JP2003133714A - Printed-wiring board and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed-wiring board that can effectively inhibit the lifting of an electrode in the packaging of an electronic component and the generation of a soldering ball and a soldering bridge, and at the same time can easily and reliably perform flux washing, and to provide a method for manufacturing the printed-wiring board. SOLUTION: An electrode 2 that is as high as approximately 35 μm is formed on the surface of a substrate 1. Then, a first solder resist layer 3 is formed on the surface of the substrate 1 at a specific interval to the electrode 2, and further a second solder resist layer 4 is formed on the first solder resist layer 3. The gap between the first solder resist layer 3 and the electrode 2 is set to approximately 30 to 50 μm. The second solder resist layer 4 is formed so that the surface of the second solder resist layer 4 becomes nearly flat, and at the same time runs nearly in parallel to the surface of the substrate 1. The plane shape of the second solder resist layer 4 is set smaller than that of the first solder resist layer 3 below the second solder resist layer 4 by approximately 100 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and a method for manufacturing the same, more specifically,
The present invention relates to a printed wiring board in which electronic components are mounted by soldering, further sealed with a resin, and mounted again by soldering as a module, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, with the rapid development of multimedia products mainly composed of portable electronic devices, printed wiring boards for mounting electronic parts have become thinner and higher in density. Furthermore, with the miniaturization of electronic components, there is a demand for improvement in mounting reliability, such as prevention of solder balls and solder bridges that occur when electronic components are mounted.

One of the prior art methods for preventing solder balls and solder bridges that occur when electronic components are mounted is disclosed in Japanese Patent Laid-Open No. 11-298130.

4 to 6 are structural explanatory views showing a printed wiring board implemented by the method of the prior art disclosed in the publication and a mounting process of electronic parts using the printed wiring board. In these figures, 1 is a substrate, 2 is an electrode for connecting electronic parts,
5 is a metal plate for solder cream printing application, 6 is solder cream, 7 is solder after reflow soldering, 8 is electronic component, 9
Represents a solder resist layer, and 10 represents characters.

Explaining with reference to these figures, an electrode 2 made of copper foil is formed on the surface of a substrate 1 made of glass epoxy or the like, and a predetermined gap is formed between the electrode 2 and the electrode 2 of the substrate 1. A solder resist layer 9 is formed on the surface, and characters 10 are formed on the solder resist layer 9 (FIG. 4).

The electrode 2 is formed so that its height is lower than the total height of the solder resist layer 9 and the characters 10. The character 10 is formed so that its surface is substantially flat. Furthermore, the gap between the solder resist layer 9 and the electrode 2 is formed to 50 to 200 μm.

In this method, the gap between the electrode 2 and the solder resist 9 layer shown in FIG. 4 is provided at 50 to 200 μm, and the height of the electrode 2 is set to be higher than the height of the solder resist layer 9 and the character 10 combined. By lowering it, the molten solder cream flows down into the gap.

However, in high-density mounting, the electronic parts are downsized, and the mounting intervals of the electronic parts are narrow,
Further, the conductor pattern is also highly densified, and for example, the conductor pattern width is 50 μm and the conductor pattern interval is 50 μm. However, since the conductor pattern is also present in the vicinity of the electrode 2, if the solder cream melted at the electrode 2 overflows in the absence of the solder resist layer 9, a short circuit will occur between the conductor pattern and the conductor pattern.

In order to prevent such a short circuit, a solder resist layer 9 is required on the conductor pattern. Therefore, it is necessary to form the solder resist layer 9 also on the conductor pattern in the vicinity of the electrode 2, and in high-density mounting, the gap between the electrode 2 and the solder resist layer 9 needs to be less than 50 μm. However, when there is no gap between the electrode 2 and the solder resist layer 9, the solder resist layer 9
If the deviation occurs, the solder resist layer 9 may be formed on the electrode 2, which is not suitable.

Further, in this prior art, when the gap between the electrode 2 and the solder resist layer 9 is less than 50 μm, there is not a sufficient gap for the amount of the melted solder cream flowing down, and the solder cream overflows. And a solder bridge has occurred.

Further, a mounting method according to this conventional technique will be described.

