FLEXIBLE ELECTRONIC STRUCTURE

Abstract

Flexible electronic structure (100) comprising at least:- a flexible substrate (102) provided with a first face (106) on which there is at least one electrically conductive track (104);- an electronic chip (110) secured to the first face (106) of the flexible substrate (102) and comprising, at a first face (112) of the electronic chip (110), connection pads (114) electrically interconnected to the electrically conductive track (104);- an opening (120) passing through the flexible substrate (102) and opening at least partly opposite the first face (112) of the electronic chip (110);- a filling material (126) disposed between the electronic chip (110) and the first face (106) of the flexible substrate (102), the thixotropic index of which is between 2 and 5 and the viscosity of which is between 5000 mPa.s and 15000 mPa.s. Figure for abstract: Figure 1.

Description

Title of the invention: FLEXIBLE ELECTRONIC STRUCTURE Technical field

[0001] The invention relates to the field of flexible electronic structures comprising one or more electronic chips placed on a flexible, or supple, substrate, i.e. capable of deforming without breaking or causing rupture, and capable of being placed on a non-planar surface such as skin, textile or an object. State of the prior art

[0002] There are many fields requiring the production of flexible electronic structures comprising electronic components arranged on a flexible substrate.

[0003] The electronic components of such a flexible electronic structure can be produced directly by printing on a flexible substrate, for example in the form of a roll or sheet. However, such components produced by printing have performances which are significantly lower than those obtained for electronic components produced conventionally from a semiconductor substrate (which is not flexible).

[0004] In the documents of J.-C. Souriau et al, “Flexible Fan-Out Wafer Level Packaging of Ultra-Thin Dies,” in Proceedings - Electronic Components and Technology Conference, 2020, and EP 3 811 744 Al, a generic method for manufacturing a flexible sticker integrating silicon components of ASIC, sensor or actuator types directly after cutting their semiconductor manufacturing wafer is proposed. This is called a bare chip because they are not packaged. The integration process in the film is carried out on a silicon wafer serving as a temporary support, by microelectronic processes. The sticker comprises a first flexible polymer layer on which a network of thin-layer electrical tracks is produced with, at one end of the lines, small pads for receiving the electronic components and at the other end, larger pads for interconnection to the outside of the sticker.The components are hybridized onto the "Flip-Chip" label, i.e., such that the active face is arranged opposite the small interconnection pads. The components are then thinned to a thickness of less than 50 pm and encapsulated with a second polymer layer. Finally, the labels are peeled from the temporary wafer and can be transferred and interconnected onto an object or a new film.

[0005] When transferring the chip onto the flexible substrate, or after this transfer, it is necessary to place a so-called filling material, or "underfill" in English, between the chip and the flexible substrate. This filling material ensures protection of the connections electrical between the chip and the flexible substrate (formed for example by microbeads of fusible material or "stud bumps", i.e. electrically conductive protrusions or bumps), reinforces the mechanical strength of the chip and also serves to absorb deformations between the chip and the flexible substrate.

[0006] Certain electronic components, such as those emitting and / or receiving electromagnetic, sound or even light waves, require that openings be formed through the substrate on which the components are located in order to emit and / or receive these waves through these openings. This is for example the case of MUT (“Micromachined Ultrasonic Transducer” in English, or micro-machined ultrasonic transducer), photodetectors, photodiodes, or even VCSEL (“Vertical-Cavity Surface-Emitting Laser” in English, or laser diode with a vertical cavity emitting by the surface). This also concerns electronic components whose face arranged on the substrate side must be in direct communication with the environment external to the chip, for example to receive a fluid as is the case for gas sensors.A chip integrating such electronic components can only be transferred in Flip-Chip on a substrate having an opening. A difficulty is then to produce the filling material between the component and the substrate without this filling material spreading into the openings. This difficulty is even greater in the case of the integration process within a flexible electronic structure as described previously. Indeed, the first flexible layer which has the opening is very thin (< 100 pm) and rests on the temporary wafer which does not have an opening. In this configuration, conventional commercial filling materials easily spread under the components and obstruct the openings. Statement of the invention

[0007] An aim of the present invention is to propose a flexible electronic structure comprising at least one electronic chip mounted on a flexible substrate and of which at least part of a face of the chip arranged opposite the flexible substrate is accessible by at least one opening passing through the flexible substrate.

