JPH0325039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for mounting electronic components on a printed circuit board.

[Technical background of the invention and its problems]

Conventionally, in the mounting method of supplying preliminary solder to the conductor rounds on the printed circuit board to which electronic components are soldered, and then performing reflow soldering, when processing both sides of the board, reflow was repeated for each side. There were drawbacks such as the parts on the surface to be mounted were exposed to high temperatures twice, resulting in deterioration of the characteristics of the parts.

Further, as shown in Fig. 1, the electronic component 1 is temporarily fixed to the lower surface of the printed circuit board 3 with adhesive 2, the electronic component 4 is mounted on the upper surface of the circuit board 3, and at the same time, the conductor round 5
When melting the upper solder paste 6 and performing so-called simultaneous reflow soldering on both sides, the problem of poor soldering of the lower electronic component 1 must be solved.

That is, solder paste 6 used as preliminary solder
While the adhesive 2 significantly reduces its volume when melted, the electronic component 1 remains supported by the adhesive 2 at a height h corresponding to the thickness of the paste, so soldering defects are likely to occur.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and provide a method for simultaneously reflowing electronic components mounted on both sides of a board and mounting the components at a high density.

[Summary of the invention]

The present invention provides a conductor round on the side to which an electronic component is to be temporarily fixed with an adhesive, in a shape in which sides facing each other across the area to which the adhesive is applied are substantially cut out, and This is a mounting method for forming a circuit by performing reflow soldering, which is characterized by performing a pressing process to crush the preliminary solder fillet on the conductor round before mounting the conductor round.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 2 to 4.

As is clear from the above, when assuming simultaneous reflow processing on both sides, adhesive is required to temporarily fix the parts on the bottom side of the board at least to prevent parts from falling. This will be explained with reference to a plan view.

The conductor round 10 in Fig. 2 is a conductor printed on an insulating substrate, and the conductor part that can be soldered is secured as a round by the shape of the conductor layer itself or by covering the conductor with solder resist. It is provided at a position corresponding to the electrode of the electronic component.

Further, the conductor round 10 has substantially symmetrical portions with smaller round areas on opposite sides, in other words, it has a shape in which the portion to which solder is attached is partially cut out. ing.

The conductor round 10 is then supplied with preliminary solder. (Figure 2) However, the preliminary solder, that is, the solder 13 in the figure, swells up due to the surface tension during melting and takes on a fillet shape, and the supply of solder onto the conductor round 10 is limited to the solder tank. This is done by printing a dip or solder paste and then melting it.

Next, a conductor round 10
A pressing process is performed to crush the fillet of solder 13 on top and obtain preliminary solder that is spread on the substrate and exhibits a uniformly flat surface.

Therefore, the solder 13 on the conductor round 10 protrudes from the round and spreads to the surrounding area as shown in Figure 4, but since there is no solder on the vicinity of the notch 11, the spread in that direction is suppressed. .

Next, an adhesive 14 whose main component is a thermosetting resin or an ultraviolet curable resin is applied using a microdispenser or the like, and the application area is applied between the opposite sides of the round as shown in the figure. It is located to intervene.

Thereafter, the mounted electronic component 15 is soldered to the conductor round 10 by reflow soldering while being temporarily fixed with the cured adhesive 14. (Figure 5) That is, in this example, since the preliminary solder is not a solder paste (a mixture of solder powder and an organic solvent), the volume change due to melt aggregation is small, and since it has been subjected to a press treatment,
The thickness of the preliminary solder is low relative to the amount of solder supplied, that is, the gap between the electrode of the electronic component and the conductor round, which is a cause of soldering defects, becomes extremely small, thereby preventing the occurrence of defects.

The purpose of the pressing process is not simply to obtain a flat surface for mounting electronic components (leadless components in this embodiment), but to minimize the preliminary solder thickness.

As a result, the solder spreads greatly on the board, so the cutout is provided to ensure an area for applying the temporary fixing adhesive regardless of the mounting density.

〔Effect of the invention〕

As described above, the electronic component mounting method of the present invention is a mounting method in which preliminary solder is supplied to conductor rounds on a printed circuit board to which electronic components are soldered, and a circuit is formed by performing reflow soldering. The conductor round on the side to which electronic components are to be temporarily fixed with adhesive has a shape in which sides facing each other across the area to which the adhesive is applied are substantially cut out, and before the electronic components are attached, The method is characterized in that a press treatment is applied in advance to crush the preliminary solder fillet on the conductor round, thereby preventing soldering defects and allowing reflow to be performed with components mounted on both sides of the board.

In particular, when small components such as leadless components are mounted at high density, the pressed solder paste does not cover the adhesive application area, which is suitable.

The present invention is not limited to the embodiments described above and illustrated, and design changes can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional example, and FIGS. 2 to 5 are plan views showing steps of an embodiment of the present invention. Explanation of symbols, 1, 4, 15...Electronic parts, 5,
10... Conductor round, 11... Notch, 13...
Solder, 14...Adhesive.

Claims (1)

[Claims] 1 Preliminary soldering is performed on the conductor rounds on the printed circuit board, and electronic components are temporarily fixed with adhesive at positions corresponding to the preliminary soldering, and then the electronic components are mounted on the substrate using a reflow soldering method. In the electronic component mounting method, the conductor round has a shape in which sides facing each other across the area to which the adhesive is applied are notched, and
The above-mentioned preliminary solder is formed by first melting the solder paste printed on each conductor round, solidifying it by cooling from the melted state, and then applying a press treatment to spread it around the conductor round. A method for mounting an electronic component, characterized in that: