JP2002026507A - Heating furnace for reflow soldering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the adhesion of flux to the substrate carrying-in section or substrate carrying-out section of a heating furnace for reflow soldering, to make adhering flux cleaning work easier, and to stably maintain the oxygen concentration in the heating chamber of the furnace at a low value. SOLUTION: This heating furnace for reflow soldering is provided with the heating chamber 5 in which an inert gas is filled up and a planar heater 1, a blower 3 for refluxing the inert gas, etc., are set up, and then, circuit boards 4 mounted with electronic parts are heated to a soldering temperature; the substrate carrying-in section 6 which carries the circuit boards 4 in the heating chamber 5; and the substrate carrying-out section 7 which carries out the circuit boards 4 from the chamber 5. In the heating furnace, a by-pass passage 13 through which part of the inert gas heated in the heating chamber 5 is refluxed to the chamber 5 after by-passing the substrate carrying-in section 6 or carrying- out section 7 is provided between at least either one of the sections 6 and 7 and the heating chamber 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow soldering heating furnace for reflow 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 reflow soldering, the circuit board on which the electronic component is mounted at a predetermined position is passed through a heating furnace, and the solder is melted and soldered. In this case, the heating furnace is filled with an inert gas such as nitrogen gas to prevent oxidation of the circuit board and the electronic components.

A conventional heating furnace for this type of soldering is shown in FIG.
As shown in the figure, the inside is filled with an inert gas, and a planar heater 1, a bar-shaped heater 2, a blower 3 for recirculating the inert gas, and the like are installed. A heating chamber 5 for heating the circuit board 4, a board loading section 6 for loading the circuit board 4 into the heating chamber 5, and a board unloading section 7 for unloading the circuit board 4 from the heating chamber 5. The circuit board 4 on which the components are mounted travels with both side edges supported by the chain conveyor 8. A mesh conveyor may be used instead of the chain conveyor 8.

The heating chamber 5 is filled with an inert gas to prevent oxidation of the circuit board 4 on which electronic components are mounted. The inert gas is supplied from an inert gas supply pipe (not shown). In order to prevent air from entering the furnace from the outside, the inert gas is gradually and gradually supplied to the outside from the substrate carry-in portion 6 and the substrate carry-out portion 7. The supply is regulated so that it flows out. In addition, in order to reduce the amount of the inert gas flowing out, a gas seal member 9 is disposed in the substrate carrying-in portion 6 and the substrate carrying-out portion 7, so that the inert gas passing through the carrying-in / out portion is reduced. Provides resistance and limits the flow of inert gas. The gas seal member 9 is usually composed of a large number of metal plates or the like arranged at predetermined intervals in the traveling direction of the circuit board 4.

Also, at the time of reflow soldering, an oxide film on the surface of the metal to be soldered is removed to prevent reoxidation by heating during soldering, and to reduce the surface tension of the solder to improve the wetting. Therefore, flux (coating material) is often used. When the circuit board 4 on which the electronic components are mounted is heated to the soldering temperature while passing through the heating chamber 5, the flux is vaporized and mixed into the inert gas. When the concentration of the vaporized flux increases, the inside of the heating chamber 5 is contaminated.
For example, as shown in FIG. 4, an inert gas bypass passage 10 is provided on a side wall of the heating chamber 5, and a part of the inert gas in the heating chamber 5 is bypassed by a recirculation fan 11 provided in the passage 10. 10, the inert gas is cooled by a heat radiating unit 12 such as a cooling fin, and the flux contained in the gas is condensed and adhered to the inner peripheral surface of the passage to be collected. Preventing.

