Substitute of FR-4 material

Abstract

A printed circuit board (PCB) substrate includes at least one top surface, at least one bottom surface. The printed circuit board (PCB) substrate further comprises 60 to 90 wt% of cellulosic fibers having a length of a maximum of 10 mm, 0 to 10 wt% of a curing catalyst, and 10 to 40 wt% of a binder selected from the group consisting of cellulose, hemicellulose, furan and derivatives thereof, lignin, and combinations thereof.

Description

Technical Field

[0001] The present invention relates to a printed circuit board (PCB) substrate comprising a sustainable composite material and a method for producing said printed circuit board substrate. Further, the present invention relates to a PCB comprising such a substrate and a method for manufacturing such a PCB. Background Art

[0002] Every electronic device includes one or more printed circuit boards ("PCBs"), which are relatively thin, layered substrates. These substrates include multiple conductive and insulating layers on which integrated circuits and other electronic components are mounted. The conductive layers typically have conductive paths or traces that are chemically or mechanically etched from the bulk conductive layer. They are therefore isolated from each other by insulating materials and routed in a plane. These traces are typically designed to make electrical contact with the conductive parts of the electronic components mounted on the PCB, thereby forming an electrical connection. Electrical connections can also be made between conductive layers through vias, which are essentially small, drilled conductive holes that extend through two or more adjacent layers.

[0003] FR-4 (woven fiberglass laminate reinforced with epoxy resin) is the material of choice for the insulating layer in PCBs used in high-end industrial, consumer and military electronic equipment because it is resistant to heat, mechanical shock, solvents and chemicals. Further, FR-4 material is flame resistant and self-extinguishing.

[0004] FR-4 epoxy resin systems typically employ bromine (halogens) to induce flame retardant properties. Flame retardants (FR) are a group of anthropogenic environmental pollutants known for their negative impacts on human health and the environment. Bromine substituents and their potential organic bromide metabolites may increase the inherent toxicity of FR-4 materials. As a result, many brominated flame retardants are toxic (acute and chronic), persistent, and bioaccumulative in the environment due to the bromide substituents. The widespread use of brominated FR-4 materials as PCBs in electronic products puts human health and the environment at risk.

[0005] Furthermore, given the growing awareness of the negative environmental impacts of global warming and ocean and soil pollution, there is a need to replace pure fossil-based plastics and fiber-reinforced plastics (FRP), such as glass fiber-reinforced plastics (GFRP) as used in FR-4 epoxy resin systems, with more environmentally friendly alternatives.

[0006] The environmental impact of these materials is high in terms of the manufacture of raw materials such as glass fibers, the production of their intermediates, and the disposal and / or recycling. Attempts have been made to replace fossil-based polymers in GFRP materials with more environmentally friendly alternatives such as bio-based or bio-attributed polymers. Further, attempts have been made to replace glass or carbon fibers with natural fibers such as flax, hemp, sisal, etc. However, the main challenge of bio-based and / or bio-attributed alternatives and renewable and / or natural fiber substitutes for GFRP composites is the lack of sufficient supply and quality consistency to compete with fossil-based polymers and man-made fibers.

[0007] In view of the challenges currently existing in the technical field, it is desirable to provide a printed circuit board substrate comprising sustainable and environmentally friendly materials while obtaining mechanical properties comparable to FR-4. Further, it is desirable to provide a method for obtaining such a printed circuit board substrate. Summary of the invention

[0008] In view of the above, the present invention aims to solve at least some problems / gaps in the prior art. To this end, the present invention provides a printed circuit board (PCB) substrate based on renewable natural resources, which includes at least one top surface and a bottom surface; and a method for manufacturing such a printed circuit board (PCB) substrate.

[0009] The PCB substrate according to the present invention comprises at least one top surface and at least one bottom surface, and is characterized in that the PCB substrate further comprises:

[0010] 60 to 90 wt. % of cellulose fibers having a length of at most 10 mm,

[0011] 0 to 10 wt% of a curing catalyst, and

[0012] 10 to 40 wt% of a binder selected from the group consisting of cellulose, hemicellulose, furan and its derivatives, lignin and combinations thereof.

