JP2024073648A - Wiring Board - Google Patents

Abstract

To provide a wiring board in which the conduction of adjacent connection parts can be suppressed.SOLUTION: A wiring board 1 includes a base material 2 having a first surface 2a and a second surface 2b opposite to the first surface, and a wire 3b including one or more layers and insulating layers 4a and 4b including one or more layers that are disposed on the first surface side of the base material. The wire including one or more layers includes at least an outermost wire 13 existing the farthest from the base material. The insulating layer including one or more layers includes at least an outermost insulating layer 14 that is disposed on a surface opposite to a surface of the outermost wire on the base material side and that includes opening parts 5a and 5b existing on the outermost wire. The wiring board further includes a connection part 8 that is disposed in the opening part of the outermost insulating layer and electrically connected to the outermost wire. The opening part of the outermost insulating layer has a tapered shape whose area of the horizontal section decreases from a surface of the outermost insulating layer on the side opposite to the outermost wire side toward the surface on the outermost wire side. The inclination angle of the side surface of the opening part of the outermost insulating layer is 10 degrees or more and 70 degrees or less. A pitch P of the connection part is 50 μm or less.SELECTED DRAWING: Figure 1

Description

This disclosure relates to a wiring board.

The mainstream method for mounting electronic components is to surface mount the electronic components on a wiring board (see, for example, Patent Documents 1 to 3).

In recent years, with the miniaturization and high functionality of electronic devices, technological developments are underway for the wiring boards on which electronic components are mounted, to make them more multi-layered, denser, and faster. This has created a demand for narrower pitches, which reduce the distance (pitch) between connections on wiring boards. Connections are also called pads or terminals.

JP 2018-22894 A JP 2017-63226 A JP 2017-220659 A

However, if the pitch of the connections is narrow, there is a problem that adjacent connections may become conductive due to the solder.

The present disclosure is an invention made in consideration of the above problems, and its main objective is to provide a wiring board that can suppress electrical continuity between adjacent connections.

In narrow-pitch wiring boards, a known cause of short circuits due to solder is, for example, solder on adjacent connections coming into contact, known as a solder bridge. However, short circuits may occur even if a solder bridge does not occur. The inventors of the present disclosure have conducted intensive research to solve the above problem and have found that when mounting electronic components on a wiring board using solder, the solder or flux penetrates into the interface between the connection and the insulating layer, causing electrical conduction between adjacent connections. They have also found that by controlling the shape of the opening in the insulating layer of the wiring board and the shape of the wiring, it is possible to control the direction in which the solder or flux penetrates into the interface between the connection and the insulating layer, thereby preventing electrical conduction between adjacent connections. The present disclosure has been completed based on the above findings.

That is, the present disclosure provides a wiring board having a substrate having a first surface and a second surface opposed to the first surface, and one or more layers of wiring and one or more insulating layers arranged on the first surface side of the substrate, the one or more layers of wiring having at least an outermost wiring located farthest from the substrate, the one or more insulating layers having at least an outermost insulating layer arranged on the surface side opposite the substrate side of the outermost wiring and having an opening located on the outermost wiring, the wiring board further having a connection portion arranged in the opening portion of the outermost insulating layer and electrically connected to the outermost wiring, the opening portion of the outermost insulating layer having a tapered shape in which the area of the horizontal cross section decreases from the surface opposite the surface of the outermost insulating layer on the outermost wiring side toward the surface on the outermost wiring side, the inclination angle of the side of the opening portion of the outermost insulating layer is 10 degrees or more and 70 degrees or less, and the pitch of the connection portion is 50 μm or less.

According to the present disclosure, the opening of the outermost insulating layer has the above-mentioned tapered shape, and the inclination angle of the side of the opening of the outermost insulating layer is within a predetermined range. Therefore, even if solder or flux penetrates into the interface between the connection portion and the outermost insulating layer when mounting an electronic component on the wiring board of the present disclosure using solder, the direction in which the solder or flux penetrates can be controlled, and it is possible to prevent adjacent connection portions from becoming conductive. Therefore, even with a narrow pitch, short circuits can be prevented.

In the present disclosure, it is preferable that the outermost wiring has a concave shape in which the surface on the side of the connection part within the opening of the outermost insulating layer is concave. By having the outermost wiring have the concave shape, it is possible to further suppress electrical conduction between adjacent connection parts when mounting electronic components on the wiring board of the present disclosure using solder.

The present disclosure also provides a wiring board having a substrate having a first surface and a second surface opposing the first surface, and one or more layers of wiring and one or more insulating layers disposed on the first surface side of the substrate, wherein the one or more layers of wiring have at least an outermost wiring located farthest from the substrate, the one or more insulating layers have at least an outermost insulating layer disposed on a surface side opposite the substrate side of the outermost wiring and having an opening located on the outermost wiring, the wiring board further has a connection portion disposed in the opening of the outermost insulating layer and electrically connected to the outermost wiring, the outermost wiring has a concave shape with a surface on the connection portion side within the opening of the outermost insulating layer being concave, and the pitch of the connection portion is 50 μm or less.

