JPH0710974U - Circuit board - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent an increase in conductor resistance in polymer-type thick metal film conductors. [Structure] 1 is an insulating substrate, 2 is a polymer-type thick metal film conductor, and 4 and 5 are electronic components and VFD mounted on the substrate 1 by solder 6. Then, the solder 6 is coated on the polymer type thick metal film conductor 2a having a relatively long conductor length.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a circuit board using a polymer-type thick metal film conductor paste.

[0002]

[Prior art]

 FIG. 2 is a circuit diagram of a display device using a fluorescent display tube (hereinafter referred to as VFD) using this type of circuit board, and FIG. 3 is a side sectional view of FIG. A conventional circuit board will be described with reference to these figures. 1 is an insulating substrate, 2 is a polymer-type thick metal film conductor formed using a copper conductor paste, 3 is a solder resist, 4 is an electronic component, and 5 is an electronic component. VFD, 6 is solder. To the VFD 5, the filament circuit 2a and the anode circuit 2b formed of the polymer type thick metal film conductor are connected. Reference numeral 8 is an IC constituting a drive circuit, 9 is a segment switch for turning on and off the segment of the display portion of the VFD 5, and 10 is a DC 12V power source.

[0003]

[Problems to be solved by the device]

 By the way, the conductor pattern length of the polymer-type metal thick film conductor 2 is different depending on the layout relationship of the electronic component on the substrate 1, and the filament circuit 2a is formed longer than other circuits such as the anode circuit 2b. . The polymer-type metal thick film conductor 2 has a conduction mechanism composed of metal conductive particles 21 and an organic material 22 such as phenol or epoxy as shown in FIG. 4, and is performed through the metal conductive particles 21. As the conductor pattern length becomes longer, the conductor resistance becomes higher than that of the copper foil used for the insulating substrate 1, etc., and as a result, the voltage drop also becomes large, and the rated voltage is not applied to the filament. Electron emission was reduced, which caused problems such as uneven brightness and reduced brightness. Fig. 5 shows the relationship between the conductor pattern length of PTM (polymer-type thick metal film conductor) and conductor sheet resistance. From the figure, in the case of only PTM copper paste conductor (graph A), the conductor resistance is It turns out that is large.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a circuit board in which an increase in the conductor resistance of a polymer-type thick metal film conductor is prevented. To do.

[0005]

[Means for Solving the Problems]

 A circuit board according to the present invention which achieves this object is a circuit board in which a conductor circuit is formed on an insulating substrate by using a polymer-type thick metal film conductor paste, and at least a part of the conductor of the conductor circuit is Provide a solder coat section.

[0006]

[Action]

 According to the present invention, by coating the solder on the conductor of the conductor circuit using the polymer-type metal thick-film conductor paste, the solder has a lower electric resistance than the polymer-type metal thick-film conductor paste, and An increase in the conductor resistance of the thick film conductor circuit is prevented.

[0007]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of a circuit board according to the present invention. In the figure, the insulating substrate 1 is made of glass epoxy, and the polymer-type metal thick film conductor 2 is formed by screen printing using a copper conductor paste. The resistance of the conductor 2 (sheet resistance) at this time is about 40 to 50 mΩ / □ as shown in the graph A 1 in FIG. The solder resist 3 is formed by screen printing.

A cream solder is used as the solder 6, and the solder 6 is printed and reflowed so as to coat the filament circuit 2 a while mounting the electronic component 4, the VFD 5 and the IC 8. Here, the conductor resistance value (1.7 × 10 ⁻⁷ Ω · m) of 60Sn-40Sb forming the solder 6 is equal to the conductor resistance value of the polymer copper forming the polymer-type thick metal film conductor 2 (2.0 × Since it is lower than 10 ⁻⁶ Ω · m), as described above, by coating the relatively long filament circuit 2a with the solder 6 having a low conductor resistance, The conductor resistance of path 2a is significantly reduced. Graph B in Fig. 5 shows the relationship between the conductor pattern length and the conductor sheet resistance when solder coating is applied to PTF copper paste, but it is about 1/10 of the conventional case where only conductor 2 is used. Has been reduced to.

As described above, since the resistance of the filament circuit 2a can be significantly reduced, it is possible to prevent uneven brightness, decrease in brightness, etc. of the VFD. In general, the conductor resistance (sheet resistance: Rs) is represented by (Equation 1), and in the case where the conductor length: 1 cannot be shortened as in the present embodiment, in order to reduce the conductor resistance, the printed film thickness can be reduced. : Either increase t or increase the line width: w. However, the method of increasing t is not preferable from the viewpoint of line resolution because it easily causes sagging and bleeding. In addition, the method of widening w leads to an increase in the substrate area, which hinders miniaturization.

[0010]

[Equation 1]

On the other hand, since the method of coating with solder can be performed in the same step as solder printing and reflow at the time of mounting an electronic component, it can be performed without increasing the number of steps and does not increase the surface area of the substrate. . Also, in terms of reliability of the solder coating, since the polymer conductor 2a is coated with solder (metal), a circuit with high reliability can be formed even against fluctuations in conductor resistance (particularly moisture resistance). 7 is an overcoat, which is coated with silicon varnish or insulating resin (epoxy / phenol), and may be deleted if there is no problem with the short between conductors.

Although the insulating substrate 1 formed of glass epoxy is used in this embodiment, it is needless to say that it may be any member as long as it is a substrate forming member such as phenol, ceramic, or glass. Further, although copper is used for the thick metal film conductor paste 2, the present invention is not limited to this, and other metal pastes such as Ni and Ag may be used.

[0013]

[Effect of device]

 INDUSTRIAL APPLICABILITY As described above, the present invention is a circuit board in which a conductor circuit is formed by using a polymer-type thick metal film conductor paste on an insulating substrate, and at least a part of the conductor of the conductor circuit is coated with solder. Since the conductor resistance of the conductor circuit is reduced by providing the section, the sheet resistance does not increase even if the conductor circuit becomes long, which increases the degree of freedom in the circuit design of the circuit board. Further, since it is not necessary to widen the width of the conductor to reduce the conductor resistance, the size of the board can be reduced. In addition, the method of coating with solder can be performed easily without increasing the number of steps because it can be performed simultaneously with solder printing and reflow when mounting electronic components in the same step. Also, since solder coating is performed, a circuit having high reliability with respect to fluctuations in conductor resistance, particularly humidity resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of a circuit board according to the present invention.

FIG. 2 is a circuit configuration diagram of a conventional circuit board.

FIG. 3 is a side sectional view of a conventional circuit board.

FIG. 4 is a diagram illustrating a mechanism of a polymer-type thick metal metal film conductor.

FIG. 5 is a diagram showing variations in conductor sheet resistance in the case of using only a PTF copper paste conductor and in the case of applying a solder coat.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Polymer type thick metal film conductor 5 VFD 6 Solder 21 Metal conductor particle 22 Organic material

Claims (1)

[Scope of utility model registration request] 1. A circuit board in which a conductor circuit is formed on an insulating substrate by using a polymer-type thick metal film conductor paste,
A circuit board, characterized in that a solder coating portion is provided on at least a part of the conductor of the conductor circuit.