[0013] A particularly useful derivative of furan is polyfurfuryl alcohol (PFA). In one embodiment, a PCB substrate is provided wherein the binder is polyfurfuryl alcohol (PFA). In such an embodiment, the catalyst is an acidic catalyst, such as an inorganic acid or an organic acid. The amount of the acidic curing catalyst is 0.1 to 10 wt%, preferably 0.1 to 5 wt%.

[0014] It should be noted that, depending on the binder used, the curing catalyst may be omitted.

[0015] In the context of the present invention, reference to an amount specified in wt% means the amount relative to the total amount of the composition.

[0016] In one embodiment, a PCB substrate is provided, wherein the cellulose fibers comprise 0-100% virgin cellulose fibers and 0-100% recycled cellulose fibers.

[0017] In one embodiment, a PCB substrate is provided, wherein the at least one top surface and / or bottom surface has at least one developable and / or non-developable surface portion.

[0018] In one embodiment, a PCB substrate is provided, wherein the cellulose fibers in the substrate are arranged substantially in parallel, or wherein the cellulose fibers in the substrate are arranged substantially crosswise, or wherein the cellulose fibers in the substrate are arranged substantially randomly, or a combination thereof.

[0019] In one embodiment, a PCB substrate is provided, wherein the substrate includes at least one cavity.

[0020] According to the present invention, the PCB substrate may further include a flame retardant. The flame retardant may be polybrominated diphenyl ether (PBDE), chlorinated and brominated flame retardants (e.g., TCPP, TCEP, TBBPA), organophosphate flame retardants (e.g., TDCPP, TPHP), aluminum trihydrate (ATH), phosphorus-based flame retardants (e.g., red phosphorus, ammonium polyphosphate (APP)), intumescent flame retardants, bio-based flame retardants (e.g., polyols and lignin-based or nanocellulose-based flame retardants), silica-based flame retardants.

[0021] The flame retardant may be present in an amount of 0 to 30 wt%.

[0022] Another aspect of the invention relates to a printed circuit board (PCB) comprising a PCB substrate according to above.

[0023] The PCB may be a single-layer PCB, a double-layer PCB or a multi-layer PCB. When a PCB comprising multiple layers is desired, each layer may be formed of a PCB substrate as disclosed above.

[0024] The PCB according to the present invention may include one or more layers of the PCB substrate disclosed above. The PCB may further include multiple layers, each of which includes the PCB substrate disclosed above. The term "multiple" should be understood as two or more.

[0025] The layers may be arranged such that the layers are oriented such that the grain directions in the layers are substantially parallel. Further, the layers may be arranged such that the grain directions in the layers are at an angle ranging from 0-90 relative to adjacent layers.

[0026] The PCB according to the present invention may comprise at least one cavity.Furthermore, the PCB may have any desired shape, such as a square or a rectangle.

[0027] According to the present invention, there is provided a method for manufacturing a printed circuit board (PCB) substrate, the method comprising the following steps:

[0028] a) providing at least one sheet of cellulose fibers having a maximum length of 10 mm;

[0029] b) impregnating the at least one sheet of cellulose fibers with a binder selected from the group consisting of cellulose, hemicellulose, furan and its derivatives, lignin and combinations thereof to obtain a PCB substrate as disclosed above.

[0030] Thus, the PCB substrate may be in the form of a sheet of impregnated cellulose fibers.

[0031] The sheet of cellulose fibers may be provided in the form of a continuous sheet or in batting.

[0032] In one embodiment, a method for manufacturing a PCB substrate is provided, wherein the binder is polyfurfuryl alcohol (PFA).According to such an embodiment, in step b) the cellulose fibers are impregnated with an acidic curing catalyst.

[0033] In one embodiment, a method for manufacturing a PCB substrate is provided, wherein the cellulose fibers comprise a mixture of 0-100% virgin cellulose fibers and 0-100% recycled cellulose fibers.

[0034] In one embodiment, a method for manufacturing a PCB substrate is provided, wherein the cellulose fibers are provided in the form of paper.

[0035] In one embodiment, a method for manufacturing a PCB substrate is provided, wherein the PCB substrate has bio-based carbon in an amount of at least 80%.

[0036] In one embodiment, a method for manufacturing a PCB substrate is provided, wherein the PCB substrate comprises 60 to 90 wt % of the cellulose fibers.

