IMPROVED ELECTRICAL CONNECTION BETWEEN A FLEXIBLE CIRCUIT AND A RIGID CIRCUIT, ASSOCIATED CONNECTION PIN

Abstract

An electrical connection according to the invention comprises superimposing a flexible printed circuit board (200) onto a rigid printed circuit board (100) by aligning a hole (231) in a contact area (230) of the flexible circuit with a plated-through hole (131) of the rigid circuit. A connecting pin (300) made of conductive material is then inserted through the hole in the flexible circuit such that a first press-fit end (310) of the connecting pin is inserted into the plated-through hole, and an opposite end (320) of the connecting pin holds the flexible circuit against the rigid circuit by pressing against the contact area. By being in contact with the contact area and with the plated-through hole, the connecting pin establishes an electrical connection between the two printed circuit boards without requiring an additional connecting component on the flexible circuit. (See Fig. 3 for abbreviations.)

Description

Title of the invention: IMPROVED ELECTRICAL CONNECTION BETWEEN A FLEX CIRCUIT AND A CIRCUIT RIGID, ASSOCIATED CONNECTION PIN technical field

[0001] The present invention relates to the electrical connection of printed circuits or PCBs (for "printed circuit board" in Anglo-Saxon terminology). Previous technique

[0002] A printed circuit board generally consists of insulating layers and electrical traces to which electronic components can be connected in order to create a complex electronic circuit.

[0003] Depending on the rigidity of the insulating support, the printed circuit can be said to be "rigid" or "flexible".

[0004] A rigid printed circuit board is typically made of an epoxy resin substrate and has a variable thickness, for example often between 0.8 and 2.4 mm.

[0005] A flexible or "soft PCB" printed circuit board is made from thin insulating material. It typically has a lower thickness (less than one millimeter), on the order of 100 pm to 500 pm.

[0006] Flexible printed circuits are developing widely because their ability to bend or curve has many applications, both in consumer electronics (telephone, camera, computer, etc.) and in means of transport (vehicle, aviation, etc.).

[0007] Printed circuits can be single-sided, double-sided and multilayer.

[0008] There is a trend towards assembling rigid and flexible printed circuits to obtain so-called "flex-rigid" circuits. To do this, it is necessary to interconnect two printed circuits of different types, in particular by electrically connecting a flexible printed circuit to a rigid printed circuit.

[0009] Generally, special connectors for flex PCBs (or flexible ribbon cables forming part of the contact area of ​​the flex PCB) are required to connect the flexible printed circuit board by crimping. These special connectors are integrated into the rigid printed circuit board using conventional techniques, for example, with push-fit pins.

[0010] US publication 2019 / 0296464 is known, which describes a method for electrically connecting a flexible printed circuit board to a plate. According to the proposed embodiments, the mechanical coupling of an additional component in the form of of sleeve with the flexible printed circuit board, before using a press-fit pin to connect the circuit to the board.

[0011] Adding this additional component is detrimental in several respects. Firstly, it entails additional costs. Secondly, it requires additional soldering steps ("soft soldering") that are incompatible with all types of flexible PCB insulators (due to temperature differences) and are time-consuming. Finally, it creates a weak point at the solder joint, which is susceptible to failure depending on the mechanical stresses it is subjected to.

[0012] There is therefore a need to improve existing techniques for electrically connecting a flexible printed circuit to a rigid printed circuit. Description of the invention

[0013] In this context, a method for electrically connecting a flexible printed circuit to a rigid printed circuit is proposed, comprising the following steps: - presenting a contact area of ​​the flexible printed circuit, opposite a hole, generally through, plated in the rigid printed circuit, - engaging a connecting pin made of conductive material through the contact area of ​​the flexible printed circuit so that a first push-fit type end of the connecting pin is pressed in, i.e., is forced into the plated hole of the rigid printed circuit to make the mechanical parts together by a locked fit, and an opposite end of the connecting pin holds, by pressing against the contact area, the flexible printed circuit against the rigid printed circuit so as to make an electrical connection between the two printed circuits.

[0014] The flexible printed circuit board is thus sandwiched between the rigid printed circuit board and the support portion of the connecting pin. The latter establishes, in itself, the electrical connection between the two circuits, from the conductive trace at the contact area to the metallization of the plated-through hole in the rigid printed circuit board.

[0015] The contact area of ​​the flexible printed circuit is understood as an area, generally terminal, of a conductive or electrical track, intended for electrical interconnection with an external element.

