A paper board for printed circuits and method of preparing the same

Abstract

A method of preparing a flexible board suitable for electroplating wherein the method comprises bringing a paper material into contact with a solution of benzoxazine monomers and polymerize the monomers. A board obtainable through the method and furthermore an electrical device comprising the board.

Description

[0001] METHOD OF PREPARING A PAPER BOARD FOR PRINTED CIRCUITS

[0002] Technical field

[0003] The present invention is within the field of preparing paper-based, or cellulose-based, printed circuit boards. In particular the present invention relates to a method of preparing paper-based, or cellulose-based, boards and printed circuit boards.

[0004] Background

[0005] An important type of composites are resins reinforced by fibrous materials. The fibrous materials are typically spread glass fibre tows or webs. In the manufacturing of composites the fibres are impregnated with the resin and when the resin is cured, that is, after a solidification process where the fluid resin monomer composition is transformed into a structurally strong solid, a reinforced composite is formed. Composites are used to create structures for constructions. Composites are also used to create substrates for electronics circuit boards, so called printed circuit boards, PCBs. PCBs are typically flat boards of rigid glass fibre reinforced epoxy resins with flame retarding additives added. On top of these composites, metal traces are patterned to create conducting paths and contact electrodes for mounting components in the board. Circuit boards may consist of single- or multiple layers of conducting traces and components. In most electronic products, PCBs consists of two or more layers of patterned conducting traces. The different layers in multilayer PCBs are connected by so-called vertical interconnect access (’’vias”). These are typically holes through layers of laminated circuit board layers that are plated on the inside with metal to create conducting paths between conducting traces in different layers. Devices comprising circuit boards are complex multi-material and multi-component structures with materials and joints designed to be stable and to tolerate harsh conditions during manufacturing processing and use. This structural and chemical stability also makes circuit boards difficult to recycle as it is difficult to separate materials and components. Therefore, it has been a strive in the electronics industry to find alternatives to the commonly used PCB-materials in order to comply to increasing demands on recyclability at reasonable costs. One approach has been to replace fiber glass with cellulose fibressuch as paper. Products made from cellulose fibres are amenable for recycling and recycling of cellulose fibres is done at large industrial scale today.

[0006] Devices on circuit boards are sensitive to dimensional variations of the circuit board materials. Dimensional variations can be caused by variations in temperature (thermal expansion) and variations in the moisture content (hygroexpansion). Circuit board materials are often selected and composed so as to match its thermal expansion coefficient to that of copper as closely as possible, since differences in thermal expansion coefficient can cause mechanical stress or mechanical failure of the copper traces. Via-interconnects are sensitive to the swelling in the thickness direction (z-direction) of board materials as expansion can cause rupture of the via-channel between the layers.

[0007] Cellulose materials or paper materials tend to swell in response to water uptake which stem from the strong interactions between cellulose and water. Even if the problem with swelling is seen in single-layer structures it is most pronounced in multilayered structures or circuit boards. There are for example circuit boards materials where paper boards, or cellulose boards, are reinforced by being sandwiched between glass-fibres composites to limit expansion in the board plane. This type of reinforced paper circuit boards is called CEM- 1. Due to lack of reinforcement in the z-direction, this type of circuit boards is not suited for multilayer structures with vias.

[0008] Fibres pre-impregnated with partially polymerized resin, so-called pre-pregs, are used to produce laminate structures in circuit boards. Hot pressing a pre-preg to a copper foil produces copper clad lamintes, and hot-pressing pre-pregs sandwiched between circuit boards produces multilayer structures. Most composites and circuit boards are manufactured from epoxy resins today. One drawback of partially polymerized epoxy-based resins is that that they can be stored, handled and transported for a limited period of time at ambient temperature. When stored for prolonged periods of time at ambient temperature, the thermal polymerization will proceed, leading to premature curing and gradual changes of the resin properties during handling and manufacturing. For this reason, epoxy-based prepregs are typically stored and transported at low temperatures. This requirement for transport in a cold chain and cold storage adds costs and complexity to the manufacturing of epoxy-based composites and circuit board materials.There is a demand for PCBs with paper-like properties, in particular highly flexible PCBs, not at least in the area of printed electronics. Some examples are labels, flexible badges, devices for everyday appliances, devices for Internet of Things, flexible sensors, flexible antennas, wearable devices, devices for med-tech (i.e. smart diapers or flexible biosensors) and single use tickets. Such mass-produced devices are typically and preferably produced in so called roll-to-roll processes. A high degree of flexibility, or bendability, is required for the materials used in a roll-to-roll process and hence, there is a need for flexible materials that could form a flexible PCB. For these types of application long term stability may not be a major issue and typically the structure is not complicated (single layer or a few layers PCB's). Therefore, some water uptake of the final PCB may be accepted, however the water uptake of for example an unimpregnated blotting paper would be unacceptably high. On the other hand, the environmental requirements are high on such mass products, both with regards to chemicals in the product and recyclability. A further challenge with a PCB comprising one or more paperlike board is the board’s ability to withstand the PCB manufacturing process, for example electroplating.SUMMARY OF THE INVENTION

[0009] One objective of the invention is therefore to provide a method of preparing a board suitable for printed circuit processes and wherein the obtained board still has paper-like properties such as bendable or foldable and porous. This would allow the formation of bendable or foldable PCB, and at the same time the porosity facilitates disintegration upon treatment with reagents commonly used in paper recycling.

[0010] Another objective of the invention is to modify paper material so that the uptake of water is limited and making the paper material suitable for PCB applications and tolerant to common PCB-manufacturing conditions, and still enable disintegration upon treatment with reagents commonly used in paper recycling. Yet another objective with the invention is to facilitate separation of materials and components in circuit board products to reduce the environmental impact of electronic products.

[0011] A further objective of the invention is to provide a board or a pre-preg, and a method of preparing a board or pre-preg, having characteristics suitable for roll-to-roll manufacturing or treatment conditions. Such characteristics include sufficient bendability or flexibility to allow the board to deform during roll-to-roll processing conditions without adversely affecting its structural integrity and / or surface properties.

[0012] The main aspect of the present invention is therefore a method of preparing a flexible board suitable for printed circuit board processes wherein the method comprises:

[0013] a. Providing a paper material and a solution comprising benzoxazine monomers, wherein the concentration of the benzoxazine monomers is 5-50wt%;

[0014] b. Bringing the paper material into contact with the solution to impregnate the paper material with the benzoxazine monomers; and c. Polymerizing the monomers. A second aspect of the present invention is a method of preparing a flexible intermediate board or pre-preg suitable for electroplating wherein the method comprises:a. Providing a paper material and a solution comprising benzoxazine monomers, wherein the concentration of the benzoxazine monomers is 5-50wt%;

[0015] b. Bringing the paper material into contact with the solution to impregnate the paper material with the benzoxazine monomers; and c. Partially polymerizing the monomers.

[0016] A third aspect of the present invention is a method of preparing a flexible electroplated board comprising the steps of:

[0017] a. Preparing a flexible board according the present invention or a flexible intermediate board or pre-preg according to the present invention; and b. Laminating a copper layer or copper foil on top of the board or pre-preg. A fourth aspect of the present invention is a flexible board suitable for printed circuits board manufacturing made of a composite material comprising a paper material, or paper-based material, impregnated with a resin wherein the resin is a polymer obtainable from benzoxazine monomers, and wherein the resin to paper weight ratio is 0.10 to 0.60.

[0018] In a fifth aspect the present invention relates to a printed circuit board comprising the flexible board according to the present invention.

[0019] In a sixth aspect the present invention relates to an intermediate board or a prepreg comprising a paper material and a non-cured resin, wherein the non-cured resin comprises partly polymerized benzoxazine monomers, and wherein the noncured resin to paper weight ratio is 0.10 to 0.60.

[0020] In a seventh aspect the present invention relates to a laminated board comprising the flexible board according to the present invention with a laminated layer of copper on top of said board.

[0021] In an eighth aspect the present invention relates to a device comprising the flexible board according to the present invention.

[0022] BRIEF DESCRIPTION OF THE FIGURES

[0023] Figure 1, flow chart of the method according to the present invention.Figure 2, (a) The PBz grammage in the paper material vs the concentration of the impregnation solution, (b) The resin / paper material ratio vs the concentration of the impregnation solution.

[0024] Figure 3, (a) the water uptake vs the concentration of the impregnation solution, (b) the water uptake vs the PBz grammage in the board and (c) the water uptake vs the resin / paper weight ratio.

[0025] Figure 4, (a) and (b) the water uptake vs the resin / paper weight ratio for the different paper materials.

[0026] Figure 5, The decrease in water uptake of paper after impregnation with the resin vs the air permeability of the pure paper material.

[0027] Figure 6, (a) The acid uptake vs the concentration of the impregnation solution, (b) the acid uptake vs the PBz grammage in the paper (board) and (c) the acid uptake vs the Resin / Paper weight ratio.

[0028] Figure 7, (a) The mass uptake of the basic or acidic solution vs the PBz grammage in the paper, (b) mass uptake vs the resin / paper ratio.

