JP2003347715A - Printed wiring board with bump and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board with bumps capable of homogeneous resin sealing by uniforming the gaps formed with a mounted electronic component. <P>SOLUTION: A substrate 2 comprising projections 1 on its surface is formed from an insulating material. Bumps 6 to be joined to connection terminals 5 of an electronic component 4 are formed by forming conductors 3 on the surface of the projections 1. A circuit 7 for operating an electronic component 4 is formed on the substrate 2 by electrically connecting it to the conductors 3 of the bumps 6. The electronic component 4 can be mounted by joining to the connection terminals 5 of the electronic component 4 without melting the bumps 6. <P>COPYRIGHT: (C)2004,JPO

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 with bumps for mounting electronic components such as semiconductor chips and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a flip chip semiconductor chip as an electronic component is mounted on the surface of a printed wiring board as shown in FIG. FIG.
As shown in FIG. 6A, a plurality of connection terminals 5 are formed on one side of the electronic component 4 so as to be exposed. As shown in FIG. 6B, solder balls are printed on the surface of each connection terminal 5. To form the bump 6. Next, the electronic component 4 on which the bumps 6 are formed is brought close to the printed wiring board 20 from above by face-down, and the bumps 6 of the electronic component 4 are placed on the connection portions 21 such as lands provided on the upper surface of the printed wiring board 20. Contact. The printed wiring board 20 is provided with a circuit 7 that is electrically connected to the connection section 21. The circuit 7 is a circuit necessary for the operation of the electronic component 4 to be mounted, such as a power supply circuit for supplying power to the electronic component 4 and an input / output circuit for inputting and outputting an electric signal to and from the electronic component. It is. These circuits 7 are provided on the surface or inside of the printed wiring board 20 and
The circuit provided on the surface of the “0” is covered with a solder resist or the like. Further, the connection portion 21 is provided so as to be exposed on the surface of the printed wiring board 20 without being covered with a solder resist or the like.

Then, after the bumps 6 formed of the solder balls are melted by heating while the bumps 6 of the electronic component 4 and the connecting portions 21 of the printed wiring board 20 are in contact with each other, the temperature of the melted bumps 6 is lowered. Then, the bump 6 and the connection portion 21 are joined by solidification (reflow soldering). Thereafter, a sealing resin (underfill resin) 22 is injected and filled into a gap between the lower surface of the electronic component 4 and the upper surface of the printed wiring board 20. The sealing resin 22 is filled to bond the electronic component 4 and the printed wiring board 20 to increase the bonding strength, or to prevent moisture from entering the gap to improve moisture resistance. . Thus, the electronic component 4 can be mounted on the printed wiring board 20.

[0004]

In the above mounting method,
After the bumps 6 formed of solder balls are melted, the bumps 6 are joined to the connecting portions 21 by solidifying the melted bumps 6, so that the height of the bumps 6 changes before and after the melting. However, the change in height of the bumps 6 may not occur uniformly for all the bumps 6, so that the lower surface of the electronic component 4 and the printed wiring board 20 are not In some cases, the size of the gap with the upper surface was not uniform. In a place where the gap between the lower surface of the electronic component 4 and the upper surface of the printed wiring board 20 is large, the filled sealing resin 22 does not adhere to the electronic component 4, or the lower surface of the electronic component 4 and the printed wiring board 20 do not adhere. There is a problem that the filled sealing resin 22 may not be filled at a place where the size of the gap between the electronic component 4 and the printed wiring board 20 is small. The strength and the moisture resistance were reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a fixed gap formed between the electronic component and a mounted electronic component. And a method for producing the same.

[0006]

According to a first aspect of the present invention, there is provided a printed wiring board with bumps, wherein a substrate having projections on its surface is formed of an insulating material, and a conductor is formed on the surface of the projections. Thereby forming a bump 6 to be joined to the connection terminal 5 of the electronic component 4, and forming a circuit 7 for operating the electronic component 4 on the substrate 2 by electrically connecting to the conductor 3 of the bump 6. It is characterized by the following.

A printed wiring board with bumps according to a second aspect of the present invention is characterized in that, in addition to the first aspect, the insulating material is a thermosetting resin.