[0008] For this, the present invention proposes a flexible electronic structure comprising at least: - a flexible substrate having a first face on which there is at least one electrically conductive track; - an electronic chip secured to the first face of the flexible substrate and comprising, at a first face of the electronic chip, connection pads electrically interconnected to the electrically conductive track; - an opening passing through the flexible substrate and opening at least partly into look at the first side of the electronic chip; - a filling material placed between the electronic chip and the first face of the flexible substrate, and whose thixotropy index is between 2 and 5 and whose viscosity is between 5000 mPa.s (or cP) and 15000 mPa.s (or cP).

[0009] The thixotropy index of a material corresponds to the ratio of the viscosity values ​​of a material at two different flow rates of this material, these rates being for example different from each other by a factor equal to ten. This value of the thixotropy index of a material is indicative of the capacity of this material to retain its shape.

[0010] The viscosity of a material such as the filler material can be measured as described in the document by D. Dupuis et al, “Measurement of viscosity - General principles”, Techniques de l'Ingénieur, R2350 V4, January 10, 2021.

[0011] The structure and the substrate are flexible, that is to say that they can for example undergo bending with a radius of curvature less than or equal to 5000 mm and preferably less than or equal to 1000 mm, without breaking.

[0012] The invention proposes a flexible electronic structure that does not have the previously mentioned drawbacks. In particular, the use of a filling material whose thixotropic index and viscosity as defined above makes it possible to carry out a transfer of the electronic chip onto the flexible substrate provided with the opening because this filling material can be dispensed, between the electronic chip and the flexible substrate from the sides of the space between the electronic chip and the flexible substrate, and therefore after the transfer of the electronic chip onto the flexible substrate, without this filling material spreading into the opening. Conventional materials known as underfill materials are not suitable for the flexible electronic structure proposed above because their viscosity is Newtonian, that is to say it does not vary during a flow.A conventional underfill material would therefore flow very easily by capillary action between the components and the substrate and fill the opening in the flexible substrate, resulting in the obstruction of this opening.

[0013] The proposed flexible electronic structure makes it possible to combine the advantages of an electronic chip whose electronic components can be made from semiconductors, and those of a flexible substrate.

[0014] The electronic chip may comprise at least one electronic component arranged opposite the opening and configured to emit and / or receive electromagnetic and / or sound and / or light waves through the opening, and / or to receive a fluid through the opening.

[0015] The total thickness of the flexible electronic structure may be less than or equal to 500 pm, and / or the thickness of the electronic chip may be less than or equal to 150 pm, and / or the thickness of the flexible substrate may be less than or equal to 250 pm, and / or a distance between the first face of the flexible substrate and the first face of the electronic chip may be less than or equal to 100 pm.

[0016] Advantageously, the thixotropy index can be between 3 and 4.

[0017] The flexible substrate may comprise at least one of the following materials: siloxane, polydimethylsiloxane, polyester, polyimide, polytetrafluoroethylene, polyetheretherketone, polyparaxylylene, plant fibers, composite material.

[0018] The flexible electronic structure may further comprise a layer of waterproof material covering at least side walls of the opening, a portion of the first face of the electronic chip arranged opposite the opening, and a second face of the flexible substrate opposite the first face. This layer of waterproof material may also cover side walls formed by the filling material in the extension of the opening.

[0019] Advantageously, the waterproof material may be biocompatible, for example neutral in contact with the skin, non-toxic, non-irritant, and preserving the biological integrity of the skin. For example, the biocompatible waterproof material may correspond to parylene. Such a biocompatible material makes it possible in particular to produce a flexible electronic structure suitable for being placed against the skin.

