JP6019012B2 - High frequency circuit board - Google Patents

Description

  The present invention relates to a high-frequency circuit board having excellent high-frequency transmission characteristics and sufficient adhesion to a film, and in particular, a thermoplastic liquid crystal polymer having excellent high-frequency transmission characteristics and sufficient adhesion to a film as an insulating layer. The present invention relates to a high frequency circuit board.

  In recent years, with the spread of high-speed transmission, a material having a small transmission loss during high-speed transmission is required. The thermoplastic liquid crystal polymer film is known as a material having a small transmission loss during high-speed transmission (Patent Document 1). However, if the shape of the metal foil serving as a transmission line, particularly the irregularities on the surface of the metal foil, is large, the thermoplastic liquid crystal polymer film. The characteristic that the transmission loss at the time of high-speed transmission of the film is small is not sufficiently exhibited, and a low-roughness metal foil with a low surface roughness is desirable (Patent Document 2). However, when a low-roughness metal foil is used, the adhesion between the metal foil and the thermoplastic liquid crystal polymer film becomes insufficient, and various attempts have been made to satisfy the characteristics of both transmission loss and adhesion. But still haven't seen enough resolution.

JP 2006-179609 A WO2005-037538 pamphlet

  The present invention has been made in view of the above points, and provides a high-frequency circuit board that can reduce electrical signal transmission loss in a high-frequency circuit and has high adhesion between a metal foil and a resin. It is the purpose.

The present inventors see the characteristics of the surface of the metal foil not only from the roughness (Rz) of the surface of the metal foil, that is, the height of the unevenness, but also from both sides of the roughness (Rz) and the interval between the unevenness ( S ). And the ratio of the roughness (Rz) to the interval ( S ) (Rz / S ) is within the specific range, and the transmission loss is small, and The present inventors have found that a high-frequency circuit board having excellent adhesion between a thermoplastic liquid crystal polymer and a metal foil (circuit) can be obtained, and the present invention has been achieved.

That is, according to the present invention, a metal foil having irregularities on the surface, the surface roughness (Rz) is in the range of 0.5 to 5 μm, and the distance between the surface roughness (Rz) and the irregularities on the surface (S ) Ratio (
Rz / S) is composed of a laminate in which a thermoplastic liquid crystal polymer film is laminated on a metal foil having a surface in the range of 1.5 to 2.5 (excluding S of 2 μm or more), at 40 GHz. There is provided a high frequency circuit board having a transmission loss of less than −0.35 db / cm and an adhesive strength between the metal foil and the thermoplastic liquid crystal film of 0.5 kgf / cm or more. In the present invention, details of the method for measuring the surface roughness (Rz) and the interval (S) between the irregularities will be described later.

In the above high-frequency circuit board, the ratio (Rz / S ) of the surface roughness (Rz) to the spacing ( S ) between the surface irregularities is preferably in the range of 1.5 to 2.5, and the metal foil Is preferably a copper foil.

The present invention provides a metal foil having a surface roughness (Rz) in a specific range and a ratio (Rz / S ) between the surface roughness (Rz) and the interval ( S ) between the irregularities within the specific range. By using it, it is possible to obtain a high-frequency circuit board having a high adhesive force between the thermoplastic liquid crystal polymer film and the metal foil and low high-frequency transmission loss.

(Metal foil)
Although it will not specifically limit if it has electroconductivity as metal foil used in this invention, Gold, silver, copper, stainless steel, nickel, aluminum etc. are illustrated. Copper foil is mentioned as metal foil used preferably. Any copper foil manufactured by a rolling method or an electrolytic method can be used. A preferable thickness range of the metal foil is 5 to 150 μm, more preferably 6 to 70 μm, and particularly preferably 9 to 35 μm.

(Surface roughness on the surface of the metal foil and the spacing between the irregularities)
The metal foil used in the present invention needs to have a surface roughness (Rz) in the range of 0.5 to 5 μm, and preferably in the range of 1 to 4 μm. When the surface roughness is less than 0.5 μm, the adhesion between the metal foil and the thermoplastic liquid crystal polymer layer becomes insufficient. On the other hand, if the surface roughness exceeds 5 μm, the transmission loss increases and the practical performance may not be satisfied.
Moreover, as metal foil used in this invention, ratio (Rz / S ) of surface roughness (Rz) and the space | interval ( S ) between the unevenness | corrugations on the surface exists in the range of 1.5-2.5. It is necessary. When this ratio is less than 1.5, even if it is practical in terms of transmission loss, it becomes difficult to form a practical circuit board because of poor adhesion, while this ratio is 2. If it exceeds 5, transmission loss increases even if it is practical in terms of adhesive strength, and a practical circuit board cannot be obtained.