In FIG. 5, the solder cream 6 is placed on the electrode 2.
A metal plate 5 is used to print and apply. When the solder cream 6 is applied by printing on the electrode 2 using the metal plate 5, the electrode 2 is connected to the solder resist layer 9 and the character 1.
Since the height is smaller than the combined height of 0 and 0, the metal plate 5 on which the solder cream 6 is applied by printing is supported at the combined height of the solder resist layer 9 and the character 10. Therefore, a gap is generated between the electrode 2 and the metal plate 5, and the solder cream 6 leaks from this gap during printing. This also causes the generation of solder balls and solder bridges, and makes it impossible to stably apply the solder cream 6.

Here, since the metal plate 5 is installed without a gap between the electrode 2 and the metal plate 5, the metal plate 5 is removed by etching to a height equal to or higher than the combined height of the solder resist layer 9 and the character 10 which is higher than the electrode 2. In some cases, the metal plate 5 is produced so that the metal plate 5 is installed without a gap between the metal plate 5 and the electrode 2, but this cannot be applied to the structure of the printed wiring board using this conventional technique.

This is because if the gap between the electrode 2 and the solder resist layer 9 is less than 50 μm, the metal plate 5 cannot be etched because it is too narrow. Even if an etchable gap is provided between the electrode 2 and the solder resist 9 layer, the metal plate 5 can be supported only on a part of the electrode 2, and the metal plate 5 is installed on the electrode 2. In this state, since there is a gap between the electrode 2 and the solder resist 9 layer, the space formed between the metal plate 5 and the substrate 1, the solder resist layer 9 and the character 10 are etched to a height higher than the combined height. Since there is a space between the etching surface and the character 10, the metal plate 5 is not closely adhered to and supported by the metal plate 5, and the printing pressure causes the metal plate 5 to bend when the solder cream 6 is printed. This is also because the solder cream 6 cannot be supplied.

FIG. 6 shows a state in which an electronic component 8 is mounted on a printed wiring board using this conventional technique. That is, FIG. 6 shows a state in which the electronic component 8 is mounted after removing the metal plate 5 of FIG.

Character 1 provided on the solder resist layer 9
Since 0 is applied by the printing method, the character 10 immediately after printing
It is difficult to flatten the surface due to surface tension, and it is difficult to flatten the surface because a sufficient coating width cannot be provided in a downsized component. For this reason, the surface of the character 10 has a semi-cylindrical shape, and the electronic component 8 cannot be supported in parallel with the electrode 2 when the electronic component 8 is mounted, and the electrode 2 is lifted up, solder balls, or solder bridges. Will be caused.

Further, in a module in which an electronic component 8 is mounted on a printed wiring board using this conventional technique to form a module sealed with resin or the like and mounted again on another printed wiring board by soldering through a reflow furnace, The solder 7 soldered by passing the electronic component 8 through the reflow furnace is re-melted, and the flux at the time of soldering remaining between the electrodes in the lower part of the electronic component 8 is also re-melted, and a short circuit occurs between the electrodes of the electronic component 8. Therefore, it is necessary to surely clean the flux so that there is no lack of cleaning.

Here, in order to make the cleaning more reliable, it is necessary to provide a space between the electrodes in the lower part of the electronic component 8 so that the cleaning liquid can sufficiently permeate. In this conventional method, specifically, the gap between the electrode 2 and the solder resist layer 9 is widened to 200 μm.

When the gap is 50 μm, there is a fear that the gap will be small and cleaning will be insufficient, and the lower portion of the electronic component 8 and the character 10 are in close contact with each other, and it is difficult to clean the gap. When the cleaning of the flux is insufficient, in the case of the resin-sealed character 10, another printed wiring board is passed through the reflow furnace again, and the electronic component 8 on which the module is mounted is mounted.
There is a possibility that the solder 7 and the residual flux after cleaning may be remelted and short-circuited.

[0020]

As described above, in the printed wiring board having a high density and the electronic parts having a high density mounting and miniaturization, the gap between the electrode 2 and the solder resist layer 9 should be less than 50 μm. However, the printed wiring board using the conventional technique cannot ensure the reliability of mounting.

That is, in the above-mentioned prior art, in the high density printed wiring board and the miniaturized electronic parts,
The rise of electrodes, the occurrence of solder balls and solder bridges, which affect the reliability when mounting electronic components, cannot be completely suppressed.