According to a third aspect of the present invention, there is provided a method of manufacturing a printed wiring board with bumps A according to the first or second aspect, wherein the method is for manufacturing a printed wiring board with bumps A. The substrate 2 is formed by press-molding a resin sheet 8.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a printed wiring board with bumps according to a third aspect of the present invention. The resin of the sheet 8 is formed into the forming holes 10 of the perforated forming plate 9.
After that, the resin sheet 8 is cured to form the substrate 2 having the projections 1 on the surface.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a printed wiring board A with bumps according to the third or fourth aspect, further comprising a perforated molded plate 9 formed of a film having releasability.
Is used.

A method of manufacturing a printed wiring board A with bumps according to a sixth aspect of the present invention includes, in addition to the fifth aspect, using a perforated formed plate 9 having a film formed with a formed hole 10 by laser. It is a feature.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a printed wiring board A with bumps according to any one of the fourth to sixth aspects, further comprising a perforated molded board 9 having a thickness of 30 to 500 μm.
Is used.

According to a eighth aspect of the present invention, there is provided a method of manufacturing a printed wiring board A with bumps according to any one of the third to seventh aspects, wherein the conductor 3 on the surface of the projection 1 is formed by using an electrodeposition coating method. And a circuit 7 are formed.

[0014]

Embodiments of the present invention will be described below.

The printed wiring board A with bumps according to the present invention is provided with the bumps 6 for joining the electronic components 4 in advance before the electronic components 4 are mounted, so that the electronic components 4 are mounted. In this case, it is not necessary to form a bump such as a solder ball on the electronic component 4, and the mounting efficiency of the electronic component 4 can be improved.

The printed wiring board A with bumps of the present invention comprises:
As shown in FIG. 1 (e), a substrate 2 having a large number of protrusions 1 on one surface, a conductor 3 provided on the surface of the protrusion 1, and a circuit 7 for operating the electronic component 4 are formed. The bumps 6 are formed by the protrusions 1 and the conductors 3 provided on the surface thereof.

The projection 1 and the substrate 2 are integrally formed using an insulating material. The shape, size, and arrangement of the projections 1 can be appropriately set according to the connection terminals 5 of the electronic component 4 to be mounted. For example, the shape of the projections 1 is substantially cylindrical, and the height of the projections 1 is 30. The projection 1 may be formed to have a diameter of 40 to 100 μm in plan view, and the dimension between the adjacent projections 1 may be formed to be 50 to 200 μm.

The conductor 3 of the bump 6 and the circuit 7 can be formed by metal plating such as copper plating. Although the conductors 3 of each bump 6 are formed independently, they are electrically connected to a predetermined circuit 7. The circuit 7 is a circuit necessary for the operation of the electronic component 4 to be mounted, such as a power supply circuit for supplying power to the electronic component 4 or an input / output circuit for inputting / outputting an electric signal to / from the electronic component. is there. These circuits 7 can be provided on both surfaces of the substrate 2, and the circuits 7 provided on one surface and the other surface can be electrically connected by through holes or the like. The circuit 7 provided on the surface of the substrate 2 is preferably covered with a solder resist or the like. The thickness of the conductor 3 of the bump 6 and the thickness of the circuit 7 may be appropriately set, and may be, for example, 5 to 30 μm.

Printed wiring board A with bumps as described above
Can be formed as follows. First, the substrate 2 is formed using an insulating material and a perforated plate 9. As the insulating material, various thermosetting resins such as an epoxy resin and a polyimide resin conventionally used for manufacturing a printed wiring board can be used. These thermosetting resins have heat resistance to the extent that they are not easily deformed by heat when cured. The insulating material is provided in the manufacture of the substrate 2 as a resin sheet 8 which is formed into a sheet shape in a semi-cured state in consideration of handling properties, productivity of the substrate 2 and the like. In addition, a prepreg in which a thermosetting resin is impregnated into a base material such as a glass cloth to be in a semi-cured state can be used as the resin sheet 8. The thickness of the resin sheet 8 can be, for example, 60 to 1000 μm. As such a resin sheet 8, for example, “R-1661” (thickness 0.18 mm) manufactured by Matsushita Electric Works, Ltd. can be used.