(Roughening of the metal foil surface)
The ratio (Rz / S ) of the surface roughness (Rz) used in the present invention is in the range of 0.5 to 5 μm and the surface roughness (Rz) and the spacing ( S ) between the irregularities on the surface. The metal foil in the range of 1.5 to 2.5 may be manufactured so that fine irregularities are formed on the surface in the process of forming the metal foil, but after forming the metal foil, the surface of the metal foil is roughened. It can also be obtained by processing. The roughening treatment is performed by adjusting the size of the particles and the interval between the particles by attaching metal particles to the base foil of the metal foil by plating, or by forming irregularities by acid cleaning or the like. It is possible to obtain a metal foil surface satisfying the ratio (Rz / S ) of the degree (Rz) and the surface roughness (Rz) and the distance between the surface irregularities ( S ). The particles to be deposited by plating are not only particles made of Cu but also alloy particles of Cu and Mo, or alloys made of Cu and at least one element selected from the group consisting of Ni, Co, Fe, C, V, and W. It may be formed by particles. As copper foil used in the present invention, SQ-VLP manufactured by Mitsui Mining & Smelting Co., Ltd., BHY and STCS manufactured by Nikko Metal Co., Ltd., FWJ-WS, F3-WS manufactured by Furukawa Electric Co., Ltd., etc. Goods can also be used.

(Thermoplastic liquid crystal polymer film)
The thermoplastic liquid crystal polymer film is formed from a liquid crystal polymer that can be melt-molded (or a liquid crystal polymer that has optical anisotropy at the time of melting), and the thermoplastic liquid crystal polymer is a liquid crystal polymer that can be melt-molded. The chemical structure is not particularly limited, and examples thereof include a thermoplastic liquid crystal polyester or a thermoplastic liquid crystal polyester amide having an amide bond introduced therein.

  The thermoplastic liquid crystal polymer may be a polymer in which an isocyanate-derived bond such as an imide bond, a carbonate bond, a carbodiimide bond, or an isocyanurate bond is further introduced into an aromatic polyester or an aromatic polyester amide.

  Specific examples of the thermoplastic liquid crystal polymer used in the present invention include known thermoplastic liquid crystal polyesters and thermoplastic liquid crystal polyester amides derived from the compounds (1) to (4) listed below and derivatives thereof. Can be mentioned. However, it goes without saying that there is an appropriate range of combinations of various raw material compounds in order to form a polymer capable of forming an optically anisotropic melt phase.

(1) Aromatic or aliphatic dihydroxy compounds (see Table 1 for typical examples)

(2) Aromatic or aliphatic dicarboxylic acids (see Table 2 for typical examples)

(3) Aromatic hydroxycarboxylic acids (see Table 3 for typical examples)

(4) Aromatic diamine, aromatic hydroxyamine or aromatic aminocarboxylic acid (see Table 4 for typical examples)

  Representative examples of the liquid crystal polymer obtained from these raw material compounds include copolymers having the structural units shown in Tables 5 and 6.

  Of these copolymers, a polymer containing at least p-hydroxybenzoic acid and / or 6-hydroxy-2-naphthoic acid as a repeating unit is preferable, and in particular, (i) p-hydroxybenzoic acid and 6-hydroxyoxy- A polymer containing a repeating unit with 2-naphthoic acid, (ii) at least one aromatic hydroxycarboxylic acid selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and 4,4 ′ A repeating unit of at least one aromatic diol selected from the group consisting of dihydroxybiphenyl and hydroquinone and at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid Polymers containing are preferred.

  For example, in the polymer (i), when the thermoplastic liquid crystal polymer contains at least repeating units of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the repeating unit (A) of p-hydroxybenzoic acid is used. And the molar ratio (A) / (B) of the repeating unit (B) to 6-hydroxy-2-naphthoic acid is (A) / (B) = about 10/90 to 90/10 in the liquid crystal polymer. Desirably, it is desirable that (A) / (B) = about 50/50 to 85/15, and more preferably (A) / (B) = 60/40 to 80/20. It may be a degree.

