Substrate manufacturing method

Abstract

The objective is to provide a method for manufacturing substrates with high thickness accuracy. [Solution] According to the embodiment, a method for manufacturing a substrate 1 is provided. The method for manufacturing a substrate 1 includes the step of bonding a film 3 containing fluororesin to each of the surface layers 22 of a glass cloth 21 having surface layers 22 containing molten fluororesin on both sides.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a substrate.

Background Art

[0002] As a method for manufacturing a substrate, there is a method of coating both sides of a glass cloth with a fluororesin. In order to adjust the thickness of the fluororesin, it is necessary to adjust the number of coating times of the fluororesin. Patent Document 1 describes that impregnation coating is repeated a plurality of times to form a fluororesin-containing layer on a glass cloth.

[0003] However, in the coating of the fluororesin, coating unevenness and generation of bubbles are likely to occur. When coating unevenness and generation of bubbles occur, the surface state of the substrate deteriorates. The more the number of coating times of the fluororesin, the more likely coating unevenness and bubbles are to occur. Further, when coating is repeated on a coating film with coating unevenness, the surface state of the substrate is more likely to deteriorate.

[0004] Therefore, when the number of coating times of the fluororesin is increased, the surface state of the substrate is likely to deteriorate. Therefore, there has been a problem in thickness accuracy in the manufacture of the substrate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a method for manufacturing a substrate with high thickness accuracy.

Means for Solving the Problems

[0007] According to the embodiment, a method for manufacturing a substrate is provided. The method for manufacturing a substrate includes a step of bonding a film containing a fluororesin to each of the surface layers of a glass cloth having surface layers containing a molten fluororesin on both sides. [Effects of the Invention]

[0008] According to embodiments of the present invention, a method for manufacturing a substrate with high thickness accuracy can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing an example of a substrate manufacturing method according to the embodiment. [Figure 2] A schematic diagram showing an example of a film manufacturing method. [Figure 3] A schematic diagram showing a manufacturing method for a substrate related to another example. [Figure 4] A schematic diagram showing an example of impregnation coating. [Modes for carrying out the invention]

[0010] Conventionally, substrates containing resin layers and glass cloths were manufactured by coating the glass cloth with a resin-containing dispersion multiple times. For example, such a method is as follows: First, a dispersion containing a melt-type fluororesin is coated onto the glass cloth to form a melt-type fluororesin layer on the surface of the glass cloth. Next, a dispersion containing a filler and a fluororesin is coated on top of the melt-type fluororesin layer to form a fluororesin layer. By this method, a substrate is obtained in which a melt-type fluororesin layer and a fluororesin layer are laminated in this order on the surface of the glass cloth.

[0011] A dispersion containing a filler and a fluororesin may, for example, contain silica as the filler and polytetrafluoroethylene (PTFE) as the fluororesin. Such a dispersion has poor adhesion to glass cloth. To improve adhesion, it is necessary to form a melt-type fluororesin layer on the surface of the glass cloth beforehand. Perfluoroalkoxyalkane (PFA), which has high adhesion to glass cloth, is used as the melt-type fluororesin.

[0012] A conventional method for manufacturing substrates will be explained with reference to Figure 3.

[0013] Figure 3 is a cross-sectional view showing a conventional substrate manufacturing method. The conventional substrate manufacturing method 100 includes stacking metal foil 4 on each of the fluororesin layers 103 provided on both sides of a composite fabric 102 and heating and pressing in the stacking direction with a press machine 11. The heating and pressing joins the fluororesin layer 103 and the metal foil 4 to obtain a substrate 101.

[0014] The composite fabric 102 includes a glass cloth 21 made of glass fibers 23 in a plain weave, and a melt-type fluororesin layer 122 provided on both sides of the glass cloth 21.

[0015] The methods for forming the melt-type fluororesin layer 122 and the fluororesin layer 103 will be described below. The method for forming the melt-type fluororesin layer 122 and the fluororesin layer 103 by impregnation coating will be described below.

[0016] Figure 4 is a schematic cross-sectional view showing an example of impregnation coating.

