FR2857166A1 - IMPROVED METHOD OF CRIMINATING AT LEAST ONE CONNECTING CONTACT ON A FLEXIBLE ELECTRONIC CIRCUIT - Google Patents

Abstract

The invention relates to an improved method for crimping at least one connection contact on a flexible electronic circuit. The invention provides for reducing an electrical resistance between the flexible circuit and the connection contact by increasing a contact surface of this same connection contact with at least one electrically conductive track (6) contained in this same flexible circuit. To do so, the invention provides for producing a flexible circuit provided with a connection contact comprising at least one piercing tooth welded to a track by heating the tooth after the tooth has passed through the flexible circuit.

Description

Improved method of crimping at least one connection contact on

  The invention relates to an improved method of crimping at least one connection contact on a flexible electronic circuit. The invention has applications in the field of connectivity and in particular, the automotive connection.

  Flexible electronic circuits, also called flexible circuits or flex circuits are generally constituted by a first sheet of a flexible insulating material, on which are arranged electrically conductive tracks, for example copper. These conductive tracks are themselves covered, either by a second sheet of insulating material or by an insulating varnish. Such flexible circuits are commonly used in the electrical industry and, in particular, in the automotive electrical industry.

  There are currently several connection techniques for connecting these flexible circuits to electrical contacts or electronic components.

  One of these techniques consists of using connection pads or connection contacts. These connecting plates are provided with piercing teeth forming one or more crown (s). Such a technique is described in US-A-4,749,368. According to this document, the connection is made by means of staples piercing the flexible circuit. These staples are distributed on a connection board above which is placed the flexible circuit to be connected. Each of these staples has a drill bit crown which passes through the flexible circuit and is then crimped onto the flexible circuit.

  The teeth are thus intended to pass through the flexible circuit from a lower face to an upper face and then fold down by crimping against the upper face of the flexible circuit.

  Such a flexible circuit pierced by such a connection board has an acceptable electrical resistance to allow the passage of a current amount conventionally used in the field of connection through the conductive tracks. In one example, the electrical resistance between a conductive track of the flexible circuit intended to be in contact with the tooth and the tooth is equal to 2 milliohms (min).

  However, this electrical resistance is not low enough to allow the passage of a greater amount of current through the tracks of the flexible circuit. Usually, the conductive tracks have a thickness of the order of 75 to 100 μm. To reduce the electrical resistance between the tooth and the track, it could increase a contact area between the tooth and the track in contact with the tooth. To increase the contact area of the tooth with the track, one could increase the thickness of such a conductive track.

  However, increasing the thickness of the conductive track would cause a possible hardening of the flexible circuit and make the manufacturing cost of such a flexible circuit high.

  It was realized that after piercing the tooth through the flexible circuit, the tooth was not perfectly in contact with the portion of the track that it is supposed to cross. Spaces remain between the tooth and the track at a point in the tooth in contact with the track after having crossed it. It has been realized that these spaces are at the origin of the high electrical resistance of such a flexible circuit provided with the connection contact.

  Therefore, the invention provides to solve this problem by increasing a contact surface between the tooth and the track at a point of the tooth intended to be in contact with the track. More particularly, the invention provides an improved method of crimping at least one connection contact on a flexible electronic circuit. After having pierced the flexible circuit, the tooth is heated in such a way that it is welded to a point of the track which it has already crossed. By welding to the track, the tooth fills the spaces between the tooth and the track at the point of the tooth crossing the track. By filling these spaces, the contact surface of the tooth with the track increases and then reduces the electrical resistance between the connection contact and the track.

  This process involves the heating of the tooth with a heating bar which has the property of heating very quickly in a few seconds so as to immediately transfer the heat to the tooth without causing burning of the tooth and without burning the tooth. flex while causing a weld of the tooth with the track at the location of the tooth in contact with the track. In one example, the bar is a tungsten bar that can heat in 1 to 3 seconds. This heating bar also has the property of performing a tooth weld without adding additional material.

  To do this, the tooth is covered with a fusible conductive product such as a mixture of tin-lead, a mixture of tin-copper, pure tin, a mixture of tin-silver-copper, or nickel.

