Metal-clad laminate

Abstract

To provide a metal-clad laminate with a low dielectric constant, a low dielectric loss tangent, and a low water absorption rate.SOLUTION: A metal-clad laminate according to the embodiment has a structure in which a metal foil is arranged on the outermost surface of a dielectric, which comprises a composite film filled with heat-resistant particles in polytetrafluoroethylene and having perfluoroalkoxyalkane layers placed on both sides. The heat-resistant particle filling rate in the dielectric is 40 to 65 vol%, the thickness of the dielectric is 25 to 100 μm, and the total thickness of the metal-clad laminate is 45 to 125 μm. The metal-clad laminate has a coefficient of thermal expansion (CTE) of 10 to 40 ppm / K, a dielectric constant (Dk) of 2.4 to 3.0, a dielectric loss tangent (Df) of 0.0005 to 0.0025, and a water absorption rate is 0.20% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a metal-clad laminate. [Background technology]

[0002] The sixth-generation mobile communication system (6G), the successor to the current fifth-generation mobile communication system (5G), will require an even faster communication environment than 5G, with communication speeds approximately 10 times faster than 5G. Accordingly, metal-clad laminates used in 6G-compatible devices will also be required to have improved properties, such as low dielectric constant (Dk) and dielectric loss tangent (Df) and low power consumption. However, there are currently no metal-clad laminates on the market that can be installed in 6G-compatible devices, and there is a demand for metal-clad laminates that meet the required properties. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 61-102243 [Patent Document 2] Japanese Patent Application Publication No. 6-119810 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the embodiments is to provide a metal-clad laminate for Beyond 5G / 6G communications, more specifically, to provide a metal-clad laminate having a low dielectric constant (Dk), a low dielectric loss tangent (Df), a low water absorption rate, and a low coefficient of linear expansion (CTE). [Means for solving the problem]

[0005] The metal-clad laminate according to the present invention has a dielectric film structure in which perfluoroalkoxyalkane layers are arranged on both sides of a composite film made of polytetrafluoroethylene filled with heat-resistant particles, with a metal foil arranged on the outermost surface of the dielectric. The heat-resistant particle filling rate in the dielectric is 40-65% by volume, the dielectric thickness is 25-100 μm, and the total thickness is 45-125 μm. The linear expansion coefficient CTE is 10-40 ppm / K, the relative dielectric constant Dk is 2.4-3.0, the dielectric loss tangent Df is 0.0005-0.0025, and the water absorption is 0.20% or less. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a cross-sectional view of a metal-clad laminate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, a metal-clad laminate according to an embodiment will be described with reference to the drawings.

[0008] Fig. 1 is a cross-sectional view of a metal-clad laminate 10 according to an embodiment. In Fig. 1, a composite film 11 is formed by filling a matrix of polytetrafluoroethylene (PTFE) 12 with heat-resistant particles 13. Perfluoroalkoxyalkane (PFA) layers 14 are disposed on both sides of the composite film 11 to form a dielectric 15, and a metal foil 16 is disposed on the outermost surface of this dielectric 15.

[0009] As the heat-resistant fine particles, for example, silica particles, alumina particles, etc. are used.

[0010] The thickness of the dielectric material including the composite film and the two perfluoroalkoxyalkane layers is preferably 25 to 100 μm.

[0011] Examples of the metal foil include copper foil, gold foil, silver foil, nickel foil, aluminum foil, stainless steel foil, etc. From the viewpoints of conductivity, ease of handling, and cost, it is preferable to use copper foil or aluminum foil as the metal foil.

[0012] The total thickness of the metal-clad laminate is preferably 45 to 125 μm, and from the viewpoint of flexibility, it is more preferably 120 μm or less.

[0013] The filling rate of the heat-resistant particles in the dielectric is preferably 40 to 65% by volume, and more preferably 45 to 60% by volume.

[0014] The coefficient of linear expansion (CTE) of the metal-clad laminate is preferably 10 to 40 ppm / K, more preferably 15 to 30 ppm / K. In an embodiment, the CTE of the dielectric is preferably as close to the CTE of the metal foil to be laminated (for example, the CTE of copper foil is 18 ppm / K, and the CTE of aluminum foil is 24 ppm / K).

[0015] The relative dielectric constant Dk of the metal-clad laminate is preferably 2.4 to 3.0, and more preferably 2.6 or less.