[0017] In Figure 4, upstream or downstream refers to being upstream or downstream in the direction of travel b, respectively. In Figure 4, upper or lower refers to being upper or lower along the direction of gravity, respectively.

[0018] Reference numeral 131a in Fig. 4 indicates a delivery roll that feeds out the glass cloth 21, which is the base material, along the traveling direction b. A tank 133b filled with a second dispersion liquid 133a in which a melt-based fluororesin is dispersed is arranged on the downstream side of the delivery roll 131a. The glass cloth 21 wound around the delivery roll 131a passes through rolls 131b and 131c in this order and is sent to a roll 131d disposed in the second dispersion liquid 133a of the tank 133b.

[0019] On the downstream side of the roll 131d and above the tank 133b, a heating furnace 136 is arranged. Inside the heating furnace 136, a pair of spacers 134 and a roll 131e are arranged in this order along the traveling direction b. Downstream of the heating furnace 136, rolls 131f to 131k and a winding roll 131l are arranged.

[0020] Using the device (vertical tower) having the above-described configuration, a melt-based fluororesin layer 122 is formed on both surfaces of the glass cloth 21 in the following procedure.

[0021] First, the glass cloth 21 wound around the delivery roll 131a is sent to the side of the roll 131d disposed in the second dispersion liquid 133a, and the second dispersion liquid 133a is applied to the glass cloth 21. Next, the excess second dispersion liquid applied to the surface of the glass cloth 21 is scraped off by the pair of spacers 134. Subsequently, the glass cloth 21 to which the second dispersion liquid 133a has been applied is sent to the heating furnace 136 and heat-treated.

[0022] By the heat treatment, a melt-based fluororesin layer 122 is formed from the second dispersion liquid 133a applied to both surfaces of the glass cloth 21. Through the above coating, a composite fabric 102 having melt-based fluororesin layers 122 formed on both surfaces of the glass cloth 21 is obtained. The composite fabric 102 passes through rolls 131f to 131k and is wound around the winding roll 131l. [[ID=​​​​ The method for forming the fluororesin layer 103 is the same as the method for forming the melt-type fluororesin layer 122 described above with reference to Figure 4, except for the following: In Figure 4, the composite fabric 102 is used instead of the glass cloth 21, and the second dispersion is changed to a third dispersion containing dispersed fluororesin. In this way, the fluororesin layer 103 can be formed on both sides of the composite fabric 102.

[0025] The thickness of the fluororesin layer 103 obtained per coating of the third dispersion is thin, between 10 μm and 20 μm per side of the glass cloth. Therefore, in order to adjust the thickness of the fluororesin layer 103, it is necessary to repeatedly coat the glass cloth with the third dispersion.

[0026] When the coating process is repeated multiple times, the composite fabric obtained by the method described above, with fluororesin layers formed on both sides, is subjected to repeated application of the third dispersion and heat treatment. This forms multiple layers of fluororesin. In this way, the thickness of the fluororesin layers is adjusted.

[0027] As described above, the conventional method for manufacturing substrates involves applying the second dispersion liquid once or more times, followed by applying the third dispersion liquid once or more times. Therefore, it is necessary to repeat the coating process multiple times.

[0028] In coating, unevenness and air bubbles can occur with each application. Therefore, the more the coating process is repeated, the more likely it is that unevenness and air bubbles will occur. Consequently, variations in thickness are more likely to occur. Furthermore, if coating is repeated on a coating film with unevenness, variations in the substrate thickness tend to increase even further. Therefore, substrates obtained by conventional manufacturing methods that involve multiple coating applications have the problem of low thickness accuracy and poor surface condition.

[0029] Specifically, in the conventional substrate manufacturing method described above, if the fluororesin layer as a dielectric is manufactured to a thickness of 127 μm, and the total thickness of the composite fabric and fluororesin layer is 140 μm, the variation in the total thickness becomes large, at ±10 to 15 μm. However, the glass cloth shows little variation in thickness. In other words, the variation in the total thickness of the composite fabric and fluororesin layer is caused by variations in the thickness of the melt-type fluororesin layer and the fluororesin layer.

