JP2019070077A - Polyester film for laser processing and release film for wiring board manufacturing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film having excellent laser workability, and to provide a release film for manufacturing a wiring board which is excellent in economy and excellent in peelability. A polyester film that does not contain an ultraviolet absorber and is irradiated with an electron beam and has a spectral transmittance of 75% or less at a wavelength of 355 nm for laser processing. Further, a release film for manufacturing a wiring board having a release layer on at least one surface of the polyester film for laser processing. [Selection diagram] None

Description

  The present invention relates to a polyester film for laser processing and a mold release film for producing a wiring board, and in detail, it has fine laser machinability in the process for producing a wiring board and can produce the wiring board at low cost. The present invention relates to a polyester film for laser processing and a release film for producing a wiring board.

  In recent years, with the development of portable information terminals and the spread of so-called mobile computing in which computers are carried and operated, there is a demand for small, thin, high-definition wiring boards.

  Conventionally, as a wiring substrate, for example, a wiring substrate used for a package for housing a semiconductor element, a ceramic wiring substrate capable of high-density wiring has been widely used. This ceramic wiring board is composed of an insulating layer such as alumina and a wiring conductor made of high melting point metal such as W or Mo formed on the surface, and a recess is formed in a part of the insulating layer. The semiconductor element is accommodated in the recess, and the recess is hermetically sealed by the lid.

  However, since the ceramic forming the insulating layer of such a ceramic wiring substrate has a hard and brittle property, chipping or cracking of the ceramic is likely to occur in the manufacturing process or the conveying process, and sealing of the semiconductor element is difficult. There is a problem such as low yield because the airtightness may be lost. In addition, since firing shrinkage occurs due to firing at high temperature, there is a problem that deformation such as warpage or variation in dimensions is likely to occur in the obtained substrate. Therefore, recently, a fine circuit is formed by etching on the surface of the insulating layer containing an organic resin to which copper foil is bonded, and then this substrate is laminated to form a multilayer printed circuit board, or a metal powder such as copper. The paste is printed on the insulating layer to form a wiring layer, and then laminated or laminated, then a via hole is formed at a desired position by micro drill, punching or the like, and a metal is attached to the inner wall of the via by plating. There have been proposed printed wiring boards in which wiring layers are connected to form multiple layers.

  In such a printed wiring board, an insulating layer in which a spherical or fibrous inorganic material is dispersed in an organic resin is also proposed in order to increase its strength. In addition, in order to achieve further densification of circuit wiring, it is desirable to reduce the diameter of via holes. The via hole is generally formed by laser drilling, and a carbon dioxide gas laser, which has a high drilling speed and is advantageous in manufacturing cost, is mainly used as the laser. However, there is a limit in reducing the diameter of the via hole, and for example, it is difficult to form a via hole having an opening diameter of 25 μm or less by using a carbon dioxide gas laser.

  As a laser which can be used for formation of a via hole, UV solid lasers, such as UV-YAG laser other than a carbon dioxide gas laser, are mentioned. The UV solid-state laser is not often used to form a via hole, but generally generates a laser in a strong ultraviolet region, and therefore, unlike an infrared laser such as a carbon dioxide gas laser, it does not generate heat. Therefore, finer processing is possible, and it is expected to contribute to reducing the diameter of the via hole.

  The portion irradiated with the laser light is decomposed and removed by heating, but the peripheral portion of the irradiated portion is also affected by the laser light especially in the vicinity of the surface of the insulating layer, and the shape of the via hole is particularly the laser light incident side The diameter was large only in the vicinity of the surface of the insulating layer. That is, the hole diameter of the via hole is largely deviated from the design value, and if this portion is filled with the conductive substance, a short circuit may occur between the adjacent via hole conductors in some cases, causing a short circuit failure between the circuit patterns. For this reason, there is a problem that the pitch of the via holes must be increased and fine wiring can not be realized.

  In addition, since the processing scraps of the processing portion adhere to the peripheral portion of the laser light irradiation portion, the peripheral portion is deformed to be raised, as a result, the flatness of the insulating layer is deteriorated, and the conductor layer can be formed well. In addition, when the wiring substrate is multilayered, there are problems such as delamination during lamination and deterioration of the flatness of the laminate. Furthermore, since the resin of the laser-irradiated portion is changed to carbon and is interposed between the resin layer and the conductor layer, there is a problem that the adhesion of the conductor layer is deteriorated.

