JP2006201434A - Photomask for exposure of solder resist and wiring substrate exposed using the same or method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem that in a wiring substrate having a solder resist layer in an uppermost surface layer, at the time of exposing the solder resist layer to form a plurality of openings in the layer, the phenomenon that the solder resist at the bottom of opening edges is cured by reflected light from a circuit pattern and cannot be removed by development occurs, and by the phenomenon, the ratio of resist residue to removed resist increases in accordance with reduction in the diameter of openings. <P>SOLUTION: At the time of exposing the solder resist layer to form a plurality of openings in the layer, a photomask having a semi-transparent part at the outer side of each light shielding part is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wiring board and a method for manufacturing the same, and more particularly to a photomask for exposure when forming a solder resist layer on a wiring board.

  The conventional wiring board has an opening such as a terminal hole on the outermost layer on at least one side of the board, and prevents the solder bridge between adjacent circuits in the opening or protects the outermost circuit from the environment where the electronic device is used. It has a solder resist layer for the purpose. That is, the solder resist layer is indispensable for forming a highly reliable wiring board.

  Conventionally, a solder resist layer is obtained by applying a resin solution of a photosensitive solder resist to a substrate on which a wiring circuit is formed, performing exposure through a photomask in accordance with a predetermined pattern, developing, and exposing an exposure light irradiation portion. It was formed by a process of curing. Further, after the solder resist layer is formed, a metal layer such as nickel and gold is provided on the wiring circuit exposed from the opening. However, in the conventional method, as the opening diameter becomes smaller, a problem of solder resist resin residue in which the solder resist resin remains at the bottom of the opening end occurs.

  FIGS. 5A to 5D are schematic side sectional views showing a solder resist layer curing step in an exposure step using a conventional photomask. As shown in FIG. 5A, the circuit pattern 2 is formed on the outermost layer on the substrate 1. The base 1 is a core substrate on which one or more wiring layers are laminated, and the circuit pattern of the core substrate and the circuit pattern 2 of the outermost layer are electrically connected (not shown). As shown in FIG. 5B, the solder resist layer 3 is applied and formed on the entire surface of the substrate and the circuit pattern. In FIG. 5C, in order to form an opening in the solder resist layer on the circuit pattern 2, an exposure process is performed with the exposure light 5 using the photomask 4. The photomask 4 is provided with a light-shielding portion 7 at the opening portion of the solder resist layer, and a portion other than the light-shielding portion 7 is a transmissive portion 6. When the exposure light is irradiated, the reflected light from the circuit pattern 2 hardens the solder resist at the bottom of the opening where it is not necessary to form a solder resist layer, and a phenomenon that cannot be removed by development occurs. Due to this phenomenon, a residue of the solder resist resin is generated at the bottom end of the opening in the cross section, and the ratio of the solder resist residue to the solder resist removal portion increases as the diameter of the opening decreases. In FIG. 5D, an unexposed portion of the solder resist layer is removed by a development process to form an opening, and a terminal hole 8 is formed. Through the above steps, a terminal hole and a solder resist layer are completed on the outermost layer.

  When patterning the solder resist, by reducing the integrated exposure amount of the solder resist layer forming portion, unnecessary solder resist at the bottom end of the opening can be easily removed. However, when the integrated exposure amount is small, there is a problem that the reliability of the solder resist layer is lowered. That is, the reliability of the circuit protection on the outermost layer is lowered, and the high reliability of the circuit pattern in the environment where the electronic device is used becomes a problem. (See Patent Document 1).

The known literature is described below.
Japanese Patent Laid-Open No. 5-29754

  Since the solder resist at the bottom end of the opening that does not require the formation of the solder resist layer by the reflected light from the circuit pattern is cured in the exposure process when forming the solder resist layer as described above, the bottom end of the opening is cured. Solder resist resin residue is generated in the solder, and the problem that the ratio of the resist residue portion to the resist removal portion becomes larger as the opening diameter becomes smaller is solved, and the solder of the wiring board having a plurality of conductor circuits in the resin insulation layer In patterning of a resist layer, there is provided a highly reliable wiring board with little solder resist residue at the bottom of the opening. In particular, the present invention is to provide a method of manufacturing a wiring board with improved productivity by a reel-to-reel method.

  In order to solve the above-mentioned problems in the present invention, first, the invention according to claim 1 has a solder resist layer on at least one outermost layer, and a wiring layer and an insulating layer are alternately laminated to form a circuit by electrically connecting each wiring. In the printed circuit board, the photomask is used for an exposure process for forming a plurality of openings in the solder resist layer, and the photomask is provided with a semi-transmissive portion outside the light shielding portion.

