JPH07159297A - Oxygen concentration measuring apparatus for inert gas atmosphere reflow furnace - Google Patents

Abstract

PURPOSE:To prevent clogging of a sampling tube by disposing a cooling vessel in the way of the sampling tube thereby condensing the flux in the gas and removing it. CONSTITUTION:A high temperature gas sampled from a reflow furnace 11 passes through a sampling tube 27 and enters a cooling vessel 33 where the flux vapor is removed temporarily by means of a mist filter 37. The gas delivered from the mist filter 37 is cooled in the cooling vessel 33 and the flux vapor in the gas is condensed to adhere onto the inner face of the cooling vessel 33. The gas, from which the flux is removed sufficiently, is sucked through the sampling tube 27 on the downstream side into an oxygen concentration meter 25 where the concentration of oxygen is measured. The flux 39 removed from the gas in the cooling vessel 33 is accumulated therein and discharged therefrom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration measuring device in an inert gas atmosphere reflow furnace for soldering and mounting electronic components on a printed circuit board.

[0002]

2. Description of the Related Art A conventional device is shown in FIG. Reference numeral 11 is a reflow furnace. The reflow furnace 11 includes a chain conveyor 13 that passes through the furnace. The chain conveyor 13 conveys the printed circuit board 15 on which electronic components are mounted. The printed circuit board 15 is in a state in which cream solder is applied to the pads in advance and the lead parts of the electronic components are placed thereon.
A heater 17 is installed in the reflow furnace 11, and the heater 17 heats the printed circuit board 15 passing through the furnace to melt the cream solder and perform soldering.

In order to prevent the printed circuit board and electronic parts from being oxidized during soldering, the inside of the reflow furnace 11 is kept in an atmosphere of an inert gas such as a nitrogen gas. Nitrogen gas is supplied from a nitrogen gas supply source 19 through a flow control valve 21, and in this example, is blown out into the furnace from an ejection pipe 23 installed in an outlet side passage of the reflow furnace 11.

To prevent oxidation, it is necessary to keep the oxygen concentration in nitrogen gas below a certain limit. The inside of the reflow furnace 11 is filled with nitrogen gas, but the oxygen concentration in the furnace changes due to the inclusion of outside air due to passage of the printed circuit board 15. The oxygen concentration in the reflow furnace 11 is measured by an oxygen concentration meter 25 installed outside the furnace. The oxygen concentration meter 25 sucks the gas in the furnace through the sampling pipe 27 and measures the oxygen concentration in the sucked gas. Since the flux of cream solder is vaporized and mixed in the gas in the furnace, a filter for removing the flux is provided in the middle of the sampling tube 27.
29 are installed.

The measured value of the oximeter 25 is input to the controller 33. The controller 31 controls the flow rate control valve 21 to increase the supply amount of nitrogen gas when the measured oxygen concentration in the furnace is higher than the set value and decrease the supply amount of nitrogen gas when the measured oxygen concentration is lower than the set value. This keeps the oxygen concentration in the furnace almost constant.

[0006]

The flux in the cream solder is vaporized and mixed in the gas in the reflow furnace.
The flux is in a gaseous state due to the high temperature inside the furnace, but when it is led out of the furnace through the sampling tube, it becomes liquid or gel as the temperature decreases. Therefore, in the conventional device, the flux is apt to adhere to the inner surface of the sampling tube, and when the amount of the flux increases, the sampling tube becomes clogged and the oxygen concentration cannot be measured. Although a filter is installed in the middle of the sampling tube, the filter cannot sufficiently remove the flux in the gas. If the sampling tube is clogged, it is difficult to clean the inside, and the sampling tube needs to be replaced. In the past, the replacement period of this sampling tube was short and maintenance was troublesome.

[0007]

The present invention provides an oxygen concentration measuring apparatus for an inert gas atmosphere reflow furnace which solves the above problems. In a device that takes gas through a sampling tube into an oxygen concentration meter installed outside the reflow furnace and measures the oxygen concentration in the gas with the oxygen concentration meter, cools the gas sampled from inside the reflow furnace in the middle of the sampling tube. A cooling container is provided to condense and remove the flux vapor in the gas.

