Circuit board

Abstract

To provide a circuit board in which transmission loss is reduced.SOLUTION: A circuit board comprising an insulating layer and two or more conductor pattern layers embedded in the insulating layer so as to be spaced apart from each other in a thickness direction of the insulating layer, wherein the insulating layer contains hollow particles and a resin, and when an average particle diameter of the hollow particles is D (μm), a distance between the conductor pattern layers adjacent to each other in the thickness direction of the insulating layer is H (μm), a width of the conductor pattern layer is Ws (μm), and a thickness of the conductor pattern layer is Wh (μm), the following formulas (1) and (2) are satisfied. 0. 8H ≤ Ws (1) 40 * π D2 ≤ Ws * Wh (2) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to circuit boards. [Background technology]

[0002] In recent years, circuit boards have become increasingly sophisticated. Circuit boards include insulating layers and conductor layers, and the insulating layers are required to have properties such as low absorption, low dielectric constant, low dielectric loss tangent, and low linear expansion. For example, Patent Document 1 describes a printed wiring board including an insulating layer and a conductor layer disposed on the surface of the insulating layer, in which the insulating layer includes a layer formed from a resin composition containing a thermosetting resin and a filler including hollow particles having a predetermined number of bubbles and a predetermined particle size. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 230661 Summary of the Invention [Problem to be solved by the invention]

[0004] In applications such as portable electronic devices, communication speeds and capacity are increasing, and signals are becoming increasingly higher in frequency, which requires further reduction in transmission loss in circuit boards.

[0005] An object of one embodiment of the present disclosure is to provide a circuit board with reduced transmission loss.

[0006] Means for solving the above problems include the following aspects. <1> The insulating layer includes two or more conductor pattern layers embedded in the insulating layer at intervals in the thickness direction thereof, the insulating layer includes hollow particles and a resin; A circuit board that satisfies the following formulas (1) and (2), where the average particle diameter of the hollow particles is D (μm), the distance between adjacent conductive pattern layers in the thickness direction of the insulating layer is H (μm), the width of the conductive pattern layer is Ws (μm), and the thickness of the conductive pattern layer is Wh (μm). 0.8H≦Ws…(1) 40×πD 2 ≦Ws×Wh…(2) <2> D is 3 or less, <1> The circuit board according to claim 1. <3> H is less than or equal to 50, <1> or <2> The circuit board according to claim 1. <4> Ws is 5 to 100. <1> ~ <3> 10. The circuit board according to claim 9, wherein: <5> Wh is 5 to 30, <1> ~ <4> 10. The circuit board according to claim 9, wherein: <6> the insulating layer contains at least one resin selected from the group consisting of epoxy resin, polyphenylene ether, fluororesin, polyimide resin, resin containing a divinylbenzene skeleton, and resin containing a pyrimidine skeleton; <1> ~ <5> 10. The circuit board according to claim 9, wherein: <7> The hollow particles include SiO2, <1> ~ <6> 10. The circuit board according to claim 9, wherein: <8> The SiO2 content in the hollow particles is 99 mass% or more. <1> ~ <7> 10. The circuit board according to claim 9, wherein: <9> The hollow particles have a 20% collapse pressure of 120 MPa or more as measured by mercury intrusion porosimetry. <1> ~ <8> 10. The circuit board according to claim 9, wherein: <10> The hollow particles have a density multiplied by the BET specific surface area of ​​120m 2 / cm 3 Below is the <1> ~ <9> 10. The circuit board according to claim 9, wherein: <11> The conductor pattern layer contains copper. <1> ~ <10> 10. The circuit board according to claim 9, wherein: <12> The content of hollow particles in the insulating layer is 20 to 80% by volume. <1> ~ <11> 10. The circuit board according to claim 9, wherein: [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, a circuit board with reduced transmission loss is provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a circuit board according to the present disclosure. [Figure 2] FIG. 1 is a diagram showing an evaluation sample of a circuit board produced in an example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, modes for carrying out embodiments of the present disclosure will be described in detail. However, the embodiments of the present disclosure are not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the embodiments of the present disclosure.

[0010] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be contained. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In this disclosure, unless otherwise specified, the term "hollow particles" refers to a group of multiple hollow particles.