[0030] Thickness variations can occur, for example, in coating using the vertical tower described above, when the spacer 134 scrapes off excess dispersion, the dispersion does not fall evenly. More specifically, when the dispersion is scraped off and flows downward, a liquid flow similar to a rip current is generated, and along this flow, areas with a locally higher liquid volume (dripping) may occur. In addition, the viscosity and / or concentration of the dispersion tends to be higher in these areas. Even after passing through the spacer 134, the thickness of the coating film that has experienced such dripping tends to be thicker in the dripped areas. As a result, the thickness of the coating film tends to be uneven in the direction perpendicular to the direction of travel b. In other words, thickness variations are likely to occur. Dripping is more likely to occur when a highly viscous dispersion is coated using a vertical tower.

[0031] In particular, dispersions containing fillers tend to have high viscosity and / or concentration. Therefore, uneven coating is likely to occur when coating using a vertical tower. When coating such high-viscosity dispersions using a vertical tower, fine-tuning the thickness becomes difficult.

[0032] In the formation of melt-type fluororesin layers and fluororesin layers, attempts have been made to adjust the thickness and amount of coating by changing various factors, such as the coating speed, the arrangement of spacers, and the shape of the spacers. However, coating that involves such adjustments is complicated and difficult. An example of changing the arrangement of spacers is to make the heights of the pair of spacers 134 shown in Figure 4 different in order to form a coating film evenly on both sides. However, even in this case, if the viscosity of the dispersion is high, more than the specified amount of dispersion can easily pass through the spacers. As a result, thicker areas may occur in the coating film.

[0033] In the conventional substrate manufacturing methods described above, it is particularly difficult to achieve high thickness accuracy when manufacturing thick substrates. In other words, when high thickness accuracy is required in substrate manufacturing, the degree of design freedom for the substrate thickness may be reduced.

[0034] Poor thickness accuracy in a circuit board can negatively affect its electrical properties. This is especially true for high-frequency circuit boards, where thickness accuracy has a significant impact on electrical characteristics.

[0035] (First Embodiment) The manufacturing method of the substrate according to the embodiment includes a step of bonding a film containing fluororesin to each of the surface layers of a glass cloth having surface layers containing molten fluororesin on both sides.

[0036] The manufacturing method involves a step of bonding a film containing fluororesin to each of the surface layers. Therefore, a layer containing fluororesin can be formed without repeatedly coating a dispersion containing fluororesin. As a result, the thickness accuracy of the substrate can be improved.

[0037] A method for manufacturing a substrate according to an embodiment will be further described with reference to the drawings.

[0038] Figure 1 is a schematic diagram showing a method for manufacturing a substrate according to an embodiment.

[0039] The substrate manufacturing method 1 according to the embodiment includes, for example, layering a film 3 on each of the surface layers 22 provided on both sides of a glass cloth 21. The glass cloth 21 is, for example, a woven fabric made of glass fibers 23 in a plain weave. The glass cloth 21 and the surface layers 22 provided on both sides of the glass cloth 21 can be collectively referred to as fabric 2. In other words, it can also be said that the method includes layering a film 3 on each of the two sides of fabric 2. A metal foil 4 may be further layered on top of the film 3.

[0040] A laminate is obtained as described above. The laminate may have a structure in which a film 3 is layered on each of the two sides of the fabric 2. For example, it may have a structure in which a film 3 and a metal foil 4 are layered on each of the two sides of the fabric 2 in that order.

[0041] The resulting laminates are joined together. Figure 1 shows an example of joining, where the laminates are heated and pressed in the lamination direction using a press machine 11. Heating and pressing can be performed, for example, by heating and pressing the laminates from both sides using a press machine equipped with a pair of plate-shaped heat sources, such as the press machine 11 shown in Figure 1. Heating and pressing is preferably performed using a vacuum press device having a heating and pressing means composed of a pair of plate-shaped heat sources. Heating and pressing may also be performed continuously using, for example, a hot roll laminating device equipped with a pair of metal rolls.

[0042] The heating method in the heating press means is not particularly limited, and conventional known methods that can heat to a predetermined temperature can be adopted, such as a heat circulation method, a hot air heating method, or an induction heating method.

