JP2022175396A - Method for manufacturing printed wiring board - Google Patents

Abstract

To provide a printed wiring board having high connection reliability.SOLUTION: A method for manufacturing a printed wiring board includes: forming a first pad on a top resin insulation layer; forming a first irregularity on the surface of the first pad; forming a first solder resist layer having a first opening to expose the first pad, on the top resin insulation layer and the first pad; decreasing the size of the first irregularity exposed from the first opening; forming a first protective film on the first solder resist layer and the first opening, after decreasing the size of the first irregularity; forming a second pad on a bottom resin insulation layer; forming a second irregularity on the surface of the second pad; forming a second solder resist layer having a second opening to expose the second pad, on the bottom resin insulation layer and the second pad; forming a second metal film on the second pad exposed from the second opening, after forming the first protective film; and removing the first protective film after forming the second metal film.SELECTED DRAWING: Figure 1

Description

The technology disclosed by this specification relates to a method for manufacturing a printed wiring board.

US Pat. No. 6,300,001 discloses a method of manufacturing a substrate structure having conductor layers on both sides of the substrate. A surface treatment layer for preventing oxidation may be formed on the lowermost conductor layer. While the surface treatment layer is formed on the bottom conductor layer, the top conductor layer is covered with a resin protective film with an adhesive material.

U.S. Patent Application Publication No. 2017/0171981

[Problem of Patent Document 1]
In the technique of Patent Document 1, after the surface treatment layer is formed on the lowermost conductor layer, the resin protective film covering the uppermost conductor layer is removed. At that time, it is conceivable that the adhesive material remains on the uppermost conductor layer. If the adhesive material remains on the uppermost conductor layer, it is thought that there will be a problem with the adhesion of the surface treatment layer when another surface treatment layer is subsequently formed on the uppermost conductor layer.

A method for manufacturing a printed wiring board according to the present invention includes forming an uppermost resin insulation layer, forming a first pad for mounting an electronic component on the uppermost resin insulation layer, and forming a first pad for mounting an electronic component on the uppermost resin insulation layer. forming a first unevenness on the surface of the uppermost resin insulation layer and forming a first solder resist layer having a first opening for exposing the first pad on the uppermost resin insulation layer and the first pad; making the arithmetic mean roughness (Ra) of the upper surface of the first pad exposed from the first opening smaller than 0.5 μm by reducing the size of the first unevenness exposed from the first opening; forming a first protective film on the first solder resist layer and the first opening after reducing the size of the first unevenness; forming a lowermost resin insulation layer; forming a second pad for connection with a motherboard on a lower resin insulation layer; forming a second unevenness on a surface of the second pad; and forming the lowermost resin insulation layer and the second pad. forming a second solder resist layer having a second opening for exposing the second pad thereon, and on the second pad exposed from the second opening after forming the first protective film; and removing the first protective film after forming the second metal film.

According to the printed wiring board manufacturing method of the embodiment of the present invention, the first protective film is formed after reducing the size of the first unevenness, and then the second metal film is formed on the second pad. Since the size of the first unevenness is reduced before the formation of the first protective film, the adhesive material remains on the surface of the first pad when the first protective film is removed after the formation of the second metal film. is suppressed. When another metal film (for example, a first metal film different from the second metal film) is subsequently formed on the first pad, high adhesion between the first pad and the other metal film is achieved. That is, according to the manufacturing method of the embodiment, a printed wiring board with high connection reliability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows typically some printed wiring boards of embodiment. FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a printed wiring board according to the embodiment; The enlarged sectional view which shows typically the 1st unevenness|corrugation exposed from 1st opening. The enlarged sectional view which shows typically the 2nd unevenness|corrugation exposed from 2nd opening. FIG. 4 is an enlarged cross-sectional view schematically showing the first unevenness after being reduced in size; FIG. 4 is an enlarged cross-sectional view schematically showing the second unevenness after being reduced in size;

[Embodiment]
FIG. 1 is a cross-sectional view showing part of a printed wiring board according to an embodiment. As shown in FIG. 1, printed wiring board 1 includes core substrate 2, uppermost resin insulation layer 4, first pads 10, first solder resist layer 30, first metal film 50, and lowermost , a second pad 20 , a second solder resist layer 40 and a second metal film 60 .