In particular, in the case of a high density printed wiring board, it is desirable to make the distance between the solder resist layer and the electrode as narrow as possible as described above, but in order to provide a region for escaping molten solder. There is no choice but to make it wider. Further, since the characters formed on the solder resist layer are also applied by printing, the application width becomes narrow when mounting a miniaturized electronic component, and it is more difficult to finish the surface flat.

The present invention has been made in view of the above circumstances, and an object thereof is to effectively suppress the floating of electrodes, the generation of solder balls and solder bridges when mounting electronic components, and It is an object of the present invention to provide a printed wiring board and a method for manufacturing the same, which can perform flux cleaning more easily and reliably.

[0024]

According to one aspect of the present invention, a substrate, a plurality of electrodes for connecting electronic components formed on the substrate at substantially the same height as each other, and an electrode on the substrate are provided. A plurality of first solder resist layers formed with a predetermined gap between these electrodes, and a plurality of second solder resist layers formed on these first solder resist layers. Thus, a printed wiring board is provided in which the planar shape of the second solder resist layer is smaller than the planar shape of the first solder resist layer formed under the layer.

The predetermined gap between the electrode and the first solder resist layer acts as a space for letting out the melted solder cream. The predetermined gap is set by appropriately changing it according to the number of electronic components, the mounting density, the type and amount of solder cream, and the like.

The second solder resist layer is formed on a predetermined first solder resist layer among the plurality of first solder resist layers. The plane shape of the second solder resist layer is made smaller than the plane shape of the first solder resist layer formed below the second solder resist layer is that a step is formed between the first solder resist layer and the second solder resist layer. Is provided to allow the melted solder cream to escape by using this step, and to perform cleaning more reliably when cleaning the flux during soldering.

In the printed wiring board according to one aspect of the present invention, the plane shape of the second solder resist layer is smaller than the plane shape of the first solder resist layer formed thereunder. Since the melted solder cream is released to the gap between the electrode and the first solder resist layer or the step between the first solder resist layer and the second solder resist layer, the electrode is lifted when the electronic component is mounted. In addition, the generation of solder balls and solder bridges can be effectively suppressed, and the penetration of the cleaning liquid is promoted when cleaning the flux, so that flux cleaning can be performed more easily and reliably.

In this printed wiring board, it is preferable that the surface of the second solder resist layer is substantially flat and substantially parallel to the surface of the substrate.

As a method of forming the surface of the second solder resist layer substantially flat and substantially parallel to the surface of the substrate, for example, the same etching method as that for the first solder resist layer is used.

By configuring the surface of the second solder resist layer in this way, it becomes possible to support the electronic component substantially parallel to the surface of the electrode with high precision even if the solder cream application width is narrow. .

In this printed wiring board, it is preferable that the height of the first solder resist layer is substantially the same as the height of the electrodes.

If the height of the first solder resist layer is configured in this way, it is possible to prevent the metal plate for solder cream printing application arranged over the electrode and the first solder resist layer from rising and prevent the electrode and the metal plate from being separated from each other. The gap can be eliminated and the solder cream can be stably supplied.

This printed wiring board has a combined height of the first solder resist layer and the second solder resist layer,
It is preferable to make it higher than the height of the electrodes.

If the combined height of the first solder resist layer and the second solder resist layer is configured in this way, the electronic component can be secured even if a large pressure is applied during mounting of the electronic component.
The second solder resist layer can support the electrode substantially parallel to the surface of the electrode on the substrate.

In this case, if the height of the second solder resist layer is too high, the gap between the electrode and the electronic component becomes too wide, the supply of solder cream becomes insufficient, and soldering becomes difficult. If the height of the second solder resist layer is too low, the distance between the electrode and the electronic component becomes too narrow, and the melted solder cream overflows, causing solder balls and solder bridges. Therefore, the height of the second solder resist layer is set to an appropriate dimension so that these problems do not occur.

According to another aspect of the invention, on the substrate:
A step of forming a plurality of electrodes for connecting electronic components, a step of forming a plurality of first solder resist layers in a predetermined shape on the substrate with a predetermined gap between these electrodes, Forming a second solder resist layer on the first solder resist layer so that its planar shape is smaller than the planar shape of the first solder resist layer formed under the layer. A method of manufacturing a featured printed wiring board is provided.

