JPH077172U - Reflow furnace - Google Patents

Abstract

(57) [Summary] [Purpose] When the printed circuit board is heated in a reflow oven, the temperature will drop due to the influence of rails and conveyors, and the ends of the printed circuit board and the central part of the printed circuit board with a slow heating rate will be localized. Heat to bring the entire printed board to a uniform temperature. [Structure] Heaters 6 are installed in the upper and lower parts of the tunnel 2, and hot air outlets 16 capable of blowing hot air are formed in the heater at a position corresponding to a portion where the temperature of the printed circuit board becomes low. ing.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a reflow furnace suitable for soldering a printed circuit board and electronic components with a solder paste.

[0002]

[Prior art]

 Generally, in a reflow furnace, heaters are installed above and below the tunnel, and a conveyor for transporting printed circuit boards runs from the entrance to the exit of the tunnel. Nets and claws are used as conveyors for transferring printed boards. However, claw conveyors are often used today because the nets impede heat from below and reduce thermal efficiency. A large number of claws are connected by a chain, and a pair of rails are installed in the tunnel to ensure stable running of the chain.

When soldering a printed circuit board and an electronic component with a solder paste, the solder paste is applied to the soldered portion of the printed circuit board by screen printing or dispenser discharge, and the printed circuit board is held by a conveyor of a reflow oven while running. The solder paste is melted by heating with a heater to perform soldering.

When a printed circuit board coated with the solder paste is heated in a reflow furnace, the entire printed circuit board must have a uniform temperature. This is because even if most of the printed circuit board has an appropriate soldering temperature, even if there is a portion that is lower than the melting temperature of the solder paste, the solder paste applied to that portion will melt. Without doing so, the solder will not adhere and will be unsoldered. Also, if only a certain part of the printed circuit board has an abnormally high temperature, the electronic components mounted on that part will be thermally damaged and its function will deteriorate.

[0005]

By the way, in order to uniformly heat the printed circuit board in the conventional reflow furnace, adjustment is performed by the preliminary heating temperature or the main heating temperature, but the whole cannot be uniformly heated easily. It was Even if the printed circuit boards do not all have a constant temperature, as long as the difference between the maximum temperature and the minimum temperature of the temperature distribution, that is, the Δt (delta tee) is small, the electronic components can be soldered well without thermal damage. Is something that can be done. Generally, if Δt is within 10 ° C., soldering failure and heat damage to electronic parts will be eliminated. Therefore, efforts have been made in the past to make a reflow furnace with a small Δt. The present invention is to provide a reflow furnace having a small Δt.

[0006]

[Means for Solving the Problems]

 When the present inventors investigated the part where the temperature locally decreased when the printed circuit board was heated in the conventional reflow oven, the part held by the claw, that is, both ends of the printed circuit board, became the lowest temperature, It was found that the central part of the printed circuit board had a low temperature. Then, as a result of pursuing the cause of the temperature of these parts becoming low, the following was found.

The temperature of both ends of the printed circuit board becomes low because the heat of the printed circuit board is transferred to the claws in contact with the printed circuit board to remove the heat, and the heat of the heater from above and below causes the claws to travel. This is because the amount of heat that reaches the printed circuit board is reduced because it is blocked or absorbed by the rails. It was also found that the temperature of the central part of the printed circuit board is low because the temperature of a flat object to be heated rises from the surroundings and the central part rises with a delay.

Therefore, the inventors of the present invention have made extensive studies as to what kind of heating should be performed in order to uniformly heat a flat printed circuit board. As a result, hot air with a high flow velocity is scanned to a portion where the temperature does not easily rise. We found that the temperature rises locally when hitting it, and completed the present invention.

The present invention is a reflow furnace in which heaters are installed in the upper and lower parts of a tunnel, and hot air having a high flow velocity is blown to the print substrate to the upper heater and the lower heater, or one of the upper and lower heaters. It is a reflow furnace characterized by being provided with a hot air outlet.

The heater used in the present invention can exhibit excellent effects when the surface blowing type heater (Japanese Patent Application No. 2-194385) which the applicant of the present invention has already proposed as a patent is used. It can also be used with a panel heater.

The hot air outlets formed in the heater according to the present invention may be multiple holes or slits.

When the hot air outlets formed in the heater according to the present invention are holes, the holes may be formed in rows and the rows may be one row or a plurality of rows.

Further, in the present invention, the hot air outlets formed in the heater may be formed only on both sides, that is, only at positions where hot air is blown to the pair of rails and the vicinity thereof, and the amount of air blown on both sides is small. The holes on both sides may be made larger so that the number becomes larger, and the center may be made smaller than that.

[0014]

【Example】

 The present invention will be described below with reference to the drawings. 1 is a perspective view of a heater installed in the reflow furnace of the present invention, FIG. 2 is a front sectional view of the reflow furnace of the present invention, and FIG. 3 is an enlarged sectional view taken along the line AA of FIG.

In the reflow furnace 1, a pair of rails 3 and 3 are installed in a tunnel 2, and chains 5 and 5 for holding and carrying a printed circuit board 4 slide on the rails in the arrow X direction. Running.

The reflow furnace 1 has a preheating zone P, a main heating zone R, and a cooling zone C in the printed circuit board traveling direction. A large number of heaters 6 ... Are installed above and below the pre-heating zone P and the main heating zone R, and cooling devices 7, 7 are installed in the cooling zone C. The heaters shown in the examples are surface blowing type heaters.

