JP2008109127A - Method for manufacturing flexible substrate - Google Patents

Abstract

Provided is a method for manufacturing a flexible substrate, which is capable of manufacturing a flexible substrate having good workability and having excellent ease of manufacturing and pattern reliability even if the pattern metal layer is thick.
A method for manufacturing a flexible substrate according to the present invention is a flexible substrate in which a pattern metal layer is embedded in a liquid crystal polymer layer, and the polymer layer surface and the outer surface of the pattern metal layer are positioned on substantially the same plane. In the method for producing a substrate, a step of preparing a substrate with a patterned metal layer having an arbitrary patterned metal layer on the liquid crystal polymer layer, and the substrate with the patterned metal layer at a temperature equal to or higher than a thermal deformation temperature of the liquid crystal polymer And a step of relatively embedding the pattern metal layer in the liquid crystal polymer layer by heating and pressurizing.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a flexible substrate. More specifically, a method for manufacturing a flexible substrate used for a wiring board, a power supply circuit board, or a thermoelectric element substrate, in which a conductive or thermally conductive pattern metal layer is embedded in a liquid crystal polymer that is an insulating layer or a low thermal conductive layer. It is about.

Conventionally, an embedded conductor in which a wiring circuit (pattern metal layer such as copper) is embedded in an insulating layer (resin layer) and the surface of the insulating layer and the outer surface of the wiring circuit are located on substantially the same plane. A flexible wiring board and a manufacturing method thereof have been proposed.
For example, a panel plating film as a base is formed on a metal plating substrate, a wiring pattern is formed on the panel plating film by plating, and a resin base plate is disposed on the wiring pattern via an adhesive layer. When the base plate is heated and pressed with a predetermined pressure, the adhesive layer fills the periphery of the wiring pattern, and the wiring pattern is adhered and transferred to the base plate in a state of being substantially flush with the wiring pattern. There has been proposed a method for manufacturing a printed circuit board in which a metal plated substrate is removed by etching and a protective film is covered on the same flat surface without the unevenness (see, for example, Patent Document 1). This is because the adhesive layer does not swell on the wiring pattern as compared with the conventional base plate with the wiring pattern plate attached via an adhesive and the pattern formed as a starting point. It is said that there is no uneven wave.

  In addition, using a laminated member in which a conductive metal foil and a support member for supporting the same are laminated, patterning the conductive metal foil to form a conductive pattern, and a resin film made of a thermoplastic resin An embedded conductor pattern comprising: embedding at least part of the conductor pattern of the laminated member; and removing the support member from the conductor pattern embedded in the resin film, wherein the conductor pattern is embedded in the resin film. A method for producing a film has been proposed (for example, Patent Document 2). Also in such a manufacturing method, the metal plate which is a support member is removed by etching, and the removed surface becomes a surface for smoothing the conductor pattern and the embedded resin.

  In addition, a method is proposed in which a conductive metal foil of a composite in which a conductive metal foil is laminated on a film-like support is patterned, an insulator layer is laminated on the patterned surface, and pressure integrated. A liquid crystal polymer is exemplified as a material for the insulator layer (see, for example, Patent Document 3). However, most of the methods shown above including this method have the disadvantage that the number of manufacturing steps is increased on the premise that an insulator such as another resin film is heated and pressurized on the prepared pattern substrate. .

  Further, as a method for manufacturing an embedded flexible substrate, a method of manufacturing while changing the processing temperature of a specific insulating resin material has been proposed (see, for example, Patent Document 4). A conductive foil is laminated on a thermoplastic resin film containing 65 to 35% by weight of a polyaryl ketone resin having a crystal melting peak temperature of 260 ° C. or more and 35 to 65% by weight of an amorphous polyetherimide resin, and the thermoplastic The resin composition is heat-sealed (laminated press) so as to satisfy the relationship between the heat of crystal fusion ΔHm represented by the following formula (I) and the heat of crystallization ΔHc generated by crystallization during temperature rising. Next, the heat-fused conductor foil is etched to form a conductor pattern, and heated and pressurized (smooth press) so that the thermoplastic resin composition satisfies the relationship represented by the following formula (II). . In the smooth press, a smooth plate is pressed against the surface of the conductor pattern, and the conductor pattern is embedded in the resin film until the surface of the conductor pattern and the surface of the resin film coincide. Heating / pressurization of the thermoplastic resin composition and the formula (I): [(ΔHm−ΔHc) / ΔHm] ≦ 0.5 and (II): [(ΔHm−ΔHc) / ΔHm] ≧ 0.7 By satisfying the conditions, an embedded conductor pattern film having no residual stress or distortion can be produced.

