JP2018110193A - Original board for printed wiring board and printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an original board for a printed wiring board of which a printed wiring board in which transmission delay and transmission loss are comparatively small can be formed, as well as a printed wiring board in which transmission delay and transmission loss are comparatively small.SOLUTION: An original board for a printed wiring board according to one embodiment of the invention comprises a base film composed mainly of a liquid-crystal polymer, copper foil laminated on at least one surface side of the base film, and an adhesive layer through which the base film is made to adhere to the copper foil, where an average relative dielectric constant of the adhesive layer is 3 or less and an average electrical loss tangent thereof is 0.005 or less. A printed wiring board according to another embodiment of the invention comprises a base film composed mainly of a liquid crystal polymer, a conductive pattern laminated on at least one surface side of the base film and composed mainly of copper, and an adhesive layer through which the base film is made to adhere to the conductive pattern, where an average relative dielectric constant of the adhesive layer is 3 or less and an average electrical loss tangent thereof is 0.005 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a printed wiring board and a printed wiring board.

  In recent years, the amount of information communication has been increasing, and in order to respond to this, communication in high frequency areas such as microwaves and millimeter waves, that is, high-speed transmission of electrical signals, has become popular in devices such as IC cards and mobile phone terminals. ing. For this reason, a printed wiring board for high-speed transmission with low transmission loss when used in a high frequency region is required.

  The transmission loss in the high frequency region includes dielectric loss in an insulating layer such as a base film or a coverlay adjacent to the conductive pattern of the printed wiring board. This dielectric loss can be reduced by using an insulating material having a small relative dielectric constant.

  Therefore, it has been proposed to use a film formed of a liquid crystal polymer having a low relative dielectric constant as the base film and the cover lay, and to integrate these base films and the cover lay by laminating them by thermocompression bonding ( JP, 2013-89710, A).

  In the above publication, the surface of the copper foil forming the conductive pattern is roughened by a method such as plasma treatment or acid cleaning, thereby improving the adhesion between the film formed of the liquid crystal polymer and the copper foil. It describes what you can do.

JP 2013-89710 A

  As disclosed in the above publication, when the surface of the copper foil forming the conductive pattern is roughened, the propagation distance when the current flows through the surface portion of the conductive pattern is increased in the high frequency region due to the skin effect. As a result, there is a disadvantage that transmission delay occurs and transmission loss increases due to resistance attenuation or the like.

  The present invention has been made based on the above-described circumstances, and a printed wiring board original plate capable of forming a printed wiring board with relatively small transmission delay and transmission loss, and printed wiring with relatively small transmission delay and transmission loss. It is an object to provide a board.

  An original board for a printed wiring board according to an aspect of the present invention made to solve the above problems is a base film mainly composed of a liquid crystal polymer, and a copper foil laminated on at least one surface side of the base film, And an adhesive layer for bonding between the base film and the copper foil, wherein the adhesive layer has an average relative dielectric constant of 3 or less and an average dielectric loss tangent of 0.005 or less.

  A printed wiring board according to another aspect of the present invention, which has been made to solve the above problems, is a base film mainly composed of a liquid crystal polymer, and is laminated on at least one surface side of the base film, and is composed mainly of copper. And an adhesive layer that adheres between the base film and the conductive pattern. The adhesive layer has an average relative dielectric constant of 3 or less and an average dielectric loss tangent of 0.005 or less.

  The printed wiring board original plate according to one embodiment of the present invention can form a printed wiring board with relatively small transmission delay and transmission loss. Further, the printed wiring board according to another aspect of the present invention has a relatively small transmission delay and transmission loss.

FIG. 1 is a schematic cross-sectional view showing a printed wiring board original plate according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a printed wiring board formed from the printed wiring board of FIG.

[Description of Embodiment of the Present Invention]
A base plate for a printed wiring board according to an aspect of the present invention includes a base film mainly composed of a liquid crystal polymer, a copper foil laminated on at least one surface side of the base film, and a gap between the base film and the copper foil. And an adhesive layer to be bonded, wherein the adhesive layer has an average relative dielectric constant of 3 or less and an average dielectric loss tangent of 0.005 or less.

