JPH0325040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a mounting method for soldering leadless components, particularly by a reflow soldering method.

[Technical background of the invention and its problems] Conventionally, in a mounting method in which preliminary solder is supplied to conductor rounds on a printed circuit board to which leadless components are soldered and reflow soldering is performed, processing is applied to both sides of the board. In this case, since reflow was repeated for each side, the components on the surface to be mounted first were exposed to high temperatures twice, resulting in deterioration of the characteristics of the components.

For this reason, a double-sided reflow method has been proposed in which the upper and lower surfaces are soldered at once, but solder paste is printed on the conductor round 5 and the leadless component is temporarily attached to the bottom surface of the printed circuit board 3 using adhesive 2 to prevent it from falling. The leadless component 4 is mounted on the upper surface of the board 3, and when this process is performed, the electrode of the lower leadless component 1 and the conductor round 5 are well connected by the solder 6, as shown in FIG. Things happen that cannot be done.

This is because while the solder paste used as preliminary solder significantly reduces its volume when melted, the leadless component 1 remains supported by the adhesive 2 at a height corresponding to the paste thickness, and the leadless component 1 remains supported by the adhesive 2 at a height corresponding to the paste thickness. The presence of gaps between component electrodes and conductor rounds is a contributing factor to soldering defects.

Solder application in such paste printing is particularly important when placing conductor rounds close to each other for the purpose of high-density mounting of components.If the solder is not applied to a considerable thickness, the solder will eventually contribute to the electromechanical connection. It is not appropriate because the amount tends to be insufficient, and paste tends to adhere to the component mounting section of the automatic mounting machine (NC control) when mounting components.

There are other ways to supply a sufficient amount of preliminary solder, such as mounting solid solder or dipping the board in a solder bath to form a fillet on a round surface, but in general, the thickness of the preliminary solder is thick. Ensures high-density mounting of leadless components,
In addition, there were drawbacks such as unreliable soldering.

[Object of the Invention] It is an object of the present invention to provide a method for reflowing leadless components mounted on both sides of a substrate at a high density by simultaneously reflowing the components to solve the above problems.

[Summary of the Invention] The present invention temporarily fixes leadless components with an adhesive, and cools and solidifies the solder from a molten state on a conductor round on the surface of a board to be soldered by reflow soldering. A leadless component is produced by chemically bonding the metal to the conductor round as a preliminary solder, and applying a press treatment to the solder to spread the solder around the conductor round, thereby substantially reducing the preliminary solder thickness. This is a mounting method in which the leadless component is mounted and soldered to a conductor round.

[Embodiment of the Invention] An embodiment of the present invention will be described using FIG. 2 and subsequent figures.

A predetermined circuit pattern is formed on both sides of the insulating board 10 using copper foil or the like, and a solder resist is applied in advance to the board surface except for the conductor round 11 for soldering with leadless components. , solder paste is once printed on each conductor round to supply a predetermined amount corresponding to the round area, and then, as shown in FIG. 2, it is held in a tunnel furnace 12 at a temperature above the melting temperature of the solder, Handa 13
are aggregated on each conductor round due to their surface tension, and after cooling they take on a raised fillet shape.

In this temperature raising process, the solder is metal-chemically bonded to the conductor rounds 11 through flux, and preliminary solder is supplied onto the conductor rounds 11 adjacent to each other as shown in FIG.

Next, as shown in FIG. 3, the substrate 10 is subjected to a pressing process, and the conductor round 1 is formed by a well-known processing technique, for example, a rolling process using rollers 14, in which the cooled and solidified solder is plasticized beyond its elastic limit and deformed.
1, crush the solder 13 fillet on the board 1.
0 to obtain preliminary solder that is spread on the surface and exhibits a uniformly flat surface.

Such a process removes the solder 13 on the conductor round 11.
However, as shown in FIG. 9, the solder 13 is applied to the extent that it protrudes from the conductor round 11 and spreads to the surrounding area, and the spread solder 13 comes into contact with each other between adjacent rounds 11.

A substrate 10 with preliminary solder as shown in FIG. 4 is obtained through the above steps, and the residual flux on the substrate 10 is immediately cleaned.

Incidentally, since the surface of the conductor round 11 is covered with the solder 13, there is no need to apply preflux for the purpose of preventing oxidation of the copper foil, and the board can be stored in this state.

Next, the mounting process shown in FIG. 5 is reached.

First, after mounting the leadless component 15,
After curing the pre-printed adhesive 16 made of thermosetting or ultraviolet curable resin to prevent the component from falling, lead the board on the opposite side of the mounting surface. Less parts 14
mount.

Although the component 14 is not particularly temporarily fixed in this embodiment, it may be temporarily fixed in order to prevent the component from shifting when the board is transported before soldering.

After the mounting process, a flux is applied to both sides of the substrate using a nozzle 17, as shown in FIG. 6, and then the leadless parts are heated in a tunnel furnace 12, as shown in FIG. 7, through a so-called reflow process. 14 and 15 solder 13 and conductor round 11
soldered to.

[Effects of the Invention] As described above, in the mounting method of the present invention, since the preliminary solder is not a solder paste (a mixture of solder powder and an organic solvent), the change in volume due to melt aggregation is small, and the mounting method does not require press processing. Therefore, the preliminary solder thickness is low compared to the amount of solder supplied, allowing stable mounting, and the gap between the electrode and conductor round of leadless components, which is a cause of soldering defects, is extremely small. This will prevent the occurrence of defects.

That is, the purpose of the pressing process is not simply to obtain a flat surface for mounting leadless components, but to minimize the preliminary solder thickness while applying a sufficient amount of solder.

In addition, as mentioned above, adjacent solders come into contact with each other during the press process when the rounds are close together, but since the solder that extends around the conductor round is only mechanically pushed out, the solder in this area is different from solder paste. , when melted, the solder is drawn towards the target round that has been previously bonded and flows easily;
As shown in FIG. 10, good soldering is achieved without short-circuiting of adjacent conductor rounds.

Although the present invention requires a press treatment process to substantially reduce the preliminary solder thickness, if a soldering failure occurs on this type of board on which leadless components are mounted, the components may be disposed in a high density. This method is extremely effective in practice compared to conventional mounting methods, considering that repair work is often difficult and productivity is not improved as a result.

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 drawings]

Fig. 1 is an explanatory diagram of a conventional example, Fig. 2 and the following show embodiments of the present invention, Figs. 2 to 7 are schematic diagrams showing the steps, and Figs. 8 to 10 are plan views of the substrate. . Explanation of symbols, 1, 4, 14, 16... Leadless parts, 5, 11... Conductor round, 6, 13...
...Solder, 3,10...Substrate, 2,16...Adhesive.

Claims (1)

[Claims] 1 Preliminary soldering is performed on the conductor rounds on the printed circuit board, and the leadless components are temporarily fixed with adhesive at the positions corresponding to the preliminary soldering, and then the leadless components are mounted on the substrate using the reflow soldering method. In the leadless component mounting method, the preliminary solder is made by first melting the solder paste printed on each conductor round, cooling and solidifying from the melted state, and then pressing the solder paste onto the conductor round. A method for mounting a leadless component, characterized in that it is formed in a state in which it is expanded to the periphery of a round.