WO2005010927A2

WO2005010927A2 - Anisotropic electroconductive film and method for the production thereof

Info

Publication number: WO2005010927A2
Application number: PCT/FR2004/050344
Authority: WO
Inventors: Jean Brun
Original assignee: Commissariat A L'energie Atomique
Priority date: 2003-07-18
Filing date: 2004-07-16
Publication date: 2005-02-03
Also published as: FR2857782A1; FR2857782B1; WO2005010927A3

Abstract

The invention relates to an anisotropic electroconductive film (300) and to a method for the production thereof. The inventive film (300) comprises an insulating layer (307) and through conductive inserts (301) which are characterised in that they can be dissymetrical with respect to the normal to a main plane of said film (300) when they are assembled with one or several connection components. Said film makes it possible to connect electronic components at a high interconnection density.

Description

ANISOTROPIC CONDUCTIVE FILM WITH IMPROVED CONDUCTIVE INSERTS

DESCRIPTION

TECHNICAL FIELD The present invention relates to an anisotropic conductive film with conductive inserts known under the name ACF for "Anisotropic Conductive Film", as well as its manufacturing process. The anisotropic conductive film makes it possible to connect two electronic components and can be used in many technical fields such as that of sensors or MEMS (English abbreviation for "Micro Electro Mechanical Systems"). There are several families of techniques for connecting chips and integrated circuits to interconnection substrates: "ire-bonding" or micro-wiring, the technique of connection by balls called "flip-chip" technique and the ACF technique concerning anisotropic conductive films. These anisotropic conductive films are made of conductive particles incorporated in an insulating film or of metallic inserts passing through an insulating film which is placed between the substrate and the chip to be connected.

STATE OF THE PRIOR ART It is known to provide the electrical connection between pads of a chip and those of an interconnection substrate or between pads of a chip and those of another chip, arranged in a screw screw, using an anisotropic conductive film by contact. This type of film provides electrical contact in the direction orthogonal to the plane of the chip between the conductive inserts and pads to be connected while ensuring insulation in the plane of the insulating film. It is suitable for high density pad connections and does not require soldering to each interconnection pad, nor to locate these pads. The interconnection of a chip 100 and a substrate 101 using a film 102 with through conductive inserts independent of the substrate is shown in FIG. 1A. The design of ACF films is based on the orderly insertion of conductive inserts 103 in an insulating layer 104. The chips 100 to be connected often have metal pads 105, for example made of aluminum and covered with an oxide layer 106. A strong redundancy in the number of contacts per metal pad 105 ensures a homogeneous contact of low resistivity making it possible to pass large currents. As shown in FIG. 1B, an anisotropic conductive film 107 with inserts can be produced directly on a substrate 108 covered on one face with a passivation layer 109 in which is formed at least one opening revealing a connection pad 110. It it is desirable to manufacture conductive inserts of very fine diameter to better penetrate the oxide layer covering the metal of a pad to be connected, thus obtaining a good quality of contact, and being able to respond to very small pad sizes and densities very high interconnections. With the conventional ACF film technique, difficulties are encountered when assembling the film with chips which have significant flatness defects. The film then has difficulties in adapting to variations in contact height, also called "hybridization" height with the surface of the chip, in particular because of a lack of flexibility of the inserts. In fact, today inserts are manufactured whose aspect ratio (height to diameter or width) is insufficient for them to be able to flame, even when they are subjected to compression. As a result, the thickness of the assembly interface between traditional ACF films and uneven topography chips is too great (greater than ten micrometers) and tends to allow moisture to intrude between the film and the chip. Variations in humidity can cause oxidation of the studs of the chip and cause the polymer of the ACF film to swell, which has the effect of disconnecting certain inserts with the studs. According to known art, the anisotropic conductive film 107 with inserts can be produced directly on the substrate 200 to be connected according to a method described in FIGS. 2A-2G. The first step described by FIG. 2A, consists in depositing a conductive layer 201 on the substrate 200. The conductive layer 201 is composed of one or more current conductive sublayers based on metal such as titanium, copper, nickel, tungsten, gold, etc. Next, a layer of photosensitive resin 202 is deposited on the conductive layer 201. This resin layer 202 is exposed through a mask

