Manufacturing method of printed circuit boards

Abstract

Providing a manufacturing method for producing high-quality printed circuit boards. [Solution] A method for manufacturing a printed circuit board includes forming a resin insulating layer, forming a protective film on a first surface, forming openings for via conductors, removing the protective film, cleaning the inside of the openings, forming a seed layer on the first surface and the exposed surface exposed by the openings, forming a plating resist on the seed layer, forming an electroplating film on the plating resist and the seed layer exposed from the plating resist, removing the plating resist, and removing the seed layer exposed from the electroplating film. The openings for via conductors are formed using laser light, the wavelength of the laser light is 400 nm or less, and the first threshold of the intensity of the laser light at which laser ablation occurs in the protective film is smaller than the second threshold of the resin insulating layer.

Description

Technical Field

[0001] The technology disclosed in the present specification relates to a method for manufacturing a printed wiring board.

Background Art

[0002] Patent Document 1 discloses a method for manufacturing a wiring board, in which an insulating layer is irradiated with a laser through a support film to form an opening, then the support film is removed from the insulating layer, and a via is formed in the opening.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] [Problems of Patent Document 1] Patent Document 1 discloses a method for manufacturing a wiring board. In the manufacturing method of Patent Document 1, the insulating layer is irradiated with a laser through a support film in order to reduce the diameter of the opening.

[0005] In general, the threshold value of the laser light intensity at which laser ablation occurs in the support film is smaller than the threshold value in the resin insulating layer. Therefore, the support film is considered to be less likely to be processed by a laser than the resin insulating layer. As a result, depending on the processing conditions, it is considered that foreign matter peeling off from the resin insulating layer may enter the gap between the resin insulating layer and the support film and adhere onto the resin insulating layer. In that case, it is considered that the flatness of the resin insulating layer is reduced and the adhesion to the pad is lowered. In addition, since a gap is formed between the support film and the resin insulating layer, it is considered that this causes irregular deformation of the opening shape and hindrance to diameter reduction.

[0006] According to the technique of Patent Document 1, it is considered difficult to form a high-quality wiring board.

Means for Solving the Problems

[0007] The present invention provides a method for manufacturing a printed circuit board, comprising: forming a resin insulating layer having a first surface and a second surface opposite to the first surface on a first conductor layer having a conductor circuit; forming a protective film on the first surface of the resin insulating layer; forming openings for via conductors that penetrate the protective film and the resin insulating layer and reach the first conductor layer; removing the protective film from the first surface of the resin insulating layer after forming the openings; cleaning the inside of the openings by a dry process after removing the protective film; forming a seed layer on the first surface of the resin insulating layer and the exposed surface exposed by the openings after cleaning; forming a plating resist on the seed layer; forming an electroplating film on the plating resist and the seed layer exposed from the plating resist; removing the plating resist after forming the electroplating film; and removing the seed layer exposed from the electroplating film. The aperture for the via conductor is formed using laser light, the wavelength of the laser light is 400 nm or less, and the first threshold of the laser light intensity at which laser ablation occurs in the protective film is smaller than the second threshold of the laser light intensity at which laser ablation occurs in the resin insulating layer.

[0008] In the manufacturing method of the embodiment of the present invention, an aperture for a via conductor is formed using laser light. The wavelength of the laser light is 400 nm or less. The threshold intensity of the laser light at which laser ablation occurs in the protective film is smaller than the threshold in the resin insulating layer. Therefore, the protective film is easier to process with a laser than the resin insulating layer. An opening is formed in the protective film, and then processing of the resin insulating layer begins. The protective film is less likely to peel off from the resin insulating layer. Therefore, foreign matter caused by laser processing is less likely to adhere to the resin insulating layer after the opening is formed. The diameter of the opening is reliably reduced. Adhesion strength between the resin insulating layer and the seed layer is ensured. In the manufacturing method of this embodiment, a high-quality printed circuit board is formed. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view showing a printed circuit board of the embodiment. [Figure 2A] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2B] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2C] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2D] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2E] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2F] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2G] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2H] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2I] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Figure 2J] A schematic cross-sectional view illustrating the manufacturing method of a printed circuit board according to this embodiment. [Modes for carrying out the invention]

[0010] <Printed wiring board of an embodiment> Figure 1 is a cross-sectional view of a printed circuit board 2 formed by the printed circuit board manufacturing method of the embodiment. As shown in Figure 1, the printed circuit board 2 has an insulating layer 4, a first conductor layer 10, a resin insulating layer 20, a second conductor layer 30, and a via conductor 40.