The core substrate 2 has an insulating substrate. The upper and lower surfaces of the insulating substrate are provided with buildup layers formed by alternately laminating conductor layers and resin insulating layers. The conductor layers facing each other via the insulating substrate may be connected via through holes. Detailed illustration of the insulating substrate and the buildup layer is omitted in FIG. The core substrate 2 has an upper surface 2a and a lower surface 2b.

Uppermost resin insulation layer 4 is provided on top surface 2 a of core substrate 2 . Uppermost resin insulation layer 4 is formed using a thermosetting resin. The uppermost resin insulation layer 4 may contain inorganic particles such as silica. The uppermost resin insulation layer 4 may contain a reinforcing material such as glass cloth.

First pad 10 is provided on uppermost resin insulation layer 4 . In FIG. 1, three first pads 10 are provided. In another example, first pads other than the three first pads 10 illustrated may be provided. A first pad 10 is a pad for mounting an electronic component. Although detailed illustration is omitted in FIG. 1 , the first pads 10 are electrically connected to the conductor layer of the core substrate 2 . The first pad 10 is made of a conductive metal such as a metal containing copper as a main component.

The first solder-resist layer 30 is formed of a type of solder-resist that is cured by UV light (ultraviolet rays) (so-called UV-curable solder-resist). The first solder resist layer 30 has first openings 32 for exposing each first pad 10 .

The surface of the first pad 10 described above is roughened. First irregularities 12 are formed on the surface of the first pad 10 . The size of the first unevenness 12 in the portion exposed from the first opening 32 is smaller than the first unevenness 12 in other portions. The arithmetic average roughness (Ra) of the upper surface of the first pad 10 exposed from the first opening 32 is 0.5 μm or less. The arithmetic average roughness (Ra) of the surface of the first pad 10 not exposed from the first opening 32 is greater than 0.5 μm.

A first metal film 50 is formed on the first pad 10 exposed from the first opening 32 . The first metal film 50 is an antioxidant film that prevents oxidation of the surface of the first pad 10 . The first metal film 50 is formed of a nickel film and a gold film on the nickel film. Alternatively, the first metal film 50 may be formed of a nickel film and a tin film on the nickel film, or a nickel film and a palladium film on the nickel film and a gold film on the palladium film.

The lower surface 2b of the core substrate 2 also has substantially the same structure as the upper surface 2a side. The lowermost resin insulation layer 6 is provided on the lower surface 2 b of the core substrate 2 . The lowermost resin insulation layer 6 is formed using a thermosetting resin. The lowermost resin insulation layer 6 may contain inorganic particles such as silica. The lowermost resin insulation layer 6 may contain a reinforcing material such as glass cloth.

Second pad 20 is provided on lowermost resin insulation layer 6 . In FIG. 1, three second pads 20 are provided. In other examples, second pads other than the three illustrated second pads 20 may be provided. A second pad 20 is a pad for connecting with the motherboard. Although detailed illustration is omitted in FIG. 1 , the second pads 20 are electrically connected to conductor layers included in the core substrate 2 . The second pad 20 is made of a conductive metal, such as a metal containing copper as a main component.

The second solder-resist layer 40 is formed of a UV-curable solder-resist. The second solder resist layer 40 has second openings 42 for exposing each second pad 20 .

The surface of the second pad 20 described above is roughened. Second irregularities 22 are formed on the surface of the second pad 20 . The size of the second unevenness 22 in the portion exposed from the second opening 42 is smaller than the size of the second unevenness 22 in other portions. The arithmetic average roughness (Ra) of the upper surface of the second pad 20 exposed from the second opening 42 is 0.5 μm or less. The arithmetic average roughness (Ra) of the surface of the second pad 20 not exposed from the second opening 42 is greater than 0.5 μm.