[0016] According to the invention, no additional components are required on the flexible printed circuit board to make the electrical connection. Furthermore, this connection can be made in a single step consisting of inserting or engaging the connecting pin through the aligned contact area and plated-through hole. Cost and time savings are therefore advantageously achieved.

[0017] Correspondingly, the invention also relates to an electrical assembly comprising: - a rigid printed circuit board with a plated-through hole, - a flexible printed circuit board with a through-hole made at a contact area and positioned opposite the plated-through hole, and - a connecting pin made of conductive material, one end of which is a push-fit type pin that is inserted into the plated hole of the rigid printed circuit board, and the opposite end holds the flexible printed circuit board against the rigid printed circuit board by pressing against the contact area so as to make an electrical connection between the two printed circuits.

[0018] In practice, an assembly between a flexible printed circuit board and a rigid printed circuit board includes such an electrical connection in a plurality of distinct contact areas (and therefore a plurality of corresponding plated holes in the rigid printed circuit board), typically associated with a plurality of conductive tracks.

[0019] The through hole made at the contact area may be pre-existing to the assembly or result from this assembly by piercing the flexible printed circuit board by the connection pin.

[0020] Optional features of embodiments of the invention are defined in the appended claims. Some of these features are explained below with reference to a method, while they can be transposed into device features (assembly and connecting pin).

[0021] In one embodiment, the flexible printed circuit board has a through-hole in the contact area, which is aligned with the plated-through hole before the connecting pin is inserted. Such a through-hole is therefore pre-drilled on the flexible printed circuit board. The two holes are simply aligned vertically, and then the connecting pin is inserted into the hole thus formed.

[0022] A hole at the contact area is preferably made in the middle of such a conductive track in order to promote electrical contacts.

[0023] As an alternative to having such a through hole, the contact area is not pre-drilled. In this case, the connecting pin may be provided with a tapered, pointed, and / or sharp end capable of piercing the flexible printed circuit board at the contact area when the connecting pin is engaged. A through hole is thus created by the engagement of the connecting pin.

[0024] In one embodiment, a support portion that provides support for the opposite end of the connecting pin on the contact area has at least one tooth oriented towards the first end, i.e., in the direction of support towards the rigid circuit, during connection. This arrangement with a pointed protrusion contributes to maintaining an electrical connection with the contact area, despite harsh external stresses and conditions (temperatures, mechanical pressure) that may occur. to alter the contact by pressure or the adhesion of the insulating layer of the flexible printed circuit board.

[0025] According to one possible embodiment, said at least one tooth is configured to pierce an insulating layer and / or a conductive trace of the flexible printed circuit board at the contact area, when the first end is inserted into the plated-through hole of the rigid printed circuit board. Improved retention is then obtained.

[0026] According to a particular feature, said at least one tooth is configured to pierce the flexible printed circuit board (i.e., through its entire thickness) at the contact area, when the first end is inserted into the plated-through hole, so as to establish electrical contact with a conductive surface (for example, an overhang of the plated-through hole) of the rigid printed circuit board adjacent to the plated-through hole. This arrangement aims to improve the electrical contact of the pin with the rigid printed circuit board, while also improving the mutual retention of the two circuits in the assembly.

[0027] According to another possible (and combinable) embodiment, said at least one tooth comprises two teeth arranged on either side of a longitudinal axis of the connecting pin formed by said two ends. Thanks to this symmetry, two supports are provided, ensuring better retention of the two circuits in the presence of more varied external mechanical stresses. Furthermore, the engagement of the connecting pin is facilitated since the latter can be inserted in two directions for the same result.

[0028] According to another possible (and combinable) embodiment, said at least one tooth comprises two sets of teeth arranged on either side of a longitudinal axis of the connecting pin formed by said two ends. This symmetry provides the same advantages with two supports, with multipoint electrical contact that improves the electrical connection. In addition, the presence of several (two or more) teeth on each side ensures improved support, and therefore retention.

[0029] All or part of these teeth may be penetrating through the insulating layer, the conductive track or the flexible printed circuit board.

[0030] In a possible combined embodiment, the opposite end of the connecting pin has an elastically deformable support portion acting as a spring to exert a bearing force on said support against the contact area when the first end is inserted into the plated hole. Advantageously, the support is improved, particularly when the assembly is subjected to external stresses. This results in better mechanical retention of the two circuits and improved electrical contact at the contact area (and therefore a better electrical connection between the two circuits).