[0016] The dielectric loss tangent Df of the metal-clad laminate is preferably 0.0005 to 0.0025, more preferably 0.0020 or less, and even more preferably 0.0010 or less.

[0017] The water absorption rate of the metal-clad laminate is preferably 0.20% or less, more preferably 0.15% or less, and even more preferably 0.10% or less. <Metal-clad laminate manufacturing method> Hereinafter, an example of a method for manufacturing a metal-clad laminate, for example, a copper-clad laminate, according to an embodiment will be described. First, a composite film is produced by filling polytetrafluoroethylene (PTFE) as a fluororesin with heat-resistant fine particles, for example, silica particles, as a filler, as follows. (Manufacturing method of composite film) Composite film manufacturing methods include the well-known (i) calendaring method, (ii) skived method, and (iii) composite method. In the (i) calendaring method, filler and PTFE microparticles are first dispersed in an aqueous solution, then coagulated by any method (physical, chemical, or mechanical). The precipitate is collected and concentrated, and the paste is adjusted to a clay-like consistency. This paste is then rolled between two calendaring rollers and dried to obtain an unsintered PTFE film. When unsintered PTFE microparticles are subjected to strong shearing forces by the calendaring rollers, their polymer chains unravel and become fibrous, forming a spider web-like network between the microparticles, even at temperatures as low as around 30°C. This property can be exploited to produce films at low temperatures. In the (ii) skived method, filler and PTFE powder are mixed to form a compound, which is then filled into a mold and compressed at low temperature to obtain a doughnut-shaped cylindrical preform. The preform removed from the mold is placed in a batch oven and baked by heating above the melting point of PTFE. The molded body, when removed after cooling, retains a donut-shaped cylindrical shape similar to the preform. PTFE is classified as a thermoplastic polymer, but its high melt viscosity allows it to maintain this shape. A mandrel is inserted into the baked body, and a blade is applied to it while it rotates, allowing it to be cut into a film, which is then wound up. (iii) The composite method involves wet-coating (casting) a solvent dispersion of filler and PTFE onto a smooth, heat-resistant carrier, drying the solvent, and baking the coating by heating above the melting point of PTFE. After cooling, the coating is peeled off from the carrier to obtain a film. Of these three methods, the composite method (iii) is particularly preferred due to the superiority of the film quality (thickness uniformity, pin-pole-free) and the properties of the double-sided metal-clad laminate.

