EP0778588B1 - Flat cable with small margin - Google Patents

Abstract

A flat flexible cable has longitudinal layers (R0-R2) folded of conductor carrier ribbon (1) over the conductor(s) (C), in one or more thicknesses, to give a ribbon core (1). They are at least partially of a thermostable material, coated on at least one inner surface with a thermofusible adhesive. Also claimed is a manufacturing process using initially an insulating substrate of a thermostable material, coated on at least one surface with a thermofusible adhesive. The core ribbon (1) is secured at a lateral end edge (1a) to the insulating substrate, with at least one conductor (C), and a spaced reinforcement on the same surface. The longitudinal layers (R0-R2) are folded in succession round the ribbon, covering the conductor(s) (C) to give at least two insulating layers and two reinforcement layers, with the conductor(s) (C) between them. The assembly is heat laminated together.

Description

The present invention relates to a flat cable.

In general and known per se, flat cables comprise at least one longitudinal conductor, interposed, between the at least two layers of an insulating material and possibly a shielding material.

Flat cables are widely used in industry electronics and IT.

The technique of manufacturing ribbon, extruded or extrudo laminates allows the assembly of conductors by a material which is then cooled.

There are also flat cables with laminated flat conductors which result from the encapsulation of said conductors between two films complex, generally composed of a thermoplastic layer thermostable intended to provide mechanical properties and electric to the cable, and one or more thermoplastic layers allowing hot pressing bonding.

Depending on the case, we can add in this complex, different layers, either to allow good bonding between the two films mentioned above and / or to allow better hanging on the encapsulated conductor.

The main advantage of this cable called FFC (flat flexible cable) is a lower installation cost compared to others products.

Consumer electronics do not require necessarily sophisticated components although the controls to reduce the risk of potential breakdowns are more and more severe. The effort for this type of market is doing a lot more on costs which tend to be as low as possible. He is coming of course some applications require very specific criteria techniques like bending tests with FFCs which must withstand millions of cycles.

FFCs are ideal for these applications and far outweigh all the other techniques mentioned above.

The FFC cables described in US-A-5,262,590 include layers of insulating material consisting of longitudinal folds around the conductors, in one or more passes, with a ribbon of lining, coated on at least its internal face with an adhesive.

However, despite the low current or voltage which must pass through these cables, their current manufacturing technique requires the use of large margins. These margins which are located at two lateral ends of the laminated FFC are compulsory to avoid deterioration and delamination of the product during use for example in bending. They can measure a few tenths from millimeters to a few millimeters wide, beyond outermost conductors.

• une tolérance inhérente aux marges nécessaires et due au procédé ;
• une largeur totale importante par rapport aux câbles en nappe extrudés ;
• un volume d'implantation plus important dû à la largeur ;
• une tenue mécanique des marges limitée notamment en cas de frottement contre d'autres pièces (tenue limitée à l'abrasion, faible résistance au déchirement, risque de délaminage etc.).

These compulsory and large margins have various other drawbacks, and in particular:

• an inherent tolerance for the margins necessary and due to the process;
• a large overall width with respect to the extruded ply cables;
• a larger implantation volume due to the width;
• limited mechanical resistance of the margins, in particular in the event of friction against other parts (resistance limited to abrasion, low tear resistance, risk of delamination, etc.).

It is clear that the margins necessary for the manufacturing these products constitutes a certain handicap, in particular for very technical applications. For example the simple use of a moving cable in a housing tolerated to dimensions of the cable containing it, need to take into account the maximum tolerance of the cable but also of a maximum tolerance of the case. This means that in case of minimum cable dimensions and maximum dimensions of the box, the very important game which results can result in premature wear of the cable and housing as well as noises generated by possible vibrations.

The surface can also be a problem. Indeed, the margins required to manufacture FFCs take the place of one, or even two conductors that could be installed instead margins if these could be removed.

In addition, in an environment where wave phenomena electromagnetic interference to signals, cables FFC are no exception to the rule. However, if the margins were reduced, the shielding deposited around these FFCs would be of smaller width and would therefore cheaper.

In addition, the various mechanical operations carried out with the cable (unwinding, twisting ...) can cause shifts of the two films trapping the conductors. These offsets eliminate any possibility of precise alignment vis-à-vis partial stripping zones, carried out beforehand on each of the encapsulation films, and thus prohibit connections transverse with the cable.

