Circuit board manufacturing method

Abstract

A method for manufacturing a circuit board that has both a high adhesive property and excellent high frequency characteristics is provided. Provided is a method for manufacturing a circuit board, the circuit board comprising a high frequency circuit that includes a base material, a ground layer, and a signal layer, at least the signal layer being a layer derived from a copper foil, the method comprising: (a) a step for, on the assumption of manufacturing a high frequency circuit using a copper foil having no adhesive agent layer, designing the specifications of a high frequency circuit having a predetermined impedance Z1; and (b) a step for forming a high frequency circuit in accordance with the specifications with the exception that the signal layer is formed by using, instead of the copper foil having no adhesive agent layer as assumed in the specifications, an adhesive agent layer-attached copper foil in such a way that an adhesive agent layer is interposed between the base material and the signal layer, to thereby manufacture a circuit board with the high frequency circuit having an impedance Z2 greater than Z1.

Description

Technical Field

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

Background Art

[0002] Circuit boards are widely used in electronic devices such as portable electronic devices. In particular, with the increasing functionality of portable electronic devices and the like in recent years, the frequency of signals has been increasing, and circuit boards suitable for such high-frequency applications have been demanded. For this high-frequency circuit board, in order to enable transmission without degrading the quality of high-frequency signals, a circuit board with low transmission loss is desired. A circuit board includes a layer derived from a copper foil processed with a wiring pattern and an insulating resin base material (resin layer), and the transmission loss mainly consists of conductor loss caused by the copper foil and dielectric loss caused by the insulating resin base material.

[0003] Therefore, in the copper foil with a resin layer applied to high-frequency applications, it is desirable to suppress the dielectric loss caused by the resin layer. For this purpose, the resin layer is required to have excellent dielectric properties, particularly a small dielectric tangent. However, there is a problem that a resin layer with a small dielectric tangent generally has low adhesion to the copper foil.

[0004] On the other hand, the conductor loss can increase due to the skin effect of the copper foil, which becomes more prominent at higher frequencies. Therefore, in order to suppress the transmission loss in high-frequency applications, smoothing of the copper foil and refinement of the roughened particles are required to reduce the skin effect of the copper foil. However, as the copper foil becomes smoother, the adhesion to the resin layer decreases.

[0005] To solve these problems, it has been proposed to manufacture copper-clad laminates or circuit boards using copper foil with an adhesive layer, in which an extremely thin adhesive layer (also called a primer layer) is provided on the surface of the copper foil. For example, Patent Document 1 (International Publication No. 2019 / 188087) discloses a copper-clad laminate comprising copper foil, an adhesive layer, and a resin layer in that order, wherein the maximum height Sz on the adhesive layer side of the copper foil is 6.8 μm or less, and the dielectric loss tangent value δa of the adhesive layer is equal to or less than the dielectric loss tangent value δr of the resin layer. It is said that such a copper-clad laminate can improve the transmission characteristics exhibited by the resin layer while ensuring sufficient peel strength between the copper foil and the resin layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2019 / 188087 [Overview of the project]

[0007] Incidentally, the circuits on a circuit board have a predetermined impedance value (for example, 50Ω), and it is known that if the impedance value deviates from this, electrical signals are reflected, causing a phenomenon called reflection loss where the signal no longer enters the circuit. For this reason, when designing circuits, the impedance is controlled by adjusting the width and height of the circuit, or the thickness and dielectric constant of the substrate.

[0008] In recent years, there has been a growing need for even higher frequencies, such as 50 GHz. It has been found that in these high-frequency bands, an extremely thin adhesive layer introduced between the resin substrate and the copper layer significantly affects the dielectric properties of the circuit board. Therefore, when an adhesive layer is introduced to improve the adhesion between the resin substrate and the copper layer, there are concerns that the circuit impedance will deviate from the design value, negatively impacting high-frequency characteristics due to reflection losses. On the other hand, when designing circuits with the adhesive layer in mind, the thickness and dielectric constant of the adhesive layer become design elements, making the design process more difficult.

[0009] The inventors have now discovered that, even when based on specifications for a high-frequency circuit designed for copper foil without an adhesive layer, it is possible to manufacture a circuit board that achieves both high adhesion and excellent high-frequency characteristics by forming the high-frequency circuit using copper foil with an adhesive layer.

[0010] Therefore, the object of the present invention is to provide a method for manufacturing a circuit board that achieves both high adhesion and excellent high-frequency characteristics.

[0011] According to one aspect of the present invention, a method for manufacturing a circuit board equipped with a high-frequency circuit, wherein the high-frequency circuit includes a substrate, a ground layer and a signal layer, and at least the signal layer is a layer derived from copper foil. (a) A step of designing the specifications of a high-frequency circuit having a predetermined impedance Z1, assuming that the high-frequency circuit will be manufactured using copper foil without an adhesive layer, (b) A step of forming a high-frequency circuit in accordance with the specifications, except that instead of the copper foil without an adhesive layer assumed in the specifications, an adhesive-coated copper foil is used to form the signal layer such that the adhesive layer is interposed between the substrate and the signal layer, thereby manufacturing a circuit board in which the high-frequency circuit has an impedance Z2 that exceeds Z1, A method for manufacturing a circuit board is provided, which includes the following.