[0031] According to one possible embodiment, the elastically deformable support portion is symmetrical with respect to a longitudinal axis of the connecting pin formed by said two ends. This symmetry provides the same advantages with two supports as those described above.

[0032] Incidentally, the invention also relates to a connecting pin for a flexible printed circuit board to a rigid printed circuit board, adapted for the electrical connection and assembly described above. The connecting pin is made of conductive material and comprises: - a first end of the push-fit or "press-fit" type, suitable for being inserted into a plated hole in the rigid printed circuit board, and - a second connecting end comprising a support portion configured so that, when the first end passes through a hole made in a contact area of ​​the flexible printed circuit board and is then inserted into the plated-through hole of the rigid printed circuit board, it holds the flexible printed circuit board against the rigid printed circuit board by pressing against the contact area of ​​the flexible printed circuit board, thus establishing an electrical connection between the two printed circuit boards, connecting pin in which the support portion: - includes at least one tooth for piercing an insulating layer and / or a conductive trace of the flexible printed circuit board at the contact area, when the first end is inserted into the plated-through hole, and / or - is elastically deformable acting as a spring to exert a bearing force for said bearing against the contact area, when the first end is fitted into the metallized hole.

[0033] In one embodiment, the connecting pin is configured in the general shape of a T, the foot of the T forming the first push-fit type end and the head of the T forming the opposite end holding, by pressing against the contact area, the flexible printed circuit against the rigid printed circuit. Brief description of the drawings

[0034] Other features and advantages of the invention will become apparent in the following description, illustrated by the accompanying figures which illustrate examples of embodiment without any limiting character.

[0035] [Fig-1] Figure [Fig.1] illustrates two rigid and flexible printed circuit boards to be connected electrically according to embodiments of the invention.

[0036] [Fig.2] Fig.2 illustrates a superposition of the two rigid and flexible printed circuits to connect them electrically using a connecting pin, according to embodiments of the invention.

[0037] [Fig.3] The [Fig.3] illustrates an electrical assembly resulting from the electrical connection of the two rigid and flexible printed circuits according to embodiments of the invention.

[0038] [Fig.4] The [Fig.4] illustrates variants of an adaptable press-fit end of connection pins according to embodiments of the invention.

[0039] [Fig.4a] Fig.4a illustrates a massive type press-fit end.

[0040] [Fig.5] The [Fig.5] illustrates variants of an end forming a support portion of connection pins according to embodiments of the invention. Detailed description

[0041] The present invention relates to the electrical connection of printed circuits or PCBs (for "printed circuit board" in Anglo-Saxon terminology), and more particularly that of a flexible printed circuit or "flex PCB" to a rigid printed circuit or "rigid PCB".

[0042] Figure 1 illustrates a rigid PCB on the left and a flexible PCB on the right, for which the electrical connection is to be made, i.e., the conductive traces are to be interconnected. For clarity, only three conductive traces are shown on these printed circuit boards. As is known, these can include a different number of traces (more or less) and / or electronic components attached to them, for example by soldering or using push-fit or "press-fit" type connection pins.

[0043] The rigid PCB 100 comprises a substrate 110, typically made of FR4 or another substrate, on which conductive tracks 120 are formed by any suitable technique such as etching or printing with conductive ink. A rigid PCB typically has a variable thickness, for example often between 0.8 and 2.4 mm, providing suitable rigidity for the press-fit insertion of pins.

[0044] The conductive tracks 120, made of copper or silver for example, terminate in contact areas 130 provided for interconnection with the flexible PCB 200. Although the contact areas 130 shown are terminal portions of associated conductive tracks, one or more, or each, contact area may constitute an intermediate portion of the conductive track. That is to say, components may be attached to the same conductive track on both sides of the contact area.

[0045] Each contact zone 130 is adapted to receive a press-fit pin as described below. The contact zone 130 is thus formed by a hole 131, preferably through (optionally blind), which has been metallized by any known technique. The metallization allows the deposition of a conductive material 132 in the passage 133 of the hole but also on the lower and upper surfaces 134 of the rigid PCB 100 near the hole 131, ensuring electrical contact with the conductive track 120.

[0046] In the illustrated example, several plated holes 131 are shown, aligned and evenly spaced on the rigid PCB 100, according to a predetermined pitch. This pitch can be adjusted according to a press-fit machine used to insert the press-fit pins into these holes 131. Typical pitch values ​​include 2.54 mm, 2.20 mm, 2.00 mm, and even other values ​​down to 1.27 mm.

