Laminate

Abstract

To provide a laminate having a low dielectric constant, a low dielectric loss tangent, and low water absorption. [Solution] A laminate comprising a prepreg and a metal foil layer is provided. The prepreg includes NE glass cloth and a fluororesin-containing layer supported on the NE glass cloth. The fluororesin-containing layer contains hollow silica particles having hydrophobic functional groups on their surface.

Description

Technical Field

[0001] The present invention relates to a laminated board.

Background Art

[0002] In recent years, as diversification and sophistication have advanced in the information and communication environment, communication systems using high-frequency bands have attracted attention. Among high-frequency bands, high frequencies of 30 GHz or more, so-called millimeter waves, have a very large transmission information capacity but are prone to large transmission losses. Therefore, the demand for low-loss substrates for millimeter waves that can reduce transmission losses even when transmitting millimeter waves is increasing.

[0003] Since fluororesin is a material with very excellent electrical properties, a laminated board including a dielectric containing fluororesin and a metal foil as a conductor is used in various applications utilizing high-frequency bands. For example, in high-frequency compatible copper-clad printed boards, first, a low dielectric tangent is required, so a sheeted fluororesin has been preferably used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a laminated board having a low relative dielectric constant, a low dielectric tangent, and low water absorption.

Means for Solving the Problems

[0006] A laminate comprising a prepreg and a metal foil layer is provided. The prepreg includes NE glass cloth and a fluororesin-containing layer supported on the NE glass cloth. The fluororesin-containing layer contains hollow silica particles having hydrophobic functional groups on their surface. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a laminate having a low dielectric constant, a low dielectric loss tangent, and low water absorption. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic cross-sectional view showing an example of a laminate according to this embodiment. [Figure 2] A schematic cross-sectional view showing another example of a laminate according to the embodiment. [Figure 3] A schematic cross-sectional view showing another example of a laminate according to the embodiment. [Figure 4] A schematic cross-sectional view showing an example of a manufacturing line related to the impregnation coating process. [Modes for carrying out the invention]

[0009] Fluororesins possess excellent electrical properties, including a low dielectric constant and low dielectric loss tangent. Therefore, prepregs for high-frequency printed circuit boards have traditionally used materials such as sheets made by impregnating glass cloth with fluororesin dispersion and sintering, fluororesin films, and fluororesin fiber paper. However, since the dielectric constant of fluororesins is 2.1, and that of general-purpose E-glass cloth is 6.8, developing printed circuit boards with a dielectric constant below 2.1 has been difficult.

[0010] Furthermore, even if the dielectric constant and dielectric loss tangent of the substrate's constituent materials are low, the electrical properties of a substrate that absorbs moisture from the air or surrounding environment will deteriorate. Since water is a substance with very high dielectric constant and dielectric loss tangent, the electrical properties of a substrate with a high water absorption rate tend to deteriorate. Therefore, in order to maintain high electrical properties over the long term, a low water absorption rate is also required for a wiring substrate.

[0011] In the laminate according to this embodiment, a prepreg and a metal foil layer are laminated together. The prepreg is a fluororesin-containing layer supported on NE glass cloth, which contains hollow silica particles having hydrophobic functional groups on its surface. By constructing the prepreg with NE glass, which has a low dielectric constant and low dielectric loss, and a fluororesin blended with hollow silica fillers with high porosity, it is possible to provide a laminate with a low dielectric constant (Dk) and dielectric loss tangent (Df). In addition, because the hollow silica fillers have hydrophobic functional groups, a low water absorption rate can be achieved. Therefore, this laminate can function as a wiring board that can exhibit high electrical properties over the long term.

[0012] The laminated board according to this embodiment will be described in detail below.

[0013] Figure 1 is a schematic cross-sectional view showing an example of a laminate according to the embodiment. The laminate 1 comprises a prepreg 2 and a metal foil layer 3. The laminate may be a metal-clad laminate used, for example, as a material for a rigid substrate or a flexible printed circuit board.