[0043] The pressurizing method in the heating press means is not particularly limited, and conventionally known methods that can apply a predetermined pressure, such as a hydraulic system, a pneumatic system, or a gap-to-gap pressure system, can be employed.

[0044] The settings for heating temperature, press pressure (surface pressure), and vacuum level during a heated press can be changed according to the elapsed time of the heated press process. For example, the heating temperature, press pressure, and vacuum level can be gradually increased according to the elapsed time of the heated press process, and then, from a certain point, the heating temperature, press pressure, and vacuum level can be gradually decreased according to the elapsed time.

[0045] The heating press can be performed for, for example, 60 minutes to 150 minutes. The heating temperature can be set, for example, within the range of room temperature to 400°C. In order to bond the surface layer and the film, it is preferable to heat to a temperature above the melting point of the molten fluororesin contained in the surface layer, for example, a temperature of 350°C to 370°C.

[0046] The pressing pressure is, for example, 5 kg / cm². 2 More than 50kg / cm 2 The pressure can be set within the following range. It is also possible to set it so that no pressure is applied. Higher pressure tends to improve peel strength. However, excessively high pressure is undesirable because it may alter the dimensions of the substrate.

[0047] In this way, the surface layer 22 and the film 3 can be bonded together. Furthermore, the film 3 and the metal foil 4 can be bonded together. Thus, a substrate 10 can be obtained in which the film 3 and the metal foil 4 are bonded in this order to the surface layers 22 provided on both sides of the glass cloth 21.

[0048] Figure 1 shows an example of bonding a laminate having a structure in which film 3 and metal foil 4 are layered in that order on both sides of fabric 2. However, the layering of metal foil 4 on top of film 3 may be omitted. In this case, a substrate can be obtained in which film is layered and bonded on each of the surface layers provided on both sides of the glass cloth.

[0049] According to the manufacturing method of the embodiment, the surface layers 22 provided on both sides of the glass cloth 21 and the film 3 are bonded together. In other words, the glass cloth and the film are bonded together via the surface layers. Since the surface layers have high bonding strength with both the glass cloth and the film, the peel strength of the substrate can be improved. The peel strength of the substrate may be, for example, 1.0 kN / m or more. Therefore, according to this manufacturing method, a substrate with high peel strength and high thickness accuracy can be manufactured.

[0050] The peel strength of the substrate refers to the strength at which peeling occurs at either the bonding surface between the glass cloth and the surface layer, or the bonding surface between the film and the metal foil, or when the film undergoes cohesive failure, when the substrate is subjected to the peel strength test specified in JIS C 6481.

[0051] Because the manufacturing method according to this embodiment has high thickness accuracy, the substrate can be suitably used in applications that require support for high frequency ranges, such as 2.5 GHz to 3.5 GHz. The substrate may be, for example, a high-frequency substrate.

[0052] The substrate manufactured by the manufacturing method according to the embodiment comprises a glass cloth, a surface layer, and a film. The substrate may further comprise a metal foil. The glass cloth, surface layer, film, and metal foil are described below.

[0053] (Glass cloth) Examples of glass cloth include woven or nonwoven fabrics containing glass fibers. Figure 1 shows an example of a glass cloth 21 in which glass fibers 23 are woven in a plain weave, but the form of the glass cloth 21 is not limited to this. For example, a woven fabric containing glass fibers may be formed by a weaving method other than plain weave, and this woven fabric may be used as glass cloth. Examples of weaving methods other than plain weave include twill weave, satin weave, gauze weave, and shaggy weave. In addition, a nonwoven fabric containing glass fibers may be used as glass cloth.

[0054] Glass cloth may be made of glass fibers. An example of glass cloth made of glass fibers is a woven fabric made by plain weaving glass fibers.

[0055] (Surface layer) The molten fluororesin contained in the surface layer may be, for example, a fluororesin with a melting point of less than 310°C. Examples of molten fluororesins include perfluoroalkoxyalkanes (PFAs) and perfluoroethylenepropene copolymers (FEPs). There may be one or more types of molten fluororesins. Conventional melt-type fluororesins used in substrates may also be used as the molten fluororesin. The melting point of the molten fluororesin may be, for example, 260°C or higher. Fluororesins with a melting point of less than 300°C may also be used as the molten fluororesin.