[0018] In the examples described below, composite films were fabricated using the (iii) composite method. A filler-containing PTFE dispersion is applied (cast) onto a smooth carrier made of a heat-resistant substrate such as polyimide or metal foil, forming a film, and then baked. Finally, the coating is peeled off the carrier to recover the composite film. The main material formulation design concept for the composite method is that, due to the process of releasing the coating from the heat-resistant carrier, it is preferable for the matrix resin to be mostly PTFE alone (95–100 wt%). Blending a small amount (1–5 wt%) of a melt-type fluororesin (e.g., PFA, FEP) with PTFE to improve the adhesion between the filler and the matrix resin interface is sometimes effective. However, depending on the melt-type fluororesin selected, blending more than 6 wt% increases the average adhesion between the heat-resistant carrier and the composite film, resulting in the composite coating being more susceptible to tearing during demolding. (Method for preparing dispersion of filler-containing resin composition) The overall formulation process is outlined below. A vehicle (water, surfactant, dispersant) and heat-resistant filler powder are premixed to obtain a suspension slurry. This is then dispersed using a disperser (media or medialess), and the aggregated filler is mechanically and physically deagglomerated (crushed) using collisions, impacts, shear, and shear stresses to obtain a suitable dispersion slurry. Next, while the aqueous dispersion of fluororesin (the matrix resin) and the dispersion slurry are mixed using a stirring blade, an aqueous thickener solution is gradually added to increase the viscosity of the water-based paste. Finally, the mixture is filtered to separate and remove any foreign matter, such as dust, or small amounts of aggregates, that may have been introduced during the formulation process. This results in a composite water-based paste with the desired liquid properties (main material concentration, main material blend ratio, surfactant and other auxiliary material ratio, liquid viscosity, surface tension, pH, filler particle size distribution, etc.). (Selection of dispersion medium) A suitable dispersion medium is selected as follows. Since it will ultimately be mixed with the fluororesin aqueous dispersion, an aqueous solvent consisting of ion-exchanged water or ultrapure water (98 wt% or more) is particularly preferred. If the final content of a hydrophilic organic solvent (low-molecular-weight alcohol, acetone, tetrahydrofuran, etc.) is approximately 2 wt% or more, the chemicals (organic molecules such as surfactants, dispersants, and thickeners) adsorbed on the surface of the fluororesin microparticles (particle size 0.2 to 5 μm) will be solvated by the organic solvent such as acetone, resulting in unstable dispersion of the fluororesin microparticles (which have μm-scale hydrophobic surfaces within the system) and causing them to settle and separate within a short period of time, making this inappropriate. (PTFE selection) When the primary fluororesin is PTFE, the following selection is made. Homo-PTFE with an average molecular weight in the range of 1 million to 10 million is selected as the PTFE. If the molecular weight of the homo-PTFE is less than 1 million, the tensile strength of the baked coating film will decrease. On the other hand, if the molecular weight of the homo-PTFE exceeds 10 million, the melt viscosity of the unbaked PTFE microparticles in the aqueous paste film-forming method will be too high, resulting in reduced self-bonding between the microparticles and a higher risk of insufficient heat supply during roll-to-roll heating (due to the large enthalpy change ΔH). However, there is no benefit to the method, as no improvement in mechanical properties can be expected. PTFE can be divided into homo-PTFE and modified PTFE, and homo-PTFE is preferred for the applications described herein. A characteristic of homo-PTFE is its high melt viscosity, which allows for a high thickness retention rate (i.e., the ratio of dielectric thickness before and after heat pressing) of the highly filled fluororesin layer (dielectric layer) during copper clad lamination (heat fusion) processing, thereby improving the thickness uniformity of the resulting copper clad laminate and further reducing Dk variation. On the other hand, modified PTFE has a lower melt viscosity than the homo-type, resulting in a lower thickness retention rate, which can lead to uneven thickness of the copper clad laminate. Similar disadvantages can be seen with other melt-type fluororesins (whether homo- or modified, PFA, FEP, and other fluororesins). (Selection of melt-type fluororesin) When the main fluororesin is a melt-type fluororesin, the following selection is made. EA2000 (AGC's adhesive modified PFA) is particularly preferred from the viewpoints of solder heat resistance (288°C) and interfacial adhesion between the fluororesin and dissimilar materials. Other examples include homo-PFA and modified PTFE. When used to produce a resin-coated copper foil (RCC), preparing a fluororesin dispersion (aqueous or organic solvent dispersion with a solids content of 20 to 50 wt%) is convenient for thin-film coating (the dry thickness will be approximately 3 μm).

