Printed circuit board manufacturing process
The method addresses interface defects in multilayer circuit boards by creating a continuous interface with photopolymerized epoxy resin, enhancing measurement stability and reproducibility in medical devices.
Patent Information
- Application Number
- FR2023010289
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-09-27
- Publication Date
- 2025-12-12
- Estimated Expiration
- 2043-09-27
AI Technical Summary
Multilayer printed circuit boards exhibit defects at the interface between conductive and insulating layers, leading to uncontrolled etching and unstable, non-reproducible measurements in medical biology testing devices due to openings at these interfaces.
A method involving continuous coating of a photopolymerizable epoxy resin on the conductive material, followed by photopolymerization to create a continuous interface, ensuring no openings or defects between layers, thereby stabilizing and reproducing measurements.
The method ensures stable and reliable electrochemical measurements by preventing fluid penetration between layers, allowing for faster and more precise manufacturing of electrodes for medical biology devices.
Smart Images
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Abstract
Description
Title of the invention: Method for manufacturing printed circuit boards technical field
[0001] The invention relates to the field of printed circuits and printed circuit board manufacturing processes. For example, it relates to the field of flexible printed circuits for medical biology examination devices. State of the art
[0002] Some printed circuit boards 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 create conductive patterns (conductive traces, 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 allow the sheet of electrically conductive material to adhere to the layer of electrically insulating material. For example, the layer of adhesive material is made of an epoxy resin.
[0004] Multilayer structures thus obtained by laminating together a sheet of electrically conductive material and a layer of electrically insulating material (optionally with a layer of adhesive material between the two) exhibit defects at the interface between the layers. An illustration of this type of defect is given in [Fig. 1]. In [Fig. 1], a pattern 1 can be seen, etched into a sheet of copper alloy laminated onto 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 laminating the sheet of electrically conductive material and the layer of electrically insulating material and etching patterns 1 into the sheet of electrically conductive material, the holes and / or channels 3 form openings 4 at the edges of the patterns 1.More specifically, these openings 4 can form entry points for etching solutions used to create 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. at the periphery of the patterns 1 engraved in the sheet of electrically conductive material. This is illustrated by [Fig.2] on which we can see that an opening 4, at the edge of the pattern 1, at the interface between the sheet of electrically conductive material and the layer of dielectric material 2, is the origin of the engraving 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 lead to many disadvantages.
[0006] This is particularly the case when these multilayer structures are used to manufacture electrodes for medical biology testing devices, and especially electrodes for point-of-care (POC) devices. These electrodes are used to detect one or more molecules in human fluids and, if necessary, to measure the respective concentration(s) of these molecules. Detection, and the possible concentration measurement, are then carried out electrochemically by immersing one or more electrodes made from these multilayer structures in the fluids in question. These fluids may contain one or more reagents designed to react with these electrodes to provide an electrical measurement representing information on their nature and / or composition.
[0007] However, it has been observed that the measurements taken at the electrodes mentioned above are not always stable and / or reproducible. The applicant investigated the cause and 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 overcome at least partially this drawback.
[0009] To this end, a method for manufacturing a printed circuit board is proposed. This printed circuit board 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 following operations: - to continuously supply a sheet of electrically conductive material, this sheet comprising two main faces, - to continuously coat 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 those areas where patterns will be created) of the epoxy resin; and - to produce at least one pattern by photolithography in the sheet of electrically conductive material, this pattern being supported only by said photopolymerized epoxy resin.
[0011] Thus, thanks to the process according to the invention, a layer of electrically insulating material is directly applied by coating to one of the faces of the sheet of electrically conductive material. The layer of electrically insulating material is therefore applied in liquid or paste form so as to form a continuous interface between this layer and the face of the sheet of electrically conductive material to which the layer of electrically insulating material is applied. In other words, the layer of electrically insulating material conforms to and fills any surface irregularities of the sheet of electrically conductive material. Thus, when engraving patterns in the sheet of electrically conductive material, the engraving 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 taken from the electrode(s) etched into 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 to which it is applied. In other words, at the micrometer or a few micrometer scale, or even at a smaller (nanometer) 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 are no holes, channels, openings, cavities, or other such defects 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 seep between the layer of insulating material and the sheet of electrically conductive material. Only the interactions between these substances and the electrode on one or more well-defined surfaces of the electrode are taken into account. This results in more stable, reliable, and reproducible measurements.
[0014] Furthermore, the implementation of coating and photopolymerization operations on the resin allows the process according to the invention to be carried out continuously, and in a fast. The process therefore allows for relatively fast and attractive manufacturing speeds.
