JP2010161091A - Support for forming interlayer insulating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film ideal for a support that copes with microfabrication of wiring and high density, is used for multilayer printed circuit boards manufactured by build-up methods, and forms film-like interlayer insulating materials. <P>SOLUTION: The support for forming interlayer insulating materials is a polyester film used as a support for spreading thermosetting resins for forming interlayer dielectrics. In the support for forming interlayer insulating materials, a centerline surface roughness Ra is 20-60 nm on one side of the polyester film, and the thickness is 20-100 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyester film suitable as a support for forming a film-like insulating layer used in a multilayer printed wiring board of a build-up system in which conductor circuit layers and insulating layers are alternately stacked.

  A printed wiring board is a board on which a copper circuit is formed in order to mount and connect electronic components such as ICs, such as consumer printed wiring boards used in household appliances such as televisions, computers, measuring instruments, etc. Examples include industrial printed wiring boards used for industrial purposes. Although there is no clear distinction, the printed wiring board base material is mainly used for consumer use, such as those made from paper-based phenolic resin laminates. The used glass cloth base laminate is used as a base for an industrial printed wiring board.

  As the number of terminals such as ICs installed on a printed wiring board increases, multilayering is achieved as means for accommodating necessary wiring in a limited area, and multilayer printed wiring boards are also mass-produced.

  By repeating the process of forming a wiring pattern on a rigid substrate, forming an insulating layer thereon, further forming a wiring pattern thereon, and further forming an insulating layer among the multilayer printed wiring boards, The build-up method for forming printed wiring boards is used as a method suitable for products that require miniaturization, such as mobile phones, and applications that require high-speed operation, such as computers. The build-up layer has been further multi-layered, and the miniaturization and high density of the wiring are further advanced.

  The insulating layer used in the multilayer printed wiring board is made of glass cloth impregnated with epoxy or polyimide resin, or ceramic material. The signal propagation speed of the wiring layer or the printed wiring board Therefore, it is necessary to select a material that satisfies such electrical characteristics. Specifically, a material having a dielectric constant as low as possible is selected. Various proposals have been made. In addition, since the insulating layer is formed on the film support with a uniform thickness, it is preferable to meet the demands for miniaturization and high performance, and a material that can be applied is used. Yes.

  The insulation layer is formed by applying a thermosetting resin as an insulation layer to a film-like support as an interlayer insulation to cope with downsizing and high performance, and curing the support film with the film. A method has been proposed in which the layers are rolled. With regard to the insulating layer in the film state, it is a film having an insulating layer for buildup that is designed to be suitable for laser processing and to improve the plating adhesion of the resin surface after the roughening treatment, by optimal selection of resin and filler, etc. Various proposals have been made regarding the insulating layer, such as to meet recent demands.

  However, the film, which is a support for forming a film-like insulating layer, has a specific effect in spite of having a great influence on the surface properties of the insulating layer and the productivity when forming the insulating layer. No proposal has been made.

In particular, the surface roughness of the interlayer insulating layer to achieve finer and higher density wiring is an important characteristic when the insulating layer is formed by coating. However, there is a proposal for a film used for the support. The situation has not been made.
JP-A-7-75274 JP-A-7-264787 JP 2004-265697 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is a film-like interlayer used for a multilayer printed wiring board manufactured by a build-up method in order to cope with miniaturization and high density of wiring. It is to provide a polyester film suitable as a support for forming an insulating material.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a polyester film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is a polyester film used as a support for applying a thermosetting resin that forms an interlayer insulating layer, and the center line average roughness (Ra) of one side of the polyester film is It exists in the support body for interlayer insulation material formation characterized by being 20-60 nm and thickness being 20-100 micrometers.

Hereinafter, the present invention will be described in more detail.
The support for forming the film-like interlayer insulating material of the present invention is preferably composed of a biaxially oriented polyester film, which is a so-called coextrusion using two or three or more melt extruders. By a method, it can be set as the laminated film of 2 layers or 3 layers or more.

  The polyester film having different surface properties on the front and back of the present invention needs to have at least two layers, and in order to obtain the target surface roughness to the polyester used for each layer, A raw material containing different particles is used.