  In a variant of the invention, to increase a contact area of the connection contact with a track of the flexible circuit, at least one end of a tooth is welded to the track after being folded against the upper face of the flexible circuit . The end of the tooth is welded to the conductive track while again piercing this second insulating sheet. The second sheet is pierced following local abrasion of the same sheet by the heating bar and driven by the heating of the end of the tooth.

  To produce such a flexible electronic circuit provided with this connection contact, the invention therefore relates to a method of crimping at least one connection contact on a flexible electronic circuit, the connection contact comprising at least one piercing tooth extending perpendicularly to a plane formed by the connection contact, the flexible circuit comprising a flexible and thick strip delimiting a lower face and an upper face while being formed by a first sheet of insulating material, by at least one track electrically conductive, and by a second sheet of an insulating material, characterized in that - the tooth is covered with a fusible conductive product, - the flexible circuit is pierced from the lower face to the upper face of the strip through the piercing tooth, - one end of the tooth is folded against the upper face of the band, and - one warms the tooth of mani era to perform a tooth weld with the track to at least one location of the tooth to be in contact with the track.

  The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented only as an indication and in no way limitative of the invention. The figures show: FIG. 1: a schematic representation of a flexible electronic circuit provided with a connection contact, according to the invention; - Figures 2a to 2b: schematic representations of an embodiment of a ring of piercing teeth of a connection contact, according to the invention; - Figure 3: a schematic three-dimensional representation of a flexible electronic circuit provided with a connection contact, according to the invention; - Figures 4a to 4d: schematic representations of the various steps of a method of crimping a connection contact on a flexible circuit, according to the invention.

  FIG. 1 illustrates a flexible electronic circuit 1 provided with a connection contact 2, according to the invention. The flexible circuit forms a flexible and thick strip delimiting a lower face 3 and an upper face 4. This flexible band is formed from the lower face 3 to the upper face 4 by a first sheet of a flexible insulating material 5, by at least one electrically conductive track 6, and a second sheet of insulating material 7. These conductive tracks can be deposited on the first sheet 5 and covered by the second sheet 7. These conductive tracks can form one or more circuit patterns printed. These tracks may be formed following printing of a layer of electrically conductive ink on the first sheet 5. This ink layer 6 may consist essentially of copper or nickel or other conductive product of electricity. In one example, this ink layer forms a thickness of 75 to 100 micrometers (μm) thick and the flexible circuit can form a thickness of 300 μm. In the case where the ink layer reaches about 100 .mu.m thick, preference will be used laminated copper. The thickness 18 is measured in a direction perpendicular to a plane formed by the flexible circuit from the lower face 3 to the upper face 4.

  The connection contact 2 is formed of an electrically conductive metal plate. This connection contact 2 may be formed by a copper plate or other conductive material. This connection contact 2 also comprises an upper face 8 and a lower face 9. In the preferred example 1, the connection contact 2 is placed with its upper face 8 contiguous to the lower face 3 of the flexible circuit 1.

  The connection contact 2 also comprises at least one piercing tooth, such as 10a, 10b, 10c, 10d, FIGS. 1 and 2b. This piercing tooth may be part of a ring of teeth 11 as shown in Figures 2a to 2b. This ring of teeth 11 may comprise four teeth 10a, 10b, 10c and 10d.

  This ring of teeth 11 is formed after cutting the material formed by the contact 2 in a whole thickness 12 of the same contact 2. To achieve this ring of teeth 11, a cross-shaped cut is made throughout the thickness 12 contact 2. The cutting throughout the thickness 12 of the connecting contact 2 is shown in dotted lines in Figure 2a. The delineation of the resulting teeth is shown in Figure 2b. Thus after cutting throughout the thickness 12 of the connection contact 2, four triangles each forming a tooth such that 10a, 10b, 10c and 10d are delimited. The teeth are intended to be oriented perpendicular to the plane formed by the contact 2. Preferably, they are located on the same side of the plane formed by the contact 2 so as to reinforce the approach of the contact 2 to the flexible circuit 1.

  In a variant, some of the piercing teeth 10 could be inclined by a first side and others by a second side of the plane formed by the contact 2 (not shown). In this case, it may be provided to provide an additional flexible circuit (not shown) against this same connection contact 2 so that the lower face 3 of this connection contact 2 is contiguous to an upper face (not shown) of this extra soft circuit. The flexible circuit 1 according to the invention and the additional flexible circuit would then be in communication with each other via the connection contact 2.

