Printed circuit board manufacturing process

Abstract

A method for manufacturing a printed circuit board, comprising the steps of: - continuously feeding a sheet of electrically conductive material (1), - continuously coating at least one layer of electrically insulating material (2) on at least one area of ​​the surface of one face of the sheet of electrically conductive material (1), this electrically insulating material (2) comprising at least one epoxy resin, - continuously photopolymerizing at least certain regions of the epoxy resin under UV radiation, and - producing at least one pattern by photolithography in the sheet of electrically conductive material (1), this pattern being supported by photopolymerized epoxy resin. Fig. 4

Description

Title of the invention: Method for manufacturing printed circuits Technical field

[0001] The invention relates to the field of printed circuits and methods for manufacturing printed circuits. For example, it relates to the field of flexible printed circuits for medical biology examination devices. State of the art

[0002] Some printed circuits are made from multilayer structures comprising at least one sheet of electrically conductive material laminated onto a layer of electrically insulating material. The sheet of electrically conductive material is used to make conductive patterns (conductive tracks, contacts, antenna, electrodes, etc.). The layer of electrically insulating material is used as a support and dielectric substrate.

[0003] For example, the sheet of electrically conductive material is made of a metal or a metal alloy of one or more of the metals included in the following list: copper, aluminum, copper alloy, aluminum alloy, steel, etc. For example, the layer of electrically insulating material forms a dielectric substrate of glass-epoxy, or polyimide, or polyethylene terephthalate, etc. A layer of adhesive material may optionally be used to adhere the sheet of electrically conductive material to the layer of electrically insulating material. For example, the layer of adhesive material is made of an epoxy resin.

[0004] The multilayer structures thus produced by laminating together a sheet of electrically conductive material and a layer of electrically insulating material (possibly with a layer of adhesive material between the two) have defects at the interface between the layers. An illustration of this type of defect is given in [Fig.l]. In [Fig.l], a pattern 1 can be seen, etched in a sheet of copper alloy laminated on a dielectric substrate 2 (in this example the dielectric substrate 2 is formed of a layer of polyethylene terephthalate). Holes and / or channels 3 are present on the surface of the dielectric substrate 2. After lamination of the sheet of electrically conductive material and the layer of electrically insulating material and etching of patterns 1 in the sheet of electrically conductive material, the holes and / or channels 3 form openings 4 at the edge of the patterns 1.More particularly, these openings 4 can form entry points for the etching solutions used to produce patterns 1 in the sheet of electrically conductive material, by chemical or electrochemical etching. This can then lead to uncontrolled etching of the sheet of electrically conductive material. on the periphery of the patterns 1 etched in the sheet of electrically conductive material. This is illustrated by [Fig.2] in which it can be seen that an opening 4, on the edge of the pattern 1, at the interface between the sheet of electrically conductive material and the layer of dielectric material 2, is at the origin of the etching of a cavity 5 in the sheet of electrically conductive material, and this even if a layer of adhesive 6 is present, between the sheet of electrically conductive material and the layer of dielectric material.

[0005] This uncontrolled engraving can cause many disadvantages.

[0006] This is the case in particular when these multilayer structures are used to produce electrodes for medical biology examination devices, and in particular electrodes for point-of-care medical biology examination devices (POC devices). Indeed, these electrodes are used to detect one or more molecules in fluids of human origin, and possibly to measure the respective concentration or concentrations of these molecules. The detection, and the possible concentration measurement, are then carried out electrochemically by immersing, in the fluids in question, one or more electrodes produced from these multilayer structures. These fluids may comprise one or more reagents intended to react with these electrodes in order to provide an electrical measurement representing information on the nature and / or composition of these.

[0007] However, it has been found that the measurements carried out at the level of the electrodes mentioned above are not always stable and / or reproducible. The applicant has sought the cause and has determined that the presence of openings 4 at the interfaces between the layers, such as those mentioned above and highlighted in Figures 1 and 2, can modify the response of these electrodes. Summary of the invention

[0008] The invention aims to at least partially overcome this drawback.

[0009] To this end, a method for manufacturing a printed circuit is proposed. This printed circuit is advantageously sufficiently flexible to allow continuous implementation ("Reel-to-reel" or "Roll-to-roll" in English) of the method according to the invention.