[0011] The circuit board of the present disclosure includes an insulating layer and two or more conductor pattern layers embedded in the insulating layer at a distance in the thickness direction thereof, the insulating layer including hollow particles and a resin, and satisfies the following formulas (1) and (2), where D (μm) is the average particle diameter of the hollow particles, H (μm) is the distance between adjacent conductor pattern layers in the thickness direction of the insulating layer, Ws (μm) is the width of the conductor pattern layer, and Wh (μm) is the thickness of the conductor pattern layer. 0.8H≦Ws…(1) 40×πD 2 ≦Ws×Wh…(2)

[0012] Patent Document 1 describes a resin composition containing hollow silica particles having a specified number of bubbles and a specified particle size, and states that it can form an insulating layer that has an excellent appearance when processed. However, Patent Document 1 does not mention any focus on the transmission loss of the resulting printed circuit board. According to the studies of the present inventors, it was difficult to reduce the transmission loss, particularly when the distance between the conductive pattern layers was shortened, i.e., when the circuit board was made low-profile. In contrast, the circuit board of the present disclosure reduces transmission loss, particularly in the high frequency range. The reason for this is not clear, but is presumed to be as follows.

[0013] In the circuit board of the present disclosure, the distance between the conductive pattern layers is short, and the overall thickness of the circuit board is thin. In this case, the circuit board of the present disclosure satisfies the above formula (2), in other words, by balancing the central cross-sectional area of ​​the hollow particles with the cross-sectional area of ​​the conductive pattern layer within a predetermined range, the hollow particles in the insulating layer are easily packed densely or closest together near the conductive pattern layer, thereby highly exhibiting their physical properties of low dielectric constant and low dielectric loss tangent. As a result, it is believed that the circuit board of the present disclosure achieves reduced transmission loss even when the distance between the conductive pattern layers is short.

[0014] Hereinafter, an example of an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0015] The drawings used in the following description are all schematic, and the dimensional relationships between elements, ratios, and the like shown in the drawings do not necessarily correspond to the actual ones.

[0016] FIG. 1 is a cross-sectional view showing an example of a circuit board according to the present disclosure. As shown in FIG. 1, the circuit board 100 includes an insulating layer 10 and two conductor pattern layers 20A and 20B embedded in the insulating layer 10 and spaced apart in the thickness direction.

[0017] <Insulating layer> The insulating layer contains at least hollow particles and a resin, and may contain other components as needed, such as solid particles, elastomers, silane coupling agents, and, if the resin is a curable resin, curing components (e.g., curing agents, crosslinking agents, etc.).

[0018] (hollow particles) The insulating layer includes hollow particles. The hollow particles may be hollow inorganic particles or hollow organic particles. From the viewpoint of improving the electrical properties (e.g., low dielectric constant and low dielectric loss tangent) of the circuit board, the hollow particles are preferably hollow inorganic particles.

[0019] Hollow particles are particles that have a shell layer and a space inside the shell layer. The space can be confirmed by observation with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like. In the present disclosure, "having a space inside the shell layer" means that when a cross section of a hollow particle is observed, a hollow state exists in which a shell layer surrounds a single space. The shell layer may have a single layer structure, or may have a multi-layer structure consisting of two or more layers.

[0020] When the hollow particles are inorganic hollow particles, examples of the inorganic component contained in the shell layer of the hollow particles include SiO2, Al2O3, B2O3, CaO, MgO, Na2O, K2O, and Li2O.

[0021] The shell layer of the hollow particles preferably contains SiO as an inorganic component, from the viewpoint of realizing a low dielectric constant and a low dielectric loss tangent of the hollow particles. Examples of hollow inorganic particles containing SiO as an inorganic component include hollow silica particles and hollow aluminosilicate particles.

[0022] The SiO content in the hollow particles is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and extremely preferably 99% by mass or more. The upper limit of the SiO content is 100% by mass, but may be 99.99% by mass. The remainder may include alkali metal oxides, alkali metal silicates, alkaline earth metal oxides, alkaline earth metal silicates, carbon, etc. The composition of the shell layer can be measured by ICP atomic emission spectrometry, flame atomic absorption spectrometry, etc. Specifically, perchloric acid and hydrofluoric acid are added to the hollow particles and the mixture is ignited to remove the main component silicon, after which the composition is measured by ICP-AES (inductively coupled plasma atomic emission spectrometry) using an ICPE-9000 (manufactured by Shimadzu Corporation).

[0023] The hollow particles have a density (Ar density) of 0.35 to 2.00 g / cm as determined by density measurement using a dry pycnometer using argon gas. 3 It is preferable that the Ar density is 0.35 g / cm 3 When the Ar density is 2.00 g / cm or more, for example, the difference in specific gravity with the resin does not become too large, so that the dispersibility in the insulating layer is improved and the above-mentioned mechanism of action is more easily realized. 3 When the Ar density is 0.40 g / cm or less, the effect of reducing the dielectric constant is easily exhibited. 3 More preferably, the Ar density is 1.50 g / cm 3 Less than 1.00 g / cm is more preferable. 3 More preferably, the Ar density is 0.35 to 1.50 g / cm. 3 More preferably, 0.40 to 1.00 g / cm 3 is more preferable.