[0011] The insulating layer 4 is formed using a thermosetting resin. The insulating layer 4 may contain inorganic particles such as silica. The insulating layer 4 may also contain reinforcing materials such as glass cloth. The insulating layer 4 has a third surface 6 (the upper surface in Figure 1) and a fourth surface 8 (the lower surface in Figure 1) opposite to the third surface 6.

[0012] The first conductor layer 10 is formed on the third surface 6 of the insulating layer 4. The first conductor layer 10 includes signal wirings 12 and pads 14. Although not shown in the drawing, the first conductor layer 10 also includes conductor circuits other than the signal wirings 12 and the pads 14. The first conductor layer 10 is formed of copper. The first conductor layer 10 is formed of a seed layer 10a and an electrolytic plating film 10b on the seed layer 10a.

[0013] The resin insulating layer 20 is formed on the third surface 6 of the insulating layer 4 and the first conductor layer 10. The resin insulating layer 20 has a first surface 22 (the upper surface in FIG. 1) and a second surface 24 (the lower surface in FIG. 1) opposite to the first surface 22. The resin insulating layer 20 is formed with an opening 26 for the via conductor 40 that exposes the pad 14. The resin insulating layer 20 is formed of a resin, inorganic particles dispersed in the resin, and an additive. The resin is, for example, epoxy or polyimide. The inorganic particles are, for example, silica or alumina.

[0014] The second conductor layer 30 is formed on the first surface 22 of the resin insulating layer 20. The second conductor layer 30 includes first signal wirings 32, second signal wirings 34, and lands 36. Although not shown in the drawing, the second conductor layer 30 also includes conductor circuits other than the first signal wirings 32, the second signal wirings 34, and the lands 36. The first signal wirings 32 and the second signal wirings 34 form pair wirings. The second conductor layer 30 is formed of copper. The second conductor layer 30 is formed of a seed layer 30a and an electrolytic plating film 30b on the seed layer 30a. The seed layer 30a is in contact with the first surface 22.

[0015] The via conductor 40 is formed in the opening 26. The via conductor 40 connects the first conductor layer 10 and the second conductor layer 30. In FIG. 1, the via conductor 40 connects the pad 14 and the land 36. The via conductor 40 is formed of the seed layer 30a and the electrolytic plating film 30b on the seed layer 30a.

[0016] <Method for manufacturing printed wiring board of embodiment> (FIGS. 2A to 2J show the method for manufacturing the printed wiring board 2 of the embodiment. FIGS. 2A to 2J are cross-sectional views. FIG. 2A shows the insulating layer 4 and the first conductor layer 10 formed on the third surface 6 of the insulating layer 4. The first conductor layer 10 is formed by a semi-additive method.

[0017] As shown in FIG. 2B, the resin insulating layer 20 and the protective film 50 are formed on the insulating layer 4 and the first conductor layer 10. The second surface 24 of the resin insulating layer 20 faces the third surface 6 of the insulating layer 4. The protective film 50 is formed on the first surface 22 of the resin insulating layer 20.

[0018] The protective film 50 completely covers the first surface 22 of the resin insulating layer 20. The protective film 50 is formed of, for example, a resin and an additive. The additive does not contain inorganic particles. The additive is an absorbent having a property of absorbing laser light. The absorbent is, for example, an organic compound such as salicylic acid-based dyes including phenyl salicylate and p-tert-butylphenyl salicylate, benzophenone-based dyes including 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone, benzotriazole-based dyes including 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-methylphenyl)benzotriazole and 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, cyanoacrylate-based dyes including 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate and ethyl-2-cyano-3,3'-diphenylacrylate, and benzoate-based dyes, or an inorganic compound such as titanium oxide powder. The absorbent is preferably blended in an amount of 0.1 to 10% by weight relative to the protective film. The absorbent is more preferably blended in an amount of 0.5 to 5% by weight relative to the protective film.