  Therefore, in the process of forming a via hole by laser light irradiation, a resin film having a specific thickness and a laser beam transmittance of not more than a specific value is provided on the surface of the insulating layer on the incident side, and a conductive material is filled in the via hole, It has been reported that by peeling the resin film, it is possible to form a via hole with high dimensional accuracy without a change in diameter, deformation and deterioration in the vicinity of the laser beam irradiated part in the vicinity of the surface of the insulating layer (Patent Document 1). In this report, polyester, polyethylene, and fluorine-based polymers having a laser light transmittance of 0.8 or less can be suitably used as the resin film, but polyester is used from the viewpoint of processing suitability and economy. However, in general, the transmittance of laser light of polyester film exceeds 0.8, and a special polyester film is required.

  In order to reduce the laser transmittance to 0.8 or less, a method of adding a UV absorber to polyester is known, but when a UV absorber is added, stains of the production machine occur and productivity is impaired. In addition, defects such as decomposition products are likely to occur, making it difficult to apply to applications requiring fine precision. In addition, a technology for dyeing the film to impart UV absorbability has also been devised, but since the surface property of the film is changed by the dyeing, it becomes a problem in the subsequent processing steps (peeling treatment, adhesion processing, etc.) And may be a source of contamination to electronic components.

Patent No. 4683758

  As a result of intensive investigations in view of the above situation, the present inventors have reduced the transmittance of a polyester film at a specific wavelength by a simple method without significantly changing the characteristics of the polyester film and without using a substance as a contamination source. It has been found that the present invention can provide a polyester film excellent in laser processability. An object of the present invention is to provide a polyester film having excellent laser processability as described above, and to provide a mold release film for producing a wiring board, which is excellent in economical efficiency and excellent in releasability.

That is, the present invention has the following constitution.
1. A polyester film which does not contain an ultraviolet absorber and is irradiated with an electron beam and has a spectral transmittance of 75% or less at a wavelength of 355 nm.
2. The polyester film for laser processing as described in the first above, wherein the polyester film is a biaxially stretched polyethylene terephthalate film.
3. The polyester film for laser processing as described in the first or second above, which is irradiated with an electron beam at 200 to 2000 kGy.
4. The release film for wiring board manufacture which has a release layer in at least one surface of the polyester film for laser processing in any one of said 1st-3rd.

  According to the present invention, it is possible to provide a polyester film which is equivalent to the conventional polyester film without largely changing the film characteristics, and to be excellent in laser processability, so that the wiring board is excellent in economy and processability. It becomes possible to provide a release film for manufacturing.

  Hereinafter, the present invention will be described in detail.

  The polyester film for laser processing of the present invention is a film which does not contain an ultraviolet light absorber in the film, is irradiated with an electron beam, and has a spectral transmittance of 355 nm or less of 75% or less. And the mold release film for wiring board manufacture using the polyester film for said laser processing makes the mold release film for wiring board manufacture which has a mold release layer in the at least single side | surface of a polyester film a preferable aspect. .

(Polyester film)
The polyester constituting the polyester film for laser processing of the present invention is not particularly limited, and it is possible to use a polyester film generally used as a release film substrate, but it is preferable to use aromatic polyesters. The crystalline linear saturated polyester comprising a basic acid component and a diol component may be, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or a component of these resins It may be a copolymer as a main component, and in particular, a polyester film formed of polyethylene terephthalate is preferable. The polyester film is preferably a biaxially stretched film from the viewpoint of good mechanical properties due to the height of elastic modulus in both longitudinal and lateral directions, and a biaxially stretched polyethylene terephthalate film is particularly preferable.

  In addition, a coating layer may be provided on the surface of the film before or during uniaxial stretching in the film forming process on the surface to improve adhesion of a release layer to be applied later or to prevent charging. Processing can also be performed.

  In the present invention, the polyester film does not contain an ultraviolet absorber. A polyester film containing an ultraviolet absorber has a small lineup of thickness commercially, is limited in applications, etc., and is excellent in laser processability, but when it is cured after being coated with an ultraviolet-curable release layer on the film. There is a possibility of causing hardening inhibition, and it is preferable not to use.

