JPS6390191A - Printed wiring board - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a printed wiring board on which circuit components are mounted and soldered.

(Prior art) Normally, when installing circuit components on a printed wiring board, such as resistors, capacitors, and ICs with lead wires, the lead wires are inserted into the mounting holes of the printed wiring board from the front side using an insert machine or manually. Also, the leadless chip components are adhesively fixed to the conductive circuits on the back side of the printed FA board using a chip mounter, and the printed wiring board on which these circuit components are mounted is soldered using a solder bath. , each circuit component is electrically and mechanically connected and fixed to the conductive circuit of the printed wiring board.

When soldering this printed wiring board, if oxidation occurs in the conductive circuit, defects are likely to occur in the soldering.

Therefore, when manufacturing printed wiring boards, a conductive circuit is formed on the back side of the insulating board by etching copper foil, and a resist film is also formed on the back side of the insulating board, leaving necessary lands around the mounting holes for circuit components. Immediately after forming the printed wiring board, a flux treatment is often applied to the back side of the insulating plate to cover the exposed portion of the conductive circuit to prevent oxidation of the conductive circuit on the printed wiring board.

However, the primary purpose of flux is to promote soldering properties, and the prevention of oxidation is secondary, and there is still a problem in that it is easily oxidized.

Furthermore, after the printed wiring board is formed, the exposed portions of the conductive circuits are plated with solder to prevent their oxidation. This solder plating process is very effective in preventing oxidation, but the mounting holes of circuit components are likely to be blocked by solder.
It is necessary to perform machining so that it does not become clogged at any time, which poses a problem of poor workability and lack of economic efficiency.

Furthermore, as described above, when circuit components are mounted and soldered to the printed circuit board, some of the circuit components may be attached later. In other words, after the entire circuit components are soldered and fixed, there are many parts that are inserted manually by machining, and special irregularly shaped parts such as adjustment parts, jumper wires, coils, volumes, connectors, switches, etc. It is installed after normal soldering process in a solder bath. In this case, the mounting holes for retrofitted circuit components are drilled at the same time as the other holes on the printed wiring board during processing, and the mounting holes for retrofitted components remain empty until the initial soldering. At this time, the empty mounting holes without lead wires are likely to be closed by the solder, and machining is required to prevent the mounting holes from being blocked.

Further, in a typical printed wiring board, flux is applied to the conductive circuit side on the back side in order to accelerate the soldering process. However, in recent printed wiring boards, in addition to conventional resistors, capacitors, transistors, ICs, and the like, components having contacts such as switches and polyimide are directly inserted into mounting holes and soldered. In this case, when a printed wiring board with circuit components attached thereto is soldered in a solder bath, a phenomenon occurs in which the flux melts and partially blows up from the mounting holes and adheres to the terminals of the circuit components. If flux adheres to the terminal, it may affect the contact portion, causing contact failure or corrosion, which may cause malfunction.

Therefore, as a method to prevent problems caused by flux, for example, cleaning the adhered flux with a cleaning solution using Freon is carried out, but the cleaning solution itself is corrosive, and depending on the function of the electronic equipment used, the cleaning solution may It has even become necessary to create a new process to remove it.

(Problems to be Solved by the Invention) As mentioned above, when applying solder plating to a printed wiring board, or when soldering to a printed wiring board with mounting holes left open for some retrofitted components, solder may cause the mounting holes to It is necessary to perform machining so that the holes are not blocked, which poses problems in workability and economy.Furthermore, there is a problem in that the flux penetrates into the surface side, resulting in defective products.

The purpose of the present invention is to prevent the mounting holes from being blocked and to prevent flux from penetrating into the surface side when soldering is performed by leaving mounting holes for solder plating or retrofitted components. It is something to do.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a printed circuit board in which a conductive circuit 2 is formed on the back surface of an insulating plate 1, and a mounting hole 3 is formed in the insulating plate 1 for inserting a lead wire 12 of a circuit component 11. In the wiring board, a foamed elastic material 5 is adhered to the surface of the insulating plate 1 so as to cover all of the mounting holes 3.

(Function) The present invention provides solder plating on the conductive circuit 2 or circuit components 1.
When performing soldering in step 1, in the mounting hole 3 which is a space, the gas generated by the solder and flux does not escape to the surface side due to the foamed elastic material 5 covering the top surface, but flows back through the mounting hole 3. The solder that is about to be plugged is blown away, and the mounting hole 3 is maintained with its lower surface open. Further, the 7 lux on the back side is prevented from penetrating into the front side by the foamed elastic material 5.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIGS. 1 and 2, reference numeral 1 denotes an insulating board of a printed wiring board, and a conductive circuit 2 made of copper foil is formed on the back side of this insulating board 1 by etching, and is mounted at a circuit component mounting position 7L 3 is drilled. Also, on the back side of the insulating plate 1, the conductive circuit 2 portion around each mounting hole 3 is left, and the portion 1 does not require soldering. Electric circuit 2
A resist crotch 4 is applied to cover the crotch.

Then, on almost the entire surface of the circuit component mounting surface of the insulating plate 1, a foamed elastic material 5 is applied to a constant thickness by printing and coating, covering all of the mounting holes 3. A circular coating material 6 is applied by printing to the upper surface of each of the mounting holes 3, approximately at the center thereof. At this time, by applying the coating material 6, it also permeates into the air bubbles on the surface of the foamed elastic material 5, forming a film.

Further, on the surface of the foamed elastic material 5, an indication 7 such as letters or symbols indicating the names of circuit components, connection states, etc. is formed. This display 7 is simultaneously printed and formed using the same material when the coating material 6 is screen printed.

Further, a mounting hole 8 is formed in the edge of the insulating plate 1, and through this mounting hole 8 it is fixed to, for example, a chassis or a case (not shown) using screws or fasteners.