[0014] The prepreg 2 comprises a glass cloth 4 as a core material and a fluororesin-containing layer 5 supported on both the front and back surfaces of the glass cloth 4. The prepreg 2 can function as a dielectric. The prepreg 2 is, for example, a sheet and has a front surface and a back surface. In the illustrated example, the fluororesin-containing layer 5 includes a first sublayer 51 and a second sublayer 52. The fluororesin-containing layer 5 may also be a single layer without being divided into sublayers. The first sublayer 51 is in contact with the glass cloth 4 and may be impregnated into openings, gaps in the weave structure, and gaps between yarns that the glass cloth 4 may have. The glass cloth 4 is NE glass cloth.

[0015] The fluororesin-containing layer 5 contains hollow silica particles as a filler in addition to the fluororesin. The hollow silica filler is an inorganic filler with a low relative dielectric constant. Therefore, in the fluororesin-containing layer 5, the relative dielectric constant is reduced because hollow silica particles are contained. Although it is known that the dielectric tangent tends to increase due to the blending of inorganic fillers, the use of NE glass cloth with a low dielectric tangent as the glass cloth 4 cancels out the increase due to the blending of inorganic fillers.

[0016] The hollow silica particles contained in the fluororesin-containing layer 5 have a hydrophobic functional group on their surface. By including a filler containing a hydrophobic functional group, the water absorption rate of the prepreg 2 is low. Therefore, the intrusion of moisture, which is a factor deteriorating the electrical characteristics, can be suppressed, and good electrical characteristics can be maintained for a long time.

[0017] The hollow silica particles having a hydrophobic functional group may not be contained in the first sublayer 51 in contact with the glass cloth 4 among the sublayers of the fluororesin-containing layer 5, for example, and may be contained only in the second sublayer 52 thereon. As described above, although the first sublayer 51 can be impregnated into the glass cloth 4, a fluororesin not containing an inorganic filler or the like has higher impregnability. Therefore, from the viewpoints of the integrity and strength of the prepreg, it is desirable that the first sublayer 51 does not contain hollow silica particles.

[0018] The metal foil layer 3 provided on the fluororesin-containing layer 5 can function as a conductor. The surface roughness of the contact surface of the metal foil layer 3 with the fluororesin-containing layer 5 is preferably 1 μm or less. Thereby, the smoothness of the interface between the metal foil layer 3 and the fluororesin-containing layer 5 can be increased, and the transmission loss can be reduced.

[0019] In FIG. 1, the case where the metal foil layer 3 is provided on both surfaces of the prepreg 2 is shown, but the metal foil layer 3 may be formed only on one of the front and back surfaces of the prepreg 2.

[0020] Figure 2 is a schematic cross-sectional view showing another example of a laminate according to the embodiment. The laminate shown in Figure 2 has the same configuration as the laminate shown in Figure 1, except that it further comprises a second fluororesin-containing layer 6 on both the front and back surfaces of the prepreg 2.

[0021] In the laminate 1 shown in Figure 2, a second fluororesin-containing layer 6 is formed between the prepreg 2 and the metal foil layer 3. Both the prepreg 2 and the second fluororesin-containing layer 6 can function as dielectrics. The second fluororesin-containing layer 6 contains, for example, a perfluoroalkoxyalkane resin. The second fluororesin-containing layer 6 functions, for example, as a layer that enhances the adhesion between the prepreg 2 and the metal foil layer 3.

[0022] Figure 3 is a schematic cross-sectional view showing another example of a laminate according to the embodiment. The laminate 1 shown in Figure 3 has the same configuration as the laminate 1 shown in Figure 1, except that it has multiple prepreg 2 layers between the metal foil layers 3 located in the outermost layer. The multiple prepreg 2 layers are laminated so that their main surfaces are in contact with each other. Figure 3 schematically shows a case where the laminate 1 has three or more prepreg 2 layers, but the number of prepreg 2 layers may be two. Alternatively, although not shown, a second fluororesin-containing layer and a metal foil layer may be sandwiched between the multiple prepreg 2 layers.

[0023] In Figure 3, a case is shown in which multiple prepregs 2 comprising glass cloth 4 and a fluororesin-containing layer 5 containing a first sublayer 51 and a second sublayer 52 are provided, but the configuration of the prepreg is not limited to this case. For example, the laminate 1 may comprise multiple prepregs, each containing a single layer of fluororesin-containing layer 5 without sublayers.