A second metal film 60 is formed on the second pad 20 exposed through the second opening 42 . The second metal film 60 is an antioxidant film that prevents oxidation of the surface of the second pad 20 . The second metal film 60 is formed of a nickel film and a tin film on the nickel film. The metal (second metal) forming the second metal film 60 is different from the metal (first metal) forming the first metal film 50 . In another example, if the second metal film 60 is made of a metal different from the first metal film 50, the second metal film 60 can be a nickel film and a gold film on the nickel film, or a nickel film and a palladium film on the nickel film and a palladium film. It may be formed of a gold film on a film.

[Manufacturing Method of Printed Wiring Board 1 of Embodiment]
2A to 2H show a method for manufacturing the printed wiring board 1 of the embodiment. 2A-2H are cross-sectional views. FIG. 2A shows core substrate 2 , uppermost resin insulation layer 4 on upper surface 2 a of core substrate 2 , and lowermost resin insulation layer 6 on lower surface 2 b of core substrate 2 .

As shown in FIG. 2B, a plurality of first pads 10 are formed on uppermost resin insulation layer 4 . A plurality of second pads 20 are formed on lowermost resin insulation layer 6 . The first pad 10 and the second pad 20 are formed by the SAP (Semi Additive Process) method. The first pad 10 and the second pad 20 may be formed by a subtractive method.

The surfaces of the first pad 10 and the second pad 20 are roughened by wet etching. A first unevenness 12 is formed on the surface of the first pad 10 . A second unevenness 22 is formed on the surface of the second pad 20 . The arithmetic mean roughness (Ra) of the surface of the first pad 10 is greater than 0.5 μm. The arithmetic mean roughness (Ra) of the surface of the second pad 20 is also greater than 0.5 μm.

As shown in FIG. 2C, a first solder resist layer 30 having a plurality of first openings 32 is formed on the uppermost resin insulation layer 4 and the plurality of first pads 10 . The upper surface of the first pad 10 is exposed through the first opening 32 . The first solder resist layer 30 is formed by sequentially performing the steps of attaching a UV curable solder resist film, arranging a mask in the area where the first openings 32 are to be formed, exposing, and developing. Similarly, a second solder resist layer 40 having a plurality of second openings 42 is formed on the lowermost resin insulation layer 6 and the plurality of second pads 20 . The upper surface of the second pad 20 is exposed through the second opening 42 . The method of forming the second solder-resist layer 40 is the same as the method of forming the first solder-resist layer 30 .

At this point, as shown in FIG. 3A, the size of the first unevenness 12 on the surface of the first pad 10 exposed from the first opening 32 is large. The arithmetic average roughness (Ra) of the surface of the first pad 10 exposed from the first opening 32 is greater than 0.5 μm. Similarly, as shown in FIG. 3B, the size of the second unevenness 22 on the surface of the second pad 20 exposed from the second opening 42 is large. The arithmetic average roughness (Ra) of the surface of the second pad 20 exposed from the second opening 42 is greater than 0.5 μm.

After the first solder-resist layer 30 and the second solder-resist layer 40 are formed (FIG. 2C), the surface of the first pad 10 exposed from the first opening 32 and the surface of the second pad 20 exposed from the second opening 42 are removed. The surface is further etched. The etching of the surface of the first pad 10 exposed from the first opening 32 and the surface of the second pad 20 exposed from the second opening 42 are performed simultaneously.

The etching performed here is so-called soft etching. Soft etching is performed for roughness reduction. Therefore, the soft etching is performed under different conditions from the etching for forming the first unevenness 12 and the second unevenness 22 (etching for roughening, FIG. 2B). For example, the etchant, etching amount, etc. are different. Thereby, as shown in FIG. 4A, the size of the first unevenness 12 of the first pad 10 exposed from the first opening 32 is reduced. As shown in FIG. 4B, the size of the second unevenness 22 of the second pad 20 exposed from the second opening 42 is reduced. As a result, the arithmetic mean roughness (Ra) of the surface of the first pad 10 exposed from the first opening 32 is 0.5 μm or less. The arithmetic average roughness (Ra) of the surface of the second pad 20 exposed from the second opening 42 is 0.5 μm or less.