According to the present disclosure, by having the outermost wiring have the above-mentioned concave shape, even if solder or flux penetrates into the interface between the connection part and the outermost insulating layer when mounting an electronic component on the wiring board of the present disclosure using solder, the direction in which the solder or flux penetrates can be controlled, and it is possible to prevent adjacent connection parts from becoming conductive. Therefore, even with a narrow pitch, short circuits can be prevented.

In the present disclosure, it is preferable that the height of the connection portion protruding from the surface of the outermost insulating layer opposite the surface on the outermost wiring side is 3 μm or less. This disclosure is useful when the height of the connection portion is within the above range.

In the present disclosure, it is preferable that the outermost insulating layer contains a cured product of a photosensitive resin composition. This is because an outermost insulating layer having an opening of a desired shape can be easily formed by photolithography.

The present disclosure has the effect of suppressing electrical continuity between adjacent connections.

1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure. 1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure. 1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure. 1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure. 1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure. 1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure. 1 is a schematic cross-sectional view illustrating a wiring board according to the present disclosure.

Below, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure can be implemented in many different forms, and should not be interpreted as being limited to the description of the embodiment exemplified below. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual form, but these are merely examples and do not limit the interpretation of the present disclosure. In this specification and each figure, elements similar to those described above with respect to the previous figures are given the same reference numerals, and detailed explanations may be omitted as appropriate.

In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" is used, unless otherwise specified, to include both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component with another component interposed between them. In addition, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface side" or "on the surface" is used, unless otherwise specified, to include both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component with another component interposed between them.

The wiring board of the present disclosure will be described in detail below. The wiring board of the present disclosure has two embodiments. Each embodiment will be described below.

I. First embodiment A first embodiment of the wiring board of the present disclosure is a wiring board having a substrate having a first surface and a second surface opposite to the first surface, and one or more layers of wiring and one or more insulating layers arranged on the first surface side of the substrate, wherein the one or more layers of wiring have at least an outermost wiring located farthest from the substrate, the one or more insulating layers are arranged on the surface side opposite to the substrate side of the outermost wiring, and have at least an outermost insulating layer having an opening located on the outermost wiring, the wiring board further has a connection portion arranged in the opening of the outermost insulating layer and electrically connected to the outermost wiring, the opening of the outermost insulating layer has a tapered shape in which the area of the horizontal cross section decreases from the surface opposite to the surface of the outermost wiring side of the outermost insulating layer toward the surface of the outermost wiring side, the inclination angle of the side of the opening of the outermost insulating layer is 10 degrees or more and 70 degrees or less, and the pitch of the connection portion is 50 μm or less.

The wiring board of this embodiment will be described with reference to the drawings.
1 is a schematic cross-sectional view showing an example of the wiring board of this embodiment. As shown in FIG. 1, the wiring board 1 of this embodiment has a base material 2 having a first surface 2a and a second surface 2b facing the first surface 2a, and one or more layers of wiring 3a, 3b and one or more insulating layers 4a, 4b arranged on the first surface 2a side of the base material 1. The one or more layers of wiring 3a, 3b have at least an outermost wiring 13 (3b) located farthest from the base material 2, and the one or more insulating layers 4a, 4b have at least an outermost insulating layer 14 (4b) arranged on the surface opposite to the surface of the outermost wiring 13 (3b) on the base material 2 side and having an opening 5b located on the outermost wiring 13 (3b), and the wiring board 1 further has a connection part 8 arranged in the opening 5b of the outermost insulating layer 14 (4b) and electrically connected to the outermost wiring 13 (3b). The opening 5b of the outermost insulating layer 14 (4b) has a tapered shape in which the area of the horizontal cross section decreases from the surface of the outermost insulating layer 14 (4b) opposite the surface on the outermost wiring 13 (3b) side toward the surface on the outermost wiring 13 (3b) side, and as shown in Fig. 2, the inclination angle θ of the side surface of the opening 5b of the outermost insulating layer 14 (4b) is within a predetermined range. Also, the pitch P of the connection parts 8 is within a predetermined range. Note that Fig. 2 is an enlarged view of Fig. 1.

The wiring board of this embodiment may have one or more layers of wiring and one or more insulating layers arranged on the first surface side of the substrate, and may have one layer of wiring and one insulating layer (not shown), or may have two layers of wiring 3a, 3b and two insulating layers 4a, 4b as shown in FIG. 1, or may have three or more layers of wiring and three or more insulating layers (not shown).