[0056] The surface layer preferably contains the same type of fluororesin as the film, in addition to the molten fluororesin. For example, if the film contains polytetrafluoroethylene (PTFE), it is preferable that the surface layer also contains PTFE. Such a surface layer can improve adhesion to the film.

[0057] The proportion of molten fluororesin in the surface layer can be, for example, 10% by mass or more and 100% by mass or less.

[0058] (film) The fluororesin contained in the film may be, for example, a fluororesin with a melting point of 300°C or higher. Examples of such fluororesins include polytetrafluoroethylene (PTFE) and perfluoroalkoxyalkanes (PFA). The proportion of fluororesin in the film can be, for example, 30% by mass or more and 100% by mass or less. The fluororesin contained in the film may be the same as or different from the molten fluororesin contained in the surface layer.

[0059] The film may further contain fillers. An example of a filler is silica. The filler may take the form of, for example, granular, plate-like, needle-like, or fibrous.

[0060] If the film does not contain fillers, the relative permittivity of the substrate obtained by the manufacturing method according to the embodiment may be close to the relative permittivity of the fluororesin contained in the film. For example, if the film containing the substrate contains PTFE but does not contain fillers, the relative permittivity of the resulting substrate may be close to 2.1, which is the relative permittivity of PTFE. If the film contains fillers, the relative permittivity of the substrate obtained by the manufacturing method according to the embodiment can be adjusted.

[0061] The dielectric constant of the substrate is preferably between 2.5 and 3.5. The dielectric constant of the substrate may vary depending on the type of fluororesin, the type and content of the filler. For example, the dielectric constant tends to increase as the filler content increases.

[0062] Furthermore, films containing fillers have a lower coefficient of thermal expansion (CTE) compared to films without fillers. Therefore, they are less susceptible to deformation such as warping due to heat. Consequently, substrates with less thermal deformation can be manufactured.

[0063] When the filler content in the film is between 55% by mass and 65% by mass, it is easier to obtain a substrate with a low coefficient of thermal expansion and a dielectric constant within an appropriate range.

[0064] (Metal foil) The type of metal foil 4 can be appropriately selected depending on the application of the substrate being manufactured. For example, when the substrate is used in electronic equipment, examples of metal foil materials include copper or copper alloys, stainless steel or its alloys, nickel or nickel alloys, and aluminum or aluminum alloys. The metal foil may also be copper foil, for example.

[0065] The substrate manufacturing method according to the embodiment may further include a surface layer formation step of providing surface layers on both sides of a glass cloth and a film manufacturing step, before the step of bonding the film to the surface layer. For example, after performing the surface layer formation step and the film manufacturing step, a substrate can be obtained by bonding the film manufactured in the film manufacturing step to the surface layers provided on both sides of the glass cloth.

[0066] The surface layer formation process and the film manufacturing process are described below.

[0067] (Surface layer formation process) The surface layer formation process involves, for example, applying a dispersion containing a molten fluororesin to a glass cloth and firing it to obtain a surface layer. Hereafter, the dispersion used in the surface layer formation process may be referred to as the first dispersion.

[0068] The first dispersion may be, for example, a dispersion in which a soluble fluororesin is dispersed in a dispersion medium. In addition to the soluble fluororesin, the same type of fluororesin contained in the film may also be dispersed.

[0069] Examples of dispersion media include water. The molten fluororesin and the same type of fluororesin contained in the film may each be included in the first dispersion, for example, in particulate form.

[0070] The mass ratio of the molten fluororesin to the same type of fluororesin contained in the film in the first dispersion can be, for example, made the same as the mass ratio of each resin in the target surface layer.

[0071] The first dispersion can be obtained, for example, by mixing a dispersion of a molten fluororesin with a dispersion of the same type of fluororesin contained in the film.

[0072] The application (primer) of the first dispersion to the glass cloth can be carried out by impregnation coating using a vertical tower, similar to the method for forming the melt-type fluororesin layer 122 described with reference to Figure 4. Specifically, the first dispersion is used instead of the second dispersion 133a shown in Figure 4. This allows the first dispersion to be applied to the glass cloth. This allows a surface layer to be formed instead of the melt-type fluororesin layer 122. Thus, a fabric with surface layers formed on both sides of the glass cloth 21 can be obtained.