[0029] Figure 8, (a) The water uptake and coarse Reject% vs the resin / paper ratio for the PBz papers based on blotting paper, (b) The mass uptake by acid immersion and coarse Reject% vs the resin / paper ratio for the PBz papers based on blotting paper. Figure 9, The Scanning Electron Microscope images for the Blotting paper impregnated and polymerized with the BPA-Bz on different impregnation solution concentrations;resin / paper ratios : (a) 0%w / w ; 0. (b) l%w / w ; 0.014 . (c) 33%w / w ; 0.32 . (d) 60%w / w ; 0.72 . (e) 100%w / w (melt impregnated) ; 2.19 .

[0030] Figure 10, The Scanning Electron Microscope images for the Alstrom filter paper impregnated and polymerized with the BPA-Bz on different impregnation solution concentrations; resin / paper ratios : (a) 0%w / w ; 0. (b) l%w / w ; 0.077 . (c) 33%w / w ; 0.32 . (d) 60%w / w ; 0.78 .

[0031] Figure 11, The Scanning Electron Microscope images for the “kraft’ paper impregnated and polymerized with the BPA-Bz on different impregnation solution concentrations; resin / paper ratios : (a) 0%w / w ; 0. (b) l%w / w ; 0.04 . (c) 33%w / w ; 0.11 . (d) 60%w / w ; 0.41.Figure 12, The air permeability (filled symbols) and the Oil absorbency (open symbols), as measured from the Oil Cobb test, of the paper composites plotted against the resin / paper ratio.

[0032] Figure 13, The Oil absorbency from the Oil Cobb test plotted against the air permeability of the paper composites.

[0033] Figure 14, The relative air permeability (air permeability of the impregnated paper composite / air permeability of the pristine paper) plotted against the resin / paper ratio for the paper composites.

[0034] Figure 15, The relative oil absorbency from the Oil Cobb test (oil absorbency of the impregnated paper / oil absorbency of the pristine paper) plotted against the resin / paper ratio for the paper composites.

[0035] Figure 16, The relative oil absorbency from the Oil Cobb test (oil absorbency of the impregnated paper / oil absorbency of the pristine paper) plotted against the relative air permeability (air permeability of the impregnated paper / air permeability of the pristine paper) for the paper composites.

[0036] ITEMIZED EMBODIMENTS

[0037] In one embodiment of the present invention the benzoxazine monomers is one type of benzoxazine or a mixture of different benzoxazine monomers.

[0038] In another embodiment of the present invention the one type of benzoxazine monomer is selected from mono-, di- or polyfunctional benzoxazine monomer or wherein the mixture of different benzoxazine monomers comprises monofunctional benzoxazine monomers, di- or polyfunctional benzoxazine monomers.

[0039] In another embodiment of the present invention the benzoxazine monomers are synthesized from monofunctional phenols bearing a benzoyl alcohol group, difunctional phenols, such as bisphenol-a, diphenolic acid or phenolphthalein, polyfunctional phenol, such as diesters of diols with diphenolic acid.

[0040] In another embodiment of the present invention the resin to paper material weight ratio is 0.10 or higher, or 0.15 or higher, or 0.20 or higher, or 0.25 or higher, but preferably 0.55 or lower, or 0.450 or lower, or 0.30 or lower.In another embodiment of the present invention the board has an air permeability of at least 10 pm / Pas, preferably at least 20 pm / Pas, more preferably at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably at least 43.4 pm / Pas, more preferably at least 50 pm / Pas, more preferably at least 70.1 pm / Pas. In another embodiment of the present invention the board has a thickness of at least 0.01 mm, preferably at least 0.1mm but preferably not higher than 5 mm. In one embodiment according to any of the aspects the concentration of the benzoxazine monomers is at least 10wt%, preferably at least 20wt% but preferably not higher than 45wt%, preferably not higher than 40wt%, more preferably not higher than 35wt%.

[0041] In one embodiment according to any of the aspects the benzoxazine monomers is one type of benzoxazine or a mixture of different benzoxazine monomers.

[0042] In one embodiment according to any of the aspects the one type of benzoxazine monomer is selected from mono-, di- or polyfunctional benzoxazine monomer or wherein the mixture of different benzoxazine monomers comprises monofunctional benzoxazine monomers, di- or polyfunctional benzoxazine monomers.

[0043] In one embodiment according to any of the aspects the benzoxazine monomers are synthesized from monofunctional phenols bearing a benzoyl alcohol group, difunctional phenols, such as bisphenol-a, diphenolic acid or phenolphthalein, polyfunctional phenol, such as diesters of diols with diphenolic acid.

[0044] In one embodiment according to any of the aspects the paper material is brought into contact with the solution by dipping or submerging.

[0045] In one embodiment according to any of the aspects the polymerization is done during heating, preferably at a temperature of at least 100°C, preferably at least 150°C but preferably not higher than 250°C.

[0046] The method according to any of the preceding claims wherein the paper material has an air permeability of at least 10 pm / Pas, preferably at least 20 pm / Pas, more preferably at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably at least 44.7 pm / Pas, more preferably at least 50 pm / Pas but preferably not higher than 100 pm / Pas, more preferably not higher than 80 pm / Pas, more preferably not higher than 78.47 pm / Pas, more preferably not higher than

[0047] 60pm / Pas.The method according to any of the aspects wherein the pristine paper material has an oil absorbency (as derived from the Oil Cobb test) of at least 50g / m2, preferably at least 100g / m2, preferably at least 120g / m2.

[0048] In one embodiment according to any of the aspects the paper material is blotting paper.

[0049] In one embodiment according to any of the aspects the solvent is an aromatic hydrocarbon, preferably selected from benzyl acetone, toluene, naphthalene, xylene or a mixture of two or more thereof.

[0050] In one embodiment according to any of the aspects of the present invention the air permeability of the flexible board is not lower than 50% of the air permeability of the pristine paper material.

[0051] In another embodiment according to any of the aspects of the present invention the oil absorbency (as derived from the Oil Cobb test) of the flexible board is not lower than 50% of the oil absorbency (as derived from the Oil Cobb test) of the pristine paper material.

[0052] In yet another embodiment according to an aspect of the present invention the board is incorporated into a device, or electrical device. Worded differently, in another embodiment according to the present invention, a device, or electrical device, comprises the board. Accordingly, a benefit of an electrical device comprising the board of the present invention having increased recyclability, is the increased recyclability of the electrical device as a whole.

[0053] In one embodiment, the electrical device comprising the board according to the present invention is a lighting device, preferably a lighting device comprising LED arrays and / or interconnected LED arrays.

[0054] In one embodiment, the electrical device comprising the board according to the present invention is a functional tag, preferably a RFID tag, NFC tag, data logger, digital product passport module, pricing tag, hotel key card, and / or public transportation ticket card.

[0055] In one embodiment, the electrical device comprising the board according to the present invention is a functional flexible module, preferably a heater, energy harvesting device, and / or an energy storage device.In one embodiment, the electrical device comprising the board according to the present invention is a flexible power electronics, preferably comprising cabling. In one embodiment, the electrical device comprising the board according to the present invention is a functional flexible shielded module, preferably comprising coaxial cabling.

[0056] In one embodiment, the electrical device comprising the board according to the present invention is a sensor, preferably a temperature sensor and / or a humidity sensor.

[0057] In one embodiment, the electrical device comprising the board according to the present invention is an interactive interface, preferably a capacitive switch.

[0058] Accordingly, an electrical device comprising the board according to the present invention includes but is not limited to:

[0059] a. lighting devices, preferably lighting devices comprising LED arrays or interconnected LED arrays;

[0060] b. functional tags, preferably tags such as RFID tags, NFC tags, data loggers, digital product passport modules, pricing tags, hotel key cards, or public transportation ticket cards;

[0061] c. functional flexible modules, preferably modules such as heaters, energy harvesting devices, or energy storage devices;

[0062] d. flexible power electronics, preferably flexible power electronics comprising cabling;

[0063] e. functional flexible shielded modules, preferably modules comprising coaxial cabling;

[0064] f. sensors, preferably temperature sensors or humidity sensors; and / or g. interactive interfaces, preferably capacitive switches.

[0065] All embodiments may be combined with each other and are applicable to all aspects unless stated otherwise.

[0066] DETAILED DESCRIPTION OF THE INVENTION

[0067] In the present application the terms “impregnated paper”, ‘paper composite’ and “board” denotes the same thing and can be used interchangeably.In the present application the terms “non-impregnated paper”, ‘pristine paper’ and “paper material” denote the same thing and can be used interchangeably.

[0068] In the present application the terms “solution”, “mixture” and “composition” denote the same thing and can be used interchangeably.

[0069] In the present application the terms “paper”, “cellulose”, “paper-based”, “cellulose-based”, “paper material”, “cellulose material” denote the same thing and can be used interchangeably. It is understood that cellulose is the fundamental material from which paper is produced and that paper comprises predominantly cellulose fibers, although it may also comprise additional additives or constituents.