In addition, the shielding of traditional flat cables raises still other difficulties because it is necessary to link electrically, the shielding layer (copper braid, sheet of aluminized polyester, etc.) to ground, for example by welding to one of the conductors.

The object of the present invention is to solve the problems previous technical and economic.

This object is achieved according to the invention by means of a flat cable comprising, at least one longitudinal conductor interposed between at at least two layers of an insulating material and possibly a shielding material, said layers consisting of pleats longitudinal around the conductor, in one or more thicknesses, at least one filling tape produced, at least partially, with a thermostable material and coated on at least its internal face with hot-melt adhesive, characterized in that the tape padding is in one piece and carries the conductor over an area lateral end, before folding.

The term “thermostable material” means a material which has been stretched in two directions and which consequently has a high thermal stability.

Hot melt adhesive is a substance which, in addition to its adhesive properties, at a lower melting temperature than thermostable tape which forms its support.

According to an advantageous characteristic, said ribbon of lining is coated with adhesive on both sides. The thicknesses adhesives may, if necessary, vary on the tape so as to locally modify the thickness of the cable or create zones prepared for stripping.

According to an alternative embodiment, the longitudinal folds are formed, at least on the lateral edges, of folds of the ribbon on itself which trap the conductor in the center of the cable.

According to another variant, the longitudinal folds are formed by folds of independent sections of several natural ribbons possibly different.

In a particular embodiment, the ribbon of lining is formed of a substrate of insulating material on the face internal of which is fixed, before folding, a strip of material of shielding.

In addition, provision may be made for the shielding strip to be in contact after folding with one of the conductors.

Furthermore, said layers may include locally cavities or interruptions allowing bare conductors and / or shielding, for cross connection without cutting no stripping of the cable.

According to another variant embodiment, the edges side ends of the tape are attached contiguously.

According to another variant, said strip has a variable thickness across its width.

Preferably, the ribbon of thermostable material is produced with a material chosen from the group consisting of polyesters thermostable (PET), terephthalates, polyolefins, polyimides, polyether ketone (pek), polyether ether ketone (peek), phenilene polysulfide (pps), polysulfone (psu), polyetherimide (pei).

Furthermore, the adhesive is preferably chosen from the group consisting of styrene polymers, polyolefins, terephthalates, cellulosic polymers, polyamides, methacrylates, polyvinyl chloride (PVC), elastomers thermoplastics (etp), polyurethane (pure), polyethylene terephthalate (pet), polybutylene terephthalate (pbt).

The shielding material, on the other hand, is aluminum or pure copper or metallized polyester, or even a complex formed from an insulating film and a conductive sheet.

• on réalise d'abord un substrat isolant avec une matière thermostable,
• on enduit au moins une face dudit substrat avec un adhésif thermofusible, puis
• on prépare un ruban de garnissage d'un seul tenant en fixant sur une zone du bord d'extrémité latérale du substrat isolant, au moins un conducteur longitudinal et éventuellement, à distance sur la même face, une bande de blindage,
• on effectue ensuite des pliages longitudinaux successifs du ruban sur lui-même, en débutant par la zone du conducteur de façon à former au moins deux couches isolantes et éventuellement deux couches de blindage, entre lesquelles est emprisonné le conducteur, et
• on procède à un laminage à chaud du ruban plié.

Another object of the invention is a method of manufacturing a flat cable characterized in that,

• first an insulating substrate is produced with a thermostable material,
• at least one side of said substrate is coated with a hot-melt adhesive, then
• a packing tape is prepared in one piece by fixing on an area of the lateral end edge of the insulating substrate, at least one longitudinal conductor and possibly, at a distance on the same face, a shielding strip,
• successive longitudinal folds of the tape are then performed on itself, starting with the conductor area so as to form at least two insulating layers and possibly two shielding layers, between which the conductor is trapped, and
• hot bending of the folded ribbon is carried out.

According to an advantageous characteristic of the process, the shielding strip on the insulating substrate at a determined distance from the nearest conductor to create a contact by bending longitudinal between said strip and one of the conductors.

According to a variant, one fixes, on at least one face of the strip of shielding, a thickness of material with low dielectric constant.

According to another characteristic, the end edge is cut out longitudinal of the insulating substrate so as to strip, at least partially on the tape, the longitudinal ends of the conductor and armor strip.