[0037] In one embodiment, a method for manufacturing a PCB substrate is provided, wherein the PCB substrate comprises 10 to 40 wt % of the binder.

[0038] The amount of the acidic curing catalyst added in step b) may be 0-10 wt %.

[0039] In one embodiment, a method for manufacturing a PCB substrate is provided, the method further comprising the step c) of creating a cavity in the PCB substrate.

[0040] The present invention further relates to a method for manufacturing a PCB, the method comprising the following steps:

[0041] i) precuring the at least one PCB substrate by applying heat in the range of 50° C.-300° C., thereby obtaining a prepreg;

[0042] ii) pressing the prepreg in a pressing tool at a pressure of at least 7 kg / cm2, preferably at least 25 kg / cm2, more preferably at least 30 kg / cm2 and a temperature of at least 60°C, preferably at least 140°C, more preferably at least 150°C, during a period of at least 10 seconds, preferably at least one minute, more preferably at least two minutes, thereby obtaining a PCB having at least one top surface and at least one bottom surface.

[0043] In one embodiment, a method for manufacturing a PCB is provided, wherein the at least one top surface and the at least one bottom surface have at least one developable and / or non-developable surface portion.

[0044] The method for manufacturing a PCB according to the present invention may further include the following steps:

[0045] iii) providing a plurality of prepregs obtained in step i);

[0046] iv) arranging the plurality of prepregs into a stack;

[0047] wherein steps iii) and iv) occur after step i).

[0048] It is conceivable that steps iii) and iv) are performed after step ii). In other words, each prepreg can be treated with heat and pressure, i.e. cured. Such cured prepregs can then be subjected to steps iii) and iv). In such an embodiment, the stack of prepregs must be subjected to a process of joining the prepregs to each other. Such a process can be the application of heat, pressure, adhesive or a combination thereof. In particular, the conditions of such a process can be the same as in step ii).

[0049] In one embodiment, a method for manufacturing a PCB is provided, wherein the method comprises the optional step of cutting the prepreg and / or the PCB substrate into a predetermined shape.

[0050] In one embodiment, a method for manufacturing a PCB is provided, wherein the method further comprises a step v) of arranging at least one conductive layer in the stack of prepregs, wherein step v) occurs simultaneously with step iv) or after step iv).

[0051] In one embodiment, a method for manufacturing a PCB is provided wherein the prepregs in a stack are oriented such that the grain directions in the prepregs are substantially parallel.

[0052] In one embodiment, a method for manufacturing a PCB is provided wherein the prepregs in a stack are oriented such that the grain direction in a prepreg is at an angle ranging from 0 to 90 relative to an adjacent prepreg.

[0053] Further features and advantages of the present invention will become apparent when studying the appended claims and the following description.Those skilled in the art will realize that different features of the present invention can be combined to produce embodiments other than those described in the following, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings, which show embodiments of the present invention, in which:

[0055] Figure 1 A cross section of a through hole in an unplated PCB substrate according to the present invention is shown.

[0056] Figure 2 A cross section of a through hole in an unplated PCB substrate according to the present invention is shown.

[0057] Figure 3 Unplated PCB substrates according to the present invention are shown with through holes of different sizes.

[0058] Figure 4 A plated PCB substrate with a conductive layer according to the present invention is shown.

[0059] Figure 5 Shown are a) a stack of 3 layers of impregnated cellulose fibers; b) a cured PCB substrate with a flat surface; c) a cured PCB substrate with a curved surface.

[0060] Figure 6 Shown are a) a single layer PCB with a PCB substrate (white) and a conductive layer (black); b) a double layer PCB, c) a multi-layer PCB with 3 conductive layers; d) a single layer PCB with blind holes and through holes; e) a double layer PCB with through holes and 2 blind holes; f) a multi-layer PCB with through holes and blind holes.

[0061] Figure 7 A cross section of a substrate according to the invention is shown.

[0062] Figure 8 Shown is a temperature diagram during a pressing step according to the invention. DETAILED DESCRIPTION

[0063] The present invention will now be described in more detail below with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments of the present invention set forth herein; rather, these embodiments of the present invention are provided by way of example so that the present disclosure conveys the scope of the present invention to those skilled in the art. In the figures, unless otherwise specifically stated, the same reference numerals represent the same or similar components having the same or similar functions.