As shown in FIG. 1A, a perforated forming plate 9 is formed by providing a large number of forming holes 10 in the resin sheet 8 and a film having releasability. As the film of the molded plate 9, a film formed of synthetic resin such as polyethylene terephthalate (PET), ethylene tetrafluoride polymer (Teflon (registered trademark)), silicone, or pulp can be used. Is
Goju Sangyo Co., Ltd. “Tough Fan” (100 μm thick)
Can be used. The forming hole 10 is formed so as to penetrate the hole forming plate 9 in the thickness direction so as to open on both surfaces of the hole forming plate 9, and irradiates the film with a laser such as a carbon dioxide gas laser. Can be formed. In the case of using the film manufactured by Goju Sangyo Co., Ltd., a 150 μm forming hole 10 can be formed with an energy of 50 mJ or less by a carbon dioxide laser.
By forming the forming hole 10 by the laser in this way, compared to the case of forming the forming hole 10 by drilling,
It is possible to make the hole diameter of the forming holes 10 fine or to form a large number of forming holes 10 at a narrow pitch. The shape, size, and arrangement of the molding holes 10 are formed in correspondence with the projections 1 of the substrate 2, and are formed by a conformal mask method (a method of covering a film with a metal mask and irradiating a laser). By forming the forming hole 10, the forming hole 10 having a hole shape other than circular can be easily formed.

In the present invention, the height of the projection 1 is formed to be substantially the same as the thickness of the perforated plate 9. Therefore, the thickness of the perforated plate 9 is preferably set to 30 to 500 μm, similarly to the height of the projection 1. If the thickness of the perforated plate 9 is less than 30 μm, the height of the projections 1 becomes too low and the height of the bumps 6 becomes too low. The height of the projections 1 may be increased if the thickness of the perforated plate 9 exceeds 500 μm because the difference in height between the projections 1 and 2 is almost eliminated due to plating variations and it becomes difficult to mount the electronic component 4. Too much, conductor 3 of bump 6
May be difficult to form uniformly on the projections 1 or the strength of the projections 1 may be reduced to cause breakage and breakage when mounting the electronic component 4.

Then, as shown in FIG. 1B, the perforated plate 9 is placed on the upper surface of the resin sheet 8 and the release film 25 is placed on the lower surface of the resin sheet 8 and the upper surface of the perforated plate 9.
Are laminated to form a laminate. The release film 25 is provided so that the laminate can be easily peeled off from a mirror plate of a press device described later, and is similar to, for example, a resin film for forming the perforated molded plate 9. Can be formed to a thickness of 25 to 100 μm using a resin such as “Tedlar HMR10S” manufactured by Somar.
M3 "can be used.

Next, the above-mentioned laminate is sandwiched between a pair of mirror plates of a press device and press-formed while heating. The resin of the resin sheet 8 is melted by this press molding, and a part of the melted resin flows into the forming holes 10 of the perforated forming plate 9 from the lower surface opening, and all the forming holes 10 are filled with the resin of the resin sheet 8. Will be. Further, since the upper opening of the molding hole 10 is closed by the release film 25, the molding hole 10
Can be prevented from leaking from the upper surface opening of the molding hole 10. Further, the resin of the resin sheet 8 melted by heating during the press molding is cured. The conditions for press molding can be appropriately set according to the type of resin of the resin sheet 8 and the like. For example, the temperature of the resin sheet 8 is set to 170 to 220 ° C., the pressure applied to the resin sheet 8 is set to 2 to 5 MPa, and the time is set to 60 to 180 minutes. When the resin sheet 8 is used, the temperature 17
5 ° C, pressure 2.9MPa, time 60 minutes (FR-4 condition)
Etc. can be adopted.

After press forming, the perforated forming plate 9 and the release film 25 are removed from the cured product of the resin sheet 8 so that a large number of protrusions 1 are formed on the surface as shown in FIG. Can be formed from a cured product of the resin sheet 8. The projection 1 is formed with the forming hole 1 of the perforated forming plate 9.
It is formed of a cured product of the resin that has flowed into zero.