  The invention according to claim 2 is the photomask according to claim 1, wherein at least one of the light shielding portions includes a pattern having a diameter of 150 μm or less.

  The invention according to claim 3 is the photomask according to claim 1 or 2, wherein the semi-transmissive portion has a diameter that is 1 to 30% larger than a diameter of the light shielding portion.

  The invention according to claim 4 is the photomask according to any one of claims 1 to 3, characterized in that a transmitted light amount of the semi-transmissive portion is 5 to 90% of that of the transmissive portion.

  According to a fifth aspect of the present invention, there is provided a method for manufacturing a wiring board in which a solder resist layer is provided on at least one outermost layer, wiring layers and insulating layers are alternately laminated, and each wiring is made conductive to form a circuit. 5. A method for manufacturing a wiring board, wherein an exposure process is performed using the photomask according to claim 1 as a photomask used in an exposure process for forming a plurality of openings in a resist layer.

  The invention according to claim 6 is the method for manufacturing a wiring board according to claim 5, wherein the exposure processing is performed by a reel-to-reel method.

  The invention according to claim 7 is a wiring board in which a plurality of openings are formed in the solder resist layer using the photomask according to any one of claims 1 to 4.

  By using the photomask of the present invention in the patterning of the solder resist layer of the wiring board having a plurality of conductor circuits in the resin insulating layer, a highly reliable wiring board with little resist residue at the bottom of the opening portion was obtained.

  Hereinafter, embodiments of the present invention will be described in more detail. FIG. 1 is a side sectional view for explaining the solder resist layer forming step of the present invention, wherein (a) is after exposure and (b) is after development. The wiring board of the present invention may be any of the case where the circuit pattern exists only on one side, the case where the circuit pattern exists on both sides, and the case where the circuit pattern is formed in multiple layers. FIG. 1 is a diagram in which a circuit pattern and a solder resist layer are formed on the outermost layer on one side, and will be described using this.

  In FIG. 1A, the circuit pattern 11 is formed on the outermost surface layer of the substrate 10. A solder resist layer 12 is formed of a negative photosensitive resin on the outermost surface of the substrate and the entire surface of the circuit pattern. The solder resist layer 12 is exposed using the photomask of the present invention. As a result, around the uncured portion 13 serving as the opening, a cured portion 14 mainly formed of light from the semi-transmissive portion is formed on the left and right sides thereof, and a cured portion 15 mainly formed of light from the transmissive portion is formed outside thereof. FIG. 1B shows a solder resist layer 16 after development. FIG. 1A shows an uncured portion 13 as an opening, and a terminal hole 17 is formed. The solder resist layer 16 is completed with a cured portion 14 mainly caused by light from the semi-transmissive portion and a cured portion 15 mainly caused by light from the transmissive portion on the outer side thereof.

  The solder resist layer of the present invention may be either a liquid or a dry film. Examples of the method for applying the liquid solder resist include, but are not limited to, a screen printing method, a roller coating method, a dip coating method, a spray coating method, a spinner coating method, and a curtain coating method. As a method for forming the dry film solder resist layer, various means such as a roll laminating method, a flat plate laminating method, and a flat plate pressing method can be used. In addition, the film thickness of a soldering resist is about 10-40 micrometers. In addition, an epoxy-based insulating resin is generally used as the solder resist layer forming resin.

  In the solder resist exposure process, as shown in FIG. 2, the photomask 18 is provided with a light shielding portion 19 corresponding to a portion of the solder resist layer to be opened. Further, the photomask has a semi-transmissive portion 20 having a constant width outside the light shielding portion. Here, the light shielding part is a part through which the exposure light is not transmitted, and the semi-transmission part is a part through which a part of the exposure light is transmitted. The semi-transmissive portion has a diameter that is 1 to 30% larger than the diameter of the light shielding portion, and is disposed so as to surround the light shielding portion. In the semi-transmissive portion, the exposure amount is relatively small, the reflection of light from the circuit pattern is reduced, and the light is easily removed by development. The material of the photomask may be anything as long as it is normally used, such as glass or a transparent film.

  The narrower the opening of the solder resist layer, the more circuit patterns can be formed and the higher functionality of the wiring board can be achieved. However, in exposure using a conventional photomask having only a light-shielding portion corresponding to the opening of the solder resist layer, a residue usually remains with a width of 10 to 20 μm at the bottom of the end of the obtained opening.