  The polyester used for the polyester film in the present invention may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyester includes polyethylene terephthalate (PET) and the like. On the other hand, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (eg, P-oxybenzoic acid). 1 type, or 2 or more types is mentioned, As a glycol component, 1 type or 2 types or more, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4- cyclohexane dimethanol, neopentyl glycol, is mentioned. In any case, the polyester referred to in the present invention refers to a polyester that is usually 60 mol% or more, preferably 80 mol% or more of polyethylene terephthalate or the like which is an ethylene terephthalate unit.

  The film of the present invention requires a specific surface roughness in order to achieve both the surface property of the interlayer insulating layer formed on the polyester film and the roll winding property of the laminated film on which the insulating layer is formed. . For that purpose, it is preferable to contain particles having an average particle diameter of 0.1 to 10 μm, more preferably 0.2 to 10 μm. If the average particle size is less than 0.1 μm, the surface roughness of the film is low, the slipping property of the film is poor, and the product may not be obtained in a roll state after forming the interlayer insulating layer. On the other hand, when the average particle diameter exceeds 10 μm, the surface roughness of the interlayer insulating layer is increased, which may adversely affect the circuit density.

  The content of the particles in the film is preferably 0.1 to 10.0% by weight, more preferably 1.0 to 5.0% by weight. If the content of the particles is less than 0.1% by weight, the slipperiness of the film may be deteriorated. Moreover, when content exceeds 10.0 weight%, the surface roughness of a film becomes large too much and planarity may be impaired.

  Examples of such particles include silicon oxide, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, titanium oxide, kaolin, talc, carbon black, silicon nitride. , Boron nitride, and crosslinked polymer fine powder as described in JP-B-59-5216 are not limited thereto, as long as the gist of the present invention is not impaired.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film in the present invention as necessary.

  The greatest feature of the present invention is that the polyester film as a support has a specific surface roughness, and the center line average roughness (Ra) on one side of the polyester film is 10 to 50 nm, preferably 20 to 30 nm. Range. When the center line average roughness Ra is less than 10 nm, the slipperiness of the film and the air escape between the films are poor, and a product cannot be obtained in a roll state after the interlayer insulating layer is formed. Further, when the center line average roughness Ra exceeds 50 nm, the surface roughness of the polyester film of the interlayer insulating layer is transferred to the surface of the interlayer insulating layer when wound in a roll shape, which is a disadvantage of the interlayer insulating layer. Absent.

  The polyester film itself of the present invention is peeled off after the interlayer insulating layer is bonded to the core substrate as an adhesive sheet, and the role is finished, but the interlayer insulation bonded to the core substrate after the polyester film is peeled off Affects the surface of the layer.

  The surface of the polyester film on which the thermosetting resin is applied and the interlayer insulating layer is to be formed has a center line average roughness (Ra) of 30 nm or less, further 20 nm or less, and a ten-point average roughness Rz. It is preferably 200 nm or less, more preferably 100 nm or less. When the centrality average roughness Ra exceeds 30 nm or the ten-point average roughness Rz exceeds 200 nm, the surface roughness of the interlayer insulating layer increases, which may adversely affect circuit density.

  The thickness of the polyester film of the present invention is in the range of 20-100 μm, preferably 25-50 μm. If the film thickness is less than 20 μm, wrinkles occur when an insulating material is applied, which is not preferable. When the film thickness exceeds 100 μm, the amount of polyester used increases, which is not preferable in terms of cost.

  The curable resin used for the interlayer insulating layer used in the present invention can be used without particular limitation as long as it can form a layer on a support and has sufficient insulating properties. System, polyimide resin system, polyimide amide resin system, polycyanate resin system, polyester resin system, thermosetting polyphenylene ether resin system, and the like. Further, two or more of these may be used in combination, or a multilayer structure may be used.

  A method for forming an interlayer insulating layer on a support is a known method in which the resin composition varnish in which the above-described thermosetting resin or the like is dissolved in a solvent is applied, and then the solvent is dried by heating to simultaneously cure the resin. Can be created by the method.

  In the present invention, a cured resin layer serving as an interlayer insulating layer is provided as a laminated film on a support made of a polyester film, and the laminated film is rolled. When making it into a roll shape, it may be either as it is, in a state where a protective film for protecting the surface of the cured resin is bonded, as long as it can be stored in a roll state. However, by protecting with a protective film, it is possible to prevent the adhesion and scratches of dust etc. to the resin composition layer surface, so even if it is a roll without a protective film, finally the protective film It is preferable to add a step of bonding.