[0070] Accordingly, paper or paper material refers to an aggregation, sheet or web of cellulose or cellulose fibers derived from plant-based sources such as wood, cotton or straw.

[0071] In the present application “resin / paper ratio”, “resin / cellulose ratio”, “resin / paper” and “resin / cellulose” denote the same thing and can be used interchangeably. In the present application the term “board” and “pre-preg” are to be understood as as paper material that has been brought into contact with the solution comprising benzoxazine monomers according to the present invention, which has then respectively fully or partially cured.

[0072] The aim of the invention is to provide a method for producing a board from a paper material that can withstand the processes of depositing (i.e. printing) a circuit and at same time the board should retain some of the properties of the paper material such as the flexibility and the recyclability of the paper. By using a paper material, both the recycling of the board and the manufacturing of printed circuit boards are possible.

[0073] Circuit board materials are part of multimaterial and multicomponent structures in electronic devices. One objective with the invention is to facilitate separation of the materials and components in a circuit boards, electronic components, metal traces, interconnect adhesives, as well as of the circuit board material itself. Ideally, the circuit board material should disintegrate upon treatments with commonly used recycling reagents so that components and materials can be separated and collected for recycling in subsequent recycling process steps. The paper-based circuit board itself should disintegrate into a recyclable form and ideally, the paper,or cellulose, should form a pulp from which new paper can be manufactured. Here, the effects of treating the impregnated papers with alkaline solutions similar to those used in paper recycling was evaluated by characterizing the material resulting from the treatments. The materials produced by the recycling emulating treatment are of four types, pulp, fine particles coarse fragments, and dissolved materials. The weight fraction of the coarse fragments, the so-called coarse reject, and the presence of pulp and fine particles are used to evaluate the effects of the treatment for papers manufactured with different degrees of benzoxazine impregnation. Ideally, the treatment product is pulp from which recycled paper and circuit boards can be manufactured to achieve circularity with a low energy and environmental impact. Fragmentation of the circuit board into fine particles is also considered a positive effect, as the fragmentation simplifies separation of other materials of the circuit boards, such as metal traces, assembly adhesives and the electronic component mounted on the circuit board. According to UNI 11743 2019 standard for analysis of recyclability level of paper-based, or cellulose-based, materials a coarse reject level of not more than 40% is acceptable and categorized as recyclable.

[0074] Even if a as low water uptake as possible is wanted a water uptake of not more than 60% has been found to be acceptable for many applications. The board has to withstand the PCB process, in particular have a low acid uptake, which in turn is a prerequisite for the board being possible to withstand the conditions for electroplating. This can be referred to as the boards “PCB processability”. The degree of impregnation affects the board’s ability to take up water where a higher degree, i.e. higher resin to paper material weight ratio, reduces the water uptake. At the same time the paper material cannot be treated to such a degree that the board is not recyclable.

[0075] As is shown herein, the aim is achieved by a method of impregnating the paper material with benzoxazine monomers using a solution and polymerizing said monomers. The concentration of benzoxazine monomers in the solution affects the degree of impregnation, i.e. resin to paper material weight ratio, and thereby the board’s ability to take up water, PCB processability and the boards mechanical properties.

[0076] What the present inventors have shown is that a concentration of benzoxazine monomers of 5-50wt% in the solution results in a board having paper-like properties and at the same surprisingly can withstand the processing associatedwith manufacturing a PCB. The water uptake of the board, and hence the final PCB product, is sufficient for many applications.

[0077] The air permeability of the obtained board should not be reduced by more than 15% in comparison with the starting paper material. Said concentration preserves more or less the porosity of the paper material enabling transport of alkaline reagents into the structure. This in turn facilitates disintegration of the composite to smaller fragments facilitating separation of materials and components for recycling.

[0078] A maintained high air permeability, as compared to the air permeability of the paper material utilized in the impregnation process is an indication of a high porosity of the board and that the paper material has maintained its paper-like properties through the process. The air permeability of the obtained board should not be reduced by more than 50%, more preferably not more than 40%, more preferably not more than 30%, more preferably not more than 20%, more preferably not more thanl5% as compared to the starting paper material.

[0079] According to one embodiment of the invention the board has an air permeability of at least 10 pm / Pas, preferably at least 20 pm / Pas, more preferably at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably 43.4 pm / Pas, more preferably 50 pm / Pas, even more perferably at least 70.1 pm / Pas.

[0080] The paper-like properties, as regards to mechanical properties, of the board is further confirmed by bendability tests. It is shown that using a solution having a concentration below 50wt% and preferably below 33wt% results in a flexible or highly flexible board.

[0081] The inventors of the present invention have further discovered that a board produced with a solution having a concentration of benzoxazine monomers above 50% results in a board having increased rigidity. While such boards may be structurally strong, they also display adverse characteristics, including brittleness and tendency to crack during bendability tests. Consequently, rendering such boards unsuitable for manufacturing or processing by methods requiring flexibility of the material to be processed, such as roll-to-roll process.

[0082] What the present inventors have shown is that when the concentration is at least 10wt%, preferably at least 15wt%, but preferably not higher than 45wt%, preferably not higher than 40wt%, more preferably not higher than 35wt% results in an optimum regarding printability, recyclability and paper-like properties.Benzoxazines are compounds of benzene ring fused with an oxazine ring where the different isomers depend on the relative position of the nitrogen and the oxygen in the oxazine ring. Benzoxazines are manufactured by reacting phenols with amines formaldehyde. The phenols can be monofunctional-, difunctional- or polyfunctional phenols and the amine can be a monoamine resulting in mono-, di- and polyfunctional benzoxazine monomers respectively. If a diamine is used instead di-or polyfunctional benzoxazines are obtained. With a monofunctional phenol is meant a molecule having a hydroxyl group on an aromatic ring. With a difunctional phenol is meant a molecules having two hydroxyl-substituted aromatic rings. A polyphenol is a molecule with more than two aromatic rings each bearing a hydroxyl group. In the phenols, the ortho-positions in relation to the hydroxyl group is preferably unsubstituted i.e. bears no other groups than hydrogen atoms. Commercially available benzoxazines today are commonly solids at ambient temperature and need to be processed as melts or solutions. One example of a suitable commercially available benzoxazine is the dibenzoxazine of bisphenol-a (BPA-Bz) . The possibility of using a commercial benzoxazine monomer to impregnate cellulose paper material to produce a board that can be processed in typical PCB-manufacturing processes and disintegrate for recycling is an advantage of this invention.

[0083] Benzoxazines that are liquid at ambient temperature represents an alternative to the solid benzoxazines. One such monomer is 4HBnzaDMPDA manufactured by reacting dimethyl propane diamine (DMPDA) with 4-hydroxybenzoyl alcohol and para formaldehyde. This molecule can be manufactured from low-cost raw materials available in bulk amounts to produce the resin monomer with simple purification methods. One practical advantage with this benzoxazines is that it has a slight solubility in water. This solubility is not high enough for water-based processing, but the water solubility simplifies cleaning of coating and impregnation tools after contact with the monomer. Impregnation of reinforcing materials with this room temperature fluid benzoxazine, and the simplicity of cleaning processing tools is one of the advantages with the invention.

[0084] One aspect of this liquid benzoxazine and other liquid benzoxazines is that these are typically monofunctional benzoxazines while many commonly used benzoxazines are difunctional. Benzoxazine ring opening coupling polymerization has many advantages, but one issue is that the degree of polymerization is generally quite low. Polymerization of monofunctional benzoxazines thus produceslow molecular weight polymers and oligomers with a short chain length. For this reason, di- and polyfunctional benzoxazines are commonly used, since they form cross-linked network even at a low degree of polymerization. Preferentially, the liquid monofunctional benzoxazine monomers should preferentially be mixed with di- or polyfunctional benzoxazines to ensure that the cross-linked thermoset network is formed upon polymerization. It is therefore important that difunctional benzoxazines can be mixed into the liquid benzoxazines while maintaining the fluidity of the mixture or solution. The benzoxazine monomer is preferably based on or obtained from benzoyl alcohol, bisphenol A, diphenolic acid, or phenolphthalein reagents.

[0085] Paper materials suitable for the inventive method to produce the board according to the invention should have a high degree of porosity, for which air permeability is an appropriate characterization. This to ensure sufficient and efficient impregnation, and the porosity of such paper materials enables efficient degradation allowing degradation solvents and reagents to penetrate the board. According to the invention the paper material should before impregnation have an air permeability of at least 10 pm / Pas, preferably at least 20 pm / Pas, more preferably at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably at least 44.7 pm / Pas, more preferably at least 50 pm / Pas but preferably less than 120pm / Pas. Such paper materials are readily available and provided as for example highly absorbing materials, filter materials or papers designed for impregnation.