  The 355 nm spectral transmittance of the polyester film is preferably 75% or less, and more preferably 70% or less. A UV solid laser is used for laser processing, and in particular, it is often processed by a UV-YAG laser etc. When the 355 nm spectral transmittance is 75% or less, the via hole processing can be easily performed. The 355 nm spectral transmittance is preferably low, but may be 10% or more, or 50% or more.

  The haze value of the polyester film is preferably 8% or less, more preferably 6% or less. If the haze value is 5% or less, a good via hole can be formed without the laser being diffused. The haze value is preferably low, but may be 0.1% or more, or 0.3% or more.

  10-100 micrometers is preferable and, as for the thickness of a polyester film, 12-75 micrometers is more preferable. A thickness of 10 μm or more is excellent in transportability in processing as a release film, and 100 μm or less is preferable because the amount of excess residue during laser processing is small.

(Electron beam)
The electron beam irradiation in the present invention preferably has an electron beam dose of 200 to 2000 kGy, more preferably 300 to 1000 kGy. If the dose is 200 kGy or more, energy can be sufficiently irradiated to the polyester film, and if it is 2000 kGy or less, the process can be performed at a sufficient processing speed, which is preferable because of its economic efficiency.

  When the electron beam is irradiated in an inert gas atmosphere, the oxygen concentration is preferably 500 ppm or less. When an electron beam is irradiated in the presence of oxygen, ozone is generated, which may adversely affect the apparatus and the environment. In order to reduce the oxygen concentration to 500 ppm or less, the film may be irradiated with an electron beam under vacuum or in an inert gas atmosphere such as nitrogen or argon, for example, by filling the inside of the electron beam irradiation apparatus with nitrogen Concentrations of 500 ppm or less can be achieved.

  As such an electron beam irradiation apparatus, a conventionally known one can be used. For example, a curtain type electron irradiation apparatus (LB 1023 manufactured by I-Electron Beam Co., Ltd.) or a line irradiation type low energy electron beam irradiation apparatus (EB-ENGINE) Hamamatsu Photonics Co., Ltd., an area-type electron irradiation apparatus (EBC-300, manufactured by NHV Corporation), and the like can be suitably used.

  Essentially, for the invention of a product, the patent application should be made by clarifying the structure and characteristics of the product, but a structure in which the polyester film is irradiated with an electron beam and the spectral transmittance of 355 nm is 75% or less, It is thought that clarifying the characteristics is technically nearly impossible, and it is thought that it is easier to express things if it is specified by the manufacturing method, and to be easy for readers to understand. In addition, the polyester film irradiated with the electron beam describes the state, and does not describe the change with time. Even if the polyester film is limited by the production method of electron beam irradiation, it is not considered to be unclear.

(Release layer)
The release layer in the present invention is not particularly limited, and in addition to silicones, polyolefins, long-chain alkyls, etc. generally used as a release agent, binder components such as acrylic resin, polyester resin, urethane resin, polyamide resin, etc. In addition, a mold release layer formed by adding a mold release component such as silicone oil or fluorine resin can also be applied.

  In the present invention, the thickness of the release layer may be set according to the purpose of use and is not particularly limited, but preferably, the range in which the release layer after curing is 0.05 to 3.0 μm is good. More preferably, it is 0.1 to 1.0 μm. When the thickness of the release layer is 0.05 μm or more, an appropriate peeling force is obtained, which is preferable. In addition, it is preferable that the thickness is 3.0 μm or less because processing can be performed without affecting the transmittance of the laser.

  In the present invention, the method for forming the releasing layer is not particularly limited, and a coating liquid in which a releasing resin is dissolved or dispersed is spread on one surface of the polyester film of the substrate by coating etc. The method of making it harden | cure after removing by drying is used.

  Any known coating method can be applied as the coating method of the above coating solution, for example, roll coating such as gravure coating or reverse coating, bar coating such as wire bar, die coating, spray coating, air knife A conventionally known method such as a coating method can be used.

  EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited by these examples. The characteristic values used in the present invention were evaluated using the following method.

(Total light transmittance and haze)
It measured using the haze meter (made by Nippon Denshoku Industries Co., Ltd., product name: NDH5000).

(Spectral transmittance)
It measured on the conditions of wavelength range 800-300 nm, scanning speed: high speed, sampling pitch: 1.0 nm using the spectrophotometer (The Shimadzu Corporation make, product name: UV-3150), and predetermined wavelength transmittance was implemented.