203 (Figure 2B) then developed to form holes

204 transverse (Figure 2C). Afterwards, the holes 204 are filled to produce conductive inserts 205 by electrolysis of metal such as nickel, using the conductive layer 201 as an electrode (FIG. 2D). The resin 202 is then removed (FIG. 2E) and then the conductive layer 201 is partially removed, by chemical etching except under the inserts 205 (FIG. 2F). Finally, an insulating layer 206 is deposited on and around the inserts 205 to form the dielectric part of the anisotropic conductive film. Finally, the insulating layer 206 is optionally etched on the surface to let the conductive inserts 205 protrude from it (FIG. 2G). The disadvantage of this process comes from the fact that it is very difficult to obtain inserts of small diameter, having a high aspect ratio. In fact, today we are able to manufacture inserts that are straight and orthogonal to a main plane of the anisotropic conductive film and which have approximately 3.5 μm in diameter and 9 μm in height, i.e. a form ratio (height to diameter or width) less than 3. Such an aspect ratio is unfavorable for flaming the inserts when they are subjected to compression. The problem arises of finding a film or a device making it possible to connect two components or two conductive zones and having more suppleness or flexibility than the known devices. PRESENTATION OF THE INVENTION The present invention does not have the drawbacks of traditional ACF films. It aims to provide an anisotropic conductive film which, unlike the ACF films according to the prior art, adapts well to variations in hybridization height with chips whose topography is uneven. The present invention makes it possible to obtain an assembly interface thickness between the chip and the film less than that obtained with current techniques, and thus to have a durability of the contact over time in particular by limiting the possibility to moisture to get between the ACF film and the chip. To achieve this object, the present invention provides an anisotropic conductive film or device comprising an insulating layer and through conductive inserts comprising a body, the body of the inserts being, or being capable of being, asymmetrical with respect to a normal to a plane. principal of the film after assembly with at least two contact zones located on either side of the inserts. The anisotropic conductive film is generally assembled between a substrate comprising conductive pads and a chip comprising connection pads. The connection pads and conductive pads are contact areas. The present invention also provides an anisotropic conductive device comprising a substrate, an insulating layer resting on the substrate and conductive inserts attached or assembled with said substrate, characterized in that a space is provided between the insulating layer and at least one insert, the inserts having an asymmetrical body with respect to a normal to a main plane of the insulating layer or capable of being asymmetrical with respect to a normal to a main plane of the insulating layer after assembly with at least two contact zones located on either side of the inserts. The inserts can be grouped into zones of inserts distributed discontinuously on the substrate. A space can be provided between the insulating layer and at least one insert. Thus the inserts which are not coated with the insulating layer, or have no contact with it, have greater freedom of movement and make the anisotropic conductive device more flexible when it is subjected to compression. According to a particular characteristic of the anisotropic conductive device according to the invention, the inserts can adopt a flamed shape after assembly with said contact zones. According to a particularly profitable characteristic of the anisotropic conductive device, the inserts can be such that the assembly with said contact zones imposes on the inserts a predetermined angle relative to normal to the main plane of the insulating layer. Thus, the angle that the inserts make after assembly can be predetermined according to several factors such as for example the pressure exerted on the inserts during assembly, the distance between said contact areas and the materials that make up the inserts. According to a particularly advantageous characteristic of the anisotropic conductive device, the inserts can end in a pointed end. Thus, instead of having inserts with a flat end, we have inserts with a pointed end which penetrates better, for example, an oxide layer protecting the connection pads of a chip to be connected. The pointed end can also allow the inserts to deform and buckle when the anisotropic conductive device is assembled for example with a chip, and subjected to compression and shearing. According to another particularly useful characteristic of the anisotropic conductive device, the inserts can end in a rough end. The rough end can create an imbalance of the inserts when the anisotropic conductive device is compressed, for example with a chip to be connected, and allow the inserts to flame and become asymmetrical with respect to a normal to the main plane of the anisotropic conductive film. According to another particularly appreciable characteristic of the anisotropic conductive device, the inserts can end with a head whose section is greater than that of the body. As with the rough end, the head can make it possible to create an imbalance of the inserts when the anisotropic conductive device is assembled by example with a chip. The head is therefore another means of inducing an asymmetry of the inserts compared to normal to the main plane of the insulating layer after assembly. According to another particularly useful characteristic of the anisotropic conductive device, the head can extend more than one side of the body of the inserts than on another side. Thus, it is easier to impose the direction of the asymmetry of the inserts relative to the normal of the insulating layer after assembly, for example with a chip. According to a particularly advantageous characteristic of the invention, the inserts can have a body inclined relative to normal to the main plane of the insulating layer. Inserts inclined with respect to normal to the main plane of the film act as springs and thus provide better flexibility to the device when the latter is subjected to compression. They can also make it possible to obtain a reduced assembly interface between the anisotropic conductive device and a chip to be connected. According to another particularly appreciable characteristic of the anisotropic conductive device, at least the body of the inserts may comprise an elastic material so that it is capable of deforming and being asymmetrical with respect to the normal to the main plane of the layer insulating after assembly with at least two contact zones located on either side of the inserts. Thus, the inserts can be made of a material like nickel, to give more flexibility to the inserts of the anisotropic conductive device when the latter is subjected to significant compressions, in particular during the assembly phase with a chip. According to another particularly advantageous characteristic of the invention, the inserts can have a body of rectangular section. A rectangular section allows for example to control the direction of buckling of the inserts when they are subjected to compression. According to a particularly advantageous characteristic of the invention, the inserts may have a base with a cross section greater than that of the body. Thus the base section larger than that of the body allows inserts of small section while being well anchored in the film. Inserts with a small cross-section otherwise tend to detach from the film even before the assembly phase with a chip to be connected. According to a particularly useful characteristic of the invention, all or part of the inserts can be covered with a deposit based on noble metal. A deposit based on noble metal can improve the conductivity of the inserts and thus create a good electrical connection with connection pads of a chip to be connected. According to another particularly profitable characteristic of the anisotropic conductive device, the conductive inserts can be composite and have a core surrounded by a sheath composed of one or more layers of materials, one of which is a surface layer of the sheath. So the inserts can for example comprise a core produced from a semiconductor material and a sheath produced from a conductive material. The composition of the core and of the sheath can vary depending on the mechanical and electrical properties that it is desired to give to the inserts. According to another particularly interesting characteristic of the anisotropic conductive device, the surface layer of the sheath can be conductive. It is preferable that at least the surface layer of the sheath be very good conductor to ensure a good electrical connection with connection pads of a chip to be connected. It can be made from a noble metal such as gold, platinum, etc. According to another particularly profitable characteristic of the anisotropic conductive device, the sheath can comprise a noble metal. According to another particularly useful characteristic of the anisotropic conductive device, the insulating layer can have adhesion properties. Thus, the insulating layer can be an adherent dielectric such as for example a polymer of the family of elastomers such as a cyclic polyisoprene. The invention also relates to a method for manufacturing an anisotropic conductive film or device comprising through inserts comprising the following steps: a) formation on a substrate of at least one layer of material having holes, said layer being called perforated layer b) filling of the holes to form through conductive inserts having a