JPH04371366A - Heating furnace for soldering - Google Patents

Abstract

PURPOSE:To simplify structure and operational control in a heating furnace and to improve cooling efficiency of a substrate by supplying inert gas from an outlet passage and flowing this into the heating furnace and an inlet passage. CONSTITUTION:The heating furnace for soldering is provided with a heating chamber 13 provided with heaters 11 for soldering both by heating a circuit substrate 21 mounting electronic parts, an inlet passage 31 for guiding the circuit substrate 21 mounting the electronic parts into the heating chamber 13 and an outlet passage 33 for guiding to outer part by cooling the circuit substrate 21 soldering the electronic parts. This heating furnace always supplies inert gas into the outlet passage 55 and a part thereof is flowed out from the outlet to out of the furnace and the remained gas is flowed out from the inlet to out of the furnace after flowing through the heating chamber 13 and the inlet passage 31 to fill up the inert gas in the whole zone in the furnace. Therefore, it is unnecessary to arrange a shutter in the furnace, and conveying of the substrate 21 is executed with a concecutive conveyor 35 and as the low temp. inert gas is supplied to the outlet passage 33, cooling of the circuit substrate after soldering is executed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering furnace for soldering electronic components to circuit boards.

When electronic components are mounted on a circuit board by soldering, the circuit board on which the electronic components are mounted at predetermined positions is passed through a heating furnace to melt the solder and perform soldering. In this case, the heating furnace is filled with an inert gas such as nitrogen gas to prevent oxidation of the circuit board and electronic components.

A conventional heating furnace of this type is shown in FIG. The heating furnace includes a heating chamber 13 in which a heater 11 is installed,
A front chamber 15 provided on the entrance side of the heating chamber 13 and a heating chamber 1
3 and a rear chamber 17 provided on the exit side. The front chamber 15 and the outside are separated by a first shutter 19A, and the front chamber 15 and the heating chamber 13 are separated by a second shutter 19B.
The heating chamber 13 and the rear chamber 17 are separated by a third shutter 19C, and the rear chamber 17 and the outside are partitioned by a fourth shutter 19D.

[0004] Further, each chamber 13, 15, and 17 is supplied with an inert gas such as nitrogen gas to prevent oxidation, and is filled therein. Moreover, since each chamber is partitioned by a shutter, the chain conveyor for conveying the circuit board 21 is provided separately for each chamber. That is 23
A is an entrance side conveyor, 23B is a front chamber conveyor, 23C is a heating chamber conveyor, 23D is a rear chamber conveyor, and 23E is an exit side conveyor.

When feeding the circuit board 21 into the front chamber 15 from the outside, the first shutter 19A is opened while the second shutter 19B is closed, and the entrance side conveyor 23A and the front chamber conveyor 23B are operated to feed the circuit board 21 into the front chamber 15. 21 enters the front chamber 15, the first shutter 19A is closed. Next, when sending the circuit board 21 from the front chamber 15 to the heating chamber 13, open the second shutter 19B while keeping the first shutter 19A closed, operate the front chamber conveyor 23A and the heating chamber conveyor 23C, and When the substrate 21 enters the heating chamber 15, the second shutter 19A is closed. In this way, the opening/closing control of the first and second shutters 19A and 19B is performed so that one of them is always closed. circuit board 2
Similar control is performed when the heating chamber 1 moves from the heating chamber 13 to the rear chamber 17 and from the rear chamber 17 to the outside.

[0006] When the circuit board 21 on which electronic components are mounted passes through the heating chamber 13, it is heated to a solder melting temperature, and the electronic components are soldered. Circuit board 2 after soldering
1 is to prevent it from being oxidized when it goes into the atmosphere.
When passing through the rear chamber 17, it is cooled with nitrogen gas.

[0007]

[Problems to be Solved by the Invention] Conventional heating furnaces have a structure in which each chamber is partitioned with a shutter, so the conveyor must also be installed separately for each chamber, making it difficult to control the opening and closing of the shutter and operate the conveyor. Control is troublesome. In addition, since one of the two shutters in the front and rear chambers must be closed, the feeding interval of the circuit board is regulated.
It is difficult to increase productivity.

Furthermore, since the rear chamber is partitioned by two shutters and has a limited capacity, it is not possible to supply a large amount of inert gas for cooling, and furthermore, when the shutter on the heating chamber side is opened, the heating chamber is Because hot air enters, it is difficult to cool the circuit board sufficiently.

[0009]

[Means for Solving the Problems] The present invention provides a soldering heating furnace that solves the above-mentioned problems, and is configured to heat a circuit board on which electronic components are mounted and solder the two together. A heating chamber equipped with a heater for attaching electronic components, an entrance passage for introducing a circuit board with electronic components mounted into the heating chamber, an exit passage for cooling the circuit board with electronic components soldered thereon and guiding it outside. An inert gas supply nozzle is installed in the passage, the inert gas is blown out from the nozzle, and a part of it flows out from the outlet (outlet of the circuit board).
The furnace is characterized in that the inside of the furnace is maintained in an inert gas atmosphere at a pressure higher than atmospheric pressure by circulating the remainder through the heating chamber and the inlet passage and flowing out from the inlet (inlet of the circuit board).

A part of the inert gas supplied to the outlet passage flows out of the furnace from the outlet, but in order to distribute as much of the supplied inert gas to the heating chamber and the inlet passage as possible, it is necessary to The gas flow resistance on the heating chamber side may be made smaller than the gas flow resistance on the exit side from the nozzle installation position.