[0024] As the dry pycnometer, an AccuPycII 1340 manufactured by Micromeritics or an equivalent device can be used.

[0025] The hollow particles have a BET specific surface area of ​​1 to 100 m 2 / g. The BET specific surface area is preferably 1 m 2 / g. 2 When the BET specific surface area is 1 to 50 m / g or less, an increase in viscosity of the insulating layer-forming material can be suppressed, and a decrease in dispersibility in the insulating layer can be suppressed, making it easier for the above-mentioned mechanism of action to be realized. 2 / g is more preferable, and 1 to 20m 2 / g is more preferable, and 1 to 15m 2 / g is most preferred.

[0026] The BET specific surface area can be measured by a multipoint method using a specific surface area measuring device (for example, Shimadzu Corporation's "Tristar II3020"), after pre-treating the hollow particles by drying them at 230°C until the pressure becomes 6.7 Pa, and then using nitrogen gas.

[0027] The hollow particles have an Ar density of A (g / cm 3 ), and the BET specific surface area is B (m 2 / g), the product of Ar density and BET specific surface area (A × B) is 120m 2 / cm 3 A × B represents the specific surface area per volume, and when added to a resin, for example, represents the specific surface area of ​​the portion of the resin that the hollow particles occupy in a given volume. When the product of the Ar density and the BET specific surface area is 120 m 2 / cm 3 When the dielectric constant of the insulating layer is less than 100%, the dielectric constant of the insulating layer is reduced, which leads to a further reduction in transmission loss. In addition, peeling between the insulating layer and the conductive pattern layer is suppressed, which makes it easier for the above-mentioned mechanism of action to be realized. A x B is 80m 2 / cm 3 Less than 40m is preferable 2 / cm 3 Less than 20m is preferable 2 / cm 3 It is more preferable that A×B is 1 m or less. 2 / cm 3 More than 2m is preferable. 2 / cm 3 More than 2.5m is preferable. 2 / cm 3 More preferably, 3m 2 / cm 3 The above is particularly preferred.

[0028] The median diameter (d50) of the hollow particles is preferably 0.1 to 10 μm, in which case the above-mentioned mechanism of action is more easily exhibited. The median diameter is more preferably 0.2 μm or more, even more preferably 0.25 μm or more, and particularly preferably 0.3 μm or more. The median diameter is more preferably 8 μm or less, even more preferably 7 μm or less, particularly preferably 5 μm or less, and most preferably 3 μm or less.

[0029] The median diameter is the volume-based cumulative 50% diameter determined using a laser diffraction particle size distribution analyzer (e.g., the MT3300EXIIJ manufactured by Microtrac-Bell Corporation). That is, particle size distribution is measured by laser diffraction / scattering, and a cumulative curve is calculated with the total volume of hollow particles set to 100%, and the median diameter is the particle diameter at the point on the cumulative curve where the cumulative volume is 50%. In the present disclosure, the median diameter of hollow particles is measured in a state including primary particles and secondary particles.

[0030] From the viewpoint of facilitating close-packing of the hollow particles in the insulating layer, the 20% burst pressure measured by mercury porosimetry is preferably 120 MPa or more, more preferably 150 MPa or more, more preferably 200 MPa or more, and even more preferably 250 MPa or more. In this case, breakage of the hollow particles densely arranged in the insulating layer is suppressed, and the above-mentioned mechanism of action is more likely to occur. Hereinafter, the 20% burst pressure measured by mercury porosimetry may be simply referred to as the “burst pressure.” The upper limit of the burst pressure of the hollow particles is not particularly limited, and the burst pressure may be, for example, 600 MPa or less. The burst pressure is measured by mercury porosimetry, and is the minimum pressure at which the capacity is reduced by 20% from the maximum accumulated capacity when pressure is applied from 0 to 400 MPa using mercury porosimetry. The collapse pressure of the hollow particles is measured in accordance with ASTM D 3102-78 using a mercury intrusion porosimeter (for example, "AutoPore IV 9500" manufactured by MICROMERITICS INSTRUMENT).

[0031] The hollow particles may contain at least one element selected from the group consisting of alkali metals belonging to Group 1 of the periodic table and alkaline earth metals belonging to Group 2 of the periodic table. The hollow particles preferably contain one or more metals M selected from the group consisting of alkali metals and alkaline earth metals, Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. The inclusion of metal M in the hollow particles acts as a flux during firing, reducing the specific surface area and the dielectric loss tangent.

[0032] From the viewpoint of availability, the hollow particles preferably contain one or more metals M selected from the group consisting of Na, K, Mg, Ca, and Sr, more preferably one or more metals selected from the group consisting of Na, Mg, and Ca, and even more preferably Na.