body, characterized in that step a) and / or step b) lead to inducing an asymmetry of the body of the inserts with respect to a normal to a main plane of the anisotropic conductive film, after assembly with at least two contact zones. The invention further relates to a method of manufacturing an anisotropic conductive device comprising a substrate, an anisotropic conductive film provided with through inserts attached to the substrate, said method comprising the following steps: a) forming on said substrate at least at least one layer of material having holes, said layer being called perforated layer b) filling the holes to form through conductive inserts having a body, characterized in that step a) and / or step b) lead to inducing an asymmetry of the body of the inserts relative to a normal to a main plane of the anisotropic conductive film, or to inducing an asymmetry of the body of the inserts compared to a normal to a main plane of the anisotropic conductive film, after assembly with at least two zones of contact. An anisotropic conductive device generally makes it possible to interconnect a chip comprising connection pads and an interconnection substrate comprising conductive pads. The connection pads and the conductive pads are contact areas. According to a particularly advantageous characteristic of the method, step b) of filling being carried out by electrolysis, step a) may comprise the deposition of a conductive layer on the substrate, prior to the formation of the perforated layer, this conductive layer being engraved after the completion of the inserts. Thus, to fill the holes in the perforated layer, it is possible, for example, to use a conductive layer previously deposited on the substrate as an electrode during the step of filling the perforated layer by electrolysis. According to a particularly advantageous characteristic of the process, the perforated layer can comprise a layer of photosensitive resin. Thus the holes in the openwork layer can be made in the photosensitive resin layer, for example using a photolithography process. The invention also relates to a method of manufacturing an anisotropic conductive device comprising conductive inserts passing through an insulating layer. According to a particularly useful characteristic of the method, the perforated layer can be removed after step b) of filling and a step of depositing an insulating layer can be carried out on the substrate to form the insulating layer of the anisotropic conductive device. The perforated layer can act as an insulating layer of the anisotropic conductive device when it is formed by example of a polymer. The perforated layer can also be produced for example on the basis of a metal layer. In this case, the perforated layer is removed after step b) of filling and a step of depositing an insulating layer is then carried out to form the insulating layer of the anisotropic conductive device. According to a particularly advantageous characteristic of the process, the insulating layer can be a photosensitive polymer. Using a photosensitive polymer as an insulating layer makes it possible to easily model, for example by photolithography, the insulating layer. According to a particularly advantageous characteristic of the process, the inserts can be grouped into zones of inserts distributed discontinuously on the substrate and in which the insulating layer is absent. According to a particularly advantageous characteristic of the method, the conductive layer may comprise one or more conductive sublayers, one of which is superficial. Thus, instead of making a single conductive layer, several stacked sublayers can be deposited to form the conductive layer. According to a particularly advantageous characteristic of the process, the layer of photosensitive resin can be composed of one or more sublayers, one of which is a surface layer, stacked above the substrate. So instead of making a single layer of photosensitive resin, can deposit several stacked sublayers to form the photoresist layer. According to a particularly advantageous characteristic of the process, the holes can be formed only in the layer of photosensitive resin. Thus, the perforated layer may for example be a layer of photosensitive resin or a stack of sublayers of photosensitive resin in which holes are made by a photolithography process. According to a particularly useful characteristic of the process, a part of the holes can be obtained by isotropic development of a sublayer of photosensitive resin lying under the surface sublayer of the layer of photosensitive resin. Thus, the holes in the perforated layer can be made only in the resin by using several sublayers of superimposed resins which have different development properties. According to a particularly advantageous characteristic of the method, part of the holes can be produced by etching the conductive layer. Thus the holes in the perforated layer can be partly made in a layer of photosensitive resin and partly made in a conductive layer. According to a particularly advantageous characteristic of the process, the holes may include an elongated part which is located in the surface photoresist underlayment and a part with an enlarged bottom situated under the elongated part, and which after filling, form inserts whose body corresponds to the elongated part filled and having a base section larger than that of the body corresponding to the part with an enlarged bottom filled. According to a particularly advantageous characteristic of the process, the holes in the perforated layer may have a rectangular section which, after filling, form inserts of rectangular section. Thus, holes of rectangular section allow to obtain inserts of rectangular section after filling of the perforated layer. According to a particularly advantageous characteristic of the method, the perforated layer may comprise holes inclined relative to a normal to a main plane of the substrate. Thus holes inclined relative to normal to the main plane of the substrate can make it possible to obtain inserts inclined relative to normal to the main plane of the anisotropic conductive film. According to a particularly useful characteristic of the process, holes can be made comprising an elongated part and an enlarged mouth in the extension of the elongated part, and which after filling, respectively form the body of the inserts, corresponding to the elongated part filled and a head in the extension of the body, corresponding to the filled mouth. According to a particularly advantageous characteristic of the method, the step of filling the holes can be done by spraying, evaporation or impregnation of the material or materials that must form the inserts. So the filling of the layer holes openwork can be achieved by methods other than electrolysis. According to a particularly advantageous characteristic of the method, the step of filling the holes can be done by electrolysis of metal from a rough conductive layer to form inserts with a rough end. According to a particularly useful characteristic of the process, the step of filling the holes may extend beyond the surface of the perforated layer to give a head to the inserts. According to a particularly advantageous characteristic of the process, a deposit based on noble metal can be produced on all or part of the inserts. Thus, a deposit of noble metal on the inserts can improve the contact resistance of the inserts. According to a particularly advantageous characteristic of the process, after the step of removing the perforated layer, one or more layers of material can be deposited on the inserts to form inserts having a core and a sheath, the sheath comprising a surface layer. According to a particularly useful characteristic of the process, a pointed end can be produced at the inserts. According to a particularly profitable characteristic of the process, a passivation layer covering the substrate, in which at least one conductive pad is housed, can be produced prior to step a). Thus, the substrate can comprise a passivation layer in which are housed conductive pads prior to the formation of the perforated layer.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood on reading the description of examples of embodiments given, purely by way of non-limiting indication, with reference to the appended drawings in which: FIGS. 1A and 1B already described represent the interconnection of a chip and a substrate, according to the known art using respectively an anisotropic conductive film independent of a substrate and an anisotropic conductive film integrated into a substrate; FIGS. 2A-2G already described represent different stages of a process for manufacturing an anisotropic conductive film according to the prior art, FIGS. 3A-3I represent variants of an anisotropic conductive film; FIGS. 4A-4H represent an alternative method of manufacturing an anisotropic conductive device; FIGS. 5A-5B represent a variant of the method for manufacturing an anisotropic conductive device; FIGS. 6A-6B, 7A-7C, 8A-8B, 9A-9E, 10, show alternative methods of manufacturing an anisotropic conductive device according to the invention; FIGS. 11A-11B represent a variant of the method for manufacturing an anisotropic conductive device according to the invention; Figures 12-13 show alternative manufacturing methods of an anisotropic conductive device; Figures 14A-14D show alternative methods of manufacturing an anisotropic conductive device according to the invention; Identical, similar or equivalent parts of the different figures may bear the same reference numerals so as to facilitate the passage from one figure to another. The different parts shown in the figures are not necessarily shown on a uniform scale, to make the figures more readable.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

