JPH11274712A - Furnace for soldering circuit substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a furnace for soldering a circuit substrate, that can maintain a smaller variation range of furnace oxygen concentration in a stable manner with a small amount of inert gas. SOLUTION: A furnace for soldering a circuit substrate is provided with a heating chamber, a carrying-in path and a carrying-out path of a circuit substrate that run to the heating chamber, and a transporting path for guiding a circuit substrate from the carrying-out path through the heating chamber to the carrying-in path. In this case, a plurality of fins is aligned toward an upper side and/or a lower side of the transporting path, on at least one of the carrying-in and carrying out paths. Each of the fins is provided with a gas nozzle for blowing off gas onto the transporting path, and a shielding board for shielding gas passing through a space which is opposite to the transporting path of the gas nozzle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace for soldering an electronic component to a circuit board.

[0002]

2. Description of the Related Art When an electronic component is mounted on a circuit board by soldering, the circuit board on which the electronic component is mounted at a predetermined position 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 the circuit board and the mounted electronic components from being oxidized.

FIG. 4 shows a conventional heating furnace of this type. The heating furnace 10 includes a heating chamber 2 in which a heater 1 is installed,
A carry-in passage 3 for carrying in a circuit board 5 provided on the inlet side of the heating chamber 2; and a circuit board 5 provided on the outlet side of the heating furnace 2.
And an unloading passage 4 for unloading.

[0004] It is desirable to supply an inert gas such as nitrogen gas in the heating furnace to keep the oxygen concentration low so as to prevent oxidation of the circuit board and electronic components. In order to make the heating chamber an inert gas atmosphere and stabilize it at a predetermined oxygen concentration, the flow rate of the inert gas to be supplied may be increased, but the running cost during operation is kept low, and the inert gas to the outside of the furnace is reduced. It is necessary to minimize the outflow.

Therefore, conventionally, the carry-in passage 3 of the circuit board 5,
A plurality of fins 7 are vertically arranged with the conveyor 6 interposed between the carry-out passages 4.
To provide a labyrinth seal effect (effect of suppressing gas inflow and outflow by trapping and retaining gas between fins)
As a result, the amount of inert gas flowing out of the furnace is reduced, and the entrainment of outside air into the furnace is reduced.

In the heating furnace 10, an inert gas outlet 8 is provided at the fin 7, the inert gas is supplied from the gas outlet 8 into the heating chamber 2, and the gas is supplied to the circuit board. The gas sealing effect which suppresses inflow and outflow of gas by blowing toward 5 is also used. The gas outlet 8 is, for example, a metal pipe 38 having a number of gas outlets 39 formed at appropriate intervals in the longitudinal direction as shown in FIG.

As described above, the heating furnace using both the labyrinth sealing effect and the gas sealing effect has an advantage that the inside of the furnace can be maintained at a low oxygen concentration with a small amount of inert gas supplied.

[0008]

However, it has been found that when the circuit board is actually transported in the heating furnace 10 shown in FIG. 4, the oxygen concentration may fluctuate greatly.

[0009]

The present inventors have studied the phenomenon that the oxygen concentration fluctuates during the transfer of the circuit board. As a result, as shown in FIG. Due to the pressure difference generated around the gas outlet 8, the inert gas in the furnace flows out of the furnace through the space 4a of the gas outlet 8 on the side opposite to the transport path, or the outside air flows in, It was found that it was affecting the oxygen concentration in the furnace.

[0010] The present invention has been made based on the above findings, and is a heating furnace for soldering a circuit board which can stably maintain the oxygen concentration in the furnace within a small fluctuation range with a small supply amount of inert gas. Is provided.

That is, in the present invention, a heating chamber,
A circuit board carry-in passage and a carry-out passage leading to the heating chamber, and a carrying passage for guiding the circuit board from the carry-in passage through the heating chamber to the carry-out passage, wherein at least one of the passages is above the carrying passage. And / or arrange a plurality of fins directed downward, and in the fin portion, a gas blowout port for blowing gas toward the transfer path and a gas passing through a space opposite to the transfer path of the gas discharge port. It is an object of the present invention to provide a heating furnace for soldering a circuit board, which is provided with a shielding plate for preventing the soldering.