[0024] The thickness of the laminate 1 is, for example, within the range of 0.025 mm to 0.50 mm, and may also be within the range of 0.1 mm to 0.2 mm. The thickness of the laminate 1 refers to the thickness of the laminate along the lamination direction of the prepreg and metal foil layers, and, if present, the second fluororesin-containing layer. The thickness of the laminate 1 can be adjusted by adjusting the thickness of each layer or by changing the number of prepreg 2 layers to be laminated.

[0025] The thickness of the prepreg 2 is, for example, in the range of 0.08 mm to 0.16 mm, and preferably in the range of 0.10 mm to 0.14 mm.

[0026] (Glass cloth) Because the laminate contains glass cloth, linear expansion in the planar direction can be suppressed. Furthermore, its increased rigidity prevents foil breakage even when bent. If the laminate does not contain glass cloth, it may have difficulty withstanding reflow soldering.

[0027] The thickness of the glass cloth is, for example, in the range of 0.01 mm to 0.2 mm, preferably in the range of 0.02 mm to 0.09 mm.

[0028] To achieve even better low-loss characteristics, it is desirable to reduce dielectric loss caused by the glass cloth. Specifically, it is preferable that the glass cloth has a relative permittivity of 5 or less and a dielectric loss tangent of 0.002 or less at a frequency of 1 GHz. When the relative permittivity and dielectric loss tangent meet this numerical range, dielectric loss can be greatly reduced. Lower relative permittivity and dielectric loss tangent are preferable. When measuring the relative permittivity and dielectric loss tangent of the glass cloth, they can be measured in accordance with JIS R 1641:2007. In this embodiment, NE glass cloth is used as a glass cloth with low relative permittivity and low dielectric loss.

[0029] The glass cloth is preferably an open-fiber cloth. In an open-fiber cloth, the filaments of the glass yarn are open, for example, in a fuzzy state, which allows the fluororesin-containing layer to penetrate well into the glass cloth. However, it is preferable that the surface of the glass fiber yarn has few defects such as fuzzy defects that can form large protrusions, and defects such as loose threads. Having fewer of these large defects helps to suppress damage to the metal foil layer. The weave structure of the glass cloth is not particularly limited, and is, for example, plain weave.

[0030] The mass per unit area of ​​glass cloth is, for example, 10 g / m². 2 ~200g / m 2 It is within the following range. The fiber density of the glass cloth is, for example, within the range of 30 threads / 25mm to 90 threads / 25mm. The fiber density in the longitudinal direction and the fiber density in the transverse direction of the glass cloth may be different. The TEX count per fiber of glass fiber yarn is, for example, within the range of 1g / 1000m to 100g / 1000m.

[0031] (Fluororesin-containing layer) The fluororesin-containing layer is formed on both sides of the glass cloth. The fluororesin-containing layer constitutes part of the prepreg and includes, for example, at least one selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and perfluoroethylenepropene copolymer (FEP). It is preferable that the fluororesin-containing layer contains polytetrafluoroethylene.

[0032] As shown in the example in Figure 2, the laminate may further include a second fluororesin-containing layer in addition to the fluororesin-containing layer as a component of the prepreg. For convenience, the fluororesin-containing layer included in the prepreg is sometimes referred to as the "first fluororesin-containing layer" to distinguish it from the second fluororesin-containing layer.

[0033] The thickness of the first fluororesin-containing layer (thickness on one side) is not particularly limited, but may be in the range of 1 μm to 50 μm, or in the range of 1 μm to 40 μm.

[0034] The first fluororesin-containing layer contains hollow silica particles having hydrophobic functional groups on their surface as fillers. The fluororesin-containing layer containing hollow silica particles having hydrophobic functional groups provides the prepreg with a low dielectric constant and low water absorption rate. The hydrophobic functional groups on the surface of the hollow silica particles may include, for example, silane groups provided by surface treatment of the hollow silica particles. Examples of surface treatments include tetramethylsilane (TMS) treatment and propylsilane treatment.

[0035] The first fluororesin-containing layer may include a first sublayer in contact with the glass cloth and not containing hollow silica particles, and a second sublayer located on the first sublayer and containing hollow silica particles. Preferably, the first sublayer does not contain any inorganic fillers other than hollow silica particles. By not containing inorganic fillers in the first sublayer supported on the glass cloth, it is easier to maintain adhesion to the glass cloth over a long period of time.