The insulating layer has an opening for placing wiring or a connection part. When the wiring board of this embodiment has two or more insulating layers, each of the two or more insulating layers has an opening, but it is sufficient that the opening of the outermost insulating layer has the above-mentioned tapered shape, and the openings of the insulating layers other than the outermost insulating layer may or may not have the above-mentioned tapered shape. For example, in FIG. 1, the two insulating layers 4a and 4b have openings 5a and 5b, respectively, but the opening 5b of the outermost insulating layer 14 (4b) has the above-mentioned tapered shape, while the opening 5a of the insulating layer 4a other than the outermost insulating layer 14 (4b) does not have the above-mentioned tapered shape.

In addition, the inclination angle of the side of the opening of the outermost insulating layer needs only to be within a predetermined range, and the inclination angle of the opening of the insulating layer other than the outermost insulating layer is not particularly limited. For example, in FIG. 1, the inclination angle of the opening 5b of the outermost insulating layer 14 (4b) is within a predetermined range, whereas the inclination angle of the opening 5a of the insulating layer 4a other than the outermost insulating layer 14 (4b) is not within a predetermined range.

In this embodiment, as shown in FIG. 1, the connection portion 8 may have a first connection layer 6 disposed in the opening 5b of the outermost insulating layer 14 (4b) and a second connection layer 7 disposed on the first connection layer 6.

According to this embodiment, the opening in the outermost insulating layer has a tapered shape in which the area of the horizontal cross section decreases from the surface opposite the surface on the outermost wiring side of the outermost insulating layer toward the surface on the outermost wiring side, and the inclination angle of the side of the opening in the outermost insulating layer is within a predetermined range, so that when mounting electronic components on the wiring board of this embodiment using solder, it is possible to prevent adjacent connections from becoming conductive due to solder or flux. The reason for this is unclear, but is presumed to be as follows.

That is, for example, as shown in FIG. 2, when an electronic component is mounted on the wiring board of this embodiment using solder, when the solder or flux penetrates the interface between the connection part 8 and the outermost insulating layer 14 and reaches the surface of the outermost wiring 13 (arrow a in FIG. 2), it is divided into two cases: when it penetrates the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 2) and when it penetrates the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 2). At this time, if the opening 5b of the outermost insulating layer 14 has the above-mentioned tapered shape and the inclination angle θ of the side of the opening 5b of the outermost insulating layer 14 is within a predetermined range, it is presumed that the solder or flux will easily penetrate the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 2) and will not easily penetrate the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 2). If solder or flux penetrates the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 2), it will cause electrical conduction with the adjacent connection parts. On the other hand, even if solder or flux penetrates the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 2), it is presumed that electrical conduction with the adjacent connection parts can be suppressed because there is a distance to the adjacent connection parts. Thus, in this embodiment, the opening of the outermost insulating layer has the above-mentioned tapered shape, and the inclination angle of the side of the opening of the outermost insulating layer is within a predetermined range, so that even if solder or flux penetrates into the interface between the connection part and the outermost insulating layer when mounting an electronic component on the wiring board of this embodiment using solder, it is considered that the direction in which the solder or flux penetrates can be controlled. Therefore, it is possible to suppress electrical conduction between adjacent connection parts. Therefore, even with a narrow pitch, electrical connection can be made without causing a short circuit.

Conventionally, lasers have been used primarily to form openings in the outermost insulating layer of wiring boards for locating connection parts. Lasers have excellent directivity (linearity), so when openings are formed in the outermost insulating layer with a laser, the opening in the outermost insulating layer does not have a tapered shape, and the inclination angle of the side of the opening in the outermost insulating layer is 90 degrees. Therefore, in this case, when mounting electronic components on a wiring board using solder, if solder or flux seeps into the interface between the connection part and the outermost insulating layer, the direction in which the solder or flux seeps in cannot be controlled, and it is thought that adjacent connection parts will become conductive.

Below, the wiring board of this embodiment will be explained in detail for each configuration.

1. Insulating Layer The insulating layer in this embodiment is disposed on the first surface side of the base material and is a member having insulating properties. The wiring board in this embodiment has one or more insulating layers.

The insulating layer may be one or more layers, and may be one layer or two or more layers.

The one or more insulating layers are arranged on the side opposite the substrate side of the outermost wiring described below, and have at least an outermost insulating layer having an opening located above the outermost wiring.

The opening in the outermost insulating layer has a tapered shape in which the area of the horizontal cross section decreases from the surface opposite the surface of the outermost insulating layer facing the outermost wiring toward the surface facing the outermost wiring.

When the wiring board of this embodiment has two or more insulating layers, it is sufficient that the opening of the outermost insulating layer has the above-mentioned tapered shape, and the openings of insulating layers other than the outermost insulating layer may or may not have the above-mentioned tapered shape.

The inclination angle of the side of the opening in the outermost insulating layer is 10 degrees or more, preferably 12 degrees or more, and particularly preferably 15 degrees or more. The inclination angle is 70 degrees or less, and particularly preferably 60 degrees or less. By having the inclination angle within the above range, when mounting electronic components on the wiring board of this embodiment using solder, the direction in which the solder or flux penetrates can be controlled, and electrical continuity between adjacent connections can be suppressed.