[0008]

According to the above construction, the gas sampled from the reflow furnace enters the cooling container and is cooled, and the flux vapor in the gas is condensed on the inner surface of the cooling container. The condensed flux accumulates in the cooling container. The accumulated flux may be discharged from the cooling container at appropriate intervals. Therefore, the amount of flux attached to the inner surface of the sampling tube is reduced, and the replacement period of the sampling tube can be extended.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, the same parts as those of the device of FIG. 3 described above are designated by the same reference numerals. The characteristic of this device is that a cooling container 33 is provided in the middle of a sampling pipe 27 for taking the gas in the reflow furnace 11 into the oxygen concentration meter 25. Cooling container 33
Is forcedly cooled by blowing air with a fan 35 installed outside. A mist filter 37 is attached to the end of the upstream sampling pipe 27 that opens in the cooling container 33.

With such a structure, the high temperature gas sampled from the reflow furnace 11 passes through the sampling pipe 27 and enters the cooling container 33, and the mist filter 37 temporarily removes the flux vapor. Mist filter 37
Although the flux removal by is not sufficient, the gas leaving the mist filter 37 is cooled in the cooling container 33, so the flux vapor in the gas is condensed and adheres to the inner surface of the cooling container 33. The gas from which the flux has been sufficiently removed in this manner is sucked into the oxygen concentration meter 25 through the sampling pipe 27 on the downstream side, and the oxygen concentration is measured. The flux removed from the gas in the cooling container 33 collects in the cooling container 33. The accumulated flux 39 is cooled by a cooling container 33 at appropriate intervals.
Emitted from.

The cooling vessel 33 is preferably arranged close to the furnace wall of the reflow furnace 11. This is to prevent the flux from adhering to the inside of the sampling pipe 27 between the reflow furnace 11 and the cooling container 33. Further, in order to prevent the flux from adhering to the inside of the sampling pipe 27 between the reflow furnace 11 and the cooling container 33, it is effective to cover the sampling pipe 27 between them with a heat insulating material. Further, in order to enhance the cooling efficiency of the gas in the cooling container 33, it is preferable to manufacture the cooling container 33 with a material having excellent thermal conductivity such as aluminum or copper. Forming heat radiation fins on the outer surface of the cooling container 33 is also effective in increasing the cooling efficiency.

FIG. 2 shows another embodiment of the present invention. This device is different from the device of FIG. 1 in that the mist filter in the cooling container 33 is omitted, and the partition wall 41 that extends the flow path of the gas in the cooling container 33 is formed. Providing such a partition wall 41 increases the chances of the gas coming into contact with the inner wall of the cooling container 33, increasing the cooling efficiency and improving the flux removal rate. Since the other configuration is the same as that of FIG. 1, the same portions are denoted by the same reference numerals and the description thereof will be omitted.

[0013]

As described above, according to the present invention, a cooling container is provided in the middle of a sampling pipe for taking the gas in the reflow furnace into the oxygen concentration meter, and the gas is forcibly cooled in the cooling container. Since the flux of (1) is condensed and removed and the removed flux is stored in the cooling container, the amount of the flux adhering to the inner surface of the sampling tube can be greatly reduced. For this reason, the sampling tube is less likely to be clogged, the replacement period of the sampling tube can be extended, and maintenance is facilitated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of an apparatus according to the present invention.

FIG. 2 is an explanatory view showing another embodiment of the device according to the present invention.

FIG. 3 is an explanatory view showing a conventional device.

[Explanation of symbols]

 11: Reflow oven 15: Printed circuit board 19: Nitrogen gas supply source 25: Oxygen concentration meter 27: Sampling tube 33: Cooling container 35: Fan 37: Mist filter 39: Flux accumulated in the cooling container 41: Partition wall

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G01N 33/20 P 7055-2J

Claims (1)

[Claims] 1. An apparatus for introducing a gas in an inert gas atmosphere reflow furnace through a sampling tube into an oxygen concentration meter installed outside the reflow furnace, and measuring the oxygen concentration in the gas with the oxygen concentration meter, wherein the sampling tube is used. In the middle of
An oxygen concentration measuring device for an inert gas atmosphere reflow furnace, comprising a cooling container for cooling a gas sampled from the inside of the reflow furnace to condense and remove flux vapor in the gas.