[0033] From the viewpoint of obtaining an insulating layer with a low dielectric constant, the dielectric constant of the hollow particles is preferably less than 3.0, more preferably 2.5 or less, and even more preferably 2.0 or less at a frequency of 1 GHz. The lower limit of the dielectric constant of the specific hollow particles at 1 GHz is not particularly limited. The dielectric constant of the hollow particles at 1 GHz may be 1.5 or more.

[0034] The dielectric loss tangent of the hollow particles is preferably 0.0001 to 0.05 at a frequency of 1 GHz. By having the dielectric loss tangent at 1 GHz be equal to or less than the above upper limit, an insulating layer with a low dielectric loss tangent can be obtained. From this viewpoint, the dielectric loss tangent at 1 GHz is more preferably 0.01 or less, even more preferably 0.005 or less, even more preferably 0.003 or less, and particularly preferably 0.002 or less. Note that it is practically difficult to synthesize hollow particles with a dielectric loss tangent of less than 0.0001 at 1 GHz. The dielectric loss tangent at 1 GHz may be 0.0002 or more, or may be 0.0003 or more.

[0035] The dielectric constant and dielectric loss tangent of hollow particles are measured using a dedicated device (for example, Keycom Corporation's "Vector Network Analyzer E5063A") using a perturbation resonator method. Specifically, measurements are performed at a test frequency of 1 GHz, a test temperature of approximately 24°C, and a humidity of approximately 45%, with three measurements. The measurement sample is prepared by vacuum-drying the obtained hollow particles at 150°C, and then filling a PTFE (polytetrafluoroethylene) cylinder with the hollow particle powder while thoroughly tapping. The dielectric constant of the entire container is measured, and then converted to a dielectric loss tangent using the filling rate of the powder in the container.

[0036] Each hollow particle may be treated with a coupling agent. Treating the surface of the hollow particle with a coupling agent suppresses elution of the components constituting the hollow particle in the insulating layer. This suppresses an increase in the dielectric constant and a decrease in the bending strength of the insulating layer due to elution, making it easier to achieve both a low dielectric constant and high bending strength in the insulating layer. Examples of the coupling agent include a silane coupling agent, a titanate coupling agent, a zirconate coupling agent, and an aluminate coupling agent.

[0037] Examples of silane coupling agents include aminosilane coupling agents, methacrylsilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, and organosilazane compounds. Examples of vinylsilane coupling agents include vinyltrialkoxysilanes such as vinyltrimethoxysilane. Examples of organosilazane compounds include hexaalkyldisilazanes such as 1,1,1,3,3,3-hexamethyldisilazane. Examples of types of titanate coupling agents include alkoxy titanate coupling agents. Examples of the zirconate coupling agent include alkoxyzirconate coupling agents, such as zirconium alkoxides such as zirconium isopropoxide. Examples of the aluminate coupling agent include alkoxyaluminate coupling agents, such as aluminum alkoxides such as aluminum isopropoxide.

[0038] The coupling agent may be used alone or in combination of two or more. From the viewpoint of realizing a low dielectric constant in the insulating layer, the hollow particles are preferably treated with at least one selected from the group consisting of a silane coupling agent, a zirconate coupling agent, and an aluminate coupling agent, and more preferably treated with at least one selected from the group consisting of a vinylsilane coupling agent, an organosilazane compound, an alkoxyzirconate coupling agent, and an alkoxyaluminate coupling agent. The amount of the coupling agent attached is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 5 parts by mass, and even more preferably 0.10 to 2 parts by mass, relative to 100 parts by mass of the hollow particles. The fact that the surfaces of the hollow particles have been treated with a coupling agent can be confirmed by detecting a peak due to a substituent of the coupling agent by infrared spectroscopy. The amount of the coupling agent attached can be measured by the carbon content.

[0039] The hollow particles may be commercially available or may be prepared by a conventional method. For example, hollow silica particles prepared by the methods described in International Publication Nos. 2019 / 131658 and 2021 / 172294 can be used.

[0040] The content of hollow particles in the insulating layer is preferably 20 to 80% by volume. The content of hollow particles is more preferably 30% by volume or more, and even more preferably 40% by volume or more. The content of hollow particles is preferably 70% by volume or less. In this case, the above-mentioned mechanism of action is more likely to be realized.

[0041] (resin) The insulating layer includes at least one resin. The resin may be a thermosetting resin or a thermoplastic resin. Examples of the thermosetting resin include epoxy resin, thermosetting polyphenylene ether, thermosetting polyimide resin, phenol resin, and orthodivinylbenzene resin. Examples of the thermoplastic resin include fluororesin, thermoplastic polyphenylene ether, and thermoplastic polyimide resin.