[0020] The flexible electronic structure may further comprise an encapsulating material coating the assembly formed at least by the electronic chip and the filling material.

[0021] The flexible electronic structure may further comprise at least one trench passing through the flexible substrate and extending in a plane parallel to the first face of the flexible substrate in at least one direction such that the flexible electronic structure is stretchable at least parallel to said direction.

[0022] The trench may be filled at least with the encapsulating material or with a material that is different from the encapsulating material and that is flexible and stretchable, such as for example polydimethylsiloxane.

[0023] A material can be described as stretchable when a tensile stress on a portion of this material causes, parallel to the direction of the tensile stress, an elongation without breaking of this portion of material which is greater than approximately 30% compared to the dimension at rest of this portion of material in the direction of the tensile stress.

[0024] The invention also relates to a method for producing a flexible electronic structure, comprising at least the following steps: - production of a flexible substrate on a support layer; - making at least one opening passing through the flexible substrate; - production, on a first face of the flexible substrate located on the side opposite the support layer, of at least one electrically conductive track; - transfer and securing of an electronic chip on the first face of the flexible substrate, the electronic chip comprising, at a first face, connection pads electrically interconnected to the electrically conductive track, and such that a part of the first face of the electronic chip is arranged opposite the opening; - addition, for example by dispensing, of a filling material between the electronic chip and the first face of the flexible substrate, and whose thixotropy index is between 2 and 5, advantageously between 3 and 4, and whose viscosity is between 5000 mPa.s and 15000 mPa.s; - separation of the flexible substrate from the support layer.

[0025] The method may further comprise a step of thinning the electronic chip from a second face opposite the first face of the electronic chip, implemented between the step of transferring and securing the electronic chip to the first face of the flexible substrate and the step of detaching the flexible substrate from the support layer. Thus, the handling of the electronic chip, during the transfer, is carried out while it is not yet thinned, which facilitates its handling. This is possible thanks to the support layer on which the flexible substrate is produced and which allows thinning of the electronic chip after its transfer to the flexible substrate.

[0026] The method may further comprise a deposition of an encapsulation material covering at least the electronic chip, implemented between the step of transferring and securing the electronic chip to the first face of the flexible substrate and the step of detaching the flexible substrate from the support layer.

[0027] The method may further comprise, after the step of separating the flexible substrate from the support layer, a step of producing a layer of waterproof material covering at least the side walls of the opening, a portion of the first face of the electronic chip arranged opposite the opening, and a second face of the flexible substrate opposite the first face.

[0028] Making the opening through the flexible substrate may also form at least one trench passing through the flexible substrate and extending in a plane parallel to the first face of the flexible substrate in at least one direction, and the encapsulation material may also be deposited in the trench, making the flexible electronic structure stretchable at least parallel to said direction.

[0029] Throughout the document, the term "on" is used without distinction of the orientation in space of the element to which this term relates. For example, in the characteristic "on a face of the substrate", this face of the substrate is not necessarily oriented upwards but can correspond to a face oriented in any direction. Furthermore, the arrangement of a first element on a second element must be understood as being able to correspond to the arrangement of the first element directly against the second element, without any intermediate element between the first and second elements, or as being able to correspond to the arrangement of the first element on the second element with one or more intermediate elements arranged between the first and second elements. Brief description of the drawings

[0030] The present invention will be better understood on reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which: [Fig.l], and

[0031] [Fig.2] represent flexible electronic structures, objects of the present invention, respectively according to first and second embodiments;

[0032] [Fig.3]

[0033] [Fig.4]

[0034] [Fig.5]

[0035] [Fig.6]

[0036] [Fig.7]

[0037] [Fig.8]

[0038] [Fig.9]

[0039] [Fig. 10], and

[0040] [Fig. 11] represent the steps of a method for producing an electrical structure flexible electronics, object of the present invention, according to the first embodiment;

[0041] [Fig. 12]

[0042] [Fig. 13]

[0043] [Fig. 14]

[0044] [Fig. 15]

[0045] [Fig. 16]

[0046] [Fig. 17], and

[0047] [Fig. 18] represent the steps of a method for producing an electrical structure flexible electronics, object of the present invention, according to the second embodiment.

