Method of manufacturing a multilayer electronic circuit

Abstract

Method for manufacturing a multilayer electronic circuit Method for manufacturing a multilayer electronic circuit (80), the method comprising:a) providing a thermoplastic interconnection plate (24) provided with at least two holes (27) passing through it and printed circuits (3, 6) each comprising:- a thermoplastic support plate (18, 34), - two electrically conductive pads (21, 36) carried by a face (15, 33) of the support plate, and- an electrically conductive track (12, 30) printed on said face and which extends between the electrically conductive pads, b) arranging the interconnection plate between the printed circuits by arranging the electrically conductive pads opposite each other through the corresponding holes, etc.) thermoforming the arrangement formed in step b) to weld each of the support plates with the interconnection plate,the electrically conductive pads facing the printed circuits being brought into contact through the holes corresponding to step b) or step c). Figure for the abstract: Fig. 1,

Description

Title of the invention: Method for manufacturing a multilayer electronic circuit

[0001] The present invention relates to the manufacture of electronic circuits, in particular having a complex three-dimensional shape.

[0002] It is known to manufacture a printed circuit having a shape complementary to the shape of the object in which it is intended to be housed.

[0003] For this purpose, flexible printed circuit supports may be used, for example made of polyimide or polyetheretherketone, also called PEEK, as described in US 2003 / 0132192 A1.

[0004] Alternatively, it is known, for example from WO 2020 / 043938 A1, to thermoform a thermoplastic support coated with an electrically conductive material forming an electronic circuit. However, the thermoforming method described in this document is unsuitable for the manufacture of printed circuits with more than two levels of electrically conductive tracks.

[0005] There is therefore a need for a new method of manufacturing electronic circuits, particularly those of complex shape.

[0006] The invention provides a method for manufacturing a multilayer electronic circuit, the method comprising: (a) the supply of a thermoplastic interconnection plate provided with at least two holes passing right through its thickness and first and second printed circuits each comprising: - a thermoplastic support plate, - two electrically conductive pads carried by one face of the support plate, and - an electrically conductive track printed on said face and which extends, at least in part, between the electrically conductive pads, b) arranging the interconnection plate between the first and second printed circuits by arranging the electrically conductive pads of the first and second printed circuits opposite each other through the corresponding holes, and c) thermoforming the arrangement formed in step b) to weld each of the support plates of the first and second printed circuits with the interconnection plate, the electrically conductive pads facing the first and second printed circuits being brought into contact through the holes corresponding to step b) or step c).

[0007] The method according to the invention electrically connects the first and second printed circuits selectively. The electrical connection is thus made by aligning, along the axes of the holes in the interconnection plate, the electrically conductive pads of the first printed circuit, the electrically conductive pads of the second printed circuit and the corresponding holes. Thus, the distance between the electrically conductive pads of the first printed circuit, the distance between the electrically conductive pads of the second printed circuit and the distance between the holes are equal. In this way, the portions of the first and second printed circuits not overlapping the holes are electrically insulated by the interconnection plate. The method thus allows the production of complex electrical diagrams in which the electrically conductive tracks cross, when observed along an axis normal to the interconnection plate, in the volume of the electronic circuit without being in electrical contact.

[0008] Preferably, in order to ensure optimal fusion between the interconnection plate and the support plates, the greatest difference, in absolute value, between the glass transition temperatures of the constituent materials of the support plate of the first printed circuit, the support plate of the second printed circuit and the interconnection plate, is less than 10 °C. The glass transition temperatures are measured according to the ASTM E1356 standard.

[0009] The support plates of the first and second printed circuits and / or the interconnection plate may be made of a material chosen from thermoplastic materials, in particular from polycarbonate (PC), polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene (ABS), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and mixtures thereof.

[0010] The support plates of the first and second printed circuits may be made of the same material, in particular when they are coated with the same ink. They may be made of different materials, for example when they are intended to be printed with different inks having specific viscosities and / or wettabilities.

[0011] The support plates of the first and second printed circuits and / or the interconnection plate may have a thickness of between 10 μm and 5 millimeters, for example approximately 100 μm.

[0012] The first printed circuit and / or the second printed circuit may comprise an additional electrically conductive track, not superimposed on the holes and which is carried by the same face as the electrically conductive track and electrically insulated from the electrically conductive track.

[0013] The method may include printing a conductive ink to form the electrically conductive track and depositing an electrically conductive substance to form the electrically conductive pads.

[0014] Printing of the conductive ink may be carried out using a wet deposition technique, preferably by screen printing.