[0047] In conventional press-fit techniques, the plated holes 131 typically have a diameter of 0.8 to 1.2 mm, for example 1 to 1.1 mm. Of course, the diameter of these holes is adjusted to the diameter of the press-fit pins used.

[0048] Although the plated-through holes 131 are intended here for separate conductive tracks 120, and therefore contact areas 130, it may be provided that one or more contact areas 130 (or conductive tracks) each comprise two or more plated-through holes. This improves the mechanical strength of the final assembly between the two PCBs, and also improves the electrical connection between them, particularly if a significant current is intended to flow between the two PCBs.

[0049] The flex PCB 200 comprises a base film 210 of plastic such as polyimide, polyetheretherketone (PEEK), polycarbonate, polyester type polyethylene naphthalate (PEN) or polyethylene terephthalate (PET), or similar, on which conductive tracks 220 are formed, by any suitable technique such as lamination, engraving or preferably printing (screen printing) of conductive ink, for example silver ink.

[0050] The face of the flex PCB 200 presenting the conductive tracks 220 is called the upper surface, while the lower face of the base film 210 is called the lower surface.

[0051] The conductive tracks 220, of copper or silver for example, terminate with contact areas 230 provided for interconnection with the rigid PCB 100.

[0052] The section (la) in the Figure represents a polycarbonate-based flexible PCB 200 on which silver traces are printed. The polycarbonate sheet 210 used has a thickness of between 125 µm and 800 µm, preferably between 200 µm and 500 µm. The silver layer 220 has a thickness of a few µm, typically between 8 and 15 µm. The silver trace 220 can optionally be covered with an insulating protective layer 211, typically a dielectric layer with a thickness of a few µm to tens of µm, for example, 8 to 40 µm. Advantageously, the deposition of the insulating protective layer 211 can be localized so as to leave the conductive trace uncovered at the contact area 230.

[0053] Section (1b) in the Figure represents a flexible PCB 200 based on polyimide or PEEK 210 onto which a conductive copper track 220 is bonded and covered, by bonding, with an insulating PET film 211. In such a design, the base 210 has a thickness of a few tens of µm, for example 50 µm, the conductive track 220 has a thickness of 35, 70, or 105 µm, and the insulating film 211 has a thickness of a few tens of µm, for example 50 µm. The adhesive used to bond each layer can be an acrylic adhesive, such as Pyralux LF Sheet Adhesive (trade name) XXXX, and has a thickness of a few tens of µm, for example 12 to 50 µm.

[0054] The flex PCB 100 therefore has a thickness of less than one millimeter, contributing, with the plastic nature of the base, to appreciable flexibility.

[0055] The contact areas 230 can be free of any perforation.

[0056] However, in certain embodiments as illustrated, each contact area 230 of the flex PCB 200 has a through hole 231 providing a cylindrical passage 233 of a diameter similar to that of the plated holes 131. Each through hole 231 is therefore surrounded by a conductive portion of the respective track 220.

[0057] In the illustrated example, several through holes 231 are shown which are aligned and regularly distributed on the flex PCB 200, according to the same pitch as the plated holes 131 of the rigid PCB 100.

[0058] Similar to the rigid PCB 100, a contact area 230 corresponding to a conductive track 220 may have two or more through holes 231 in order to make several electrical connections according to the invention per contact area.

[0059] According to the invention, the two PCBs are electrically connected without the addition of dedicated connectors, either on the rigid PCB 100 or on the flex PCB 200. To do this, the contact areas 130 and 230 are first superimposed so as to present a hole 231 made at the level of a contact area 230 of the flex PCB 200, opposite a plated hole 131 of the rigid PCB 100. This is the operation illustrated in [Fig.2].

[0060] The flex PCB 200 is positioned lower surface on the rigid PCB 100 so that its upper surface including the contact area 230 (uncovered or covered by the insulating film 211) is directly accessible and in contact with the inserted connection pin, as described below.

[0061] In the illustrated example, the three through holes 231 are superimposed on the three plated holes 131, each creating a continuous passage 031 through both PCBs. More generally, the contact areas 230 are superimposed on the plated holes 131.

[0062] The superimposed positioning of the two PCBs can be carried out manually or automatically by a press-fit machine using, for example, guides or optical alignment means.

