engages behind the edge of the circuit carrier under the end face of the conductor track. This plugging process, in which the contact leg is pushed under spring pressure over the edge of the circuit carrier with corresponding friction onto the end face of the conductor track there, represents a considerable mechanical stress on the end face of the conductor track, which can thereby be damaged at the edge of the circuit carrier or even detached from the circuit carrier. If the end of the conductor track is plated with noble metal for example in the interest of a low contact resistance, the risk of such a contact-making coating being destroyed is also reduced by the contact spring being pushed on.In circuits constructed using thick-film technology, the line guidance is not provided by thin copper strips laminated onto the circuit carrier, but by pasty strands of conductive adhesive applied to the surface of the planar or unevenly profiled circuit carrier. This is an adhesive with electrically conductive fillers, in particular with silver particles. This design of the conductor tracks on the circuit carrier is at least more cost-effective in small production numbers than the production of thin-film conductor tracks on the circuit carriers. Furthermore, SMD components can be mounted and simultaneously contacted more easily because they need only be pressed into the adhesive conductor tracks which have not yet cured; while wired components can easily be inserted with their wire ends into blind holes filled with conductive adhesive. Due to the elasticity remaining to a certain extent even after the conductive adhesive has cured, such thick-film conductor tracks are relatively insensitive to mechanical loads such as vibrational loads. However, they are slightly deformed, even destroyed by compressive and shear forces acting on them at certain points, especially when a contact spring is pushed against the end at the end of such a thick-film conductor track. Therefore, the connector strips inserted for copper-laminated printed circuit boards cannot be successfully used in thick-film circuits.According to U.S. Pat. No. 5,414,220 A, the wires of a cable are connected to conductor tracks running parallel to one another in the plug-in direction on a plate-shaped dielectric serving as a multiple plug contact, the opposite surface of which is coated over its full surface with a common counter electrode or ground electrode in order to form a plurality of capacitances connected with one another in a single pole. The flexible spring contact legs of the plug-in clutch rub during the plugging process directly on the contact coatings on both sides and thus pose a risk of their functions as described above.In order to minimize such mechanical stresses, it is known from US 2003 / 0079907 A1 to provide the run-on edge of the printed circuit board plug with a protective coating of insulating material on the end face, which is designed with a chamfer for running on a flexible spring contact leg. As a result, only beyond the end of the protective coating facing away from the front is the contact leg inserted into the coupling placed against a contact region of the plug.In so-called force-free plug connectors, the printed circuit board is inserted into the connector strip when the contact springs are locked in a folded-up position. This releases a locking and the contact springs snap back onto the conductor track ends. However, such a prestressing mechanism requires comparatively large installation space, and it is structurally complicated and more susceptible to faults than the classic U-contacting at the edge of the plate-shaped circuit carrier.It is also known to solder wire ends to the end faces of the conductor strands of thick-film and thick-film hybrid modules, with which the modules, such as wired components, are soldered in printed circuit boards with through-holes; however, for easy-to-handle, functionally reliable repeated plugging operations, such bare wire ends to be soldered are not suitable.In the realization of the circumstances discussed above, the present invention is based on the technical problem of increasing the quality of the contacting of conductor tracks on circuit carriers independently of the circuit carrier surface found in terms of type and structure and the conductor track technology realized thereon.This object is achieved according to the essential features indicated in the main claim. Thereafter, the contacting takes place via an electrically conductive plate, which is material- or coating-dependent and is bonded over the contact point to a conductive adhesive strand which itself is part of a thick-film conductor track-or else contact means to a thin-film conductor track. By means of the plate, the compressive stress, which is in itself pointwise, on the part of the spring-loaded contact is distributed over a larger area and, as a result, the specific area load is reduced, as a result of which the risk of destruction of the thick-film conductor in the vicinity of the contact point is prevented.In the case of a contact point which is not located in the course of a conductor track but at its end at the edge of the circuit carrier and therefore