JP2006156487A - Equipment and method of reducing nitrogen gas consumption of reflow furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the nitrogen gas consumption of a nitrogen type reflow furnace. <P>SOLUTION: Into the reflow furnace wherein solder is melted by blowing out the hot air of nitrogen gas against a circuit board from above and below it, a little amount of nitrogen gas is blown out in the same direction as or in the opposite direction from the circuit board transfer direction to control the flow of nitrogen gas inside the furnace and thereby reduce nitrogen gas consumption of the reflow furnace. By controlling the flow of nitrogen gas inside the furnace, diffusion of flux inside the furnace can also be prevented, and thereby a facility operation cost for removing the flux can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reflow furnace for heating and soldering a circuit board on which electronic components are mounted in an inert gas such as nitrogen.

  Currently, an SMD (Surface Mounted Device) in which various electronic components are mounted on the surface of a circuit board and soldered is widely used in electronic devices. This SMD is manufactured by inserting a component into a substrate and then soldering the back surface with a solder bath, mounting the mounted component on a substrate printed with cream solder, and then mounting the substrate with a heating device called a reflow furnace. There is a reflow process in which the cream solder is melted by heating.

  Cream solder is a material for holding a mounting component on a circuit board and refers to solder in which solder particles are kneaded with a solvent and a catalyst called flux to form a cream. The flux contained in the cream solder is filled in the furnace after the solder is melted, and this is recovered by a flux recovery device.

Also, the reflow furnace is a method in which the solder is melted by blowing hot air on the circuit board or heating it with an infrared heater or the like while the circuit board on which electronic components are mounted is transported by a transport device comprising a chain conveyor. This is a heating furnace for soldering circuit boards and electronic components.
Hereinafter, the semiconductor substrate heating apparatus is referred to as a reflow furnace or simply a furnace.

  There are two types of reflow furnaces: an atmospheric furnace that allows intrusion of outside air, and a nitrogen furnace type reflow furnace that prevents the ingress of outside air by filling the furnace with nitrogen gas in order to improve the wettability (melting state) of the solder. The background art will be described by taking a nitrogen furnace type reflow furnace as a main embodiment of the present invention as an example. Hereinafter, the concept including atmospheric air or nitrogen gas is referred to as atmospheric gas.

The structure of a conventional reflow furnace will be described with reference to the drawings of Japanese Patent Application Laid-Open No. 2001-308512 of Patent Document 1.
FIG. 8 shows a structural example of a conventional nitrogen furnace type reflow furnace. The reflow furnace is provided with a plurality of zones. Five zones from the inlet on the left side of the figure are heating zones (that is, the preheating zone 117 and the peak heating zone 123), and one zone before the outlet is a cooling zone 135. The number of heating zones and cooling zones varies depending on the type of reflow furnace.
A transport rail (not shown) having a variable width between the rails is provided in the furnace, and a plurality of circuit boards are sequentially transported in the furnace by a chain conveyor from the entrance toward the exit. In accordance with the size of the circuit board, the movable rail moves in the width direction and the width between the transport rails is adjusted.
An air flow prevention device called a labyrinth schematically shown in FIG. 8 is provided at the inlet and the outlet of the reflow furnace. The labyrinth is composed of a plurality of fin-shaped metal plates, and the shape of the metal plates generates an air vortex to prevent intrusion of outside air.

Among the heating zones, the first three zones are referred to as the preheating zone 117, and the flux contained in the cream solder is sufficiently activated in this zone.
Thereafter, the circuit board 2 is heated to a predetermined temperature in a peak heating zone 123 (hereinafter referred to as a reflow zone) for melting the solder. After the solder is melted, the circuit board 2 is cooled in the cooling zone 135.

The furnace temperature rises from the preheating zone 117 to the reflow zone 123, and the solder of the circuit board 2 is melted in the reflow zone. Thereafter, it is cooled in the cooling zone 135 and carried out from the outlet.
At the inlet and outlet of the reflow furnace, as described above, an air flow prevention device called a labyrinth prevents outside air from entering the reflow furnace. However, since the circuit boards flowing on the transport rail are successively carried in from the entrance, it is difficult to completely prevent the outside air from entering. Therefore, generally, the pressure of nitrogen gas in the furnace is set higher than the external atmospheric pressure, and the gas flow in the vicinity of the labyrinth is set so as to go from the inside of the furnace to the outside of the furnace.