[0012] According to another aspect of the present invention, a circuit board manufactured by the above method, A circuit board is provided in which the impedance excess rate, calculated by the formula ((Z2-Z1) / Z1)×100, is between 1% and 20%. [Brief explanation of the drawing]

[0013] [Figure 1] This is a process diagram showing an example of a method for manufacturing a circuit board according to the present invention. [Figure 2] This is a schematic diagram of a high-frequency circuit, with arrows indicating the electric field lines of the circuit. [Figure 3A]This graph shows the transmission loss up to a frequency of 50 GHz in circuit boards with a circuit length of 100 mm, as fabricated in Examples 1-5. [Figure 3B] This is a magnified view of the graph in Figure 3A up to a frequency of 20 GHz. [Modes for carrying out the invention]

[0014] Circuit board manufacturing method The present invention relates to a method for manufacturing a circuit board. In this specification, a circuit board may also be referred to as a printed circuit board and is defined to include both a printed wiring board, which is a printed wiring board in which wiring is provided on the surface and / or inside an insulating resin substrate and before electronic components are mounted, and a printed circuit board, which is a printed wiring board in which electronic components are mounted.

[0015] Figure 1 shows an example of a circuit board manufacturing method according to the present invention. The method of the present invention includes the steps of designing the specifications of a high-frequency circuit and manufacturing a circuit board using copper foil with an adhesive layer. Each step will be described below with reference to the drawings.

[0016] (1) Specification design of high-frequency circuits First, assuming the manufacture of a high-frequency circuit using copper foil without an adhesive layer, the specifications of a high-frequency circuit having a predetermined impedance Z1 are designed. As shown in the schematic cross-sectional view of the high-frequency circuit in Figure 1(i), the high-frequency circuit 10 includes a substrate 12, a ground layer 14, and a signal layer 16. That is, the high-frequency circuit 10 designed in this process does not have an adhesive layer between the substrate 12 and the ground layer 14, and between the substrate 12 and the signal layer 16. In this way, various specifications are designed so that the high-frequency circuit 10 without an adhesive layer has a predetermined impedance Z1. Examples of standard values ​​for impedance Z1 are set to values ​​between 40Ω and 120Ω, such as 50Ω, 75Ω, 100Ω, and 120Ω, more typically 50Ω and 100Ω, and even more typically 50Ω.

[0017] The specific specifications of the high-frequency circuit 10 may be designed according to known methods, and this specification preferably includes various sizes of the base material 12, the ground layer 14, and the signal layer 16, as well as their materials (specific materials, etc.). In particular, since the impedance (characteristic impedance) of the circuit depends on the dielectric properties and thickness h of the base material 12, and the width w and height t of the signal layer 16, it is desirable to determine these conditions. In any case, since the high-frequency circuit 10 designed in this process does not include an adhesive layer, circuit design can be easily performed without considering the influence of the adhesive layer. Hereinafter, preferred embodiments of the base material 12, the ground layer 14, and the signal layer 16 will be described.

[0018] The base material 12 can be one generally used as a resin base material in a circuit board or a copper-clad laminate, and is not particularly limited. Preferably, from the viewpoint of ensuring rigidity and insulation, the base material 12 includes a glass cloth and an insulating resin impregnated in the glass cloth, and is typically a prepreg. Preferred examples of the insulating resin used as the prepreg include epoxy resin, cyanate ester resin, polyimide resin, bismaleimide triazine resin (BT resin), polyphenylene ether resin, phenol resin, liquid crystal polymer resin, polytetrafluoroethylene resin (PTFE), and the like. However, the base material 12 is not limited to those having the above rigidity, and may have flexibility. In that case, it is preferably one that does not include a glass cloth.

[0019] The relative dielectric constant of the base material 12 at a frequency of 1 GHz is desirably low from the viewpoint of reducing transmission loss, preferably 10 or less, more preferably 1 or more and 8 or less, still more preferably 1 or more and 5 or less, and particularly preferably 1 or more and 4 or less. The relative dielectric constant at 1 GHz means the relative dielectric constant measured in accordance with IPC-TM-650 2.5.5.9 by the parallel plate method.

[0020] The dielectric tangent of the base material 12 at a frequency of 1 GHz is desirably small from the viewpoint of reducing transmission loss, preferably 0.03 or less, more preferably 0.0001 or more and 0.02 or less, still more preferably 0.0002 or more and 0.01 or less, particularly preferably 0.0003 or more and 0.005 or less, and most preferably 0.0004 or more and 0.004 or less. The dielectric tangent at 1 GHz means the dielectric tangent measured in accordance with IPC-TM-650 2.5.5.9 by the parallel plate method.

[0021] The thickness h of the base material 12 may be appropriately determined according to the use and the specified value of the impedance Z1 and is not particularly limited, but is preferably 1 μm or more and 2000 μm or less, more preferably 5 μm or more and 1500 μm or less, and still more preferably 10 μm or more and 1200 μm or less.

[0022] The ground layer 14 is provided on the surface and / or inside of the base material 12, and is typically provided on at least one surface of the base material 12. The ground layer 14 may be a layer derived from a copper foil (i.e., a copper layer), or may be a layer made of a metal other than copper, but is preferably a copper layer. The ground layer 14 can be a known configuration employed in a circuit board. The width of the ground layer 14 is typically larger than the width w of the signal layer 16 described later, and may be provided over the entire surface of the base material 12. The thickness of the ground layer 14 is not particularly limited, but is typically 1 μm or more and 100 μm or less, and more typically 1 μm or more and 35 μm or less.

[0023] The signal layer 16 is a layer derived from copper foil (i.e., a copper layer) and is provided on the surface and / or inside the substrate 12, and is spaced apart from the ground layer 14. The width w of the signal layer 16 is not particularly limited and can be appropriately determined according to the application and the specified value of impedance Z1, but is preferably 1 μm to 5000 μm, more preferably 1 μm to 3000 μm, and even more preferably 1 μm to 1000 μm. The height t of the signal layer 16 is also not particularly limited and can be appropriately determined according to the application and the specified value of impedance Z1, but is preferably 1 μm to 5000 μm, more preferably 1 μm to 3000 μm, and even more preferably 1 μm to 1000 μm.