[0048] Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the transition from one figure to another.

[0049] The different parts represented in the figures are not necessarily on a uniform scale, in order to make the figures more readable.

[0050] The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other.

[0051] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0052] A flexible electronic structure 100 according to a first embodiment is described below in connection with [Fig.l].

[0053] The structure 100 comprises a flexible substrate 102 comprising for example at least one of the following materials: siloxane, polydimethylsiloxane, polyester, polyimide, polytetrafluoroethylene, polyetheretherketone, polyparaxylylene, plant fibers, composite material. The thickness of the flexible substrate 102 (dimension parallel to the Z axis shown in [Fig.l]) is for example less than or equal to 250 μm, and advantageously between 20 μm and 100 μm.

[0054] The structure 100 also comprises one or more electrically conductive tracks 104 arranged on a first face 106 of the flexible substrate 102. These tracks 104 comprise at least one electrically conductive material, for example deposited by cathode sputtering, by electrodeposition or by printing on the flexible substrate 102. According to an exemplary embodiment, the track(s) 104 are formed by depositing a stack of tungsten / tungsten nitride / gold on the first face 106 of the flexible substrate 102, then by performing photolithography and etching of this stack according to the desired pattern of the tracks 104. According to another example, the track(s) 104 may be made with at least one of the following materials: W, Au, TiAu, CrAu, WNiAu, TiCu, Ag. The tracks 104 are also flexible.

[0055] The structure 100 advantageously comprises first connection pads 108 arranged on the first face 106 of the flexible substrate 102 and electrically coupled to the tracks 104. In the embodiment described here, the first pads 108 are arranged on the electrically conductive tracks 104. The first pads 108 comprise at least one electrically conductive material, for example silver, gold, TiNiAu, or a fusible material such as In or su SnAgCu. These first pads 108 are for example produced by cathode sputtering, by electrodeposition or by screen printing.

[0056] The structure 100 further comprises at least one electronic chip 110 secured to the first face 106 of the flexible substrate 102. The chip 110 comprises, at a first face 112 arranged opposite the flexible substrate 102, second connection pads 114 electrically interconnected to the first pads 108 to provide electrical connections between the chip 110 and the tracks 104, and also a mechanical connection between the chip 110 and the flexible substrate 102. In the example of [Fig.l], the interconnections between the pads 108 and 114 are formed by elements 116, here of the “stud bumps” type, for example based on gold. The remainder of the first face 112 of the chip 110 is covered with a passivation layer 118, comprising for example oxide. The thickness of the chip 110 (dimension parallel to the Z axis shown in [Fig.l]) is for example less than or equal to 150 μm, and advantageously included between 10 pm and 100 pm.

[0057] Alternatively, it is possible that the structure 100 does not include the first connection pads 108. In this case, the contact resumption of the chip 110 can be made directly on the track(s) 104 via the elements 116.

[0058] The structure 100 also comprises at least one opening 120, or hole, passing through the flexible substrate 102 and opening at least partly opposite the first face 112 of the chip 110. In the example of [Fig. 1], the opening 120 also passes through a layer 122 covering a second face 124 of the flexible substrate 102, opposite the first face 106. This layer 122 comprises for example an oxide or TEOS. The role of this layer 122 will be described later in connection with the method for producing the structure 100. The dimensions and shape of the opening 120 in the plane of the flexible substrate 102, that is to say a plane parallel to the first face 106 of the flexible substrate 102, depend on the type of chip 110 and the functions fulfilled by this chip 110. By way of example, the opening 120 may have, in a plane parallel to the first face 106 of the flexible substrate 102, a circular shape.

