JP2584411Y2 - Reflow furnace - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow furnace for heating a printed circuit board to perform soldering, and more particularly to a reflow furnace for setting the inside of the furnace to an inert atmosphere.

[0002]

2. Description of the Related Art Solder paste, which is a material for soldering a printed circuit board and an electronic component, is prepared by mixing a flux obtained by dissolving solid components such as rosin, an activator and a thixotropic agent with a solvent, and a powdered solder. Things.

Conventionally, soldering using a solder paste has been performed in a reflow furnace in which air exists. When a solder paste having a small solid component is used in a reflow furnace in which air exists, poor soldering such as generation of unsoldered or minute solder balls occurs. In other words, when the printed circuit board on which the solder paste is applied is heated in a reflow oven where air is present, oxygen in the air oxidizes the copper lands of the printed circuit board and the powder solder in the solder paste, and the molten solder becomes This is because the powder solder hardly gets wet and the powder solder melted outside the land is not pulled back to the land due to surface tension.

[0004] However, if a large amount of solid components are added to the flux of the solder paste, the oxidized lands and powdered solder reduce solid oxides such as rosin and activator to form a clean metal surface. Thus, the surface tension of the molten solder is reduced, so that the above-described soldering failure does not occur. Therefore, soldering defects are less when a large amount of solid components are added to the solder paste flux.

[0005] When a printed circuit board is soldered with a solder paste containing a large amount of solid components in the flux, a large amount of flux residue remains after soldering. In some cases, the insulation resistance may be lowered, or migration may occur between lands to cause a short circuit.
Therefore, when soldering with a solder paste containing a large amount of solid components, a flux residue must be cleaned after soldering in a printed circuit board to be incorporated in an electronic device requiring reliability such as a computer or a communication device.

[0006] Solvents such as chlorofluorocarbon and trichlene, which dissolve solid components well, are suitable for cleaning flux residues, but these solvents destroy the ozone layer surrounding the earth,
Since a large amount of ultraviolet rays from the sun reach the earth and cause skin cancer to occur in humans, the use thereof has been regulated. Therefore, today, to eliminate the need to clean flux residues after soldering,
So-called "no-cleaning solder paste" in which the solid component in the flux is reduced has been used.

[0007] The solder paste for non-cleaning contains a small amount of solid components in the flux. Therefore, when it is used in a reflow furnace where air is present, a large amount of defective soldering occurs as described above. However, if the solder paste for non-cleaning is also heated in a reflow furnace without air, no soldering defects will occur, so nitrogen gas reflow furnaces filled with nitrogen gas in furnaces have been used today. Have been.

In a nitrogen gas reflow furnace, the oxygen concentration greatly affects the solderability, and the lower the oxygen concentration, the less the occurrence of poor soldering. Therefore, in the nitrogen reflow furnace, there is a problem how to reduce the oxygen concentration.

In other words, in a nitrogen reflow furnace, nitrogen gas is supplied into the furnace to allow the nitrogen gas to flow out of the furnace from the inlet / outlet of the furnace, so that air does not enter the furnace from the outside. The most effective means of preventing air intrusion is to install a shutter at the entrance and exit of the furnace. However, if a shutter is installed, it will not only be able to continuously operate with the devices before and after the reflow furnace, but also will have a complicated shutter mechanism. Therefore, there is a problem that the cost becomes very high.

The applicant of the present invention has already proposed a reflow furnace in which an air intrusion prevention zone is provided at the entrance and exit of the furnace, and a resistor for preventing gas flow is installed in the air intrusion prevention zone (Japanese Utility Model Application No. 3-17855). issue). This reflow furnace
A lot of heat-resistant resin in the shape of a noren is installed on the upper and lower or upper part of the air intrusion prevention zone. Since the reflow furnace is open at the entrance and exit of the furnace, continuous operation with the preceding and following processes is possible, and even though it is in the open state, there is almost no intrusion of external air. It has an excellent effect of lowering.