[0042] From the viewpoint of electrical properties, the insulating layer preferably contains at least one resin selected from the group consisting of epoxy resin, polyphenylene ether, fluororesin, polyimide resin, resin containing a divinylbenzene skeleton, and resin containing a pyrimidine skeleton.

[0043] Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, alicyclic epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, diglycidyl ethers of polyfunctional phenols, and diglycidyl ethers of polyfunctional alcohols.

[0044] The polyphenylene ether may be modified or unmodified, but from the viewpoint of adhesion, modified polyphenylene ether is preferred. The modified polyphenylene ether has a substituent bonded to the polyphenylene ether chain or the end of the polyphenylene ether chain. The substituent is preferably a group having a reactive group, more preferably a group having a vinyl group, a (meth)acryloyloxy group, or an epoxy group.

[0045] Examples of fluororesins include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-fluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer, and modified polytetrafluoroethylene.

[0046] Examples of modified polytetrafluoroethylene include (i) a copolymer of tetrafluoroethylene (hereinafter also referred to as "TFE") with a trace amount of CH2=CH(CF2)4F or CF2=CFOCF3, (ii) the above (i) further copolymerized with a trace amount of a monomer containing an adhesive functional group, (iii) a copolymer of TFE with a trace amount of a monomer containing an adhesive functional group, (iv) polytetrafluoroethylene into which an adhesive functional group has been introduced by plasma treatment or the like, and (v) the above (i) into which an adhesive functional group has been introduced by plasma treatment or the like.

[0047] Furthermore, the fluororesin more preferably has, as an adhesive functional group, at least one functional group selected from the group consisting of a carbonyl group-containing group, a hydroxy group, an epoxy group, an amide group, an amino group, an isocyanate group, a fluoroformyl group, and an acid anhydride residue. The fluororesin having an adhesive functional group provides excellent adhesion to hollow particles, thereby preventing the hollow particles from detaching from the resin composition. The functional group may be contained in a unit within the fluororesin or in a terminal group of the main chain of the fluororesin.

[0048] The carbonyl group-containing group is a group containing a carbonyl group (>C(O)), and is preferably a carboxy group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.), or a carbonate group (-OC(O)O-).

[0049] Examples of polyimide resins include aromatic polyimides and aromatic polyamic acids.

[0050] An example of a resin containing a divinylbenzene skeleton is ODV-XET manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0051] Examples of resins containing a pyrimidine skeleton include ELPAC HC-G series manufactured by JSR Corporation.

[0052] (Insulating layer characteristics) The thickness of the insulating layer is not particularly limited, and may be, for example, 50 to 1,000 μm, or may be 75 to 700 μm, or may be 100 to 500 μm. From the viewpoint of reducing transmission loss, the relative dielectric constant of the insulating layer is preferably 3.0 to 5.5, and more preferably 3.0 to 5.0, at a frequency of 10 GHz. From the viewpoint of reducing transmission loss, the dielectric loss tangent of the insulating layer is preferably 0.001 or less, more preferably 0.0009 or less, and even more preferably 0.0008 or less at a frequency of 10 GHz. The relative permittivity and dielectric loss tangent of the insulating layer were measured using a split post dielectric resonator (SPDR) at a temperature of 25° C. and a frequency of 10 GHz.

[0053] <Conductive pattern layer> The conductor pattern layers are embedded in the insulating layer at intervals in the thickness direction. The number of conductor pattern layers is not particularly limited as long as it is two or more. In FIG. 1, only one conductor pattern layer is arranged on the same plane parallel to the main surface of the circuit board, but two or more conductor pattern layers may be arranged. For example, another conductor pattern layer may be arranged on the same plane as the conductor pattern layer 20A but spaced apart from the conductor pattern layer 20A. In addition, in FIG. 1, the conductor pattern layer 20A and the conductor pattern layer 20B are arranged in positions where the entire conductor pattern layers overlap each other in a plan view of the circuit board, but they may be arranged in positions where only a portion of the conductor pattern layers overlap, or where they do not overlap at all. In addition, in FIG. 1, two conductor pattern layers, 20A and 20B, are arranged in the thickness direction of the insulating layer, but three or more conductor pattern layers may be arranged.

[0054] In the circuit board of the present disclosure, when the average particle diameter of the hollow particles is D (μm), the distance between adjacent conductive pattern layers in the thickness direction of the insulating layer is H (μm), the width of the conductive pattern layer is Ws (μm), and the thickness of the conductive pattern layer is Wh (μm), the following formulas (1) and (2) are satisfied. 0.8H≦Ws…(1) 40×πD 2 ≦Ws×Wh…(2)

[0055] In the present disclosure, the "average particle size of hollow particles" means the above median size (d50).