[0073] However, the fewer the number of times the first dispersion is applied, the more preferable it is, and the more preferable it is to be applied once. Fewer applications of the first dispersion make it easier to obtain a surface layer with suppressed coating unevenness and bubbles, thus enabling the production of a fabric with high thickness accuracy.

[0074] (Film production process) The film manufacturing process involves, for example, coating a raw material liquid containing fluororesin onto a support material, drying and firing it to form a film, and then separating the film from the support material to obtain a film containing fluororesin. The film obtained through this film manufacturing process is sometimes called a cast film.

[0075] An example of the film manufacturing process will be explained with reference to Figure 2.

[0076] The manufacturing line used in the film production process, as illustrated in Figure 2, comprises rolls 31a to 31g, a liquid holding unit 32, a coater 34, and a drying oven 36.

[0077] The rolls are arranged in the order of rolls 31a to 31g along the direction of travel a. A support material (carrier film) 30 can be wound around roll 31a. The support material 30 wound around roll 31a is fed out in the direction of travel a and comes into contact with each of the rolls 31b to 31g in sequence.

[0078] The liquid-holding section 32 is provided so as to be in contact with a part of the support material 30. For example, the part of the support material 30 that is in contact with the roll 31c is in contact with the liquid-holding section 32. The raw material liquid 33 can be accumulated and held in the space defined by the support material 30 and the liquid-holding section 32.

[0079] The coater 34 is positioned so that its sides face the sides of the roll 31c at regular intervals.

[0080] The drying oven 36 is located between rolls 31d and 31e.

[0081] The method for manufacturing cast film using the above-mentioned manufacturing line (horizontal single-sided coating machine) is described below.

[0082] First, the support material 30 wound around the roll 31a is unwound in the direction of travel a, so that one side of the support material 30 comes into contact with the side of the roll 31c, and the other side comes into contact with the raw material liquid 33.

[0083] Next, the support material 30 is advanced further in the direction of travel a, passing between the roll 31c and the coater 34. At this time, the raw material liquid 33 that is in contact with the other of the two main surfaces of the support material 30 is scraped off by contact with the side surface of the coater 34. As a result, a coating film 35 of the raw material liquid 33 can be formed on the other surface of the support material 30 with a uniform thickness.

[0084] The coating film 35 formed in this manner is sent to a drying oven 36 for drying and firing. Thus, a film 37 can be formed. The support material 30 and the film 37 formed on the surface of the support material 30 are wound onto a roll 31g.

[0085] Subsequently, the obtained film 37 and the support material 30 are separated (not shown). Separation can be performed, for example, by peeling the film from the support material. The film 37 separated from the support material 30 can be obtained as a film (cast film).

[0086] In the method described above, the support material 30 can pass between the roll 31c and the coater 34 while remaining in close contact with the roll 31c. Therefore, the distance between the support material 30 and the coater 34 is easily kept constant, which reduces unevenness in the coating of the raw material liquid. As a result, even when coating a dispersion liquid with high viscosity and / or concentration, such as a dispersion liquid containing a filler, the thickness accuracy can be improved.

[0087] The thickness of the film obtained by the above method may be between 20 μm and 60 μm. The film thickness can be, for example, greater than 20 μm. According to the above method, accuracy can be particularly improved in the manufacture of films with a thickness of 60 μm or less.

[0088] Any known type of coater can be used as the coater 34. For example, a comma head coater can be used. A die coater may also be used as the coater 34. Note that the form of the liquid holding section 32 is not limited to the form shown in Figure 2 and can be appropriately changed depending on the type of coater.

[0089] The thickness of the coating film can be adjusted, for example, by adjusting the gap between the coater and the roll facing the coater, according to the desired coating thickness. By adjusting the coating thickness in this way, a thick film of 20 μm or more can be obtained in a single coating process. It is preferable that the coating film thickness is not excessively thick. The upper limit of the film thickness obtainable in a single coating process may be, for example, 60 μm. By keeping the coating film thickness at 60 μm or less, it is possible to suppress the flow of the raw material liquid before the coating film dries, thereby maintaining high thickness accuracy. In addition, it is possible to suppress the formation of cracks on the surface during drying, thus enabling the manufacture of substrates with a good surface condition.