[0019] Preferred heat-resistant fine particles (fillers) will be described below. (Filler selection: Dk2.4~3.0 dielectric compatible) The main filler for dielectrics with Dk2.4 to 3.0 standards is selected as follows, as outlined above. Spherical (relatively narrow particle size distribution, maximum particle size D 100 However, it is selected from a group of relatively inexpensive substances and materials that simultaneously possess properties such as high heat resistance (a 2 wt% mass loss temperature of 420°C or higher, and an organic or inorganic insulator whose chemical composition and form / morphology do not change), and a thickness of approximately 0.5 times the designed coating thickness. (Selection of surfactants, dispersants, and thickeners suitable for aqueous dispersions of resin compositions) The surfactants, dispersants, and thickeners used as auxiliary materials are selected as follows: The range of application of the auxiliary materials is such that when the dielectric layer is heated above the melting point of unsintered homo-PTFE microparticles (approximately 343°C), the main components of the auxiliary materials (low-molecular to high-molecular organic compounds) are removed from the system (from the low-temperature side by evaporation, boiling, oxygen decomposition, hydrolysis, and pyrolysis). (In TGA pyrolysis measurements in a N2 atmosphere, the ash content of the main components at 400°C is preferably 1.0% or less, with 0.1% or less being particularly preferred.) The main roles of the auxiliary materials in aqueous pastes containing PTFE and heat-resistant fillers, which are suitable for film formation, are as follows: First, the surfactant reduces surface tension. The surface tension should preferably be 28.0 mN / m or less, which prevents the paste from peeling off when cast and applied to a heat-resistant film. Next, dispersants prevent filler particles from re-agglomerating (a common phenomenon between materials with the same interfacial tension) after mechanically and physically breaking down filler powder agglomerates larger than 100 μm (by providing steric repulsion and promoting water penetration between fillers). Finally, thickeners play an important role not only by delaying the settling and flotation phenomena caused by the difference in specific gravity of the paste constituent materials (approximately 1.0 for water, 2.1 for PTFE, and 2.2 for silica) (for example, the Stokes equation, which models terminal velocity, includes a term for liquid viscosity), but also by stabilizing the coating film thickness in the wet coating process (in the case of low-viscosity pastes, no matter how evenly applied with a doctor bar, web vibration, flapping, and gravity-induced sagging can result in significant variations in dry film thickness in both the width and length directions of the web). These amphiphilic substances (surfactants, dispersants, thickeners) interact with the filler surface (through intermolecular forces that cause repeated adsorption and desorption), slowing the settling and floating separation rate of the filler and suppressing the formation of sedimentation or floating aggregates (cake) during medium-term storage (approximately 1-3 months) of the resin composition aqueous dispersion. Furthermore, we confirmed that the sedimentation cake that forms after long-term storage (approximately 6-12 months) can be easily redispersed by low-speed stirring, providing improved usability. This excellent redispersibility is thought to be due to the fact that the dispersants remain adsorbed to the surface of each of the main fine particles (PTFE, fused fluororesin, and filler) that make up the cake, thereby preventing troublesome aggregation between particles of the same type (especially between PTFE fine particles and ceramic fine particles). Other precautions to take when storing aqueous dispersions include controlling the liquid temperature and preventing the growth of aquatic microorganisms (bacteria, mold, etc.). Since the transition temperature of PTFE is 19°C, maintaining a storage temperature of 1 to 18°C prevents plastic deformation of PTFE primary particles in Brownian motion dispersions and cakes, even when they are in contact with or near each other, preventing the progression of fibrosis and aggregation. Meanwhile, in aqueous systems, it is preferable to adjust the pH to around 8.5 to 11, for example, by adding a small amount of ammonia water, to prevent aerobic and anaerobic microorganisms from using the BOD components (hydrocarbons such as surfactants) in the system as food to grow and prevent the growth of microorganisms. (Selection of water-based dispersion equipment for fillers) The selection of a media disperser or media-less disperser is based on the following criteria. Dispersers are primarily used to break down agglomerates (deagglomeration, dispersion) in aqueous vehicle suspensions of ceramic microparticles. Suitable media-less dispersers can be selected from common devices based on known technologies, such as ultrasonic homogenizers, high-shear mixers, and triple-roll mills. The end point of the dispersion process (completion of agglomeration) can be determined by evaluating the particle size of the ceramic microparticle dispersion slurry using a particle size distribution analyzer or particle gauge. If the maximum particle size exceeds 0.5 times the design composite coating thickness at this point, it is important to determine that the end point has not been reached and continue the dispersion process. If the dispersion proceeds to the next compounding process (mixing with PTFE microparticles) without sufficient disintegration, progress in deagglomeration cannot be expected. Furthermore, attempts to separate the particles using a mesh with a small opening or to disintegrate them by applying shear force often fail. If aggregates or primary particles with particle sizes exceeding 1.0 times the design composite coating thickness are used in wet coating, the tops of the filler will inevitably be exposed on the surface when the coating dries, resulting in increased surface roughness of the copper-clad laminate due to the filler. Furthermore, even a thickness of just over 0.5 times the design composite coating thickness is undesirable because it can easily lead to a lack of flexibility in the copper-clad laminate's dielectric, specifically, resistance to seam folding. Specifically, if the composite coating (cast film) is designed to be 50 μm thick, it is recommended that a maximum particle size of 25 μm or less at the time of preparing the dispersed slurry be deemed acceptable.

