JP2008258501A - Circuit board, circuit board fixing method, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To readily and economically obtain an electrical connection that is stable over an extended time period. <P>SOLUTION: On a circuit board 10, a conductive paste is used to form a conductive film 13 on a connection region 12a of a ground pattern 12 that is located at a position around a mounting hole 11. In a housing 20, a screw hole 21 is previously made at a position facing a mounting hole 11 of the circuit board 10. The circuit board 10 is disposed at a prescribed position of the housing 20, such that a bearing surface of a screw 31 faces the conductive film 13; the screw 31 is screwed into the screw hole 21 from the circuit board 10 side to fix the circuit board 10 to the housing 20. At this time, the ground pattern 12 of the circuit board 10 becomes electrically continuous with the housing 20 via the conductive film 13 and the screw 31. Since the connection region 12a of the ground pattern 12 is covered with the conductive film 13, stable continuity between the circuit board 10 and the housing 20 can be secured over a long time period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a circuit board, a circuit board fixing method, and an electronic apparatus. Specifically, by forming a conductive film in a conductor pattern region of a circuit board to which a conductor is connected, the conductor and the conductor pattern of the circuit board can be electrically connected stably over a long period of time. .

  In a conventional electric device, when the circuit board is fixed to the casing, the ground pattern of the circuit board is connected to the ground of the casing. For example, in the invention of Patent Document 1, when a plurality of members are fixed with bolts and nuts, the outer surface of the nut flange portion is provided with a protrusion that cuts off the coating film on the seating surface in contact with the nut, thereby coating the surface. It is disclosed that when a metal part and a mating member are fixed, they can be fixed in an electrically conductive state.

  In the invention of Patent Document 2, a through hole through which a set screw is inserted is provided in the circuit board, and the through hole is electrically connected to the ground conductor pattern. The ground conductor pattern and the housing frame are electrically connected by inserting a set screw into the through hole and fixing the circuit board and the housing frame.

  Furthermore, in the connection between the ground pattern of the circuit board and the housing, a method of mounting a tin-plated thin ground terminal board on the circuit board and fixing the circuit board from above the ground terminal board to the housing with a set screw, For example, a grounding pattern in which a solder portion is formed around the screw hole and a set screw is inserted into the screw hole to fix the circuit board and the housing may be used.

Japanese Patent Laid-Open No. 11-223208 JP 2006-165261 A

  By the way, when using a nut provided with a protrusion on the outer periphery of the flange portion or using a toothed washer or the like, as in the invention of Patent Document 1, since the seat surface side is cut off, conductive cutting waste May occur. When such conductive cutting waste is generated, the cutting waste may cause a malfunction such as a short circuit accident of the circuit unless the cutting waste is reliably removed. However, the cutting waste may be sandwiched between the nut or the toothed washer and the circuit board, and it is difficult to remove the cutting waste reliably. Further, even if the cutting waste is sandwiched, it is assumed that the cutting waste is removed and scattered due to vibration during transportation and the like, which causes a problem. Furthermore, when the cut surface is oxidized, the resistance increases and connection failure occurs.

  In addition, when a through hole is provided as in the invention of Patent Document 2, if the surface of the conductor layer is oxidized, poor connection is caused. Here, if noble metal plating (for example, gold plating) is used, it is possible to prevent oxidation and reduce contact resistance. However, it becomes impossible to connect the ground pattern of the circuit board and the housing with an inexpensive configuration.

  Further, in the method of mounting the ground terminal plate on the circuit board, there are restrictions on the mounting position when mounting the ground terminal plate, and for example, the ground terminal plate cannot be provided at the end of the plate. In addition, the use of a ground terminal plate increases the cost. Further, if a plurality of ground terminal plates are mounted, the time required for mounting becomes long and the production efficiency is lowered. Further, in the method of providing a grounding pattern in which a solder layer is formed around the screw hole, depending on the position of the screw hole, the solder part may not be formed due to positional restrictions of the mounting machine or the solder printer. In addition, when a plurality of solder parts are provided or the area of the solder part is large, if the thickness of the solder varies, the contact state of the set screw becomes unstable.

  Therefore, the present invention provides a circuit board, a circuit board fixing method, and an electronic apparatus that can realize long-term stable electrical connection easily and inexpensively.

  The concept of the present invention is that when a circuit board is electrically and mechanically connected and fixed, a conductive film is formed in a conductor pattern region of the circuit board to which a conductor is connected, so that it can be stably conducted over a long period. It enables electrical connection between the body and the conductor pattern of the circuit board.