As shown in FIG. 2D, a first protective film 70 is formed on the first solder resist layer 30 and the first openings 32 . The first protective film 70 is a protective film made of resin. The first protective film 70 is, for example, a polyethylene terephthalate (PET) film. The first protective film 70 is closely adhered onto the first solder resist layer 30 and the first opening 32 via an adhesive material. The first protective film 70 adheres to the upper surface of the first solder resist layer 30 and the upper surface of the first pad 10 exposed from the first opening 32 via the adhesive material.

As shown in FIG. 2E, a second metal layer 60 is formed on the second pads 20 exposed through the second openings 42 . The second metal film 60 is formed by electrolytic plating. First, a nickel film is formed, and then a tin film is formed on the nickel film, thereby forming the second metal film 60 . On the other hand, no electrolytic plating film is formed on the first pad 10 covered with the first protective film 70 . Alternatively, the second metal film 60 may be formed of a different metal than the first metal film 50 (FIG. 1), such as a nickel film and a gold film on the nickel film, or a nickel film and a palladium film on the nickel film. It may be formed of a gold film on a membrane and a palladium membrane.

As shown in FIG. 2F, the first protective film 70 is removed. As described above, the size of the first unevenness 12 exposed from the first opening 32 is small (FIG. 4A). The arithmetic average roughness (Ra) of the surface of first pad 10 exposed from first opening 32 is 0.5 μm or less. Therefore, it is possible to prevent the adhesive material from remaining on the surface of the first pad 10 when the first protective film 70 is removed. No adhesive material adheres to the surface of the first pad 10 exposed from the first opening 32 .

As shown in FIG. 2G, a second protective film 80 is formed on the second solder resist layer 40 and the second openings 42 . The second protective film 80 is a protective film made of resin. The second protective film 80 is a polyethylene terephthalate (PET) film, for example. The second protective film 80 is closely adhered onto the second solder resist layer 40 and the second opening 42 via an adhesive material. The second protective film 80 adheres to the upper surface of the second solder resist layer 40 and the upper surface of the second metal film 60 exposed from the second opening 42 via the adhesive material.

As shown in FIG. 2H, a first metal layer 50 is formed on the first pads 10 exposed through the first openings 32 . The first metal film 50 is formed by electrolytic plating. First, a nickel film is formed, and then a gold film is formed on the nickel film, thereby forming the first metal film 50 . On the other hand, no electrolytic plating film is formed on the second metal film 60 covered with the first protective film 70 . Alternatively, if the first metal film 50 is formed of a different metal than the second metal film 60, the nickel film and the tin film on the nickel film, or the nickel film and the palladium film on the nickel film and the palladium film. It may be formed of a gold film on top. As described above, no adhesive material adheres to the surface of the first pad 10 exposed from the first opening 32 . Therefore, when the first metal film 50 is formed, high adhesion between the upper surface of the first pad 10 and the first metal film 50 is realized.

After that, the second protective film 80 is removed. A printed wiring board 1 (FIG. 1) of the embodiment is obtained.

In the manufacturing method of the embodiment, the first protective film 70 is formed on the first solder resist layer 30 and the first openings 32 after the size of the first unevenness 12 exposed from the first openings 32 is reduced. Therefore, even if the first protective film 70 is subsequently removed, the adhesive material is prevented from remaining on the surface of the first pad 10 . Therefore, when the first metal film 50 exposed from the first opening 32 is formed, high adhesion between the upper surface of the first pad 10 and the first metal film 50 is realized. According to the manufacturing method of the embodiment, printed wiring board 1 with high connection reliability is provided.

