JP2003179342A - Reflow furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflow furnace not generating fine metal powder, for which the problems of a conventional reflow furnace that the fine metal powder is generated at the time of soldering a printed board, is stuck between adjacent conducting parts of the printed board and lowers a function of an electronic appliance are solved. <P>SOLUTION: A heat resistant non-metallic material 10 is installed to a rail 6 laid inside a tunnel of the reflow furnace, rollers 14 of a chain are brought into contact on the non-metallic material and the chain is made to travel. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reflow furnace for soldering a printed circuit board.

[0002]

2. Description of the Related Art Generally, a soldering method for a printed circuit board includes a troweling method, a dipping method and a reflow method.

In the troweling method, an operator or a robot performs soldering using a soldering iron, and there is a problem in workability because soldering is performed at each place of the soldering portion. Therefore, the troweling method is suitable for correcting a soldering defect generated by another soldering method and for soldering an electronic component which is weak to heat after another soldering method.

Further, the dipping method is excellent in productivity because it is possible to perform soldering at a large number of places by one soldering operation, but since the entire back surface of the printed circuit board is brought into contact with the molten solder, it is possible to reach unnecessary places. However, there was a problem that solder adhered.

In the reflow method, since soldering can be carried out only on the required parts of the printed circuit board, soldering can be carried out on a large number of places, and solder is not attached to unnecessary parts, which is excellent in productivity and reliability. Is. Therefore, this reflow method is often used for soldering a printed circuit board of an electronic device that requires reliability.

As shown in FIG. 4, the reflow furnace used in this reflow method has a tunnel 1 having a preheating zone.
P, main heating zone R, and cooling zone C. A heating device 2 such as an infrared heater or a hot air heater is installed above and below the preheating zone P and main heating zone R, and the cooling zone is cooled. The device 3 is installed. A pair of chains 4 travel in the direction of arrow A between the heating device and the cooling device. A large number of projecting pins are installed in the pair of chains in opposite directions, and the printed circuit board 5 is placed on the projecting pins and runs in the tunnel. The printed circuit board that runs in the tunnel of the reflow furnace is pre-coated with solder paste only in the necessary places by the printing method or the discharge method, and is heated by the heating device 2 installed in the tunnel while traveling in the tunnel. It is melted and then cooled by the cooling device 3 to solder the printed circuit board.

When the chain running in the reflow furnace has a large gap between the pair of chains during running or the chain vibrates violently, the printed circuit board mounted on the projecting pin is used as a heating device in the tunnel. It will fall on top. Then, the printed circuit board is scorched by the heating device to give off a bad odor, and expensive electronic parts are also scorched to cause a great loss. Therefore, in the reflow furnace, rails for guiding the chain are laid in order to ensure stable running of the chain. The guide rail is made of metal such as aluminum or iron.

[0008]

By the way, the printed circuit boards used in recent electronic devices are highly densified, and the adjacent soldered portions are also very close to each other. Therefore, when soldering dust or dirt, especially metal powder that has electrical conductivity, short-circuits between adjacent conducting parts or the insulation resistance drops significantly, which may reduce the functionality of electronic devices. Will end up. When a high-density printed circuit board is soldered in a conventional reflow furnace, the above-mentioned problems such as short circuit and reduction in insulation resistance may occur. The present invention is to provide a reflow furnace that does not cause these problems even when soldering a high-density printed circuit board.

[0009]

Means for Solving the Problems As a result of intensive studies on the cause of generation of fine metal powder in a conventional reflow furnace, the inventors have found that it occurs between a chain and a rail on which the chain runs. It was In other words, in the reflow furnace, the metal chain runs on the metal rail, so that the chain and the rail rub against each other. Then, the rail, which is the softer metal, is scraped to become metal powder. Therefore, it is possible to apply a heat-resistant lubricant to prevent scraping of metal due to rubbing, but no matter how heat-resistant lubricant is exposed to high temperature for a long time, it loses lubricity or carbonizes. In addition, metal powder is generated again. The present inventors have completed the present invention by paying attention to the fact that metal powder is not generated when a non-metallic material having heat resistance and having lubricity is used.

According to the present invention, in a reflow furnace in which a printed circuit board is soldered while being conveyed by projecting pins installed on a chain, a rail on which the chain runs is installed on the rail rather than between inner plates of inner links of the chain facing each other. A narrow and long heat-resistant non-metallic material is installed, and the chain is a reflow furnace characterized in that the rollers of the chain run in contact with the heat-resistant non-metallic material.