In the method of manufacturing a printed wiring board according to another aspect of the present invention, the second solder resist layer has a planar shape smaller than that of the first solder resist layer formed below the second solder resist layer. By forming so that
Since the melted solder cream is released to the gap between the electrode and the first solder resist layer or the step between the first solder resist layer and the second solder resist layer,
It is possible to effectively suppress the floating of electrodes, the generation of solder balls, and solder bridges when mounting electronic components, and facilitate the penetration of the cleaning liquid when cleaning the flux to facilitate flux cleaning. it can.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. The present invention is not limited to this. In addition, since the steps and manufacturing conditions described below are the same as those used for manufacturing an ordinary printed wiring board and mounting electronic components using the same, unless otherwise specified. hand,
Detailed description thereof will be omitted.

1 to 3 are structural explanatory views showing a printed wiring board P according to one embodiment of the present invention and a mounting process of electronic parts using the printed wiring board P. As shown in FIG. In these figures, 1 is a substrate, 2 is an electrode for connecting electronic components, 5 is a metal plate for solder cream printing application, 6 is solder cream, 7 is solder after reflow soldering, and 8 is an electronic component.

The printed wiring board P is manufactured as follows. First, as shown in FIG. 1, an electrode 2 made of copper foil is formed on the surface of a substrate 1 made of glass epoxy or the like. The height of the electrode 2 is about 35 μm. Next, a predetermined gap is opened between the electrode 2 and the first electrode on the surface of the substrate 1.
The solder resist layer 3 is formed, and further, the second solder resist layer 4 is formed on the first solder resist layer 3 by etching by the same method as that of the first solder resist layer 3.

The height of the first solder resist layer 3 is about the same as the height of the electrode 2 in order to prevent the metal plate 5 from rising when the solder cream 6 is applied by printing.
It is set to μm. Further, the surface of the first solder resist layer 3 is made substantially flat so that the metal plate 5 does not tilt and is substantially parallel to the surface of the substrate 1. First
The solder resist layer 3 plays a role of protecting the substrate 1 against heat and moisture.

If the gap between the first solder resist layer 3 and the electrode 2 is too wide, it cannot play a role of protecting the substrate 1. On the contrary, if the gap is too narrow, the melted and flowing solder overflows. , Need to be set properly.

Even if this gap is less than about 50 μm, the plane shape of the second solder resist layer 4 is, as will be described later, the first solder resist layer 3 formed below the layer.
Of the electronic component 8 by allowing the melted and overflowed solder to escape to the stepped region between the first solder resist layer 3 and the second solder resist layer 4 which is formed to be smaller than the planar shape of It is possible to prevent the generation of solder balls and solder bridges between them. As an example, this gap is preferably set to about 30 to about 50 μm in consideration of the positional deviation of the first solder resist layer 3.

The second solder resist layer 4 is formed so that its surface is substantially flat and substantially parallel to the surface of the substrate 1. In addition, the second solder resist layer 4 can support the metal plate 5 for solder cream printing application, and the first solder resist layer 3 formed under the second solder resist layer 4 can support the metal plate 5. Separated from the edge, the planar shape is smaller than the planar shape of the first solder resist layer 3 thereunder by about 100 μm.

The total height of the first solder resist layer 3 and the second solder resist layer 4 is higher than the height of the electrode 2. Therefore, even if a large pressure is applied when the electronic component 8 is mounted, the electronic component 8 is supported by the second solder resist layer 4 substantially parallel to the surface of the substrate 1.

Here, if the height of the second solder resist layer 4 is too high, the distance between the electrode 2 and the electronic component 8 becomes too wide, the supply of the solder cream 6 becomes insufficient, and soldering becomes difficult. On the other hand, if the height of the second solder resist layer 4 is too low, the distance between the electrode 2 and the electronic component 8 becomes too narrow, and the melted solder cream 6 overflows, causing solder balls or solder bridges. . Therefore, the height of the second solder resist layer 4 is set to an appropriate dimension so that these problems do not occur.