FIG. 3A represents an example of anisotropic conductive film 300 with conductive inserts 301 assembled to a chip 302 comprising connection pads 303. The anisotropic conductive film 300 rests on a substrate 304 for example made of silicon, glass or ceramic, covered with a passivation layer 305 in which there are openings in which conductive pads 306 are housed. The anisotropic conductive film comprises an insulating layer 307 in which the through conductive inserts 301 are placed. The insulating layer 307 can for example be a polymer, a photosensitive resin, a thermoplastic material or a dielectric material. having adhesive properties such as a polymer of the elastomer family such as a polyisoprene. The conductive inserts 301 rest on a conductive layer 308 integrated into the substrate 304 and which provides the electrical connection with the conductive pads 306 of the substrate. The inserts 301 have a body 309 asymmetrical with respect to a normal to a main plane of the film 300 after assembly with the chip 302 and have a flamed shape. Thus, certain inserts are assembled with two contact zones: the conductive pads 306 of the substrate 304 and the connection pads 303 of the chip 302. FIG. 3B shows another example of an anisotropic conductive film 300 with conductive inserts 301, placed on a substrate 304 and assembled to a chip 302 comprising connection pads 303. This example differs from the first in that the conductive inserts 301 have a pointed end 310 free. The pointed end 310 makes it possible, for example, to better penetrate oxide layers 311 covering the connection pads 303 of the chip 302 to be connected. The pointed end 310 free also helps to create an asymmetry of the body 309 of the inserts compared to a normal n ₁ to a main plane of the film after assembly with the chip 302. Indeed, the pointed end 310 helps to create an imbalance inserts 301 and force them to deform when the anisotropic conductive film 300 is subjected for example to compression. FIG. 3C shows another example of anisotropic conductive film 300 with conductive inserts 301, according to the invention, placed on a substrate 304 and assembled to a chip 302 comprising connection pads 303. This example differs from that of FIG. 3A in that the inserts have a body 309 having a rough end 312 free. The rough end 312 helps to create an asymmetry of the body 309 of the inserts 301 compared to a normal _t to a main plane of the film 300 after assembly with the chip