  Since the printed wiring board original plate is bonded between the base film and the copper foil using an adhesive layer having an average relative dielectric constant and an average dielectric loss tangent of the upper limit or less, the peel strength of the copper foil forming the conductive pattern is Despite being relatively large, transmission delay and transmission loss are relatively small.

  The average thickness of the adhesive layer is preferably 2 μm or more and 25 μm or less. Thus, the peeling strength of copper foil can fully be improved by making the average thickness of the said adhesive bond layer into the said range.

  The main component of the adhesive layer is preferably a modified polyphenylene ether or styrene resin. As described above, since the main component of the adhesive layer is a modified polyphenylene ether or styrene resin, it is possible to easily form an adhesive layer having a relatively small relative dielectric constant and dielectric loss tangent and a relatively large adhesive strength. it can.

  A printed wiring board according to another aspect of the present invention includes a base film mainly composed of a liquid crystal polymer, a conductive pattern principally composed of copper, laminated on at least one surface side of the base film, and the base film. And an adhesive layer for adhering between the conductive patterns, wherein the adhesive layer has an average relative dielectric constant of 3 or less and an average dielectric loss tangent of 0.005 or less.

  Since the printed wiring board adheres between the base film and the conductive pattern using an adhesive layer whose average dielectric constant and average dielectric loss tangent are not more than the above upper limits, the peel strength of the conductive pattern is relatively large and the transmission delay is And transmission loss is relatively small.

  Here, the “relative permittivity” is a value measured according to JIS-C2138 (2007). The “dielectric loss tangent” is a value measured at a frequency of 1 GHz in accordance with JIS-C2138 (2007). Further, the “main component” refers to a component having a content of 50% by mass or more, preferably 90% by mass or more.

[Details of the embodiment of the present invention]
Hereinafter, an embodiment of a printed wiring board according to the present invention will be described in detail with reference to the drawings.

[Original printed circuit board]
The base plate for a printed wiring board in FIG. 1 includes a base film 1, a copper foil 2 laminated on one surface side of the base film 1, and an adhesive layer 3 that bonds the base film 1 and the copper foil 2. Prepare.

<Base film>
The base film 1 is a sheet-like member having a liquid crystal polymer as a main component and having an insulating property, and is a base material that supports the copper foil 2 via the adhesive layer 3.

  By using a liquid crystal polymer having a relatively small relative dielectric constant and dielectric loss tangent as the main component of the base film 1, the dielectric loss when transmitting a high-frequency signal through a wiring formed by patterning the copper foil 2 is reduced. Can do.

  The lower limit of the average relative dielectric constant of the base film 1 is preferably as small as possible. However, in order to satisfy other conditions such as insulation and mechanical strength, 1.5 is considered to be the limit in practice. On the other hand, the upper limit of the average relative dielectric constant of the base film 1 is preferably 4, and more preferably 3. When the average relative dielectric constant of the base film 1 exceeds the upper limit, dielectric loss may increase when a high-frequency signal is transmitted by a printed wiring board formed from the printed wiring board original plate.

  The lower limit of the average dielectric loss tangent at a frequency of 1 GHz of the base film 1 is preferably as small as possible, but in reality, 0.0001 is considered the limit. On the other hand, the upper limit of the average dielectric loss tangent of the base film 1 at a frequency of 1 GHz is preferably 0.05, and more preferably 0.005. When the average dielectric loss tangent of the base film 1 at a frequency of 1 GHz exceeds the above upper limit, there is a possibility that the transmission loss of the high-frequency signal of the printed wiring board formed from the printed wiring board original plate is increased.

  The thickness of the base film 1 is appropriately set according to the use of the original printed wiring board, and is not particularly limited. In general, the lower limit of the average thickness of the base film 1 is 5 μm. Is preferably 10 μm, more preferably 25 μm. On the other hand, the upper limit of the average thickness of the base film 1 is preferably 500 μm, and more preferably 150 μm. When the average thickness of the base film 1 is less than the above lower limit, the strength of the base film 1 may be insufficient. On the contrary, when the average thickness of the base film 1 exceeds the upper limit, the flexibility of the printed wiring board original plate may be insufficient, or the printed wiring board original plate may be unnecessarily thick. .