[0063] According to the invention, the electrical connection of the two PCBs is made at the level of the superimposed holes thus formed, using connecting pins made of material conductor, an example of which is illustrated in [Fig.2] under reference 300. The pins can be inserted simultaneously or one after the other.

[0064] Such a pin 300 is substantially elongated, having two ends (upper and lower in the Figure) defining a longitudinal axis A, typically of symmetry. The pin shown is generally T-shaped.

[0065] The foot 310 of the T forms a first press-fit end designed to be inserted into one of the plated holes 131 of the rigid PCB 100. By forcing this end into the plated hole, the pin 300 and the rigid PCB 100 are secured together by a locking fit. The press-fit end therefore has dimensions adapted to the plated holes 131 to perform the press-fit function.

[0066] Several embodiments of this press-fit end can be envisaged, as described below.

[0067] On the other side, the head 320 of the T forms another end, opposite to the first, forming a support zone or portion intended to maintain, by pressing against the contact zone 230 of the flex PCB 200, the latter against the rigid PCB 100 as explained later and illustrated by [Fig.3].

[0068] Similarly, several embodiments of this support end can be envisaged, as described below.

[0069] As shown in [Fig. 2] by the solid arrow, the connecting pin 300 is engaged, press-fit end 310 forward, in the passage 031 first through the through hole 231 of the flex PCB 200, and then through the plated hole 131 opposite it. When the contact areas 230 are free of through holes, it is the engagement of the connecting pin 300 at a contact area that pierces or penetrates the flex PCB 200 and thus creates a through hole 231. For this purpose, the foot (press-fit end 310) of the connecting pin 300 has a tapered, pointed, and / or sharp end.

[0070] The connecting pin 300, and in particular its press-fit end 310, is then inserted, i.e., press-fitted, into the plated hole 131 of the rigid PCB 100, ensuring a locked fit between the two parts (pin and rigid PCB). Figure 3 illustrates the final state of the electrical connection once the press-fit end 310 is inserted into the plated hole 131.

[0071] In this final state, the opposite end 320 of the connecting pin holds the flex PCB 200 against the rigid PCB 100 by pressing against the contact area 230. In effect, the flex PCB 200 is sandwiched or clamped between the rigid PCB 100 and the head 320 of the pin, which has a dimension larger than that of the passage 031. The pin 300 is locked in place with the rigid PCB 100 by the insertion of the end press-fit 310 in the plated hole 131 ensures the plating, and therefore the holding, of the two PCBs against each other.

[0072] In this configuration, on the one hand, the head 320 of the connecting pin 300 makes electrical contact with the conductive track 220, at the contact area 230 and, on the other hand, the press-fit end 310 makes electrical contact with the conductive track 120, via the metallization of the metallized hole 131. Thus, the connecting pin 300 establishes, by itself, an electrical connection between the two printed circuits 100 and 200, without the need to add a connector or other conductive sleeve on the flex PCB 100 before connection.

[0073] A press-fit pin insertion machine allows such an electrical connection between flex PCB and rigid PCB, in particular by simultaneously fitting several pins 300 (three in the Figures) taken from a roll of pins in strip, into passages 031 arranged according to a predetermined pitch.

[0074] Figures 2 and 3 illustrate a 300 type adaptable press-fit pin, that is, one that compresses or is elastically deformable or "adapts" during forced insertion. The invention also applies to solid type press-fit pins, also called solid pins or solid pins.

[0075] Figure 3 illustrates the adaptable press-fit pin in a compressed state, ensuring a locked fit. By forcing the pin into the passage 031, the plated hole 131 is typically slightly deformed (in particular the metal layer), improving the locking.

[0076] Figure 4 illustrates some variations of the adaptable press-fit end 310 of a spindle 300 adapted to the invention. Other variations not illustrated here are also usable for an implementation of the invention.

[0077] These pins are preferably manufactured by cutting (laser or waterjet cutting, follow-through cutting tool, press cutting, etc.) from a conductive sheet typically about half a millimeter thick, for example 0.635 mm. Examples of conductive sheets include stainless steel, iron-nickel alloy, copper, copper alloy such as phosphor bronze, or equivalent. Thus, the 300 pins are made in one piece.

[0078] The press-fit end 410a is the same as that shown in Figures 2 and 3 and shows a press-fit portion 310 of the "eye of needle" type, EON, or needle eye, symmetrical with respect to its longitudinal axis A. This pin is flat.