[0024] The high-frequency circuit 10 is not particularly limited except that it comprises the substrate 12, ground layer 14, and signal layer 16 described above, and can be a known configuration. For example, the high-frequency circuit 10 may be a microstrip line circuit in which the signal layer 16 is wired on the surface of a circuit board, or it may be a stripline circuit in which the signal layer 16 is embedded and wired inside a circuit board. Furthermore, the high-frequency circuit 10 may be a circuit that outputs a single-ended signal in which one signal line is used for data transmission, or it may be a circuit that outputs a differential signal in which a pair of signal lines is used for data transmission.

[0025] The circuit board may have multiple microstrip line circuits and multiple strip line circuits. Alternatively, the circuit board may be a multilayer substrate with multiple ground layers 14 and multiple signal layers 16 provided on the surface and / or inside the substrate 12. When the circuit board is a multilayer substrate, it typically has microstrip line circuits on the surface layer and strip line circuits in the inner layers.

[0026] The circuit board may include circuits other than the high-frequency circuit 10 (for example, low-frequency circuits of 100 MHz or less). The high-frequency circuit 10 and the other circuits can generally be identified by considering their linearity and position and checking whether they are preferentially placed compared to other circuits on the circuit board. More reliably, they can be identified by checking whether they are connected to the high-speed transmission portion of an electronic component such as an IC chip.

[0027] This process may include not only the design of the high-frequency circuit 10 but also the design of the specifications of the entire circuit board. The specifications of the circuit board may include, for example, the selection of various constituent materials, the determination of the components to be mounted on the circuit board and their arrangement, the mounting design which determines the mounting method, and the wiring design which determines the layer configuration and wiring rules.

[0028] (2) Manufacturing of circuit boards A circuit board equipped with a high-frequency circuit is manufactured. As shown in the schematic cross-sectional view of the high-frequency circuit in Figure 1(ii), in the manufacture of this circuit board, instead of copper foil without an adhesive layer as assumed in the above specifications, copper foil with an adhesive layer is used to form the signal layer 16, with the adhesive layer 18 interposed between the substrate 12 and the signal layer 16. Otherwise, the high-frequency circuit 20 is formed according to the above specifications. In this way, a circuit board is manufactured in which the high-frequency circuit 20 has an impedance Z2 that exceeds Z1. A preferred embodiment of the copper foil with an adhesive layer will be described later.

[0029] As mentioned above, the circuits on a circuit board have a predetermined impedance value (for example, 50Ω), and it is known that if the impedance value deviates from this, electrical signals are reflected, resulting in a phenomenon called reflection loss where the signal no longer enters the circuit. For this reason, when designing circuits, the impedance is controlled by adjusting the width and height of the circuit, or the thickness and dielectric constant of the substrate.

[0030] As described above, with the increasing need for higher frequencies, there are concerns that the impedance of the circuit may deviate from the design value due to the extremely thin adhesive layer introduced between the substrate and the copper layer (signal layer), and that reflection losses may adversely affect the high-frequency characteristics. Therefore, when forming a high-frequency circuit 20 using copper foil with an adhesive layer, it is assumed that the circuit design should take into account the influence of the adhesive layer 18 so that the high-frequency circuit 20 has a predetermined impedance Z1.

[0031] In this regard, the inventors investigated and found that even when the high-frequency circuit 20 including the adhesive layer 18 has an impedance Z2 that exceeds Z1, the adhesive layer 18 can reduce the transmission loss caused by the substrate 12, and that this reduction in transmission loss unexpectedly outweighs the adverse effects of reflection loss. Furthermore, they found that this reduction effect is more pronounced in the high-frequency band of 10 GHz or higher. Therefore, according to the method of the present invention, as described above, it is possible to easily design circuits without considering the influence of the adhesive layer 18. Nevertheless, the circuit board manufactured by the method of the present invention has excellent adhesion between the substrate 12 and the signal layer 16 due to the introduction of the adhesive layer 18, and also has excellent high-frequency characteristics.

[0032] The impedance Z2 of the high-frequency circuit 20 is calculated using the formula ((Z2-Z1) / Z1)×100, and it is preferable that the impedance excess rate is 1% to 20%, more preferably 1% to 15%, even more preferably 1% to 10%, particularly preferably 1% to 7%, and most preferably 1% to 5%. This allows for a more effective reduction of transmission loss while minimizing the effects of reflection loss.

[0033] When the length of the high-frequency circuit 20 is L (mm), Z2 is given by the following formula: Z1 <Z2≦{(1 / 15)×(L+755)}×Z1 / 50 It is preferable that the following conditions be met. That is, the further the impedance Z2 of the high-frequency circuit 20 deviates from a predetermined impedance Z1, the greater the reflection loss will be, but it has been found that the degree of this reflection loss varies depending on the length L of the high-frequency circuit 20. In this respect, by having the impedance Z2 of the high-frequency circuit 20 satisfy the above formula, it is possible to reduce transmission loss more effectively while minimizing the effect of reflection loss. The length L of the high-frequency circuit 20 (typically the length of the signal layer 16) is preferably 1 mm or more and 1000 mm or less, more preferably 1 mm or more and 500 mm or less, even more preferably 1 mm or more and 300 mm or less, and particularly preferably 1 mm or more and 100 mm or less.

[0034] If the high-frequency circuit 20 has a bent section, the total length of the lines passing through the center of the circuit in the plan view of the circuit board shall be defined as the length L of the high-frequency circuit 20. Furthermore, if the circuit board is multilayered and the high-frequency circuits are arranged three-dimensionally (i.e., there are sections that connect in the depth direction (thickness direction of the circuit board) in the plan view), the length of those sections shall also be added to the total length.