acts as a plug contact, it is provided according to a further expedient development of the invention to provide the edge in front of this end of the conductor track with a run-on body by means of which, in a manner known as such, the spring-loaded contact of a plug is raised above the level of the plate in order then, advanced further, to lower it onto the plate covering the contact point. As a result, mechanical stresses against the end face of the conductor track and thus damage thereof are avoided, because only the plate, and this practically only orthogonally, is still stressed by the spring-loaded contact.Additional refinements and alternatives to the solution according to the invention are evident from the further claims and, also taking into account the advantages thereof, from the following description of a preferred exemplary embodiment of the invention, which is outlined in detail in the drawing, not on an enlarged scale. The single drawing figure shows, in a greatly exaggerated longitudinal section, the plugging process in the case of a conductor track contact point designed according to the invention at the circuit carrier edge.The circuit carrier 11 outlined in section can be a printed circuit board 11.1, which can typically consist of fiber-reinforced thermosetting plastic (FR4), of ceramic or in principle also of any other desired electrically insulating material; or the circuit carrier 11 is an MID component 11.2, injection-molded from thermoplastic, of in principle any desired topography of its surface 12. Conductor tracks 13, for example thin-film conductor tracks 13.1, which are laminated on or printed on, run along at least one surface 12 of the circuit carrier 11.If a spring-loaded contact 14 presses against an electromechanical contact point 15 along the conductor track 13, deformation or even destruction of the contact point 15 would threaten, especially in the case of vibrational loads, as occur when the circuit carrier 11 is used in a vehicle.In order to counteract this, according to a preferred variant, it is provided according to the invention that a conductive adhesive strand is applied separately as a short thick-film conductor track 13.2, at least in the vicinity of the contact point 15, and an electrically conductive plate 16 is applied to its conductive adhesive parallel to the conductor track 13.2, on which plate the contact 14 finally comes to bear resiliently. This strand at the contact point 15 can, however, also be a section in the course of a thick-film conductor track 13.2, into the freshly applied conductive adhesive of which the plate 16 is pressed. In this case, the thick-film conductor track 13.2 can be applied to the circuit carrier 11 in sections with different conductances, depending on the geometry or material, in order to thereby form resistors as circuit components, as is described in more detail in the present parallel application "circuit arrangement"; to which reference is made here in its entirety for supplementing the present description of the invention.The plate 16, which can also have a non-planar, arbitrary cross-sectional geometry in principle, absorbs the local pressure of the contact 14 and distributes it, in the interest of a lower surface pressure, uniformly over the region of the contact point 15 which is thus sprung away by the conductive adhesive. The conductor track 13 is thereby no longer subject to shear and is only slightly subject to pressure by the spring-elastically applied contact 14. A certain elasticity of the cured conductive adhesive of the thick-film conductor track 13.2, too, leads under mechanical actions to slight displacements of the spring-loaded contact 14 on the plate 16 and thus to a desirable friction cleaning, such as possibly descaling the access to the contact point 15.The plate 16, whose cross-sectional dimensions preferably measure only by 1.5 mm x 0.1 mm, is preferably a section of a flat-rolled wire with a highly conductive coating based on silver or gold. This plate 16 can be provided individually and in a belted manner in a feeder; or the section is cut to a programmed dimension from a roll only at the SMD applicator, optionally deformed and provided for SMD application, i.e. applied to the short strand of conductive adhesive which is discharged on site from a metering device in a positionally appropriate manner. For quality control, the plate 16 recorded for mounting can be measured geometrically in relation to reference marks in the conductor track image on the circuit carrier 11 and placed thereon after precisely positioned adhesive dispensing.If, as outlined, the contact point 15 is located at the end 17 of a conductor track 13 at the edge 18 of a printed circuit board 11.1, this edge 18, now acting as a plug contact 19, is surrounded in a U-shaped cross section supported by a pushed-on plug 20 via bending springs. A resilient contact leg 14.1 with a connected cable strand 21 and a support leg 14.2 can likewise be connected to one another in a U-shaped manner via a yoke 14.3; or the two legs 14.1 / 14.2 are separately anchored in the U-shaped insulating material body of the plug 20.For contacting, the contact leg 14.1 is pushed beyond the