[0086] Commercially available suitable paper materials include, but is not limited to: blotting paper, filter paper such as ‘Munktell’ from Alstrom Munksjo (the company Alstrom Munksjo went through a company split or demerger, resulting in two companies Alstrom and Munksjo, the relevant filter paper may, currently as of the year 2026, be purchased from the Alstrom brand), layered toilet paper, impregnation basis paper such as ‘Guaflex’ from Fedrigoni, absorbent papers, such as ‘Wettex’ from Freudenberg, papers manufactured from recycled or waste materials, such as ‘Elephant POOPOOPAPER’ from the Poopoopaper company or ‘Cyclus Offset’ from Antalis. In the investigations performed by the inventors blotting paper has been used as a model system and the results have been verified with other paper materials in the group of paper materials with high air permeability. The results have been compared with the results using paper materials with less porosity (lower air permeability) such as kraft paper and coated paper.The paper material should have a sufficiently large thickness to provide mechanical stability of the board but to ensure a homogeneous impregnation of the paper material the thickness should not be too large. Therefore, the thickness is at least 0.01 mm, preferably at least 0.1mm but preferably not higher than 5 mm. The grammage of the paper material is preferably at least 25g / m2, preferably at least 50g / m2. Allowing such thickness and grammage enables the use of commonly produced paper material to produce boards for PCB manufacturing.

[0087] The board suitable for printed circuits board manufacturing obtained by the present invention is made of a composite material comprising a paper material impregnated with a resin wherein the resin to paper material weight ratio is 0.10 to 0.60. The resin is a benzoxazine based resin, meaning that resin is a polymer obtainable from benzoxazine monomers.

[0088] According to embodiments of the invention the benzoxazine monomers is one type of benzoxazine or a mixture of different benzoxazine monomers and may be mono-, di- or polyfunctional benzoxazine monomer. If a mixture of different benzoxazine monomers is used, the mixture may comprises monofunctional benzoxazine monomers, di- or polyfunctional benzoxazine monomers but preferably the mixture comprises di- or polyfunctional monomers.

[0089] According to embodiments of the invention the benzoxazine monomers have been synthesized from monofunctional phenols bearing a benzoyl alcohol group, difunctional phenols, such as bisphenol-a, diphenolic acid or phenolphthalein, polyfunctional phenol, such as diesters of diols with diphenolic acid.

[0090] What the present inventors have shown herein is that the board according to the present invention may be treated so that the paper material may be turned into a pulp after repulping. This is a result of the resin to paper material weight ratio, degree of impregnation, obtained when using a solution having a concentration of 5-50wt%. At low degree and no impregnation, a pulp is formed after repulping. At intermediate degrees of impregnation, a pulp may be formed after repulping and fine solid particles are formed from the resin. At a high degree of impregnation, the composite papers do not disintegrate but remain mainly as large fragments, coarse reject. The fine particles resulting from the papers with a high degree of impregnation cannot be used directly to form new papers as they do not form the structure of intertwined fibers needed to form papers.The finding of the invention is that a cured benzoxazine-impregnated paper material creates a board that can withstand the temperatures and chemicals used in repeated thermal curing, as well as etching and metal plating for creating patterned metal traces and contact areas and via hole plating, while being susceptible to disintegration be exposure to alkaline reagent solutions commonly used in recycling pf paper. Further, by partially curing or polymerizing the benzoxazine monomers in the paper material an intermediate board or a pre-preg is formed which can be stored or transported at ambient temperature. This simplifies and lowers the cost of the production of boards and especially multilayer boards. According to the present invention a specific impregnation method is provided to enable manufacturing of a board which would facilitate the fulfillment of the requirements on a PCB as described above and at the same time have paper-like properties.

[0091] The boards of the present invention are prepared by impregnating the paper material with the benzoxazine monomers by bringing the paper material into contact with a solution comprising said monomers. Bringing the paper material into contact with the solution can be done using any suitable technique but preferably by dipping or submerging the paper material in the solution. Dipping or submerging is a fast way of impregnating the paper material since the paper material only has to be in the solution for a few seconds.

[0092] By adjusting the amount or concentration of monomers in the solution the obtained board will have different weight ratio between the resin and the paper material. The monomers are then polymerized or cured to form the resin.

[0093] Polymerization or curing may be done at a temperature of at least 100°C, preferably at least 150°C, but preferably not higher than 250°C so that the paper material is not damaged. The polymerization may be done at reduced pressure. During the polymerization the solvent is evaporated leaving a solid and cured resin.

[0094] The solvent used should be able to dissolve the monomers, preferably at a high concentration. Further, the solvent should preferably pose minimal flammability at ambient conditions, minimum odour, minimal exposure risks in processing handling, and disposal. Furthermore, the facilities that the solvents are used should be properly equipped, for example the solvents can be recovered from the ventilation air by condensation or activated carbon filters, or destroyed for example by flaring, or located in placed where there are no regulations on organic vaporexhausts. Aromatic hydrocarbons, ketones, esters, terpenes, or cycloalcanones may be used as solvents and a non-limited list of possible solvents are toluene, xylene, benzyl acetone, 2-butanone, naphthalene, acetone, cyrene, ethyl acetate, hexyl acetate, dibasic esters, eucalyptol, limonene, menthol or a mixture of two or more thereof.

[0095] Combinations of benzoxazine monomers and solvents suitable for a solution-based impregnation process includes, but is not limited to di- or polyfunctional benzoxazine monomers or a mixture of di- or polyfunctional benzoxazine monomers and monofunctional benzoxazine monomers and a suitable organic solvent such as benzyl acetone. Example of suitable benzoxazine monomers are those obtained from bisphenol-a, diphenolic acid and phenolphthalein.

[0096] The method according to the invention of producing a board suitable for a PCB fulfilling the above discussed requirements will be described with reference to Figure 1. The method comprises the steps of

[0097] 110: Providing a porous paper material;

[0098] 120: Providing a solution comprising benzoxazine monomers wherein the concentration of the benzoxazine monomers is 5-50wt%;

[0099] 130: Bringing the paper material into contact with the solution to impregnate the paper material with the benzoxazine monomers;; and

[0100] 140: Polymerizing the monomers.

[0101] Step 120 of providing a substance comprising benzoxazine monomers, comprises preparing a solution wherein the concentration of the monomers is preferably 10 to 45wt%, more preferably 20 to 40wt%, and even more preferably 20 to 35wt%. Step 130 of impregnation, may be performed by dipping the paper material in the solution. The solvent used should be able to dissolve the monomers, preferably at a high concentration, but should have a low boiling point to allow fast and complete removal of the solvent. Further, the solvent should pose minimal exposure risks in processing handling and disposal.

[0102] The method may also comprise one or more drying steps, typically at elevated temperatures in order to remove solvents and / or additional curing.Step 140 of polymerizing the monomers may comprise the polymerization or curing by applying heat to the paper and monomers, preferably at a temperature of at least 100°C, preferably at least 150°C but preferably not higher than 250°C.

[0103] According to one embodiment of the invention the method is a method of manufacturing an intermediate board, a prepreg as disclosed above. According to the embodiment, step 140 of polymerizing the monomers is replaced with a step 140b comprising partly polymerizing the monomers. The skilled person will know how to adapt temperature and / or time to achieve a partly polymerized board. A non-limiting example would be to initiate the polymerization by exposing the monomers in the paper material to a temperature of at least 100°C, preferably at least 150°C, but only for a limited period of time such as after 30-90 minutes.

[0104] Adjusting the time and temperature in order to prepare the intermediate board, pre-preg, having the wanted properties such as stickiness does not require any major tests for a person skilled in the art.

[0105] The method according to the invention may be extended to producing a PCB comprising one or more boards provided by steps 110-140. Hence, the method will comprise a further step:

[0106] 150a Producing a PCB comprising one or more boards. The step may comprise one or several substeps including, but not limited to electroplating, etching, drilling vias, laminating etc.

[0107] The method according to the invention may also be extended to producing an electroplated board comprising one or more boards provided by steps 110-140. Hence, the method will comprise a further step:

[0108] 150b Producing an electroplated board. The step may comprise laminating a copper layer or foil on top of an intermediate board obtained from step 140b. The step of laminating may including heating and pressing the copper layer or foil on to the intermediate layer.

[0109] Electroplating metals is one of the pathways to form circuits on the PCBs. A seeding layer can be deposited on the board which is then exposed to a precursor solution that under certain conditions enables the deposition of a metal (i.e. Copper or Gold) on the board. There are two potential ways that this process may be realized. The seeding layer can be an electrically conductive material such as carbon and it can be printed i.e. screen printing, enabling the formation of differentpatterns for the electroplating of the metals. In this case, the seeding layer / board is exposed to the metal precursor solution and then exposed to an external electric field for the electrodeposition of the metal. Alternatively, a seeding layer can be non-electrically conductive i.e. a monomeric unit such as 3,4-ethylenedioxy thiophene which is deposited on the board. The seeding layer / board is then exposed to an oxidative solution i.e. potassium permanganate, that polymerizes the monomers forming an electrically conductive film - namely Poly(3,4-ethylenedioxythiphene), PEDOT. The PEDOT / board is then dipped in an metal precursor solution and then exposed to an electric field in order to electroplate the metal of interest (i.e. copper, gold).