302. Indeed, the rough end 312 helps to create an imbalance of the inserts 301 and force them to deform when the anisotropic conductive film 300 is subjected for example to compression, because the rough end 312 allows a good attachment with the chip while making non-planar and non-symmetrical contact therewith. FIG. 3D represents another example of anisotropic conductive film 300 with conductive inserts 301, according to the invention, placed on a substrate 304 and assembled to a chip 302 comprising connection pads 303. This example differs from that of FIG. 3A in that the inserts 301 have a head 313 of section S3 greater than that, SI, of the body. The head 313 helps to create an asymmetry of the body of the inserts 301 compared to a normal 5 _d to a main plane of the film after assembly with the chip 302. Indeed, the head 313 helps to create an imbalance of the inserts 301 and forces them to deform when the anisotropic conductive film 300 is subjected for example to compression. FIG. 3E shows another example of an anisotropic conductive film 300 with conductive inserts 301, according to the invention, placed on a substrate 304. This example differs from that of FIG. 3A in that the inserts 301 have a body inclined 314 relative to a normal 5 _j to a main plane of the film before assembly with a bullet (not shown so as not to overload the figure). The inclined body 314 allows for example the inserts 301 to play the role of small springs and gives more flexibility to the anisotropic conductive film 300 when the latter is subjected to compression. The example of anisotropic conductive film illustrated in FIG. 3E, also differs from the anisotropic conductive device of FIG. 3A in that the inserts have a rectangular section. As Figure 3E is a sectional view, we do not distinguish the rectangular section. FIG. 13 illustrates a method for producing inserts of rectangular section. The square being a particular rectangle, the inserts can also have a square section. The rectangular section makes it possible, for example, to determine the direction of the buckling of the body of the inserts when the latter is subjected to compression and therefore to determine the direction of the asymmetry of the inserts relative to a normal to a main plane of the film. FIG. 3F represents another example of an anisotropic conductive film 300 which differs from that of FIG. 3A in that the inserts 301 have, on the side of the conductive layer 308, a base 315 of section S2 greater than that SI of the body 309. The base 315 allows the inserts 301 to be well anchored in the film even when they have a small diameter. The anisotropic conductive device 300 of FIG. 3F also differs from that of FIG. 3D in that the head 313 of the inserts 301 is covered with a deposit 316 based on a noble metal which is a good electrical conductor such as gold, platinum, etc. to improve the contact resistance of the inserts 301 with connection pads 303 of a chip 302 and reduce their resistivity. FIG. 3G represents another example of an anisotropic conductive film which differs from that of FIG. 3A in that the conductive inserts 301 are composite with a core 317 surrounded by a sheath 318 composed of one or more layers of different materials including one is a surface layer 319 of the sheath. The heart 317 can be conductive, insulating or semiconductor. It can be formed from metals such as copper, nickel, tungsten, an SnPb alloy, gold, etc. or doped silicon for the category of conductors. However, it can also be formed from a semiconductor material such as silicon, or even from an insulating material such as for example a polymer. The sheath 318 is generally conductive or semiconductive. It can be formed from metals such as nickel or from noble metals. The surface layer 319 of the sheath 318 is conductive and may be formed of very good conductive metals such as gold or platinum. The composition of the inserts 301 depends on the mechanical and electrical properties that it is desired to give them. A conductive core 317 can allow more current to pass through the inserts 301. A ^' 317 core using a polymer or a elastic material for example based on nickel can for example make it possible to give more flexibility to the inserts 301 and to allow them to deform and be asymmetrical with respect to a normal to the plane of the film, when the latter is assembled with a puce as in the example illustrated by figure 3G. FIG. 3H represents another example of an anisotropic conductive film 300 with conductive inserts 301, according to the invention, placed on a substrate 304 and which differs from the first example in that the inserts 301 are grouped into zones of inserts 320 distributed in a manner discontinuous on the substrate 304. Furthermore, instead of the insulating layer 307 coating the inserts 301 as in FIGS. 3A-3G, it is distributed on the substrate 304 around the areas of the inserts 320, without being in contact with any of the inserts 301. A space 321 is therefore provided between the insulating layer 307 and the zones of inserts 320. Thus the inserts 301 are free to move and can more easily exhibit an asymmetrical body with respect to a normal to the main plane of the anisotropic conductive film. 300 when the latter is subjected to compression. The insulating layer 307 can then serve as a support surface during assembly with a chip 302. FIG. 31 shows another example of anisotropic conductive film 300 with conductive inserts 301 comprising a body 309, according to the invention, placed on a substrate 304 and assembled to a chip 302 comprising connection pads 303. This example differs from the first in that the conductive inserts 301 have a head 313 which projects more than one side of the body of the inserts than another. In addition, the inserts 301 make a predetermined angle with a normal to a main plane of the substrate 304 comprising conductive pads 306. The conductive pads 306 of the substrate 304 and the connection pads 303 of the chip 302 are contact areas. The angle α made by the inserts 301 after assembly can be predetermined according to several factors such as for example the pressure exerted on the inserts during assembly, the distance between said contact zones and the materials that make up the inserts. The head which overflows more on one side of the body of the inserts than on another can make it possible to determine the direction of the asymmetry of the inserts relative to normal to the main plane of the anisotropic conductive film after assembly, for example with a chip. A first example of a method for manufacturing an anisotropic conductive device with conductive inserts is illustrated by FIGS. 4A to 4H. The first step of this process illustrated in FIG. 4A consists in depositing a conductive layer 401 on a substrate 400. The conductive layer 401 can be formed from one or more conductive sublayers (402,403) one of which is a conductive sublayer surface 403. The substrate 400 may for example be made of silicon or glass. The conductive sub-layer 402 deposited directly on the substrate 400 can be based on a conductive and adherent material such as titanium, tungsten, etc. and the surface sublayer 403 can be produced for example by depositing at least one layer of metallic material such as titanium, copper, nickel, gold, etc. The conductive layer 401 is intended in particular to serve as an electric current supply layer at the time of the electrolytic growth of the conductive inserts formed subsequently. A layer of photosensitive resin 404 (for example a polyimide layer of ten micrometers thick) is then deposited on the conductive layer 401. The following steps consist in making holes in the resin layer 404 and the sub- surface conductive layer 403 to form an openwork layer. Then by filling the holes in the openwork layer, inserts having a body are formed. The production and / or filling of the holes in the perforated layer leads to inducing an asymmetry of the body of the inserts compared to a normal to the main plane of the film after assembly. The perforated layer can be produced other than by the resin layer and the conductive sublayer. It can be carried out on the basis of metal, of polymer, of silicon oxide. According to a variant of the method described above, by a photolithography technique which consists in insolation of the photosensitive resin layer 404 through a mask 405 (FIG. 4B) then a development of this resin layer 404, holes 406 are produced. (Figure 4C) in the resin up to the conductive layer 401. Typically, these holes 406 can have a depth of a few microns to a few tens of microns. Then eventually by a conventional method of etching the conductive surface sublayer 403, the holes 406 are extended to the conductive sublayer 402 in order to form an openwork layer 444. The openwork layer comprises the photosensitive resin layer 404 photo-structured and the etched sub-layer 403 (FIG. 4D). Then, the holes 406 of the perforated layer 444 are filled, for example by electrolytic growth of metal such as copper, nickel, titanium, tungsten, an SnPb alloy, gold, etc. using the conductive underlay 402 as an electrode. The holes 406 are filled from the bottom located at the level of the conductive sub-layer 402 to beyond the surface of the perforated layer 444, therefore by overflowing the holes. Conductive inserts 407 are thus obtained having a body 408 and a head 409 of section greater than that of the body 408 (FIG. 4E). The photosensitive resin 404 is then removed, for example by dissolution, and the surface conductive sublayer 403 is selectively etched so as to completely remove the perforated layer (FIG. 4F). The conductive sub-layer 402 is then etched with the exception of the body 408 of the conductive inserts 407 below (FIG. 4G). The next step consists in depositing an insulating layer 410 to constitute the dielectric part of the anisotropic conductive film. The conductive inserts 407 are thus electrically isolated from each other. The insulating layer 410 can be deposited dry or liquid, for example by screen printing. The insulating layer 410 may for example be a polymer, a photosensitive resin, a thermoplastic material, a fusible glass such as SOG (SOG for "Spin On Glass" which means rotation on the glass) or an adherent dielectric such as a polymer from the family of elastomers. If the inserts 407 are covered with insulating material after deposition of the insulating layer 410, an etching can be carried out to allow inserts of one end of the body 408