[0010] The method according to the invention comprises the operations consisting of: - to continuously provide a sheet of electrically conductive material, this sheet comprising two main faces, - continuously coating at least one layer of electrically insulating material on at least one area of ​​the surface of one of the main faces of the sheet of electrically conductive material, this electrically insulating material comprising at least one epoxy resin, - to continuously photopolymerize at least certain regions (i.e. at least the region(s) at which patterns will be made) of the epoxy resin; and - to produce at least one pattern by photolithography in the sheet of electrically conductive material, this pattern being supported solely by said photopolymerized epoxy resin.

[0011] Thus, thanks to the method according to the invention, a layer of electrically insulating material is directly applied by coating on one of the faces of the sheet of electrically conductive material. The layer of electrically insulating material is therefore applied in liquid or pasty form so as to form a continuous interface between this layer and the face of the sheet of electrically conductive material on which the layer of electrically insulating material is applied. In other words, the layer of electrically insulating material conforms to and seals any surface roughness of the sheet of electrically conductive material. Thus, when etching patterns in the sheet of electrically conductive material, the etching liquid(s) do not penetrate between the sheet of electrically conductive material and the layer of electrically insulating material.Similarly, when used in a medical biology examination device, the fluids to be analyzed do not penetrate between the sheet of electrically conductive material and the layer of electrically insulating material. The measurement carried out from the electrode(s) etched in the sheet of electrically conductive material is therefore more reliable and more precise.

[0012] In this document, the expression "continuous interface" means that the layer of electrically insulating material completely wets the surface of the sheet of electrically conductive material on which it is applied. In other words, at the scale of a micrometer or a few micrometers, or even at a lower (nanometric) scale, the interface is homogeneous and continuous, between the layer of insulating material and the sheet of electrically conductive material. In other words, at these scales, there is no hole, channel, opening, cavity, or other defects of this type, between the layer of insulating material and the sheet of electrically conductive material.

[0013] Without such a defect, the substances (reagents and other liquids) in which the electrode is immersed do not infiltrate between the layer of insulating material and the sheet of electrically electrical material. Only the interactions between these substances and the electrode on one or more well-defined surfaces thereof are taken into account. This results in more stable, more reliable and more reproducible measurements.

[0014] Furthermore, the implementation of coating and photopolymerization operations of the resin allows the process according to the invention to be carried out continuously, and in a manner fast. The process therefore makes it possible to obtain relatively fast and interesting manufacturing speeds.

[0015] The method according to the invention further comprises one of the following characteristics, considered in isolation and independently of one another, or in combination with one or more others:

[0016] - the pattern is an electrode configured for use in an examination device medical biology;

[0017] - the epoxy resin(s) represent at least 30% by dry weight of the layer of insulating material coated on one side of the sheet of electrically conductive material;

[0018] - the layer of insulating material coated on one of the faces of the sheet of material electrically conductive comprises a mineral filler representing between 10% and 70% of its dry weight; for example, the mineral filler is essentially made up of glass microspheres;

[0019] - the epoxy resin(s) are chosen from the following monomers: 3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate, and other cycloaliphatic epoxy resins;

[0020] - the layer of electrically insulating material comprises at least one photoinitiator (in other words, an element, molecule or compound that promotes polymerization under UV radiation), for example, the photoinitiator(s) are chosen from the following molecules: bis(4,4'-(C10-C13)-alkylphenyl)-iodonium hexafluoroantimonat, propylene carbonate, and other cationic photoinitiator;

[0021] - the layer of electrically insulating material comprises a regulator of the photopolymerization kinetics or photosensitizer; for example, the regulator of photopolymerization kinetics is phenothiazine;

[0022] - the layer of electrically insulating material comprises at least one agent rheological; for example, the rheological agent(s) are pyrogenic silicas (or their derivatives);

[0023] - the layer of electrically insulating material has a thickness of between 50 and 350 micrometers. Brief description of the figures

[0024] Other aspects, aims and advantages of the invention will appear on reading the detailed description which follows, as well as with the aid of the appended figures, given as non-limiting examples:

[0025] - [Fig.l] is an image taken with a scanning electron microscope of the interface between the layer of insulating material and the sheet of electrically electrical material, in a multilayer structure of the prior art,

[0026] - [Fig.2] is also an image taken with a scanning electron microscope of a cut at the interface between the layer of insulating material and the sheet of electrically conductive material, in a multilayer structure of the prior art;

[0027] - [Fig.3] is an image taken with a scanning electron microscope of the interface between the layer of insulating material and the sheet of electrically electrical material, in a multilayer structure according to the invention; and

[0028] - [Fig.4] is also an image taken with a scanning electron microscope of a section at the interface between the layer of insulating material and the sheet of electrically conductive material, in a multilayer structure according to the invention. Detailed description

[0029] The invention is exemplified below in the context of a method for manufacturing an electrode for a medical biology examination device. However, the method described below can be transposed to other applications.

[0030] According to this method, an electrically insulating material is prepared in a form sufficiently liquid to be able to be coated on a sheet of conductive material.

[0031] Advantageously, the electrically insulating material has a viscosity of the order of IPa.s.

[0032] According to the invention, this electrically insulating material is an epoxy resin photopolymerizable under UV radiation. To this end, a homogeneous mixture of liquid monomers and / or prepolymers is produced, protected from UV radiation.

[0033] These liquid monomers and / or prepolymers are epoxy resins. They are chosen from the following prepolymers or monomers: 3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate, or other UV-polymerizable cycloaliphatic epoxy resins.

[0034] For example, a mixture of 35% by weight of 3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate and 65% by weight of bis(3,4-epoxycyclohexylmethyl) adipate is made. The concentration by weight of the resins is adjusted so as to be between 30 and 90% in the final mixture (including the epoxy resins, the fillers, and the other additives).

[0035] When a homogeneous mixture is obtained from the epoxy resins, reinforcing fillers or additives are added to this mixture. For example, these fillers are gradually added to the epoxy resin mixture, in a shear mixer, until a homogeneous mixture is again obtained.

[0036] The concentration by weight of the filler(s) is adjusted so as to be between 30 and 90% in the final mixture. For example, these fillers are mineral fillers. For example, a mineral filler essentially consisting of mi glass microspheres 7 is used (microspheres can be distinguished in [Fig.4]). The weight concentration of these glass microspheres in the final mixture is then close to 50%.

[0037] When a homogeneous mixture is again obtained, at least one photopolymerization kinetics regulator and at least one photoinitiator agent are added and mixed with the resins and the filler(s). For example, the weight concentration of the photopolymerization kinetics regulator(s) is less than or equal to 1% in the final mixture. For example, the photopolymerization kinetics regulator is phenothiazine. For example, the weight concentration of the photoinitiator(s) is less than or equal to 5% in the final mixture. For example, the photoinitiator(s) is bis(4,4'-(C10-C13)-alkylphenyl)-iodonium hexafluo-roantimonat, or another cationic photoinitiator

[0038] At least one rheological agent is optionally added at a rate of approximately 1% by weight in the final mixture. For example, this rheological agent is fumed silica.

[0039] Furthermore, a sheet of electrically conductive material in a coil is unwound. For example, the sheet of electrically conductive material is a sheet of a flexible copper alloy with a thickness of 35 micrometers.

[0040] The sheet of electrically conductive material is continuously coated, on at least a portion of the surface of one of its main faces, with the previously obtained mixture. The sheet of electrically conductive material is thus at least partly covered with a layer of electrically insulating material. For example, the thickness of the layer of electrically insulating material is between 50 and 350 micrometers. For example, this thickness is close to 100 micrometers so as to form a support and a dielectric substrate suitable for supporting patterns subsequently made in the sheet of electrically conductive material.

[0041] For example, the coating of the sheet of electrically conductive material is carried out using a “slot die” type technology.

[0042] Still continuously, the layer of electrically insulating material which at least partially coats the sheet of electrically conductive material is exposed to ultraviolet light. For example, this ultraviolet light is emitted by light-emitting diodes or by a mercury vapor lamp. For example, the layer of electrically insulating material is continuously exposed for 10 seconds with an energy of 100 mW per square centimeter, to light having a wavelength close to 385 nm, emitted by light-emitting diodes. According to another example, the layer of electrically insulating material is continuously exposed for 60 seconds to a light emitted by a mercury vapor lamp, with a power of 100 milliwatts per square centimeter.