This latter arrangement allows mass recovery by connection of the perimeter of the shielding strip to a connector end.

In the cable of the invention, the margins are reduced to minimum to the thickness of the ribbon, which is itself very small. Through therefore, there is no risk of delamination of the side edges cable, as is the case with traditional flat cables, when subjected to mechanical attack or shock thermal.

When the end edges of the ribbon are arranged so contiguous, the forces produced by repetitive flexions applied to the cable, do not work in the bonding area, which allows to improve the cable's resistance to bending and therefore its service life.

In addition, each layer consisting of a longitudinal fold with a single section of ribbon, it becomes possible to make zones of partial stripping opposite the cable on both sides and without positioning offset. As a result, partial connections transverse are easily achievable.

Furthermore, it is possible to obtain very good properties. dielectric of the cable giving it a great thickness by several folds of tape around the conductor (s).

The cable of the invention is easy to make and has a structure which is more homogeneous and more compact than that of cables traditional dishes.

• la figure 1 représente une vue schématique en coupe transversale d'un premier mode de réalisation du câble de l'invention ;
• les figures 2, 3, 4 et 5 représentent des vues schématiques d'autres modes de réalisation du câble de l'invention ;
• les figures 6a et 6b représentent des vues respectivement de face et en plan d'un mode de réalisation du ruban de garnissage selon l'invention, avant pliage ;
• les figures 7a et 7b représentent des vues respectivement en plan et de face du câble de l'invention selon le mode de réalisation des figures 6a et 6b, après pliage ;
• les figures 8a et 8b représentent des vues respectivement de face et en plan d'un autre mode de réalisation du ruban selon l'invention, avant pliage, et
• les figures 9a et 9b représentent des vues respectivement en plan et de face du câble de l'invention selon le mode de réalisation des figures 8a et 8b, après pliage.

The invention will be better understood on reading the description which follows, accompanied by the drawings in which:

• Figure 1 shows a schematic cross-sectional view of a first embodiment of the cable of the invention;
• Figures 2, 3, 4 and 5 show schematic views of other embodiments of the cable of the invention;
• Figures 6a and 6b show respectively front and plan views of an embodiment of the packing tape according to the invention, before folding;
• Figures 7a and 7b show respectively plan and front views of the cable of the invention according to the embodiment of Figures 6a and 6b, after folding;
• FIGS. 8a and 8b show respectively front and plan views of another embodiment of the ribbon according to the invention, before folding, and
• Figures 9a and 9b show respectively plan and front views of the cable of the invention according to the embodiment of Figures 8a and 8b, after folding.

The flat cable of the invention generally comprises at least one, and in the embodiment of FIGS. 1 to 5, for example, three longitudinal conductors C interposed between, at least two layers of an insulating material. The insulating layers consist of longitudinal folds R ₀ , R ₁ , R _2, etc. around the conductors C, of a packing tape 1 made, at least partially, with a substrate of thermostable material. The substrate is coated prior to folding, on at least its internal face, with a hot-melt adhesive.

The longitudinal folds R ₀ , R ₁ , ... of the tape 1, thus form one or more thicknesses of insulating material around the conductors C.

The thermostable material is preferably chosen from the group made up of thermostable polyesters (PET), terephthalates, polyolefins, polyimides, polyether ketone (pek), polyether ether ketone (peek), phenilene polysulfide (pps), polysulfone (psu), polyetherimide (pei).

The adhesive is preferably chosen from the group consisting of styrene polymers, polyolefins, terephthalates, polyamides, methacrylates and cellulosic polymers, polyvinyl chloride (PVC), thermoplastic elastomers (etp), polyurethane (pure), polyethylene terephthalate (pet), polybutylene terephthalate (pbt). This adhesive can be applied to the substrate, by example, in the form of a hot liquid or gel resulting from the prior melting of granules.

In the embodiment of Figure 1, the folds R ₀ , R ₁ , R ₂ are formed, at least on the side edges, by folds of the tape 1 on itself which trap the conductors in the center of the cable. The free edge of the external lateral end 1b of the ribbon 1 is fixed to the base fold R ₀ . The free edge of the internal lateral end 1a of the strip 1 is, for its part, fixed, for example, in contact with the lateral conductor C.