[0035] The method for manufacturing the circuit board is preferably used for high-frequency circuits that transmit data at 1 GHz or higher, more preferably at 3 GHz or higher, and even more preferably at 10 GHz to 400 GHz.

[0036] In this process, it is preferable to use copper foil without an adhesive layer for forming the ground layer 14. A schematic diagram of the high-frequency circuit 10 is shown in Figure 2. In the high-frequency circuit 10 shown in Figure 2, electric field lines from the signal layer 16 to the ground layer 14 are indicated by arrows. Since the electric field becomes stronger where the density of electric field lines is higher, as shown in Figure 2, the electric field around the signal layer 16 is stronger than the electric field around the ground layer 14. Furthermore, if the interlayer distance between the ground layer 14 and the signal layer 16 is increased (i.e., the thickness h of the substrate 12 is increased), the electric field around the ground layer 14 will become even weaker. Therefore, it can be said that providing the adhesive layer 18 between the substrate 12 and the signal layer 16 is more effective in reducing transmission loss than providing the adhesive layer 18 between the substrate 12 and the ground layer 14. However, copper foil with an adhesive layer may also be used to form the ground layer 14, and in this case, although the effect is inferior to that when copper foil with an adhesive layer is used to form the signal layer 16, it will still provide a certain level of transmission loss reduction.

[0037] The formation of the high-frequency circuit 20 and the circuit board equipped therewith may be carried out according to the designed specifications, except that the signal layer 16 is formed using copper foil with an adhesive layer instead of copper foil without an adhesive layer. In other words, the manufactured high-frequency circuit 20 may be identical to the high-frequency circuit 10 at the time of design, except that it includes an adhesive layer 18 (which increases the impedance from Z1 to Z2).

[0038] Circuit board According to a preferred embodiment of the present invention, a circuit board manufactured by the method described above is provided. As shown in Figure 1(ii), the circuit board of the present invention comprises a high-frequency circuit 20 including a substrate 12, a ground layer 14, a signal layer 16, and an adhesive layer 18. Preferred embodiments of the substrate 12, the ground layer 14, and the signal layer 16 are as described above. Preferred embodiments of the adhesive layer 18 will be described later.

[0039] As described above, the high-frequency circuit 20 has an impedance exceedance of 1% or more and 20% or less, calculated by the formula ((Z2-Z1) / Z1)×100, preferably 1% or more and 15% or less, more preferably 1% or more and 10% or less, even more preferably 1% or more and 7% or less, and particularly preferably 1% or more and 5% or less. Also, when the length of the high-frequency circuit is L (mm), Z2 is given by the following formula: Z1 <Z2≦{(1 / 15)×(L+755)}×Z1 / 50 It is preferable to satisfy the following conditions.

[0040] As described above, the high-frequency circuit 20 is preferably used for data transmission of 1 GHz or higher, more preferably 3 GHz or higher, and even more preferably 10 GHz to 400 GHz.

[0041] Copper foil with adhesive layer The copper foil with adhesive layer used in the method of the present invention comprises a copper foil and an adhesive layer 18 provided on the surface of the copper foil.

[0042] The copper foil may be in the form of electrolytically manufactured or rolled copper foil (so-called raw foil), or it may be in the form of surface-treated foil with a surface treatment applied to at least one side. The surface treatment can be any type of surface treatment performed to improve or impart certain properties (e.g., rust prevention, moisture resistance, chemical resistance, acid resistance, heat resistance, and adhesion to the substrate) to the surface of the copper foil. The surface treatment may be performed on at least one side of the copper foil, or on both sides of the copper foil. Examples of surface treatments performed on copper foil include rust prevention treatment, silane treatment, roughening treatment, and barrier formation treatment.

[0043] The maximum height Sz on the surface of the copper foil on the adhesive layer 18 side is preferably 6.8 μm or less, more preferably 0.15 μm to 6.8 μm, even more preferably 0.25 μm to 5.0 μm, and particularly preferably 0.3 μm to 3.0 μm. Within this range, sufficient adhesion to the substrate 12 via the adhesive layer 18 can be ensured while desirablely reducing transmission loss. In other words, it is possible to reduce conductor loss caused by the copper foil, which may increase due to the skin effect of the copper foil, and to achieve further reduction of transmission loss. In this specification, "maximum height Sz" is a parameter that represents the distance from the highest point to the lowest point on the surface, measured in accordance with ISO 25178.

[0044] The kurtosis Sku on the surface of the copper foil on the adhesive layer 18 side is preferably 2.0 to 4.0, more preferably 2.2 to 3.8, and even more preferably 2.4 to 3.5. Within this range, transmission loss can be desirablely reduced. That is, it is possible to reduce the conductor loss caused by the copper foil, which may increase due to the skin effect of the copper foil, and to achieve further reduction of transmission loss. In the present invention, "kurtosis Sku" is a parameter that represents the sharpness of the height distribution, measured in accordance with ISO 25178, and is also called the degree of sharpness. Sku = 3 means that the height distribution is a normal distribution, Sku > 3 means that there are many sharp peaks and valleys on the surface, and Sku < 3 means that the surface is flat.

[0045] The maximum peak height Sp on the surface of the copper foil on the adhesive layer 18 side is preferably 3.3 μm or less, more preferably 0.06 μm to 3.1 μm, even more preferably 0.06 μm to 3.0 μm, and particularly preferably 0.07 μm to 2.9 μm. Within this range, sufficient adhesion to the substrate 12 via the adhesive layer 18 can be ensured while desirablely reducing transmission loss. In other words, it is possible to reduce conductor loss caused by the copper foil, which may increase due to the skin effect of the copper foil, and to achieve further reduction of transmission loss. In this specification, "maximum peak height Sp" is a three-dimensional parameter representing the maximum height from the average plane of the surface, measured in accordance with ISO 25178.