[0059] The chip 110 comprises at least one electronic component arranged opposite the opening 120 and configured to emit and / or receive electromagnetic and / or sound and / or light waves through the opening 120, and / or to receive a fluid through the opening 120. According to an advantageous application, the chip 110 corresponds to a micro-machined ultrasonic transducer, or MUT. According to other advantageous applications, the chip 110 may comprise one or more photodetectors and / or one or more photodiodes and / or one or more laser diodes. It is also possible for the chip 110 to comprise at least one gas sensor provided with a detection face arranged on the side of the opening 120.

[0060] The structure 100 also comprises at least one filling material 126, also called “underfill” in English, arranged between the chip 110 and the first face 106 of the flexible substrate 102. The filling material 126 makes it possible in particular to encapsulate and protect the elements 116, or more generally the interconnections between the chip 110 and the track(s) 104, and also to reinforce the mechanical strength of the chip 110 and absorb any deformations undergone by the chip 110 and the flexible substrate 102. A distance between the first face 106 of the flexible substrate 102 and the first face 112 of the chip 110, corresponding to the thickness of the space in which the filling material 126 is dispensed (dimension parallel to the Z axis shown in [Fig.l]) and therefore to the thickness of filling material 126 between the chip 110 and the flexible substrate 102, may be less than or equal to 100 pm, and advantageously between 10 pm and 30 pm.

[0061] In order to be able to deposit the filling material 126 between the chip 110 and the flexible substrate 102 from the periphery of the chip 110 without the filling material 126 flowing into the opening 120, the filling material 126 is chosen such that its thixotropy index is between 2 and 5, and advantageously between 3 and 4, and that its viscosity is between 5000 mPa.s and 15000 mPa.s. For example, the filling material 126 may correspond to epoxy glue of the EPO-TEK® 353ND-T type marketed by the company EPOXY TECHNOLOGY and dispensed at a temperature for example between 60°C and 90°C, or DELO DUALBOND® SJ4765 glue marketed by the company DELO and dispensed at a temperature equal to approximately 20°C.

[0062] In the embodiment described here, the structure 100 also comprises a layer of waterproof material 128 covering at least side walls of the opening 120 passing through the flexible substrate 102, a portion of the first face 112 of the chip 110 arranged opposite the opening 120, and the second face 124 of the flexible substrate 102 (indirectly in the example of [Fig. 1], given the presence of the layer 122 on the second face 124 of the flexible substrate 102). The layer 128 also covers side walls formed by the encapsulation material 126 in the extension of the opening 120. The material of the layer 128 may be biocompatible, in particular when the structure 100 is intended for medical applications and to be arranged on a living being, for example on skin. For example, the layer of waterproof material 128 may comprise parylene. The thickness of the layer of waterproof material 128 is for example between 1 μm and 5 μm..

[0063] Alternatively, the structure 100 may not include this layer of waterproof material 128, in particular when the structure 100 is not intended for applications requiring biocompatibility and / or in contact with a humid environment.

[0064] The structure 100 also comprises an encapsulation material 130 coating the assembly formed by the chip 110 and the filling material 126. The encapsulation material 130 corresponds for example to PDMS (Polydimethylsiloxane) or another suitable polymer such as Siloxane. The thickness (dimension parallel to the Z axis shown in [Fig. 1]) of the deposited encapsulation material 130 is for example less than or equal to 250 μm, and advantageously between 30 μm and 200 μm. This thickness is adapted according to the thicknesses of the chip 110 and the filling material 126 to be coated or encapsulated.

[0065] The total thickness of the structure 100 (dimension parallel to the Z axis shown in [Fig.l]) is less than or equal to 500 pm, and advantageously between 100 pm and 200 pm.

[0066] A flexible electronic structure 100 according to a second embodiment is described below in connection with [Fig.2].