(Release processability)
100 parts by mass of a release material (made by Arakawa Chemical Industries, product name: SILIKOLYS (registered trademark) UV POLY 215, solid content concentration: 100% by mass), photo curing catalyst (manufactured by Arakawa Chemical Industries, made by SILIKORESE (registered trademark) UV CATA 211 The solid content concentration: 18.5 mass%) 5 parts by mass was diluted with a mixed solvent of toluene / MEK = 1/1 to prepare a release layer coating liquid having a solid content concentration of 1.0 mass%.
The release layer coating solution was applied to the surface of a polyethylene terephthalate film using a Meyer bar so that the film thickness after drying was 0.1 μm, and then dried at 100 ° C. for 20 seconds. Next, UV (high pressure mercury lamp, 100 mJ / cm ² ) was irradiated to form a release layer, and the release processability was judged from the state.
:: The release layer is sufficiently cured, and the release layer does not separate even when rubbed with a finger.
X: The curing of the release layer is insufficient, and the release layer falls off when rubbed with a finger.

(Laser processability)
88.65 parts by mass of ceramic powder (alumina powder and glass powder), 9.85 parts by mass of binder resin (PVB, Tg 65 ° C.), 1.50 parts by mass of di-n-butyl phthalate, 100 parts by mass of ethanol, 100 parts by mass of toluene The resulting composition was stirred and mixed, and dispersed for 1 hour using a bead mill using beads as a dispersion medium to prepare a ceramic slurry.
After degassing the obtained slurry, it is applied on a polyethylene terephthalate film sample that has been subjected to the release treatment as described above using an applicator so that the film thickness after drying becomes 30 μm, and dried at 90 ° C., ceramic green A release film for manufacturing a sheet-attached wiring board was obtained. Next, a UV-YAG laser (wavelength: 355 nm) was irradiated from the release film surface to process a via hole of 50 μmφ, and the shape of the via hole and the state of the polyester film were visually confirmed.
○: Via hole processing and polyester film can be processed without problems.
X: There is a portion where the via hole is deformed, or the polyester film is not sufficiently penetrated.

Example 1
Accelerated by using an electron beam irradiator (product name: EBC-300, manufactured by NHV Corporation) on a biaxially stretched polyethylene terephthalate film (Toyobo Co., Ltd., product number: E5100, film thickness: 50 μm, no ultraviolet absorber included) A dose of 300 kGy was applied under the conditions of a voltage of 200 kV, an electron current of 24.3 mA, and a velocity of 10 m / min. After irradiation, aging was performed for 3 days, and each measurement was performed.

(Examples 2-4, comparative examples 1-5)
The polyethylene terephthalate film was changed to the film described in Table 1, and the dose was adjusted to a predetermined dose, and electron beam irradiation was performed according to Example 1 except that irradiation was performed.
The Cosmo Shine (registered trademark) product number: A4100 used in Example 2 and Comparative Examples 2 and 4 and the film thickness of 50 μm are also biaxially stretched polyethylene terephthalate films containing no ultraviolet light absorber.
Moreover, about Comparative Examples 3-5, each measurement of the polyethylene terephthalate film was implemented, without irradiating an electron beam. Here, Tetron (registered trademark) film HB manufactured by Teijin Film Solutions, Ltd. of Comparative Example 5 is a biaxially stretched polyethylene terephthalate film containing an ultraviolet absorber.

  The thing using the polyester film of each Example was able to form a via hole precisely, and was satisfactory without inhibition of curing of the ultraviolet curing release layer. On the other hand, what used the polyester film of each comparative example was a thing with bad laser processability with a bad precision by via-hole formation, or it was unpreferable with a cure inhibition of a ultraviolet curing mold release layer. .

  According to the present invention, it is possible to provide a polyester film for laser processing and a release film for producing a wiring substrate, which have fine laser processability in the process of producing the wiring substrate and can produce the wiring substrate at low cost. It became.

Claims (4)

  A polyester film which does not contain an ultraviolet absorber and is irradiated with an electron beam and has a spectral transmittance of 75% or less at a wavelength of 355 nm.   The polyester film for laser processing according to claim 1, wherein the polyester film is a biaxially stretched polyethylene terephthalate film.   The polyester film for laser processing according to claim 1 or 2, which is irradiated with an electron beam at 200 to 2000 kGy.   The release film for wiring board manufacture which has a release layer in at least one surface of the polyester film for laser processing in any one of Claims 1-3.