[0046] The root mean square gradient Sdq on the surface of the copper foil on the adhesive layer 18 side is preferably 0.01 to 2.3, more preferably 0.02 to 2.0, and even more preferably 0.04 to 1.8. Within this range, sufficient adhesion to the substrate 12 via the adhesive layer 18 can be ensured while desirablely reducing transmission loss. In other words, it is possible to reduce conductor loss caused by the copper foil, which may increase due to the skin effect of the copper foil, and to achieve further reduction of transmission loss. In this specification, "root mean square gradient Sdq" is a parameter calculated by the root mean square of the slope at all points in the defined area, measured in accordance with ISO 25178. That is, it is a three-dimensional parameter that evaluates the magnitude of the local slope angle, and can quantify the roughness of the surface irregularities. For example, Sdq is 0 for a perfectly flat surface, and Sdq is large when there is a slope on the surface. Sdq is 1 for a plane with a 45-degree slope component.

[0047] The above-mentioned maximum height Sz, kurtosis Sku, maximum peak height Sp, and root mean square gradient Sdq are measured over a predetermined area (e.g., 10,000 μm²) on the copper foil surface. 2 The surface profile of the region can be calculated by measuring it with a commercially available laser microscope.

[0048] The thickness of the copper foil is not particularly limited, but is preferably between 1 μm and 200 μm, more preferably between 1 μm and 100 μm, and even more preferably between 1 μm and 35 μm. With a thickness within this range, general pattern formation methods for wiring, such as the MSAP (Modified Semi-Additive) method, SAP (Semi-Additive) method, and subtractive method, can be employed. In addition, copper foil with a carrier may be used.

[0049] The adhesive layer 18 functions as a primer layer to improve the adhesion between the copper foil and the substrate 12. Typically, the adhesive layer 18 is applied to the copper foil to obtain an adhesive-coated copper foil, and then this adhesive-coated copper foil is attached to the substrate 12 for use. However, it is also possible to first coat the substrate 12, then laminate the adhesive layer 18 so that it is in contact with the copper foil, thereby manufacturing a circuit board comprising the substrate and the adhesive-coated copper foil. The thickness of the adhesive layer 18 is preferably 20 μm or less, more preferably 0.5 μm to 15 μm, even more preferably 0.5 μm to 12 μm, particularly preferably 1 μm to 8 μm, and most preferably 1 μm to 5 μm. This makes it possible to achieve a better balance between reducing transmission loss and improving the adhesion between the substrate 12 and the signal layer 16 while minimizing the effects of reflection loss.

[0050] The dielectric loss tangent of the adhesive layer 18 is preferably smaller than the dielectric loss tangent of the substrate 12. This allows for a more effective reduction in transmission loss. Specifically, the dielectric loss tangent of the adhesive layer 18 at a frequency of 10 GHz is preferably 0.0035 or less, more preferably 0.0001 to 0.0030, even more preferably 0.0001 to 0.0020, and particularly preferably 0.0001 to 0.0015. The relative permittivity of the adhesive layer 18 at a frequency of 10 GHz is preferably 6 or less, more preferably 1 to 5.5, even more preferably 1 to 5, and particularly preferably 1 to 4. The dielectric loss tangent and relative permittivity at 10 GHz are measured by the perturbation cavity resonator method.

[0051] The ratio of the relative permittivity of the substrate 12 to the relative permittivity of the adhesive layer 18 (relative permittivity of the substrate / relative permittivity of the adhesive layer) is preferably 0.5 to 5.0, more preferably 0.6 to 4.0, even more preferably 0.8 to 3.5, and particularly preferably 0.9 to 3.0. This reduces the electric flux density of the ground layer, thereby more effectively reducing transmission loss. Each relative permittivity is measured at 50 GHz using the Fabry-Perot resonator method.

[0052] The adhesive layer 18 preferably contains one or more selected from the group consisting of arylene ether compounds (e.g., polyphenylene ether resins), polyimide resins (typically low-dielectric polyimide resins), olefin resins (e.g., polyethylene resins, polypropylene resins, polymethylpentene resins, or cycloolefin resins), liquid crystal polymers, polyester resins, polystyrene resins, hydrocarbon elastomers, benzoxazine resins, activated ester resins, cyanate ester resins, bismaleimide resins, butadiene resins, styrene copolymers (e.g., hydrogenated or unhydrogenated styrene-butadiene resins), epoxy resins (e.g., dicyclopentadiene type epoxy resins), fluororesins, resins having vinyl groups, and copolymers thereof. All of these resins not only exhibit excellent adhesion performance to the substrate 12 and copper foil, but also have a small dielectric loss tangent, and therefore contribute to reducing transmission loss.

[0053] The adhesive layer 18 is particularly preferably composed of an arylene ether compound. The weight-average molecular weight of this arylene ether compound is preferably 30,000 or more, more preferably 30,000 to 300,000, even more preferably 40,000 to 200,000, and particularly preferably 45,000 to 120,000. An arylene ether compound with a weight-average molecular weight of 30,000 or more is typically a polyarylene ether. The arylene ether compound is preferably a phenylene ether compound, such as polyphenylene ether. The arylene ether compound or phenylene ether compound is given by the following formula: [ka] (In the formula, R1, R2, R3, and R4 are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.) It is preferable that the compound contains a skeleton represented by in its molecule. Examples of phenylene ether compounds include styrene derivatives of phenylene ether compounds, phenylene ether compounds containing a maleic anhydride structure in their molecule, terminal hydroxyl group-modified phenylene ether compounds, terminal methacrylate-modified phenylene ether compounds, and terminal glycidyl ether-modified phenylene ether compounds. Examples of arylene ether compounds with a weight-average molecular weight of 30,000 or more that contain a maleic anhydride structure in their molecule include PME-80 and PME-82 manufactured by Mitsubishi Engineering Plastics Corporation.