[0006]

In this type of heating furnace,
The vaporized flux contained in the inert gas in the heating chamber 5 can be recovered to some extent. However, it is difficult to completely remove the flux in the heating chamber 5, and when the inert gas containing the vaporized flux flows out of the furnace through the narrow passage of the substrate carrying-in portion 6 or the substrate carrying-out portion 7, The vaporized flux is condensed in the substrate carry-in section 6 or the substrate carry-out section 7 and adheres to the inner wall surface or the like. When the operation of the heating furnace is continued for a long time, the flux attached to the substrate carry-in portion 6 or the substrate carry-out portion 7 drops on the circuit board 4 and contaminates the circuit board 4 and electronic components, thereby deteriorating the performance. Failure occurs. In particular, the substrate carrying-in portion or the substrate carrying-out portion, which is far from the place where the inert gas is replenished and supplied into the heating chamber 5, is less susceptible to the action of the fluid curtain caused by the replenishment and supply of the inert gas. There is a problem that more inert gas containing ash flows out of the furnace, and the flux easily adheres.

In addition, the substrate loading section 6 to which the flux has adhered
Alternatively, it is necessary to frequently clean the substrate unloading section 7, and since the passages of the loading and unloading sections 6 and 7 are generally narrow, cleaning is not easy and the cleaning work becomes complicated.

On the other hand, in order to facilitate cleaning of the flux adhering to the inside of the substrate carrying-in section 6 or the substrate carrying-out section 7, the passage area and the opening size of the substrate carrying-in section 6 or the substrate carrying-out section 7 may be increased. However, as shown in FIG. 5, for example, the substrate carry-out unit 7 (the substrate carry-in unit 6 is not shown).
Inside, the high temperature inert gas in the heating chamber 5 flows out of the heating chamber 5 above the substrate 4 with the circuit board 4 passing through this passage as a boundary, and the low temperature Horizontal convection in which outside air flows into the heating chamber 5 is likely to occur, and the oxygen concentration in the heating chamber 5 increases due to invasion of the outside air into the heating chamber 5,
In addition, there is a problem that the circuit board and the electronic components are easily oxidized due to instability.

The present invention solves the above-mentioned problems, eliminates the adhesion of the flux to the board carry-in section or the board carry-out section and the adverse effect on the circuit board and the like, and also facilitates the work of cleaning the adhered flux. Another object of the present invention is to provide a heating furnace for reflow soldering that stably maintains the oxygen concentration in a heating chamber at a low concentration.

[0010]

According to a first aspect of the present invention, there is provided a heating furnace for reflow soldering, wherein the inside of the heating furnace is filled with an inert gas. A blower or the like for circulating the active gas is installed, a heating chamber for heating the circuit board on which the electronic components are mounted to a soldering temperature, a board loading section for loading the circuit board into the heating chamber, and the circuit board from the heating chamber. In a heating furnace for reflow soldering having a substrate carrying-out part to carry out, between at least one of the substrate carrying-in part or the substrate carrying-out part and the heating chamber, a part of the inert gas heated in the heating chamber, It is characterized in that a bypass passage is provided for bypassing into the substrate carry-in portion or substrate carry-out portion and returning to the heating chamber.

[0011] With such a configuration, the substrate carry-in portion or the substrate carry-out portion is heated by the high-temperature inert gas in the heating chamber, so that the flux does not adhere to the substrate carry-in portion or the substrate carry-out portion due to gas condensation. The problem of defective generation due to flux dripping is eliminated. Further, since the flux is not easily adhered, the cleaning operation of the substrate carrying-in portion or the substrate carrying-out portion becomes easy, and maintenance becomes easy. Further, since the inert gas bypassed to the substrate carry-in portion or the substrate carry-out portion is recirculated into the heating chamber, even when the passage area of the substrate carry-in portion or the substrate carry-out portion becomes large, the inert gas flows in the vertical direction (for the circuit board). A fluid curtain in the direction perpendicular to the running direction is formed, and horizontal convection hardly occurs. Unnecessary outflow of inert gas (nitrogen gas, etc.) and intrusion of outside air are suppressed, and oxygen concentration in the heating chamber is reduced. It is possible to stably maintain the concentration and to prevent the oxidation of the circuit board and the electronic components.