That is, the height of the first solder resist layer 3 is about 3 which is the same as the height of the electrode 2 as described above.
Since the thickness is 5 μm, the maximum height of the second solder resist layer 4 is preferably set to about 20 to about 40 μm.

Next, the effect of providing the metal plate 5 will be described together with the method of mounting the electronic component 8.

As shown in FIG. 2, the metal plate 5 is used for printing and applying the solder cream 6 on the electrode 2. Solder cream 6 using metal plate 5 on electrode 2
In order to place the metal plate 5 on the electrode 2 without any gap when printing, the metal plate 5 avoids the maximum height of the second solder resist layer 4 of about 20 to about 40 μm. Etching is performed up to about 50 μm as described above.

The first solder resist layer 3 is formed at the same height as the electrode 2 and has a flat surface so that the metal plate 5 does not tilt, and further the second solder resist layer 4 is formed.
Is formed in a planar shape smaller than the first solder resist layer 3 by about 100 μm. Therefore, the metal plate 5 placed on the electrode 2 is supported together with the first solder resist layer 3.

In order to etch the metal plate 5, the gap between the electrode 2 and the first solder resist layer 3 is too small to be produced in the range of about 30 to about 50 μm, but the second solder resist layer is not available. Since the plane shape of No. 4 is smaller than the plane shape of the first solder resist layer 3 by about 100 μm, the width of the region that can be etched is about 130 μm.
Since the thickness is up to 150 μm, a sufficient area for etching is secured, and the metal plate 5 can be easily etched and manufactured.

As described above, the metal plate 5 is supported together with the electrode 2 and the first solder resist layer 3 and can be installed without any gap between the electrode 2 and the extra solder cream 6 without the risk of leakage. Obviously, the solder cream 6 can be stably applied on the electrode 2.

In the metal plate 5 not subjected to such etching, the metal plate 5 is supported by the height of the first solder resist layer 3 and the second solder resist layer 4 together, and the metal plate 5 and the electrode 2 are not supported. A gap is created between the plate 5 and the plate 5.
Then, since the melted solder cream 6 leaks from this gap, it causes solder balls and solder bridges, and the solder cream 6 cannot be applied stably.

FIG. 3 shows a state in which an electronic component 8 is mounted using this printed wiring board P. That is, FIG.
The state where the electronic component 8 is mounted after removing the metal plate 5 of FIG. 2 is shown.

By forming the second solder resist layer 4 by etching in the same method as the first solder resist layer 3, the surface of the second solder resist layer 4 is made flat and accurate, and the first solder resist layer 3 is formed. Can be formed substantially parallel to the surface of the. Furthermore, even when the second solder resist layer 4 is formed between the connection electrodes 2 of the miniaturized electronic component 8, the second solder resist layer 4 can be formed flat and substantially parallel with a narrow coating width, so that the electronic component can be mounted during mounting. 8 can be supported substantially parallel.

Further, the electrode 2 and the first solder resist layer 3
Even when the gap between and is narrowed to about 30 to about 50 μm, the planar shape of the second solder resist layer 4 is formed to be smaller than the planar shape of the first solder resist layer 3 by about 100 μm. The melted and overflowing solder can escape to the step region.

Further, in a module in which the printed wiring board on which the electronic component 8 is mounted is sealed with resin or the like, and another printed wiring board is passed through the reflow furnace to be mounted again by soldering, the electronic component 8 is passed through the reflow furnace. The solder 7 that has been soldered by re-melting is re-melted, and the flux that remains between the electrodes under the electronic component 8 during soldering is also re-melted, causing a short circuit between the electrodes of the electronic component 8, so there is no insufficient cleaning of the flux. It is necessary to make sure that cleaning is performed.

Here, in order to make the cleaning more reliable,
It is necessary to provide a space between the electrodes below the electronic component 8 so that the cleaning liquid can sufficiently permeate. In this printed wiring board P, the planar shape of the second solder resist layer 4 is about 10 times larger than that of the first solder resist layer 3.
Since the electronic component 8 is formed to be 0 μm smaller,
It is supported by the solder resist layer 4. Then, between the electronic component 8 and the first solder resist layer 3, the maximum height of the second solder resist layer 4 is about 20 to about 40 μm.
A gap of about 30 between the electrode 2 and the first solder resist layer 3
A gap including about 50 μm to about 50 μm is surely formed. Therefore, the gap makes it easier for the cleaning liquid to permeate, and the flux can be cleaned more easily and reliably.