[0054] The arylene ether compound preferably has a reactive unsaturated bond. Alternatively, the adhesive layer 18 may further contain an additional arylene ether compound having a reactive unsaturated bond. In this case, the additional arylene ether compound does not need to have a weight-average molecular weight of 30,000 or more. That is, the additional arylene ether compound can have a weight-average molecular weight of less than 30,000 (although it may have a weight-average molecular weight of 30,000 or more), for example, a number-average molecular weight of 500 to 10,000. A reactive unsaturated bond is defined as an unsaturated bond that exhibits reactivity in response to heat or ultraviolet light. Preferred examples of reactive unsaturated bonds include cyanate groups, maleimide groups, vinyl groups, (meth)acryloyl groups, ethynyl groups, styryl groups, and combinations thereof. Styryl groups are particularly preferred because they are highly reactive and allow for reaction control (reactions are less likely to occur over time, allowing for resin storage and ensuring a long product life).

[0055] In arylene ether compounds, reactive unsaturated bonds are preferably located at or adjacent to the ends of the molecular structure to exhibit high reactivity. For example, the 1,2-vinyl group is an example of a functional group having an unsaturated bond at the end of the molecular structure, and because the 1,2-vinyl group exhibits high reactivity, it is a common functional group that can be used in radical polymerization. In contrast, ethylenically unsaturated bonds located in the molecular skeleton (vinyl groups not located at the ends of the molecular structure) exhibit lower reactivity. Also, exceptionally, when a benzene ring is adjacent to the unsaturated bond (for example, a styryl group), it exhibits high reactivity. Therefore, the position of the reactive unsaturated bond may be a) at the end of the molecular structure (regardless of whether it is on the main chain or a side chain), or b) if a benzene ring is located at the end of the molecular structure (regardless of whether it is on the main chain or a side chain), it may be adjacent to the terminal benzene ring. For example, arylene ether compounds may have styryl groups as reactive unsaturated bonds at both ends of the molecular structure. Examples of arylene ether compounds having styryl groups at both ends of the molecule include OPE-2St-1200 and OPE-2St-2200, manufactured by Mitsubishi Gas Chemical Company, Inc.

[0056] The content of the arylene ether compound with a weight-average molecular weight of 30,000 or more in the adhesive layer 18 is not particularly limited, but from the viewpoint of achieving both compatibility (which is related to peel strength and water resistance reliability) and dielectric properties, it is preferably 10 to 60 parts by weight, more preferably 15 to 55 parts by weight, even more preferably 20 to 50 parts by weight, and particularly preferably 25 to 35 parts by weight, per 100 parts by weight of the total amount of resin components (solids).

[0057] The adhesive layer 18 preferably further contains a styrene copolymer in addition to the arylene ether compound. The styrene copolymer may be hydrogenated or unhydrogenated. That is, the styrene copolymer is a polymer that contains a styrene-derived moiety and may also contain moieties derived from compounds having polymerizable unsaturated groups other than styrene, such as olefins. If a double bond is further present in the moiety of the styrene copolymer that contains polymerizable unsaturated groups, the double bond moiety may be hydrogenated or unhydrogenated. Examples of styrene copolymers include acrylonitrile-butadiene-styrene copolymer (ABS), methacrylate-butadiene-styrene copolymer (MBS), acrylonitrile-acrylic acid-styrene copolymer (AAS), acrylonitrile-ethylene-styrene copolymer (AES), styrene-butadiene copolymer (SBR), styrene-butadiene-styrene copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), styrene-4-methylstyrene-isoprene-butadiene block copolymer, and combinations thereof. Preferably, styrene-butadiene block copolymer (SBR), styrene-4-methylstyrene-isoprene-butadiene block copolymer, and combinations thereof are used, with styrene-4-methylstyrene-isoprene-butadiene block copolymer being particularly preferred. The weight-average molecular weight of the styrene copolymer is not particularly limited, but is preferably 40,000 to 400,000, more preferably 60,000 to 370,000, and especially preferably 80,000 to 340,000.

[0058] Styrene copolymers preferably contain reactive unsaturated bonds in their molecules. Reactive unsaturated bonds are defined as unsaturated bonds that exhibit reactivity in response to heat or ultraviolet light. Preferred examples of reactive unsaturated bonds include cyanate groups, maleimide groups, vinyl groups, (meth)acryloyl groups, ethynyl groups, styryl groups, and combinations thereof. Styryl groups are particularly preferred because they are highly reactive and allow for reaction control (reactions are less likely to occur over time, allowing for resin storage and ensuring a long product life).

[0059] In styrene copolymers, reactive unsaturated bonds are preferably located at or adjacent to the ends of the molecular structure, similar to arylene ether compounds, in order to exhibit high reactivity. For example, the 1,2-vinyl group is an example of a functional group with an unsaturated bond at the end of the molecular structure, and because the 1,2-vinyl group exhibits high reactivity, it is commonly used as a functional group for radical polymerization. In contrast, ethylenically unsaturated bonds located in the molecular backbone (vinyl groups not located at the ends of the molecular structure) exhibit lower reactivity. Furthermore, exceptionally, when a benzene ring is adjacent to the unsaturated bond (for example, a styryl group), high reactivity is observed. Therefore, the location of the reactive unsaturated bond may be a) at the end of the molecular structure (regardless of whether it is on the main chain or a side chain), or b) adjacent to the benzene ring at the end of the molecular structure (regardless of whether it is on the main chain or a side chain). An example of a styrene copolymer product containing reactive unsaturated bonds is Septon, manufactured by Kuraray Co., Ltd. (R) V9461 (containing a styryl group), Ricon manufactured by Cray Valley. (R) Examples include 100, 181, and 184 (styrene-butadiene copolymers having 1,2-vinyl groups), and Epofriend AT501 and CT310 (styrene-butadiene copolymers having 1,2-vinyl groups) manufactured by Daicel Corporation.