  All these teeth 10a, 10b, 10c and 10d form the ring of teeth 11 and define a central hollow space 13. Each of the teeth has an end 10e, 10f, 10g, and 10h respectively with a shape that can be advantageously pointed to facilitate the piercing of the contact 2 through the flexible circuit. Or each of these ends may have a rounded shape or a flattened shape.

  The process of crimping the connection contact 2 on the flexible circuit 1 can be carried out as follows, FIGS. 4a to 4d. The teeth are first covered with a fusible electrical conductor. At least one of the teeth may be covered with a fusible conductor product 1 to 5 μm thick. This fusible electrical conductor product may be formed preferentially by a mixture of lead tin. This product may also be a mixture of copper tin, or a mixture of tin-copper silver or pure tin. FIG. 4a shows a cross-section of the flexible circuit 1 and the connection contact 2 with the flexible circuit 1 detached from the connection contact 2. In a first step, the connection contact 2 is intended to come into contact with the flexible circuit 1 so that the upper face 8 of the same contact 2 comes into contact with the lower face 3 of the circuit 1. This approach of the upper face 8 to the lower face 3 is represented by arrows F in FIG. 4a .

  It follows from FIG. 4b that the teeth 10a, 10b, 10c, and 10d completely pass through the flexible circuit 1 from the lower face 3 to the upper face 4, passing successively through the first insulating layer 5, through the conductive layer 6 and through the second insulating layer 7. Each of the teeth 10a, 10b, 10c and 10d completely crosses the circuit 1 with a position of each of the teeth relatively perpendicular to a plane formed by the contact 2. The piercing of the teeth 10a, 10b , 10c and 10d through the flexible circuit 1 can be facilitated because of the pointed shape of the ends of the teeth. Each of the teeth 10 is then in contact with the track in a first portion 15 of the tooth. The size of this first portion 15 depends on a thickness 20 of the track 6.

  Then, after passing through the flexible circuit 1, each of the teeth 10a, 10b, 10c and 10d is crimped on the upper face 4 of this flexible circuit 1, Figures 3 and 4c. The crimping of the teeth is represented by arrows F 'in FIG. 4b. FIG. 3 illustrates a perspective representation of a flexible circuit 1 provided with the connection contact 2 according to the invention. Crimping each of the teeth 10a, 10b, 10c and 10d on the upper face 4 of the flexible circuit 1, the fact of folding against the upper face 4 of the flexible circuit each of these teeth 10 in the direction opposite to the central space 13 The teeth 10 are folded against the upper face 4 of the flexible circuit towards the outside of the ring of teeth 11. These teeth can be folded down by means of a punch.

  Each tooth has a height 17 at least greater than the thickness 18 of the flexible circuit 1, Figure 2b. This height 17 is measured in a direction perpendicular to the plane formed by the contact 2 between the upper face 8 of the contact 2 and the end of each of the teeth. In one example, a flexible circuit 1 has a thickness of 300 μm and in this case the height 17 of each of the teeth must be at least greater than 300 μm to allow the tooth to fall back against the upper face 4.

  According to a preferred embodiment of the invention, at least one of the teeth such as 10a, 10b, 10c and 10d is heated so as to perform a welding of the tooth with the track to at least one point of the tooth in contact with the tooth. Track. The tooth is in contact with the track in a first portion of the tooth. The conductive product allows the tooth to be welded to the track by its first portion 15.

  Each of the teeth may be heated by means of a heating bar 14. The heating is represented by the corrugated arrows F "in FIG 4c.The heating bar is intended to produce a weld which is similar to a braze of the tooth on the track The term "solder" means that the portion of the tooth is welded to the corresponding portion of the track without adding any additional material but only an addition of the fusible conductive product covering the tooth. Heating bar also has the property of immediate heating of the tooth in a few seconds while rising very high temperature so as to transfer heat to the tooth immediately without causing burning of the tooth or flex. bar heated to 1000 C in 1 to 3 seconds The application of such a heating bar on the tooth can be done in 1 to 3 seconds only. t be a tungsten bar.