[0020] For solid particle powders with relatively strong cohesion, there is no problem in using a media disperser such as a bead mill, as long as the material and compatibility are such that there is no risk of crushing or pulverization. (Metal foil selection) As the metal foil, it is preferable to use copper foil or aluminum foil from the viewpoints of conductivity, ease of handling, and cost. The thickness of the metal foil is, for example, preferably in the range of 5 to 35 μm, and particularly preferably in the range of 8 to 20 μm. Reducing the thickness of the metal foil is preferable in terms of imparting flexibility, improving bending resistance, and facilitating the formation of fine patterns during circuit processing. The metal foil used in this embodiment preferably has a surface roughness Rz (ten-point average roughness) of the M side that contacts the dielectric layer in the range of 0.5 to 2.5 μm. By setting the surface roughness Rz within the above range, it is possible to achieve both high adhesion between the metal foil and the dielectric layer and reduced conductor loss. (Method of manufacturing resin-coated copper foil) Next, for example, a resin coated copper foil (RCC) is produced as follows. A perfluoroalkoxyalkane (PFA) resin, such as Fluon+® EA2000 manufactured by AGC Corporation, is prepared and dispersed in water or an organic solvent to prepare a PFA dispersion. EA2000 exhibits a low dielectric constant, a low dielectric dissipation factor, and excellent adhesion to copper foil. For example, CF-T9DA-SV-12 manufactured by Fukuda Metal Foil & Powder Co., Ltd. is prepared as the copper foil. CF-T9DA-SV-12 is an ultra-low roughness copper foil made by applying the non-roughening treatment T9DA to a low-roughness copper foil, SV. The PFA dispersion is then applied to the copper foil to form a film, which is then fired at a melting point Tm exceeding approximately 300°C to produce a resin-coated copper foil. The design concept of the layer (coating) shown as 14 in Figure 1 can be roughly divided into two types. The first is when the majority of the main component (90-100vol%) is EA2000 and the remaining (0-10vol%) is a heat-resistant filler, and the dry coating thickness T 14 is the dielectric thickness after heat sealing press, T 15 For (T 14 ×2) / (T 15 ×1) is about 8 to 20%, and T 14It is preferable to coat the film so that the thickness is ≥ 1.5 μm. Within this range, it is possible to suppress the increase in dielectric CTE caused by the EA2000 layer with a large CTE (the CTE of neat fluororesin is approximately 100 to 150 ppm / K), while forming a pinhole-free film of EA2000 with a primary particle size of approximately 2 to 3 μm. If pinholes exist in the EA2000 layer, the dielectric in direct contact with the copper foil in the FCCL form becomes a PTFE composite, which directly leads to a local decrease in peel strength. In addition, (T 14 ×2) / (T 15 × 1) exceeds 25%, even if we aim for a dielectric CTE of 40 ppm / K or less and a dielectric thickness of 100 μm or less, there is a concern that the increased burden on the composite film (which will require an extremely high filler blending ratio) will deteriorate the mechanical properties of the composite film, making it extremely difficult to maintain a dielectric water absorption rate of 0.20% or less. The second design concept for the 14 layers in Figure 1 is that EA2000 accounts for 60 to 85 vol% of the main component, and the majority of the remaining (15 to 40 vol%) is a heat-resistant filler (a small amount of PTFE may also be included). In this case, the dry coating thickness T 14 is the dielectric thickness after heat sealing press, T 15 For (T 14 ×2) / (T 15 ×1) is approximately 8 to 40%, and T 14 It is preferable to coat the composite film so that the CTE is ≥ 3.0 μm. As mentioned above, due to the upper limit of the filler that can be loaded into the composite film and its thickness restrictions, it is difficult to achieve a CTE of ≤ 40 ppm / K within the dielectric thickness range of 25 to 40 μm. However, by combining a resin-coated copper foil with as much filler as possible loaded into the 14-layer composite film, it is possible to achieve the target CTE of ≤ 40 ppm / K. On the other hand, if the filler loading in the 14-layer is as high as 50 vol% or more, the flexibility of the 14-layer (composite layer) is lost when the EA2000 adheres strongly to the filler, resulting in an extremely hard (high elastic modulus) layer. Furthermore, the effective contact area between the copper foil and EA2000 cannot be sufficiently secured, which raises concerns that it may ultimately be impossible to maintain a copper foil peel force of ≥ 0.6 kN / m. (Manufacturing method for flexible double-sided copper-clad laminates) Furthermore, flexible double-sided copper clad laminates (FCCL) are manufactured by batch heat pressing or roll-to-roll heat pressing.