Here, the "inclination angle of the side of the opening in the outermost insulating layer" refers to the smaller angle between the side of the opening in the outermost insulating layer and the surface on the connection side of the outermost wiring. For example, in Figure 2, it refers to the angle indicated by θ.

When the side of the opening of the outermost insulating layer is curved rather than flat, the "tilt angle of the side of the opening of the outermost insulating layer" refers to the smaller angle θ between the tangent 5 at the contact point between the center line of the thickness d of the outermost insulating layer 14 located on the outermost wiring 13 in the opening 5b of the outermost insulating layer 14 and the side of the opening 5b of the outermost insulating layer 14, and the surface of the outermost wiring 13 on the connection part 8 side, as shown in FIG. 3, for example.

The inclination angle of the side of the opening in the outermost insulating layer can be measured, for example, by observing a vertical cross section using a scanning electron microscope (SEM).

When the wiring board of this embodiment has two or more insulating layers, the inclination angle of the side of the opening of the outermost insulating layer may be within a predetermined range, and the inclination angle of the side of the opening of insulating layers other than the outermost insulating layer is not particularly limited.

The material for the insulating layer is not particularly limited as long as it is an insulating material, and insulating materials that are generally used for insulating layers of wiring boards can be used, and both organic and inorganic materials can be used.

The material of the outermost insulating layer is not particularly limited as long as it is an insulating material capable of forming an opening having the above-mentioned tapered shape. In particular, the material of the outermost insulating layer is preferably a photosensitive resin. In other words, the outermost insulating layer preferably contains a cured product of a photosensitive resin composition. This is because the opening having the above-mentioned tapered shape can be easily formed by photolithography.

The thickness of the insulating layer can be the same as that of a typical wiring board.

As a method for forming the insulating layer, a general method for forming an insulating layer can be used, and is appropriately selected depending on the material of the insulating layer, etc. Also, as a method for forming an opening in the insulating layer, a general method for forming an opening can be used, and is appropriately selected depending on the material of the insulating layer, etc. Examples of methods for forming an opening include laser irradiation, etching such as plasma etching and wet etching, mechanical processing methods such as sandblasting and ultrasonic drilling, and photolithography. Among them, the method for forming the outermost insulating layer is preferably photolithography. This is because photolithography can easily form an opening having the above-mentioned tapered shape.

2. Wiring The wiring in this embodiment is disposed on the first surface side of the base material and is a conductive member.
The wiring board of this embodiment has one or more layers of wiring.

The wiring may be one or more layers, and may be one layer or two or more layers.

The wiring in one or more layers has at least an outermost wiring located furthest from the substrate.

As shown in FIG. 4, for example, the outermost wiring 13 preferably has a concave shape with a surface on the connection part 8 side within the opening 5b of the outermost insulating layer 14 (4b). By having the outermost wiring have the above-mentioned concave shape, it is possible to further prevent adjacent connection parts from becoming conductive due to solder or flux when mounting electronic components on the wiring board of this embodiment using solder. The reason for this is not clear, but is presumed to be as follows.

That is, as described above, for example, as shown in FIG. 5, when an electronic component is mounted on the wiring board of this embodiment using solder, the solder or flux penetrates into the interface between the connection part 8 and the outermost insulating layer 14 and reaches the surface of the outermost wiring 13 (arrow a in FIG. 5), and then it is divided into two cases: when it penetrates into the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 5) and when it penetrates into the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 5). At this time, if the outermost wiring 13 has the above-mentioned concave shape, it is presumed that the solder or flux is more likely to penetrate into the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 5), and is less likely to penetrate into the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 5). In this way, it is considered that by having the outermost wiring have the above-mentioned concave shape, even if the solder or flux penetrates into the interface between the connection part and the outermost insulating layer when an electronic component is mounted on the wiring board of this embodiment using solder, the direction in which the solder or flux penetrates can be controlled. This makes it possible to prevent adjacent connection parts from becoming conductive. Therefore, even with a narrow pitch, electrical connections can be made without causing short circuits.

The cross-sectional shape of the concave recess may be, for example, a semi-elliptical shape.

The depth of the concave recess is not particularly limited as long as it is deep enough to obtain the above-mentioned effect, but can be, for example, 0.5 μm to 2.0 μm, and preferably 0.5 μm to 1.5 μm. The depth of the concave recess refers to the maximum depth of the concave recess. By having the depth of the concave recess within the above range, it is possible to control the direction in which solder or flux enters when mounting electronic components on the wiring board of this embodiment using solder, and to prevent adjacent connections from becoming conductive.

The depth of the recesses can be measured by observation using a scanning electron microscope (SEM).