  The protective film is not particularly limited as long as it has a function of protecting the surface of the interlayer insulating layer, and a plastic film such as polyethylene, polypropylene, or polyester is used.

  The thickness of the interlayer insulating layer formed of a polyester film is preferably equal to or greater than the thickness of the conductor layer. Since the thickness of the conductor layer of the circuit board is usually in the range of 5 to 70 μm, the thickness of the resin composition layer is preferably 10 to 100 μm.

  The film having an interlayer insulating layer obtained by using the film of the present invention is laminated on the core substrate by peeling off the protective film of the interlayer insulating layer as an adhesive film when patterning the conductive layer to form a circuit. The Structure of core base material / interlayer insulating layer / polyester film support, or structure of polyester film support / interlayer insulation / core base material / interlayer insulating layer / polyester film support in which both sides of the core base material are sandwiched between interlayer insulating layers The core substrate and the interlayer insulating layer are adhered to each other by heating, and the support made of the polyester film is peeled off.

  As a method of adhering the interlayer insulating layer to the core substrate, a method of laminating on the circuit board under reduced pressure by a vacuum laminating method is suitably used. The laminating method may be a batch method or a continuous method using a roll. Further, the adhesive film and the circuit board may be heated (preheated) as necessary before lamination.

The laminating conditions are preferably a pressure bonding temperature (lamination temperature) of preferably 70 to 140 ° C., a pressure bonding pressure of preferably 1 to 11 kgf / cm ^2, and lamination under a reduced pressure of 20 mmHg (26.7 hPa) or less. . The vacuum lamination can be performed using a commercially available vacuum laminator.

  The circuit board in the present invention mainly includes a conductor layer (circuit) patterned on one or both sides of a substrate such as a glass epoxy, metal substrate, polyester substrate, polyimide substrate, BT resin substrate, thermosetting polyphenylene ether substrate, or the like. The one formed. Also included in the circuit board of the present invention is a multilayer printed wiring board in which conductor layers and insulating layers are alternately formed and a conductor layer (circuit) is patterned on one or both sides. The surface of the conductor circuit layer is preferably roughened by blackening or the like in advance from the viewpoint of adhesion of the insulating layer to the circuit board.

  In this way, when the support film is peeled after laminating the adhesive film on the circuit board, the insulating layer can be formed on the circuit board by peeling and thermosetting. The conditions of heat curing are selected in the range of 20 to 180 minutes at 150 to 220 ° C, more preferably 30 to 120 minutes at 160 to 200 ° C. If the support film is not peeled off after the insulating layer is formed, it is peeled off here.

  Next, a hole is made in the insulating layer formed on the circuit board to form a via hole and a through hole. Drilling can be performed by a known method such as drilling, laser, or plasma, or a combination of these methods if necessary. However, drilling by a laser such as a carbon dioxide laser or YAG laser is the most common method. .

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.

  First, the method of using the polyester raw material mentioned above and cooling and solidifying the molten sheet extruded from the die with a cooling roll is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the extending | stretching temperature orthogonal to the 1st step | paragraph extending | stretching direction is 70-170 degreeC normally, and a draw ratio is 3.0-7 times normally, Preferably it is 3.5-6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  The simultaneous biaxial stretching method can also be adopted for the production of the polyester film in the present invention. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is as follows: The area magnification is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Furthermore, a so-called coating stretching method (in-line coating) in which the film surface is treated during the above-described polyester film stretching step can be applied. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with stretching and the thickness of the coating layer can be reduced according to the stretching ratio, producing a film suitable as a polyester film. it can.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  In this invention, it does not necessarily limit regarding the curing conditions at the time of forming a coating layer on a polyester film, For example, when providing a coating layer by the coating extending | stretching method (in-line coating), it is 170-280 degreeC normally. The heat treatment may be performed for 3 to 40 seconds, preferably 200 to 280 ° C. for 3 to 40 seconds.