When solder plating is applied to the exposed portion of the conductive circuit 2 on this printed wiring board, the printed wiring board is sent to the soldering process as shown in Figure 3, and usually after a preheating process, the soldering process is performed. Soldering is performed using a bath, and a solder plating layer 10 is formed on the exposed portion of the conductive circuit 2.

During this solder plating, flux is applied to the conductive circuit 2 side to facilitate the soldering process.
During the soldering process, gas is generated due to the high temperature, and this gas enters the mounting hole 3, but the foamed elastic material 5 prevents the gas from escaping outward and flows backwards, trying to block the bottom surface of the mounting hole 3. The solder that was present is blown away by the gas flowing backward, and the mounting hole 3 reliably maintains its initial open state.

In addition, when soldering circuit components to the above-mentioned printed wiring board, as shown in FIG.
Circuit parts 1 such as electronic parts such as capacitors and connecting wires
1 is loaded by an insert machine. That is, the lead wire 12 of the circuit component 11 is inserted into the mounting hole 3 through the foamed elastic material 5.

Further, the lead wires of some of the circuit components 11 are manually inserted into the mounting holes 3 through the foamed elastic material 5.

At this time, the coating material 6 at the center of each attachment hole 3 makes the positional relationship with respect to the attachment hole 3 clear, and the lead wire 12 can be easily inserted into a predetermined position.

As the lead wire 12 is inserted, the lead wire 12 is reliably held by the elastic action of the foamed elastic material 50 and temporarily fixed.

In addition, as shown in FIG. iR4 and FIG.
is fixed with an adhesive, and the terminal portions 12a at both ends thereof are brought into contact with the conductive circuit 2.

In this state, the printed wiring board is sent to the soldering process, and after passing through the preheating process, the soldering process is performed in a soldering bath, and the lead wires 12 and terminal portions 12a of the circuit components 11 and 118 of the insulating board 1 are connected to conductive wires. The lead wire 12 and terminal portion 12a of the circuit component 11.11a are electrically and mechanically connected to the conductive circuit 2 of the insulating plate 1 by soldering to the circuit 2.

At this time, the mounting holes 3 for retrofitted parts are open and are about to be closed with solder, but as in the case of the solder plating process, the initial open state is maintained due to the backflow of gas, and the holes are then closed. It becomes easier to insert lead wires of attached parts.

In addition, by applying the coating material 6 to the upper surface of the mounting hole 3 on the surface of the foamed elastic material 5 to form a film, the mounting hole 3
It is possible to more reliably prevent the gas from flowing upward.

Furthermore, since the mounting hole 3 of the circuit component 11 is closed by the foamed elastic material 5, the terminals of the circuit component 11 may be penetrated by melted flux into the foamed elastic material 5 during soldering work. Since the flux does not reach the point of welding, it is possible to prevent the flux from affecting the electronic components.

In addition, as shown in FIG. 6 and FIG. The upper surface of the mounting hole 3 may be further reinforced by applying a coating material 6a in a ring shape to the upper surface of the mounting hole 3.

The foamed elastic material 5 is, for example, a foamed ink made of an oligomer blended with microcapsules encapsulating water, acrylic resin, MMA (methyl methacrylate), other acrylic esters, ethylene vinyl acetate, etc. Use. This foaming ink is a screen-printable engineering type with 100 to 140
It is possible to obtain an expansion coefficient of 5 to 7 times by heating at °C or by irradiation with ultraviolet rays, and it also has excellent electrical properties such as insulation and moisture absorption resistance. Further, as the coating materials 6, 6a,
Solder resist ink, which is used as an insulating material for solder, is suitable in terms of hardness and adhesion.

〔Effect of the invention〕

According to the present invention, when applying solder plating to the exposed part of the conductive circuit on the back side of the insulating plate, or when inserting the lead wire of the circuit component into the mounting hole and soldering, the mounting hole of the retrofitted component When soldering is carried out with the mounting holes left blank, the mounting holes that are open during the soldering process will not be blocked by solder due to the gas backflow phenomenon.
It is possible to easily attach circuit components after solder plating and attach retrofitted components.

In addition, since solder plating of conductive circuits is easy,
It becomes easy to apply solder plating and store it for a relatively long period of time while preventing oxidation.

Also, since the mounting holes of circuit components are covered with foamed elastic material, during soldering work, even though the melted flux may seep into the foamed elastic material, it will not be possible to weld it to the terminals of the circuit components. 11 to electronic components due to flux can be prevented.

In addition, by forming a foamed elastic material on the surface side of the mounting hole of the insulating plate, the inserted lead wire can be held elastically, and the circuit components can be held stably and reliably temporarily fixed.
When soldering, it is possible to perform good soldering without the circuit components tilting or falling off. Furthermore, when installing and stacking chip components, the foamed elastic material on the entire surface provides a cushion. It can also be used as a material to protect circuit components.

Furthermore, the foamed elastic material can be easily formed by screen printing or the like, and can be manufactured easily and inexpensively.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing one embodiment of the printed wiring board of the present invention, FIG. 2 is a sectional view thereof, FIGS. 3 to 5 are sectional views showing the state of the solder, and FIG. A cross-sectional view of a part of the embodiment, and FIG. 7 is a plan view thereof. 1. Insulating plate, 2. Conductive circuit, 3. Mounting hole, 5.
Foamed elastic material, 11...Circuit parts, 12...Lead wire.

Claims (1)

[Claims] (1) In a printed wiring board in which a conductive circuit is formed on the back side of the insulating board and mounting holes are drilled in the insulating board for inserting lead wires of circuit components, all of the mounting holes are covered on the front surface of the insulating board. A printed wiring board characterized by being coated with a foamed elastic material.