This method is excellent in operability and manufacturability in that there is no etching removal operation of the used support member. However, since the insulating resin material substrate is also an embedded resin, the reliability of the bonding position between the insulating resin material and the pattern layer of the conductive foil is low at the time of heating and pressurizing smooth pressing, and the pattern layer is slightly shifted at the time of pressing, There is a possibility that a highly accurate flexible substrate cannot be obtained. In particular, when used for a wiring board or the like, there is no problem even if the metal foil pattern layer is thin. However, when a thermoelectric element substrate is used, the pattern layer is thermally conductive and requires a considerable amount in the thickness direction, for example, 40 μm or more. There is a concern that the pattern layer is likely to be displaced. Further, the film-like insulator used here has a plurality of thermoplastic resin compositions, is a special material, and has difficulty from a practical point of view.
Japanese Patent Laid-Open No. 2-1198 JP 2003-218500 A JP 2001-68824 A JP 2000-277875 A

  The object of the present invention is to produce a flexible substrate in a simple method, which has good workability in manufacturing a flexible substrate, and is excellent in manufacturing ease and pattern position accuracy even if the pattern metal layer has a thickness. An object of the present invention is to provide a method for manufacturing a flexible substrate that can be manufactured.

  As a result of intensive studies to solve the above problems, the present inventors have used a patterned metal layer-containing substrate having a patterned metal layer having a liquid crystal polymer as an insulating layer, which is heated and heated under certain conditions. It has been found that the above-mentioned problems can be solved by pressing, and the present invention has been completed. That is, the present invention relates to a method for producing a flexible substrate in which a patterned metal layer is embedded in a liquid crystal polymer layer, and the polymer layer surface and the outer surface of the patterned metal layer are positioned on substantially the same plane. A step of preparing a substrate with a patterned metal layer having an arbitrary patterned metal layer on the layer, and the liquid crystal by heating and pressurizing the substrate with the patterned metal layer at a temperature equal to or higher than a thermal deformation temperature of the liquid crystal polymer. It is a manufacturing method of a flexible substrate, comprising a step of relatively embedding a patterned metal layer in a polymer layer.

Here, the pattern metal layer constituting the flexible substrate is advantageously formed from a copper foil.
The liquid crystal polymer preferably has a thermal deformation temperature in the range of 200 to 330 ° C., and the embedding process is performed by a laminating press machine that can be heated and pressurized, and the surface temperature of the laminating portion of the laminating press machine is that of the liquid crystal polymer. It is lower than the temperature higher than the heat distortion temperature and 50 ° C. higher than the heat deformation temperature of the liquid crystal polymer, Heating and pressurizing within the range of 1 to 20 MPa is a preferred embodiment of the present invention. And in this embedding process, it is preferable to heat and pressurize the pressurization surface of the said board | substrate with a pattern metal layer through a hard mold release sheet | seat whose thickness is 0.02-5 mm.

According to the method for producing a flexible substrate of the present invention, by using a liquid crystal polymer exhibiting good flow characteristics at a processing temperature in a resin that supports a patterned metal layer, that is, a patterned metal layer serving as a conductor layer or a heat conductive layer, Even if the pattern metal layer has a considerable thickness, a flexible substrate with excellent pattern position accuracy can be obtained. Further, even in the manufacture, since there is no substrate etching step, the manufacturing is excellent. In particular, since the insulating layer is made of a thermoplastic liquid crystal polymer, a flexible substrate can be obtained by a simple method without requiring another resin film.
Further, when the pressure is specified and the heating temperature is adjusted when pressing with a laminating press in the embedding process, a more reliable substrate can be obtained with a high yield. Conventionally, the resin film surface is pressed through an elastic material such as silicon rubber. However, when this is carried out through a hard releasable sheet having releasability with respect to the resin film, the pattern metal layer surface The smoothness becomes even better.