Thereafter, the circuit 7 is formed on both the upper and lower surfaces of the substrate 2 and the conductor 3 is formed on the surface of the projection 1, whereby the printed wiring board A with bumps of the present invention as shown in FIG. In forming the circuit 7 and the conductor 3 of the bump 6, a subtractive method or an additive method can be employed.

FIGS. 2A to 2F show steps of forming the circuit 7 and the conductor 3 of the bump 6 by a subtractive method. First, a conductor layer 26 as shown in FIG. 2B is formed on both surfaces (including the surface of the protrusion 1) of the substrate 2 formed as shown in FIG. The conductive layer 26 can be formed by plating. For example, the conductive layer 26 can be formed by performing electroless copper plating on the surface of the substrate 2 and then performing electrolytic copper plating. Although the thickness of the conductor layer 26 is arbitrary, it can be formed, for example, to 5 to 30 μm similarly to the thickness of the conductor 3 of the bump 6 and the thickness of the circuit 7.

Next, as shown in FIG. 2C, an etching resist (photoresist) 30 is formed on the entire surface of the conductor layer 26. In forming the etching resist 30 on the surface of the conductor layer 26, a dry film is attached to the surface of the conductor layer 26, or the etching resist 30 is deposited on the surface of the conductor layer 26 by an electrodeposition coating method (ED method). can do. When a dry film is attached to the surface of the conductor layer 26, it is preferable to employ a vacuum lamination method, whereby the adhesion between the etching resist 30 and the conductor layer 26 can be improved. The electrodeposition coating method energizes the conductor layer 26 while immersing the substrate 2 in a resist solution containing an emulsified etching resist, thereby depositing a film of the etching resist 30 over the entire surface of the conductor layer 26. . In the present invention, a large number of fine projections 1 are formed at a narrow pitch on the surface of the substrate 2, and it is necessary to form the etching resist 30 between the fine projections 1. Therefore, it is preferable to form the etching resist 30 by an electrodeposition coating method that can infiltrate the resist solution between the fine projections 1, thereby ensuring more reliable formation between the fine projections 1 than using a dry film. The etching resist 30 can be formed.

Next, as shown in FIG. 2D, the etching resist 30 is exposed and developed to form an etching resist 30 having a desired circuit pattern. For the exposure at this time, for example, a stepper projection exposure machine manufactured by Ushio can be used. Thereafter, as shown in FIG. 2E, unnecessary portions of the conductor layer 26 which are not covered with the etching resist 30 by the etching process are formed.
Is removed. Thereafter, by removing the etching resist 30 attached to the surface of the remaining conductor layer 26, the remaining conductor layer 26 is formed as the conductor 7 of the circuit 7 and the bump 6 as shown in FIG. The printed wiring board A with bumps can be manufactured.

FIGS. 3A to 3E show steps of forming the circuit 7 and the conductor 3 of the bump 6 by the additive method. First, a plating resist 31 as shown in FIG. 3B is formed on both surfaces (including the surface of the protrusion 1) of the substrate 2 formed as shown in FIG. The plating resist 31 can be formed by, for example, attaching a dry film to the surface of the substrate 2.
It is preferable to employ a vacuum laminating method in order to enhance the adhesion to the substrate. Next, as shown in FIG. 3C, the plating resist 31 is exposed and developed to form a plating resist 31 having a desired circuit pattern. For the exposure at this time, for example, a stepper projection exposure machine manufactured by Ushio can be used. After this, FIG.
As shown in (d), the conductor layer 26 is formed on the surface of the substrate 2 that is not covered with the plating resist 31 by the plating process. The conductor layer 26 can be formed, for example, by performing electroless copper plating on the surface of the substrate 2 and then performing electrolytic copper plating. The thickness of the conductor layer 26 is the same as that described above and in the case of the subtractive method. Thereafter, by removing the plating resist 31 adhering to the surface of the substrate 2, as shown in FIG.
The printed wiring board A with the bumps formed as the conductors 3 of the circuit 7 and the bumps 6 can be manufactured.

The above-described subtractive method and additive method can be performed under known manufacturing conditions conventionally used for manufacturing printed wiring boards.