[0060] The styrene copolymer preferably has modified styrene-butadiene. Alternatively, the adhesive layer 18 may further contain an additional styrene copolymer having modified styrene-butadiene. In this case, the additional styrene copolymer can be the same as described above, except that it does not need to have reactive unsaturated bonds. That is, the additional styrene copolymer can be one that does not have reactive unsaturated bonds (although it may have reactive unsaturated bonds). The modified styrene-butadiene may be any styrene-butadiene that has been chemically modified by introducing various functional groups, such as amine modification, pyridine modification, carboxy modification, etc., but amine modification is preferred. An example of a styrene copolymer having modified styrene-butadiene is ToughTec, manufactured by Asahi Kasei Corporation, which is a hydrogenated styrene-butadiene block copolymer and is an amine-modified product. (R) MP10 is one example. Another example of an unmodified styrene copolymer is TR2003, a styrene-butadiene block copolymer manufactured by JSR Corporation.

[0061] The content of the styrene copolymer having reactive unsaturated bonds in the adhesive layer 18 is not particularly limited, but from the viewpoint of achieving both compatibility and dielectric properties, it is preferably 5 to 75 parts by weight, more preferably 10 to 65 parts by weight, even more preferably 15 to 55 parts by weight, and particularly preferably 20 to 43 parts by weight, per 100 parts by weight of the total amount of resin components (solids).

[0062] The content ratio of the arylene ether compound with a weight-average molecular weight of 30,000 or more and the styrene copolymer having a reactive unsaturated bond in its molecule in the adhesive layer 18 is not particularly limited. However, from the viewpoint of balancing adhesion, compatibility, and dielectric properties, when the content of the arylene ether compound with a weight-average molecular weight of 30,000 or more is P, and the content of the styrene copolymer having a reactive unsaturated bond in its molecule is S, the weight ratio obtained by dividing S by P (S / P ratio) is preferably 0.2 or more and 2.0 or less, more preferably 0.4 or more and 1.8 or less, even more preferably 0.6 or more and 1.7 or less, and particularly preferably 1.0 or more and 1.5 or less.

[0063] The adhesive layer 18 may contain additives commonly added to resins and polymers. Examples of additives include reaction initiators, reaction accelerators, flame retardants, silane coupling agents, dispersants, and antioxidants.

[0064] The adhesive layer 18 may further contain a filler. Examples of fillers include silica, talc, alumina, boron nitride (BN), and resin. The filler is not particularly limited as long as it can be dispersed in the adhesive layer 18, but silica is preferred from the viewpoint of dispersibility and dielectric properties. The average particle size D50 of the filler is preferably 0.1 μm or more and 3.0 μm or less, more preferably 0.3 μm or more and 2.0 μm or less. An average particle size D50 within this range reduces the interface (i.e., specific surface area), thereby reducing the adverse effect on dielectric properties, and also brings about desirable properties as an electronic material, such as improved interlayer insulation and the elimination of coarse particles in the resin layer. The filler may be in any form, such as crushed particles, spherical particles, core-shell particles, or hollow particles. The filler content can be any amount and is not particularly limited, but from the viewpoint of ease of filler dispersion and fluidity of the resin composition, it is preferably 0 to 150 parts by weight, more preferably 10 to 130 parts by weight, even more preferably 20 to 100 parts by weight, and particularly preferably 30 to 80 parts by weight, relative to 100 parts by weight of the total amount of resin components (solids) described above. Here, the total amount of resin components (solids) of 100 parts by weight includes not only the polymer and resin, but also the weight of additives that constitute part of the resin, such as reaction initiators, and does not include the filler. [Examples]

[0065] The present invention will be further explained by the following examples.

[0066] Example 1 (comparison) (1) Circuit board design As shown in Figure 1(i), a circuit board was designed that included a high-frequency circuit 10 comprising a substrate 12, a ground layer 14, and a signal layer 16. First, the thickness h of the substrate 12 was set to 136 μm, the relative permittivity of the substrate 12 at 50 GHz was set to 3.1, and the width w of the signal layer 16 was set to 300 μm. Then, patterns were selected that resulted in a microstrip line circuit impedance of 50 Ω when the circuit length of the signal layer 16 was set to 30 mm, 50 mm, 75 mm, or 100 mm.

[0067] (2) Fabrication of the circuit board Based on the design determined in (1) above, a circuit board was fabricated. First, a high-frequency substrate (manufactured by Panasonic Corporation, part number: MEGTRON7 series "R-5680", relative permittivity at 50 GHz measured by the Fabry-Perot resonator method: 3.1, dielectric loss tangent: 0.003) was prepared as the base material 12. Roughened copper foil (manufactured by Mitsui Mining & Smelting Co., Ltd., SI-VSP, thickness 18 μm) was laminated on both sides of this base material 12 so that the roughened side was in contact with the base material 12. Using a vacuum press, it was pressed at a temperature of 190°C and a pressing time of 120 minutes to obtain a copper-clad laminate with an insulation thickness of 136 μm. Subsequently, the copper-clad laminate was etched to obtain the pattern selected in (1) above. In this way, circuit boards equipped with microstrip line circuits with circuit lengths of 30 mm, 50 mm, 75 mm, or 100 mm were fabricated.