[0064] As mentioned above, the PCB substrate contains cellulose fibers having a length of up to 10 mm. The cellulose fibers are made from ethers or esters of cellulose, which can be obtained from bark, wood or leaves of plants or from other plant-based materials. The cellulose fibers can be derived from the conversion of wood to wood pulp. The length of each cellulose fiber in the composite material can be the same or different from the length of other cellulose fibers. In fact, it is conceivable that some of the cellulose fibers may have a length greater than 10 mm, but the amount of these fibers should be considered negligible. The term "negligible" should be understood as an amount less than 0.01 wt%. The cellulose fibers can be provided in any suitable form such as sheets, rolls, flocs, etc.

[0065] The cellulose fibers that can be used in the composite material for making the PCB substrate according to the present invention can be recycled cellulose fibers, which provides the advantages of reducing the cost of the PCB substrate and contributing to the circular economy. On the other hand, the cellulose fibers can be virgin cellulose fibers, which provide an improved tensile and / or bending strength of the circuit board compared to when using recycled cellulose fibers. Further, it is conceivable that the cellulose fibers are a mixture of recycled cellulose fibers and virgin cellulose fibers. Such a mixture can contain 0-100% virgin cellulose fibers and 0-100% recycled cellulose fibers. The cellulose fibers can include paper, such as softwood kraft paper, hardwood kraft paper, sulfite fibers, organic solvent fibers, nonwovens or combinations thereof. It is conceivable that the cellulose fibers account for 50 to 90wt% of the kraft paper. The paper can be provided in the form of a sheet and / or in the form of a continuous sheet such as a paper roll.

[0066] The PCB substrate of the present invention comprises 60 to 90 wt % of cellulose fibers and 10 to 40 wt % of a binder. The PCB substrate may have at least 80 %, preferably at least 90 %, and more preferably at least 95 % of bio-based carbon. Bio-based carbon is derived in whole or in part from biomass resources. Biomass resources are organic materials that are available on a renewable or recurring basis, such as crop residues, wood residues, grasses, and aquatic plants. In contrast, non-bio-based carbon is made entirely from petrochemical resources. The amount of bio-based carbon mentioned above is a measure of the amount of bio-based carbon in the product compared to the sum of the bio-based carbon and petroleum-based carbon in the product. The term bio-based carbon describes carbon from non-fossil sources and relates to cellulose fibers and / or binders and / or additives.

[0067] The PCB substrate according to the present invention comprises a binder selected from the group consisting of cellulose, hemicellulose, lignin, furan and its derivatives (preferably polyfurfuryl alcohol (PFA)) and combinations thereof.

[0068] PCB substrates may contain additives such as UV agents, conductive compounds, pigments, hydrophobic substances, softeners, hardeners, curing agents, etc. Additives may be added to improve chemical resistance, fire resistance, and abrasion resistance, and / or to increase curing speed to maximize production.

[0069] When manufacturing a PCB, the PCB substrate of the present invention unexpectedly shows advantageous floating properties during the curing step, which is most likely due to the combination of relatively short fibers and a binder with a certain viscosity. It is conceivable that, for example, up to 20% of ethanol is added to the process to further improve the floating ability. The term floating is to be understood as the property of the cellulose fibers to be able to move and fill cracks and tears that may occur during the manufacture of the PCB. The floating property enables the cellulose fibers to adapt to the shape of a mold or tool during the manufacturing process. As Figure 5 As shown in , the floating property enables the fabrication of complex shapes such as 3D shapes as well as flat surfaces, and provides control over the micro-surface structure, thereby enabling custom fabrication of additional properties such as surface properties, such as smooth and blank or matte and rough surfaces. Figure 5 Demonstrates how a single sheet of prepreg can be transformed into a single homogeneous material in a flat or curved structure. Figure 7 Showing a cross section through a PCB, it is not possible to distinguish the individual cellulose fiber layers used during the manufacturing process. This property is made possible due to the unexpected floating effect of the short fibers during the manufacturing process according to the invention.

