JPH04190967A - Atmosphere furnace - Google Patents

Abstract

PURPOSE:To perform satisfactory heat treatment at a low cost by monitoring the concentration of oxygen in a furnace and setting it at an arbitrary value. CONSTITUTION:The concentration of oxygen in the furnace is monitored by a sensor 9. When it exceeds a prescribed concentration of oxygen, the gas in the furnace is circulated by an instruction of a control part 12 through a fan 11 and a duct 10. The oxygen in the gas in the furnace is eliminated by oxygen eliminating catalyst 13 and kept at an arbitrary constant concentration of oxygen. After the oxygen eliminating catalyst eliminates a constant volume of oxygen it is changed and reproduced. This invention does not require large scale inert gas replenishing tank and piping equipment in a plant as in the conventional manner. Further, a large volume of N2 gas, etc., is not consumed and the running cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a furnace 1 that performs continuous heat treatment and has an inert atmosphere inside the furnace, such as an atmospheric furnace such as a N2 gas reflow apparatus.

Conventional technology Conventionally, in electronic component reflow equipment, thick film hybrid IC substrate firing furnaces, etc., in order to prevent conductors such as Cu printed on the substrate from being oxidized during heat treatment in the furnace, Attempts have been made to keep the oxygen concentration in the furnace low and constant by injecting inert gases such as nitrogen gas (N) and grease (N2.N2).
A large number of rollers.

There is an opening at the entrance and exit of the blast furnace, which continuously conveys the heated material using a chain belt, etc., and a large amount of inert gas in the furnace must be injected every day, resulting in high running costs. For this reason, a shutter part that opens only when the object to be heated is passed through the entrance and exit of the furnace is provided, or a buffer is provided at the entrance and exit of the furnace as disclosed in Japanese Utility Model Application Publication No. 180076/1983. When carrying objects into or out of the furnace, the objects to be heated are placed in a buffer and sealed, and the gas in the buffer is vacuum-sucked to remove N2.
Attempts have been made to keep gas consumption low.

Problems to be Solved by the Invention However, even when the vacuum buffer, shutter, etc. are used, the atmosphere gas inside the furnace is gradually diffused and consumed outside the furnace as the object to be heated is brought in and taken out. For this reason, equipment for monitoring the O2 concentration in the furnace and for supplying an inert atmosphere gas was still required within the factory.

Means for Solving the Problems In the present invention, in order to solve the above problems, firstly, an opening is provided in the furnace wall to provide a path for circulating the furnace atmosphere gas and to remove 02 in the gas in the middle of the path. It is equipped with a pipe line filled with catalyst and a sensor inside the furnace to detect the oxygen concentration.

Second, when a plurality of 02 removal catalyst tubes are arranged circumferentially or in parallel and their positions are shifted, the passage port is held so as to be connected to a new 02 removal catalyst tube.

Operation The present invention has the above configuration to detect the oxygen concentration in the furnace atmosphere, and when the oxygen concentration deviates from a predetermined oxygen concentration, the furnace gas is circulated and the oxygen is removed by the catalyst. The operation is stopped when the oxygen concentration in the furnace reaches a predetermined value.

In addition, just before a catalyst tube becomes used up, it is replaced with another catalyst tube to continuously maintain the oxygen concentration in the furnace.

Example (Example 1) Next, the present invention will be explained using the drawings. FIG. 1 shows an inert gas atmosphere furnace equipped with a dryer at the inlet and outlet. In an atmospheric furnace consisting of a main heating or firing zone 1, a preheating or vane-out zone 2, an in-furnace conveying section 3 provided at the bottom of the furnace, and a cooling section 4 for the object to be heated such as an electronic board, an inlet shank 5, an outlet section Shutter 6, shunter opening/closing nolinders 7, 8, sensors 9a, 9b for detecting oxygen concentration in the furnace, duct 10 for circulating air in the furnace, pump 11 for blowing gas in the furnace, operating pump 11, It consists of a control unit 12 for stopping the operation, and a tube 3 filled with a catalyst (for example, Ni catalyst) for removing oxygen.

Note that 14 is an object to be heat treated (the figure shows a pre-reflow molded board with electronic components mounted on cream solder), and 15 is a charging conveyor.

The operation of the atmospheric furnace having the above configuration will be explained below.

As mentioned above, when the substrate 14 is withdrawn by the converter 15, the inlet iron yatter 5 is opened by the unlinder 7, and the substrate 14 is moved into the furnace by the conveyor heald 3 (a conveyor system such as a chain roller may also be used). After being heated in the preheating section 27 and heating section 1, it is heated to a predetermined temperature (approximately 100°C in the case of printed circuit boards) in the cooling section 4.
After the substrate has been cooled down to a certain temperature, the exit shutter 6 is opened and the substrate 14 is carried out.

During continuous processing, the oxygen concentration in the furnace is monitored by one or more oxygen concentration sensors 9 (9a, 9b), and when the oxygen concentration reaches a predetermined level (for example, 50 ppm) or higher, the control unit 12 triggers a reset. 11 is issued to circulate the furnace gas through the furnace gas circulation duct 10. Oxygen in the furnace gas is removed by an oxygen removal catalyst 13 provided in the middle of the duct 10, and when the oxygen concentration in the furnace reaches a predetermined value, the fan 11 is stopped by the control unit 12. As described above, the oxygen concentration in the furnace is maintained at an arbitrary constant value. The catalyst is operated intermittently, and after a certain amount of oxygen has been removed, the oxygen removal catalyst is replaced for regeneration, but this is done infrequently.