[0079] The EON 410a press-fit portion consists of two arms 411a, 412a projecting laterally from the longitudinal axis A, obtained by forming a hole 415a, thus resembling the eye of a sewing needle. By choosing a suitable material and an appropriate arm width, this hole provides greater or lesser flexibility, and therefore a spring effect, to the arms. The distance between the outer edges of the two arms 41 la, 412a is greater than the diameter of passage 031, so as to require forced insertion.

[0080] The tip 420a, typically tapered or conical, allows for easier insertion into the passage 031.

[0081] The press-fit end 410b is a variant, still of the EON type, symmetrical with respect to its longitudinal axis A, known as "MultiSpring". This variant further comprises multiple folded strips 416b (obtained, for example, by stamping after cutting), acting as springs, inside the eye 415b. Typically, the strips are alternately in the general shape of a V and in the general shape of an inverted V (or even a W and an inverted W), and do not protrude beyond the thickness of the spindle 330 (thickness defined by that of the sheet metal from which it is cut).

[0082] Again, the 420b tip, typically tapered or conical, allows for easier insertion into the 031 passage.

[0083] The press-fit end 410c is an "Action PIN" type variant having two arms or slats or "half-pins" 411c, 412c offset, typically by stamping, from the longitudinal axis A, in a direction perpendicular to the plane of the pin (the illustration on the right is a side view, within the thickness of the pin). Alternatively, only one of the two half-pins may be offset, the other remaining parallel to the axis. This offset gives the press-fit portion the spring effect necessary for press-fit insertion.

[0084] Again, the 420c tip, typically tapered or conical, allows for easier insertion into the 031 passage.

[0085] The press-fit end 410d is another variant of the "Action PIN" type, featuring a single half-pin 41 Id offset from the longitudinal axis A, in the plane of the pin (and not in a perpendicular direction). The second half-pin 412d is held parallel to the longitudinal axis. Alternatively, the two half-pins may be offset symmetrically. This offset gives the press-fit portion the spring effect necessary for forceful insertion.

[0086] Again, the 420d tip, typically tapered or conical, allows for easier insertion into the 031 passage.

[0087] Figure 4a illustrates a solid press-fit end. The solid pin or solid here includes a press-fit end 410e whose single arm 41 is of square and constant section, with the exception of the terminal tip 420e, typically tapered or conical, allowing easy insertion into the passage 031.

[0088] Figure 5 illustrates some variants of the end 320 forming a zone or portion support for a 300 spindle where the 310 press-fit end is of type EON. However, the press-fit end 310 of these variants can be according to any of the embodiments described in Figures 4 and 4a.

[0089] The head 520a is similar to that of Figures 2 and 3 and shows a support portion 320 formed by two symmetrical arms 521a (the T-bar) which extend substantially perpendicularly to the longitudinal axis A from a point (or zone) 599 from which the press-fit portion 310 extends. At least one arm of the support portion 320 has, on its bearing surface against the flex PCB, at least one tooth 522a oriented towards the press-fit end 310. Typically two teeth 522a, 523a arranged on either side of the longitudinal axis A (therefore one per arm) are provided.

[0090] Such teeth give the bearing portion 320 an irregular or abrasive area which allows gripping of the contact area 230 and thus retention of the flex PCB 200. Other protrusions more or less irregular than teeth can be used as an alternative, for example hemispheres or semi-spherical studs.

[0091] Advantageously, this or these sharp teeth can pierce the insulating layer 211 which can cover the contact area 230 in order to make electrical contact with the conductive track 220 at the level of this contact area, or even pierce the conductive track 220 itself at the level of the contact area, when the connection ([Fig.3]) has been made.

[0092] Such teeth may have a length less than half the thickness of the flex PCB 200, preferably less than one-third of that thickness. By way of illustration, for a flex PCB with a total thickness of 300 µm at the contact area, the length of the teeth can be set at 80 µm.

[0093] The upper end of the head 520a terminates in a finger 525 which extends from the point 599 along the longitudinal axis A on the side opposite the press-fit portion 310. This finger typically allows the manipulation (grasping, moving) of the connecting pin 300 by the press-fit pin insertion machine.

[0094] Variant 520b features elongated teeth configured to pierce the flex PCB 200 through its thickness (base 210, trace 220, and optional insulating film 211) at the contact area 230 during connection. By penetrating the entire thickness, these teeth also establish electrical contact with a conductive surface (specifically, the overhang 134 of the hole plating) of the rigid PCB 100 near the plated hole 131. This contributes to improved electrical interconnection between the two printed circuit boards.