407 to protrude from the insulating layer 410 (Figure 4H). In this example of a method, the step of filling the holes 406 with the perforated layer described by FIG. 4E therefore leads to the formation of a head 409, with the inserts 407. This head 409 makes it possible for example to induce an asymmetry of the body 408 of the inserts 407 with respect to a normal H _j to a main plane of the anisotropic conductive film after assembly, because the head 409 creates an imbalance of the inserts 407 when the anisotropic conductive film is subjected to compression. A variant method according to the present invention consists in producing a head 409 with the inserts 407 by a second method. This variant first follows the steps of the method illustrated in FIGS. 4A-4B. Then, instead of developing the photosensitive resin layer 404, a second exposure of the photosensitive resin layer 404 is added, offset from the first exposure illustrated previously by FIG. 4B. This second exposure is carried out, right next to the first parts already exposed, with a lower exposure energy. We then develop the layer of exposed photoresist 404 to obtain a layer perforated 555 on the substrate 400 comprising holes 406. The holes 406 of the perforated layer 555 have an elongated part 501 and an enlarged mouth 502 in the extension of the elongated part 501 which projects more than one side of the elongated part 501 than the other. The enlarged mouth 502 corresponds to an enlargement of the entrance to the holes 406. The enlarged mouth 502 has a section greater than the section of the elongated part 501 (FIG. 5A). Then, by filling the elongated part and the enlarged mouth of the holes in the perforated layer 555, for example by metal electrolysis, inserts 407 conductors are obtained. The inserts 407 have a body 408 corresponding to the elongated part of the holes 406 filled and a head 409 corresponding to the enlarged mouth of the holes filled (FIG. 5B). The enlarged mouth filled with holes projecting more on one side of the elongated part of the holes than on the other, the head 409 projects more on one side of the body 408 of the inserts than on the other. Then, the method follows the same steps as those of the first example of method illustrated by FIGS. 4F-4H. The openwork layer is removed and the conductive layer is etched except under the inserts. Then, an insulating layer is deposited to constitute the dielectric part of the anisotropic conductive film. In this example process, the step of producing the perforated layer therefore leads to forming a head for the inserts. This head allows for example to induce an asymmetry of the body of the inserts compared to a normal to a main plane of the film after assembly. Another variant of the preceding method consists in forming inserts with rough ends. A rough conductive layer 601 is produced from a conductive layer deposited on the substrate 400 (FIG. 6A). For this, if the conductive layer consists of a metal such as aluminum, it suffices for example to deposit an oxide layer on top of the conductive layer, then to remove it. The conductive layer becomes a rough conductive layer 601. Indeed, the aluminum tends to diffuse in the oxide layer and the conductive layer then becomes rough. Then, after the rough conductive layer 601 has been formed, the process is continued in the same way as the example process previously illustrated in FIGS. 4B-4C until the step of forming holes in the photosensitive resin layer. Holes are therefore made in the photosensitive resin layer in order to produce an openwork layer 555 without etching the rough conductive layer 601. Next, the holes are filled by electrolysis of metal using the rough conductive layer 601 as an electrode for forming inserts 407. During filling, the roughness of the conductive layer 601 is transferred to the free end of the body 408 of the inserts while amplifying. In fact, the roughness of the conductive layer 601 leads to a non-uniformity of the electric field perpendicular to the rough conductive layer 601 during the electrolysis step and causes the holes in the non-uniform perforated layer 555 to be filled. We then obtain 407 inserts at the end rough 600 (Figure 6B). In this example of a method, the step of filling the holes in the perforated layer leads to forming a rough end 600 at the inserts 407. This rough end 600 makes it possible for example to induce an asymmetry of the body 408 of the inserts 407 with respect to a normal to the main plane of the anisotropic conductive film after assembly. Indeed, the rough end 600 makes it possible to create an imbalance of the inserts 407 when the anisotropic conductive film is subjected to compression. A variant of one or other of the examples of the preceding methods consists in forming inserts with pointed ends. To achieve this, after the step illustrated in FIG. 4D, the holes are filled, without protruding from the surface of the perforated layer. A process similar to that described in FIGS. 4E to 4H is then followed to obtain headless inserts coated with an insulating layer. A photosensitive polymer layer 701 is then deposited over the insulating layer 410 and the inserts 407. Then, by a conventional photolithography method illustrated in FIG. 7A, the photosensitive polymer layer 701 is exposed through a mask 702, which is the negative of mask 405 used in the step illustrated in FIG. 4B. This mask 702 has openings aligned with the inserts 407. The layer of polymer 701 is developed so that only one patch 703 of polymer 701 remains at the top of each insert 407 (FIG. 7B). Isotropic etching of the inserts 407 is then carried out. Isotropic etching then gives the inserts a pointed end 700. We then remove the photosensitive polymer tablet 701 (FIG. 7C). A variant according to the present invention consists in producing inserts with a body inclined relative to a normal to a main plane of the substrate. To do this, the process steps illustrated in FIGS. 4A-4B are followed. Then in the step of forming the perforated layer, the photosensitive resin 404 is exposed with the mask 405 attached to the photosensitive resin 404, under a beam of light rays inclined 800 relative to a normal to a main plane of the substrate 400, so as to obtain an openwork layer 555 comprising inclined holes 801 (FIG. 8A). Next, the same steps as those of the method illustrated in FIGS. 4D-4H are followed to obtain an anisotropic conductive film with inserts 407 with inclined body 802 passing through the insulating layer 410 (FIG. 8B). In this exemplary method, the step of forming the perforated layer leads to making holes inclined relative to a normal to a main plane of the substrate. The filling of these inclined holes with the perforated layer makes it possible to form inserts inclined relative to a normal to a main plane of the anisotropic conductive film and therefore to obtain asymmetrical inserts relative to a normal to a main plane of the anisotropic conductive film. when the anisotropic conductive film is subjected to compression. Another example of an alternative method for manufacturing an anisotropic conductive film according to the present invention will now be described. She consists in making inserts having a body, a head and a base. It is illustrated by FIGS. 9A to 9E. The first step of this example process is identical to that illustrated in FIG. 4A. Next, a layer of photosensitive resin 901 is deposited on the conductive layer 401. This layer of photosensitive resin 901 is formed of a sublayer of removal photosensitive resin 902, coated with one or more sublayers of photosensitive resin. one of which is a surface sublayer 903. The removal resin 902 can for example be LOR resin (registered name) developed by the company Michrochem or a resin of PMGI type (PMGI for polydimethylglutarimide). These resins have the property of developing isotropically and make it possible to obtain, after development, resin blanks in cantilever. By a conventional photolithography technique which consists of exposure of the surface photosensitive resin layer 903 and of the removal photosensitive resin 902 through a mask 904 (FIG. 9A) and an isotropic development of these resin sublayers, obtains an openwork layer 999 comprising holes 406 with an enlarged bottom. The widened bottom holes 406 include an elongated portion 905 which is located in the surface photoresist sublayer 903 and an enlarged bottom portion 906 located under the elongated portion 905, with cantilever blanks, and located in the removal photoresist sublayer 902 (FIG. 9B). Then, for example by electrolytic growth of conductive material such as copper, nickel, tungsten, gold by using the conductive layer 401 as an electrode, conductive inserts 407 are formed in the holes 406 with an enlarged bottom of the perforated layer 999. The holes 406 are filled from the bottom located at the level of the conductive layer 401 to beyond the surface of the surface photosensitive resin sublayer 903, projecting from the surface of the holes 406. thus produces conductive inserts 407 having a base 900 corresponding to the part with an enlarged bottom 906 filled with holes 406, a body 408 corresponding to the elongated part 905 filled with holes 406 and a head 409 corresponding to the part of conductive material projecting from the hole surface. The perforated layer 999 consisting of the photosensitive resin layer (FIG. 9C) is then removed by a conventional method and the layer of conductive material 401 is selectively etched except for the underside of the base 900 of the inserts 407 (FIG. 9D). Finally, an insulating layer 410 is deposited to form the dielectric part of the anisotropic conductive film with conductive inserts. The deposition of the insulating layer 410 can be done by dry or liquid route. If the inserts 407 are covered with insulating material, an etching can then be carried out to allow one end of the body 408 and / or the head 409 of the inserts to protrude out of the insulating layer 410. The insulating layer 410 can be for example a polymer, a photosensitive resin, a thermoplastic material or a fusible glass such as SOG (SOG for "Spin On Glass") (Figure 9E). A variant of the method starting from the example described above consists of filling the holes in the perforated layer by spraying, evaporation of conductive materials, or impregnation in place of the electrolysis step during the filling of the holes 406 illustrated. for example by FIG. 9B. This filling of the holes by spraying, evaporation or impregnation can even be carried out using conductive materials such as nickel, or semiconductors such as silicon. Another variant of one of the previous examples of methods according to the present invention consists in making a deposit based on a noble metal such as gold on the top of the body 408 or on the head 409 of the inserts 407. This deposition is carried out by example, from the first example of the process, after for example the step of filling the holes 406 illustrated in FIG. 4E and before the step of etching the conductive layer 401, by evaporation, spraying, chemical or electrochemical deposition. The result is illustrated in Figure 3F. A variant of the process according to the present invention consists in forming composite inserts with a core 1000 surrounded by a sheath 1001 composed of one or more layers of material, one of which is a surface layer 1002 of the sheath. After the step of removing the photosensitive resin and etching the conductive sublayer described in FIG. 4G, we performs one or more metallic deposits on the inserts 407, for example using an electrolytic deposition or anelectrolytic plating process. One can even deposit an insulating or semiconductor material. The role of the inserts 407 is to provide an electrical connection, it is therefore necessary to make them conductive: for this it is possible to carry out a final deposition based on noble metal, for example by anelectrolytic plating to constitute the surface layer 1002 of the sheath (FIG. 10 ). During the production of the anisotropic conductive film, provision is made to have inserts grouped into zones of inserts 1100 distributed discontinuously on the substrate 400. A variant of one of the preceding methods according to the present invention then consists, for the step of forming the insulating layer 410 described in FIG. 4H, to obtain zones of inserts 1100 clipped with insulating layer 410. The insulating layer 410 can be formed by a photosensitive polymer 1101. By a conventional photolithography process, the following is exposed this photosensitive polymer through a mask 1102 which protects the zones of inserts 1100 (FIG. 11A). The photosensitive polymer 1101 is then developed. The protected areas, corresponding to the zones of inserts 1100, are then no longer covered with photosensitive polymer 1101 (FIG. 11B). Thus, zones of inserts 1100 are obtained in which the insulating layer does not coat the inserts. There is therefore at least one space 1103 between an insert and the layer of photosensitive polymer 1101. Another variant of the process according to the invention consists in using, from the first step, a substrate (previously represented in FIGS. 3A-3H) provided with a passivation layer in which there is at least one opening revealing a conductive pad. The rest of the process follows one or other of the examples of processes previously cited. A variant of the process according to the invention consists in producing an anisotropic conductive film comprising conductive inserts provided with a head using a preformed perforated layer. For this, an perforated layer 1200 preformed, for example made of metal or polymer, is deposited on a substrate 400 (FIG. 12). The preformed perforated layer 1200 comprises holes 406 having a first part 1201 flared and a second part 1202 elongated. Then, the holes 406 of the preformed perforated layer 1200 are filled by spraying, evaporation or impregnation of conductive material. Conductive inserts are thus formed having a body corresponding to the second elongated part 1202 filled with holes and a head corresponding to the first flared part 1201 filled with holes 406. In the case where the perforated layer is a metallic layer, this n 'is not compatible with the insulation of the inserts. The perforated layer 1200 is then removed then an insulating layer is deposited on the substrate, for example by screen printing to form the insulating layer of the anisotropic conductive film. In the case where the perforated layer is a layer based on polymer or on a dielectric, this can constitute the insulating layer of the anisotropic conductive film. It is not then withdrawn. Another variant of the method according to the invention consists in making holes of rectangular section 1301 during the step described in FIG. 4C, using a mask 1302 with rectangular openings 1303 to achieve the exposure of the photosensitive resin 404 (figure 13). The process then takes place by following the same steps as the first process illustrated in FIGS. 4D-4H. With an anisotropic conductive film 300 obtained by such methods it is possible to cause the inserts 407 to flame by effecting compression, using a press object. It is thus possible, for example, to flame inserts 407 having a rough end 600 (FIG. 14A) or those having a head 409 (FIG. 14B) by carrying out compression, using a press object, for example a press forming chip 1400 to be connected comprising connection pads 1401. The compression is represented by two forces (Fι, F ₂ ) of opposite directions and normal to the main plane of the film. The force Fi is applied perpendicular to the pressing chip 1400 and the force F ₂ perpendicular to the base of the substrate 400. During the pressurization, the inserts 407 provided with a head 409 slide on the connection pads and flex. The inserts provided with a rough end 600 hang on the connection pads 1401 and flex. Inserts 407 having a body 408 are thus advantageously obtained. asymmetrical with respect to a normal _t to a main plane of the anisotropic conductive film. On the other hand, when the inserts 407 with a rough end 600 or the inserts 407 provided with a head 409 are bent, the hooking or sliding of the inserts 407 on the connection pads of the press 1400 chip leads to the scratching of the connection pads 1401 of the chip 1400 and therefore to the mechanical removal of surface oxides from the connection pads 1401 of the chip 1400. This thus improves the contact resistance with the chip 1400. It is also possible to flame inserts 407 having for example a pointed end 700 by performing a first compression using a press chip 1400 comprising connection pads 1401. The compression is applied by forces