[0036] The second sublayer may further contain inorganic fillers other than hollow silica particles having hydrophobic functional groups. Examples of such other inorganic fillers include silica, boron nitride, aluminum nitride, aluminum oxide such as alumina, titanium oxide, zinc oxide, calcium oxide, iron oxide, tin oxide, antimony oxide, dawsonite, calcium silicate, montmorillonite, bentonite, sepiolite, imogolite, yttria, magnesium oxide, forsterite, cordierite, steatite, silica balloons, and low-dielectric glass. One or more of these can be used in combination.

[0037] The inorganic filler mentioned above has a higher thermal conductivity compared to fluororesin. Therefore, when the first fluororesin-containing layer contains an inorganic filler, the laminate will have high thermal conductivity due to the high thermal conductivity of the prepreg. In addition, in this case, the thermal expansion coefficient of the prepreg can be reduced. Furthermore, the mechanical strength, such as the rigidity of the prepreg, can be increased.

[0038] From the viewpoint of improving thermal conductivity, the first fluororesin-containing layer preferably contains at least one inorganic filler selected from the group consisting of boron nitride, aluminum nitride, and aluminum oxide.

[0039] The average particle size of the inorganic filler is, for example, in the range of 0.0001 mm or more and 0.1 mm or less, preferably in the range of 0.0001 mm or more and 0.01 mm or less, and more preferably in the range of 0.0001 mm or more and 0.002 mm or less.

[0040] (Second fluororesin-containing layer) The second fluororesin-containing layer contains perfluoroalkoxyalkane (PFA) resin. If the first fluororesin-containing layer of the prepreg contains PFA and molten fluororesins such as FEP, the second fluororesin-containing layer contains PFA as a molten fluororesin, which has the effect of facilitating fusion between the first and second fluororesin-containing layers. Therefore, the second fluororesin-containing layer can function as a layer that enhances the adhesion between the prepreg and the metal foil layer. The second fluororesin-containing layer may also contain other components such as inorganic fillers to adjust the coefficient of thermal expansion and dielectric constant. To increase the peel strength of the metal foil layer, it is effective to use adhesive modified PFA as the PFA contained in the second fluororesin-containing layer. The second fluororesin-containing layer may consist only of adhesive modified PFA.

[0041] Adhesive-modified PFA resin is a modified PFA resin that exhibits excellent adhesion to other materials. While ordinary PFA resin is a copolymer of tetrafluoroethylene and perfluoroether, adhesive-modified PFA resin further contains modified monomer units that improve adhesion to metal foil layers.

[0042] The reason why the fluororesin's inclusion of adhesive modified PFA resin improves its adhesion to the metal foil layer is unclear, but it is possible that this improvement is due to specific functional groups present in the modified monomer units.

[0043] Adhesive modified PFA resin is melt-mold and possesses the same heat resistance, chemical resistance, weather resistance, low friction, non-stick properties, water and oil repellency, and electrical properties as ordinary PFA resin. The electrical properties of adhesive modified PFA resin refer, for example, to a low relative permittivity and dielectric loss tangent. The relative permittivity of adhesive modified PFA resin at a frequency of 1 GHz is preferably 2.06 or less, and the dielectric loss tangent is preferably 0.002 or less. The relative permittivity and dielectric loss tangent of adhesive modified PFA resin can be measured in accordance with JIS 2138:2007. By satisfying the above numerical ranges for the relative permittivity and dielectric loss tangent of adhesive modified PFA resin, the laminate can have excellent low-loss characteristics.

[0044] The melt flow rate of the adhesive modified PFA resin is preferably in the range of 10 g / 10 min to 25 g / 10 min. The tensile strength of the adhesive modified PFA resin is, for example, 35 MPa or more. The flexural modulus of the adhesive modified PFA resin is, for example, in the range of 600 MPa to 680 MPa. The melting point of the adhesive modified PFA resin is, for example, 290°C to 300°C.

[0045] An example of an adhesive modified PFA resin is Fluon+ EA-2000 manufactured by AGC Inc.

[0046] The second fluororesin-containing layer may further contain other fluororesins besides PFA, and may also contain additives. The other fluororesins are, for example, fluororesins that can be melt-molded. A fluororesin that can be melt-molded is a fluororesin whose melt flow rate is, for example, in the range of 2 g / 10 min to 40 g / 10 min. Preferably, the second fluororesin-containing layer contains 80% by mass or more of PFA resin.