[0021] The batch type hot pressing is carried out as follows. The composite film and resin-coated copper foil are each cut to fit the size of the platen of a flat press. Resin-coated copper foil is placed on both sides of the composite film with the copper foil on the outermost surface, and both sides of this stack are sandwiched between cushioning material such as stainless steel (SUS) plates. The flat press heats the composite film to above the melting point of the resin, applies pressure, and heat-presses the composite film and resin-coated copper foil to fuse them together, forming a flexible copper-clad laminate. The cushioning material is peeled off and removed from the flexible copper-clad laminate, yielding the finished flexible double-sided copper-clad laminate.

[0022] The roll-to-roll heat pressing process is carried out as follows: The composite film and resin-coated copper foil are each cut to a specified width to fit the laminator size. The composite film is set in a multi-axis unwinder on the laminator so that resin-coated copper foil is placed on both sides of the composite film, and a protective material such as polyimide is placed on both sides of the resin-coated copper foil. The composite film and resin-coated copper foil are heat-pressed and fused together using a roll press or double-belt press to form a flexible double-sided copper-clad laminate. The protective material is peeled off and removed from the flexible double-sided copper-clad laminate, yielding the finished flexible double-sided copper-clad laminate.

[0023] By using specific PTFE, silica particles, PFA, and copper foil and employing a predetermined manufacturing method, the filling rate of the silica particles in the dielectric can be set within a predetermined range, and the thickness of the dielectric and the total thickness of the copper-clad laminate can be set within a predetermined range, thereby providing a copper-clad laminate with a low relative dielectric constant (Dk) and dielectric dissipation factor (Df) and a low water absorption rate. Key factors in the heat-sealing press process for obtaining suitable flexible double-sided copper-clad laminates include the appropriate combination of temperature, pressure, and hold time, as well as the flatness of the press surface. Taking into account the characteristics of the materials (thickness of each layer, CTE, thermal damage to the adhesive surface of the copper foil, etc.) and the desired properties of the resulting flexible double-sided copper-clad laminate (outgassing, dielectric thickness retention of approximately 85±10% before and after pressing, improved mechanical properties due to densification of the dielectric layer, and improved adhesion to the copper foil, etc.), we have found that the optimal heat-sealing conditions are a maximum temperature of 340–360°C, an actual pressure of 2–7 MPa, and a hold time of 1–30 minutes. Temperatures higher than these limits result in thermal decomposition of the adhesive functional groups contained in the copper foil surface treatment agent and EA2000 over time. If the pressure is below 1 MPa, the dielectric layer will not densify over time, which can lead to a decrease in cohesive strength and copper foil peel strength, while if the pressure exceeds 8 MPa, the molten matrix resin will be pushed out across the surface, which can lead to an extreme decrease in dielectric thickness retention.If you want the resulting dielectric thickness to be uniform across the entire surface (within a variation of the average value ±5%), you should adjust the dielectric thickness retention before and after pressure to a higher level within the above 85 ± 10% range. [Example]

[0024] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. It is not something that can be done. In the examples and comparative examples, the methods for preparing the composite film, the resin-coated metal foil, and the double-sided metal-clad laminate and the evaluation of their properties (SEM observation, water absorption, coefficient of linear expansion CTE, dielectric properties Dk·Df, solder heat resistance, metal foil peel strength, and tensile properties) are as follows: (Examples 1 to 8 and Comparative Examples 1 to 4: Production of Composite Films) Using polytetrafluoroethylene (homo-PTFE), silica (SiO2), and titanium dioxide (TiO2) particles, composite films with the ceramic particle loading and thickness shown in Table 1 were fabricated using the composite method described above. A ceramic particle-loaded PTFE resin aqueous dispersion was applied to one side of a heat-resistant carrier (a non-thermoplastic polyimide PI film) using a Comma Direct Coater (roll-to-roll). The film was then dried at approximately 100°C, baked at approximately 280°C (to volatilize and remove hydrocarbons such as surfactants by oxygen decomposition), and finally baked at a temperature above the PTFE melting point (Tm) (approximately 343°C). This resulted in a composite-coated PI film with a uniform coating thickness (within a range of ±5% of the average thickness) by air-cooling. The film was then unwound using an outliner, and the composite coating was peeled off from the PI and wound up. At this time, the coating / PI peel force was approximately 0.2 to 0.3 N / cm, which was a light peel, the coating film was hardly stretched, and the width shrinkage rate was within 0 to 2%.