  On the other hand, the nitrogen gas used as the atmospheric gas is a part of the manufacturing cost. Therefore, in order to reduce the manufacturing cost, it is required to reduce the consumption amount of the nitrogen gas.

The heating method in each zone of the reflow furnace will be described with reference to FIG.
FIG. 9 is a sectional view taken along line XX in FIG. The circuit board 102 is transported on the transport rail 103 at right angles to the paper surface and in the front direction.
A circulation fan 108 driven by a motor 109 sucks in-furnace nitrogen gas from above and blows it out downward. During this suction, the nitrogen gas is heated by the heater 110. The circuit board 102 is heated by the heated nitrogen gas and the infrared heater 125.
The infrared heater 125 is also provided below the circuit board 102, and the lower part of the circuit board is also heated at the same time.
The nitrogen gas that has heated the circuit board is heated by the heater 110, and then is sucked by the circulation fan 108 and blown downward again. New nitrogen gas is supplied from a filling port (not shown), and the pressure of the nitrogen gas in the furnace is maintained at a constant value, thereby preventing outside air from entering the reflow furnace.

  In recent years, solder containing no lead (hereinafter referred to as lead-free solder) has become mainstream from the viewpoint of environmentally conscious product development. The melting point of tin-lead eutectic solder, which has been widely used in the past, is 183 ° C, whereas lead-free solder has a high melting point of around 220 ° C, so the circuit board heating temperature is about 230 ° C to 240 ° C. There is a need to.

On the other hand, some electronic components have low heat resistance, and when heated to 240 ° C. or higher, they may be damaged and lose their reliability.
Conventional tin-lead solder has a melting point of 183 ° C, and the circuit board has a heat-resistant temperature limit of 240 ° C, and the difference is about 50 ° C. Lead-free solder has a high melting point of 220 ° C. Nevertheless, the heat-resistant temperature limit of the circuit board is also 240 ° C. Therefore, the allowable temperature difference is 20 ° C. or less. Therefore, the temperature adjustment for heating the circuit board in the reflow furnace is more severe due to the use of lead-free solder.

Therefore, a hot air method is often employed in which a circuit board is heated by hot air heated to a predetermined temperature on both the upper and lower sides of the circuit board, avoiding a heating method using an infrared heater, which makes it difficult to control the temperature of the circuit board. In general, a method of heating a circuit board by blowing hot air on the surface of the circuit board is called a collision jet type and has a feature of high heat transfer rate and excellent heating ability.
JP 2001-308512 A

  As described above, lead-free solder that is environmentally friendly in recent years is increasingly used for circuit boards. However, even though lead-free solder has a high melting point, the heat resistance temperature of electronic components does not change, so strict temperature control is required for reflow furnace heating. For this reason, in recent years, reflow furnaces that heat circuit boards exclusively with hot air have become mainstream from conventional reflow furnaces that heat circuit boards using a combination of hot air and an infrared heater.

  On the other hand, in order to prevent deterioration of the circuit board due to oxidation during soldering and to ensure high reliability of the circuit board, an increasing number of users require soldering work at a low oxygen concentration. As described above, in a nitrogen-type reflow furnace that cannot completely prevent outside air from entering or exiting the furnace due to restrictions on the structure of the furnace, a large amount of nitrogen is constantly added to achieve a low oxygen concentration in the furnace. Since it is necessary to blow into the furnace, the production cost cannot be ignored. Therefore, the nitrogen-type reflow furnace has a problem that it is necessary to realize a predetermined solder melting temperature in a low oxygen state and to reduce the consumption of nitrogen.

In general, in a reflow furnace, the flow of nitrogen gas from the inlet to the outlet tends to occur as the circuit board moves. In addition, the flow of nitrogen gas varies depending on the presence or absence of a circuit board. As the nitrogen gas flow fluctuates, an unpredictable flow of nitrogen gas occurs in the furnace. With this flow, outside air enters from the furnace inlet or outlet, and the oxygen concentration in the furnace rises.
In order to prevent this, there is a method of increasing the flow rate of nitrogen gas and increasing the gas pressure in the furnace. However, this method leads to an increase in consumption of nitrogen gas.