The heat resistant non-metal material used in the present invention includes heat resistant glass, heat resistant ceramics, heat resistant resins and the like. The heat-resistant glass or ceramic may be loosely fitted in the groove formed in the metal rail. In other words, when heat-resistant glass or ceramic is fixed to a metal rail, the heat expansion coefficient of heat-resistant glass or ceramic is greatly different from that of metal rails, so the temperature inside the tunnel becomes high during use and the temperature inside the tunnel becomes low when not in use. , Because they will crack. The heat-resistant non-metallic material is installed on the running path of the chain, but it does not have to be the same length as the entire running path, and short ones may be added.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reflow furnace of the present invention will be described below with reference to the drawings. In the embodiment, a heat-resistant glass rod is used as the non-metal material. 1 is a partially enlarged perspective view of the reflow furnace of the present invention, FIG. 2 is a partial plan view of the reflow furnace of the present invention, and FIG. 3 is a sectional view taken along line XX of FIG.

Inside the tunnel 1, a pair of rails 6 and 7 are laid. One rail 6 is fixed and immovable, and the other rail 7 can move in parallel in the arrow Y direction. A flange 8 is formed on each of the rails 6 and 7 so as to face each other, and a groove 9 is formed in the flange in the longitudinal direction. And the heat-resistant glass rod 1 is placed in the groove 9.
0 is installed in a loosely fitted state. The width a of the heat-resistant glass rod 10 is slightly narrower than the width b between the inner plates of the chain which will be described later.

A chain 4 is placed on the heat-resistant glass rod 10 so as to run. Chain 4 is shown in Figure 1.
As shown in, the inner link 11 and the outer link 12 are connected in an endless state. The inner link 11 is a pair of inner plates 1
The roller 14 is sandwiched between the inner plates 13 and 13. And outside link 1
2 is composed of a pair of outer plates 15, 15 installed outside the inner plates 13, 13 of the inner links.
The inner plate 13 and the outer plate 15 are provided with protruding pins 16 ... Concentric with the roller 14. The projecting pins 16 project in opposite chain directions.

Next, soldering in the reflow furnace of the present invention having the above structure will be described. First, when one rail 7 is moved in the arrow Y direction and the printed circuit board 5 is placed on the projecting pins facing each other, the printed circuit board 5 can be easily taken out between the outer plates 15 facing each other. Adjust to about the same width. Next, the printed circuit board 5 is placed on the protruding pins 16 of the pair of chains from the entrance of the reflow furnace, and is run in the tunnel 1. Then, the printed circuit board 5 is preheated in the preheating zone P at a temperature lower than the melting temperature of the solder paste applied to the printed circuit board, and then heated in the main heating zone R to a temperature higher than the melting temperature of the solder paste to melt the solder paste. . The printed circuit board is then cooled in the cooling zone C and soldered.

When the printed circuit board is transported in the tunnel 1 for soldering, the roller 14 of the chain 4 is used.
Runs on a heat-resistant glass rod 10 installed on the flanges 8 of the rails 6 and 7. Since the width a of the heat-resistant glass rod 10 is narrower than the width b between the pair of inner plates 13 and 13, the roller 10 rides on the heat-resistant glass rod and runs without coming off the heat-resistant glass rod. The heat-resistant glass rod has excellent lubricity, so the chain runs smoothly without being scraped.

[0017]

As described above, in the reflow furnace of the present invention, the heat-resistant non-metallic material installed on the rail causes the metal to slide smoothly. It runs smoothly without being scraped or vibrating. Therefore, not only is fine metal powder not generated in the tunnel of the reflow furnace and adhering to the printed circuit board, but at the time of soldering the printed circuit board, the printed circuit board falls off the chain and burns, or the soldered part This is soldering with excellent reliability that it will not crack due to vibration.

[Brief description of drawings]

FIG. 1 is a partially enlarged perspective view of a reflow furnace of the present invention.

FIG. 2 is a partial plan view of the reflow furnace of the present invention.

FIG. 3 is a sectional view taken along line XX of FIG.

FIG. 4 is a front sectional view of a reflow furnace.

[Explanation of symbols]

6 rails 9 grooves 10 Heat-resistant glass rod 11 Internal links 12 outside links 13 Inner plate 14 roller 15 Outer plate 16 protruding pin

Claims (3)

[Claims] 1. In a reflow furnace for soldering while carrying a printed circuit board by projecting pins installed on a chain, the rail on which the chain runs has a width wider than the inner plates of the inner links of the chain facing each other. A narrow and long heat-resistant non-metallic material is installed, and the chain is a reflow furnace characterized by the roller of the chain running in contact with the heat-resistant non-metallic material. 2. The heat resistant non-metallic material is glass, ceramic or resin.
Reflow oven as described. 3. The reflow furnace according to claim 1, wherein the heat-resistant non-metallic material is installed in a groove formed in a metal rail.