  The circuit board according to the present invention is such that a conductive film is formed in a region of a conductor pattern with which a conductor comes into contact when the circuit board is fixed at a predetermined position in the circuit board on which the conductor pattern is formed.

  The circuit board fixing method according to the present invention is a circuit board fixing method for fixing a circuit board on which a conductor pattern is formed. The circuit board fixing method includes: The method includes a step of forming a conductive film in the region and a step of fixing the circuit board at a predetermined position with the conductor and the conductive film in contact with each other.

  The electronic device according to the present invention includes a circuit board having a region in which a conductor pattern is formed and a conductive film is formed on the conductor pattern, and a board fixing member that fixes the circuit board to the housing. When the circuit board is fixed at a predetermined position of the casing by the board fixing member, the conductive pattern is brought into contact with a conductor electrically connected to the casing, and the conductive pattern and the casing are formed. Are electrically connected.

  According to this invention, when the circuit board is electrically and mechanically connected and fixed, the conductive film is formed in the conductor pattern region of the circuit board to which the conductor is connected, and the conductive film and the conductor are contacted. Electrical connection is made by contact. For this reason, oxidation of the conductor pattern is prevented, and long-term stable electrical connection can be realized easily and inexpensively.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a circuit board 10 of the present invention. The circuit board 10 may be a rigid printed wiring board using a hard insulating substrate or a flexible wiring board using a flexible insulating substrate. Also, a single-sided printed wiring board in which a conductor layer is provided only on one surface of an insulating substrate, a double-sided printed wiring board in which a conductor layer is provided on both sides of the insulating substrate, and a multilayer printed wiring board in which a plurality of conductor layers are laminated. Also good. Hereinafter, the case where a printed wiring board in which a conductor layer is provided only on one surface of a hard insulating substrate is used as the circuit board 10 will be described.

  The circuit board 10 has a mounting hole 11 for fixing the circuit board 10 to a housing (not shown). A conductor pattern, for example, a ground pattern 12 is formed on the conductor surface of the circuit board 10. Note that various circuit patterns other than the ground pattern 12 are formed on the circuit board 10 in addition to the ground pattern 12 although not shown as conductor patterns.

  The ground pattern 12 is provided with a connection region for electrical connection with the housing. For example, when a conductive fixing member such as a metal screw or bolt is inserted into the mounting hole 11 and this circuit board 10 is screwed into the casing in an electrically conductive state with the screw or bolt or the like, A connection region 12a is provided around the periphery. In the ground pattern 12 and the wiring pattern, a solder resist layer is formed in areas other than the soldering area and the connection area 12a to prevent solder adhesion and pattern corrosion.

  Thus, since the connection region 12a is in a state where the pattern is exposed without the solder resist layer being formed, for example, a metal screw or bolt is inserted into the mounting hole 11 to enclose the circuit board 10. If it is screwed to the body, the connection area 12a of the ground pattern 12 and the seat surface of the screw or bolt come into contact with each other, and the circuit board 10 and the housing are in an electrically conductive state. However, if the pattern of the connection region 12a is oxidized, the resistance between the circuit board 10 and the housing may increase, resulting in a connection failure or the like. Therefore, a conductive film 13 for preventing pattern oxidation is formed on the pattern of the connection region 12a.

  It is desirable that the conductive film 13 is difficult to peel off from the pattern and has low resistance and high hardness. Further, it is desirable to use a material whose resistance value does not increase due to aging of characteristics. For example, assuming that a polymer-type conductive paste is used as the conductive paste, this conductive paste is applied to the connection region 12a and thermally cured to form the conductive film 13. Further, a conductive paste using a conductive oxide (for example, RuO2) may be used.

  Next, the manufacturing method of the circuit board 10 is demonstrated using FIG. In the etching treatment process ST1, a conductor layer (for example, a copper foil surface) provided on the printed wiring board is etched to form a ground pattern and a wiring pattern.

  For example, when a printing method is used in this etching process, an etching resistant material is applied to the pattern formation position of the conductor layer. Thereafter, the conductor layer is dissolved with an etching solution. At this time, since the etching resistant material is applied to the pattern forming position, when the conductor layer is dissolved, the conductor is not dissolved in the region where the etching resistant material is applied. The non-conductive layer has a pattern shape.