The depth of the recessed portion of the above-mentioned concave shape can also be measured by a stylus method in which a stylus is used to trace the surface of the outermost insulating layer on the connection side inside the opening to detect unevenness and calculate the thickness. Specifically, it can be measured using a stylus thickness gauge P-15 manufactured by KLA Tencor Corporation under conditions of a stylus pressure of 5 mg and a scanning speed of 50 μm/sec. The average value of the measurement results at multiple points may also be used.

When the wiring board of this embodiment has two or more layers of wiring, it is sufficient that the outermost wiring has the above-mentioned concave shape, and wiring other than the outermost wiring may or may not have the above-mentioned concave shape.

The material for the wiring is not particularly limited as long as it is a material having electrical conductivity, and conductive materials used for general wiring can be used. Examples of conductive materials that can be used include metals such as copper, molybdenum, titanium, tungsten, tantalum, aluminum, gold, silver, nickel, and palladium, alloys containing at least one selected from these metals, and conductive oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO). By using copper or aluminum, which have high electrical conductivity, it is possible to suppress an increase in resistance. In addition, by using copper, which has a relatively low hardness, it is possible to provide a wiring board that can establish electrical connections with higher reliability.

The wiring may be single-layered or multi-layered with multiple layers stacked on top of each other.

The thickness of the wiring can be the same as that of a typical wiring board. The thickness of the wiring can be, for example, 0.05 μm or more and 20 μm or less, or 0.1 μm or more and 15 μm or less, or 0.2 μm or more and 10 μm or less. This allows sufficient conductivity to be obtained.

The wiring can be formed using any common wiring formation method, such as CVD, sputtering, plating, etc.

In addition, examples of methods for forming the above-mentioned concave shape in the outermost wiring include etching. If etching is performed when forming the connection portion described below, the above-mentioned concave shape can be formed in the outermost wiring during the etching.

3. Connection Portion The connection portion in this embodiment is a member that is disposed in the opening of the outermost insulating layer and is electrically connected to the outermost wiring.

The pitch of the connection parts is 50 μm or less, and can be 10 μm or more and 50 μm or less, and is preferably 15 μm or more and 45 μm or less. In this embodiment, the pitch of the connection parts is in the above range, and even with a narrow pitch, electrical connection can be made without causing a short circuit.

Here, the pitch can be measured, for example, by observation using an optical microscope or a scanning electron microscope (SEM).

The material of the connection part is not particularly limited as long as it is a conductive material, and can be the same as the material of the wiring described above.

The connection part may be a single layer or a multi-layer structure in which multiple layers are stacked.

The thickness of the connection portion is not particularly limited and is set appropriately according to the shape of the terminal portion of the electronic component to be mounted on the wiring board of this embodiment, but can be, for example, the same as the thickness of the wiring.

The connection portion 8 may protrude from the surface of the outermost insulating layer 14 opposite the surface on the outermost wiring 13 side, as shown in, for example, Figures 1 and 2. In this case, the height of the connection portion protruding from the surface of the outermost insulating layer opposite the surface on the outermost wiring side is preferably 3 μm or less. For example, in the CVD method, sputtering method, plating method, etc., film growth is usually isotropic. Therefore, for example, as shown in Figure 2, the height H1 of the connection portion 8 protruding from the surface opposite the surface on the outermost wiring 13 side of the outermost insulating layer 14 is approximately the same as the length H2 of the portion where the connection portion 8 and the outermost insulating layer 14 overlap on the surface opposite the surface on the outermost wiring 13 side of the outermost insulating layer 14. If the length H2 of the overlapping portion of the connection portion 8 and the outermost insulating layer 14 on the surface of the outermost insulating layer 14 opposite the surface on the outermost wiring 13 side is 3 μm or less, it is believed that when electronic components are mounted on the wiring board of this embodiment using solder, solder or flux will easily penetrate into the interface between the connection portion 8 and the outermost insulating layer 14. Therefore, it is preferable that the height of the connection portion protruding from the surface of the outermost insulating layer opposite the surface on the outermost wiring side is 3 μm or less.

The method for forming the connection portion can be the same as the method for forming the wiring described above.

4. Substrate The substrate in this embodiment has a first surface and a second surface opposite to the first surface, and is a member that supports the insulating layer, wiring, and connection portion.

The substrate is not particularly limited as long as it has insulating properties, and insulating substrates generally used for wiring boards can be used. Examples include glass substrates, glass epoxy substrates, glass composite substrates, ceramic substrates such as alumina substrates, fluororesin substrates, polyimide substrates, and paper phenol substrates.

As described below, when the wiring board of this embodiment has a second wiring that electrically connects the first surface and the second surface of the substrate, the substrate may or may not have a through hole. When the substrate has a through hole, the second wiring becomes a through wiring arranged in the through hole.

The diameter of the through hole can be appropriately selected depending on the application of the wiring board and is not particularly limited, but may be, for example, 10 μm or more and 200 μm or less, or 20 μm or more and 100 μm or less.