[0015] The conductive ink may comprise a solvent and particles of a metal, preferably silver, in solution in the solvent having a size which may be between 10 nm and 10 μm, preferably approximately 500 nm. The size of a particle may be measured by laser granulometry. The solvent is chosen for its chemical inertness with respect to the support plate on which the ink is deposited. For example, terpineol is a chemically inert solvent with respect to polycarbonate.

[0016] The conductive ink may comprise a thermoplastic compound chosen from polyurethane, an epoxy resin and mixtures thereof.

[0017] Preferably, the conductive ink has, after drying, an elongation rate greater than 50% according to standard NF EN ISO527-1. For example, the conductive ink may be ME603 ink marketed by the company DUPONT®, BECTRON CP6680 ink marketed by the company ELANTAS® or DM-SIP-1005 from DYCOTEC Materials®.

[0018] The electrically conductive substance may be the same as the electrically conductive ink for printing the electrically conductive track. Alternatively, the electrically conductive substance is an adhesive.

[0019] The quantities of substance deposited on the facing faces of the support plates of the first and second printed circuits are adapted according to the dimensions of the hole so that at the end of step c), the electrical connection is established between the first and second printed circuits.

[0020] Preferably, the ratio of the volume of the electrically conductive substance to form one of the electrically conductive pads to the volume occupied by a hole is between 0.15 and 0.35. In this way, optimal contact is ensured between the first and second printed circuits to bring them into electrical contact through the corresponding hole, while avoiding the substance being in excess in the hole.

[0021] In step a), for each of the printed circuits, the pads and the electrically conductive track are in contact. Preferably, the pads are arranged on the electrically conductive track. In particular, the electrically conductive track can be printed on the support plate and the pads are formed on and in contact with said track.

[0022] The pad preferably forms an excess thickness which projects from the electrically conductive track, when observed along an axis included in the median plane of the support plate.

[0023] Annealing may be carried out, after the deposition of the electrically conductive track and the electrically conductive pads, in order to evaporate the solvents. preferably, the annealing is carried out at a temperature lower than the glass transition temperature of the material constituting the support plate.

[0024] The first and second integrated circuits may be brought into contact in step b) by flow of the substance under the effect of temperature during thermoforming.

[0025] The sum of the thicknesses of the facing pads may be greater than or equal to the height of the corresponding hole, preferably in the embodiment according to which the electrically conductive pads facing the first and second printed circuits are brought into contact through the holes corresponding to step b).

[0026] Preferably, the electrically conductive pads facing the first and second printed circuits are brought into contact through the holes corresponding to step c) under the effect of the thermoforming pressure which increases the contact surface between the electrically conductive pads and the electrically conductive tracks.

[0027] As regards the holes of the interconnection plate, they preferably have a cylindrical side wall, preferably of revolution. The diameter of each hole can be between 100 μm and 5 millimeters.

[0028] The ratio of the diameter of each hole to the thickness of the interconnecting plate may be between 0.1 and 100.

[0029] The holes can be drilled using a laser, which ensures that holes of regular shape and identical diameter are obtained.

[0030] The support plate of the first printed circuit and / or the support plate of the second printed circuit and / or the interconnection plate may be coated with alignment patterns. The alignment patterns may be deposited by screen printing during the step of printing the conductive ink patterns.

[0031] Furthermore, the method may comprise the deposition of an electronic component, for example a diode, a resistor or a transistor, on the electrically conductive track of the first printed circuit and / or the electrically conductive track of the second printed circuit.

[0032] Preferably, the electronic component is entirely sandwiched between the integrated circuit on which it is deposited and the interconnection plate. The electronic component is thus entirely immersed between the integrated circuit and the interconnection plate at the end of step c). It is thus advantageously protected, and the method can thus dispense with a step of applying a protective varnish to the electronic component.

[0033] Preferably, the other face of the support plate of the second printed circuit, which is opposite the first printed circuit, carries an additional electrically conductive track which extends at least partly between two electrically conductive pads, step a) further comprising the provision of an additional interconnection plate provided with holes passing right through its thickness and a third printed circuit comprising - a support plate, - two electrically conductive pads carried by one face of the support plate, and - an electrically conductive track printed on said face and which extends, at least in part, between the electrically conductive pads, step b) further comprising the arrangement of the additional interconnection plate between the second and third printed circuits by arranging the electrically conductive pads carried by the other face of the support of the second printed circuit and the electrically conductive pads of the third printed circuit facing each other through the corresponding holes of the additional interconnection plate, the thermoforming of the assembly in step c) being carried out in order, in addition, to weld each of the support plates of the second and third printed circuits with the interconnection plate, the electrically conductive pads carried by the other face of the support of the second printed circuit and the electrically conductive pads of the third printed circuit being brought into electrical contact through the corresponding holes of the additional interconnection plate in step b) or in step c).