[0110] According to one aspect of the present invention a flexible board is provided suitable for printed circuits board manufacturing in a roll-to-roll process. The board comprises a paper material impregnated with a resin wherein the resin is a polymer obtainable from benzoxazine monomers, and wherein the resin to paper weight ratio is 0.056 to 0.32. The flexibility is such that the board passes a bendability test according to the standard ISO 3270 using mandrel with a diameter of 9mm.

[0111] According to embodiments of the invention the board has an air permeability of at least at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably at least 43.4 pm / Pas, more preferably at least 50 pm / Pas, more preferably at least 70.1 pm / Pas.

[0112] According to one aspect an electroplated board is provided in which a layer of copper is laminated onto the surface of the board.

[0113] According to one aspect an electroplated board is provided in which a layer of a seeding layer is deposited on the surface of the board.

[0114] The main starting materials comprises benzoxazine monomers and a paper material with high air permeability, which also may be characterized as a paper material with high porosity. The produced board is a composite material comprising a paper material impregnated with a resin wherein the resin is a polymer obtainable from benzoxazine monomers.

[0115] Another aim of the invention is to facilitate recycling of printed circuit boards. In order to achieve that the board has to be made of a recyclable material which at the same time has to withstand the manufacturing processes of patterning a circuit.Use of a paper material for the board would be suitable from a recyclability point of view however such materials are limited regarding printability due to high water uptake.

[0116] As is shown herein, the aim is achieved by impregnating the paper material with a polymer obtainable from benzoxazine monomers. A weight ratio between the resin and the paper material of 0.10 to 0.60 results in a degree of impregnation which imparts a reduced uptake of water of the resulting composite and at the same balance the mechanical properties as well as the degradability of the board. The degree impregnation produces a porosity of the material that enables transport of alkaline reagents into the structure resulting in disintegration of the composite to smaller fragments facilitating separation of materials and components for recycling. What the present inventors have shown is that when the resin to paper material weight ratio is 0.10 or higher, or 0.15 or higher, or 0.20 or higher, or 0.25 or higher, but preferably 0.55 or lower, or 0.450 or lower, or 0.30 or lower an optimum regarding the water uptake and coarse reject is reached. A board with the weight ratio between the resin and the paper material of 0.10 to 0.60 is also shown to be suitable for common PCB manufacturing processes.

[0117] One such PCB manufacturing process is roll-to-roll processing, where the present inventors have discovered that resin to paper material weight ratio is an important factor in determining some physical characteristics of a board, such as bendability or flexibility. It has been discovered that a board with the weight ratio between resin and the paper material above 0.6 exhibit high structural strength but also adverse characteristics, including brittleness and tendency to crack during bendability tests. Consequently, rendering such boards unsuitable for manufacturing or processing by methods requiring flexibility of the material to be processed, such as the roll-to-roll process.

[0118] What the present inventors have shown herein is that the board according to the present invention may be treated so that the paper material may be turned into a pulp after repulping. This is a result of the resin to paper material weight ratio, degree of impregnation being below 0.6. At low degree and no impregnation, a pulp is formed after repulping. At intermediate degrees of impregnation, a pulp may be formed after repulping and fine solid particles are formed from the resin. At a high degree of impregnation (larger than 0.6), the composite papers (boards) do not fully disintegrate but remain mainly as large fragments, coarse reject. The fine particles resulting from the papers with a high degree of impregnation cannot be useddirectly to form new papers as they do not form the structure of intertwined fibers needed to form papers.

[0119] The finding of the invention is that an interval in resin to paper material weight ratio exists wherein the composite material of the board is formed such that it can withstand the temperatures and chemical used in repeated thermal curing, as well as etching and metal plating for creating patterned metal traces and contact areas and via hole plating, and the board has a sufficiently low water uptake during use, while being susceptible to disintegration be exposure to alkaline reagent solutions commonly used in recycling pf paper.

[0120] The thickness of the board may be adapted to be suitable for a wide range of applications, for example if a PCB comprising the board is a single layer or multilayer. The board may typically have a thickness of at least 0.01 mm, preferably at least 0.1mm but preferably not more than 5 mm.

[0121] Applications of the board

[0122] According to one aspect of the invention a printed circuit board (PCB) is provided. The PCB according to the invention comprises at least one board as described above and a printed circuit provided on the board. As appreciated by the skilled person a PCB may comprise several boards and also other layers and structures such as vias. The PCB according to the invention maintains the properties with regards to the water uptake and recyclability associated with the board.

[0123] According to one aspect an electroplated board is provided in which a layer of copper is laminated onto the surface of the board.

[0124] According to one aspect an electroplated board is provided in which a layer of a seeding layer is deposited on the surface of the board.

[0125] Recyclability tests

[0126] Standardized methods to classify paper, or cellulose paper, and board for recyclability follow procedures that emulates industrial recycling processes. These methods start with repulping of centimeter-sized paper pieces by agitation in a repulping solution. After the agitation, large remaining objects, coarse reject, are separated from the pulp and weighed. The weight fraction of the coarse reject to thedry weight provides a measure of recyclability. The quality of papers formed by the pulp is also a measure of the recyclability. Aticelca® 501 UNI 11743:2019 is an example of a standardized method to classify paper and board for recyclability. Here, the evaluation for recyclability differs from the standardized methods in the following ways. The mass processed is smaller as the substrate here is taken from the standardized methods to evaluate uptake of water in circuit boards, 5x5 cm. The size of the circuit board substrate pieces is also smaller, ca. 1 cm2, as compared to the 3x3 + / - 0.5 cm used in paper recycling tests. The coarse reject is separated by filtering through 4 mm diameter holes instead of the 5 mm holes used in standardized recyclability tests. In recyclability tests of papers, or cellulose papers, the resulting material is either pulp or coarse reject in the form of fine particles and soluble materials. In samples where pulp and fine particles co-exist, no separation of these two materials was done, the coarse reject mass fraction was used as a measure of recyclability of the board and not to assess the repulpability of the board.Examples

[0127] In the Examples here below following paper materials have been used:

[0128] Papers with high air permeability: Blotting paper, Filter aper ‘Munktell’ from Alstrom Munksjo and Toilet paper (a commercially available 2-layered toilet paper); Papers with moderate or low air permeability: Paper for printed electronics ‘XD200’ from Fedrigoni, , an experimentally produced paper from bleached sulphated pulp with 70% softwood pulp and 30% hardwood pulp, , a packaging paper from recycled fibers ‘Multiboard (R) Kraft 500’ from Fiskeby and a packaging ‘Kraft Paper’ from Kontorsgiganten. The characteristics of these papers are presented in Table 1 (air permeability determined according to ISO 5636-5 Gurley).

[0129] Table 1 : The different papers used

[0130]

[0131] The mass per unit area of impregnated (board) and unimpregnated papers (paper material), and the resin mass per unit area of impregnated papers are key measures in describing and the characterization of the impregnated papers. The term grammage is used herein as gram per square meter, as a measure for mass per unit area. Grammage determinations are the base for measurements of uptake of water and mass-uptake after treatments with acids and alkali. Measurements for uptake of water follows the immersion procedures described for circuit board materials. More specifically, samples are dried in vacuum oven and cooled in dessicators to obtain dry grammage values of papers without moisture or solvent for both pristine paper, papers after impregnation and curing and after immersion exposure tests.A key advantage of the invention is the reduced uptake of water at various degrees of impregnation. For this reason, water uptake experiments are carried out. As the main objective is the manufacture of electronic circuit boards, measurements of the uptake of water after water immersion tests follow the procedures from standards for uptake of water in circuit board substrates.

[0132] Fabrication of PCB’s involve exposure to aggressive aqueous conditions. Tolerance to acid exposure was tested by measuring the uptake of mass upon exposure to acidic and alkaline conditions. The alkaline conditions differ from the conditions tested in degradation in that the temperature is kept at ambient temperature.

[0133] The investigations performed using the paper materials listed in Table 1 and varying the process parameters are described in detail below and the results are listed in Tables 2.1-2.2.

[0134] Example 1. Synthesis of liquid benzoxazine of 4-hydroxybenzoyl alcohol and N,N-dimethyl- 1 , 3 -propanediamine , (3 - (dimethylaminopropyl) -3 , 4-dihydro-2 H-benzo[e][l,3] oxazin-6-yl)-methanol, (4HBnzaDMPDA)

[0135] 4-Hydroxybenzoyl alcohol, 24.83 g, N,N-dimethyl-l,3-propanediamine, 22.48 g, and para-formaldehyde 13.21 g, were placed in a 250 mL flask with toluene 100 mL and isopropanol, 50 ml, and a magnetic stirrer. The mixture was heated and kept at reflux for four hours. During the reaction, a dark viscous minority phase separated and adhered to the vessel wall. After the reaction and while still hot, the lightly brown liquid was decanted to leave the dark minority phase in the vessel. The solvents were removed in a rotary evaporator and degassing under reduced pressure to yield 38.3 g of the product. The product was slightly soluble in water, 2.5 % can be dissolved at 40 C. A water-insoluble impurity can be removed by dissolving the product in warm water followed by decantation and filtration.