Methods for forming through holes include, for example, etching such as plasma etching or wet etching, laser irradiation, or mechanical processing such as sandblasting or ultrasonic drilling.

The thickness of the substrate is not particularly limited as long as it can support the insulating layer, wiring, and connection parts, and can be appropriately selected depending on the application of the wiring board. The thickness of the substrate can be, for example, 10 μm or more and 800 μm or less, or 100 μm or more and 600 μm or less, or 300 μm or more and 400 μm or less.

II. Second embodiment A second embodiment of the wiring board of the present disclosure is a wiring board having a base material having a first surface and a second surface opposite to the first surface, and one or more layers of wiring and one or more insulating layers arranged on the first surface side of the base material, wherein the one or more layers of wiring have at least an outermost wiring located farthest from the base material, the one or more insulating layers are arranged on the surface side opposite to the surface of the outermost wiring on the base material side, and have at least an outermost insulating layer having an opening located on the outermost wiring, the wiring board further has a connection portion arranged in the opening of the outermost insulating layer and electrically connected to the outermost wiring, the outermost wiring has a concave shape in which the surface on the connection portion side in the opening of the outermost insulating layer is concave, and the pitch of the connection portion is 50 μm or less.

Figure 6 is a schematic cross-sectional view showing an example of a wiring board of this embodiment. As shown in Figure 6, the wiring board 1 of this embodiment has a substrate 2 having a first surface 2a and a second surface 2b facing the first surface 2a, and one or more layers of wiring 3a, 3b and one or more insulating layers 4a, 4b arranged on the first surface 2a side of the substrate 1. The one or more layers of wiring 3a, 3b have at least an outermost wiring 13 (3b) located farthest from the substrate 2, and the one or more insulating layers 4a, 4b have at least an outermost insulating layer 14 (4b) arranged on the surface opposite to the substrate 2 side of the outermost wiring 13 (3b) and having an opening 5b located on the outermost wiring 13 (3b), and the wiring board 1 further has a connection portion 8 arranged in the opening 5b of the outermost insulating layer 14 (4b) and electrically connected to the outermost wiring 13 (3b). The outermost wiring 13 (3b) has a concave shape on the surface on the connection part 8 side within the opening 5b of the outermost insulating layer 14 (4b). In addition, the pitch P of the connection parts 8 is within a predetermined range.

The wiring board of this embodiment may have one or more layers of wiring and one or more insulating layers arranged on the first surface side of the substrate, and may have one layer of wiring and one insulating layer (not shown), or may have two layers of wiring 3a, 3b and two insulating layers 4a, 4b as shown in FIG. 6, or may have three or more layers of wiring and three or more insulating layers (not shown).

When the wiring board of this embodiment has two or more layers of wiring, it is sufficient that the outermost wiring has the above-mentioned concave shape, and wiring other than the outermost wiring may or may not have the above-mentioned concave shape. For example, in FIG. 6, the outermost wiring 13 (3b) has the above-mentioned concave shape, while wiring 3a other than the outermost wiring 13 (3b) does not have the above-mentioned concave shape.

In this embodiment, as shown in FIG. 6, the connection portion 8 may have a first connection layer 6 arranged in the opening 5b of the outermost insulating layer 14 (4b) and a second connection layer 7 arranged on the first connection layer 6.

According to this embodiment, the outermost wiring has a concave shape with a concave surface on the side of the upper connection part within the opening of the outermost insulating layer, so that when an electronic component is mounted on the wiring board of this embodiment using solder, it is possible to prevent adjacent connection parts from becoming conductive due to solder or flux. The reason for this is not clear, but it is presumed to be as follows.

That is, for example, as shown in FIG. 7, when an electronic component is mounted on the wiring board of this embodiment using solder, when the solder or flux penetrates into the interface between the connection part 8 and the outermost insulating layer 14 and reaches the surface of the outermost wiring 13 (arrow a in FIG. 7), it is divided into two cases: when it penetrates into the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 7) and when it penetrates into the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 7). At this time, if the outermost wiring 13 has the above-mentioned concave shape, it is presumed that the solder or flux is more likely to penetrate into the interface between the connection part 8 and the outermost wiring 13 (arrow b in FIG. 7) and is less likely to penetrate into the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 7). When the solder or flux penetrates into the interface between the outermost insulating layer 14 and the outermost wiring 13 (arrow c in FIG. 7), it becomes a cause of conduction with the adjacent connection part. On the other hand, even if solder or flux penetrates into the interface between the connection 8 and the outermost wiring 13 (arrow b in FIG. 7), it is presumed that since there is a distance to the adjacent connection, it is possible to prevent electrical continuity between the adjacent connection. In this embodiment, since the outermost wiring has the above-mentioned concave shape, it is believed that even if solder or flux penetrates into the interface between the connection and the outermost insulating layer when mounting an electronic component on the wiring board of this embodiment using solder, the direction in which the solder or flux penetrates can be controlled. Therefore, it is possible to prevent electrical continuity between adjacent connection parts. Therefore, even with a narrow pitch, electrical connection can be made without causing a short circuit.