  This solder has the advantage of filling any gaps 20 between the tooth and the track at a point on the tooth in contact with the track. These spaces 20 are likely to remain after the drilling of the tooth through the flexible circuit 1. These spaces are responsible for a decrease in the contact surface between the tooth and the track. These spaces 20 are filled following the welding of the tooth to the track at a location of the tooth in contact with the track. More specifically, the welding of the tooth with the track is performed in such a way that gaps 20 between the portion 15 of the tooth and the corresponding track portion are filled. The tooth is then in contact with the track over an entire area delimited by the portion 15. Thus, the electrical conductivity is increased and the electrical resistance decreased. In one example, the electrical resistance of such a flexible circuit provided with this connection contact according to the invention is 0.2 mS2.

  According to a variant of the invention, at least one of the teeth can also be welded to a second location 16 of the tooth on the conductive track 6. This tooth is welded a second time in such a way that the second sheet 7 is entirely pierced a once again from the upper face 4 of the flexible circuit and towards the conductive track 6. This second sheet 7 is entirely pierced following local abrasion in a thickness 19 of the second insulating sheet 7. The localized abrasion is performed following heating by the heating bar 14 on one end of the tooth. The heating of the ends 10e and 10g of the teeth 10a and 10c respectively is represented by an arrow F "'in FIG. 4d.

  This abrasion localized through the second insulating layer 7 is made so that the end of the tooth comes into contact with the conductive track 6, as shown in Figure 4d. This local abrasion of the second insulating sheet 7 is performed while heating one end of each of the teeth so as to melt the conductive product covering the end of the tooth. The conductive product thus melted creates a weld of at least one of the ends of the teeth on the conductive track 6 at a second location of the tooth 16.

  The connection contact 2 is then in contact with the conductive track 6 in a first contact zone 15 and in a second contact zone 16, FIGS. 1 and 4d. The first contact zone 15 corresponds to a point of the tooth intended to be in contact with the track 6 following a first piercing of the tooth through the flexible circuit 1. The second contact zone 16 corresponds to a place of the tooth intended to be in contact with the track 6 following a second piercing of the tooth through the second sheet 7.

  This results in a flexible electronic circuit having a substantially reduced electrical resistance with respect to another flexible circuit provided with a connection contact usually encountered in the state of the art. In one example, the electrical resistance can be decreased by a factor of 10 or 2 minutes to 0.2 minutes. This also results in an increase in electrical conductivity. This electrical conductivity is all the more important as the first contact zone 15 and the second contact zone 16 of the end of the tooth are extended.

Claims (6)

  1 - Method of crimping at least one connection contact (2) on a flexible electronic circuit (1), the connection contact comprising at least one piercing tooth (10a, 10b, 10c, 10d) extending perpendicularly to a plane formed by the connection contact, the flexible circuit comprising a flexible and thick strip (1) delimiting a lower face (3) and an upper face (4) while being formed by a first sheet (5) of a material insulation, by at least one electrically conductive track (6), and by a second sheet (7) of an insulating material, characterized in that - the tooth is covered with a fusible conductive product, - the circuit is pierced flexible from the lower face to the upper face of the band via the piercing tooth, - one end of the tooth is folded against the upper face of the band, and - the tooth is heated to achieve a tooth weld with the runway at one to less a place of the tooth intended to be in contact with the track.   2 - Process according to claim 1, characterized in that the tooth is heated for a period of 1 to 3 seconds by means of a heating bar.   3 - Process according to claim 2, characterized in that one uses a tungsten heating bar.   4 - Process according to one of claims 1 to 3, characterized in that covers the tooth of a fuse conductive product of 1 to 5 pm thick.   - Method according to one of claims 1 to 4, characterized in that covers the tooth of a mixture of tin-lead, or a mixture of étaincuivre, or a mixture of tin-copper -money, or pure tin.   6 - Method according to one of claims 1 to 5, characterized in that one obtains an electrical resistance between the tooth and the track at a location of the tooth in contact with the track of 0.2 milliohms (mg-2) .   7 - Method according to one of claims 1 to 6, characterized in that one end of the tooth is heated so that the end of the tooth is welded to the electrically conductive track after crossing a second time the second sheet of insulating material.