[0025] In Examples 1 to 6 and Comparative Examples 1 and 2, silica was used to prepare low Dk composite films in which the dielectric Dk was ultimately around 2.5. In Examples 7-8 and Comparative Examples 3-4, silica was used as the main filler, and in Comparative Example 3, a composite film was produced using two types of filler, with a small amount of titanium oxide further mixed in. As a result, a medium Dk composite film was produced, with a dielectric Dk of around 2.7. (Examples 1 to 8 and Comparative Examples 1 to 4: Production of Resin-Coated Copper Foil) Using CF-T9DA-SV-12 manufactured by Fukuda Metal Foil & Powder Co., Ltd. as the copper foil and Fluon+® EA2000 manufactured by AGC Inc. as the perfluoroalkoxyalkane (PFA), the resin-coated copper foils (RCC) listed in Table 1 were produced by the above method. An aqueous dispersion of EA2000 was applied to one side of the copper foil substrate using a kiss-reverse gravure coater (roll-to-roll), dried at approximately 100°C, baked at approximately 280°C (to volatilize and remove hydrocarbons such as surfactants by oxygen decomposition), and finally baked at a temperature above the melting point Tm (approximately 300°C) of the EA2000. The foil was then air-cooled and wound up to produce neat resin-coated copper foils with a uniform coating thickness (minimum 2 μm to maximum 4 μm). (Examples 1 to 8 and Comparative Examples 1 to 4: Production of Double-Sided Copper-Clad Laminates) Using the composite film and resin-coated copper foil thus produced, flexible double-sided copper-clad laminates (FCCLs) with the average thicknesses listed in Table 1 were fabricated using the above method. The composite film and resin-coated copper foil were cut to 350 mm square and then stacked. Protective sheets (aluminum foil as a supplementary material) were then applied to both sides of the resulting FCCL for easy demolding and recovery. A 1-mm-thick stainless steel plate was placed on the outside to maintain the flatness of the FCCL. This sandwich structure was then created. Using a 500 mm square hot press (batch), the laminate was held at a maximum temperature of 350°C and a maximum actual pressure of 3.1 MPa for 30 minutes. The heater was then turned off while maintaining the pressure at 3.1 MPa, allowing for slow cooling. The pressure was finally released once the laminate had cooled to 250°C, well below the crystallization temperature Tc of the matrix resins (homo-PTFE and EA2000). The entire workpiece was then transferred to another water-cooled press for cooling and pressing. After confirming that the entire workpiece had cooled to room temperature, the cooling press was opened and the auxiliary plates (stainless steel plate, aluminum foil) were removed to obtain the final product, FCCL. By cutting and removing the 350mm square edges by approximately 2cm each, a flexible double-sided copper-clad laminate (FCCL) was produced that was approximately 310mm square and had a uniform total thickness (the range from minimum to maximum thickness was within the average value ±5%). The thickness and silica particle filling rate of the dielectric (total of three layers) consisting of the composite film and two PFA layers that make up the manufactured flexible copper-clad laminate are shown in Table 1.