In this case, the thickness of the flat cable is not uniform but there is a larger bonding surface. The insulating layers formed by the folds R ₀ , R ₁ , R ₂ are, where appropriate, provided locally with interruptions or cavities forming as many areas of exposure of the conductors and allowing complete or partial transverse connections with only certain conductors without the need to cut the cable and without risk of offset.

In the embodiment of FIG. 2, the free edges 1a, 1b of lateral ends, respectively of the fold R ₀ , and of the fold R ₂ of the tape 1, are fixed contiguously, which makes it possible to obtain a thickness uniform and better finish.

In the embodiment of Figure 3, the flat cable has several longitudinal folds made with sections independent of predetermined widths of several strips 1, 2, 3 of different natures. We can thus achieve, if necessary, a coating composite of conductors C, using insulating materials different for each fold.

The end edges of the folds of each fold are here also joined, which requires increasing widths for sections of ribbons 1, 2, 3 superimposed. In addition, the thicknesses respective of each of the sections of ribbons 1, 2, 3 may be different. It may be possible to provide that the sections of tapes 1, 2, 3 are coated with adhesive on both sides, to reinforce holding the layers together.

Of course, if you want to use sections distinct but of equal widths, the lateral end edges 1a, 1b folds can no longer be joined for all layers, due to gradual increase in thickness.

In these conditions, it is necessary to determine, at beforehand, the unique width of the sections, so that each layer completely covers the layer immediately in below, as shown in Figure 4. In the embodiment represented in this figure, there remain empty spaces V, in the different layers, which are possibly filled with adhesive.

These empty spaces V are created because the single width of the sections is insufficient for the ends of the folds R ₃ , R ₅ on the one hand, and R ₆ , R ₈ , on the other hand, to be united.

Here, only the ends of the folds R ₀ , R ₂ overlap and the end of the fold R ₂ is fixed opposite that of the fold R ₃ .

In the embodiment of Figure 5, the flat cable has four conductors. C conductors have dimensions different from those of C conductors, so it's better use a ribbon 1 whose thickness is not uniform and varies over the width or a ribbon of uniform thickness but with a coating adhesive whose thickness is variable.

Figures 6a, 6b and 8a, 8b showing the trim tape 1 before folding.

The method of manufacturing the shielded cable according to the invention is described below with reference to Figures 6a, 6b and following.

The ribbon 1 is here formed of a substrate 10 in one piece in thermostable insulating material coated on at least one side with a hot melt adhesive as described above. 1 door ribbon the two conductors C on an area of the lateral end edge 1a. The if necessary, the hot-melt adhesive ensures the flat fixing of the conductors on the ribbon 1. On the internal face (here upper) of the substrate 10 is here fixed before folding a strip 11 of material shielding. The fixing of the shielding strip 11 can, of course, be also provided by hot melt adhesive coating.

The shielding material is a conductive material, for example example of aluminum or copper (sheet or braided) or else metallized polyester or a complex formed from a insulating film and a conductive sheet.

Then successive longitudinal folds R ₀ , R ₁ , R ₂ , R _{3 are carried out} , of the strip 1 on itself, starting with the area of the conductors C so as to form at least two insulating layers, and two shielding layers, between which the conductors C are trapped. The fold lines R ₀ , R ₁ , R ₂ , R ₃ , are shown in FIGS. 6b and 8b.

Finally, hot rolling of the ribbon folded in such a way is carried out. to make the cable flat and compact; the hot-melt coating participating in cohesion, on the one hand, between the different folds and, on the other hand, between the folds and conductors and / or shielding.

The rolling step is preferably carried out by means of heated rollers.

In the embodiment of FIGS. 6a, 6b, 7a and 7b, one fixes the shielding strip 11 on the substrate 10 at a determined distance d of the closest conductor C so as to create, by folding, a contact longitudinal between the strip 11 and one of the conductors C, as shown on the left in Figure 7b. The distance d is therefore in this case less than the distance D separating the extreme lateral edges of the two conductors.

The difference Δ represents the width of the contact area created by bending between conductor C and the shielding strip 11.

In FIG. 8b, the distance d, separating the shielding strip 11 of the nearest conductor, is greater than the distance D separating the extreme edges of C conductors.

In the latter case, there is then, after folding, no contact between the conductors and the shield 11 as shown in the figure 9b.

The shield 11 is then separated from the conductors at least by the thermostable insulating material of the substrate 10.