Next, the above-mentioned printed wiring board A with bumps
The mounting of the electronic component 4 to the electronic component will be described. First, FIG.
As shown in FIG. 4A, a plurality of connection terminals 5 are formed on one surface of an electronic component 4 such as a semiconductor chip, and are exposed. As shown in FIG. The conductive paste 27 is provided by printing such as screen printing. The conductive paste 27 is formed by mixing conductive particles and a resin. For example, a known paste such as cream solder can be used. Cream solder is solder that is made into a uniform paste by mixing granular solder and flux. The conductive paste 27 is provided on the connection terminal 5 with a thickness smaller than that of a conventional solder ball.

Next, as shown in FIG. 4 (c), the electronic component 4 to which the conductive paste 27 has been applied is brought close to the bumped printed wiring board A from above by face-down, and on the upper surface of the bumped printed wiring board A. The electronic component 4 is mounted on the printed wiring board A with bumps so that the conductive paste 27 is brought into contact with the conductor 3 of the formed bump 6. Next, the conductive paste 27 is blown by blowing hot air or the like.
Is heated and cured, so that the conductor 3 of the bump 6
Printed wiring board A with bumps
The electronic component 4 is attached to the surface of. Thereafter, FIG.
As shown in (2), a sealing resin (underfill resin) 22 is injected and filled into the gap between the lower surface of the electronic component 4 and the upper surface of the substrate 2. As the sealing resin 22, a known resin such as a liquid epoxy resin can be used. Thereafter, the electronic component 4 is mounted on the surface of the printed wiring board A with bumps by bonding the printed wiring board A with bumps and the electronic component 4 with the sealing resin 22 by curing the sealing resin 22 by heating or the like. can do.

In the printed wiring board A with bumps according to the present invention, the bumps 6 are formed of an insulating material such as a thermosetting resin, and the connection terminals 5 of the electronic component 4 are formed without melting the bumps 6.
Is to be joined. Therefore, the bump 6 can be
Is formed, the gap between the lower surface of the electronic component 4 and the upper surface of the substrate 2 does not change due to the joining of the electronic component 4, and the above gap can be kept constant. The sealed resin 22 and the electronic component 4 do not adhere to each other and the injected sealing resin 22 is not filled, so that uniform resin sealing can be performed.

In the above embodiment, the conductive paste 2
7 are used to connect the conductor 3 of the bump 6 and the connection terminal 5 of the electronic component 4.
However, the present invention is not limited to this. Gold plating is applied to the conductor 3 of the bump 6 and the connection terminal 5 of the electronic component 4, and as shown in FIG. The ultrasonic bonding may be performed after the state is brought into direct contact with 5.

[0035]

As described above, according to the first aspect of the present invention, a substrate having projections on its surface is formed of an insulating material, and a conductor is formed on the surface of the projections, whereby the substrate is joined to a connection terminal of an electronic component. The bumps are formed, and the circuit for operating the electronic components is electrically connected to the conductors of the bumps and formed on the substrate.Then, the electronic components are mounted by bonding to the connection terminals of the electronic components without melting the bumps The gap between the lower surface of the electronic component and the upper surface of the substrate does not change due to the bonding of the electronic component, as in the case where the bump is formed with a solder ball, and the size of the gap can be made constant. It is possible to perform uniform resin sealing without preventing the sealing resin filling the gap and the electronic component from adhering or not filling the injected sealing resin. If the printed wiring board with bumps of the present invention is used as the outermost layer of a multilayer printed wiring board such as a build-up board, a multilayer printed wiring board with higher density can be manufactured.

According to the second aspect of the present invention, since the insulating material is a thermosetting resin, the substrate can be formed by molding the insulating material, and the substrate can be easily formed into an arbitrary shape. Things.

According to a third aspect of the present invention, there is provided a method of manufacturing the printed wiring board A with bumps according to the first or second aspect, wherein the substrate is formed by press-molding a resin sheet formed of an insulating material. Since the resin sheet is used as the insulating material, the handling of the insulating material can be facilitated, and the substrate can be formed efficiently. Also, since the bumps are formed by press molding, the surfaces of the protrusions are likely to have a uniform flat surface, so that the conductors provided on the surface of the protrusions can be easily formed on the flat surface with a uniform thickness, and the bump connection can be easily achieved. Reliability can be increased.