[0136] Example 2. Synthesis of the benzoxazine of phenolphthalein and furfuryl amine (PhPh-Bz).

[0137] Phenolphthalein (20 g) and paraformaldehyde (7.4 g) were suspended in toluene (50 mL) and ethanol (10 mL) in a round bottomed flask. After being kept at 80 C for two hours, furfurylamine (12,2 g) was added dropwise whereafter the suspension gradually dissolved. The reaction was kept at reflux temperature overnight. Solventwas removed from the reaction mixture to form a viscous fluid. The fluid was poured on a plate and placed in a vacuum oven for one day to yield 33 g of a white solid.

[0138] Example 3. Liquid mixtures of solid benzoxazines and 4HBnzaDMPDA

[0139] The dibenzoxazine of bisphenol-a, DPA-Bz, Huntsman MT35600, 0,506 g, was dissolved in 5 mL of acetone together with 1,59 g of 4HBnzaDMPDA from example 1. Evaporation of the solvent yielded a viscous liquid showing no signs of phase separation of solidification after two months.

[0140] Example 4: Solvent-based impregnation

[0141] Bisphenol a dibenzoxazine (BPA-Bz) (Araldite MT 35600) supplied by Huntsman, was dissolved in benzyl acetone (BA). Impregnation solutions were prepare by mixing 10g, 25g, 50g, 55g, 60, 65g and 75g of BPA-Bz with 90g, 75g, 50g, 45, 40g, 35g and 25g of BA respectively . The solutions were mixed at 50C for 3h in order to assist the BPA-Bz to dissolve in the BA. Then each impregnation solution was arranged in a Teflon-made impregnation bath of volume 160cm3for the paper impregnation.

[0142] The impregnation was done by placing the blotting paper (thickness of approximately 0.75 mm) on the surface of the impregnation solution for 30 s and then dipped in the solution for one minute, in order to ensure a full impregnation of the BPA-Bz in the paper. Then the soaked paper was removed from the solution and the excess BPA-Bz and BA were removed mechanically from the paper with a mandrel. The samples were then introduced in a ventilated oven at 165C for 90min and subsequently at 200C for 90min to form the boards. The boards were then removed from the oven and were left to cool down in ambient conditions. The boards were denoted as PBz papers. For higher concentrations of impregnation solution i.e. 65% and 75%, the impregnation bath was put on a hot plate so that the impregnation solution’s temperature was at 100C. The impregnation process was then repeated as described above.

[0143] As seen in Table 2.1, column denoted “Resin / paper ratio”, the Resin to paper, or Resin to cellulose, ratio increases with the concentration of the impregnation solution used. However the air permeability of the board after the impregnation is to a large degree maintained at least for low and moderate concentrations which is an indication of that the paper-like structure remains, see column denoted “Airpermeability Board (pm / Pas)”, air permeability determined according to ISO 5636-5 Gurley. The high porosity of the board may be further utilized in that the board may be further impregnated / exploited towards enhancing other aspects of the board properties such as fire retardancy etc.

[0144] In order to show that the invention works using other paper materials, tests were done using a 33% impregnation solution using the paper materials presented in Table 1, and the results presented in Table 2.1-2.2. In the tables indicates that the property was not measured.

[0145] Example 5: Melt impregnation - Reference example

[0146] 100g of solid BPA-Bz was introduced in the Teflon-made bath described in Example 4. The bath was then introduced in a ventilated oven at 130C for lh so that the solid BPA-Bz melts. A blotting paper was introduced on the surface of the melt (in the oven) for 5 min, and then the blotting paper was dipped in the melt for lmin (the bath remains in the oven). Thereafter the impregnated sample was removed from the melt and the surplus melt was mechanically removed from the sample with a mandrel. The sample was then left in the ventilated oven for 20min at 130C in order to assist further diffusion of the melted BPA-Bz in the pores of the paper. Subsequently, the sample was introduced in vacuum oven at 165 C for 90 min and dynamic vacuum. Finally, the sample was introduced in a ventilated oven at 200 C for 90 min. After the final annealing step, the sample was removed from the oven and cooled to ambient temperature.

[0147] Example 6: Impregnation with a liquid benzoxazine - Reference example

[0148] The liquid benzoxazine, 10 g, described in Example 1, was blade coated on a 5x5cm piece of the blotting paper used in Example 4. After removal of excess of the liquid benzoxazine with a mandrel the sample was placed on a 100 C hot plate for lmin. In a similar manner, smaller pieces were prepared by coating 5 g of the liquid benzoxazine on 2 x 2 cm pieces of blotting paper. The samples were introduced into a vacuum oven at 165 C and under dynamic vacuum for 90 min. Subsequently, the samples were introduced into a ventilated oven at 200 C and kept at this temperature for 90min. After the final annealing step, the sample was removed from the oven and cooled to ambient temperature.Example 7: Grammage of impregnated paper

[0149] The dry content of the paper material and the board were measured with a technique adapted from the standard IPC-TM-650, number 2.6.2.1. Blotting paper was cut in 5x5cm area pieces.

[0150] Plastic ziplock bags were then numbered and weighted (WO) and the blotting paper pieces were then dried in a vacuum oven at 140C for lh and thereafter placed in the ziplock bags and weighted (Wl) Then the samples were removed from the bags and introduced in a ventilated oven at 140C for lh and then subsequently introduced in a desiccator for 30min to cool down. The samples were then placed and weighed (W2) and the dry content of the samples were acquired as W2-W0.

[0151] The blotting paper pieces were then impregnated with the benzoxazines following the processes as described in the examples 4, 5 and 6. The dry content of the boards was determined as disclosed above. The grammage of the samples was calculated as (W2-W0) / Area and is presented in g / m2. In order to acquire the PBz grammage in the board, the grammage of the paper material was subtracted from the grammage of the board. In Figure 2 the PBz grammage in the paper material vs the concentration of the impregnation solution is presented. It should be noted that the BPA-Bz melt of Example 5 is denoted as a 100% concentration, while the no impregnation is denoted as 0% concentration. The result values are presented in Tables 2.1-2.2 and the resin to paper material was also plotted against the concentration of the impregnated solution (Figure 2). All standard deviations originate from values from 3 different samples. As seen in Figure 2 and Table 2.1, the PBz grammage increased nearly linearly with the concentration of the impregnation solution.

[0152] The PBz grammage in the board from the concentration of the impregnation solution is found in Tables 2.1-2.2 in the column denoted Grammage (g / m2).

[0153] Example 8: Water uptake measurements

[0154] The water uptake of the board samples was determined following the standard IPC-TM-650, number 2.6.2.1. Three samples per species from Example 7 were introduced in pre-weighed plastic bags (W0). The samples were then dried in a vacuum oven at 140C for lh. Subsequently the samples were removed, and they were quickly introduced in the ziplock bags. The Ziplock bags with the enclosed paper wereweighed (W4). Then the samples were removed from the bags and were introduced in a ventilated oven at 140C for lh and then subsequently were introduced in a desiccator for 30min to cool down. The samples were then introduced in a ziplock bag and the ziplock bag + sample was weighted (W5) and the dry content of the samples was acquired as W5-W0. The samples were then removed from their ziplock bags and introduced in a container with de-ionized distilled water (DIW) (150ml) for 24 h at 23 C. The samples were then removed from the container and the water from the surface was removed with a dry cloth. The samples were then put in their respective preweighted ziplock bags and the ziplock bag plus sample was weighted (W6). The weight of the wet sample was then extracted as W6-W0. The water uptake i i i . i (ive-ivoi-qvs-ivo)

[0155] of the samples was then calculated as: - - — - - ■ 100%

[0156] (IV5-IV0)

[0157] In Tables 2.1-2.2 the results for the various samples are presented (standard deviations obtained from values of three different samples). Figure 3 discloses the water uptake vs the concentration of the impregnation solution, vs the PBz grammage in the paper and vs the resin to paper ratio, or resin to cellulose ratio. It was observed that the water uptake decreases logarithmically from -200% for the non-impregnated samples down to -50-10% water uptake for the solvent-based impregnated samples and -5% water uptake for the melt impregnated samples. It is noteworthy that even the samples that originated from dilute solvent-based impregnations (10% in impregnation solution) had a decreased water uptake from -200% to -50%. In Figure 4 are the results on the water uptake presented for the other papers. For all the papers, impregnation and crosslinking with the benzoxazine resin water uptake decreased heavily, this underlines that the impact on the Water Uptake of the benzoxazine / paper composite is paper material independent. Paper materials such as the blotting paper and the toilet paper have the highest decrease in water uptake after impregnation (Figure 5). It was observed that the decrease in water uptake after impregnation seemed to be related to the air permeability of the paper material.

[0158] The uptake of water for papers impregnated with solutions of different concentrations is found in Tables 2.1-2.2 in the column denoted Water uptake (%).