[0070] One of the reasons for the high tensile and / or flexural strength of the PCB substrate of the present invention is believed to be the good adhesion between the fibers and the binder. The binder facilitates the internal mechanical cross-linking of the fibers with each other, so that the fibers are captured and locked in each other, thereby contributing to the tensile and / or flexural strength of the PCB substrate.

[0071] Another reason for a high tensile and / or bending strength of a PCB is the possibility to determine the orientation of the fibers in the PCB during manufacturing.

[0072] The cellulose fibers in the PCB can be randomly oriented, or can be oriented so that the longitudinal extensions of the fibers are substantially parallel or substantially crossed. To this end, the fibers can be positioned so that the longitudinal extensions (texture directions) of the main parts of the fibers are aligned in the same direction. This can be achieved by arranging one or more layers of the PCB substrate into a stack in a certain direction. In particular, the at least one layer can be oriented so that the texture direction of the cellulose fibers in the at least one layer is substantially parallel to the texture direction of the cellulose fibers of another of the at least one layer. It has been shown that the tensile and / or bending strength in the direction parallel to the texture direction is significantly higher, for example up to twice as high, compared to the tensile and / or bending strength in the direction perpendicular to the texture direction. Therefore, the PCB can be designed so that the tensile and / or bending and / or bending strength is suitable for the intended use.

[0073] The cellulose fibers of each of the at least one layer may also be oriented so that the cellulose fibers are arranged in a cross shape. The at least one layer may then be arranged so that the texture direction of the cellulose fibers of one of the at least one layer is perpendicular to the texture direction of the cellulose fibers of another of the at least one layer. The at least one layer may also be arranged so that the texture direction of the cellulose fibers of one of the at least one layer is at an angle of 0°-90° to the texture direction of the cellulose fibers of another of the at least one layer, thereby achieving a cross shape with an angle ranging from zero to a right angle.

[0074] The PCB can be manufactured so that it has at least one developable and / or non-developable surface portion. In the context of the present invention, a developable surface is a smooth surface with zero Gaussian curvature. Gaussian curvature is defined as the product of the two principal curvatures of a surface. In other words, a developable surface is a non-flat surface that can be flattened onto a plane without deformation, i.e. it can be bent without stretching or compressing. Conversely, it is a surface that can be made by transforming a plane by means of folding, bending, rolling, cutting and / or gluing. Examples of developable surfaces are cylinders and cones. In contrast, a non-developable surface is a surface with non-zero Gaussian curvature. Therefore, a non-developable surface is a non-flat surface that cannot be flattened onto a plane without deformation. Most surfaces are typically non-developable surfaces. Non-developable surfaces can be referred to as hyperbolic surfaces. One of the most commonly used non-developable surfaces is a sphere.

[0075] The PCB substrate according to the invention exhibits high moisture resistance due to the possible combination of the properties of the binder and the production process. The short cellulose fibers are impregnated with the binder in their entirety, and the PCB material becomes waterproof to a greater extent than a product containing long cellulose fibers. The term "waterproof" means hydrophobic and / or having a density that prevents water from penetrating the material. Since the short cellulose fibers can easily move within the composite material during manufacture, the prepreg is enabled to fuse during the pressing step, because the fibers can float and fill cracks and tears that may occur during the manufacture of the PCB.

[0076] Further, it has been found that the PCB substrate according to the present invention is flammable and self-extinguishing. According to the glow wire test performed according to IEC60695-2-12:2021, the PCB substrate according to the present invention passed the temperature test at 650° and 850°C when cured with PFA as a binder. The PCB substrate according to the present invention is fire resistant according to STD 104-0001 / ISO3795, UV resistant according to STD 423-0061, scratch resistant according to STD 423-0030, heat resistant according to Volvo STD 423-0055, impact resistant according to EN 13087, and VOC-free according to the Volvo STD429-0003 test.

[0077] The PCB substrate of the present invention may be rigid.The term "rigid" in the context of the present invention is intended to mean lacking or having no flexibility.

[0078] like Figure 4 As shown in , the PCB may have an additional conductive layer on at least one of its top and bottom surfaces and or on both the top and bottom surfaces. The conductive layer may be arranged directly on the top and / or bottom surfaces, or may be arranged on an additional insulating layer different from the PCB substrate, wherein the insulating layer is arranged on the top and / or bottom surfaces of the PCB. The conductive layer may contain, for example, copper, aluminum, iron, graphene, a conductive polymer, or a combination thereof.