  In the case of the polymer (ii), at least one aromatic hydroxycarboxylic acid (C) selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and 4,4′-dihydroxy At least one aromatic diol (D) selected from the group consisting of biphenyl and hydroquinone, and at least one aromatic dicarboxylic acid (E) selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid. The molar ratio of each repeating unit in the liquid crystal polymer is about aromatic hydroxycarboxylic acid (C): aromatic diol (D): aromatic dicarboxylic acid (E) = about 30-80: 35-10: 35-10. More preferably, (C) :( D) :( E) = 35 to 75: 32.5 to 12.5: 3 May be about .5～12.5, more preferably, (C) :( D) :( E) = 40~70: it may be about 30 to 15: 30-15.

  Moreover, it is preferable that the molar ratio of the repeating structural unit derived from aromatic dicarboxylic acid and the repeating structural unit derived from aromatic diol is (D) / (E) = 95 / 100-100 / 95. Outside this range, the degree of polymerization does not increase and the mechanical strength tends to decrease.

  The optical anisotropy at the time of melting referred to in the present invention can be recognized by, for example, placing a sample on a hot stage, heating and heating in a nitrogen atmosphere, and observing the transmitted light of the sample.

  The thermoplastic liquid crystal polymer preferably has a melting point (hereinafter referred to as Mp) in the range of 260 to 360 ° C, more preferably Mp of 270 to 350 ° C. Mp is determined by measuring the temperature at which the main endothermic peak appears with a differential scanning calorimeter (Shimadzu Corporation DSC).

  The thermoplastic liquid crystal polymer may include a thermoplastic polymer such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyarylate, polyamide, polyphenylene sulfide, polyester ether ketone, and fluororesin within a range not impairing the effects of the present invention. It may be added.

  The thermoplastic liquid crystal polymer film used in the present invention is obtained by extrusion molding of a thermoplastic liquid crystal polymer. Any extrusion molding method can be applied as long as the direction of the rigid rod-like molecules of the thermoplastic liquid crystal polymer can be controlled, but the known T-die method, laminate stretching method, inflation method and the like are industrially advantageous. In particular, in the inflation method and the laminate stretching method, stress is applied not only in the mechanical axis direction of the film (hereinafter abbreviated as MD direction) but also in the direction orthogonal to this (hereinafter abbreviated as TD direction). A film with controlled dielectric properties in the TD direction is obtained.

  In extrusion molding, it is preferable to involve a stretching process in order to control the orientation. For example, in extrusion molding by the T-die method, the melt sheet extruded from the T-die is used in the machine axis direction of the film (hereinafter referred to as MD direction). (Not abbreviated), and may be simultaneously stretched in both directions perpendicular to this (hereinafter abbreviated as TD direction), or the melt sheet extruded from the T-die is once stretched in the MD direction. You may extend | stretch in TD direction.

  In addition, in the extrusion molding by the inflation method, a predetermined draw ratio (corresponding to a stretching ratio in the MD direction) and a blow ratio (corresponding to a stretching ratio in the TD direction) with respect to a cylindrical sheet melt-extruded from a ring die. May be stretched.

  The stretch ratio of such extrusion molding may be, for example, about 1.0 to 10, preferably about 1.2 to 7, more preferably about 1. as the stretch ratio (or draw ratio) in the MD direction. It may be about 3-7. Further, the draw ratio (or blow ratio) in the TD direction may be, for example, about 1.5 to 20, preferably about 2 to 15, and more preferably about 2.5 to 14.

  And ratio (TD direction / MD direction) of each draw ratio of MD direction and TD direction may be 2.6 or less, for example, about 0.4-2.5 may be sufficient.

  Further, if necessary, the extruded raw sheet is subjected to a known or conventional heat treatment (for example, a melting point (Mp) or higher of the liquid crystal polymer (for example, about Mp to Mp + 30 ° C., preferably about Mp + 10 to Mp + 20 ° C.). ) To adjust the melting point and thermal expansion coefficient of the thermoplastic liquid crystal polymer film.

  The thermoplastic liquid crystal polymer film may be stretched as necessary after extrusion. The stretching method itself is known, and either biaxial stretching or uniaxial stretching may be adopted, but biaxial stretching is preferred because it is easier to control the degree of molecular orientation. For stretching, a known uniaxial stretching machine, simultaneous biaxial stretching machine, sequential biaxial stretching machine or the like can be used.