[0011]

However, in a reflow furnace in which a resistor made of a heat-resistant resin is installed, the resistor is directly installed in an air intrusion prevention zone. However, installing a plurality of rows of resistors in a narrow opening in the air intrusion prevention zone in a state where the gaps are small not only requires much time and effort, but also makes it difficult to install a flexible resistor.

Further, the solid component of the flux of the solder paste is liquefied when heated, and vaporized when further heated to high temperature to form flux fume. When this flux fume comes into contact with a low temperature part, it liquefies and adheres there. When the reflow furnace is used for a long time, a large amount of the flux fume attached to a low temperature portion liquefies and drips.

The parts of the reflow furnace having a lower temperature are the cooling zone and the entrance and exit of the furnace. Therefore, in a reflow furnace in which an air intrusion prevention zone is provided at the entrance and exit of the furnace, and a resistor is provided here, liquefied flux fume (hereinafter, referred to as fume liquefied matter) adheres to the resistor. In a conventional reflow furnace, the resistor placed at the entrance and exit of the furnace is made of resin.If a large amount of fume liquefaction adheres to the resistor here, it drops down along the resistor and falls on the printed circuit board passing below. Adheres to When the fume liquefaction adheres to the printed circuit board, it not only deteriorates the appearance but also degrades the function of the electronic component mounted on the printed circuit board.

[0014]

Means for Solving the Problems The present inventor has found that when attaching a flexible object, it is difficult to attach it alone, but once it is fixed to a hard object and then attached, it becomes easier to attach. In addition, the present invention has been completed by focusing on the fact that when a liquid adheres to paper or fiber, the liquid has a property of penetrating into the inside.

The present invention provides a reflow furnace in which an air intrusion prevention zone is provided at the entrance and exit of the reflow furnace, and a number of resistors are installed in the air intrusion prevention zone to prevent the invasion of outside air. A reflow furnace, wherein the reflow furnace is mounted on a piece, the mounting piece is provided in an air intrusion prevention zone, and the resistor is formed of a moisture absorbing material.

The moisture-absorbing material used in the present invention is paper, fiber, or the like. When it is installed below the air intrusion prevention zone, it is so-called that it does not bend easily even if it stands up.
Use a strong material.

[0017]

[Effect] Even a flexible resistor such as paper or fiber is once mounted on a hard mounting piece and then placed in the air intrusion prevention zone, so that the resistor can be easily installed. Further, when a hygroscopic material is used for the resistor, the fume liquefied material penetrates into the resistor to prevent dripping.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG.
FIG. 2 is a front sectional view of the reflow furnace of the present invention, FIG. 2 is a perspective view showing a state where a resistor is attached to a mounting piece, and FIG. 3 is an enlarged front sectional view of an air intrusion prevention zone.

The reflow furnace of the present invention has a tunnel 1 inside.
In the tunnel 1, a chain conveyor 3 held by a frame 2 runs in the direction of arrow A.

The reflow furnace has a preheating zone P, a main heating zone R, and a cooling zone C in the traveling direction of the conveyor. The entrance and exit of the reflow furnace, that is, the front of the preheating zone P and the rear of the cooling zone C are: These are air intrusion prevention zones S, S, respectively.

Hot air blowout type heaters 4 are provided above and below the preheating zone P and the main heating zone R.
A nitrogen gas supply pipe 5 is provided inside the hot air blowout type heater installed in the main heating zone R, so that nitrogen gas is supplied from outside the furnace into the furnace.

The hot air blowout type heater has a blowout port 6 and a suction port 7 on the same surface, and has an electric heater 8 inside.
And a blower 9 are installed. The outlet 6 is provided with a number of holes, and a current change plate 10 is provided near the holes. Therefore, in the hot air blowout type heater, the nitrogen gas heated by the electric heater 8 is blown out from the hole of the blowout port 6 by the blower 9, and the blown out nitrogen gas is changed by the current changing plate 10 toward the suction port 7. Then, it flows in from the suction port 7 of the same hot air blowout type heater. When nitrogen gas is circulated in one hot-air blowout type heater in this way, the heated nitrogen gas emits less heat to the other, which not only reduces energy loss, but also circulates only nitrogen gas. Therefore, there is an excellent feature that the inflow of air from the outside is reduced.