According to a second aspect of the present invention, there is provided a heating furnace according to the first aspect, wherein the bypass passage is connected to at least one of the substrate carrying-in portion and the substrate carrying-out portion and a blower of a blower in a heating chamber. It is characterized by being provided between the side part. With such a configuration, the suction side of the blower is lower than the atmospheric pressure in the heating chamber on the discharge side and in the substrate carry-in section or the substrate carry-out section, so that a part of the inert gas heated in the heating chamber is transferred to the substrate carry-in section or the substrate. In addition to the bypass in the carry-out section, it is easy to return to the heating chamber through the bypass passage, and it is not necessary to provide a separate blower for returning the inert gas to the bypass passage. The size can be reduced.

Further, according to a third aspect of the present invention, in the heating furnace according to the first or second aspect, an inert gas circulating in the bypass passage is cooled in the middle of the bypass passage. And a cooling means for collecting and recovering the flux contained in the inert gas by gas condensation. With such a configuration, the vaporized flux adheres to the bypass passage, not in the substrate carry-in portion or the substrate carry-out portion, by gas condensation, so that it becomes easy to efficiently collect the flux, and the heating chamber is filled. The flux concentration in the inert gas can be reduced as much as possible.

[0014]

Next, embodiments of the present invention will be described in detail with reference to the drawings. 1, the same components as those of the heating furnace shown in FIGS. 3 to 5 described above are denoted by the same reference numerals. The reflow soldering heating furnace of this embodiment is filled with an inert gas, and is provided with a planar heater 1, a bar-shaped heater 2, a blower 3 for recirculating the inert gas, and the like, and electronic components are mounted thereon. A heating chamber 5 for heating the circuit board 4 to a soldering temperature;
And a board unloading section 7 for unloading the circuit board 4 from the heating chamber 5. The circuit board 4 on which the electronic components are mounted is separated by a chain conveyer 8 on both sides thereof. It travels in a supported state. The blower 3 has a low pressure and a large air volume, for example,
A centrifugal blade type blower such as a sirocco fan is used. A mesh conveyor or the like may be used instead of the chain conveyor 8.

The heating chamber 5 is filled with an inert gas such as nitrogen gas by pressurizing it slightly above atmospheric pressure in order to prevent oxidation of the circuit board 4 on which the electronic components are mounted. This inert gas is supplied from an inert gas supply pipe (not shown), and in order to prevent air from entering the furnace from outside,
The supply amount of the inert gas is adjusted so that the inert gas always flows out little by little from the substrate carry-in portion 6 and the substrate carry-out portion 7. In addition, in order to reduce the amount of the inert gas flowing out, a gas seal member 9 is disposed in the substrate carrying-in portion 6 and the substrate carrying-out portion 7, so that the insides of the carrying-in and carrying-out portions 6 and 7 are reduced. This provides resistance to the passing inert gas and limits the flow of the inert gas. The gas seal member 9 is usually composed of a large number of metal plates or the like arranged at predetermined intervals in the traveling direction of the circuit board 4. Although not shown, as in the case of the conventional heating furnace, on the side wall of the heating chamber 5, during the reflow soldering, the flux that has been vaporized and mixed into the inert gas is removed and collected. For this purpose, a bypass passage is provided, and a part of the inert gas in the heating chamber 5 is introduced into the passage by a recirculation fan, and is cooled by a heat radiating part in the middle of the passage to condense the flux. It is designed to adhere to the inner peripheral surface.

The heating furnace having such a configuration is the same as the conventional one. In the heating furnace according to the present embodiment, the heating chamber 5 is further provided between the substrate loading section 6 and the substrate unloading section 7 and the heating chamber 5.
A part of the inert gas heated in the substrate
In addition, a bypass passage 13 is provided for bypassing the inside of the substrate carrying-out section 7 and returning to the heating chamber 5. The bypass passage 13 includes a pipe, a duct, and the like.