[0159] Example 9: Mass uptake by acid immersionDuring PCB manufacturing, the PCBs were exposed to acidic conditions in order to undergo a variety of processes i.e. metal electroplating or metal etching processes. A common denominator for the acid used in these processes is that it contains up to 2.5M sulfuric acid and the samples are exposed for ~18min. Thus, the acid uptake / acid impact of the samples is important and is determined by an adapted IPC-TM-650 2.6.2.1.

[0160] Samples used were prepared according to Example 4 and 5. In Tables 2.1-2.2 are the results presented for the various samples and standard deviations from values of three different samples. In Figure 6 the uptake of mass after acid treatment of the boards plotted vs different loading of resin expressed as (a) the BPA-Bz concentration of the impregnation solution, (b) the resin grammage of the board, and (c) as the resin to paper ratio, or resin to cellulose ratio. It was observed that the acid uptake decreases abruptly from -200% for the non-impregnated samples (paper material) down to a plateau -10% for all the solvent-based impregnated samples and -0.5% for the melt impregnated samples. It is noteworthy that even the samples that originated from dilute solvent-based impregnations (10% in impregnation solution) had a decreased acid uptake from -200% to -10%, which translates into the fact that even a low PBz grammage board can withstand the acid-based processes of the PCB technology.

[0161] The uptake of mass after acid exposure for papers impregnated with solutions of different concentrations is found in Tables 2.1-2.2 in the column denoted “Acid uptake (%)”.

[0162] Example 10: Mass uptake by base immersion and relative comparisons

[0163] In order to compare the impact of immersion in a basic and neutral environment, the impregnated papers were exposed to 2.5M NaOH and at deionized water for ~18min, as a comparison to Example 9.

[0164] The dry content and uptake of the paper materials and impregnated paper was determined using an adapted standard IPC-TM-650, number 2.6.2.1 as described above.

[0165] Figure 7 presents the water uptake vs the PBz grammage in the paper and water uptake vs the resin to paper ratio, or resin to cellulose ratio. Note that the value for the 2.5M sulfuric acid absorbate was taken from Example 9. It is observed that theimpregnated papers seem to be more sensitive to the presence of NaOH, which might be explained by a synergy between the chemical interactions between the paper fibrils and NaOH and the PBz and NaOH. As seen in Example 12, below, a diluted NaOH solution assists in the degradation of the papers.

[0166] Example 11: Uptake of mass in papers impregnated with liquid benzoxazine The process described in Example 6 for the impregnation of paper with the liquid benzoxazine of Example 1 was applied to the methodologies described in Examples 7 and 8. Blotting paper were cut into one piece of 5x5cm and one piece of 2x2 cm for the impregnation with the liquid benzoxazine from Example 6. Following the drying and grammage calculation processes described in Example 7, the grammage of PBz impregnated in the paper was 333.6 g / m2. Additionally, by applying the water uptake calculation experiments and procedure described in Example 8, the water uptake for the 5x5 cm liquid benzoxazine impregnated sample was 26.65%. The 2x2 cm impregnated sample was then used for a degradation study in Example 12 below.

[0167] Example 12: Recyclability of impregnated and non-impregnated samples

[0168] The disintegration of the samples manufactured in Examples 2, 3 and 4 were investigated by analyzing the materials resulting from hot alkaline treatment of the impregnated papers under agitation. The samples were cut into centimeter-sized pieces and added to a loading of 4 wt% of impregnated paper in 0.6% NaOH solutions. The solutions were first heated to 50 C for 30 min and then it was kept at 100 C for 24 hours with intermissions after one, and six hours where the mixture was allowed to settle and cool down to ambient temperature to evaluate the progress of the process. The intermission time was not added to the process time. After the process fine particles, pulp and liquid were passed through holes with 4 mm diameter to separate the coarse reject. The coarse reject was collected, dried and the mass compared with the mass of the starting material. The mass and fraction of the coarse reject was a measure of the recyclability of the impregnated papers. The results show that fully impregnated papers (100%) do not form pulp or fine particles and were apparently not recyclable by the process. However, samples impregnated less than 100% do disintegrate by the treatment. With lower degree of impregnation, there was a decrease in the mass and share of coarse reject as can be seen in Table 2.1. Atintermediate impregnation level, the main product was fine particles. At low levels of impregnation, one can also observe pulp of intertwined cellulose fibres. It is noteworthy that the other papers used in Examples 4 and 8 have higher coarse reject in respect to the blotting paper; this was possibly due to the presence of additives in the paper (e.g. strengthening or sizing agents) or to different sizes of paper fibers. The test applied herein acts as an indication for the disintegration of the impregnated paper. In Figure 8 the water uptake and mass uptake by acid immersion are compared with the coarse reject % for the blotting paper samples where it is identified a range of resin / paper ratio in which low water uptake, low mass uptake by acid immersion and disintegration can be achieved. It is observed that the coarse reject has a minimum at a resin / paper ratio, or resin / cellulose ratio, of 0.08. In lower resin / paper ratios, or resin / cellulose ratios, than that the paper behaves more as a pulp and consequently it can’t pass through the 4mm diameter holes of the test that was conducted in this experiment. An alternative test methodology should be then used in order to assess the disintegration of those composites. However, at these very low concentrations recyclability is not considered to be a problem

[0169] The disintegration results for the PBz papers (boards) are found in Tables 2.1-2.2 in the column denoted “Coarse reject part of total mass (%)”.

[0170] Example 13: Copper electroplating

[0171] Based on the observations from Example 9, the PBz impregnated papers were examined for their capability of being used as a board for electroplating of copper. Carbon ink 7102 from DuPont was screen printed on the impregnated and nonimpregnated papers and the carbon contact was used as the working electrode in a 2 -electrode electrochemical cell (Pt wire acting as a counter / reference electrode), that was connected with an Ivium Octostat. As the electrolyte of the electrochemical cell, a commercial copper plating solution was used (2.5M Sulfuric Acid) and the working electrodes were exposed to 3V for 18min. The copper plating failed for the nonimpregnated paper, since the electrolyte was absorbed in the paper. Meanwhile, a copper foil was electroplated successfully for the -impregnated paper. In order to further unravel the applicability of the technique of the present invention, one impregnated paper obtained from a 25% concentration solution (blotting paper), one from 33% concentration solution (Fiskeby MultiBoard Kraft 500) and one from 33% concentration solution (2 layered Toilet Paper) were used as well for electroplating.Copper was successfully electroplated on all the impregnated papers. To investigate the lower limit of impregnation solution concentration required for a successful electroplating impregnation Blotting paper was used as a model system. Blotting papers was subjected to impregnation solution concentration of 0.1%, 1%, 5%, 10%, 33%. Copper foils were electroplated successfully for concentrations above 5%. The result of the copper electroplating tests is summarized in Tables 2.1-2.2 in the column denoted “Copper Electroplate”.

[0172] Example 14: Model study, lamination with a copper laminate and copper patterning This example was conducted to show that the concept of copper laminating and copper patterning is feasible using the present invention. The impregnated papers from the example 4, where the Fedrigoni XD200 paper, were used as a model board in this Example. The adhesive KIWOTHERM DI 23 was bar coated on a copper laminate. The coated side of the copper laminate was then brought in contact with the board and the copper / pboard system was laminated at 120C for 15min. Then a photoresist material (AS 500-DJ from TAIYO Ink) was screen printed on top of the copper and UV cured in a UV oven belt to crosslink. The samples were subsequently introduced in an oxidant solution of iron chloride (45% w / w) to etch the uncovered copper. Then the photoresist was removed by dipping the substrate in acetone. After cleaning of the leftover photoresist, we could observe the clear formation of the Cu circuits on the board.

[0173] Example 15: Bendability tests

[0174] The bendability of the samples was investigated using an Elcometer 1506 cylindrical mandrel bend tester following the standard ISO 3270 and using mandrels of diameters of 2,4,6,9,12,32 and 45mm. The samples are placed in the bender with the different mandrels and bended to the radius of the mandrel. This test is a pass / fail test which translates that the if the material remains intact after the bending, it passes the test. For the Roll-to-Roll processing , typically used in the paper industry, the bendability of the substrate is crucial, as it needs to withstand the bending radia of the roll-to-roll facility. Furthermore, roll-to-roll processing can facilitate the mass production of printed electronic devices. For the Roll-to-Roll processing, a radius of 9 mm for the mandrel is the chosen one as a means toevaluate the ability of the board to be processed in a Roll-to-Roll facility. As seen in Table 2.1 and 2.2, the boards made with blotting paper and from a solution concentration up to 50% withstood the bending conditions. For boards of higher concentrations, the resin / paper ratio is increasing and consequently the rigidity of the board increased; these boards failed the tests. However, for different qualities of papers i.e. different grammages and thicknesses the bendability changes as well and as seen in Table 2.2, boards resulting from a 33% impregnation solution pass the bendability tests for roll-to-roll processing, even at higher resin / paper ratios.