  As a minimum of melting | fusing point of the base film 1, 250 degreeC is preferable and 280 degreeC is more preferable. On the other hand, the upper limit of the melting point of the base film 1 is preferably 400 ° C., more preferably 350 ° C. When the melting point of the base film 1 is less than the above lower limit, the dimensional accuracy may be insufficient due to deformation during solder reflow for mounting electronic components or the like. On the other hand, when the melting point of the base film 1 exceeds the above upper limit, there is a possibility that the cost may increase unnecessarily, and other characteristics such as the relative dielectric constant and dielectric loss tangent may not be preferable. The “melting point” is a value measured according to JIS-K7121 (1987).

  The liquid crystal polymer as the main component of the base film 1 includes a thermotropic type that exhibits liquid crystallinity in the molten state and a lyotropic type that exhibits liquid crystallinity in the solution state. In the present invention, the thermotropic liquid crystal polymer is used. Is preferred.

  The liquid crystal polymer is, for example, an aromatic polyester obtained by synthesizing an aromatic dicarboxylic acid and a monomer such as an aromatic diol or an aromatic hydroxycarboxylic acid. A typical example is a polymer having structural units represented by the following formulas (1), (2) and (3) synthesized from parahydroxybenzoic acid (PHB), terephthalic acid and 4,4′-biphenol. A polymer having a structural unit of the following formulas (3) and (4) synthesized from PHB, terephthalic acid and ethylene glycol, the following formula (2) synthesized from PHB and 2,6-hydroxynaphthoic acid, Examples thereof include polymers having the structural units (3) and (5).

  The liquid crystal polymer is not particularly limited as long as it exhibits liquid crystallinity, and the above-mentioned polymers are the main components (in the liquid crystal polymer, 50 mol% or more), and other polymers or monomers may be copolymerized. . The liquid crystal polymer may be a liquid crystal polyester amide, a liquid crystal polyester ether, a liquid crystal polyester carbonate, or a liquid crystal polyester imide.

  The liquid crystal polyester amide is a liquid crystal polyester having an amide bond, and examples thereof include a polymer having a structural unit represented by the following formula (6) and the above formulas (2) and (4).

  The liquid crystal polymer is preferably produced by melt polymerization of raw material monomers corresponding to the constituent units constituting the liquid crystal polymer, and solid-phase polymerization of the obtained polymer (prepolymer). Thereby, a high molecular weight liquid crystal polymer having high heat resistance, strength and rigidity can be produced with good operability. Melt polymerization may be carried out in the presence of a catalyst. Examples of this catalyst include metal compounds such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, And nitrogen-containing heterocyclic compounds such as 4- (dimethylamino) pyridine and 1-methylimidazole, and nitrogen-containing heterocyclic compounds are preferably used.

  The base film 1 may contain a filler, an additive, and the like in addition to the liquid crystal polymer.

<Copper foil>
The copper foil 2 is bonded to the base film 1 by the adhesive layer 3. The surface of the copper foil 2 may be plated with, for example, gold.

  The average thickness of the copper foil 2 is not particularly limited, but the lower limit of the average thickness of the copper foil 2 is preferably 1 μm and more preferably 5 μm. On the other hand, the upper limit of the average thickness of the copper foil 2 is preferably 100 μm, more preferably 50 μm, and even more preferably 25 μm. If the average thickness of the copper foil 2 is less than the lower limit, the transmission loss (Joule loss) in the wiring formed from the copper foil 2 may be too large. On the contrary, when the average thickness of the copper foil 2 exceeds the upper limit, the flexibility of the printed wiring board original plate may be insufficient.

  The upper limit of the surface roughness Ra of the copper foil 2 is preferably 4 μm, more preferably 2 μm, and even more preferably 1 μm. When the average surface roughness Ra of the copper foil 2 exceeds the above upper limit, the transmission delay and transmission loss may increase due to an increase in the propagation distance of the current flowing along the surface of the conductive pattern on which the copper foil 2 is patterned. On the other hand, the lower limit of the surface roughness Ra of the copper foil 2 is not particularly limited. The “average surface roughness Ra” means arithmetic average roughness measured in accordance with JIS-B0601 (2013), with an evaluation length (l) of 3000 nm and a cutoff value (λc) of 1000 nm. .

