JPS6088495A - Circuit board - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a wiring board used in general home appliances such as televisions and stereos.

Conventional configurations and their problems In recent years, home appliances have rapidly become smaller, lighter, and more energy efficient.One of the factors that has made this possible is the smaller size, higher performance, and higher packaging density of components. It can be said that there is In order to improve packaging density, a method of mounting leadless components on both sides of a wiring board is often adopted. For example, solder is pre-coated on the electrodes of the part where the parts are to be mounted, then flux is applied on top of this, the parts are then mounted, placed in an infrared oven, etc., and the solder is remelted. A construction method that involves attaching is often used.

Another method is to supply cream solder to the electrodes of the predetermined component mounting area using silk printing or a dispenser.
A commonly used method is to mount a leadless component on top of this, place it in an infrared furnace, etc., and melt and congeal cream solder for soldering.

When attempting to solder leadless components to both sides of a wiring board using this method, the board is placed in an infrared oven to melt the solder, but at this time the components mounted on the bottom side of the board are To prevent this from falling off, it is necessary to individually adhesively fix the components mounted on the lower surface of the wiring board. Adhesives used for this purpose are thermosetting, ultraviolet curable, or adhesives having both properties. Screen printing or a dispenser method is generally used to supply the adhesive to a predetermined location, but the screen printing method cannot be used if flux or cream solder has already been supplied. Therefore, the adhesive must be sequentially supplied to the required locations using a dispenser, and heat curing and ultraviolet curing steps are required, which consumes a lot of working time.

Furthermore, in the case of small parts, since the solder and adhesive are in close proximity, they mix with each other and have an adverse effect on soldering, resulting in problems such as soldering defects. Fixing with this adhesive is originally unnecessary and does not contribute to electrical bonding in any way.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and aims to shorten working time, reduce costs, and improve soldering reliability.

Structure of the Invention In order to achieve the above object, the wiring board of the present invention uses solder having a different melting point on the first side and the second side when soldering components on both sides of the board. Reflow solder the leadless components using the higher melting point solder, then flip the board over, second side up, and reflow solder the leadless components using the lower melting point solder. It is configured to do so.

An example will be explained. FIG. 1 is a partial side view of a completed wiring board according to the present invention. 1 is a wiring board, and wiring electrodes 4 and 5 are formed on a first surface 2 and a second surface 3, respectively.

Leadless components 8 and 9 are provided on both sides 2 and 3 of the wiring board 1.
It is soldered onto the wiring electrodes 4 and 5 with solders 6 and 7.

Next, we will explain the soldering process. First, solder 6 is placed on the wiring electrode 4 on the first surface 2 of the wiring board 1.
A cream solder is supplied in quantity using a method such as screen printing, a leadless component 8 is further mounted on this solder, and in this state the wiring board 1 is placed in a solder reflow oven such as an infrared furnace or an atmosphere furnace. The leadless components 8 are carried in and soldered. FIG. 2 is a diagram showing an overview at this time.

1o is a solder reflow oven, and 11 is a conveyor belt or chain. 12 is a heating element for preheating and solder reflow, and 13 is a wiring board with components mounted on its first surface.

In this manner, only the first surface 2 of the wiring board 1 is soldered to the dress component 8.

Next, the wiring board 1 is turned over, and a quantity of solder 7 in the form of cream solder is supplied onto the wiring electrodes 5 on the second surface 3 in the same manner as before. Thereafter, the leadless component 9 is mounted, carried into a reflow oven, and soldered. Naturally, the temperature setting conditions for the solder reflow at this time are different from those for the first solder reflow because the melting points of the solders 6 and 7 are different. FIG. 3 is a diagram showing an outline of the second solder reflow process. 14 is a solder reflow oven, and 15 is a conveyor belt or chain. -1
6 is a heating element for preheating and soldering IJ flow, 17
is a wiring board with leadless components mounted on both sides.

Components are mounted on both sides of the board, and a board holder 18 is used to hold the self-wired board by applying buoyancy to the parts on the bottom side from the belt surface. However, this substrate holder 18 is not necessary in the chain-type conveyance method in which the substrate is conveyed by holding the end surface of the substrate.

Now, when reflowing the solder 7 on the second surface 3, the first surface is facing downward, but the solder 6 used on the first surface 2
has a higher melting point than the solder 7 used on the second surface,
Even if the solder 7 melts, the solder 6 does not melt. Therefore, although the first surface 2 faces downward, the component 8 soldered to this surface will not fall off.

As explained above, IJ-)' on both sides of the wiring board
When soldering non-resistance parts, by using solder with different melting points on the first and second sides, and by making good use of the difference in melting points, soldering can be done on one side (Ill. The cost is reduced by eliminating the need for fixing and shortening the adhesive supply and drying time. Since no defects occur, the number of defects can be reduced during soldering, and highly reliable soldering can be performed.

[Brief explanation of the drawing]

FIG. 1 is a side view when leadless components are soldered to both sides of a wiring board according to an embodiment of the present invention, and FIGS. It is a figure showing the outline of the second time. 1...Wiring board, 4, 5. Wiring electrode, 6, 7
...Solder, 8,9...Leadless parts, 10゜14...Reflow oven, 11.15.
...conveyor belt or chain, 12.16...
... Heating element, 18... Board holder.

Claims (2)

[Claims] (1) A wiring board characterized in that leadless components are soldered to both sides of the board using solder having different melting points on the front and back sides. (2) Eutectic point tin in soldering components to the surface
When soldering components on the back side using lead solder, the temperature must be at least 20°C higher than the tin-lead solder.
The wiring board according to claim 1, characterized in that a solder having a low melting point is used.