[0090] In other words, in film manufacturing, it is not necessary to apply the dispersion solution multiple times to adjust the thickness. Therefore, the film thickness can be adjusted while maintaining thickness accuracy. For example, even when manufacturing thick films, high thickness accuracy can be achieved. Thus, it is possible to achieve both high thickness accuracy and a high degree of freedom in substrate design.

[0091] From the viewpoint of achieving high thickness accuracy, it is preferable to obtain a film by separating a film formed by a single coating on a support material from the support material. Compared to a fabric made by repeatedly coating glass cloth multiple times, a film formed in this way is less prone to coating unevenness, bubbles, etc., and thus thickness variations can be reduced. Specifically, the thickness variation of the film can be within ±2 μm from the target thickness. The thickness variation may be within ±1 μm from the target thickness. In other words, a film with a smooth surface can be obtained.

[0092] Substrates manufactured by bonding such films and fabrics can have reduced thickness variations. For example, the thickness variation can be kept within ±3 μm of the target thickness. The thickness variation may be within ±2 μm of the target thickness. Therefore, electrical losses can be reduced.

[0093] The raw material liquid used in the film manufacturing process may be, for example, a dispersion liquid in which fluororesin is dispersed in a dispersion medium. An example of a dispersion medium is water. The fluororesin may be included in the raw material liquid in particulate form. The raw material liquid may further contain fillers.

[0094] The mass ratio of fluororesin to filler in the raw material liquid can be, for example, made the same as the mass ratio of fluororesin to filler in the target film.

[0095] Examples of support materials include sheets containing polyimide or aluminum. Polyimide and aluminum are preferred because they have high heat resistance. Furthermore, sheets containing polyimide or aluminum can be smooth. Therefore, the surface of the film in contact with the support material can be made smooth, allowing for the production of a film with a smooth surface.

[0096] The coating can be dried, for example, by drying it at a temperature of 80°C to 120°C, followed by firing at a temperature of 250°C to 360°C. The total drying and firing time can be between 1 and 5 minutes.

[0097] According to the manufacturing method described above, the thickness accuracy of both the fabric and the film can be increased. Therefore, when a substrate is constructed by joining fabric and film, the substrate can be constructed from components with high thickness accuracy, thus increasing the thickness accuracy of the substrate.

[0098] The manufacturing method of the substrate according to the embodiment includes a step of bonding a film containing fluororesin to each of the surface layers of a glass cloth having surface layers containing molten fluororesin on both sides. Therefore, the thickness accuracy of the substrate can be improved.

[0099] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of Symbols]

[0100] 1...Manufacturing method, 2...Fabric, 3...Film, 4...Metal foil, 10...Substrate, 11...Press machine, 21...Glass cloth, 22...Surface layer, 23...Glass fiber, 30...Support material, 31a...Feeding roll, 31b~31g...Roll, 32...Liquid holding part, 33...Raw material liquid, 34...Coater, 35...Coating film, 36...Drying oven, 37...Membrane, 102...Composite fabric, 103...Fluororesin layer, 122...Melt-type fluororesin layer, 131a...Feeding roll, 131b~131k...Roll, 131l...Winding roll, 133a...Second dispersion liquid, 134...Spacer, 136...Heating oven, a...Direction of travel, b...Direction of travel.

Claims

1. A method for manufacturing a substrate, comprising the step of bonding a film containing a fluororesin to each of the surface layers of a glass cloth having surface layers containing a molten fluororesin on both sides.

2. The manufacturing method according to claim 1, wherein the film is obtained by coating a raw material liquid containing the fluororesin onto a support material to form a film, and then separating the film from the support material.

3. The manufacturing method according to claim 2, wherein the coating is performed using a comma head coater.

4. The manufacturing method according to any one of claims 1 to 3, wherein the film has a thickness of 20 μm or more.

5. The manufacturing method according to any one of claims 1 to 3, further comprising a filler in the aforementioned film.

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