[0059]

In the printed wiring board according to the first aspect, the plane shape of the second solder resist layer is smaller than the plane shape of the first solder resist layer formed thereunder. Since the melted solder cream is released to the gap between the electrode and the first solder resist layer or the step between the first solder resist layer and the second solder resist layer, the electrode is lifted when the electronic component is mounted. In addition, the generation of solder balls and solder bridges can be effectively suppressed, and the penetration of the cleaning liquid is promoted when cleaning the flux, so that flux cleaning can be performed more easily and reliably.

In the printed wiring board according to the second aspect, since the surface of the second solder resist layer is substantially flat and substantially parallel to the surface of the substrate, the solder cream application width is Even when the width is narrow, it becomes possible to support the electronic component substantially parallel to the surface of the electrode with high accuracy.

In the printed wiring board according to the third aspect, since the height of the first solder resist layer is substantially the same as the height of the electrodes, the printed wiring board is arranged so as to extend over the electrodes and the first solder resist layer. Therefore, it is possible to prevent the metal plate for solder cream printing application from rising and eliminate the gap between the electrode and the metal plate, and to stably supply the solder cream.

In the printed wiring board according to the fourth aspect, since the total height of the first solder resist layer and the second solder resist layer is made higher than the height of the electrodes, mounting of electronic parts is performed. Even when a large pressure is sometimes applied, the electronic component can be supported by the second solder resist layer substantially parallel to the surface of the electrode on the substrate.

In the method for manufacturing a printed wiring board according to the fifth aspect, the plane shape of the second solder resist layer is smaller than the plane shape of the first solder resist layer formed below the second solder resist layer. Since the molten solder cream is released to the gap between the electrode and the first solder resist layer or the step between the first solder resist layer and the second solder resist layer, the solder cream can be mounted on the electronic component. It is possible to effectively suppress the floating of the electrodes, the generation of solder balls and solder bridges,
When cleaning the flux, the penetration of the cleaning liquid is promoted, and the flux cleaning can be performed more easily and reliably.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view of a printed wiring board according to one embodiment of the present invention.

FIG. 2 is a structural explanatory view when a metal plate for solder cream printing application is combined with the printed wiring board of FIG.

FIG. 3 is a configuration explanatory diagram when an electronic component is mounted on the printed wiring board of FIG.

FIG. 4 is a configuration explanatory view of one conventional printed wiring board.

FIG. 5 is a configuration explanatory view when a solder cream printing application metal plate is combined with the printed wiring board of FIG. 4;

6 is a configuration explanatory view when an electronic component is mounted on the printed wiring board of FIG.

[Explanation of symbols]

1 substrate 2 electrodes 3 First solder resist layer 4 Second solder resist layer 5 Solder cream printing coating metal plate 6 solder cream 7 Solder after reflow soldering 8 electronic components

Claims (5)

[Claims] 1. A substrate, a plurality of electrodes for connecting electronic components, which are formed on the substrate at substantially the same height as each other, and a predetermined gap is formed between the electrodes on the substrate. A plurality of first solder resist layers formed and a plurality of second solder resist layers formed on these first solder resist layers, wherein the planar shape of the second solder resist layer is A printed wiring board having a size smaller than a planar shape of a first solder resist layer formed underneath. 2. The printed wiring board according to claim 1, wherein the surface of the second solder resist layer is substantially flat and substantially parallel to the surface of the substrate. 3. The printed wiring board according to claim 1, wherein the height of the first solder resist layer is substantially the same as the height of the electrodes. 4. The total height of the first solder resist layer and the second solder resist layer is higher than the height of the electrodes.
Printed wiring board according to item 1. 5. A step of forming a plurality of electrodes for connecting electronic components on a substrate, and forming a plurality of first solder resist layers on the substrate with a predetermined gap between these electrodes. A step of forming the second solder resist layer on the first solder resist layer so that the planar shape of the second solder resist layer is smaller than the planar shape of the first solder resist layer formed under the layer. And a step of forming the printed wiring board.