[0056] In FIG. 1, "the distance between adjacent conductive pattern layers in the thickness direction of the insulating layer" means the average value of the distance between the conductive pattern layer 20A and the conductive pattern layer 20B. When three or more conductive pattern layers are arranged in the thickness direction of the insulating layer, the shortest distance between adjacent conductive pattern layers is selected, and the selected distance is defined as H (μm).

[0057] The "width of the conductive pattern layer" means the average width of the conductive pattern layer in a cross section obtained by cutting the circuit board along the thickness direction in parallel to the short side direction of the conductive pattern layer.

[0058] The "thickness of the conductive pattern layer" means the average thickness of the conductive pattern layer in a cross section obtained by cutting the circuit board along the thickness direction in parallel to the short direction of the conductive pattern layer.

[0059] In addition, it is sufficient that one of two adjacent conductive pattern layers satisfies formulas (1) and (2) in relation to the average particle diameter of the hollow particles, or both of two adjacent conductive pattern layers may satisfy formulas (1) and (2).

[0060] As described above, the hollow particles preferably have an average particle size of 0.1 to 10 μm. D is more preferably 0.2 or more, even more preferably 0.25 or more, and particularly preferably 0.3 or more. D is more preferably 8 or less, even more preferably 7 or less, particularly preferably 5 or less, and most preferably 3 or less.

[0061] From the viewpoint of reducing the height of the circuit board, H is preferably equal to or less than 50, more preferably equal to or less than 40, and even more preferably equal to or less than 30. Furthermore, from the viewpoint of transmission loss of the circuit board, H is preferably equal to or greater than 1, and more preferably equal to or greater than 10.

[0062] From the viewpoint of transmission loss and miniaturization of the circuit board, Ws is preferably 5 to 100. Ws is preferably 5 or more, more preferably 15 or more, and even more preferably 30 or more. Furthermore, Ws is preferably 100 or less, more preferably 75 or less, and even more preferably 50 or less.

[0063] From the viewpoint of reducing the height of the circuit board, Wh is preferably 5 to 30. Wh is more preferably 10 or more. Furthermore, Wh is more preferably 25 or less, and even more preferably 20 or less.

[0064] Examples of metals constituting the conductive pattern layer include copper, copper alloys, stainless steel, etc. Among these, from the viewpoint of electrical conductivity, it is preferable that the conductive pattern layer contains copper.

[0065] The circuit board of the present disclosure is manufactured, for example, by the following method. A conductor layer is formed on a first insulating layer, and then the conductor layer is etched in a pattern to obtain a first conductor pattern layer. A second insulating layer is further formed on the first conductor pattern layer. A conductor layer is formed on the second insulating layer, and then the conductor layer is etched in a pattern to obtain a second conductor pattern layer. A third insulating layer is further formed on the second conductor pattern layer.

[0066] The conductor layer can be etched by a commonly known method.

[0067] The circuit board of the present disclosure is useful as a substrate for electronic devices such as radar, network routers, backplanes, and wireless infrastructure that require high-frequency characteristics, as well as a substrate for various automotive sensors and a substrate for engine management sensors, and is particularly suitable for applications aimed at reducing transmission loss in the millimeter wave band. [Example]

[0068] Next, embodiments of the present disclosure will be described in detail using examples, but the embodiments of the present disclosure are not limited to these examples. Examples 1-1 to 1-4 and Examples 2-1 to 2-4 are examples, and Examples 1-5, 1-6, 2-5, and 2-6 are comparative examples.

[0069] [Preparation of hollow particles 1] 4 g of EO-PO-EO block copolymer (ADEKA Pluronic® F68) was added to 1250 g of purified water and stirred until dissolved. 42 g of an n-decane solution containing 4 g of sorbitan acid monooleate (Sanyo Chemical Industries, Ltd., Ionet S-80) dissolved in n-decane was added to this aqueous solution, and the mixture was stirred using an IKA homogenizer until the entire solution was homogenous, producing a coarse emulsion. This coarse emulsion was then emulsified using a high-pressure emulsifier (SMT Corporation, LAB1000) at a pressure of 50 bar to produce a fine emulsion with an emulsion diameter of 1 μm. The resulting fine emulsion was allowed to stand at 40°C for 12 hours to obtain an aged emulsion.