[0015] The method according to the invention further comprises one of the following features, considered in isolation and independently of each other, or in combination with one or more others:
[0016] - the motif is an electrode configured for use in an examination device of 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 with electrically conductive material;
[0018] - the layer of insulating material coated on one face of the material sheet electrically conductive includes 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 cyclo-aliphatic 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 hexafluoroantimonate, propylene carbonate, and other cationic photoinitiator;
[0021] - the layer of electrically insulating material includes 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 pyrogenated silicas (or their derivatives);
[0023] - the layer of electrically insulating material has a thickness between 50 and 350 micrometers. Brief description of the figures
[0024] Other aspects, objectives and advantages of the invention will become apparent from the following detailed description and from the accompanying figures, given by way of non-limiting examples:
[0025] - [Fig.1] is a scanning electron microscope image of the interface between the layer of insulating material and the sheet of electrically conductive material, in a multilayer structure of the prior art,
[0026] - [Fig.2] is also an image obtained by scanning electron microscopy of a cross-section at the interface between the insulating material layer and the electrically conductive material sheet, in a prior art multilayer structure;
[0027] - [Fig.3] is a scanning electron microscope image of the interface between the layer of insulating material and the sheet of electrically charged material, in a multilayer structure according to the invention; and
[0028] - [Fig.4] is also an image obtained by scanning electron microscopy of a cross-section at the interface between the insulating material layer and the electrically conductive material sheet, 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 adapted to other applications.
[0030] According to this process, an electrically insulating material is prepared in a sufficiently liquid form to be able to be coated onto a sheet of conductive material.
[0031] Advantageously, the electrically insulating material has a viscosity on the order of IPa.s.
[0032] According to the invention, this electrically insulating material is a photopolymerizable epoxy resin under UV radiation. To this end, a homogeneous mixture of liquid monomers and / or prepolymers is prepared in the absence of UV radiation.
[0033] These liquid monomers and / or prepolymers are epoxy resins. They are selected from the following prepolymers or monomers: 3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate, or other UV-curable 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 prepared. The weight concentration of the resins is adjusted to be between 30 and 90% in the final mixture (comprising the epoxy resins, fillers, and other additives).
[0035] When a homogeneous mixture is obtained from the epoxy resins, fillers or reinforcing additives are added to this mixture. For example, these fillers are added gradually to the mixture of epoxy resins in a shear mixer until a homogeneous mixture is again obtained.
[0036] The weight concentration of the filler(s) is adjusted to be between 30 and 90% in the final mixture. For example, these fillers are mineral fillers. For example, a mineral filler consisting essentially of... Glass microspheres 7 are 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 obtained again, at least one photopolymerization kinetics regulator and at least one photoinitiator 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 hexafluorantimonate, or another cationic photoinitiator.
[0038] At least one rheological agent is optionally added at a level 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 unrolled. 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 principal faces, with the previously obtained mixture. The sheet of electrically conductive material is thus at least partially 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 with electrically conductive material is carried out using a slot die type technology.
[0042] Continuously, the layer of electrically insulating material that 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 kept 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 resting phase, or by providing heat 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 implementation 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 strength: 55 MPa, - good flexibility and not being brittle - good resistance to chemical baths, quantified by a mass difference of less than 1% of the material after immersion for 5 minutes in the bath followed by drying for 4 hours, - good punching quality (limiting the amount 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 process according to the invention, the sheet of electrically conductive material coated with the electrically insulating layer obtained as indicated above, can undergo adapted steps to create, in the sheet of electrically conductive material, patterns such as conductive tracks, electrical contacts, electrodes, etc.
[0048] For example, drive holes are punched along the edges of a strip formed from the sheet of electrically conductive material, and photolithography operations are performed to define the patterns in the sheet of electrically conductive material. Operations to deposit one or more metals onto at least some of these patterns may also optionally be performed. Operations to deposit one or more protective layers onto at least some of these patterns may also optionally be performed.
Claims
Demands
1. A method for manufacturing a printed circuit board, comprising the operations of: - continuously supplying 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 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 said photopolymerized epoxy resin.
2. A method according to claim 1, wherein the motif is an electrode configured for use in a medical biology examination device.
3. Method according to claim 1 or 2, wherein the epoxy resin(s) represent by dry weight of the insulating material layer between 30% and 70% coated on one face of the sheet of electrically conductive material (1).
4. A method according to any one of the preceding claims, wherein the layer of insulating material (2) coated on one face of the sheet of electrically conductive material (1) comprises between 10% and 70% by dry weight of a mineral filler.
5. Method according to claim 4, wherein the mineral filler is essentially made up of glass microspheres (7).
6. A method according to any one of the preceding claims, wherein the epoxy resin(s) are selected from UV-curable cycloaliphatic epoxy resins.
7. A process according to the preceding claim, wherein the epoxy resin(s) are selected from the following molecules: 3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate.
8. A method according to any one of the preceding claims, wherein the layer of electrically insulating material comprises at least one photoinitiator.
9. A method according to claim 8, wherein the photoinitiator is a cationic photoinitiator.
10. The process according to claim 9, wherein the photoinitiator is bis(4,4'-(C10-C13)-alkylphenyl)-iodonium hexafluoroantimonate, or propylene carbonate.
11. A method according to any one of the preceding claims, wherein the layer of electrically insulating material (2) comprises a regulator of the kinetics of the photopolymerization.
12. A method according to claim 11, wherein the regulator of the photopolymerization kinetics is phenothiazine.
13. A method according to any one of the preceding claims, wherein the layer of electrically insulating material (2) comprises at least one rheological agent.
14. A process according to claim 13, wherein the rheological agent(s) are selected from the following molecules: silicones, siloxanes, silica fume.
15. A method according to any one of the preceding claims, wherein the layer of electrically insulating material (2) has a thickness of between 50 and 350 micrometers.