[0067] Compared to the structure 100 according to the first embodiment previously described, the structure 100 further comprises trenches 132 passing through the flexible substrate 102 and extending in a plane parallel to the first face 106 of the flexible substrate 102 in one or more directions so that the structure 100 can be stretched at least parallel to this or these directions. In the example of [Fig.2], trenches 132 extend parallel to the X axis so that the structure 100 can be stretched parallel to this axis. The trenches 132 are advantageously filled with the encapsulating material 130. Alternatively, it is possible for the trenches 132 to be filled with a flexible and stretchable material different from the encapsulating material 130, or for the trenches 132 to be left empty, without material filling these trenches 132. The trenches 132 are for example made according to shapes such as described in the document WO 2010 / 086416 AL

[0068] In the example embodiment visible in [Fig.2], the structure 100 does not include the layer of waterproof material 128. As a variant of this second embodiment, it is possible for the structure 100 according to the second embodiment to include such a layer of waterproof material 128, in particular when the structure 100 is intended for applications requiring biocompatibility and / or in contact with a humid environment.

[0069] The variants previously described for the first embodiment also apply to this second embodiment.

[0070] A method of producing the structure 100 according to the first embodiment is described below in connection with FIGS. 3 to 11.

[0071] A first step of this method consists in producing the flexible substrate 102 on a support layer 134 which comprises, for example, a semiconductor such as silicon (other types of materials are, however, conceivable). According to an exemplary embodiment, one or more layers of materials intended to allow the subsequent separation of the flexible substrate 102 from the support layer 134 are first produced on a first face 136 of the support layer 134. In the exemplary embodiment described here, these layers correspond to a bilayer 138, the first layer of which comprises SiO2 and / or a silicon nitride (SiN or Si3N4) and the second layer of which comprises a noble metal (platinum, gold, silver, rhodium, osmium, palladium, ruthenium, iridium) (see [Fig. 3]).

[0072] Alternatively, depending on the technique that will be used to separate the flexible substrate 102 and the support layer 134, it is possible that the flexible substrate 102 is produced directly on the support layer 134, or that the layers present at the interface between the flexible substrate 102 and the support layer 134 are different from those described above.

[0073] The flexible substrate 102 is then deposited on the layer 122, for example by “spin coating” or spin coating when its thickness is less than 30 μm, or by laminating a film when its thickness is greater than 30 pm.

[0074] An etching, for example chemical, is then implemented in order to produce the opening 120 through the flexible substrate 102.

[0075] The layer 122 is then etched, for example by chemical etching, according to the same pattern so that the opening 120 also passes through the layer 122 (see [Fig.4]).

[0076] The electrically conductive track(s) 104 are produced on the first face 106 of the flexible substrate 102 which is on the side opposite the support layer 134. According to an exemplary embodiment, the tracks 104 are obtained by depositing one or more electrically conductive layers, advantageously metallic as previously described in connection with [Fig. 1], on the first face 103, then by etching this or these electrically conductive layers according to the pattern desired for these tracks 104.

[0077] In one variant, the first connection pads 108 are then made such that they are electrically coupled to the tracks 104 (see [Fig.5]). The first pads 108 are for example made by screen printing a silver or gold-based paste. According to another variant, it is possible not to make the first connection pads 108.

[0078] The chip 110, which has been previously produced and cut from a semiconductor substrate, is transferred and secured to the side of the first face 106 of the flexible substrate 102. This securing of the chip 110 to the flexible substrate 102 is obtained by the interconnection between the first pads 108 and the second pads 114, for example by thermocompression using stud bump type elements 116 (see [Fig.6]). During this transfer, the chip 110 is not yet thinned in order to be able to handle it. At the end of this transfer, a part of the first face 112 of the chip 110 is placed opposite the opening 120.

[0079] Alternatively, when the first pads 108 are not produced, the elements 116 are arranged directly against the track(s) 104.

[0080] The filling material 126 is then dispensed between the chip 110 and the flexible substrate 102 (see [Fig.7]).

[0081] The chip 110 is then thinned to the desired thickness, for example by chemical-mechanical polishing (CMP). This thinning may be followed by finer polishing and / or chemical cleaning, in particular to reduce or eliminate the stresses exerted on the chip 110 (so-called “de-stressing” step). The structure obtained at this stage of the process is visible in [Fig. 8].