  When using a photographic method in the etching process, an etching resist is applied to the conductor layer, exposure and development are performed, and an etching resistant film is left at the pattern forming position. Thereafter, the conductor layer is dissolved with an etching solution. Here, since the etching resistant film is formed at the pattern formation position, when the conductor layer is dissolved, the region where the etching resistant film is formed is dissolved without dissolving the conductor. The non-conductive layer has a pattern shape.

  In the next resist stripping step ST2, the pattern is exposed by stripping and removing the etching resistant material and the etching resistant film.

  In the printing processing step ST3, silk printing such as solder resist printing and symbol mark display is performed. In this solder resist printing or silk printing, resist ink or marking ink is prevented from being applied to the connection region 12a in order to make electrical connection with a soldering region for connecting the terminals of the component and the housing.

  In the drilling step ST4, a component terminal hole for inserting a component terminal, an attachment hole 11 for fixing the circuit board 10 to the housing, and the like are drilled.

  In the conductive film forming step ST5, the conductive film 13 is formed on the pattern of the connection region 12a. Here, when using the above-mentioned polymer type conductive paste, the polymer type conductive paste is printed on the pattern of the connection region 12a, and then heated and cured to form the conductive film 13. As the polymer-type conductive paste, for example, a phenol resin or the like is used as a binder, and conductive powder such as carbon is mixed with the binder as a filler (TU-1-SL manufactured by Asahi Chemical Research Laboratory). This polymer type conductive paste is printed with a thickness of about 10 microns and then heat-cured to form the conductive film 13. In addition, if not only carbon conductive powder but also silver powder is added as a filler, the resistance value of the conductive film 13 can be lowered.

  In the preflux application step ST6, a water-soluble preflux is applied onto the exposed pattern where the solder resist is not applied. This water-soluble preflux is for preventing deterioration of solderability and pattern corrosion, and is a film that is formed only on a copper foil. Therefore, a conductive film formed using a polymer-type conductive paste. It is not formed on top. That is, a layer serving as a barrier for electrical connection is not formed on the conductive film 13 when the circuit board 10 is fixed by the conductive fixing member.

  FIG. 3 shows a configuration of an electronic device using the circuit board shown in FIG. In FIG. 3, a conductive screw is used as a board fixing member for fixing the circuit board to the casing, and the conductor pattern of the circuit board placed at a predetermined position of the casing is represented by the screw and the conductor pattern. The case where it electrically connects with a housing | casing through the electrically conductive film formed on the top is shown.

  A screw hole 21 is screwed into the housing 20 at a position facing the mounting hole 11 of the circuit board 10 placed at a predetermined position. As shown in FIG. 3A, the circuit board 10 on which the components have been mounted is placed at a predetermined position of the housing 20 so that the seat surface of the screw 31 and the conductive film 13 face each other. At this time, the screw hole 21 of the housing 20 has the same hole position as the mounting hole 11 of the circuit board 10. Therefore, by inserting the conductive screw 31 into the screw hole 21 from the circuit board 10 side, the circuit board 10 can be fixed to the housing 20 as shown in FIG.

  Further, as shown in FIG. 3B, when the circuit board 10 is fixed to the housing 20, the ground pattern 12 and the housing 20 of the circuit board 10 are electrically connected via the conductive film 13 and the screw 31. It becomes a conductive state. Here, since the connection region 12a of the ground pattern 12 is covered with the conductive film 13, the conductive state between the circuit board 10 and the housing 20 is stable over a long period of time.

  As described above, when the circuit board 10 is fixed to the housing 20, the conductive region 13 is formed in the connection region 12a of the ground pattern 12 with which a conductive fixing member such as a screw 31 abuts, thereby connecting the connection region 12a. Therefore, the electrical connection between the circuit board 10 and the housing 20 can be stably performed over a long period of time.

  In addition, since the conductive film is formed on the pattern, it can be easily applied without any positional restriction as in the case of mounting a ground terminal plate or the case of providing a solder portion. Furthermore, since the conductive film can be formed at a lower cost than when noble metal plating is used, a stable conduction state can be ensured with an inexpensive configuration over a long period of time. In addition, since no new parts are used, manufacturing lead time and parts handling man-hours are not increased. Moreover, since there is no generation | occurrence | production of cutting waste, malfunctions, such as a short circuit accident of a circuit, will not be generated.

  Next, a change in high-frequency transmission characteristics due to the provision of the conductive film 13 will be described. FIG. 4 shows a substrate mounting state when measuring high-frequency transmission characteristics. A conductor pattern 52 for inputting and outputting a high frequency signal is formed on one surface of the circuit board 51, and a connection pattern 54 is formed around the screw hole 53 on the other surface. Furthermore, the conductor pattern 52 and the connection pattern 54 are electrically connected by a via hole 55. A conductive film 56 is formed on the connection pattern 54 of the circuit board 51.