[0019] The resin is, for example, epoxy, polyimide, or polyethylene terephthalate. Alternatively, the protective film 50 is formed of a metal film. The metal film has a thickness of 200 nm or less. The metal film is, for example, copper. A release agent is formed between the protective film 50 and the resin insulating layer 20. The protective film 50 is subjected to heat treatment. The protective film 50 is partially cured.

[0020] As shown in Figure 2C, a laser beam L is shone onto the protective film 50. The laser beam L is, for example, a UV laser beam, a carbon dioxide laser beam, or a YAG laser beam. The laser beam L penetrates both the protective film 50 and the resin insulating layer 20 simultaneously. An opening 26 for via conductors leading to the pad 14 of the first conductor layer 10 is formed. The pad 14 is exposed by the opening 26.

[0021] When the aperture 26 is formed by the laser beam L, the first surface 22 is covered with a protective film 50. The wavelength of the laser beam L is 400 nm or less. For example, the laser beam L is a YAG 3rd harmonic laser with a wavelength of 355 nm. Alternatively, the laser beam L is an excimer laser with a wavelength of 308 nm using a mixed gas of xenon and chlorine. Alternatively, the laser beam L is a YAG 4th harmonic laser with a wavelength of 266 nm. Alternatively, the laser beam L is an excimer laser with a wavelength of 248 nm using a mixed gas of krypton and fluorine. Alternatively, the laser beam L is an excimer laser with a wavelength of 193 nm using a mixed gas of argon and fluorine.

[0022] The first threshold intensity of the laser light L at which laser ablation occurs in the protective film 50 is smaller than the second threshold intensity of the laser light L at which laser ablation occurs in the resin insulating layer 20. Laser ablation is a general term for the phenomenon in which, when a solid (or liquid) material is irradiated with laser light having an intensity above a certain magnitude (threshold), the material constituting the surface of the material is explosively ejected in various forms such as atoms, molecules, ions, clusters, and electrons, and the material surface is removed. The ratio of the second threshold to the first threshold (second threshold / first threshold) is greater than 2. Alternatively, the ratio of the second threshold to the first threshold (second threshold / first threshold) is greater than 5. Alternatively, the ratio of the second threshold to the first threshold (second threshold / first threshold) is greater than 10. Therefore, when the opening 26 is formed, the protective film 50 is easier to process with the laser beam L than the resin insulating layer 20. After the opening 26 is formed in the protective film 50, processing of the resin insulating layer 20 begins. The protective film 50 is difficult to peel off from the resin insulating layer 20. Therefore, foreign matter caused by laser processing is less likely to adhere to the first surface 22 of the resin insulating layer 20 after the opening 26 has been formed. The opening 26 is reliably reduced in diameter. Adhesion strength between the resin insulating layer 20 and the seed layer 30a (described later) on the first surface 22 is ensured. In the manufacturing method of this embodiment, a high-quality printed circuit board 2 is formed.

[0023] As shown in Figure 2D, the protective film 50 is removed from the first surface 22 of the resin insulating layer 20.

[0024] As shown in Figure 2E, the inside of the opening 26 is cleaned. The primary cleaning includes removing the release agent between the protective film 50 and the resin insulating layer 20. By cleaning the inside of the opening 26, resin residue (smear) generated during the formation of the opening 26 is removed. The cleaning of the inside of the opening 26 (primary cleaning) is performed by plasma D using a gas containing, for example, carbon tetrafluoride. That is, the primary cleaning is performed in a dry process. The primary cleaning includes a desmear (dry desmear) treatment. The resin is selectively removed by plasma D. Plasma D removes epoxy resin faster than inorganic particles.