(Fι, F ₂ ) opposite and normal directions to the main plane of the film (Figure 14C). The pointed end 700 of the inserts 407 then allows good anchoring to the connection pads 1401 of the pressing chip 1400. Then, shear is applied by forces (F ₃ , F ₄ ) in opposite directions in the direction of the main plane. from the film

(Figure 14D). The force F ₃ is applied to the press chip 1401 and the force F ₄ to the substrate 400. The pointed end 700 makes it possible to keep the anchoring of the inserts 407 in the connection pads 1401 of the press chip 1400 while that the body of the inserts 407 is deformed. Inserts 407 having a body 408 are thus advantageously obtained. asymmetrical with respect to a normal to a _pla n _x n principal anisotrop conductive film _e.

Claims

1. Anisotropic conductive device (300) comprising a substrate, an insulating layer (307) resting on the substrate and conductive inserts (301) assembled with said substrate, characterized in that a space (321) is provided between the insulating layer (307) and at least one insert (301), the inserts (301) having a body capable of being asymmetrical with respect to a normal (n _x ) to a main plane of the insulating layer (307) after assembly with at least two contact zones (303,306) located on either side of the inserts.

2. Device according to claim 1, characterized in that the inserts (301) are such that the assembly with said contact areas (303,306) imposes a predetermined angle α by _. compared to normal (r ^).