[First modification of the embodiment]
When the embodiment and the first modification of the embodiment are compared, the order in which first protective film 70 and second protective film 80 are formed in the manufacturing process of printed wiring board 1 is different. In the first modified example, the surface of the first pad 10 exposed through the first opening 32 and the surface of the second pad 20 exposed through the second opening 42 are soft-etched at the same time, and then the second solder resist layer 40 is first etched. A second protective film 80 is formed over the second opening 42 . The second protective film 80 adheres to the upper surface of the second solder resist layer 40 and the upper surface of the second pad 20 exposed through the second opening 42 via the adhesive material.

A first metal film 50 is then formed on the first pad 10 exposed through the first opening 32 . The second protective film 80 is removed. A first protective film 70 is formed on the first solder resist layer 30 and the first openings 32 . The first protective film 70 adheres to the upper surface of the first solder resist layer 30 and the upper surface of the first metal film 50 exposed from the first opening 32 via an adhesive material. A second metal layer 60 is formed on the second pad 20 exposed through the second opening 42 . The first protective film 70 is removed. A printed wiring board 1 (FIG. 1) of the embodiment is obtained.

In the manufacturing method of the first modified example, the second protective film 80 is formed on the second solder resist layer 40 and the second openings 42 after the size of the second unevenness 22 exposed from the second openings 42 is reduced. . Therefore, even if the second protective film 80 is subsequently removed, the adhesive material is prevented from remaining on the surface of the second pad 20 . Therefore, when the second metal film 60 exposed from the second opening 42 is formed, high adhesion between the upper surface of the second pad 20 and the second metal film 60 is realized. A printed wiring board 1 with high connection reliability is provided.

[Second modification of the embodiment]
When the embodiment and the second modified example of the embodiment are compared, the timing of etching the surface of the first pad 10 exposed through the first opening 32 and the etching of the surface of the second pad 20 exposed through the second opening 42 are different. different. In the second modified example, after the first solder-resist layer 30 and the second solder-resist layer 40 are formed (FIG. 2C), only the surface of the first pad 10 exposed from the first opening 32 is further etched (soft etching). ) is done. At this time, the surface of the second pad 20 exposed from the second opening 42 is not etched at the same time as the surface of the first pad 10 exposed from the first opening 32 . The surface of the second pad 20 exposed through the second opening 42 may be protected by any protective film. Although the size of the first unevenness 12 exposed from the first opening 32 decreases (FIG. 4A), the size of the second unevenness 22 exposed from the second opening 42 remains large (FIG. 3B).

After that, a first protective film 70 is formed on the first solder resist layer 30 and the first openings 32 (FIG. 2D). After the first protective film 70 is formed, the surface of the second pad 20 exposed from the second opening 42 is further etched (soft etched). Since the first pad 10 exposed through the first opening 32 is covered with the first protective film 70, only the surface of the second pad 20 exposed through the second opening 42 is etched (soft-etched). The size of the second unevenness 22 exposed from the second opening 42 is reduced (FIG. 4B).

Subsequent steps are common to the embodiment. A second metal layer 60 is formed on the second pad 20 exposed through the second opening 42 (FIG. 2E). The first protective film 70 is removed (FIG. 2F). A second protective film 80 is formed (FIG. 2G). A first metal film 50 is formed (FIG. 2H). The second protective film 80 is removed. A printed wiring board 1 (FIG. 1) is obtained.

[Another example of the second modified example]
Comparing the second modified example and another example of the second modified example, the order of etching the first pad 10 exposed from the first opening 32 and the etching the second pad 20 exposed from the second opening 42 is different. In another example of the second modification, after the first solder-resist layer 30 and the second solder-resist layer 40 are formed (FIG. 2C), only the surfaces of the second pads 20 exposed from the second openings 42 are further etched. (soft etching). At this time, the surface of the first pad 10 exposed from the first opening 32 is not etched at the same time as the surface of the second pad 20 exposed from the second opening 42 . The surface of the first pad 10 exposed through the first opening 32 may be protected by any protective film. Although the size of the second unevenness 22 exposed from the second opening 42 becomes smaller (FIG. 4B), the size of the first unevenness 12 exposed from the first opening 32 remains large (FIG. 3A).