[0047] Other fluororesins may be, for example, at least one selected from the group consisting of ethylene-tetrafluoroethylene copolymer (ETFE), perfluoroethylene propene copolymer (FEP), and polyvinylidene fluoride (PVDF).

[0048] The thickness of the second fluororesin-containing layer is, for example, within the range of 1 μm to 50 μm, preferably within the range of 1 μm to 5 μm. If the thickness of the second fluororesin-containing layer is excessively small, it tends to be difficult to obtain the effect of bonding the prepreg and the metal foil layer. If the thickness of the second fluororesin-containing layer is excessively large, the resin may flow during heating and pressing, which may result in uneven thickness of the laminate or defects in appearance.

[0049] (metal foil layer) The metal foil layer is a layer made of metal foil. The type of metal foil is not particularly limited and can be appropriately selected according to the application of the laminate. For example, when a laminate is used in electronic equipment, the material of the metal foil can be copper or copper alloy, stainless steel or its alloy, nickel or nickel alloy, or aluminum or aluminum alloy. In ordinary laminates used in electronic and electrical equipment, copper foil such as rolled copper foil and electrolytic copper foil is widely used, and copper foil is also preferred in the laminate according to this embodiment.

[0050] The surface roughness of the surface of the metal foil layer in contact with the fluororesin-containing layer may be, for example, 1 μm or less. A smaller surface roughness is preferable, as long as the peel strength between the metal foil layer and the fluororesin-containing layer meets the desired value. The desired value refers to the peel strength required depending on the application of the laminate, and is, for example, 0.4 kN / m or more, preferably 0.8 kN / m or more. The surface roughness of the surface of the metal foil layer on the back side of the interface with the fluororesin-containing layer is not particularly limited, but is, for example, 1.8 μm or less in Rz.

[0051] The surface of the metal foil may have a rust-preventive layer (an oxide film such as chromate) or a heat-resistant layer formed on it. Furthermore, to increase the peel strength with respect to the fluororesin-containing layer, the surface of the metal foil layer may be treated with a coupling agent or the like.

[0052] The thickness of the metal foil is not particularly limited; it should be a thickness that allows the laminate to perform adequately depending on its intended use. For example, the thickness of the metal foil layer is within the range of 10 μm to 40 μm.

[0053] <Method for manufacturing laminated boards> An example of a method for manufacturing a laminate according to the embodiment will be described with reference to the drawings. The laminate can be manufactured, for example, by a method including the following steps (1) to (4).

[0054] (1) A prepreg is prepared in which a fluororesin-containing layer is formed on a glass cloth. The prepreg can be prepared by, for example, the impregnation coating method shown in Figure 4. Figure 4 is a schematic cross-sectional view showing the process of preparing a prepreg by the impregnation coating method.

[0055] In Figure 4, reference numeral 110 indicates a feed roll that feeds out the glass cloth 4, which is the base material. Downstream of the feed roll 110 is an impregnation tank 120 filled with an aqueous dispersion 121 containing, for example, PTFE particles and / or FEP particles. The glass cloth 4 wound on the feed roll 110 is sent via roll 130a to roll 130b, which is located in the aqueous dispersion 121 in the impregnation tank 120, and the aqueous dispersion 121 is applied to the glass cloth 4. Above the impregnation tank 120 are a pair of doctor rolls 131. Above the doctor rolls 131 is a heating furnace 140 divided into sections with different heat treatment temperatures. This heating furnace 140 is divided into three blocks from bottom to top: a drying section 140a, a heat treatment section 140b, and a firing section 140c, and is controlled to have a temperature distribution where the temperature increases sequentially from the drying section 140a to the firing section 140c. Downstream of the heating furnace 140, rolls 130c, 130d, and 130e, and a winding roll 111 are arranged.

[0056] Using the apparatus having the above configuration, a fluororesin-containing layer is formed on the woven fabric by the following procedure.