  Moreover, you may use together heat processing and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of the coating extending | stretching method (in-line coating) or offline coating. The polyester film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  According to the present invention, it is suitable as a support for forming a film-like interlayer insulating material used for a multilayer printed wiring board manufactured by a build-up method in order to cope with miniaturization and high density of wiring. A polyester film can be provided, and the industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measuring method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Measurement of average particle diameter (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(3) Surface roughness (Ra)
The center line average roughness Ra (μm) is defined as the surface roughness. It calculated | required as follows using the Kosaka Laboratory Co., Ltd. surface roughness measuring machine (SE-3F). That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of the center line, the center line of the extracted portion is the x axis, and the direction of the vertical magnification is the y axis. When represented by (x), the value given by the following equation is represented by [μm]. The center line average roughness was represented by the average value of the center line average roughness of the extracted portion obtained from 10 cross section curves obtained from the sample film surface. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.
Ra = (1 / L) ∫ ₁ ^L | f (x) | dx

(4) Ten-point average roughness (Rz)
Elevation of the peak from the highest to the fifth in the cross-section curve of the portion extracted by the reference length (2.5 mm) from the cross-section curve obtained by the surface roughness measuring machine (SE-3F) manufactured by Kosaka Laboratory Ltd. And the average value of the altitude of the bottom of the valley from the deepest to the fifth. The ten-point average roughness was represented by the average value of the ten-point average roughness of the extracted portion obtained from 10 cross-sectional curves obtained from the sample film surface. The radius of the stylus used at this time is 2.0 μm, the load is 30 mg, and the cutoff value is 0.08 mm.

The polyester used in the examples and comparative examples was prepared as follows.
<Manufacture of polyester>
Production Example 1 (Polyethylene terephthalate A) Diluent raw material 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate are placed in a reactor, the temperature is raised by heating, methanol is distilled off, It took 4 hours from the start of the reaction, and the temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of ethylene glycol slurry ethyl acid phosphate and 0.03 part of antimony trioxide were added, and then the temperature was reached to 280 ° C. and the pressure to 15 mmHg in 100 minutes. It was 0.3 mmHg. After 4 hours, the system was returned to atmospheric pressure to obtain polyethylene terephthalate A1 having an intrinsic viscosity of 0.61.

Production Example 2 (Polyethylene terephthalate B) Silica particles 3.4 μm
100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate are placed in a reactor, the temperature is raised by heating, methanol is distilled off, transesterification is performed, and 4 hours are required from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of ethylene glycol slurry ethyl acid phosphate, 0.03 part of antimony trioxide and 0.01 part of silica particles having an average particle size of 3.4 μm were added, and then the temperature was 280 ° C. and the pressure was increased in 100 minutes. The pressure reached 15 mmHg, and the pressure was gradually reduced thereafter to finally reach 0.3 mmHg. After 4 hours, the system was returned to normal pressure to obtain polyethylene terephthalate B having an intrinsic viscosity of 0.61.

Production Example 3 (Polyethylene terephthalate C) CaCO3 0.70 μm
In the same manner as in Production Example 1, except that 0.01 parts of silica particles having an average particle diameter of 3.4 μm are added in an amount of 0.01 parts, synthetic polyethylene carbonate particles having an average particle diameter of 0.70 μm are added. Terephthalate C was obtained.

Production Example 4 (Polyethylene terephthalate D) CaCO3 0.27 μm
In the same manner as in Production Example 1, except that 0.01 parts of synthetic calcium carbonate particles having an average particle diameter of 0.27 μm are added instead of 0.01 parts of silica particles having an average particle diameter of 3.4 μm, polyethylene is added. Terephthalate D was obtained.

Production Example 5 (polyethylene terephthalate E) CaCO3 1.5 μm
In the same manner as in Production Example 1, except that 0.01 parts of synthetic calcium carbonate particles having an average particle diameter of 1.50 μm are added in place of 0.01 parts of silica particles having an average particle diameter of 3.4 μm, polyethylene is added. Terephthalate E was obtained.