[0079] PCB can include Figure 1-Figure 3 and Figure 6 d)- Figure 6f) shown in the cutout. These cutouts can be non-plated or plated, and can be at least one of a hole, a slot, a groove or other cavity. The hole, slot or other cavity can be formed as a through hole, slot or other cavity, in which case this means that they extend through the entire thickness of the PCB, or can be formed as a blind hole, slot or other cavity, which means that they do not extend through the entire thickness of the PCB, but only extend to a certain depth in the PCB, wherein the depth is understood to have an extension less than the thickness of the PCB. The hole can have a circular shape, and the slot can be understood to have an elongated shape. The groove can be understood as an elongated indentation in the substrate, which can have a v-shaped or u-shaped cross-section.

[0080] The cellulose fibers are impregnated with a mixture of an acidic curing catalyst and a binder and precured to obtain a so-called prepreg, as mentioned in step i) above. In the context of the present invention, a prepreg is understood to be an intermediate in the manufacturing process of the PCB according to the present invention. A prepreg is understood to be a cellulose fiber sheet impregnated with a catalyst and a binder and heat-treated in a precuring step. In the precuring step, the impregnated cellulose fibers are treated by applying heat in the range of 50°C–300°C. This treatment produces a viscous semi-solid structure, allowing lay-up of layers, which forms a stack of desired thickness that can be cured in a later step.

[0081] The prepreg stack for making the PCB of the present invention may be in the form of at least one precured cellulose fiber layer impregnated with a binder and an additive. Further, the prepreg stack for making the PCB of the present invention may include at least two layers, preferably at least three layers. Each of these layers preferably contains a cellulose fiber and binder mixture as described above.

[0082] The at least one prepreg may be arranged as a stack so that the cellulose fibers of each of the at least one prepreg may be oriented so that the longitudinal extension of the cellulose fibers is substantially parallel. The at least one prepreg may also be arranged so that the longitudinal extension of the cellulose fibers of one of the at least one prepreg is perpendicular to the longitudinal extension of the cellulose fibers of another of the at least one prepreg.

[0083] It has been unexpectedly found that, although the prepreg stack of the present invention comprises at least one impregnated fiber layer, the final PCB according to the present invention is considered to be made of a homogeneous material. Without wishing to be bound by theory, it is believed that such an effect is achieved due to a cellulose fiber length of less than 10 mm. As described above, the short hydrophilic cellulose fibers are substantially completely impregnated with the binder. Further, when the stack of prepregs is subjected to high pressure and high temperature and formed into a PCB, cracks are hardly formed because the cellulose fibers can float and rearrange without breaking due to the short fiber length. The pressure may be at least 7 kg / cm2, preferably at least 25 kg / cm2, more preferably at least 30 kg / cm2, and the temperature may be at least 60°C, preferably at least 140°C, more preferably at least 150°C. In particular, the temperature may be from 148°C to 152°C. The time period may be at least 10 seconds, preferably at least one minute, more preferably at least two minutes.

[0084] Figure 8 The behavior of the cellulose fibers during the pressing step is demonstrated. The cellulose fibers in the prepreg start to exhibit floating properties at a temperature of about 60°C, and the material cures at a temperature of about 150°C.

[0085] Further, during the manufacturing process, even if a crack occurs in one of the layers of the laminate, it may be filled with cellulose fibers from at least one of the adjacent layers of the laminate.

[0086] The PCB according to the present invention may be manufactured by air bag molding, injection molding or by thermoforming.

[0087] The prepreg and / or PCB substrate can be cut into a predetermined shape by a cutting device, which may include scissors, saws, stamping, punching, cutting machines (such as water jet cutting machines), computer numerical control (CNC) routers, laser cutting machines or presses. The prepreg and / or PCB substrate can be cut into small sizes by the aforementioned devices, for example, a minimum size of 1*1 mm in the xy direction is achievable.

[0088] The method for manufacturing a PCB may include creating a cutout or cavity by means of a cutout creating device. The cutout creating device may include drilling, milling, stamping, punching, water jet cutting, cutting with a CNC engraver, laser cutting, engraving and / or scraping.