[0057] First, the glass cloth 4 wound on the delivery roll 110 is sent to the roll 130b located in the impregnation tank 120, and the aqueous dispersion 121 is applied to the glass cloth 4. Next, the excess aqueous dispersion 121 applied to the surface of the glass cloth 4 is scraped off by a pair of doctor rolls 131. Subsequently, the glass cloth 4 coated with the aqueous dispersion 121 is sent to the drying section 140a of the heating furnace 140, and the applied aqueous dispersion 121 is dried at a temperature of 100°C or less to evaporate the water in the aqueous dispersion 121. Next, the glass cloth 4 is sent to the heat treatment section 140b, and is slowly heat-treated, for example at 305°C, to remove surfactants, additives, binders, etc. from the aqueous dispersion 121.

[0058] In the subsequent firing section 140c, firing may or may not be performed. If firing is performed in the firing section 140c, the firing temperature shall be, for example, above the melting point of the fluororesin used to form the fluororesin-containing layer. By passing through the firing section 140c, the fluororesin, or a mixture of fluororesin and hollow silica filler, is fused to the glass cloth to produce the prepreg 2. The prepreg 2 is wound onto the winding roll 111 via rolls 130c, 130d, and 130e.

[0059] The above operations may be repeated multiple times. That is, by repeatedly applying the aqueous dispersion to the wound prepreg, drying it, and firing it, a fluororesin-containing layer containing multiple sublayers can be formed. This allows the thickness of the fluororesin-containing layer in the prepreg to be adjusted. In addition, in the multiple applications, a dispersion without fillers may be applied in the earlier stages, and a dispersion containing fillers may be applied in the later stages. By using a dispersion without fillers in the initial stage, which is applied directly to the glass cloth 4, the impregnation of the fluororesin into the glass cloth 4 can be improved. In this way, a prepreg with a fluororesin-containing layer formed on the glass cloth is obtained.

[0060] Here, the "drying" in the drying section 140a is preferably a process of evaporating the water in the coated aqueous dispersion at a temperature of 100°C or lower. Furthermore, the "heat treatment" in the heat treatment section 140b is preferably a process of removing components other than resin particles, such as surfactants, additives, and binders, from the coated aqueous dispersion by treating them within a predetermined temperature range. The temperature range for the heat treatment is preferably 305°C or higher and less than 340°C.

[0061] (2) A second fluororesin-containing layer can be further laminated on both sides of the prepreg formed as described above by the impregnation coating method described above to enhance the adhesion between the prepreg and the metal foil layer. However, the formation of the second fluororesin-containing layer may be omitted.

[0062] As an aqueous dispersion for forming the second fluororesin-containing layer, for example, a dispersion containing PFA resin is prepared. The prepreg, which has the first fluororesin-containing layer formed on both sides of the glass cloth, is further impregnated with the prepared aqueous dispersion. In this way, the second fluororesin-containing layer can be formed on the first fluororesin-containing layer.

[0063] (3) Prepare a metal foil and laminate the metal foil onto the first fluororesin-containing layer of the prepreg, or onto a second fluororesin-containing layer formed on the prepreg, if any, to obtain a laminate. The metal foil may be laminated on one side of the laminate or on both sides.

[0064] After step (3), a protective backing foil may be laminated on the metal foil contained in the laminate to protect the metal foil. The protective backing foil is not particularly limited as long as it can withstand the heating temperature during the hot-press press described later, and examples include heat-resistant plastic film (non-thermoplastic polyimide film, etc.) and metal foil (copper foil, aluminum foil, SUS foil, etc.). The protective backing foil is provided, for example, to protect the metal foil layer when the laminate is cut to a desired size after the laminate has been manufactured. After the laminate has been cut to the desired size, the protective backing foil can be peeled off from the metal foil layer.

[0065] (4) The laminated body is subjected to hot-pressing to obtain a laminated plate according to the embodiment.

[0066] As an example, the details of the hot-pressing process in step (4) will be explained. To suppress contamination of the laminate, it is desirable that the hot-pressing process be carried out in a cleanroom.

[0067] Hot pressing is preferably performed by a vacuum press apparatus having a hot pressing means consisting of a pair of hot plates. Alternatively, hot pressing may be performed continuously by, for example, a hot roll laminating apparatus equipped with a pair of metal rolls.

[0068] The vacuum press apparatus has one or more heating plates capable of pressing two or more components together while heating them. The vacuum press apparatus also has a mechanism for performing hot-pressure pressing in a vacuum state. Other apparatus configurations are not particularly limited.