[0011] It is also an effective means to make the inert gas blowing direction of the inert gas supply nozzle adjustable, and by adjusting the inert gas blowing direction, to feed a large amount of inert gas into the heating chamber and the inlet passage side. be.

0012

[Function] This heating furnace constantly supplies inert gas to the outlet passage, part of which flows out of the furnace from the outlet, and the remainder flows through the heating chamber and the inlet passage and flows out of the furnace from the inlet. , the entire area inside the furnace is filled with inert gas. Therefore, there is no need to provide a shutter in the furnace, and the circuit boards can be transported by one continuous conveyor. Furthermore, since a large amount of low-temperature inert gas is supplied to the exit passage, the circuit board can be efficiently cooled after soldering.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the invention. This soldering heating furnace has a heating chamber 13 similar to the conventional one, in which a plurality of heaters 11 are provided. An inlet passage 31 is provided on the inlet side of the heating chamber 13, and an outlet passage 33 is provided on the outlet side. Inside the entrance passage 31, the heating chamber 13, and the exit passage 33, a continuous chain conveyor 35 runs in the direction of arrow S for conveying the circuit board 21 on which electronic components are mounted.

Further, nozzles 37 for supplying an inert gas, such as nitrogen gas, are installed above and below the conveyor 35 in the outlet passage 33. Various types of nozzles 37 can be used, but for example, as shown in FIG. 2, a metal pipe 38 with a number of gas blowing holes 39 formed at appropriate intervals in the longitudinal direction may be used. good. By arranging such nozzles 37 in a direction perpendicular to the running direction of the conveyor 35 and supplying pressurized nitrogen gas from both ends, nitrogen gas can be uniformly blown out in the width direction of the circuit board 21.

A seal plate 41 is also provided within the outlet passage 33 to prevent the nitrogen gas supplied from the nozzle 35 from flowing out to the outlet side. The purpose of this seal plate 41 is to minimize the distance between its leading edge and the conveyor 35 and circuit board 21 to increase the flow resistance of nitrogen gas and to minimize the amount of nitrogen gas flowing out to the exit side. Further, a seal plate 43 of an appropriate size is provided within the inlet passage 31 in order to adjust the opening area of the inlet.

[0016] With this arrangement, more than half of the nitrogen gas supplied from the nozzle 35 flows toward the heating chamber 13, passes through the heating chamber 13 and the inlet passage 31, and flows out of the furnace from the inlet. I come to do it. As a result, the furnace is filled with nitrogen gas, and the pressure of this nitrogen gas is slightly higher than atmospheric pressure, which prevents air from entering the furnace from the inlet and outlet, lowering the oxygen concentration inside the furnace. can be kept. Furthermore, since a large amount of nitrogen gas is blown out from the outlet passage 33, the cooling efficiency of the circuit board 21 is also extremely high.

It is preferable that a large number of seal plates 41 be installed at predetermined intervals in the running direction of the conveyor 35 to provide a labyrinth seal effect.

By the way, in order to make the nitrogen gas supplied from the nozzle 35 flow as much as possible from the outlet side toward the heating chamber 13, the nozzle 35 is made rotatable about its axis to blow out the nitrogen gas. It is a good idea to be able to adjust the direction. Experiments have shown that, rather than facing the conveyor 35, it is better to point the gas blowout hole 39 toward the opposite side of the conveyor 35, as shown in FIG. 3, so that the gas flow becomes uniform and the flow rate can be adjusted more easily. There was found.

Angle adjustment of this nozzle 35 and seal plate 41
Due to the sealing effect, it is possible to send 60 to 80% of the nitrogen gas supplied from the nozzle 35 to the heating chamber 13 side.

[0020]

[Effects of the Invention] As explained above, according to the present invention, inert gas is supplied from the outlet passage and distributed to the heating chamber and the inlet passage, so there is no need to partition the inside of the furnace with a shutter. circuit boards can be transported by a continuous conveyor. As a result, the structure and operation control of the heating furnace are simplified, equipment costs are reduced, and the feeding interval of circuit boards is not restricted, which has the advantage of improving productivity. Further, since a large amount of inert gas is blown into the exit passage, the cooling efficiency of the circuit board is increased, and there is an advantage that sufficient cooling can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a soldering furnace according to an embodiment of the present invention.

[Fig. 2] A front view of the nozzle used in the heating furnace of Fig. 1.

FIG. 3 is an enlarged sectional view of the outlet passage portion of the heating furnace in FIG. 1.

FIG. 4 is a cross-sectional view showing a conventional soldering furnace.

[Explanation of symbols]

11: Heater 13: Heating chamber 21: Circuit board 31: Inlet passage 33: Outlet passage 35: Chain conveyor
37: Nozzle 41, 43: Seal plate

Claims (2)

[Claims] Claim 1: A heating chamber equipped with a heater that heats a circuit board on which electronic components are mounted and solders them together; an entrance passage for introducing the circuit board on which electronic components are mounted into the heating chamber; An inert gas supply nozzle is installed in the outlet passage, and an inert gas is blown out from the nozzle, and a part of the inert gas flows out from the outlet. A heating furnace for soldering, characterized in that the inside of the furnace is maintained in an inert gas atmosphere at a pressure higher than atmospheric pressure by circulating the remainder through a heating chamber and an inlet passage and flowing out from an inlet. [Claim 2] The soldering heating furnace according to Claim 1, comprising:
The device is characterized in that the inert gas blowing direction of the inert gas supply nozzle can be adjusted.