Embodiments of the present invention will be described below.
1 is a cross-sectional view of a flexible substrate according to a manufacturing process showing an embodiment of a method for manufacturing a flexible substrate according to the present invention, FIG. 2 is a top view of the flexible substrate after pattern formation shown in the embodiment, and FIG. FIG. 4 is a schematic view of a laminating press used in the examples, and FIG. 4 is a cross-sectional photograph of a flexible substrate manufactured according to the examples.
As shown in FIG. 1C, the flexible substrate manufactured according to the present invention has a liquid crystal polymer layer 16 embedded with a pattern metal layer (conductor pattern layer) 13, and a liquid crystal polymer layer surface 14s and an outer surface 13s of the pattern metal layer. Are formed on substantially the same plane. The liquid crystal polymer layer 16 supports the pattern metal layer 13 and is also located between patterns (between circuits) 13a of the pattern metal layer 13, and the pattern metal layer 13 is embedded in the liquid crystal polymer.

  In the method for manufacturing a flexible wiring board, first, a substrate material in which a metal layer 11 having an arbitrary thickness is laminated on a liquid crystal polymer layer 12 is prepared (see FIG. 1A). A patterned metal layer (wiring circuit) 13 having a predetermined pattern is formed on the metal layer 11 (FIG. 1B).

  The metal layer 11 is made of copper foil. In the present invention, the type of the metal layer is not particularly limited as long as it is usually used as a substrate material in addition to the copper foil. For example, a plate or foil of silver, platinum, gold, aluminum, nickel or the like can be used. Although the thickness of a metal layer is not specifically limited, It is the range of 3-200 micrometers. The purpose of the present invention is to produce a flexible substrate that can be applied as a multi-purpose substrate. Therefore, the thickness of the metal foil varies depending on the purpose, but the thickness suitable for application to a flexible printed circuit board is in the range of 3 to 35 μm. Moreover, the thickness suitable for applying to a power supply circuit or a thermoelectric element board | substrate is 30-200 micrometers, Preferably it is the range of 40-150 micrometers. Further, if the thickness exceeds the set range, a problem arises in the flexibility of the entire substrate. Especially preferably, it is the range of 5-100 micrometers.

  The lamination of the metal layer 11 and the liquid crystal polymer layer 12 can be directly joined by thermocompression bonding or the like. The metal layer 11 can form the patterned metal layer 13 by etching. As the pattern processing, laser processing, drill processing, and the like can be employed in addition to etching processing. In the present invention, as shown in FIG. 2, a pattern that leaves the peripheral portion 13b of the metal layer 11 is formed, and the peripheral portion 13b is cut at the time of final manufacture of the substrate, whereby the desired conductor pattern layer 13 is obtained. It is preferable to do so. It is preferable that the metal layer 11 and the liquid crystal polymer layer 12 are laminated | stacked by moderate intensity | strength by heating and pressurization, without using an adhesive agent. This prevents the pattern layer 13 from being displaced during the embedding process. However, in order to further reduce the positional deviation between the patterns 13a, which is likely to occur during heating and pressure bonding, which will be described later, the conductor pattern layer 13 is formed with the peripheral edge portion 13b that prevents the positional deviation as described above. Is preferred. In this way, it is possible to prepare a substrate with a patterned metal layer having a convex arbitrary patterned metal layer on the liquid crystal polymer layer.

  Next, in order to fill the liquid crystal polymer layer 12 between the patterns 13a, the flexible printed circuit board manufacturing method is subjected to an embedding process using a heating and pressurizing laminating press as shown in FIG. The laminating press comprises a pair of piston-added hot press plates 1 that press against each other. The substrate with a patterned metal layer is disposed between a pair of press plates 1 of a laminating press. The surface temperature of the laminated part (contact part between the substrate with the patterned metal layer and the hard release sheet) in the laminating press is less than the temperature higher than the thermal deformation temperature of the liquid crystal polymer and 50 ° C. higher than the thermal deformation temperature of the liquid crystal polymer. It is preferable to heat so that. At a heating temperature lower than the heat distortion temperature, the liquid crystal polymer does not sufficiently permeate between the patterns 13a of the substrate with the patterned metal layer even if the pressure is increased. In addition, when the temperature is higher by 50 ° C. than the heat distortion temperature, there is a concern that the liquid crystal polymer melts, deteriorates, decomposes, and the like.