3. Device according to claim 1 or 2, characterized in that the inserts (301) end in a pointed end (310).

4. Device according to claim 1 or

2, characterized in that the inserts (301) end in a rough end (312).

5. Device according to claim 1 or 2, characterized in that the inserts (301) end by a head (313) whose section (S3) is greater than that (SI) of the body (309).

6. Device according to claim 5, characterized in that the head (313) projects more than one side of the body (309) of the inserts (301) than on another side.

7. Device according to one of claims 1 to 6, characterized in that the inserts

(301) have a body inclined (314) relative to the normal (f ^) to the main plane of the insulating layer (307).

8. Device according to one of claims 1 to 7, characterized in that at least the body (309) of the inserts (301) comprises an elastic material so that it is capable of deforming and being asymmetrical with respect to normal (n ^ to the main plane of the insulating layer (307) after assembly with at least two contact zones (303,306) located on either side of the inserts.

9. Device according to one of claims 1 to 8, characterized in that the inserts (301) have a body (309) of rectangular section.

10. Device according to one of claims 1 to 9, characterized in that the inserts (301) have a base (315) of cross section greater than that of the body (309).

11. Device according to one of claims 1 to 10, characterized in that all or part of the inserts (301) is covered with a deposit (316) based on noble metal.

12. Device according to one of claims 1 to 11, characterized in that the conductive inserts (301) are composite and have a core (317) surrounded by a sheath (318) composed of one or more layers of materials including one is a surface layer (319) of the sheath.

13. Device according to claim 12, characterized in that the surface layer (319) of the sheath (318) is conductive.

14. Device according to claim 13, characterized in that the sheath (318) comprises a noble metal.

15. Device according to one of claims 1 to 14, characterized in that the insulating layer (307) has adhesion properties.

16. Method for manufacturing an anisotropic conductive device comprising a substrate (400), an anisotropic conductive film provided with through inserts attached to the substrate, said method comprising the following steps: a) forming on said substrate (400) at least one layer (404) of material having holes (406), said layer being called perforated layer (444,555,999,1200) b ) filling the holes (406) to form through conductive inserts (407) having a body (408), characterized in that step a) and / or step b) lead to inducing an asymmetry of the body (408) inserts (407) relative to a normal to a main plane of the anisotropic conductive film, after assembly with at least two contact zones.

17. The method of claim 16, characterized in that the filling step b) being carried out by electrolysis, step a) comprises depositing a conductive layer (401) on the substrate (400), prior to the formation of the perforated layer, this conductive layer (401) being etched after the inserts (407) have been produced.

18. Method according to one of claims 16 or 17, characterized in that the perforated layer (444,555) comprises a layer of photosensitive resin (404).

19. Method according to one of claims 16 to 18, wherein the conductive inserts pass through an insulating layer (410), characterized in that the perforated layer is removed after step b) of filling and a step of depositing an insulating layer (410) is produced on the substrate (400) to form the insulating layer (410) of the anisotropic conductive film.

20. The method of claim 19, characterized in that the insulating layer (410) is a photosensitive polymer (1101).

21. Method according to one of claims 19 or 20 characterized in that the inserts are grouped into zones of inserts (1100) distributed discontinuously on the substrate (400) and in which the insulating layer (410) is absent.

22. Method according to one of claims 17 to 21, characterized in that the conductive layer

(401) comprises one or more conductive sub-layers (402), one of which is superficial (403).

23. Method according to one of claims 18 to 22, wherein said perforated layer comprises a layer of photosensitive resin, characterized in that the layer of photosensitive resin (404) is composed of one or more sublayers (901,902) one of which is a surface layer (902), stacked above the substrate (400)

24. Method according to one of claims 18 to 23, wherein said perforated layer comprises a layer of photosensitive resin, characterized in that the holes (406) are formed only in the layer of photosensitive resin (404).

25. The method of claim 23 characterized in that a portion of the holes (406) is obtained by isotropic development of a sublayer of photosensitive resin (901) located under the surface sublayer (902) of photosensitive resin (404).

26. Method according to one of claims 17 to 23, characterized in that part of the holes (406) is produced by etching the conductive layer (401).

27. Method according to one of claims 23 or 25, characterized in that the holes (406), comprise an elongated part (905) which is located in the sublayer of surface photosensitive resin (903) and a bottom part enlarged (906) located under the elongated part (905), and which after filling, form inserts (407) having a body (408) corresponding to the elongated part (905) filled and a base section larger than that of the body ( 407) corresponding to the filled bottom part (906) filled.

28. Method according to one of claims

16 to 27, characterized in that the holes (406) of the perforated layer have a rectangular section which after filling forms inserts (407) of rectangular section.

29. Method according to one of claims 16 to 28, characterized in that the perforated layer (444,555) comprises inclined holes (801) relative to a normal to a main plane of the substrate (400).

30. Method according to one of claims 16 to 29, characterized in that holes are made (406) in the perforated layer comprising an elongated part (501) and an enlarged mouth (502) in the extension of the elongated part , and which after filling, respectively form the body (408) of the inserts (407), corresponding to the filled elongated part and a head (409) in the extension of the body (408), corresponding to the filled mouth.

31. Method according to one of claims

16 to 30, characterized in that the filling step of the holes (406) is done by spraying, evaporation or impregnation of the material or materials to form the inserts (407).

32. Method according to one of claims

17 to 30, in which step a) comprises depositing a conductive layer on the substrate (400), prior to the formation of the perforated layer, characterized in that the step of filling the holes (406) is made by electrolysis of metal from a rough conductive layer (601) to form inserts (407) with a rough end (600).

33. Method according to one of claims 16 to 32, characterized in that the step of filling the holes (406) extends beyond the surface of the perforated layer (444,555) to give a head (409) to the inserts (407) .

34. Method according to one of claims 16 to 33, characterized in that after the filling of the holes (406), a deposit based on noble metal is carried out on all or part of the inserts (407).

35. Method according to one of claims 19 to 34 characterized in that after the step of removing the perforated layer (444,555), one or more layers of material are deposited on the inserts to form inserts (407) having a core (1000) and a sheath (1001), the sheath comprising a surface layer (1002).

36. Method according to one of claims

16 to 35 characterized in that a pointed end (700) is produced at the inserts (407).

37. Method according to one of claims 16 to 36, characterized in that a passivation layer

(305) covering the substrate (400), in which accommodates at least one conductive pad (306), is produced prior to step a).