[0095] Variant 520c features two arrays 522c, 523c of teeth arranged on either side of the longitudinal axis A (on the arms 521c), instead of isolated teeth. Although three teeth are shown per array, the number of teeth per array may be different (2, 4 or more) and may vary from one array to another.

[0096] In addition, all or part of the teeth can be sized to pierce or not the flex PCB 200 in its entire thickness (as in variant 520b) or only certain layers (as in variant 520a).

[0097] In variants 520d to 520i, the bearing portion 320, always formed by two symmetrical arms 521d to 521i extending substantially perpendicularly to the longitudinal axis A from point 599, is elastically deformable, acting as a spring to stress the contact zone 230, i.e., to exert the bearing force against it, when the press-fit end 310 is engaged in the passage 031 from the flexible PCB 200 and is fitted into the plated hole 131. The elastic property of these bearing portions can be obtained by a well-chosen compromise between the width of the arms (their smallest dimension in the plane shown in the figures) and the material used. Preferably, a metal with good elastic properties is used, for example, phosphor bronze.

[0098] In these variants, the support portion includes a curved portion of conductive material whose convex surface (lower surface in the illustrations) acts as a support surface against the contact area 230, when the pin 300 is fitted into the assembly of the two circuits.

[0099] The bearing surface of these variants may be provided with teeth or equivalent irregularities mentioned above (variants on the right, the number of teeth may be other than that illustrated, including networks of teeth) or be devoid of them (variants on the left).

[0100] In variants 520d to 520g, the pin gripping finger 525 extends from point 599 from which both the arms constituting the support portion 320 and the press-fit portion 310 extend.

[0101] In variant 520d, each arm 521d forming a support portion consists of a first arm portion 526d extending perpendicularly to the longitudinal axis A from the point 599, and a second curved portion 527d extending outwards from the end of the first portion, the convex surface of which (with or without a tooth, oriented towards the press-fit portion 310) constitutes the support surface against the contact zone 230.

[0102] In variant 520e, each arm 521e forming a support portion consists of the single curved portion 527e which extends from point 599 and whose convex surface (with or without teeth) constitutes the support surface against the contact zone 230.

[0103] In variant 520f, each arm 521f forming a support portion consists of a first curved arm portion 526e extending from point 599, the concavity of which is oriented towards the press-fit portion 310, and a second curved portion 527f extending outwards from the end of the first portion, the surface of which convex (with or without teeth, oriented towards the press-fit portion 310) constitutes the bearing surface against the contact zone 230.

[0104] In the 520g variant, each arm 521g forming the support portion consists of a first curved arm portion 526g extending from the point 599 whose concavity is oriented towards the press-fit portion 310, and a second curved portion 527g extending from the end of the first portion in the general shape of a C or an inverted C directed towards the longitudinal axis A and of which a convex surface (with or without a tooth, oriented towards the press-fit portion 310) constitutes the support surface against the contact zone 230.

[0105] In variants 520h and 520i, the pin gripping finger 525 no longer extends from point 599, but from a common end of the loop-forming support arms.

[0106] In these variants, the arms 521h / 521i are similar to the arms 521f described above, except that their second curved portions 527h / 527i, extending from the end of their first portions 526h / 526i, extend to form a loop at a point 598 on the axis A, from which the gripping finger 525 extends. The finger 525 is thus located at a distance from the point 599 from which the press-fit portion 310 extends. The flexibility of the loop-forming arms ensures that sufficient pressure from said two arms is maintained over time on the contact area to guarantee electrical contact.

[0107] The convex surface (with or without teeth, oriented towards the press-fit portion 310) of the second portions 527h / 527i always constitutes the bearing surface against the contact zone 230.

[0108] In variant 520h, the second portions 527h are extended so as to form a loop in the general shape of an inverted heart.

[0109] In variant 520i, the second portions 527i are extended so as to form a loop in the general shape of a horizontal 8.

[0110] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to those specific embodiments, and modifications, which are within the scope of the present invention, will be apparent to a person skilled in the art.