  The set pressure of the laminating press is preferably in the range of 1-20 MPa, particularly in the range of 3-12 MPa. When the pressure of the laminating press is less than the above set pressure, the liquid crystal polymer of the insulating layer does not sufficiently penetrate between the patterns 13a of the substrate with the patterned metal layer, and the patterned metal layer 13 cannot be embedded relatively. When the pressure of the lamination press exceeds the set pressure, the conductor pattern layer 13 of the substrate with a pattern metal layer may be crushed.

  In the present invention, it is preferable that the hard releasable sheet 2 is inserted between the press plate 1 and the liquid crystal polymer layer 12 of the substrate with a patterned metal layer, at least on the patterned metal layer side of the substrate with the patterned metal layer. It is more preferable that the hard releasable sheet 2 is inserted between the pressing plate 1 and the side facing the surface. Usually, the hot press plate 1 is molded from SUS or the like whose press surface can be heated to a high temperature. As described above, because of the relationship that the surface temperature of the laminated portion is maintained at a temperature equal to or higher than the thermal deformation temperature of the liquid crystal polymer, the molten liquid crystal polymer may adhere to the press surface of the press plate 1. For this reason, conventionally, a releasable elastic plate such as silicon rubber has been provided. However, in the case of the embedded substrate which is the object of the manufacturing method of the present invention, it is preferable to arrange a hard plate instead of arranging such a buffer plate. Therefore, the flexible substrate manufactured by disposing the hard releasable sheet 2 can be easily separated from the press plate without causing undulations.

  As the hard releasable sheet, a heat-resistant material is preferable in which the laminated substrate can be easily peeled off from the press plate after heating and pressing, or the adhesive strength with the laminated substrate is low. For example, a metal plate such as SUS, aluminum, or Cu that has a surface structure that does not adhere to the laminated substrate or that has been polished or surface-treated by applying a surfactant, or Teflon (registered trademark), polyimide And a resin plate. The hard releasable sheet has a releasability and is a releasable sheet having a hardness that enables the pattern metal layer and the liquid crystal polymer layer to be formed on substantially the same plane, for example, 0.02 to 5 mm. A releasable aluminum plate is preferable. A preferable thickness range of the hard release sheet is 0.02 to 5 mm, and a range of 0.05 to 2 mm is particularly preferable. With such a thickness, heat from the hot press plate 1 can be transmitted quickly and sufficiently, and the laminated substrate can be heated smoothly.

  In this invention, although the board | substrate with a pattern metal layer which used the liquid crystal polymer as the resin layer is used, the preferable thickness range of the insulating layer in a board | substrate with a pattern metal layer is 10-250 micrometers, and it is more preferable that it is 25-150 micrometers. preferable. In the present invention, since it is necessary to embed the pattern metal layer 13 almost completely with the liquid crystal polymer of the resin layer of the substrate with the pattern metal layer, the ratio of the total area of the substrate and the total area and volume of the pattern metal layer 13a is taken into consideration. Thus, the resin layer thickness can be determined. When a flexible substrate is used as a thermoelectric element substrate, it is preferable to reduce the thickness of the liquid crystal polymer layer below the pattern metal layer 13 in order to suppress a decrease in thermal conductivity of the substrate. In this case, the thickness of the pattern metal layer is h1. When the thickness of the liquid crystal polymer layer below the patterned metal layer after embedding the patterned metal layer is h2, it is preferable that h1> h2. The thickness of the liquid crystal polymer layer below the patterned metal layer is preferably in the range of 5 to 60 μm.

  In the present invention, a liquid crystal polymer that is a thermoplastic resin is used for the liquid crystal polymer layer 12. And from a viewpoint of workability, it is preferable that the heat distortion temperature of a liquid crystal polymer exists in the range of 230-300 degreeC. The substrate with a patterned metal foil prepared in the present invention can be obtained by laminating a liquid crystal polymer film on a metal foil such as a copper foil, and processing the metal foil into an arbitrary pattern. As the polymer film, a commercially available liquid crystal polymer film can be used. Moreover, the laminated board which laminated | stacked the liquid crystal polymer on metal foil is also marketed, and these can be obtained and processed into a board | substrate with a pattern metal foil.