After that, a second protective film 80 is formed on the second solder resist layer 40 and the second openings 42 . After the second protective film 80 is formed, the surface of the first pad 10 exposed from the first opening 32 is further etched (soft etched). Since the second pad 20 exposed through the second opening 42 is covered with the second protective film 80, only the surface of the first pad 10 exposed through the first opening 32 is etched (soft-etched). The size of the first unevenness 12 exposed from the first opening 32 is reduced (FIG. 4A).

Subsequent steps are in common with the first modified example described above. A first metal layer 50 is formed on the first pad 10 exposed through the first opening 32 . The second protective film 80 is removed. A first protective film 70 is formed. A second metal film 60 is formed. The first protective film 70 is removed. A printed wiring board 1 (FIG. 1) is obtained.

[Third modified example of the embodiment]
The third modified example of the embodiment and other embodiments (embodiment, first modified example, second modified example, another example of the second modified example) are substantially the same. The points of difference are shown below. In a third modification, the first metal film 50 and the second metal film 60 are made of the same metal.

1: Printed wiring board 2: Core substrate 2a: Top surface 2b: Bottom surface 4: Resin insulation layer 6: Resin insulation layer 10: First pad 12: First unevenness 20: Second pad 22: Second unevenness 30: First solder Resist layer 32 : First opening 40 : Second solder resist layer 42 : Second opening 50 : First metal film 60 : Second metal film 70 : First protective film 80 : Second protective film

Claims (9)

forming an uppermost resin insulation layer;
forming a first pad for mounting an electronic component on the uppermost resin insulation layer;
forming a first unevenness on the surface of the first pad;
forming a first solder resist layer having a first opening for exposing the first pad on the uppermost resin insulation layer and the first pad;
making the arithmetic mean roughness (Ra) of the upper surface of the first pad exposed from the first opening smaller than 0.5 μm by reducing the size of the first unevenness exposed from the first opening;
forming a first protective film on the first solder resist layer and the first opening after reducing the size of the first unevenness;
forming a lowermost resin insulation layer;
forming a second pad for connection with a motherboard on the lowermost resin insulation layer;
forming second unevenness on the surface of the second pad;
forming a second solder resist layer having a second opening for exposing the second pad on the lowermost resin insulation layer and the second pad;
forming a second metal film on the second pad exposed from the second opening after forming the first protective film;
and removing the first protective film after forming the second metal film. 2. The method of manufacturing a printed wiring board according to claim 1, further comprising reducing the size of the second unevenness exposed from the second opening, thereby reducing the size of the upper surface of the second pad exposed from the second opening. making the average roughness (Ra) 0.5 μm or less; and forming a second protective film on the second solder resist layer and the second opening after reducing the size of the second unevenness. forming a first metal film on the first pad exposed from the first opening after forming the second protective film; forming the first metal film and then forming the second metal film; and removing the overcoat. 3. The method of manufacturing a printed wiring board according to claim 2, wherein the first metal forming the first metal film is different from the second metal forming the second metal film. 3. The method of manufacturing a printed wiring board according to claim 2, wherein the first metal film comprises a nickel film and a gold film over the nickel film, a nickel film and a tin film over the nickel film, or a nickel film. The second metal film is formed of a palladium film on the nickel film and a gold film on the palladium film, and the second metal film is the nickel film and the gold film on the nickel film, or the nickel film and the tin film on the nickel film. film, or a nickel film, a palladium film on the nickel film, and a gold film on the palladium film. 3. The method of manufacturing a printed wiring board according to claim 2, wherein forming the second protective film is performed after removing the first protective film. 3. The method of manufacturing a printed wiring board according to claim 2, wherein forming the first protective film is performed after removing the second protective film. 3. The method of manufacturing a printed wiring board according to claim 2, wherein reducing the size of said second unevenness is performed after forming said first protective film. 3. The method of manufacturing a printed wiring board according to claim 2, wherein reducing the size of said first unevenness is performed after forming said second protective film. 2. The method of manufacturing a printed wiring board according to claim 2, wherein reducing the size of said first unevenness and reducing the size of said second unevenness are performed at the same time.

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