<Adhesive layer>
The adhesive layer 3 is formed from an adhesive and fixes the copper foil 2 on the base film 1.

  The lower limit of the average relative dielectric constant of the adhesive layer 3 is preferably as small as possible. However, in order to satisfy other conditions such as insulation and mechanical strength, 1.5 is considered to be the limit in practice. On the other hand, the upper limit of the average relative dielectric constant of the adhesive layer 3 is 3, preferably 2.8, and more preferably 2.6. In addition, when the average relative dielectric constant of the adhesive layer 3 exceeds the upper limit, dielectric loss may increase when a high-frequency signal is transmitted by a printed wiring board formed from the printed wiring board original plate.

  The average relative dielectric constant of the adhesive layer 3 is preferably smaller than the average relative dielectric constant of the base film 1. Thus, the average relative dielectric constant of the adhesive layer 3 is smaller than the average relative dielectric constant of the base film 1, compared to the case where the base film 1 and the copper foil 2 are directly thermocompression bonded without using an adhesive. In addition, dielectric loss in the case of transmitting a high-frequency signal by wiring formed by patterning the copper foil 2 can be reduced.

  The lower limit of the average dielectric loss tangent at the frequency 1 GHz of the dielectric loss tangent of the adhesive layer 3 is preferably as small as possible, but 0.0001 is considered to be the limit in practice. On the other hand, the upper limit of the average dielectric loss tangent of the adhesive layer 3 at a frequency of 1 GHz is 0.005, preferably 0.003, and more preferably 0.002. When the average dielectric loss tangent of the adhesive layer 3 at a frequency of 1 GHz exceeds the above upper limit, there is a possibility that transmission loss of a high-frequency signal of the printed wiring board formed from the printed wiring board original plate is increased.

  The average dielectric loss tangent of the adhesive layer 3 is preferably smaller than the average dielectric loss tangent of the base film 1. Thus, since the dielectric loss tangent of the adhesive layer 3 is smaller than the average dielectric loss tangent of the base film 1, the printed wiring can be compared with the case where the copper foil 2 is directly thermocompression bonded to the base film 1 without using an adhesive. The dielectric loss in the case of transmitting a high frequency signal with the printed wiring board formed from the board | substrate original board can be made small.

  The main component of the adhesive forming the adhesive layer 3 is preferably one having excellent flexibility and heat resistance. For example, adhesives of various resins such as modified polyphenylene ether, styrene resin, epoxy resin, butyral resin, acrylic resin, etc. Among them, modified polyphenylene ether and styrene resin that can relatively reduce the relative dielectric constant and dielectric loss tangent of the adhesive layer 3 are preferably used.

  As the main component of the adhesive layer 3, that is, the main component of the adhesive forming the adhesive layer 3, a thermosetting resin is preferable. Therefore, as the main component of the adhesive layer 3, a thermosetting modified polyphenylene ether and a thermosetting styrene resin are particularly preferably used.

  The lower limit of the curing temperature of the thermosetting resin as the main component of the adhesive layer 3 is preferably 120 ° C., more preferably 150 ° C. On the other hand, the upper limit of the curing temperature of the thermosetting resin that is the main component of the adhesive layer 3 is preferably 250 ° C, more preferably 230 ° C, and even more preferably 200 ° C. When the curing temperature of the thermosetting resin that is the main component of the adhesive layer 3 is less than the lower limit, it may be difficult to handle the adhesive that is the raw material of the adhesive layer 3. Conversely, when the curing temperature of the thermosetting resin that is the main component of the adhesive layer 3 exceeds the upper limit, the base film 1 is deformed by heat when the adhesive is cured to form the adhesive layer 3. There is a risk.

  The lower limit of the average thickness of the adhesive layer 3 is preferably 2 μm and more preferably 5 μm. On the other hand, the upper limit of the average thickness of the adhesive layer 3 is preferably 25 μm, more preferably 20 μm, and even more preferably 15 μm. When the average thickness of the adhesive layer 3 is less than the lower limit, the adhesive force may be insufficient. On the contrary, when the average thickness of the adhesive layer 3 exceeds the upper limit, the thickness of the printed wiring board original plate may be unnecessarily increased.