  The liquid crystal polymer film is made of a liquid crystal polymer that forms an optically anisotropic melt phase. A liquid crystal polymer that forms an optically anisotropic melt phase is also called a thermotropic liquid crystal polymer. As is well known to those skilled in the art, a polymer that forms an optically anisotropic melt phase is polarized when a molten sample is observed under a polarizing microscope orthogonal Nicol equipped with a heating device. Is a polymer that permeates.

The raw material of the liquid crystal polymer is not particularly limited, and examples thereof include known thermotropic liquid crystal polyesters and polyester amides derived from the compounds (1) to (4) exemplified below and derivatives thereof. it can. However, in order to form a polymer liquid crystal, there is an appropriate range for each combination of raw material compounds.
(1) Aromatic or aliphatic dihydroxy compounds (2) Aromatic or aliphatic dicarboxylic acids (3) Aromatic hydroxycarboxylic acids (4) Aromatic diamines, aromatic hydroxyamines or aromatic aminocarboxylic acids

  Typical examples of the liquid crystal polymer obtained from these raw material compounds include a copolymer having a structural unit represented by the following formula.

  The heat distortion temperature of the liquid crystal polymer as used in the present invention is a temperature at which the liquid crystal polymer is sufficiently filled in the pattern metal layer 13a when it is pressed at the set pressure of the above-described laminating press, As an example, in the storage elastic modulus (E ′)-temperature curve obtained by measurement with a dynamic viscoelasticity measuring device (DMA), it refers to the temperature at which E ′ rapidly decreases.

  In combination with the use of such a liquid crystal polymer and the peripheral treatment of the conductor pattern layer 13, even if the liquid crystal polymer layer 12 is a thin layer, there is no displacement even under the above-mentioned heating and pressurizing conditions. There can be no substrate. As long as the liquid crystal polymer layer exhibits its function, the liquid crystal polymer layer may contain other polymers, fillers, and other additives as necessary, as long as the effects of the present invention are not impaired.

The flexible substrate obtained by such a configuration is fixed on the liquid crystal polymer layer 16 in a state where the pattern metal layer 13 is embedded in the liquid crystal polymer layer 16 as shown in FIGS. . In this case, the surface 14s of the liquid crystal polymer layer 16 and the surface 13s of the conductor pattern layer 13 are parallel and do not wave. In particular, it is preferable that the patterned metal layer 13 appears as the outer surface 13s in parallel with the liquid crystal polymer layer (in the same plane as the liquid crystal polymer layer surface). A substrate manufactured by the method for manufacturing a flexible wiring board according to the above-described embodiment is easy to manufacture even if the conductor pattern layer 13 is thick, and the position accuracy of the embedded pattern is high.
In addition, the manufacturing method of the flexible substrate of this invention is not limited to above-described embodiment, Of course, various changes can be added within the range which does not deviate from the summary of this invention.

(Example 1)
A metal layer (copper foil) 11 having a thickness of 70 μm is heated and pressurized on a liquid crystal polymer film (product name: Bexter, grade: FA-X100) 12 having a thickness of 50 μm and a heat distortion temperature of 260 ° C. A flexible copper-clad laminate using a liquid crystal polymer as a resin layer was prepared by thermocompression bonding (FIG. 1 (a)).
A dry film was laminated on the copper foil 11 to form a copper etching resist, and unnecessary copper foil was removed by etching to form a patterned metal layer (FIG. 1B). However, the copper pattern has a shape connected to the copper of the outer frame of the flexible copper-clad laminate 13 (FIG. 2).
Next, the substrate with the patterned metal layer formed in this way was sandwiched between stainless plates, and heated and pressurized with a press machine at 260 ° C. and 11.0 MPa (FIG. 1C). At this time, an aluminum foil having a thickness of 75 μm was interposed as a hard releasable sheet between the stainless steel plate and the substrate with the patterned metal layer. The aluminum foil had dimensions larger than the resin protruding by thermocompression bonding. Regarding the heating and pressurizing conditions, the liquid crystal polymer was held at a heat distortion temperature of 260 ° C. for 25 minutes, then pressurized at 11.0 MPa, and held in this state for 15 minutes. Then, it cooled to room temperature over 20 minutes. The flexible substrate thus produced was taken out from the press.