In the present invention, a shielding plate is provided for preventing gas from flowing out of the furnace through a space opposite to the conveying path of the gas outlet. Thereby, it is possible to suppress the outflow of gas in the heating chamber and the intrusion of air outside the furnace into the heating chamber, and it is possible to stably keep the fluctuation range of the oxygen concentration in the heating chamber small.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the figure, FIG.
The same parts as those of the heating furnace of FIG. 6 are denoted by the same reference numerals, and detailed description is omitted. Here, the features of the present invention will be mainly described.

In the heating furnace shown in FIG. 1, fins 7 are provided on the upper wall W ₁ and the lower wall W ₂ of the carry-in passage 3 and the carry-out passage 4. Between the fins provided in the discharge passage 4 gas outlet 8 as shown in FIG. 5, it is provided on the upper wall W ₁ side and the lower wall W ₂ side. Then, the shielding plate 9 is provided on the upper wall W ₁ and the lower wall W ₂ between fins gas outlet 8 is provided. As shown in FIG. 2, the gas outlet 8 and the upper wall W ₁ are transferred by the shielding plate 9 when the circuit board is transported.
Or or the gap between the lower wall W ₂ flows out of the furnace pass through a gas, since outside air can be prevented from or flow into the furnace, stable oxygen concentration in the heating chamber to a predetermined concentration Can be maintained.

[0015] Incidentally, the shielding plate 9 shown in FIG. 1, the top wall W ₁ or lower wall W as shown in FIG. 2 is an enlarged view thereof
₂ , it is provided in parallel with the fin 7, but it may be attached to the fin 7 at a position sandwiching the gas outlet 8 as shown in FIG. Shielding plate 9 in the present invention has only to have the function of preventing outflow of the gap between the gas outlet 8 and the upper wall W ₁ or lower wall W ₂ out of the furnace pass through a gas, shape, location Is not particularly limited. However, since the angle of the gas blown from the gas outlet 8 may be adjusted depending on the driving situation, it is desirable that the shielding plate has a position and a shape that do not hinder the angle adjustment.

[0016]

EXAMPLE The flow rate of the gas supplied from the gas outlet 8 was 200 l / min, and the speed of the chain conveyor 6 was 0.8.
When 10 circuit boards 5 each having a size of 250 mm × 330 mm were conveyed at a loading time of 50 seconds at a rate of m / min, the oxygen concentration in the furnace was stabilized within 100 ppm ± 30%. On the other hand, when the circuit board was transported under the same conditions in a heating furnace having the same structure except that the shielding plate 9 was not provided, the oxygen concentration in the furnace varied greatly in the range of 100 ppm ± 200%.

[0017]

As described above, in the heating furnace for soldering a circuit board according to the present invention, the space between the fins provided with the gas outlets and opposite to the transport path of the gas outlets is provided. A shielding plate is provided to prevent gas passing through the furnace, so it is possible to suppress the inflow and outflow of gas in the furnace even when transferring the circuit board, and to reduce the oxygen concentration in the heating chamber with a small fluctuation width by supplying a small amount of inert gas. It can be kept stable.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a heating furnace for soldering a circuit board according to the present invention.

FIG. 2 is a cross-sectional view of a carry-out passage in a heating furnace for soldering the circuit board of FIG. 1;

FIG. 3 is a cross-sectional view of a carry-out passage in a heating furnace for soldering the circuit board of FIG. 1;

FIG. 4 is a cross-sectional view of a conventional heating furnace for soldering a circuit board.

FIG. 5 is a front view of a gas outlet.

FIG. 6 is a sectional view of a carry-out passage in a conventional heating furnace for soldering circuit boards.

[Explanation of symbols]

Reference Signs List 1 heater 2 heating chamber 3 carry-in passage 4 carry-out passage 5 circuit board 6 transfer path (conveyor) 7 fin 8 gas outlet 38 metal pipe 39 gas outlet 9 shielding plate 10 heating board for soldering circuit board W ₁ top wall W ₂ Lower wall

Claims (1)

[Claims] 1. A heating chamber, a circuit board carry-in passage and a carry-out passage leading to the heating chamber, and a conveyance passage guiding the circuit board from the carry-in passage through the heating chamber to the carry-out passage, and at least one of the passages A plurality of fins facing the upper side and / or the lower side of the transport path are arranged in the passage, and a gas outlet for blowing gas toward the transport path and a transport path for the gas outlet are provided in the fin portion. And a shielding plate for preventing gas passing through a space on the opposite side of the heating furnace.