<Manufacturing method>
The base plate for printed wiring board is formed by applying an adhesive composition containing a solvent to the base film 1 and drying the adhesive composition, then laminating the copper foil 2 and thermocompression bonding (thermosetting in a pressure contact state). Can be produced by forming the adhesive layer 3.

<Advantages>
Since the base plate for printed wiring board adheres the base film 1 and the copper foil 2 using the adhesive layer 3 having a relatively small relative dielectric constant and dielectric loss tangent, the peel strength of the copper foil 2 is relatively large. Regardless, the transmission delay and transmission loss of the printed wiring board formed from the printed wiring board original plate can be made relatively small.

[Printed wiring board]
The printed wiring board in FIG. 2 includes a base film 1 mainly composed of a liquid crystal polymer, a conductive pattern 4 laminated on one surface side of the base film 1 and mainly composed of copper, the base film 1 and the conductive pattern. And an adhesive layer 3 for bonding the four.

  The printed wiring board can be formed from the printed wiring board original plate of FIG. For this reason, with respect to the printed wiring board of FIG. 2, the same components as those of the printed wiring board original plate of FIG.

<Conductive pattern>
The conductive pattern 4 can be formed by patterning the copper foil 2 of the printed wiring board original plate of FIG. More specifically, a portion exposed from the opening of the resist pattern in plan view of the copper foil 2 is removed by forming a resist pattern on the surface of the copper foil 2 of the printed wiring board original plate of FIG. Formed by.

  The conductive pattern 4 has a planar shape including the linear wiring 5. The conductive pattern 4 may include, for example, a land for mounting an electronic component, a lead wire, or the like.

  The average width of the wiring 5 of the conductive pattern 4 is not particularly limited, but the lower limit of the average width is preferably 25 μm, and more preferably 60 μm. On the other hand, the upper limit of the average width is preferably 500 μm, and more preferably 250 μm. If the average width is less than the lower limit, the transmission loss (copper loss) in the wiring 5 may be too large. Conversely, when the average width exceeds the upper limit, the area of the printed wiring board may become unnecessarily large.

<Advantages>
In the printed wiring board, since the base film 1 and the conductive pattern 4 are bonded using the adhesive layer 3 having a relatively small average relative dielectric constant and average dielectric loss tangent, the peel strength of the conductive pattern 4 is relatively large. Nevertheless, transmission delay and transmission loss can be made relatively small.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  The said printed wiring board original plate may laminate | stack copper foil on both the surface sides of a base film. The printed wiring board may be a double-sided board in which conductive patterns are laminated on both sides of the base film, or may be a multilayer board having a plurality of base films and conductive patterns.

  The printed wiring board may include additional components such as a cover lay covering the conductive pattern.

  The surface of the original printed wiring board and the base film of the printed wiring board may be roughened or modified in order to improve adhesion to the adhesive layer.

  The printed wiring board is not limited to transmitting high-frequency signals, and may handle low-frequency signals.

  The original printed wiring board and the printed wiring board can be suitably used, for example, as a high-speed transmission flexible printed wiring board that transmits a high-frequency signal.

1 Base film 2 Copper foil 3 Adhesive layer 4 Conductive pattern 5 Wiring

Claims (4)

A base film mainly composed of a liquid crystal polymer;
A copper foil laminated on at least one side of the base film;
An adhesive layer for bonding between the base film and the copper foil,
A printed wiring board master having an average relative dielectric constant of 3 or less and an average dielectric loss tangent of 0.005 or less.   The printed wiring board original board according to claim 1, wherein an average thickness of the adhesive layer is 2 μm or more and 25 μm or less.   3. The printed wiring board original plate according to claim 1, wherein a main component of the adhesive layer is modified polyphenylene ether or styrene resin. A base film mainly composed of a liquid crystal polymer;
Laminated on at least one surface side of this base film, and a conductive pattern mainly composed of copper;
An adhesive layer for bonding between the base film and the conductive pattern,
A printed wiring board having an average relative dielectric constant of 3 or less and an average dielectric loss tangent of 0.005 or less.

Images