Here, the surface blowing type heater will be briefly described. The surface blowing type heater has a metal porous plate 8 coated with ceramic on one surface of the box body 7 and forms a gas outlet 9. An electric heater 10 is installed on the back side of the porous plate 8. Further, an elongated opening 11 is formed on the side opposite to the installation surface of the porous plate 10, and a cross fan 13 rotated by a motor 12 is installed near the opening. A duct 14 is installed in the opening 11, and the duct is opened adjacent to the surface on which the porous plate 8 is installed, and forms a gas suction port 15.

When the electric heater 10 is energized, the surface blowing type heater heats the metal porous plate 8 and also heats the inside of the box body 7. Therefore, when the fan 13 is rotated by the motor 12, the external gas is introduced into the box 7 from the gas suction port 15 through the duct 14 and heated by the box 7. When passing through the metal porous plate 8, it is also heated and flows out from the gas outlet 9 as hot air, hits the printed circuit board, and heats the printed circuit board. Further, since the metal porous plate 8 of the surface blowing type heater is coated with ceramic, when the porous plate is heated by the electrothermal heater, far infrared rays are radiated from the ceramic and the printed board is effectively combined with the hot air. It comes to heat.

A large number of hot air outlets 16 ... Are bored at appropriate places on the porous plate 8. In the surface-blow-out heater, since the gas outlet 9 is the metal porous plate 8 having resistance, the hot air flowing out from the heater has a slow flow velocity, but the hot air outlets 16 ... When installed, hot air with a high velocity will blow out from here. When this hot air with a high flow velocity hits a running printed circuit board, a large amount of heat is added to the contacted part, and the temperature rises locally.

The hot air blowing holes 16 provided in the surface blowing type heater are provided at positions where the temperature is low when the printed circuit board is heated. For example, if the lowest temperature part of the printed circuit board is the holding part of the chain conveyor and the next lowest temperature part is the central part of the printed circuit board, then the printed circuit board as shown in Figs. It is advisable to provide two rows in the lateral direction with respect to the traveling direction. One of the two rows is not formed in the center, but a large number of holes 16 are formed on both sides so that hot air is blown to both ends of the printed circuit board, and the other row is formed as described above. A hot air outlet like this should be provided, and a slightly smaller hot air outlet should be provided in the center.

As described above, when the hot air outlets are formed in a row laterally with respect to the traveling direction of the printed circuit board, the traveling printed circuit board is hit by the hot air while scanning, and the temperature of the printed circuit board is controlled. A large amount of heat is added to the lower part, resulting in a uniform temperature.

Next, the heating state of the printed circuit board in the reflow furnace of the present invention will be described. When the printed circuit board 4 is run in the direction of the arrow X with the chain 5, the printed circuit board is heated by the surface blowing type heaters 6 ... At this time, the hot air blowing port is formed in the gas outlet 9 of the surface blowing type heater 6 at a position that coincides with the rail part that hinders the heating of the printed circuit board and the central part where the heating is slow. Since a large amount of heat is applied to the parts, the parts with low temperature and the parts with slow temperature rise are heated, and the entire printed circuit board has a uniform temperature.

Thermocouples were attached to nine printed circuit boards of 150 × 250 (mm), and heated in the reflow oven of the above embodiment and a conventional reflow oven (comparative example) in which no hot air outlet was provided. When the temperature profile was drawn, Δt was 3 ° C in the reflow furnace of the present invention, and Δt was as large as 12 ° C in the conventional reflow furnace.

In addition, as a result of soldering in a reflow oven of the example and a reflow oven of a comparative example after applying a solder paste on a printed board by printing and mounting electronic components on the printed circuit board, the reflow oven of the example did not Although there was no solder at all, in the reflow furnace of the comparative example, a large amount of unsoldered solder was generated at the edges of the printed board.

[0025]

[Effect of device]

 As described above, the reflow furnace of the present invention can raise the temperature of the low temperature part of the printed circuit board and uniformly heat the entire printed circuit board. Reliable soldering is possible without causing problems such as damage.

[Brief description of drawings]

FIG. 1 is a perspective view of a surface blowing type heater used in the reflow furnace of the present invention.

FIG. 2 is a front sectional view of the reflow furnace of the present invention.

FIG. 3 is an enlarged sectional view taken along line AA of FIG.

[Explanation of symbols]

 1 Reflow oven 2 Tunnel 3 Rail 4 Printed circuit board 5 Chain 6 Heater 9 Gas outlet 16 Hot air outlet P Preheating zone R Main heating zone C Cooling zone

Claims (5)

[Scope of utility model registration request] 1. In a reflow furnace in which a heater is installed above and below a tunnel, hot air with a high flow velocity can be blown to a printed circuit board to an upper heater and a lower heater, or one of upper and lower heaters. A reflow furnace having a mouth. 2. The reflow furnace according to claim 1, wherein the heater is a surface blowing type heater. 3. The reflow furnace according to claim 1, wherein the heater is a panel type heater. 4. The reflow furnace according to claim 1, wherein the hot air outlet is a large number of holes. 5. The reflow furnace according to claim 1, wherein the hot air outlet is a slit.