Below, we will explain each configuration of the wiring board in this embodiment.

1. Insulating Layer The insulating layer in this embodiment is disposed on the first surface side of the base material and is a member having insulating properties. The wiring board in this embodiment has one or more insulating layers.

The insulating layer may be one or more layers, and may be one layer or two or more layers.

The one or more insulating layers are arranged on the side opposite the substrate side of the outermost wiring described below, and have at least an outermost insulating layer having an opening located above the outermost wiring.

The material, thickness, formation method, etc. of the insulating layer can be the same as that of the insulating layer in the first embodiment described above.

2. Wiring The wiring in this embodiment is disposed on the first surface side of the base material and is a conductive member.
The wiring board of this embodiment has one or more layers of wiring.

The wiring may be one or more layers, and may be one layer or two or more layers.

The wiring in one or more layers has at least an outermost wiring located furthest from the substrate.

The outermost wiring has a concave shape on the surface facing the connection part within the opening in the outermost insulating layer.

The cross-sectional shape, depth, etc. of the concave recess can be the same as that of the outermost wiring in the first embodiment.

When the wiring board of this embodiment has two or more layers of wiring, it is sufficient that the outermost wiring has the above-mentioned concave shape, and wiring other than the outermost wiring may or may not have the above-mentioned concave shape.

The wiring may be single-layered or multi-layered with multiple layers stacked on top of each other.

The material, thickness, and forming method of the wiring can be the same as that of the wiring in the first embodiment described above.

3. Connection Portion The connection portion in this embodiment is a member that is disposed in the opening of the outermost insulating layer and is electrically connected to the outermost wiring.
The connection portion may be the same as the connection portion in the first embodiment.

4. Substrate The substrate in this embodiment has a first surface and a second surface opposite to the first surface, and is a member that supports the insulating layer, wiring, and connection portion.
The substrate may be the same as that in the first embodiment.

This disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and anything that has substantially the same configuration as the technical ideas described in the claims of this disclosure and provides similar effects is included within the technical scope of this disclosure.

The following examples and comparative examples will explain this disclosure in more detail.

[Example 1]
(Formation of wiring and insulating layer)
A glass substrate (AN100, 300 mm x 400 mm, manufactured by AGC) was irradiated with ultraviolet light and washed. Then, the glass substrate was subjected to chromium sputtering and copper sputtering, and a resist pattern was formed thereon using a dry film resist (Sunfort AQ4038, manufactured by Asahi Kasei Electronics). Next, copper sulfate electrolytic plating (Top Lucina SF, manufactured by Okuno Pharmaceutical Co., Ltd.) was performed on the openings of the resist pattern to form a wiring layer with a thickness of 3 μm. Next, the dry film resist was peeled off with a sodium hydroxide solution at 50°C, and the exposed chromium layer and copper layer were removed with a chromium etching solution (Esclean S-24, manufactured by Sasaki Chemical Industry Co., Ltd.) and a copper etching solution (AD-331, manufactured by Meltec Co., Ltd.), respectively. This formed the wiring. Then, a photosensitive resist (Photoneece PW-1000, manufactured by Toray Industries, Inc.) was used to form an insulating layer with a thickness of 3 μm and an opening pitch of 45 μm so as to cover the wiring.

(Formation of connection part)
Next, electroless nickel plating was performed on the opening of the insulating layer to form a connection part. First, the surface of the wiring exposed in the opening of the insulating layer was degreased using an acid cleaner (ICP Clean S-135K, manufactured by Okuno Chemical Industries Co., Ltd.). Next, soft etching was performed by immersing for 5 seconds in a copper etching solution (AD-331, manufactured by Meltec Co., Ltd.) kept at 25°C. Next, Pd was applied to the surface of the wiring using an activator (ICP Accela, manufactured by Okuno Chemical Industries Co., Ltd.), and electroless nickel plating (ICP Nicoron GM-SE, manufactured by Okuno Chemical Industries Co., Ltd.) was performed to form a nickel-plated part. Then, electroless gold plating (Flash Gold NC, manufactured by Okuno Chemical Industries Co., Ltd.) was performed on the surface of the nickel-plated part to form a protective plating part with a thickness of 0.05 μm.
This resulted in a wiring board having connections, the pitch of which was 45 μm.

The vertical cross-section of the resulting wiring board was observed using a scanning electron microscope (SEM) to measure the inclination angle of the side of the opening in the insulating layer. The results are shown in Table 1.

[Examples 2 to 3 and Comparative Examples 1 to 2]
A wiring board was produced in the same manner as in Example 1, except that the insulating layer was formed so that the inclination angle of the side surface of the opening in the insulating layer was the angle shown in Table 1.