[0034] Preferably, the thermoforming comprises compressing the arrangement onto a counter-form having at least one raised area and / or one recessed area. An electronic circuit having a complex 3D shape, for example having different curvatures around different axes, can be obtained.

[0035] The thermoforming can be carried out at a temperature between Tgmax + 20°C and Tgmax - 20°C, Tgmax being the highest glass transition temperature of the materials constituting the support plates of the first and second printed circuits and the interconnection plate. For example, when the support plates and the interconnection support are made of polycarbonate, the thermoforming is preferably carried out between 140°C and 180°C.

[0036] The thermoforming pressure can be between 2 MPa and 12 MPa.

[0037] Finally, the multilayer electronic circuit is for example chosen from an element of a dashboard of a motor vehicle, an element, for example a shell, of a mobile telephone, an element of a computer, in particular a portable computer.

[0038] Other characteristics and advantages of the invention will become apparent upon reading the detailed description which follows and upon reading the attached drawing in which:

[0039] [Fig.l] schematically and explodedly represents the constituents of an electronic circuit manufactured by the method according to the invention, and

[0040] [Fig.2] schematically represents an example of implementation of the arrangement and thermoforming steps of the process, the constituents of the integrated circuit being represented in cross-section.

[0041] The implementation of the method according to the invention requires the supply or production of at least two printed circuits.

[0042] In the example illustrated in [Fig.l], there are first 3, second 6 and third 9 printed circuits. Obviously, this number of printed circuits is not limiting.

[0043] In the illustrated example, the following constituents are used: - 8010 #n polycarbonate plates marketed by the company LEXAN® with a thickness e equal to 100 pm, - ME603 silver-based conductive ink marketed by DUPONT®, - silver-based conductive glue LT2216 marketed by the company DETO®, and - silver-based conductive glue IC343 marketed by the company DETO®.

[0044] An electrically conductive track 12 is formed by printing the conductive ink by screen printing, on a face 15 of one of the polycarbonate plates, which is thus a support plate 18 of the first printed circuit 3. Electrically conductive pads 21 are formed on this face 15 by depositing the glue LT2216 on the electrically conductive track 12. Annealing at a temperature between 80°C and 130°C is then carried out to bond the track and the pads to the support plate and form the first printed circuit 3. An electronic component 22 is then bonded to the electrically conductive track 12 using the glue IC343

[0045] An interconnection plate 24 is then formed by drilling another of the polycarbonate plates right through its thickness using a laser beam. The distance between the holes 27 thus formed in the plate is equal to the distance d between the pads on the face. The holes have a diameter ¢) for example of approximately 100 μm.

[0046] The interconnection plate 24 is then arranged on the face 15 of the first printed circuit by superimposing the holes 27 with the pads 21.

[0047] An electrically conductive track 30 is then formed by printing the conductive ink by screen printing, on a face 33 of one of the polycarbonate plates, which is thus a support plate 34 of the second printed circuit 6. For the sake of clarity, the track 30 is shown in broken lines. The face 33 is opposite the face 15 of the first printed circuit. Electrically conductive pads 36 are formed on this face 33 by depositing the LT2216 adhesive on the electrically conductive track 30. The distance between the pads 36 is equal to the distance between the pads 21 of the first integrated circuit 3 and between the holes 30 of the interconnection plate 24.

[0048] Furthermore, an additional electrically conductive track 42 and electrical pads additional conductors 45 are formed in an identical manner on the face 45 of the support plate 34 which is opposite the face 33.

[0049] Annealing at a temperature between 80°C and 130°C is then carried out. Another electronic component 39 is then glued onto the electrically conductive track 30 using the glue IC343.

[0050] The electrically conductive pads 51 on the face 33 of the second integrated circuit are then arranged opposite the electrically conductive pads 21 on the face 15 of the first integrated circuit 3 through the holes 27. Thus, the electrically conductive pads 33, 36 and the corresponding holes 27 are aligned along the same axis X, as illustrated in [Fig.2].

[0051] An additional interconnection plate 48 is then formed by drilling one of the polycarbonate plates right through its thickness using a laser beam. The distance between the holes 51 thus formed in the plate is equal to the distance between the pads on the face 45 of the support plate 34.

[0052] An electrically conductive track 54, shown in broken lines, is then formed by printing the conductive ink by screen printing, on a face 57 of one of the polycarbonate plates, which is thus a support plate 60 of the third printed circuit 9. Electrically conductive pads 63 are formed on this face 57 by depositing the LT2216 glue on the electrically conductive track 54. The distance between the pads 63 is equal to the distance between the pads 42 of the second integrated circuit 6 and between the holes 51 of the additional interconnection plate 48.