  If the diameter of the opening is 200 μm or more, this is not a problem, but the reliability of the wiring board is greatly affected as the opening is reduced. In particular, when the diameter of the opening is 150 μm or less, the effective opening diameter is greatly reduced to about 110 to 130 μm in diameter and about half the area, and sufficient connection reliability cannot be obtained. Since the photomask of the present invention has a semi-transmissive portion around the light shielding portion, a fine pattern can be formed with high accuracy. If the diameter of the light shielding portion is 150 μm or less, the photomask has an opening having a diameter of 150 μm or less. A wiring board having an opening with little residue at the bottom can be obtained.

  The semi-transmission part 20 shown in FIG. 2 is for reducing the residue at the bottom of the opening part, and is preferably one concentrically enlarged by 1 to 30% with respect to the diameter of the light shielding part 19. When the diameter of the semi-transmissive portion is less than this range, the effect of removing the residue at the bottom of the opening is not confirmed. Moreover, when the diameter of a semi-transmissive part exceeds this range, the reliability of a soldering resist layer falls.

  The light shielding part 19 in FIG. 2 is not particularly limited as long as it is made of a light shielding material. Generally, it is classified into those using photographic emulsions formed with emulsions in which silver halide fine particles are dispersed in gelatin, and those using light-shielding material thin films such as chromium metal thin films, silicon and iron oxide. Is done. Any light can be used as long as it shields light to be shielded used in the exposure process, for example, ultraviolet rays.

  The semi-transmissive portion 20 shown in FIG. 2 is formed by arranging a fine light-shielding film pattern having a resolution equal to or lower than the resolution of the solder resist or a uniform film corresponding to a predetermined transmission amount. FIG. 3 shows a schematic diagram when a fine pattern of the light shielding film 22 is arranged in the semi-transmissive portion 21. A portion excluding the light shielding film 22 is a transmission portion 23. In FIG. 3, the pattern of the light shielding film is circular, but the present invention is not limited to this. The amount of light transmitted through the semi-transmissive portion and the size of the semi-transmissive portion need to be optimized because they affect the opening shape, dimensions, and the like. The average amount of transmitted light in the semi-transmissive portion is 5 to 90% of the transmissive portion, and more preferably 20 to 70%. As a pattern of a fine light shielding film, it is preferable that a light shielding portion having a diameter of 50 μm or more cannot be formed when the pattern is circular. When the pattern is circular, if there is a light-shielding part having a diameter of 50 μm or more in the semi-transmissive part, a part that is shielded by the solder resist at a position corresponding to the semi-transmissive part is formed, and a part that is not sufficiently cured is formed. In the case of a circular pattern, a pattern having a diameter of 25 μm or less is preferable.

  Next, the manufacturing method of the wiring board of this invention is demonstrated in detail using drawing. FIG. 4 is a schematic cross-sectional side view illustrating a solder resist layer curing step in an exposure step using the photomask of the present invention.

  The substrate 24 on which the circuit pattern 25 is formed on the insulating resin is coated with a photosensitive solder resist resin solution on a single side of the substrate using a screen, and then the substrate is semi-cured to form a solder resist layer 26. It forms (refer FIG. 4 (a), (b)). Next, exposure with the exposure light 27 is performed through a photomask provided with a light-shielding portion at a location where the solder resist layer is not formed. At this time, a photomask 28 having a semi-transmissive portion 30 in the vicinity of the light shielding portion 29 is used. A portion other than the light shielding portion 29 and the semi-transmissive portion 30 is a transmissive portion 31. After the development of the unused portion, the solder resist layer 33 having the terminal holes 32 is formed by curing with heat and, if necessary, ultraviolet rays. (See FIGS. 4C and 4D)

  By performing the exposure, the portion of the solder resist layer irradiated with light is cured. At this time, as shown in FIG. 1A, a cured portion 15 mainly caused by light from the transmissive portion, a cured portion 14 mainly caused by light from the semi-transmissive portion, and an uncured portion 13 are generated. The uncured portion 13 is removed by development. Since the uncured portion is surrounded by a portion having a relatively small exposure amount and mainly cured by the light from the semi-transmissive portion, there is little reflected light from the circuit pattern and is easily removed by development. On the other hand, when a mask having only a light shielding portion is used, the end of the uncured portion is hardened by the reflected light from the circuit pattern and is not easily removed by development.

  Furthermore, since the light which becomes the suitable exposure amount of a soldering resist is irradiated in the exposure process, the reliability of a soldering resist layer is also ensured.