(Manufacture of polyester film)
The above polyesters A to E are mixed raw materials of the X layer and the Y layer at the compounding ratios shown in Tables 1 to 3, and each is supplied to two twin-screw extruders and melted at 285 ° C. Thus, a non-oriented sheet was obtained by co-extrusion on a casting drum cooled to 20 ° C. in a two-layer / two-layer configuration so that the thickness ratio of X layer / Y layer = 50% / 50%. . Next, the film was stretched 2.8 times in the longitudinal direction at 100 ° C., then subjected to a preheating step in the tenter and subjected to transverse stretching of 4.6 times at 120 ° C., followed by heat treatment at 225 ° C. for 10 seconds, 10% relaxation was applied in the width direction at 180 ° C. to obtain polyester films having thicknesses shown in Tables 1 and 2 below.

<< Epoxy resin composition >>
20 parts of liquid bisphenol A type epoxy resin (“Epicoat 828EL” manufactured by Japan Epoxy Resin Co., Ltd.), 20 parts of brominated bisphenol A type epoxy resin (YDB-500 manufactured by Toto Kasei Co., Ltd.), cresol novolac type epoxy resin (epoxy) Equivalent 215, softening point 78 ° C., Dainippon Ink Chemical Co., Ltd. Epicron N-673) 20 parts, terminal epoxidized polybutadiene rubber (Nagase Kasei Kogyo Co., Ltd. Denarex R-45EPT) 15 parts are stirred into MEK. The solution was heated and dissolved, and brominated phenoxy resin varnish (non-volatile content 40% by weight, bromine content 25% by weight, solvent composition, xylene: methoxypropanol: methyl ethyl ketone = 5: 2: 8, YPB- manufactured by Toto Kasei Co., Ltd. 40-PXM40) 50 parts, 2,4-diamino as epoxy curing agent 6- (2-methyl-1-imidazoliethyl) -1,3,5-triazine / isocyanuric acid adduct 4 parts, 2 parts of finely pulverized silica, 4 parts of antimony trioxide and 5 parts of calcium carbonate A composition varnish was prepared.

<< Resin composition varnish application to polyester film: Formation of interlayer insulation layer >>
The resin composition varnish produced by the above method is applied to the surface of the B layer of the polyester film obtained in Examples 1 to 8 and Comparative Examples 1 to 4 with a die coater so that the resin thickness after drying becomes 70 μm. It apply | coated and dried at 80-120 degreeC (average 100 degreeC), and the interlayer insulation layer which made the polyester film the support body was produced.

  In Comparative Example 4, the polyester film was wrinkled during drying after the resin composition varnish was applied, and a product was not obtained.

<Roll appearance>
The resin composition varnish was applied onto a polyester film, and in the production of a film having an interlayer insulating layer, the appearance of the product roll of the film was visually observed and evaluated. Table 4 shows the results. In particular, the deviation of both end faces of the roll was observed.
(Roll appearance is good) ◎>○>△> × (Roll appearance is bad)
Among the above criteria, those above Δ are levels that can be used without any problem in actual use.

<Surface characteristics>
The surface corresponding to the polyester film of the obtained interlayer insulating layer was observed, and the presence or absence of protrusions affecting the electric characteristics and the surface characteristics of the uniformity of the protrusions were evaluated as follows. The results are shown in Table 4.
◎: Projection uniformity, no large projections that adversely affect electrical characteristics are observed ○: Projection uniformity is slightly inferior, and some large projections are seen △: Uniformity at a level that can be used practically without problems X: Protrusions that are inferior in the uniformity of the protrusions and have an adverse effect on the electrical characteristics are observed. Among the above judgment criteria, those above Δ are levels that can be used without problems in actual use.

《Cost advantage》
The obtained characteristics and the cost evaluation related to the production such as yield are evaluated as follows, and the results are shown in Table 3 below.
◯: Advantage in terms of cost Δ: Slightly inferior in cost ×: Inferior in cost Among the above criteria, those above Δ are at a level that can be used without problems in actual use.

  In Comparative Example 4, the polyester film was wrinkled during drying after the resin composition varnish was applied, and a product was not obtained.

  The polyester film of the present invention can be suitably used as a support for forming a film-like interlayer insulating material used for a multilayer printed wiring board produced by a build-up build-up method.

Claims (1)

A polyester film used as a support for applying a thermosetting resin for forming an interlayer insulating layer, the center line average roughness (Ra) on one side of the polyester film being 20 to 60 nm, and having a thickness Is a support for forming an interlayer insulating material, characterized by being 20 to 100 μm.