[0025] As shown in Figure 2F, the first surface 22 of the resin insulating layer 20 is cleaned (secondary cleaning). By cleaning the first surface 22, a portion of the upper part of the resin insulating layer 20 is removed. A thickness of several nanometers from the upper part of the resin insulating layer 20 is removed. The secondary cleaning of the first surface 22 is performed, for example, by reactive ion etching. The secondary cleaning allows the seed layer 30a (described later) to be smoothly formed on the first surface 22.

[0026] As shown in Figure 2G, a seed layer 30a is formed on the first surface 22 of the resin insulating layer 20. The seed layer 30a is in contact with the first surface 22. The seed layer 30a is formed by sputtering. The formation of the seed layer 30a is carried out by a dry process. The seed layer 30a is formed with a two-layer structure, for example, copper and titanium. For example, a sputtering apparatus is used to form the seed layer 30a. The seed layer 30a is formed on the exposed surface that is exposed from the opening 26. The exposed surface is the upper surface of the pad 14 and the inner wall surface of the opening 26.

[0027] As shown in Figure 2H, a plating resist 60 is formed on the seed layer 30a. The plating resist 60 has openings 60a for forming the first signal wiring 32, the second signal wiring 34, and lands 36 (see Figure 1).

[0028] As shown in Figure 2I, an electroplated film 30b is formed on the plating resist 60 and the seed layer 30a exposed from the plating resist 60. The electroplated film 30b is copper. The electroplated film 30b fills the opening 26.

[0029] As shown in Figure 2J, the plating resist 60 is removed. The seed layer 30a exposed from the electrolytic plating film 30b is removed. The first signal wiring 32, the second signal wiring 34, and the land 36 are formed. The second conductor layer 30 is formed. The via conductor 40 is formed. The second conductor layer 30 and the via conductor 40 are formed simultaneously. The printed circuit board 2 of the embodiment (see Figure 1) is obtained. [Explanation of Symbols]

[0030] 2: Printed circuit board 4: Insulating layer 10: First conductor layer 12: Signal Wiring 14: Pad 20: Resin insulating layer 22: 1st page 24:Second side 26 :Aperture 30: Second conductor layer 30a: Seed layer 30b: Electrolytic plating film 32: First signal wiring 34: Second signal wiring 36: Land 40: Via conductor 50:Protective film 60: Plating Resist 60a: Opening D: Plasma L: Laser light

Claims

1. A resin insulating layer having a first surface and a second surface opposite to the first surface is formed on a first conductor layer having a conductor circuit. A protective film is formed on the first surface of the resin insulating layer, To form an opening for a via conductor that penetrates the protective film and the resin insulating layer and reaches the first conductor layer, After forming the opening, the protective film is removed from the first surface of the resin insulating layer, After removing the protective film, the inside of the opening is cleaned by a dry process, After the cleaning, a seed layer is formed on the first surface of the resin insulating layer and the exposed surface exposed by the opening. Forming a plating resist on the seed layer, Forming an electroplating film on the plating resist and the seed layer exposed from the plating resist, After forming the electrolytic plating film, the plating resist is removed, To remove the seed layer exposed from the electroplated film, A method for manufacturing a printed circuit board, including the following: The opening for the via conductor is formed using laser light, The wavelength of the laser light is 400 nm or less. The first threshold of the laser light intensity at which laser ablation occurs in the protective film is smaller than the second threshold of the laser light intensity at which laser ablation occurs in the resin insulating layer.

2. A method for manufacturing a printed circuit board according to claim 1, wherein the ratio of the second threshold to the first threshold (second threshold / first threshold) is greater than 2.

3. A method for manufacturing a printed circuit board according to claim 2, wherein the ratio of the second threshold to the first threshold (second threshold / first threshold) is greater than 5.

4. A method for manufacturing a printed circuit board according to claim 2, wherein the ratio of the second threshold to the first threshold (second threshold / first threshold) is greater than 10.

5. A method for manufacturing a printed circuit board according to claim 1, wherein the protective film is formed of a resin and an additive, or a metal film with a thickness of 200 nm or less, and the resin insulating layer is formed of a resin, inorganic particles and an additive.

Images