[0082] The encapsulation material 130 is then deposited, for example by vacuum lamination of a film forming the encapsulation material 130, or by spin coating when the encapsulation material 130 corresponds to PDMS. Photolithography and etching steps can then be implemented in order to retain only a portion of the deposited material 130, the remaining material coating the assembly formed by the chip 110 and the filling material 126 (see [Fig.9]).

[0083] The flexible substrate 102 is then detached from the support layer 134 (see [Fig. 10]). In the embodiment described here, given the materials of the layers 122 and 138 (respectively SiO2 or SiN or Si3N4 and a noble metal), this detachment is implemented at the interface between the layers 122 and 138, the layer 122 remaining integral with the flexible substrate 102 and the layer 138 remaining integral with the support layer 134.

[0084] Finally, the layer of waterproof material 128 is deposited so as to cover at least the side walls of the opening 120, a part of the first face 112 of the chip 110 arranged opposite the opening 120, the second face 124 of the flexible substrate 102 opposite the first face 106 as well as the side walls formed by the filling material 126 in the extension of the opening 120 (see [Fig. 11]).

[0085] A method of producing the structure 100 according to the second embodiment is described below in connection with FIGS. 12 to 18.

[0086] As in the first embodiment previously described, the flexible substrate 102 is produced on the support layer 134. In [Fig. 12], as in the previous exemplary embodiment, the layers 138 and 122 are formed beforehand on the support layer 134 in order to allow the flexible substrate 102 to be detached.

[0087] Photolithography and etching steps are then implemented in order to produce the opening 120 through the flexible substrate 102. The etching pattern used for these steps also includes the pattern of the trenches 132 which are formed through the flexible substrate 102 (see [Fig. 12], on which only one trench 132 is visible).

[0088] Layer 122 is then etched according to the pattern of opening 120 so that the latter also passes through layer 122.

[0089] The electrically conductive tracks 104 and the first connection pads 108 are then produced on the flexible substrate 102, for example as in the first embodiment previously described (see [Fig. 13]). As in the first embodiment, it is possible that the first connection pads 108 are not produced.

[0090] The chip 110, which has been previously produced and cut from semiconductor, is transferred and secured to the side of the first face 106 of the flexible substrate 102, for example as in the first embodiment previously described (see [Fig. 14]).

[0091] The filling material 126 is then dispensed between the chip 110 and the flexible substrate 102 (see [Fig. 15]).

[0092] The chip 110 is then thinned to the desired thickness, for example as previously described for the first embodiment (see [Fig. 16]).

[0093] The encapsulation material 130 is then deposited so as to coat the assembly formed by the chip 110 and the filling material 126, and to fill the trenches 132 (see [Fig. 17]).

[0094] The flexible substrate 102 is then separated from the support layer 134, for example as previously described for the first embodiment (see [Fig.18]).

Claims

Claims

1. Flexible electronic structure (100) comprising at least: - a flexible substrate (102) provided with a first face (106) on which there is at least one electrically conductive track (104); - an electronic chip (110) secured to the first face (106) of the flexible substrate (102) and comprising, at a first face (112) of the electronic chip (110), connection pads (114) electrically interconnected to the electrically conductive track (104); - an opening (120) passing through the flexible substrate (102) and opening at least partly opposite the first face (112) of the electronic chip (110); - a filling material (126) disposed between the electronic chip (110) and the first face (106) of the flexible substrate (102), the thixotropy index of which is between 2 and 5 and the viscosity of which is between 5000 mPa.s and 15000 mPa.s.

2. Flexible electronic structure (100) according to claim 1, wherein the electronic chip (110) comprises at least one electronic component arranged opposite the opening (120) and configured to emit and / or receive electromagnetic and / or sound and / or light waves through the opening (120), and / or to receive a fluid through the opening (120).