  A conductor pattern 62 for inputting and outputting a high frequency signal is formed on one surface of the circuit board 61, and a connection pattern 64 is formed around the screw hole 63 on the other surface. Furthermore, the conductor pattern 62 and the connection pattern 64 are electrically connected by a via (via hole) 65.

  The circuit boards 51 and 61 formed in this way are overlapped with each other via the metal plate 71 with the connection pattern 54 and the connection pattern 64 facing each other. Further, in a state where the circuit boards 51 and 61 are overlapped, the bolts 72 are inserted into the screw holes 53 and 63 and screwed into the nuts 73 to fix the circuit board 51 and the circuit board 61 integrally.

  FIG. 5 shows the reflection impedance when a high frequency signal is input to the conductor pattern 52 of the circuit board 51. Here, the reflection impedance characteristic when the conductive film 56 is provided and the circuit board 51 and the circuit board 61 are fixed integrally is a characteristic A. Further, after loosening the bolt 72 and the nut 73 to separate the circuit board 51, the circuit board 61 and the metal plate 71, the bolt 72 is tightened again and the circuit board 51 and the circuit board 61 are fixed together via the metal plate 71. In this case, the reflection impedance characteristic is characteristic A (solid line).

  When the conventional circuit board is fixed integrally with the circuit board 61, that is, when the circuit board without the conductive film 56 and coated with the water-soluble preflux is fixed integrally with the circuit board 61, the reflection impedance The characteristic was characteristic A. The reflection impedance characteristics when the bolt 72 and the nut 73 are loosened to separate the circuit board and the metal plate 71 and then the bolt 72 and the nut 73 are tightened again and the circuit board is fixed integrally via the metal plate 71 are as follows. Characteristic B (broken line) was obtained.

  That is, in the conventional circuit board in which the conductive film 56 is not formed, when the circuit board is reattached, the reflection impedance in the frequency band of 1 GHz or less is increased and the characteristics are deteriorated as compared with the case where the conductive film 56 is formed. It has become a thing. However, if a circuit board on which the conductive film 56 is formed is used, stable high-frequency transmission characteristics can be obtained with little change in characteristics even when the circuit board is reattached.

  Even when a shield case is used as a housing and the circuit board 10 is provided in the shield case for electrical and mechanical connection, a polymer type conductive paste is printed and cured on the circuit board 10 side. If the conductive film is formed and the metal part is brought into contact with the conductive film, the high-frequency conduction is stabilized, and the electromagnetic radiation noise can be reduced and the reduction can be stabilized.

It is a figure which shows the structure of a circuit board. It is a figure which shows the manufacturing method of a circuit board. It is a figure which shows the structure of an electronic device. It is a figure which shows the board | substrate attachment state in the case of measuring a high frequency characteristic. It is a figure which shows a reflective impedance characteristic.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,51,61 ... Circuit board, 11 ... Mounting hole, 12 ... Grounding pattern, 12a ... Connection area, 13, 56 ... Conductive film, 20 ... Housing, 21, 53, 63 ... screw hole, 31 ... screw, 52, 62 ... conductor pattern, 54, 64 ... connection pattern, 71 ... metal plate, 72 ... bolt, 73 ... nut

Claims (5)

In the circuit board on which the conductor pattern is formed,
A circuit board, wherein a conductive film is formed in a region of the conductor pattern in contact with a conductor when the circuit board is fixed at a predetermined position. The circuit board according to claim 1, wherein the conductive film is formed using a conductive paste. A circuit board fixing method for fixing a circuit board on which a conductor pattern is formed,
Forming a conductive film in a region of the conductor pattern with which a conductor contacts when the circuit board is fixed in place;
And a step of fixing the circuit board at the predetermined position in a state where the conductor and the conductive film are in contact with each other. A circuit board having a region in which a conductive pattern is formed and a conductive film is formed on the conductive pattern;
A board fixing member for fixing the circuit board to the housing;
When the circuit board is fixed at a predetermined position of the housing by the substrate fixing member, the conductive film is brought into contact with a conductor electrically connected to the housing to form the conductive film. An electronic device characterized in that the conductor pattern and the housing are electrically connected. The electronic device according to claim 4, wherein the conductor electrically connected to the casing is a substrate fixing member having conductivity.

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