[0043] The layer of electrically insulating material, after this photopolymerization step, is maintained at room temperature for a minimum period of between 1 hour and 12 hours (the waiting time allows the polymerization to be finalized - this time can be more or less shortened, for example, by using a higher temperature during this rest phase, or by increasing the temperature during exposure to UV radiation) before being used for the following steps of the process.

[0044] It is important that the layer of electrically insulating material obtained at the end of the steps described above has properties suitable for its use as a dielectric substrate in a continuous manufacturing process for printed circuits.

[0045] For example, this layer of electrically insulating material must have the following properties: - elongation: 1.9%, - tensile force: 55 MPa, - good flexibility and not being brittle, - good resistance to chemical baths quantified by a mass differential of the material of less than 1% after 5 minutes of immersion in the bath followed by 4 hours of drying, - good punching quality (limiting the quantity of dust generated during cutting and leaving perfectly defined holes).

[0046] The values ​​mentioned above are those corresponding to those measured in the example described here. They give an order of magnitude from which variations can be observed and tolerated.

[0047] According to an example of implementation of the method according to the invention, the sheet of electrically conductive material coated with the electrically insulating layer obtained as indicated above, can undergo steps adapted to produce, in the sheet of electrically conductive material, patterns such as conductive tracks, electrical contacts, electrodes, etc.

[0048] For example, drive holes are punched on the edges of a strip formed from the sheet of electrically conductive material and photolithography operations are implemented to define the patterns in the sheet of electrically conductive material. Operations of depositing one or more metals on at least some of these patterns may also be implemented. Operations of depositing one or more protective layers on at least some of these patterns may also be implemented.

Claims

Claims

1. A method of manufacturing a printed circuit, comprising the operations of: - continuously providing a sheet of electrically conductive material (D, - continuously coating at least one layer of electrically insulating material (2) on at least one area of ​​the surface of one of the faces of the sheet of electrically conductive material (1), this electrically insulating material (2) comprising at least one epoxy resin, - continuously photopolymerizing at least certain regions of the epoxy resin under UV radiation, and - producing at least one pattern by photolithography in the sheet of electrically conductive material (1), this pattern being supported by said photopolymerized epoxy resin.

2. The method of claim 1, wherein the pattern is an electrode configured for use in a medical biology testing device.

3. Method according to claim 1 or 2, in which the epoxy resin(s) represent by dry weight of the layer of insulating material between 30% and 70% coated on one of the faces of the sheet of electrically conductive material (1).

4. Method according to one of the preceding claims, in which the layer of insulating material (2) coated on one of the faces of the sheet of electrically conductive material (1) comprises between 10% and 70% by dry weight of a mineral filler.

5. A method according to claim 4, wherein the mineral filler consists essentially of glass microspheres (7).

6. Method according to one of the preceding claims, in which the epoxy resin(s) are chosen from UV-polymerizable cycloaliphatic epoxy resins.

7. Method according to the preceding claim, in which the epoxy resin(s) are chosen from the following molecules: 3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate.

8. Method according to one of the preceding claims, in which the layer of electrically insulating material comprises at least one photoinitiator.

9. The method of claim 8, wherein the photoinitiator is a cationic photoinitiator.

10. The method of claim 9, wherein the photoinitiator is bis(4,4'-(C10-C13)-alkylphenyl)-iodonium hexafluoroantimonate, or propylene carbonate.

11. Method according to one of the preceding claims, in which the layer of electrically insulating material (2) comprises a regulator of the kinetics of photopolymerization.

12. The method of claim 11, wherein the photopolymerization kinetics regulator is phenothiazine.

13. Method according to one of the preceding claims, in which the layer of electrically insulating material (2) comprises at least one rheological agent.

14. Method according to claim 13, in which the rheological agent(s) are chosen from the following molecules: silicones, siloxanes, silica fume.

15. Method according to one of the preceding claims, in which the layer of electrically insulating material (2) has a thickness of between 50 and 350 micrometers.

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