[0089] The method for manufacturing a PCB may include a step of adding a conductive layer during the manufacturing process. The conductive layer may be added during the temperature and pressure treatment of the prepreg. At least one conductive layer may be added to the top or bottom surface of the stack when placed in a pressing tool. The stack of conductive layers and prepregs is then subjected to a pressing step in the pressing tool, and the conductive layer adheres to the surface of the prepreg stack. Tests have shown that adhesion is strong even without the addition of an adhesive. However, it is conceivable that an additional adhesive may be added. During the manufacturing process, a conductive layer may be added to one or two or more surfaces of the prepreg stack, thereby producing a PCB substrate coated with a conductive layer on one or both sides. When copper is used as the conductive material, it is unexpectedly noted that the good adhesion properties of copper to the PCB substrate (without being bound by theory) may also be attributed to the manufacturing process of curing the stack of impregnated cellulose fibers with the conductive layer (in this case, copper) in the pressing tool.

[0090] The produced PCB substrates with or without a conductive layer are suitable for use in the manufacture of printed circuit boards (PCBs), where the PCB substrate is the physical material that holds the traces and components of the PCB, provides a structure that physically holds circuit components and printed wiring in place, and provides electrical insulation between conductive parts.

[0091] These PCB substrates have insulating properties and are suitable for use as PCB substrates without the use of an insulating layer between the conductive layer and the PCB substrate, but it is conceivable that an additional insulating layer may be provided. An electrical insulator is understood to be a material within which electric charge does not flow freely and therefore does not conduct electricity under the influence of an electric field.

[0092] The PCB substrate can be manufactured according to the needs of the PCB industry. The most common industry standard PCB thicknesses are 0.78 mm, 1.57 mm and 2.36 mm, but thicker or thinner thicknesses can also be achieved with the present invention.

[0093] Figure 6 3 different types of PCBs that can be implemented with the concept of the present invention are shown. A single layer PCB can be manufactured with the PCB substrate according to the present invention. A single layer PCB has only a single conductive layer of conductive material (e.g. copper) on one side of a non-conductive PCB substrate.

[0094] A double layer PCB has one conductive layer on top of a non-conductive substrate, and another conductive layer on the opposite side (top and bottom surfaces of the PCB substrate). The two conductive sides can be connected using, for example, plated holes in the substrate (so-called vias), which connect to pads on both sides of the circuit board. A double layer PCB can also be manufactured using a PCB substrate according to the present invention.

[0095] A multilayer PCB is a circuit board with three or more conductive layers (e.g. copper). The conductive layers are at the top and bottom, and at least one conductive layer is sandwiched between a non-conductive substrate. This arrangement of layers increases the surface area for wiring connections and also allows it to be packed more densely and, therefore, covers a much smaller space. Multilayer PCBs are also manufactured using a PCB substrate according to the present invention.

[0096] It is contemplated that one or more layers of conductive material may be added on and / or between one or more prepreg layers during the manufacturing process. In this case, the layered structure of conductive material and prepreg will be cured, with at least one layer of conductive material being sandwiched between at least two prepreg layers, thereby producing a PCB substrate in which at least one layer of conductive material is sandwiched between at least two prepreg layers, such as Figure 6 c) as shown.

[0097] In summary, the present invention provides a PCB substrate comprising cellulose fibers, which are natural, readily available, highly recyclable, and therefore environmentally friendly and cost-effective materials. Another advantage of the present invention is that by-products from the food and agricultural industries are used as binders, which contributes to the circular economy and is environmentally beneficial.

[0098] Although the invention has been shown in the drawings and the foregoing description, such showing is to be considered illustrative or exemplary rather than restrictive; the invention is not limited to the disclosed embodiments. From a study of the drawings, the present disclosure and the appended claims, a person skilled in the art can understand and effect other variations of the disclosed embodiments in practicing the claimed invention. In the appended claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a, an" does not exclude a plurality. The mere fact that certain measures are cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A printed circuit board (PCB) substrate, comprising: at least one top surface, at least one bottom surface, Characterized in that the printed circuit board (PCB) further comprises: 60 to 90 wt. % of cellulose fibers having a length of at most 10 mm, 0 to 10 wt% of a curing catalyst, and 10 to 40 wt% of a binder selected from the group consisting of cellulose, hemicellulose, furan and its derivatives, lignin and combinations thereof.