[0069] The heating method in the hot-pressure pressing means is not particularly limited, and conventionally known methods that can heat to a predetermined temperature can be employed, such as a heat circulation method, a hot air heating method, or an induction heating method.

[0070] The pressurizing method in the hot-pressure press means is not particularly limited, and conventionally known methods that can apply a predetermined pressure, such as hydraulic systems, pneumatic systems, or gap-to-gap pressure systems, can be employed.

[0071] The settings for heating temperature, press pressure (surface pressure), and vacuum level during hot-pressing can be changed according to the elapsed time of the hot-pressing process. For example, the heating temperature, press pressure, and vacuum level can be gradually increased according to the elapsed time of the hot-pressing process, and then, from a certain point, the heating temperature, press pressure, and vacuum level can be gradually decreased according to the elapsed time.

[0072] The hot press can be performed for, for example, 60 to 150 minutes. The heating temperature can be set, for example, within a range of room temperature or above 400°C.

[0073] The pressing pressure is, for example, 5 kg / cm². 2 -50kg / cm 2 It can be set within this range. It is also possible to set it so that no press pressure is applied. If the press pressure is insufficient, the peel strength of the metal foil layer tends to be poor. If the press pressure is excessively high, it is undesirable because it may cause the dimensions of the laminate to change.

[0074] The vacuum level can be set, for example, within the range of 0.1 Torr to 800.0 Torr. If the vacuum level is too low, air may be trapped between the layers of each material, potentially causing delamination and / or oxidation of the metal foil (copper foil). If the vacuum level is too high, the slippage of each material may also cause delamination.

[0075] According to the manufacturing method of the embodiment described above, the prepreg is equipped with NE glass cloth as a core material, and the fluororesin-containing layer of the prepreg contains not only fluororesin but also hollow silica particle fillers having hydrophobic functional groups on their surface, so a laminate with low dielectric constant, dielectric loss tangent, and water absorption can be obtained.

[0076] Such laminates can be mounted in various devices, including image sensors, in-vehicle radar for collision avoidance, and high-capacity wireless communication applications such as IoT (Internet of Things) and 5G. [Examples]

[0077] Examples are described below, but the embodiments are not limited to those described below.

[0078] (Example 1) The laminate was fabricated using the following procedure.

[0079] As the glass cloth, we prepared NE-1035, a type 2 open-fiber cloth made of aminosilane-treated NE glass manufactured by Nanya. As the first aqueous dispersion for forming the first sublayer of the fluororesin-containing layer on the glass cloth, we prepared an aqueous dispersion containing a solid content of 52% by weight of a resin mixed with 60% PTFE 34-JR and 40% FEP D121, both manufactured by Mitsui Chemours Fluoroproducts Co., Ltd. (MCF Co., Ltd.). Hereafter, this dispersion will be referred to as "FEP(6:4)". As the second aqueous dispersion for forming the second sublayer on the first sublayer, we prepared an aqueous dispersion with the materials and quantities shown in Tables 1 and 2. Specifically, as shown in Table 2, hollow silica filler manufactured by AGC Inc. was dispersed in water together with the dispersant DAPRO® W-77 manufactured by Elementis to prepare a hollow silica dispersant. The obtained hollow silica dispersant was then dispersed in water together with materials such as fluororesin as shown in Table 1 to prepare a second aqueous dispersion. As shown in Table 1, polytetrafluoroethylene (PTFE) DISP40 and perfluoroalkoxyalkane (PFA) 334-JR manufactured by MCF Co., Ltd. were added to the second aqueous dispersion as fluororesins in a ratio of PTFE:PFA = 8:2.

[0080] [Table 1]

[0081] [Table 2]

[0082] Next, an impregnation tank filled with the first aqueous dispersion and an impregnation tank filled with the second aqueous dispersion were prepared. The glass cloth was fed out according to the method described with reference to Figure 4, and in the first pass the first aqueous dispersion was applied, and in subsequent passes the second aqueous dispersion was applied in layers to produce a prepreg with a fluororesin-containing layer on both sides of the glass cloth. The detailed conditions are summarized in Table 3. In addition, the weight ratio, volume ratio, and volume percentage of fluororesin to hollow silica filler in the second sublayer contained in the formed fluororesin-containing layer are summarized in Table 4.