[0026] The results of measuring various properties of the manufactured flexible copper-clad laminate are shown in Table 1. The methods for measuring various properties are as follows. (Water absorption rate) Water absorption: Measured according to IPC-TM-650 2.6.2.1. (coefficient of linear expansion CTE) Coefficient of linear expansion (CTE-X / Y / Z): The dielectric was measured by thermomechanical analysis (TMA) in the plane direction (X / Y) according to IPC-TM-650 2.4.41 and in the thickness direction (Z) according to IPC-TM-650 2.4.24. The dielectric film obtained by etching the copper foil was heated to 265°C using a Shimadzu TMA-60 thermomechanical analyzer, cooled at a rate of 5°C / min, cooled to a minimum of -70°C by introducing liquid nitrogen, and then heated back to 265°C at a rate of 5°C / min. The average coefficient of linear expansion (CTE) was measured over the temperature range of -65 to 260°C during the second heating process. (Dielectric properties Dk, Df) Dielectric constant (Dk) and dielectric loss tangent (Df): Measured using a balanced disk resonator method in accordance with IPC-TM-650 2.5.5.9. Pretreatment was performed in the normal state, and the dielectric property values in the 11 to 14 GHz frequency band are shown in Table 1. (Solder heat resistance temperature) Solder heat resistance temperature: In accordance with IPC-TM-650 2.4.13.1 Method B, flexible copper-clad laminates were immersed in 288°C solder for 10 seconds three times, and then the appearance was evaluated. If no abnormal changes (such as copper foil peeling or swelling) were observed, the board was judged as pass (white circle). (copper foil peel strength) Copper foil peel force: In accordance with IPC-TM-650 2.4.8, a flexible copper-clad laminate was peeled in the normal state at an angle of 90° with a copper foil thickness of 12 μm using an autograph. (Tensile properties of dielectrics) Tensile strength, elongation at break, tensile modulus: The dielectric was subjected to a tensile test in the normal state using an autograph in accordance with IPC-TM-650 2.4.18.3. (Results and Discussion: Examples 1 to 6 and Comparative Examples 1 and 2) Examples 1-6 and Comparative Examples 1 and 2 primarily investigated silica, and the resulting copper-clad laminates exhibited dielectric properties with a Dk of approximately 2.5. The CTEs were all within the 10-40 ppm / K range, and the Dk values were all within the 2.50 ± 0.10 range (Dk ≤ 2.6), which is believed to be strongly correlated with the high silica loading. Overall, the difference in Df was small. The water absorption rate differed by more than five times between the Examples and Comparative Examples, which is presumably related to the greater voids observed at the interface between the spherical filler and the matrix resin in Comparative Example 2 compared to Example 5. The greater the voids in the dielectric, the greater the space available for water retention. It is known that fluororesins (especially PTFE) generally have difficulty adhering to heat-resistant dissimilar materials (here, spherical silica) even after heat-sealing press bonding. Therefore, an effective strategy for improving adhesion is to bring the surface tension of the heat-resistant dissimilar material closer to that of PTFE (surface tension of approximately 18 mN / m). Next, the copper foil peel strength is 0.6 kN / m or more, which can be said to have practically acceptable performance for a general copper-clad laminate. (Results and Discussion: Examples 7 and 8 and Comparative Examples 3 and 4) Examples 7 and 8 and Comparative Examples 3 and 4 primarily investigated silica, and the resulting copper-clad laminates exhibited dielectric properties with a Dk of approximately 2.72. While Examples 7 and 8 satisfied the CTE range of 10 to 40 ppm / K, Comparative Examples 3 and 4 exceeded 41 ppm / K. This is believed to be primarily due to the filler content. The fact that Dk was within the range of 2.72 ± 0.10 in all cases is believed to be strongly correlated with the high silica loading. Overall, the difference in Df was small. The water absorption was good, at 0.20% or less, which is believed to be closely related to the good filler dispersion observed in dielectric SEM observations. The copper foil peel force was 0.6 kN / m or greater, indicating acceptable performance for practical use as a general copper-clad laminate.

[0027] [Table 1]

[0028] As shown in Table 1, in Examples 1 to 6, flexible double-sided copper-clad laminates having low relative permittivity (Dk) and dielectric loss tangent (Df), as well as low water absorption, and excellent overall properties were obtained.

[0029] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0030] 10...metal-clad laminate, 11...composite film, 12...PTFE, 13...heat-resistant fine particles, 14...PFA layer, 15...dielectric, 16...metal foil.

Claims

1. The composite film is made of polytetrafluoroethylene filled with heat-resistant fine particles, and perfluoroalkoxyalkane layers are disposed on both sides of the composite film. A metal foil is disposed on the outermost surface of the dielectric. the filling rate of the heat-resistant particles in the dielectric is 40 to 65% by volume, the thickness of the dielectric is 25 to 100 μm, and the total thickness is 45 to 125 μm; A metal-clad laminate having a linear expansion coefficient CTE of 10 to 40 ppm / K, a relative dielectric constant Dk of 2.4 to 3.0, a dielectric loss tangent Df of 0.0005 to 0.0025, and a water absorption rate of 0.20% or less.

2. 2. The metal-clad laminate according to claim 1, wherein the filling rate of the heat-resistant fine particles in the dielectric is 45 to 60% by volume.

3. The metal-clad laminate according to claim 1 , wherein the water absorption rate is 0.10% or less.

4. The metal-clad laminate according to claim 1, wherein the coefficient of linear expansion CTE is 15 to 30 ppm / K.

5. The metal-clad laminate according to claim 1 , wherein the dielectric loss tangent Df is 0.0010 or less.

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