  Further, by manufacturing these wiring boards by the reel-to-reel method, the time can be significantly reduced as compared with the case where the boards are manufactured one by one in a single sheet.

  This will be described with reference to FIG. All of the examples were performed by a reel-to-reel method. A photo solder resist PSR-4000 (manufactured by Taiyo Ink Co., Ltd., trade name) was solid-printed on the wiring board prepared by the above method using a screen, and then semi-cured at 80 ° C. for 30 minutes.

An exposure process is performed using the photomask 28 having the light-shielding portion 29 and the semi-transmissive portion 30 of the present invention. The amount of light transmitted through the semi-transmissive portion is 60%. The irradiated exposure dose is 600 mJ / cm ² . The substrate was developed and post-cure and post-exposure were performed to form a photo solder resist layer.

  In the evaluation of the substrate of the example, when the light shielding portion of the photomask is circular and the diameter is 150 μm, and the semi-transmissive portion provided around the light shielding portion is circular and the diameter is 170 μm, the upper part of the photo solder resist layer in the opening portion Was 149 μm in diameter, and the diameter of the lower part of the photo solder resist layer was 135 μm.

(Comparative Example 1)
This will be described with reference to FIG. In the exposure step, a photo solder resist layer was formed in the same manner as in the example except that the photomask 4 having no transflective portion was used. In the evaluation of the substrate of the comparative example, when the light shielding portion of the photomask was circular and the diameter was 150 μm, the diameter of the upper portion of the photo solder resist layer in the opening portion was 123 μm, and the diameter of the lower portion of the photo solder resist layer was 99 μm.

(Comparative Example 2)
In Example 1, the exposure process was performed by the reel-to-reel method, whereas in Comparative Example 2, it was performed one sheet at a time. Other substrate creation conditions are the same. The time required for performing the exposure processing 100 times was 30 minutes when continuously performed by the reel-to-reel method, and 120 minutes when performed one sheet at a time.

It is a sectional side view explaining the soldering resist layer formation process of this invention. It is a schematic diagram of the photomask of the present invention. It is an enlarged view of the semi-transmissive part in the photomask of this invention. It is the model side sectional view which showed the hardening process of the soldering resist layer in the exposure process using the photomask of this invention. It is the model side sectional view which showed the hardening process of the soldering resist layer in the exposure process using the conventional photomask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2 Circuit pattern 3 Solder resist layer 4 Photomask 5 Exposure light 6 Transmission part 7 Light-shielding part 8 Terminal hole 10 Base material 11 Circuit pattern 12 Solder resist layer 13 Unhardened part 14 The hardening part mainly by the light of a semi-transmission part DESCRIPTION OF SYMBOLS 15 Curing part mainly by the light from a transmission part 16 Solder resist layer 17 Terminal hole 18 Photomask 19 Light-shielding part 20 Semi-transmission part 21 Semi-transmission part 22 Light-shielding film 23 Transmission part 24 Base material 25 Circuit pattern 26 Solder resist layer 27 Exposure Light 28 Photomask 29 Light-shielding part 30 Semi-transmission part 31 Transmission part 32 Terminal hole 33 Solder resist layer

Claims (7)

  At the time of the exposure process for forming a plurality of openings in the solder resist layer in a wiring board having a solder resist layer on at least one outermost layer and alternately laminating wiring layers and insulating layers to form a circuit by electrically connecting each wiring. A photomask to be used, wherein a transflective portion is provided outside the light shielding portion.   2. The photomask according to claim 1, wherein at least one of the light shielding parts includes a pattern having a diameter of 150 [mu] m or less.   3. The photomask according to claim 1, wherein the semi-transmissive portion has a diameter expanded by 1 to 30% with respect to a diameter of the light shielding portion.   The photomask according to any one of claims 1 to 3, wherein the translucent light quantity of the semi-transmissive part is 5 to 90% of the transmissive part.   In a method for manufacturing a wiring board in which a solder resist layer is provided on at least one outermost layer and a wiring layer and an insulating layer are alternately laminated and each wiring is conducted to form a circuit, a plurality of openings are formed in the solder resist layer. 5. A method of manufacturing a wiring board for performing an exposure process, wherein the photomask according to claim 1 is used as a photomask used during the exposure process.   6. The method of manufacturing a wiring board according to claim 5, wherein the exposure processing is performed by a reel-to-reel method.   A wiring board in which a plurality of openings are formed in the solder resist layer using the photomask according to claim 1.

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