[0070] To 1,300 g of the resulting aged emulsion, 23 g of diluted sodium silicate aqueous solution (SiO2 concentration 10.4 mass%, Na2O concentration 3.6 mass%) and 2 M hydrochloric acid were added so that the pH was adjusted to 2, and the mixture was stirred thoroughly while maintaining the temperature at 30°C. To this solution, 1 M sodium hydroxide aqueous solution was slowly added dropwise while stirring thoroughly so that the pH was adjusted to 6, yielding an oil core-silica shell particle dispersion. The resulting oil core-silica shell particle dispersion was maintained at 30°C for 10 minutes to age. The entire aged oil core-silica shell particle dispersion was heated to 70°C, and 1M NaOH aqueous solution was slowly added with stirring to adjust the pH to 9. Next, 330 g of diluted sodium silicate aqueous solution (SiO concentration 10.4 mass%, NaO concentration 3.6 mass%) was gradually added together with 0.5M hydrochloric acid to adjust the pH to 9. This suspension was kept at 80°C for 1 day and then cooled to room temperature (25°C), yielding a hollow silica precursor dispersion.

[0071] The entire hollow silica precursor dispersion was adjusted to pH 2 with 2M hydrochloric acid and then filtered using a 5C quantitative filter paper. 350 ml of 80°C ion-exchanged water was then added, and the mixture was again pressure-filtered to wash the hollow silica cake. The filtered cake was dried in a nitrogen atmosphere at 100°C for 1 hour and then at 400°C for 2 hours (heating rate: 10°C / min) to remove organic components and obtain hollow silica precursor. The obtained hollow silica precursor was then calcined at 1000°C for 1 hour (heating rate: 10°C / min) to sinter the shell layer and obtain calcined hollow silica particles. 10 g of hollow calcined silica particles, 150 ml of isopropanol, and 0.1 g of vinyltrimethoxysilane were added to a 200 mL glass beaker and refluxed at 100°C for 1 hour. The mixture was then filtered under reduced pressure using a hydrophobic PTFE membrane filter, washed with 20 ml of isopropanol, and vacuum-dried for 2 hours in a vacuum dryer adjusted to 150°C to obtain surface-treated hollow silica particles (hollow particles 1).

[0072] [Preparation of hollow particles 2] Hollow particles 2 were obtained under the same conditions as hollow particles 1, except that the amount of EO-PO-EO block copolymer (Pluronic (registered trademark) F68 manufactured by ADEKA Corporation) added was changed to 2 g, and the amount of sorbitan acid monooleate (IONET S-80 manufactured by Sanyo Chemical Industries, Ltd.) added was changed to 2 g.

[0073] [Preparation of hollow particles 1A] Aluminosilicate hollow particles 1A were produced in accordance with the method of Example 1 of JP 2021-143089 A.

[0074] The median diameter d50 ("average particle diameter" in the table), density, BET specific surface area ("specific surface area" in the table), and 20% burst pressure of the produced hollow particles were measured. The product of density and BET specific surface area ("density x specific surface area" in the table) was also calculated. The measurement method was as follows. The measurement results are shown in Table 1. The SiO2 content in the hollow particles was 99.9 mass% or more in all cases.

[0075] -Average particle size- Measurements were made using a laser diffraction particle size distribution measuring device ("MT3300EXIIJ" manufactured by Microtrack Bell Co., Ltd.).

[0076] -density- Measurement was carried out using argon gas with a dry pycnometer (Micromeritics "AccuPycII 1340").

[0077] -BET specific surface area- Using a specific surface area measuring device (Shimadzu Corporation's "Tristar II3020"), the hollow particles were pre-dried at 230°C until the pressure reached 6.7 Pa, and then the surface area was measured by a multi-point method using nitrogen gas.

[0078] -20% burst pressure- Measurement was carried out using a mercury intrusion porosimeter ("AutoPore IV 9500" manufactured by MICROMERITICS INSTRUMENT) in accordance with ASTM D 3102-78.

[0079] [Table 1]

[0080] [Creating a circuit board] (Example 1-1) A double-sided copper-clad laminate was prepared by laminating copper foil (18 μm thick), a prepreg formed from a thermosetting varnish containing hollow particles 1 and acrylic-modified polyphenylene ether, and another copper foil (18 μm thick) in this order and thermocompression bonding. One of the copper foils in the obtained double-sided copper-clad laminate was etched to form a conductor pattern layer (transmission path width 30 μm, height 18 μm). The prepreg and copper foil were then laminated in this order on the surface of the conductor pattern layer and thermocompression bonding was performed to prepare an evaluation sample of the circuit board shown in Figure 2, which is a microstrip line with the configuration shown in Table 2. Note that by using this evaluation sample, evaluation results similar to or correlative with those obtained for a circuit board including an insulating layer and two or more conductor pattern layers embedded in the insulating layer at a distance in the thickness direction, as shown in Figure 1, were obtained.