As shown in Figures 6b and 8b, the end edge longitudinal 1c of the ribbon 1 is produced with a slot cut 100 of the insulating substrate 10 so as to strip, at least partially, the respective longitudinal ends of conductors C and strip shielding 11.

According to an alternative embodiment, not shown, it is fixed on at minus one face of the shielding strip 11 a thickness of material to low dielectric constant to obtain a higher impedance or decrease the capacitive values by moving the conductors away from the shielding layer.

Claims (16)

1. Flat cable comprising at least one longitudinal conductor (C, C') interposed between at least two layers of an insulating material and, if appropriate, a screening material, said layers being constituted by longitudinal folds (R₀, R₁, ...) around the conductor (C, C'), in one or more thicknesses of at least one lining tape (1) made, at least partly, from a thermostable material and coated, on at least its inner face, with a hot-melt adhesive, characterised in that the lining tape (1) is in a single piece and, prior to folding, carries the conductor (C) on one lateral end area.
2. Cable according to Claim 1, characterised in that said lining tape (1) is coated with adhesive on both faces.
3. Cable according to Claim 1 or 2, characterised in that the longitudinal folds (R₀, R₁, R₂, ...) are formed, at least on the side edges, by folding the tape (1) back onto itself, thereby capturing the conductor (C) in the centre of the cable.
4. Cable according to Claim 1 or 2, characterised in that the longitudinal folds (R₀, R₁, R₂, ...) are formed by folding independent sections of several tapes (1, 2, 3), possibly of different kinds.
5. Flat cable according to one of the preceding claims, characterised in that the lining tape (1) is formed of a substrate (10) made of insulating material, on the inner face of which a strip (11) of screening material is fixed prior to folding.
6. Flat cable according to Claim 5, characterised in that the screening strip (11) is in contact, after folding, with one of the conductors (C).
7. Cable according to one of the preceding claims, characterised in that said layers comprise, locally, cavities or gaps allowing the conductors (C, C') and/or the screening (11) to be left bare with a view to connecting the conductors transversely without cutting or stripping the cable.
8. Cable according to one of the preceding claims, characterised in that the free lateral end edges (1a, 1b) of the tape (1) are fixed so as to be contiguous.
9. Cable according to one of the preceding claims, characterised in that said tape (1) is of a thickness that varies across its width.
10. Cable according to one of the preceding claims, characterised in that the thermostable material is selected from the group constituted by thermostable polyesters (PET), terephthalates, polyolefins, polyimides, polyetherketone (pek), polyetheretherketone (peek), polyphenylene sulphide (pps), polysulphone (psu) and polyetherimide (pei).
11. Cable according to one of the preceding claims, characterised in that the hot-melt adhesive is selected from the group constituted by styrene polymers, polyolefins, terephthalates, cellulose polymers, polyamides, methacrylate, polyvinylchloride (PVC), thermoplastic elastomers (etp), polyurethane (pur), polyethylene terephthalate (pet) and polybutylene terephthalate (pbt).
12. Cable according to one of the preceding claims, characterised in that the screening material is aluminium or pure copper, or metal-coated polyester, or else a complex formed by an insulating film and a conducting sheet.
13. Method of manufacturing a flat cable, characterised in that

    an insulating substrate (10) is first made with a thermostable material,

    at least one face of said substrate (10) is coated with a hot-melt adhesive, then

    a lining tape (1) is prepared in a single piece by fixing at least one longitudinal conductor (C) and optionally a screening strip (11), at a distance therefrom and on the same face, to an area of the lateral end edge (1 a) of the insulating substrate (10);

    successive longitudinal folds (R₀, R₁, ...) of the tape back onto itself are then made, starting from the area of the conductor (C), so as to form at least two insulating layers and optionally two screening layers, between which the conductor is captured, and

    the folded tape is hot-rolled.
14. Method according to Claim 13, characterised in that

    the screening strip (11) is fixed to the insulating substrate (10) a given distance (d) away from the nearest conductor so as to create, by folding, longitudinal contact between said strip and one of the conductors (C).
15. Method according to Claim 13 or Claim 14, characterised in that

    a thickness of material having a low dielectric constant is fixed to at least one face of the screening strip (11).
16. Method according to one of Claims 13 to 15, characterised in that

    the longitudinal end edge (1c) of the insulating substrate (10) is cut out so as to lay bare on the tape (1), at least in part, the respective longitudinal ends of the conductors (C) and of the screening strip (11).

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