3. Flexible electronic structure (100) according to one of the preceding claims, wherein the total thickness of the flexible electronic structure (100) is less than or equal to 500 pm, and / or wherein the thickness of the electronic chip (110) is less than or equal to 150 pm, and / or wherein the thickness of the flexible substrate (102) is less than or equal to 250 pm, and / or wherein a distance between the first face (106) of the flexible substrate (102) and the first face (112) of the electronic chip (110) is less than or equal to 100 pm.

4. Flexible electronic structure (100) according to one of the preceding claims, in which the flexible substrate (102) comprises at least one of the following materials: siloxane, polydimethylsiloxane, polyester, polyimide, polytetrafluoroethylene, polyetheretherketone, polypara-xylylene, plant fibers, composite material.

5. Flexible electronic structure (100) according to one of the preceding claims, further comprising a layer of waterproof material (128) covering at least side walls of the opening (120), a portion of the first face (112) of the electronic chip (110) arranged opposite the opening (120), and a second face (124) of the flexible substrate (102) opposite the first face (106).

6. The flexible electronic structure (100) of claim 5, wherein the sealing material is biocompatible.

7. Flexible electronic structure (100) according to one of the preceding claims, further comprising an encapsulating material (130) coating the assembly formed at least by the electronic chip (110) and the filling material (126).

8. Flexible electronic structure (100) according to one of the preceding claims, further comprising at least one trench (132) passing through the flexible substrate (102) and extending in a plane parallel to the first face (106) of the flexible substrate (102) in at least one direction such that the flexible electronic structure (100) is stretchable at least parallel to said direction.

9. Flexible electronic structure (100) according to claims 7 and 8, wherein the trench (132) is filled at least by the encapsulating material (130).

10. Method for producing a flexible electronic structure, (100) comprising at least the following steps: - producing a flexible substrate (102) on a support layer (134); - producing at least one opening (120) passing through the flexible substrate (102); - producing, on a first face (106) of the flexible substrate (102) located on the side opposite the support layer (134), at least one electrically conductive track (104); - transfer and securing of an electronic chip (110) on the first face (106) of the flexible substrate (102), the electronic chip (110) comprising, at a first face (112), connection pads (114) electrically interconnected to the electrically conductive track (104), and such that a part of the first face (112) of the electronic chip (110) is arranged opposite the opening (120);- adding a filling material between the electronic chip (110) and the first face (106) of the flexible substrate (102), and whose thixotropy index is between 2 and 5, and whose viscosity is between 5000 mPa.s and 15000 mPa.s; - separating the flexible substrate (102) from the support layer (134).;

11. Method according to claim 10, further comprising a step of thinning the electronic chip (110) from a second face opposite the first face (112) of the electronic chip (110), implemented between the step of transferring and securing the electronic chip (110) on the first face (106) of the flexible substrate (102) and the step of detaching the flexible substrate (102) from the support layer (134).

12. Method according to one of claims 10 and 11, further comprising, after the step of detaching the flexible substrate (102) from the support layer (134), a step of producing a layer of waterproof material (128) covering at least the side walls of the opening (120), a part of the first face (112) of the electronic chip (110) arranged opposite the opening (120), and a second face (124) of the flexible substrate (102) opposite the first face (106).

13. The method of claim 12, wherein the waterproof material is biocompatible.

14. Method according to one of claims 10 to 13, further comprising a deposition of an encapsulation material (130) covering at least the electronic chip (110), implemented between the step of transferring and securing the electronic chip (110) on the first face (106) of the flexible substrate (102) and the step of detaching the flexible substrate (102) from the support layer (134).

15. The method of claim 14, wherein making the opening (120) through the flexible substrate (102) also forms at least one trench (132) passing through the flexible substrate (102) and extending in a plane parallel to the first face (106) of the flexible substrate (102) in at least one direction, and wherein the encapsulating material is also deposited in the trench (132), making the flexible electronic structure (100) stretchable at least parallel to said direction.

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