[0081] That is, the evaluation sample of the circuit board shown in Figure 2 corresponds to a circuit board in which a conductor pattern layer 50 is embedded in an insulating layer 40, the transmission path width of the conductor pattern layer is Ws, the height of the conductor pattern layer is Wh, and the distance between adjacent conductor pattern layers is H.

[0082] (Example 1-2 to Example 1-6) As shown in Table 2, a circuit board was produced in the same manner as in Example 1-1, except that H was adjusted and the composition of the insulating layer was changed.

[0083] (Example 2-1 to Example 2-6) As shown in Table 3, a circuit board was produced in the same manner as in Example 1-1, except that Ws was adjusted and the composition of the insulating layer was changed. In Tables 2 and 3, "solid particles" refers to solid silica with an average particle size of 2 μm.

[0084] [evaluation] (Dielectric constant (Dk) and dissipation factor (Df)) The relative permittivity (Dk) and dielectric loss tangent (Df) at 10 GHz were measured at room temperature (25°C) by the SPDR method using a vector network analyzer ("E8361C" manufactured by Agilent Technologies).

[0085] (Transmission loss) Signals from 2 GHz to 40 GHz were processed using a vector network analyzer ("E8361A" manufactured by Keysight Technologies) and measured using a high-frequency contact probe (manufactured by Picoprobe, 250 μm pitch) from GSG. The characteristic impedance of the transmission line was set to 50Ω. The surface of the conductor layer of the circuit board was subjected to gold flash plating. The calibration method used was TRL calibration (Thru-Reflect-Line calibration). The transmission loss per unit length was measured. As a measure of transmission loss, we used the "S-parameter" (hereinafter also referred to as "S value"), which is one of the circuit network parameters used to express the characteristics of high-frequency electronic circuits and components. The closer the S value is to 0, the smaller the transmission loss.

[0086] [Table 2] [Table 3]

[0087] As shown in Table 2, Examples 1-1 to 1-4 include an insulating layer and two or more conductive pattern layers embedded in the insulating layer at a distance in the thickness direction, and the insulating layer contains hollow particles, satisfying formulas (1) and (2), and therefore exhibiting excellent electrical properties. Also, it was found that Example 1-4 had the smallest S value, followed by Example 1-3, Example 1-2, Example 1-1, and Example 1-5 in that order. On the other hand, it was found that Example 1-5 did not satisfy formula (2) and had a large transmission loss, and Example 2-6 did not contain hollow particles and had a large transmission loss.

[0088] As shown in Table 3, Examples 2-1 to 2-4 include an insulating layer and two or more conductive pattern layers embedded and spaced apart in the thickness direction of the insulating layer, and the insulating layer contains hollow particles and satisfies formulas (1) and (2), thereby reducing transmission loss. On the other hand, it was found that Example 2-5 did not satisfy formula (2) and had a large transmission loss, and Example 2-6 did not contain hollow particles and had a large transmission loss.

Claims

1. an insulating layer; and two or more conductor pattern layers embedded in the insulating layer at intervals in a thickness direction thereof; the insulating layer includes hollow particles and a resin; A circuit board, wherein the average particle diameter of the hollow particles is D (μm), the distance between adjacent conductive pattern layers in the thickness direction of the insulating layer is H (μm), the width of the conductive pattern layer is Ws (μm), and the thickness of the conductive pattern layer is Wh (μm), the following formulas (1) and (2) are satisfied: 0.8H≦Ws... (1) 40×πD ２ ≦Ws×Wh…(2)

2. The circuit board according to claim 1 , wherein D is 3 or less.

3. 3. The circuit board according to claim 1, wherein H is 50 or less.

4. 3. The circuit board according to claim 1, wherein Ws is 5 to 100.

5. 3. The circuit board according to claim 1, wherein Wh is 5 to 30.

6. 3. The circuit board according to claim 1, wherein the insulating layer comprises at least one resin selected from the group consisting of epoxy resin, polyphenylene ether, fluororesin, polyimide resin, resin containing a divinylbenzene skeleton, and resin containing a pyrimidine skeleton.

7. The hollow particles are made of SiO ２ The circuit board according to claim 1 or 2, comprising:

8. SiO in the hollow particles ２ The circuit board according to claim 1 or 2, wherein the content of

9. 3. The circuit board according to claim 1, wherein the hollow particles have a 20% burst pressure of 120 MPa or more as measured by mercury intrusion porosimetry.

10. The hollow particles have a density and a BET specific surface area of ​​120 m ２ / cm ３ 3. The circuit board according to claim 1, wherein:

11. The circuit board according to claim 1 , wherein the conductor pattern layer contains copper.

12. 3. The circuit board according to claim 1, wherein the insulating layer contains 20 to 80% by volume of the hollow particles.

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