[0175] Example 16. SEM of impregnated samples

[0176] Scanning Electron Microscopy (SEM) was conducted on paper and board samples that were manufactured following the methods presented in Examples 4 and 5 for three pristine paper materials; the blotting paper, the Alstrom filter paper and the kraft paper. A thin Au film (~20nm) was evaporated on all samples in order to enhance the SEM signal. A Hitachi TM-1000 tabletop SEM was used. The pristine paper materials were chosen due to their air permeabilities (as presented in Table 1) with Filter paper being on the ‘high-end’ of a paper permeability, kraft paper being in the low-end’ of air permeability and blotting paper being in the middle. As seen in Figures 9-10, as the resin / paper ratio is increasing, the gaps between the paper fibers start to also being filled in from the resin. Particularly in Figure 9 which presents the Blotting Paper-based boards, in the highest Resin / Paper ratios, the gaps between the fibers appear to be completely filled, which explains why these boards can’t disintegrate easily - as presented in Example 12. On the other hand, in Figure 11 for the kraft paper-based samples, the visual variations on the SEM images become apparent only in higher resin / paper ratios. The findings in Figure 9-11 underline that porous pristine paper material (i.e. with a high air permeability) is important for the successful manufacturing of the board presented in the current invention.

[0177] Example 17: Oil absorbance measurements and comparative air permeability tests for boards

[0178] To obtain porosity measures of the paper samples with different degrees of impregnation, oil absorbance was measured. Oil absorbance is normally measured using the Cobbs-Unger test in which the grammage of absorbed oil is measuredafter oil immersion. As it turned out that certain impregnated samples trapped air during oil immersion, the method was modified to include application of vacuum during oil immersion to remove trapped air.

[0179] Samples were placed in open and weighed plastic Ziploc® bags and were exposed to a vacuum (lxlOE-1 Torr) at ambient temperature for 3o minutes before being weighed. After weighing, castor oil was added to cover the papers and vacuum was applied at ambient temperature until the samples stopped releasing bubbles.

[0180] Thereafter, the paper samples were taken out and visible bulk oil fluid on the paper surface were removed by wiping with polypropylene non-woven lint-free lab wipes before being placed in a weighed Ziploc® bag for weighing. Oil absorbance is reported as the grammage of absorbed oil.

[0181] In Figure 12 are presented the air permeability and oil absorbance of the paper and board materials vs the resin / paper ratio for boards manufactured from blotting paper, Alstrom filter paper and kraft paper, following the procedures in examples 4-5. It is observed that both oil absorbance and air permeability of the boards are decreasing with increasing resin / paper ratio, which translates to filling of the pores in the paper after impregnation. Subsequently, in figure 13 the oil absorbency is plotted against the air permeability for the paper and board materials, where a nearly linear behavior is observed between the two parameters for the materials. In order to further gain an understanding of the impact of the impregnation method on the porosity of the board, the relative air permeability and the relative oil absorbency are plotted in figures 14-16. By relative air permeability we define the ratio between the air permeability after impregnation and the air permeability before impregnation, while with relative oil absorbency we define the ratio between the oil absorbency after impregnation and the oil absorbency before impregnation. Thus, the pristine paper materials should have a relative air permeability equals to 1 and relative oil absorbency equals to 1. In Figures 14-15 it is observed that the relative air permeability and relative oil absorbency decrease linearly with the resin / paper ratio - while for the relative oil absorbency the trend is independent of the pristine paper material, which further highlights the importance of a highly porous material as a pristine material for our method and product presented in this invention. Additionally, when the relative oil absorbency is plotted against the relative air permeability, it is observed the they are nearly linearly related. The findings in figures 14-16 in combination with the findings in Figures 8a-b underline that when the air permeability and oil absorbency of the impregnated board are 50% decreased incomparison to the initial values of the pristine paper, then the board can still be disintegrated (given that the board is manufactured with the procedure in Example 4).Table 2.1: Summary of test results for the tested paper materials and impregnation solution concentrations, Blotting paper.

[0182]

[0183]

[0184] Table 2.2: Summary of test results for the tested paper materials and impregnation solution concentrations

[0185]

Claims

CLAIMS1. A flexible board suitable for printed circuits board manufacturing made of a composite material comprising a paper material impregnated with a resin wherein the resin is a polymer obtainable from benzoxazine monomers, wherein the resin to paper material weight ratio is 0.10 to 0.60; and wherein the board has an air permeability of at least 10 pm / Pas.

2. The board according to claim 1 wherein the benzoxazine monomers is one type of benzoxazine or a mixture of different benzoxazine monomers.

3. The board according to claim 2 wherein the one type of benzoxazine monomer is selected from mono-, di- or polyfunctional benzoxazine monomer or wherein the mixture of different benzoxazine monomers comprises monofunctional benzoxazine monomers, di- or polyfunctional benzoxazine monomers.

4. The board according to any one of claim 1 to 3 wherein the benzoxazine monomers are synthesized from monofunctional phenols bearing a benzoyl alcohol group, difunctional phenols, such as bisphenol-a, diphenolic acid or phenolphthalein, polyfunctional phenol, such as diesters of diols with diphenolic acid.

5. The board according to any one of claim 1 to 4 wherein the resin to paper material weight ratio is 0.10 or higher, or 0.15 or higher, or 0.20 or higher, or 0.25 or higher, but preferably 0.55 or lower, or 0.450 or lower, or 0.30 or lower.

6. The board according to any of the preceding claims wherein the board has an air permeability of at least 20 pm / Pas, more preferably at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably at least 43.4 pm / Pas, more preferably at least at 50 pm / Pas, more preferably at least 70.1 pm / Pas.

7. The board according to any of the preceding claims wherein the board has a thickness of at least 0.01 mm, preferably at least 0.1mm but preferably not higher than 5 mm.

8. A method of preparing a a flexible board according to any one of claims 1 to 7 wherein the method comprises:a. Providing a paper material and a solution comprising benzoxazine monomers, wherein the concentration of the benzoxazine monomers is 5-50wt%; wherein the paper material has an air permeability of at least 20pm / Pas;b. Bringing the paper material into contact with the solution to impregnate the paper material with the benzoxazine monomers; and c. Polymerizing the monomers.

9. The method according to claim 8 wherein the concentration of the benzoxazine monomers is at least 10wt%, preferably at least 20wt% but preferably not higher than 45wt%, preferably not higher than 40wt%, more preferably not higher than 35wt%.

10. The method according to claim 8 or 9 wherein the benzoxazine monomers is one type of benzoxazine or a mixture of different benzoxazine monomers.1 l.The method according to claim 10 wherein the one type of benzoxazine monomer is selected from mono-, di- or polyfunctional benzoxazine monomer or wherein the mixture of different benzoxazine monomers comprises monofunctional benzoxazine monomers, di- or polyfunctional benzoxazine monomers.

12. The method according to any one of claim 10 or 11 wherein the benzoxazine monomers are synthesized from monofunctional phenols bearing a benzoyl alcohol group, difunctional phenols, such as bisphenol-a, diphenolic acid or phenolphthalein, polyfunctional phenol, such as diesters of diols with diphenolic acid.

13. The method according to any one of claims 8 to 12 the paper material is brought into contact with the solution by dipping or submerging.

14. The method according to any one of claims 8 to 13 wherein the polymerization is done during heating, preferably at a temperature of at least100°C, preferably at least 150°C but preferably not higher than 250°C.

15. The method according to any of claims 8 to 14 wherein the paper material has an air permeability of at least at least 30 pm / Pas, more preferably at least at 40 pm / Pas, more preferably at least 44.7 pm / Pas, more preferably at least 50 pm / Pas, but preferably not higher than 100 pm / Pas, more preferably not higher than 80 pm / Pas, more preferably not higher than 60pm / Pas.

16. The method according to any of claims 8 to 15 wherein the paper material is blotting paper.

17. The method according to any of claims 8 to 16 wherein the solvent is an aromatic hydrocarbon, preferably selected from benzyl acetone, toluene, naphthalene, xylene or a mixture of two or more thereof.

18. The method according to any one of claims 8 to 17 wherein the process steps are performed in a roll-to-roll process.

19. The method according to any one of claims 8 to 18 the air permeability of the flexible board is not lower than 50% of the air permeability of the paper material.

20. The method according to any one of claims 8 to 19 the oil absorbency of the flexible board is not lower than 50% of the oil absorbency of the paper material.

21. A method of preparing a flexible intermediate board or pre-preg suitable for electroplating wherein the method comprises:a. Providing a paper material and a solution comprising benzoxazine monomers, wherein the concentration of the benzoxazine monomers is 5-50wt%;b. Bringing the paper material into contact with the solution to impregnate the paper material with the benzoxazine monomers; and c. Partially polymerizing the monomers.

22. A method of preparing a flexible electroplated board comprising the steps of:a. Providing a board according to any one of claims 1 to 7or preparing a flexible intermediate board or pre-preg according to claim 21 ; and b. Laminating a copper layer or copper foil on top of the obtained board or pre-preg.

23. An electrical device comprising the board according to any one of claims 1-7.

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