[0053] The electrically conductive pads 63 located on the face 57 of the third integrated circuit are then arranged opposite the electrically conductive pads 42 located on the face 45 of the second integrated circuit 6 through the holes 57 of the additional interconnection plate. Thus, the electrically conductive pads 63, 42 and the corresponding holes 51 are aligned along the same axis Y.

[0054] Obviously, since the electrical diagram of the electronic circuit is known prior to the preparation of the printed circuits and the interconnection plates, the latter can be prepared in a different order from that presented above. For example, the printed circuits are first formed and then the interconnection plates are drilled.

[0055] The arrangement 70 thus formed is then placed in a mold, the temperature of which is 130°C. It is thus thermoformed, as indicated by the arrow T, under a pressure of 8 MPa of air at a temperature of 200°C, so that the temperature of the arrangement is approximately 160°C. As illustrated in [Fig.2], the thermoforming welds the interconnection plates to the printed circuits and an electrical connection is established between the integrated circuits by electrically conductive ink dots formed in the holes.

[0056] A multilayer electronic circuit 80 as shown in [Fig. 1] is thus obtained.

[0057] Of course, the invention is not limited to the example described above for illustrative and non-limiting purposes.

Claims

Claims

1. A method of manufacturing a multilayer electronic circuit (80), the method comprising: a) providing a thermoplastic interconnection plate (24) provided with at least two holes (27) passing right through its thickness and first (3) and second (6) printed circuits each comprising: - a thermoplastic support plate (18, 34), - two electrically conductive pads (21, 36) carried by a face (15, 33) of the support plate, and - an electrically conductive track (12, 30) printed on said face and which extends, at least in part, between the electrically conductive pads, b) arranging the interconnection plate between the first and second printed circuits by arranging the electrically conductive pads of the first and second printed circuits opposite each other through the corresponding holes,and c) thermoforming the arrangement formed in step b) to weld each of the support plates of the first and second printed circuits with the interconnection plate, the electrically conductive pads facing the first and second printed circuits being brought into contact through the holes corresponding to step b) or step c).,

2. Method according to claim 1, the thermoforming comprising the compression of the arrangement on a counter-form having at least one raised zone and / or one hollow zone.

3. Method according to any one of claims 1 and 2, the glass transition temperatures of the materials constituting the support plate of the first printed circuit, the support plate of the second printed circuit and the interconnection plate, being less than 10 “C

4. V-. Method according to any one of the preceding claims, comprising printing, preferably by screen printing, an ink to form the electrically conductive track and depositing an electrically conductive substance to form the electrically conductive pads.

5. A method according to any preceding claim, the ratio of the volume of the substance to form one of the electrically conductive pads to the volume occupied by a hole being between 0.15 and 0.

35.

6. Method according to any one of the preceding claims, the support plate of the first printed circuit and / or the support plate of the second printed circuit and / or the interconnection plate being coated with an alignment pattern.

7. A method according to any preceding claim, comprising drilling the holes using a laser.

8. A method according to any preceding claim, comprising depositing an electronic component (22, 39), for example a diode, a resistor or a transistor, on the electrically conductive track of the first printed circuit and / or the electrically conductive track of the second printed circuit.

9. Method according to the preceding claim, the electronic component being entirely sandwiched between the integrated circuit on which it is deposited and the interconnection plate.

10. Method according to any one of the preceding claims, the other face (45) of the support plate of the second printed circuit, which is opposite the first printed circuit (3), carrying an additional electrically conductive track (42) which extends at least in part between two electrically conductive pads, step a) further comprising the provision of an additional interconnection plate (48) provided with holes passing right through it and a third printed circuit (9) comprising - a support plate (60), - two electrically conductive pads (63) carried by a face (57) of the support plate, and - an electrically conductive track (54) printed on said face and which extends, at least in part, between the electrically conductive pads,step b) further comprising the arrangement of the additional interconnection plate between the second and third printed circuits by arranging the electrically conductive pads carried by the other face of the support of the second printed circuit and the electrically conductive pads of the third printed circuit facing each other through the corresponding holes of the additional interconnection plate, the thermoforming of the assembly in step c) being carried out in order, in addition, to weld each of the support plates of the second and third printed circuits with the interconnection plate, the electrically conductive pads carried by the other face of the support of the second printed circuit and the electrically conductive pads of the third printed circuit being brought into electrical contact through the corresponding holes of the additional interconnection plate in step b) or in step c).

11. Method according to any one of the preceding claims, the multilayer electronic circuit being chosen from an element of a dashboard of a motor vehicle, an element, for example a shell, of a mobile telephone, an element of a computer, in particular a portable computer.

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