2. The PCB substrate according to claim 1, wherein: The binder is polyfurfuryl alcohol (PFA).

3. The PCB substrate according to claim 2, wherein: The curing catalyst is an acidic curing catalyst present in an amount of 0.1 to 10 wt %.

4. A PCB substrate according to any one of the preceding claims, wherein: The cellulose fibers include 0-100% virgin cellulose fibers and 0-100% recycled cellulose fibers.

5. A PCB substrate according to any one of the preceding claims, wherein: The at least one top surface and / or bottom surface has at least one developable and / or non-developable surface portion.

6. A PCB substrate according to any one of the preceding claims, wherein: The cellulose fibers in the substrate are arranged substantially in parallel, or wherein the cellulose fibers in the substrate are arranged substantially crosswise, or wherein the cellulose fibers in the substrate are arranged substantially randomly, or a combination thereof.

7. A PCB substrate according to any one of the preceding claims, wherein: At least one conductive layer is adhered to the at least one top and / or bottom surface of the PCB substrate.

8. A PCB substrate according to any one of the preceding claims, wherein: The substrate includes at least one cavity.

9. A printed circuit board (PCB) comprising a substrate according to any one of the preceding claims.

10. The PCB according to claim 9, wherein: The PCB is a single-layer PCB, a double-layer PCB, or a multi-layer PCB.

11. A method for manufacturing a printed circuit board (PCB) substrate, the substrate comprising at least a top surface and a bottom surface, the method comprising the steps of: a) providing at least one sheet of cellulose fibers having a maximum length of 10 mm; b) impregnating the at least one sheet of cellulose fibers with a mixture of an acidic curing catalyst and a binder selected from the group consisting of cellulose, hemicellulose, furan and its derivatives, lignin and combinations thereof to obtain a PCB substrate.

12. The method for manufacturing a PCB substrate according to claim 11, wherein: The binder is polyfurfuryl alcohol (PFA).

13. The method for manufacturing a PCB substrate according to claim 11 or 12, wherein: The cellulose fibers comprise a mixture of 0-100% virgin cellulose fibers and 0-100% recycled cellulose fibers.

14. The method for manufacturing a PCB substrate according to claims 11 to 13, wherein: These cellulose fibers are provided in the form of paper.

15. The method for manufacturing a PCB substrate according to claims 11 to 14, further comprising the step c) of creating a cavity in the PCB substrate.

16. A method for manufacturing a printed circuit board (PCB), the method comprising the steps of: i) precuring the PCB substrate according to any one of claims 1 to 8 by applying heat in the range of 50° C. to 300° C., thereby obtaining a prepreg; ii) in the pressing tool at a pressure of at least 7 kg / cm 2 , preferably at least 25kg / cm 2 , more preferably at least 30kg / cm 2 The prepreg is pressed under a pressure of at least 60°C, preferably at least 140°C, more preferably at least 150°C, for a period of at least 10 seconds, preferably at least one minute, more preferably at least two minutes, thereby obtaining a PCB having at least one top surface and one bottom surface.

17. The method for manufacturing a PCB according to claim 16, wherein: The top and / or bottom surface has at least one developable and / or non-developable surface portion.

18. The method according to claim 16 or 17, further comprising the steps of: iii) providing a plurality of prepregs obtained in step i); iv) arranging the plurality of prepregs into a stack; wherein steps iii) and iv) occur after step i).

19. The method for manufacturing a PCB according to claim 18, wherein: The method further comprises a step v) of arranging at least one electrically conductive layer in the stack of prepregs, wherein step v) occurs simultaneously with step iv) or after step iv).

20. The method for manufacturing a PCB according to claim 18 or 19, wherein: The prepregs in the stack are oriented so that the grain directions are substantially parallel in the prepregs.

21. The method for manufacturing a PCB according to claims 18 to 20, wherein: The prepregs in the stack are oriented such that the grain direction in the prepregs is in the range of 0° to 90° relative to adjacent prepregs.

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