edge of the edge 18 onto the region at the end 17 of the conductor track 13. In contrast, the support leg 14.2 engages behind the printed circuit board 11; or it engages into a cavity 22 which opens in the MID component 11.2 in the manner of a blind hole.When the plug 20 is pushed with its spring-elastic contact leg 14.1 onto the front end 17 of a conductor track 13, there is in principle the risk that a thin-film conductor track 13.1 will rub, a thick-film conductor track 13.2 will be squeezed or a plate 16 applied to the latter will be displaced. As a remedy, on the other hand, the front end 17 of the conductor track 13, as viewed in the plug-in direction of the plug 20, bears behind a run-on body 23 which is fitted or formed onto the edge 18 of the circuit carrier 11. Its height projects beyond the plane through the apex of the thick-film conductor track 13.2 or beyond the plane of a lamina 16 bonded thereto. Such a run-on body 23 does not have to be profiled in the shape of a wedge or ramp for this purpose; it can also be, for example, as outlined, a cuboid in which the flanks of the run-on body 23 are chamfered in both plug-in directions towards, preferably rounded, run-on bevels 24.The contact 14, which is initially lifted onto the run-on body 23 when the plug contact 19 and the plug 20 are joined together, then drops down onto the contact point 15 of the thick-film conductor track 13.2 or onto the lamina 16 bonded thereto, whereby the electromechanical connection is produced without shear and shear stresses of the end 17 of the conductor track 13.In order to avoid damage to thin-film as well as thick-film conductor tracks 11; 11.1, 11.2 on the planar and uneven surfaces 12 of circuit carriers 11, in particular printed circuit boards 11.1 and MID components 11.2, by sliding spring-loaded contacts 14 onto contact points 15, a plate 16 which is electrically conductive due to the material or coating is thus bonded by means of a conductive adhesive strand to the respective contact point 15 in the course of a conductor track 13. Such platelets 16 can be positioned in SMD technology on the strand, which had previously been applied from a conductive adhesive dosing device to a thin-film layer support 13.1; unless such a strand itself is already part of the course of a thick-film conductor track 13.2 made of conductive adhesive, provided that they are provided in a belted manner at the mounting location or cut to length from a flat-rolled wire and, if necessary, also formed. If the contact point 15 at an edge 18 of the circuit carrier 11 is to serve as an edge plug contact 19, the end 19 of the conductor track 13 is preferably behind a run-on body 23, which, when being pushed onto the circuit carrier 11, first raises the spring-loaded contact leg 14.1 in the vicinity of the strip-equipped conductive adhesive strand above its level and then causes it to fall back onto the strip 16 in order to avoid mechanical stresses on the end 17 of the conductor track 13.List of reference characters11 Circuit carrier; 11.1 Printed circuit board, 11.2 MID component 12 Surface (of 11, with 13) 13 Conductor track; 13.1 Thin-film contact, 13.2 Thick-film 14 Spring-loaded contact; 14.1 Contact leg, 14.2 Support leg, 14.3 U yoke 15 Contact point (of 13) 16 Platelets (over 15) 17 Front end (of 13 at 18) 18 Edge (of 11.1) 19 Plug contact (with 15 at 18) 20 Plug (to 19; with 14.1) 21 Cable strand (on 14.1 / 14.1 / 14.3) 22 Cavity (for engaging 20.with 14.2; under 12 in 11.2) 23 Run-on body (for 14.1 at 18, before 17 of 13 / 16) 24 Run-on chamfer (on 23 for 14.1)

Claims

Contact point (15) of a conductor track (13) on a circuit carrier (11), wherein an electrically conductive plate (16), which is cut to length from a flat-rolled wire, is adhesively bonded to the contact point (15).Contact point according to the preceding claim, characterized in that the plate (16) is designed for mounting the circuit carrier (11) using SMD technology.Contact point according to one of the two preceding claims, characterized in that the plate (16) is adhesively bonded by means of a conductive adhesive strand.Contact point according to the preceding claim, characterized in that the conductive adhesive strand is part of a thick-film conductor track (13.2).Contact point according to one of the preceding claims, characterized in that it is situated at the edge (18) of the circuit carrier (11) at the end face (17) of the conductor track (13).Contact point according to the preceding claim, characterized in that a run-on body (23) for a spring-loaded plug contact (14) is provided between the edge (18) of the circuit carrier (11) and the end face (17) of the conductor track (13).Contact point according to the preceding claim, characterized in that the run-on body (23) rises above the level of the plate (16) bonded to the circuit carrier (11).Contact point according to one of the two preceding claims, characterized in that the run-on body (23) is formed with run-on bevels (24) for the contact (14).Contact point according to one of the four preceding claims, characterized in that it is designed as a plug contact (19) for the circuit carrier (11).

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