As described above, since the bypass passage 13 is provided in the substrate carrying-in portion 6 and the substrate carrying-out portion 7, the substrate carrying-in portion 6 and the substrate carrying-out portion 7 are heated by the high-temperature inert gas in the heating chamber 5. Therefore, the flux does not adhere to the inner wall surface of the substrate carry-in portion 6 or the substrate carry-out portion 7 or the surface of the gas seal member 9 due to gas condensation, and the problem of the occurrence of defects due to the dripping of the flux is solved. . Further, since the flux is not easily adhered, the cleaning operation of the substrate carrying-in section 6 and the substrate carrying-out section 7 is facilitated, and the maintenance is facilitated. Further, these substrate loading / unloading units 6, 7
The inert gas that has been bypassed into the heating chamber 5 is returned to the heating chamber 5, so that even if the passage area becomes large, a fluid curtain in a vertical direction (a direction perpendicular to the running direction of the circuit board 4) is formed at this portion. Horizontal convection is unlikely to occur, and it is possible to suppress the outflow of the inert gas more than necessary and the invasion of the outside air, and it is possible to stably maintain the oxygen concentration in the heating chamber 5 at a low concentration. There is an advantage that the oxidation of can be prevented.

In the present embodiment, the bypass passage 13
Are provided between the substrate carry-in unit 6 and the substrate carry-out unit 7 and the suction side portion of the blower 3 in the heating chamber 5. According to such a configuration, the suction side of the blower 3 becomes lower than the atmospheric pressure in the heating chamber 5 on the discharge side and in the substrate loading / unloading sections 6 and 7. It is necessary to provide a recirculation fan that recirculates the inert gas to the bypass passage 13 by easily bypassing the part into the substrate carry-in part 6 and the substrate carry-out part 7 and circulating the inert gas into the heating chamber 5 through the bypass passage 13. This has the advantage that power costs can be reduced and the heating furnace can be downsized.

Further, in the present embodiment, the bypass passage 13
A cooling means 14 is provided in the middle of the cooling device 14 for cooling the inert gas refluxing in the passage and condensing and recovering the flux contained in the inert gas. As the cooling means 14, a radiator using a cooling fin, a heat pipe, a water-cooled jacket, or the like is used. With such a configuration, the vaporized flux adheres by gas condensation in the bypass passage 13, so that it is easy to efficiently collect the flux, and the flux in the inert gas filled in the heating chamber becomes easy. The flux concentration can be reduced as much as possible.
In addition, it is preferable that the flux adhesion recovery portion has a structure that can be easily removed from the bypass passage 13 because maintenance is easier.

The heating furnace of the present embodiment has a structure in which the bypass passage 13 is provided in both the substrate carrying-in section 6 and the substrate carrying-out section 7. By the way, the amount of the flux adhering to the substrate carry-in section 6 and the substrate carry-out section 7 may vary depending on the location where the inert gas is replenished and supplied into the heating chamber 5 and the flow state of the inert gas flowing through the heating chamber 5. is there. For example, a large amount of flux tends to adhere to the substrate carrying-in portion 6 or the substrate carrying-out portion 7 far from the location where the inert gas is replenished and supplied. In such a case, the bypass passage 13 may be provided only in the substrate carrying-in portion 6 or the substrate carrying-out portion 7 where a large amount of flux tends to adhere. The effect is obtained, and the object of the present invention can be achieved.

FIG. 2 shows an example of a structure in which a bypass passage 13 is provided between the substrate unloading section 7 and the heating chamber 5 where the blower 3 is not disposed. In this case, a part of the inert gas heated in the heating chamber 5 is bypassed into the substrate unloading section 7 as shown by the arrow in FIG. In order to recirculate quickly, a recirculation fan 15
Is preferably provided. By circulating the inert gas between the substrate unloading section 7 and the heating chamber 5 in this manner, the boundary between the heating chamber 5 and the substrate unloading section 7 is formed in a vertical direction by the inert gas (for the circuit board 4). (A direction perpendicular to the running direction) is formed. For this reason, horizontal convection of gas, which has occurred in the conventional heating furnace, is unlikely to occur, and unnecessary outflow of inert gas and intrusion of outside air are suppressed, and the oxygen concentration in the heating chamber becomes stable and low. In addition, oxidation of the circuit board and the electronic components can be prevented. The structure shown in FIG. 2 can be applied to the substrate carrying-in section 6 or both the substrate carrying-in section 6 and the substrate carrying-out section 7.