(Example 2) Next, an example of application in an atmospheric furnace shown in FIG. 2 will be described. The difference from Embodiment 1 is that the atmosphere furnace is provided with a vacuum buffer 16 (inlet) and a vacuum buffer 17 instead of an inlet shutter 5 and an outlet shutter 6, and the furnace can be accessed from inside the vacuum buffers before and after this. Front duct h provided inside
lOa and a rear duct 10b are provided.

As in the above embodiment, when the substrate 14 approaches the furnace inlet, the shutter 16a of the charging side vacuum buffer 16 is opened, and when the substrate 14 enters the charging side vacuum buffer 16, the shutter 16a is closed (the shutter 16b is closed). closed.)
, here the air in the vacuum buffer 16 is exhausted and the duct 10
The air exhausted by pump lla is passed through oxygen removal catalyst 13 through a, and after being made into a gas having a predetermined 02 concentration or less, it is exhausted into the furnace. In this case, the exhaust gas may be returned into the vacuum buffer 16.

Next, the heated substrate 14 is carried into the buffer 17 by opening the front shutter 17b of the rear vacuum buff 7a 17. At this time, the aforementioned Kunyasotar 17a,
Pump the air in the buffer with 17b closed 1.1
The gas is exhausted through duct 10b, and oxygen is removed by oxygen removal catalyst 13. After the above operations, the rear exit shutter 17b is opened and the substrate is carried out of the furnace.

This completes the series of heat treatments, and in the case of an atmospheric furnace in which buffers are provided before and after the furnace, the influence of outside air on the inside of the furnace will be even smaller than in the case of Example].

In both the furnaces of the embodiments 1.2 above, Fig. 3(a)
, (bl shows the configuration of the 02 removal device. As shown in the figure, a plurality of oxygen removal catalyst tubes are arranged on the circumference, and the catalyst tube 18a that has lost the 02 removal catalytic action is replaced with the next new catalyst tube 1.
8b, it has a structure that can be rotated by a handle 19 in the direction of the arrow. Figure 4 (at, fb), fcl
As shown in FIG.
The pipe opening 18'' is held by two elastic plates 20a, 20b so that a new catalyst tube 18° can be inserted at 0° with one touch.When taking out the catalyst tube 18a, the elastic plates 20a, 20
Widen the gap between b and insert a new catalyst tube 18b in the specified position.
In this case, the catalyst tube 18b can be fixed with a light elastic force.

In the furnace body shown in FIG. 5, the catalyst tube group in FIG. 4 is arranged on a plane instead of on the circumference, and the catalyst tube group is moved in a straight line by a table 22 and a guide 23, and the catalyst tubes are replaced. It is a structure that performs.

Effects of the Invention As is clear from the above explanation, according to the present invention, there is no need to provide a large-scale inert gas replenishment tank (for N2 gas, etc.) or piping equipment in the factory, unlike in the past. Furthermore, a large amount of gas such as N 2 gas is not consumed, and running costs are reduced.

Furthermore, since the oxygen concentration in the furnace is monitored by a sensor and the 02 concentration can be set arbitrarily, high-quality heat treatment (reflow, firing) can be performed.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an atmosphere furnace having a shutter at the entrance and exit of the first embodiment, and Fig. 2 shows a vacuum buffer provided at the entrance and exit of the second embodiment, and the air in this vacuum buffer is removed by 02. A configuration diagram of an atmospheric furnace, Figure 3 is a configuration diagram of a removal device with multiple catalyst tubes mounted on the circumference, Figure 4 is an enlarged view of the catalyst tube fixing part in Figure 3, and Figure 5 is a diagram of a catalyst tube. It is a block diagram when these are arranged side by side on a plane. 1...Main heating section, 2...Preheating section, 3.
...Conveyance section, 5...Front nya soter, 6...
... Rear shutter, 7...Front rear shutter, 8...Rear upper and lower shutters, 9a, 9b...Oxygen concentration sensor, 10... ...Ventilation duct, 1]...Pump, 12...Controller, 13...
Oxygen removal device, 14... Printed circuit board, 16.
...Front vacuum buffer, 16a...Front Rochasota, 16b...Front exit shutter,
17a... Rear entrance shutter, 17b...
...Rear exit shutter, 18...Oxygen removal catalyst pipe, 19...Lever, 20a, 20b...
...Entrance guide, 22...Plate, 23.
...LM Guide. Name of agent: Patent attorney Haruaki Koebi and 2 otherscq
Hakuhina 13 Figure 8b Figure 4 Room 5 Figure

Claims (4)

[Claims] (1) For reflow soldering of electronic circuit boards, etc., the furnace has a heating means for heating the object to be heated and a transport means for transporting the object, and the atmosphere inside the furnace is an inert gas such as N_2 gas. In the furnace, 1. 2. a circulation means for circulating the gas in the furnace; 3. means for removing oxygen from the circulating gaseous body; 4. means for measuring oxygen concentration in the furnace; In order to maintain the oxygen concentration inside the furnace at a predetermined level, 1. An atmosphere furnace characterized by comprising a control means for operating an in-furnace gas circulation means. (2) The apparatus according to claim 1, wherein the inlet and outlet of the furnace are provided with a buffer part capable of sealing and opening the object to be heated, and a hole part for exhausting gas in the buffer. An atmospheric furnace characterized by having means for removing oxygen that has entered the buffer. (3) In order to enable continuous oxygen removal in the apparatus according to claims 1 or 2, a plurality of oxygen removal sections are provided, and used oxygen removal sections and unused oxygen removal sections are arranged on the circumference. An atmosphere furnace characterized by the following. (4) An atmospheric furnace according to claim 3, characterized in that a plurality of oxygen removing sections are arranged in a plane.