Further, according to the invention of claim 4 of the present invention, after forming a perforated plate on the surface of a resin sheet and allowing the resin of the resin sheet to flow into the forming holes of the perforated plate by press molding,
By curing the resin sheet, a substrate having projections on the surface is formed, so that the projections can be formed with the resin that has flowed into the molding holes of the perforated molding plate, and the substrate having projections on the surface can be easily formed. What can be done.

In the invention of claim 5 of the present invention, since the perforated plate formed of a film having a releasing property is used, the perforated plate is easily formed after the substrate is formed from the resin sheet. From the substrate, and the substrate can be easily formed.

Further, in the invention according to claim 6 of the present invention, since a perforated plate in which a forming hole is formed in a film by a laser is used, the diameter of the forming hole is reduced as compared with the case where the forming hole is formed by drilling. It is possible to make fine or to form a large number of molding holes at a narrow pitch.

In the invention of claim 7 of the present invention, since a perforated plate having a thickness of 30 to 500 μm is used, the bumps can be formed without making the height of the bumps too low or too high. It is possible to form bumps with excellent connection reliability and strength.Moreover, the height of the bumps can be arbitrarily selected depending on the perforated molding plate used,
Higher bumps can be formed more easily than when bumps are formed only by electroplating.

According to the invention of claim 8 of the present invention, since the conductor and the circuit on the surface of the projection are formed by using the electrodeposition coating method, the gap between the fine projections can be more reliably formed than when a dry film is used. An etching resist can be formed, and the formation of conductors and circuits of bumps can be easily performed with high accuracy.

[Brief description of the drawings]

FIG. 1 shows an example of an embodiment of the present invention, and (a) to (e) are cross-sectional views.

FIGS. 2A to 2F are sectional views showing a subtractive method according to the first embodiment; FIGS.

FIGS. 3A to 3E are sectional views showing the additive method according to the first embodiment; FIGS.

FIGS. 4A to 4D are cross-sectional views showing a mounting method of the electronic component according to the first embodiment; FIGS.

FIG. 5 is a sectional view of the same.

FIG. 6 shows a conventional example, and (a) to (d) are cross-sectional views.

[Explanation of symbols]

1 protrusion 2 substrate 3 conductor 4 Electronic components 5 Connection terminal 6 Bump 7 circuits 8 Resin sheet 9 Perforated plate 10 Forming hole A Printed wiring board with bump

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Naoki Saito             Kosai Industrial Park, Kosai Town, Nakakoma County, Yamanashi Prefecture Yamanashi             Matsushita Electric Works, Ltd. F term (reference) 5E319 AA03 AB05 AC01 AC11 AC15                       AC17 CC12 CC61 CD26 GG09                 5E338 AA05 BB75 CD05 CD32 EE21                       EE31

Claims (8)

[Claims] A circuit for operating an electronic component by forming a substrate having projections on the surface thereof from an insulating material, forming a conductor on the surface of the projections to form a bump to be joined to a connection terminal of the electronic component, and operating the electronic component. A printed wiring board with bumps, wherein the printed wiring board is formed on a substrate by electrically connecting to a conductor of the bump. 2. The printed wiring board with bumps according to claim 1, wherein the insulating material is a thermosetting resin. 3. A method for manufacturing a printed wiring board with bumps according to claim 1, wherein the substrate is formed by press-molding a resin sheet formed of an insulating material. Of manufacturing a printed wiring board with bumps. 4. A perforated plate is disposed on the surface of the resin sheet, and after the resin of the resin sheet is flowed into the perforations of the perforated plate by press molding, the resin sheet is cured to form protrusions on the surface. The method for producing a printed wiring board with bumps according to claim 3, wherein a substrate having: 5. The method for manufacturing a printed wiring board with bumps according to claim 3, wherein a perforated formed plate formed of a film having releasability is used. 6. The method for producing a printed wiring board with bumps according to claim 5, wherein a perforated formed plate having formed holes in the film by laser is used. 7. The method for manufacturing a printed wiring board with bumps according to claim 4, wherein a perforated formed plate having a thickness of 30 to 500 μm is used. 8. The method for manufacturing a printed wiring board with bumps according to claim 3, wherein the conductor and the circuit on the surface of the projection are formed by using an electrodeposition coating method.