Claims

Demands

1. A method for electrically connecting a flexible printed circuit board (200) to a rigid printed circuit board (100), comprising the following steps: - presenting a contact area (230) of the flexible printed circuit board opposite a plated hole (131) of the rigid printed circuit board, - engaging a connecting pin (300) made of conductive material through the contact area (230) of the flexible printed circuit board such that a first push-fit end (310) of the connecting pin is inserted into the plated hole of the rigid printed circuit board, and an opposite end (320) of the connecting pin holds the flexible printed circuit board against the rigid printed circuit board by pressing against the contact area, thus establishing an electrical connection between the two printed circuit boards,a method in which a support portion (320) providing support for the opposite end of the connecting pin on the contact area (230) has at least one protrusion (522a, 523a, 522b, 523b, 522c, 523c), such as a tooth, a hemisphere or a semi-spherical pin, oriented towards the first end (310).

2. Method according to claim 1, wherein the flexible printed circuit (200) has a through hole (231) made at the contact area, which through hole is aligned with the plated hole (131) before engaging the connecting pin (300).

3. Method according to claim 1 or 2, wherein said at least one protrusion is a tooth configured to pierce an insulating layer (210, 211) and / or a conductive track (220) of the flexible printed circuit board (200) at the contact area (230), when the first end (300) is fitted into the plated hole (131) of the rigid printed circuit board (100).

4. A method according to claim 1 or 2, wherein said at least one protrusion is a tooth configured to pierce the flexible printed circuit board (200) at the contact area (230), when the first end is inserted into the plated hole, so as to make electrical contact with a conductive surface (134) of the rigid printed circuit board in the vicinity of the plated hole (131).

5. A method according to any one of claims 1 to 5, wherein said at least one protrusion comprises two teeth arranged on either side of a longitudinal axis (A) of the connecting pin (300) formed by said two ends.

6. A method according to any one of claims 1 to 5, wherein said at least one protrusion comprises two sets of teeth (522c, 523c) arranged on either side of a longitudinal axis (A) of the connecting spindle (300) formed by said two ends.

7. A method according to any one of the preceding claims, wherein the opposite end (320) of the connecting pin (300) has an elastically deformable bearing portion (520a-i) acting as a spring to exert a bearing force for said bearing against the contact area (230), when the first end (310) is fitted into the plated hole (131).

8. Method according to claim 7, wherein the elastically deformable bearing portion is symmetrical with respect to a longitudinal axis (A) of the connecting pin (300) formed by said two ends.

9. A method according to any one of the preceding claims, wherein the connecting pin (300) is configured in the general shape of a T, the foot of the T forming the first push-fit end (310) and the head of the T forming the opposite end (320) holding, by pressing against the contact area (230), the flexible printed circuit board against the rigid printed circuit board.

10. An electrical assembly comprising: - a rigid printed circuit board (100) having a plated-through hole (131), - a flexible printed circuit board (200) having a through hole (231) formed at a contact area (230) and disposed opposite the plated-through hole, and - a connecting pin (300) made of conductive material, a first end (310) of the push-fit type of the pin being inserted into the plated-through hole of the rigid printed circuit board, and an opposite end (320) holding, by bearing against the contact area, the flexible printed circuit board against the rigid printed circuit board so as to make an electrical connection between the two printed circuit boards, the electrical assembly in which a bearing portion (320) provides the bearing of the opposite end of the connecting pin on the area of contact (230) has at least one protrusion (522a, 523a, 522b, 523b, 522c, 523c), such as a tooth, a half-sphere or a semi-spherical spike, oriented towards the first end (310).

11. A connecting pin (300) of a flexible printed circuit board (200) to a rigid printed circuit board (100), the connecting pin being made of conductive material and comprising: - a first end (310) of the press-fit type adapted to be inserted into a plated hole (131) of the rigid printed circuit board, and - a second connecting end (320) comprising a bearing portion (520a-i) configured so that, when the first end passes through a hole made in a contact area (230) of the flexible printed circuit board and is inserted into the plated hole of the rigid printed circuit board, it holds the flexible printed circuit board against the rigid printed circuit board by bearing against the contact area (230) of the flexible printed circuit board, thus making an electrical connection between the two printed circuit boards, connecting pin (300) in which the bearing portion: - has at least one tooth (522a, 523a, 522b, 523b, 522c,523c) for piercing an insulating layer (210, 211) and / or a conductive track (220) of the flexible printed circuit board at the contact area, when the first end is inserted into the plated hole. A connecting pin (300) according to claim 11, wherein the bearing portion is further elastically deformable, acting as a spring to exert a bearing force on said bearing against the contact area, when the first end is inserted into the plated hole.