[0068] Example 2 A circuit board was fabricated in the same manner as in Example 1, except that instead of roughened copper foil, an adhesive layer 18 with a thickness of 4 μm (relative permittivity at 50 GHz measured by the Fabry-Perot resonator method: 2.6, dielectric loss tangent: 0.0017) was provided on the surface of the roughened copper foil, and the adhesive layer 18 was laminated so that it was in contact with the substrate 12.

[0069] Copper foil with an adhesive layer was prepared as follows. First, as raw material components, 30.10 parts by weight of an arylene ether compound with a weight-average molecular weight of 30,000 or more, 38.20 parts by weight of a styrene copolymer having a reactive unsaturated bond in its molecule, 0.50 parts by weight of a reaction initiator, and 50.00 parts by weight of a filler (not included in the resin solids) were measured into a round flask per 100 parts by weight of resin solids, and toluene and methyl ethyl ketone were added as a mixed solvent. After dissolving or dispersing the raw material components by heating and stirring, a resin varnish with a raw material component concentration of 13% by weight was obtained by allowing it to cool. The obtained resin varnish was applied to the roughened surface of the roughened copper foil using a gravure coating machine so that the resin thickness after drying was 4 μm, and it was dried in an oven at 150°C for 2 minutes to obtain copper foil with an adhesive layer.

[0070] Example 3 The circuit board was fabricated in the same manner as in Example 2, except that the thickness of the adhesive layer was changed to 7 μm.

[0071] Example 4 The circuit board was fabricated in the same manner as in Example 2, except that the thickness of the adhesive layer was changed to 10 μm.

[0072] Example 5 The circuit board was fabricated in the same manner as in Example 2, except that the thickness of the adhesive layer was changed to 15 μm.

[0073] Various evaluations The circuit boards fabricated in Examples 1-5 were evaluated as follows:

[0074] <Impedance Measurement> The impedance of the microstrip circuit on the circuit board was measured as follows. First, an oscilloscope (Tektronix, part number: DSA8200) with a TDR sampling module (part number: 80E04) attached was used, and the module and the circuit board were connected with a high-frequency cable with a 2.4 mm connector. Next, the measurement was performed with the resolution of the horizontal scale on the screen set to 1.25 ps. The average of the impedance values ​​obtained in the range of 0.3 ns to 0.6 ns from the input side circuit end face was taken as the impedance value of the circuit. Here, the input side circuit end face refers to the point in time (in ns) when the impedance value of the measurement system diverged when the connection point between the measurement system and the circuit (mainly probes or connectors) was disconnected during the measurement. For example, if the input side circuit end face is 42.6 ns, the average of the impedance values ​​obtained in the range of 42.9 ns to 43.2 ns is the impedance value of the circuit. The results are shown in Table 1.

[0075] <Measurement of transmission loss> The transmission loss of the microstrip line circuit on the obtained circuit board was measured from 10 MHz to 50 GHz using a network analyzer (Agilent, part number: PNA-X N5245A). The device and the circuit board were connected with a high-frequency cable with a 2.4 mm connector, and the settings were as follows. (Setting conditions) - Power: -15dBm - IF Bandwidth: 150Hz - Number of measurement points: 501 points - Smoothing and Average are OFF - Electronic calibration kit: Use Ecal N4693-60001 and perform calibration at the cable end before measurement.

[0076] For Examples 2-5, the transmission loss reduction effect was confirmed by comparing the transmission loss (dB / cm) from 10MHz to 50GHz with that of Example 1. Furthermore, the magnitude of ripple, a wave-like phenomenon in the attenuation characteristics caused by reflected waves resulting from impedance exceeding the specified value (50Ω), was examined. For reference, transmission loss graphs for a circuit length of 100mm in Examples 1-5 are shown in Figure 3A (up to 50GHz) and Figure 3B (enlarged view up to 20GHz). Based on the confirmed transmission loss reduction effect and ripple magnitude, high-frequency characteristics were evaluated according to the following criteria. The results are shown in Table 1. - Evaluation A: Ripple is absent or minimal, and the reduction in transmission loss significantly outweighs the ripple across the entire measurement frequency range. - Evaluation B: Ripple is present, but the reduction in transmission loss outweighs it at most measurement frequencies. - Evaluation C: Ripple is large, but the effect of reducing transmission loss can be confirmed in the high frequency band above 10 GHz. - Rating D: No effect on reducing transmission loss.

[0077] [Table 1]

Claims

1. A method for manufacturing a circuit board equipped with a high-frequency circuit, wherein the high-frequency circuit includes a substrate, a ground layer, and a signal layer, and at least the signal layer is a layer derived from copper foil. (a) Assuming that the high-frequency circuit is manufactured using copper foil without an adhesive layer, a predetermined impedance Z １ The process of designing the specifications of a high-frequency circuit having, (b) A high-frequency circuit is formed in accordance with the specifications, except that instead of the copper foil without the adhesive layer assumed in the specifications, a copper foil with an adhesive layer is used so that the adhesive layer is interposed between the substrate and the signal layer to form the signal layer, thereby the high-frequency circuit is Z １ Impedance Z exceeding this value ２ A process for manufacturing a circuit board having, A method for manufacturing a circuit board, including [the following].

2. The method for manufacturing a circuit board according to claim 1, wherein copper foil without an adhesive layer is used to form the ground layer.

3. ((Z ２ -Z １ ) / Z １ A method for manufacturing a circuit board according to claim 1 or 2, wherein the impedance excess rate calculated by the formula ) × 100 is 1% or more and 20% or less.

4. When the length of the high-frequency circuit is L (mm), the Z ２ The formula is as follows: Z １ <Z ２ ≦{(1 / 15)×(L+755)}×Z １ / 50 A method for manufacturing a circuit board according to any one of claims 1 to 3, which satisfies the requirements.

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