At the upper and lower portions of the cooling zone C, a cooler 11 having the same structure as that of the hot air blowout type heater but without the electric heater is provided.

In the air intrusion prevention zones S, a number of resistors 12 are provided. Here, blotting paper was used as the resistor. The resistor 12 has a plurality of plate-like resistors installed in a direction perpendicular to the traveling direction of the conveyor. When a plurality of plate-shaped members are provided in this manner, the gas that is going to flow there is blocked by the resistor, and is difficult to flow. Therefore, the nitrogen gas supplied into the furnace has a high pressure inside the furnace, and flows out against the resistor. However, the outside air having a lower pressure than the inside of the furnace is blocked by the resistor and the inside of the furnace is blocked. Will not invade.

The resistor 12 is mounted on a mounting piece 13, and the mounting piece 13 is set in the air intrusion prevention zone S. That is, the resistor 12 is attached to the mounting piece 13.
And is indirectly installed in the air intrusion prevention zone S via.

The mounting piece 13 has a U-shaped cross section.
The resistor 12 is attached to both side walls of the mounting piece 13 with a heat-resistant adhesive. A mounting hole 14 is formed in the bottom surface of the mounting piece 13. The mounting hole 14 is a so-called daruma hole in which a large hole through which the screw head passes and a small hole through which the screw head does not pass are integrated. A screw 15 is provided upright in the air intrusion prevention zone, and the mounting piece can be easily mounted by simply passing the screw through the large hole of the mounting hole and moving the mounting piece a little and aligning the screw with the small hole. Can be performed.

The resistor shown in the embodiment has a number of cuts 16 on one side. If the resistors are cut in this way, even if the electronic parts of the printed circuit board conveyed by the conveyor frame or the conveyor come into contact with the resistors divided by the cuts, the resistors in the contacted part will only bend. The other resistors are in an upright state. Therefore, since the resistor can be lengthened until it comes into contact with the conveyor or the printed circuit board, the outside air hardly enters. However, even if the tip of the resistor is made close to the frame or the printed circuit board without making a cut on one side of the resistor, it is effective in preventing air from entering. In addition, if the length of the portion of the resistor that protrudes to the outside of the frame is increased, the effect of blocking air passing on both sides of the frame is further improved.

[0028]

[Effect of the Invention] In the reflow furnace of the present invention, since the resistor is installed in the air intrusion prevention zone through the mounting piece, when the resistor is replaced by a large amount of fume liquefaction adhered to the resistor, A resistor that can be replaced by a very simple operation of simply removing the mounting piece from the air intrusion prevention zone, attaching a new resistor to the mounting piece outside the furnace, and then installing this mounting piece again in the air intrusion prevention zone In addition, since the resistor is a hygroscopic material such as paper or cloth, the fume liquefaction adhering to the resistor does not penetrate into the inside and hang down from the resistor, so that it is not below the resistor. The present invention has an unprecedented excellent effect that the printed circuit board passing therethrough is not stained.

[Brief description of the drawings]

FIG. 1 is a front sectional view of the reflow furnace of the present invention.

FIG. 2 is a perspective view showing a state where a resistor is attached to a mounting piece.

FIG. 3 is an enlarged front sectional view of an air intrusion prevention zone.

[Explanation of symbols]

 12 Resistor 13 Mounting piece 14 Mounting hole 15 Screw 16 Notch S Air intrusion prevention zone P Preheating zone R Main heating zone C Cooling zone

Claims (4)

(57) [Scope of request for utility model registration] 1. A reflow furnace in which an air intrusion prevention zone is provided at an entrance and exit of a reflow furnace, and a plurality of resistors are installed in the air intrusion prevention zone to prevent the invasion of outside air. A reflow furnace which is mounted, wherein the mounting piece is installed in an air intrusion prevention zone, and wherein the resistor is formed of a moisture absorbing material. 2. The reflow furnace according to claim 1, wherein the resistor is paper. 3. The reflow furnace according to claim 1, wherein the resistor is a fiber. 4. The reflow furnace according to claim 1, wherein the resistor has one continuous side and a plurality of cuts formed in the other side.