[0083] [Table 3]

[0084] [Table 4]

[0085] Next, multiple prepreg pieces were cut out for each example, with dimensions of 1020mm x 1220mm. Multiple first-layer structures were obtained by stacking two of the cut prepreg pieces together.

[0086] Subsequently, low-roughness copper foil SV-18 manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd. was prepared as the metal foil. The thickness of each copper foil sheet was 0.018 mm. One sheet of copper foil was laminated on each side of the first laminate to obtain the second laminate.

[0087] Subsequently, the obtained second laminate was covered with aluminum foil and transported to a cleanroom. Then, the second laminate was subjected to a hot-press press for 30 minutes to complete the laminate. The temperature during the hot-press press was 370°C and the press pressure was 10 MPa. For each example, the overall thickness of the laminate, the dielectric thickness, and the copper foil thickness were measured at 10 locations on each of the resulting laminates, and the average values ​​were calculated. The range of the measured values ​​and the calculated values ​​are summarized in Table 5. Here, the dielectric thickness refers to the total thickness of the two layers of prepreg sandwiched between copper foil (excluding the thickness of the copper foil). The copper foil thickness refers to the sum of the thicknesses of the copper foil on both sides of the laminate.

[0088] <Measurement of peel strength of metal foil (copper foil)> The peel strength of one of the two copper foils in each laminate prepared in the example was measured in accordance with JIS C 6481. Measurements were taken on five laminates of each type, and the average value was calculated. The range of the measured values ​​and the calculated values ​​are summarized in Table 5.

[0089] <Measurement of electrical characteristics> For each example, the relative permittivity (Dk) and dielectric loss tangent (Df) were measured at a frequency of 16 GHz in accordance with JIS R 1641:2007. Measurements were performed on three laminates at a time, and the average value was calculated. The range of measured values ​​and the calculated values ​​are summarized in Table 5.

[0090] <Checking for warping of the circuit board> In each example, one of the two copper foils on the fabricated laminate was removed by etching, and the warping of the remaining laminate was checked. As shown in Table 5, the degree of curling was small in all substrates, and it did not cause any problems as a wiring board.

[0091] [Table 5]

[0092] In all of Examples 1 and 2, as well as Comparative Example 1, laminates exhibiting good electrical properties with low dielectric constant (Dk) and dielectric loss tangent (Df) were obtained. Comparing Examples 1 and 2 with Comparative Example 1, it can be seen that the water absorption rate of Examples 1 and 2, in which hollow silica filler having hydrophobic groups was added to the prepreg by surface treatment, was reduced to about one-tenth of the water absorption rate of Comparative Example 1, in which the added hollow silica filler was not surface treated. In addition, in Example 1, in which the surface of the hollow silica filler was treated with propylsilane, the peel strength of the copper foil was significantly higher compared to Example 2, in which the surface of the hollow silica filler was treated with tetramethylsilane.

[0093] 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]

[0094] 1...Laminate, 2...Prepreg, 3...Metal foil layer, 4...Glass cloth, 5...Fluororesin-containing layer, 6...Second fluororesin-containing layer, 51...First sublayer, 52...Second sublayer, 110...Feeding roll, 111...Winding roll, 120...Impregnation tank, 121...Aqueous dispersion, 130...Roll, 131...Doctor roll, 140...Heating furnace.

Claims

1. A prepreg comprising NE glass cloth and a fluororesin-containing layer supported on the NE glass cloth, It comprises a metal foil layer, The fluororesin-containing layer is a laminate containing hollow silica particles having hydrophobic functional groups on its surface.

2. The laminate according to claim 1, wherein the hydrophobic functional group includes a silane group.

3. The laminate according to claim 1 or 2, wherein the fluororesin-containing layer contains polytetrafluoroethylene.

4. The laminate according to claim 1 or 2, wherein the fluororesin-containing layer comprises a first sublayer in contact with the NE glass cloth and not containing hollow silica particles, and a second sublayer located on the first sublayer and containing hollow silica particles.

5. The laminate according to claim 1 or 2, wherein the metal foil layer is copper foil.

6. A laminate according to claim 1 or 2, wherein the thickness is within the range of 0.1 mm or more and 0.2 mm or less.

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