[Evaluation 1]
In the wiring boards of Examples 1 to 3 and Comparative Examples 1 and 2, solder paste was applied to adjacent unconnected connection parts, and the parts were held in a reflow furnace at 150°C for 2 minutes, and then at 210°C for 10 seconds, after which the presence or absence of conductivity between the adjacent connection parts was confirmed.

[Example 4]
(Formation of wiring and insulating layer)
A glass substrate (AN100, 300 mm x 400 mm, manufactured by AGC) was irradiated with ultraviolet light and washed. Then, the glass substrate was subjected to chromium sputtering and copper sputtering, and a resist pattern was formed thereon using a dry film resist (Sunfort AQ4038, manufactured by Asahi Kasei Electronics). Next, copper sulfate electrolytic plating (Top Lucina SF, manufactured by Okuno Pharmaceutical Co., Ltd.) was performed on the openings of the resist pattern to form a wiring layer with a thickness of 3 μm. Next, the dry film resist was peeled off with a sodium hydroxide solution at 50°C, and the exposed chromium layer and copper layer were removed with a chromium etching solution (Esclean S-24, manufactured by Sasaki Chemical Industry Co., Ltd.) and a copper etching solution (AD-331, manufactured by Meltec Co., Ltd.), respectively. This formed the wiring. Then, a photosensitive resist (Photoneece PW-1000, manufactured by Toray Industries, Inc.) was used to form an insulating layer with a thickness of 3 μm and an opening pitch of 45 μm so as to cover the wiring.

(Formation of connection part)
Next, electroless nickel plating was performed on the opening of the insulating layer to form a connection part. First, the surface of the wiring exposed to the opening of the insulating layer was degreased using an acid cleaner (ICP Clean S-135K, manufactured by Okuno Chemical Industries Co., Ltd.). Next, soft etching was performed by immersing for 60 seconds in a copper etching solution (AD-331, manufactured by Meltec Co., Ltd.) heated to 45°C. Next, Pd was applied to the surface of the wiring using an activator (ICP Accela, manufactured by Okuno Chemical Industries Co., Ltd.), and electroless nickel plating (ICP Nicoron GM-SE, manufactured by Okuno Chemical Industries Co., Ltd.) was performed to form a nickel-plated part. Then, electroless gold plating (Flash Gold NC, manufactured by Okuno Chemical Industries Co., Ltd.) was performed on the surface of the nickel-plated part to form a protective plating part with a thickness of 0.05 μm.
This resulted in a wiring board having connections, the pitch of which was 45 μm.

When the vertical cross section of the obtained wiring board was observed with a scanning electron microscope (SEM), the wiring had a concave shape with the surface on the connection side in the opening of the insulating layer being concave. In addition, the inclination angle of the side surface of the opening of the insulating layer and the depth of the concave shape were measured by observing the vertical cross section of the obtained wiring board with a scanning electron microscope (SEM).
The inclination angle of the side surface of the opening in the insulating layer was 90 degrees, and the depth of the recess in the recess shape was 1.2 μm.

[Evaluation 2]
In the wiring board of Example 4, solder paste was applied to adjacent unconnected connection parts, and the board was held in a reflow furnace at 150° C. for 2 minutes, and then held at 210° C. for 10 seconds, after which the presence or absence of conduction between the adjacent connection parts was confirmed. In the wiring board of Example 4, there was no conduction between the adjacent connection parts.

When the vertical cross section of the wiring board of Comparative Example 1 was observed using a scanning electron microscope (SEM), the wiring did not have a concave shape on the surface on the connection side within the opening of the insulating layer. In the wiring board of Comparative Example 1, as shown in Table 1 above, adjacent connection parts were conductive.

REFERENCE SIGNS LIST 1 wiring board 2 substrate 2a first surface of substrate 2b second surface of substrate 3a, 3b wiring 4a, 4b insulating layer 5a, 5b opening 6 first connection layer 7 second connection layer 8 connection portion 13 outermost wiring 14 outermost insulating layer P pitch of connection portion

Claims (1)

A wiring board having a base material having a first surface and a second surface opposite to the first surface, and one or more layers of wiring and one or more insulating layers disposed on the first surface side of the base material,
the one or more layers of wiring have at least an outermost wiring located farthest from the substrate, the one or more insulating layers have at least an outermost insulating layer disposed on a surface side opposite to a surface side of the outermost wiring facing the substrate, the outermost insulating layer having an opening located above the outermost wiring,
the wiring board further includes a connection portion disposed in an opening of the outermost insulating layer and electrically connected to the outermost wiring;
the opening in the outermost insulating layer has a tapered shape in which the area of a horizontal cross section decreases from a surface of the outermost insulating layer opposite to a surface on the outermost wiring side toward a surface on the outermost wiring side,
the inclination angle of the side surface of the opening in the outermost insulating layer is 10 degrees or more and 70 degrees or less;
A wiring board, wherein the pitch of the connection portions is 50 μm or less.

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