[0022]

As described above, according to the present invention,
A bypass that allows a part of the inert gas heated in the heating chamber to be bypassed in the substrate loading section or the substrate unloading section and to be returned to the heating chamber between at least one of the substrate loading section or the substrate unloading section and the heating chamber. Since the passage is provided, the flux does not adhere to the substrate carrying-in portion or the substrate carrying-out portion due to gas condensation, and the problem of the occurrence of defects due to the dripping of the flux is solved. Further, since the flux does not easily adhere to the substrate, the work of cleaning the substrate carry-in portion or the substrate carry-out portion becomes easy, and maintenance becomes easy. Furthermore, unnecessary outflow of inert gas and intrusion of outside air are suppressed, and the oxygen concentration in the heating chamber can be kept low and stable.
Oxidation of circuit boards and electronic components can be prevented.

Further, when the bypass passage is provided between at least one of the substrate carry-in portion and the substrate carry-out portion and the suction side of the blower in the heating chamber, one of the inert gas heated in the heating chamber is provided. In addition to bypassing the unit into the substrate carry-in unit or the substrate carry-out unit, it is easy to recirculate the heat into the heating chamber through the bypass passage, and it is not necessary to provide a separate blower for recirculating the inert gas in the bypass passage, thereby reducing power costs. In addition, the heating furnace can be reduced in size.

Further, a cooling means is provided in the middle of the bypass passage for cooling the inert gas circulating in the passage and for collecting and recovering the flux contained in the inert gas by gas condensation. The vaporized flux can be attached by gas condensation in the bypass passage, not in the substrate carry-in or substrate carry-out part, so that the flux can be easily collected efficiently, and the inert gas filled in the heating chamber can be easily collected. The flux concentration in the medium can be reduced as much as possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a heating furnace for reflow soldering according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a modification in the case where a bypass passage is provided on the substrate carry-out portion side in the heating furnace of the present invention.

FIG. 3 is a sectional view showing a conventional heating furnace for reflow soldering.

FIG. 4 is a sectional view showing a flux collecting means in a conventional heating furnace.

FIG. 5 is an explanatory view showing an outflow state of an inert gas and an intrusion state of outside air in a substrate carrying-out section in a conventional heating furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Planar heater 2 Bar heater 3 Blower 4 Circuit board 5 Heating chamber 6 Substrate carry-in part 7 Substrate carry-out part 8 Chain conveyor 9 Gas seal member 10 Bypass passage 11 Reflux fan 12 Heat radiator 13 Bypass passage 14 Cooling means 15 Reflux fan

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B23K 101: 42 B23K 101: 42

Claims (3)

[Claims] 1. A heating chamber in which an inert gas is filled, a planar heater, a blower for circulating the inert gas, and the like are installed, and a circuit board on which electronic components are mounted is heated to a soldering temperature. In a heating chamber for reflow soldering, comprising a board loading section for loading the circuit board into the heating chamber and a board loading section for unloading the circuit board from the heating chamber, at least one of the board loading section or the board loading section. Between the heating chamber and the heating chamber, a bypass passage for recirculating a part of the inert gas heated in the heating chamber into the substrate carrying-in portion or the substrate carrying-out portion and returning to the heating chamber is provided. heating furnace. 2. The heating for reflow soldering according to claim 1, wherein the bypass passage is provided between at least one of the substrate carry-in portion and the substrate carry-out portion and a suction side portion of a blower in a heating chamber. Furnace. 3. A cooling means for cooling an inert gas circulating in the bypass passage and collecting and collecting a flux contained in the inert gas by gas condensation is provided in the middle of the bypass passage. The reflow soldering heating furnace according to claim 1.