On the other hand, in order to cancel out the flow of the gas in the furnace, a method of blowing nitrogen gas from the furnace entrance side or the exit side can be considered. However, with the adoption of lead-free solder, as described above, a reflow furnace having a structure in which hot air is blown from the vertical direction of the circuit board is adopted, and there is a steady and powerful flow of nitrogen gas in the vertical direction in the furnace. . Therefore, it is difficult to suppress the flow of nitrogen gas in the furnace by blowing nitrogen gas from the furnace entrance side or exit side. It is considered that the strong nitrogen gas flow in the vertical direction of each zone functions as a so-called air curtain.
Thus, the inventors have repeatedly conducted various experiments and researches and discovered that the flow of nitrogen gas in the reflow furnace can be suppressed by the means described below.

In order to solve the above-mentioned problems, the inventors have conducted intensive research and experiments. As a result, by providing a steering mechanism that blows out nitrogen gas in the same or opposite direction to the circuit board transport direction at a predetermined location in the reflow furnace, the flow of nitrogen gas in the furnace is suppressed, and the nitrogen gas in the furnace is made stationary. As a result, the present inventors have found that the amount of nitrogen necessary to maintain a predetermined oxygen concentration can be greatly reduced.
In addition, since the flow of nitrogen gas in the furnace is suppressed by this steering mechanism, compared with the method that prevents the ingress of outside air by blowing out nitrogen gas in the vertical direction of the air curtain at the inlet / outlet of the furnace, etc. It has also been found that it is possible to prevent the diffusion of the flux generated inside. By preventing the diffusion of the flux, the operation of removing the flux adhering to the in-furnace device is reduced, and the operating cost of the reflow furnace can be reduced.

  A first aspect of a reflow furnace according to the present invention is a reflow furnace for heating a circuit board transported by a transport device, wherein a circulation fan that circulates atmospheric gas, a heater that heats the atmospheric gas, and the heater A spray nozzle that blows the atmosphere gas heated by the circuit board on the circuit board, a suction port that sucks the atmosphere gas in the reflow furnace, and a steering that blows out the atmosphere gas in the same direction as or in the opposite direction to the transport direction of the circuit board. A reflow furnace nitrogen gas consumption reduction device comprising a mechanism.

  A second aspect of the reflow furnace according to the present invention is the reflow furnace nitrogen gas according to the first aspect, wherein the atmosphere gas is an inert gas such as nitrogen and is filled in the reflow furnace. This is a device for reducing consumption.

  In a third aspect of the reflow furnace according to the present invention, the steering device is provided with one or a plurality of blowout nozzles at one or a plurality of locations in the preheating zone, the heating zone, or the cooling zone in the reflow furnace. It is the reflow furnace nitrogen gas consumption reduction apparatus as described in the 1st or 2nd aspect characterized by the above-mentioned.

  In a fourth aspect of the reflow furnace according to the present invention, one or a plurality of the blowing nozzles are provided in one or a plurality of pipes arranged from the reflow furnace entry side or the exit side toward the center of the reflow furnace. A reflow furnace nitrogen gas consumption reduction device according to any one of the first to third aspects, wherein the apparatus is provided individually.

  In a fifth aspect of the reflow furnace according to the present invention, any one of the first to fourth aspects is characterized in that the pipe is disposed along an operation conveyance rail and / or a fixed conveyance rail of the reflow furnace. It is a reflow furnace nitrogen gas consumption reduction device described in one embodiment.

  A sixth aspect of the reflow furnace according to the present invention is such that the blowout nozzle has a U-shape, and the pipe has an atmosphere in a direction opposite to a direction from the inlet side or outlet side toward the central part of the reflow furnace. The apparatus for reducing nitrogen gas consumption in a reflow furnace according to any one of the first to fifth aspects, which is the blowing nozzle for blowing gas.

  In a seventh aspect of the reflow furnace according to the present invention, one or a plurality of temperature measuring devices in the reflow furnace are further installed in the reflow furnace, and the atmospheric gas of the steering mechanism is changed by a change in measured temperature of the measuring device. A reflow furnace nitrogen gas consumption reduction device according to any one of the first to sixth aspects, comprising a device for controlling a blowing direction and a blowing amount.