  In the thermoplastic liquid crystal polymer film obtained as described above, the SOR (Segment Orientation Ratio) indicating the degree of molecular orientation is, for example, SOR ≦ 1.20 (for example, 1.02 to about 1.20), preferably 1.05 to 1.19, and more preferably 1.07 to 1.19. Here, the molecular orientation SOR refers to an index that gives the degree of molecular orientation, and is a value that takes into account the thickness of an object, unlike conventional MOR (Molecular Orientation Ratio). The SOR of the thermoplastic liquid crystal polymer film used in the present invention needs to improve the dielectric properties in the MD direction and consider the good balance of mechanical and thermal properties between the MD and TD directions, SOR shows the value measured by the method described in the Example mentioned later.

  The thermoplastic liquid crystal polymer film used in the present invention may have any thickness, and includes a plate or sheet having a thickness of 5 mm or less. However, when it is used for a high-frequency transmission line, the transmission loss decreases as the thickness increases, so it is necessary to increase the thickness as much as possible. However, when a thermoplastic liquid crystal polymer film is used alone as the electrical insulating layer, the film thickness is preferably in the range of 10 to 500 μm, and more preferably in the range of 15 to 200 μm. When the thickness of the film is too thin, the rigidity and strength of the film are reduced. Therefore, a method of obtaining an arbitrary thickness by laminating films having a film thickness in the range of 10 to 200 μm may be used.

(Circuit board)
The high-frequency circuit board of the present invention comprises a laminate in which a metal such as copper is formed as an electrically conductive layer on both surfaces of a thermoplastic liquid crystal polymer film that is an electrically insulating layer. Formation of the metal layer on the surface of the thermoplastic liquid crystal polymer film can be performed by thermocompression bonding the metal foil using a vacuum hot press apparatus or a heating roll laminating equipment. A multilayer circuit board can be formed by laminating a plurality of laminates of thermoplastic liquid crystal polymer film layers and metal foils. After thermocompression bonding, a printed circuit board can be obtained by forming a circuit pattern on the metal foil by a method such as etching.

The laminate of the present invention is not limited to a two-layer structure of a thermoplastic liquid crystal polymer film and a copper foil. That is, the laminated body should just contain at least 1 layer of thermoplastic liquid crystal polymer film and at least 1 layer of copper foil, for example, the laminated body shown to following I) -III) can be illustrated.
In addition, the film layer may be not only a single layer composed of one film but also a film laminate in which several films are laminated.
I) Copper foil / film / copper foil II) Film / copper foil / film III) Copper foil / film / copper foil / film / copper foil

  In the present invention, the circuit board refers to a board in which a conductor layer (conductor circuit layer) is formed on one or both sides of a board made of a thermoplastic liquid crystal polymer film layer. Also, a multilayer printed wiring board in which conductor layers and insulating layers are alternately formed and the outermost layer of the multilayer printed wiring board has a conductor layer (conductor circuit layer) on one side or both sides. It is included in the circuit board referred to in the invention. The conductor layer is patterned to form a printed circuit board.

  As a method for forming a through hole in the high-frequency circuit board of the present invention, a processing method using a drill or a processing method using a laser such as a carbon dioxide laser, a YAG laser, or an excimer laser can be employed. It is preferable to chemically remove and remove cutting waste (smear) of the thermoplastic liquid crystal polymer adhering to the inside of the hole due to heat generated during the formation of the through hole.

  In addition, as a method of plating the through hole of the high-frequency circuit board of the present invention, a conventionally known method can be adopted, and if pattern plating and / or panel plating by electroless copper plating and electrolytic copper plating are sequentially performed, Good.

(High frequency circuit)
In the present invention, the high-frequency circuit is not only a circuit that transmits only a high-frequency signal, but also a transmission path that converts a high-frequency signal into a low-frequency signal and outputs the generated low-frequency signal to the outside, or a high-frequency circuit. A transmission path for transmitting a signal that is not a high-frequency signal, such as a transmission path for supplying power to drive the corresponding component, is also included.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Measurement method of roughness and uneven spacing of copper foil surface)
Using a shape measuring microscope (manufactured by Keyence Corporation, model: VK-810), the surface roughness (Rz) of the copper foil and the spacing ( S ) between the irregularities were measured at a measurement magnification of 1000 times. The surface roughness was measured by a method based on JISB0601-1994. For surface roughness (Rz), the reference length is extracted from the roughness curve in the direction of the average line, the average value of the altitude of the highest peak to the fifth peak (convex peak), and the bottom from the deepest to the fifth peak. The difference from the average value of the altitude of (concave bottom) is expressed in μm, and the ten-point average roughness is shown. Further, the spacing between irregularities (S), the direction to the reference length of the average line from the roughness curve while the Tsu sampling by a method in accordance with JISB0601-1994, in which Karaso top of one of the projections the length of the flat Hitoshisen to the bottom of one recess adjacent the (interval between irregularities) calculated, the arithmetic mean value of the spacing between the number of irregularities is obtained expressed in [mu] m. In addition, the space | interval (S) between unevenness | corrugation is Mitsui Kinzoku Mining Co., Ltd. SQ-VLP, Nikko Metal Co., Ltd. BHY, STCS, Furukawa Electric FWJ-WS, F3-WS etc. The values shown in Table 8 for the commercial products shown in Table 7.