The thicknesses of the copper pattern forming part (in Table 1: Cu pattern layer) and the part consisting only of the liquid crystal polymer layer (in Table 1: LCP layer) of the flexible substrate thus obtained are respectively determined with a dial gauge film thickness meter. As a result, a flat substrate with a maximum thickness difference of 5 μm was obtained. It is shown in Table 1.
This thickness difference is also a value within the range of thickness variation of the liquid crystal polymer film used as a raw material. Further, when the cross section of the obtained flexible substrate was observed with a microscope, the pattern metal layer made of copper was buried in the liquid crystal polymer layer, and the liquid crystal polymer layer surface and the pattern metal layer surface were positioned on substantially the same plane. I understood it. In addition, no voids were observed between copper and the liquid crystal polymer layer (FIG. 4).

(Example 2)
A liquid crystal polymer film (made by Kuraray Co., Ltd., product name: Bexter, grade: FA-X100) 12 having a thickness of 50 μm and a heat distortion temperature of 260 ° C. is heated and pressurized with a metal layer (copper foil) 11 having a thickness of 12 μm. A flexible substrate was produced in the same manner as in Example 1 except that a flexible copper-clad laminate having a liquid crystal polymer as a resin layer was prepared by thermocompression bonding. The results are shown in Table 1.

(Example 3)
A 12 μm thick metal layer (copper foil) 11 is heated and pressurized on a liquid crystal polymer film (Kuraray Co., Ltd., product name: Bexter, grade: FA-X100) 12 having a thickness of 25 μm and a heat distortion temperature of 260 ° C. A flexible substrate was produced in the same manner as in Example 1 except that a flexible copper-clad laminate having a liquid crystal polymer as a resin layer was prepared by thermocompression bonding. The results are shown in Table 1.

  The method for manufacturing a flexible substrate of the present invention has good workability, and the manufactured flexible substrate is excellent in ease of manufacturing and pattern reliability even if the pattern metal layer has a thickness. The industrial applicability is high.

FIG. 1 is a sectional view of a flexible substrate according to a manufacturing process showing an embodiment of a method for manufacturing a flexible substrate according to the present invention. FIG. 2 is a top view of the flexible substrate after pattern formation shown in the embodiment. FIG. 3 is a schematic view of a laminating press used in the examples. FIG. 4 is a cross-sectional photograph of a flexible substrate manufactured according to the example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating press board 2 of laminating press machine Hard release sheet 11 Metal layer (copper foil)
DESCRIPTION OF SYMBOLS 12 Liquid crystal polymer 13 Conductive pattern layer 13a Conductive pattern metal interlayer 13b Peripheral part 13s of conductive pattern layer Surface 14s of conductive pattern layer Surface 16 of liquid crystal polymer layer 16 Liquid crystal polymer layer

Claims (4)

In a method for producing a flexible substrate, wherein a pattern metal layer is embedded in a liquid crystal polymer layer, and the liquid crystal polymer layer surface and an outer surface of the pattern metal layer are formed on substantially the same plane,
A step of preparing a substrate with a patterned metal layer having an arbitrary patterned metal layer having a convex shape on a liquid crystal polymer layer, and heating and pressurizing the substrate with a patterned metal layer at a temperature equal to or higher than a thermal deformation temperature of the liquid crystal polymer. A method for producing a flexible substrate comprising the step of relatively embedding a patterned metal layer in the liquid crystal polymer layer.   The method for producing a flexible substrate according to claim 1, wherein the pattern metal layer is formed from a copper foil.   The thermal deformation temperature of the liquid crystal polymer is in the range of 200 to 330 ° C., and the embedding process is performed by a laminating press machine that can be heated / pressurized. The method for producing a flexible substrate according to claim 1, wherein the temperature is lower than a temperature higher by 50 ° C than the heat distortion temperature of the polymer, and the pressure is heated and pressurized in the range of 1 to 20 MPa.   The method for producing a flexible substrate according to claim 3, wherein in the embedding step, the pressure surface of the resin film is heated and pressurized via a hard releasable sheet having a thickness of 0.02 to 5 mm.