(Measurement method of adhesive strength)
In accordance with JIS C5016-1994, while pulling the copper foil at a rate of 50 mm per minute in the direction of 90 ° with respect to the copper foil removal surface, a tensile tester [Nidec Sympo Co., Ltd., Digital Force Gauge FGP-2] was used to measure the peel strength of the copper foil, and the obtained value was defined as the adhesive strength.

(Transmission loss measurement method)
Measurement was performed at a measurement frequency of 40 GHz using a microwave network analyzer [manufactured by Agilent, model: 8722ES] and a probe (manufactured by Cascade Microtech, model: ACP40-250).

(Copper foil)
About the copper foil shown in Table 7, according to said measuring method, the surface roughness (Rz) of each copper foil and the space | interval (S) between unevenness | corrugations were measured, and it showed in Table 8 and Table 9.

(Thermoplastic liquid crystal polymer film)
Thermoplastic having a film thickness of 50 μm obtained by melt-extruding a thermoplastic liquid crystal polymer having a melting point of 280 ° C. and blow-molding with a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. A liquid crystal polymer film (degree of molecular orientation: 1.05) was used.

(Circuit board)
The copper foil shown in Table 7 is overlaid on the upper and lower sides of the above thermoplastic liquid crystal polymer film, and using a vacuum hot press apparatus, the heating platen is set at 295 ° C., and is crimped for 10 minutes under a pressure of 4 MPa, A laminate (A) having a configuration of electrolytic copper foil / thermoplastic liquid crystal polymer film / electrolytic copper foil was produced. A circuit pattern was produced on the copper foil surface of the obtained laminate by a chemical etching method to obtain a laminate (B) having a circuit pattern.

  About the laminated board produced using each copper foil shown in Table 7, the transmission strength was measured using the laminated board (A) and the adhesive strength, and the laminated board (B). The results are shown in Table 8 and Table 9. Indicated.

As is clear from the results of the above examples and comparative examples, the results of the examples in which the Rz / S ratio is in the range of 1.5 to 2.5 indicate that the adhesive strength is 0.5 kgf / It can be seen that this is a laminated circuit board that is equal to or greater than cm and has a transmission loss that is less than -0.35, and is balanced in terms of both adhesive strength and transmission loss.
On the other hand, in Comparative Examples 1, 2, and 5, even if the transmission loss is lower than −0.35, the adhesive strength is lower than 0.5 kgf / cm and shows a practically unacceptable value. In 3 and 4, even though the adhesive strength showed a high value of 0.5 kgf / cm or higher, the transmission loss was larger than -0.35, indicating an impractical result.

  According to the present invention, since a high-frequency circuit board with low transmission loss and high adhesion can be obtained, the present invention is useful as various high-frequency circuit boards for high-speed transmission, and thus has high industrial applicability.

  While the preferred embodiments of the present invention have been described above by way of example, those skilled in the art can make various modifications, additions and substitutions without departing from the scope and spirit of the present invention disclosed in the claims. It will be understandable.

Claims (2)

A metal foil having irregularities on the surface, the surface roughness (Rz) is in the range of 0.5 to 5 μm, and the ratio (Rz) between the surface roughness (Rz) and the interval (S) between the irregularities on the surface / S) is composed of a laminate in which a thermoplastic liquid crystal polymer film is laminated on a metal foil having a surface in a range of 1.5 to 2.5 (excluding S of 2 μm or more), and transmission at 40 GHz. A high frequency circuit board having a loss of less than -0.35 db / cm and an adhesive strength between the metal foil and the thermoplastic liquid crystal film of 0.5 kgf / cm or more.   The high-frequency circuit board according to claim 1, wherein the metal foil is a copper foil.