  An eighth aspect of the method for reducing nitrogen gas consumption of the reflow furnace according to the present invention is a reflow furnace for heating a circuit board transported by a transport device, wherein the atmosphere gas is circulated by the circulation fan, and the atmosphere gas is circulated. The atmosphere gas heated by the heater is blown to the circuit board by a jet nozzle, and the atmosphere gas in the reflow furnace is sucked from the suction port, and is the same as or opposite to the transport direction of the circuit board. The flow rate of the atmosphere gas in the reflow furnace is controlled by changing the blowing direction and the blowing amount of the atmosphere gas by a steering mechanism in a direction. .

  The ninth aspect of the method for reducing nitrogen gas consumption of a reflow furnace according to the present invention is the temperature from a temperature measuring device in the reflow furnace provided in the reflow furnace in addition to the eighth aspect. Based on the change, the flow direction of the atmospheric gas in the reflow furnace is controlled by detecting the flow direction of the atmospheric gas and controlling the blowing direction and the blowing amount of the steering mechanism in a direction to cancel the flow direction. This is a method for reducing nitrogen gas consumption of a reflow furnace.

  According to a tenth aspect of the method for reducing nitrogen gas consumption of the reflow furnace according to the present invention, the steering mechanism is configured such that the blowing nozzle is provided at one or a plurality of locations in a preheating zone, a heating zone, or a cooling zone in the reflow furnace. One or a plurality of the reflow furnaces are provided with a method for reducing nitrogen gas consumption.

  In an eleventh aspect of the method for reducing nitrogen gas consumption of the reflow furnace according to the present invention, the blowout nozzle is disposed from the inlet side or outlet side of the reflow furnace toward the central portion of the reflow furnace. One or more pipes are attached to each of the pipes, and the method for reducing nitrogen gas consumption in the reflow furnace.

  A twelfth aspect of the method for reducing nitrogen gas consumption of a reflow furnace according to the present invention is characterized in that the pipe is piped along an operation conveyance rail and / or a fixed conveyance rail of the reflow furnace. This is a method for reducing furnace nitrogen gas consumption.

  In a thirteenth aspect of the method for reducing nitrogen gas consumption of the reflow furnace according to the present invention, the blowout nozzle has a U-shape, and the pipe extends from the reflow furnace entry side or exit side to the reflow furnace center. A method of reducing nitrogen gas consumption in a reflow furnace, characterized in that atmospheric gas is blown out in a direction opposite to the direction of heading.

The flow of nitrogen gas in the furnace is controlled by a small amount of nitrogen gas blown out from a blowing nozzle provided at a predetermined location in the furnace. As a result, it is possible to reduce the amount of nitrogen gas necessary to maintain a predetermined furnace oxygen concentration, thereby reducing the cost of equipment operation. In addition, the necessary equipment can be reduced by reducing the necessary nitrogen gas flow rate.
Moreover, since the flow of the atmospheric gas in the reflow furnace can be controlled by the present invention, the diffusion of the flux in the furnace can be prevented. Thereby, it is possible to prevent the flux from adhering extensively to the in-furnace facility, and it is possible to reduce the facility operating cost for removing the flux. This effect is not limited to the nitrogen-type reflow furnace, but can be similarly exerted in an atmospheric-type reflow furnace that allows entry of the atmosphere.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing the overall configuration of a nitrogen-type reflow furnace according to the first embodiment of the present invention. From the entrance side of the furnace shown on the left side of FIG. 1, a plurality of circuit boards (not shown) mounted on a transfer line (not shown) are transported in the direction of arrow A toward the furnace exit side on the right side of the figure.
On the entry side and the exit side, the above-described air flow prevention device called a labyrinth is provided. FIG. 1 schematically shows the structure. This labyrinth prevents outside air from entering and exiting the furnace. However, as described above in the background art, it is impossible to completely prevent the outside air from entering because the circuit board is carried on the transfer line.

  Extending from the entrance side of the furnace toward the center of the furnace is the piping for the blowing nozzle of the steering mechanism according to the present invention. One or a plurality of blowing nozzles are attached to this pipe, and nitrogen gas is blown out in the same direction as or in the opposite direction to the circuit board transport direction to control the flow of nitrogen gas in the furnace.

In the nitrogen-type reflow furnace according to the first embodiment, a total of 7 zones are heating zones from the entrance side of the furnace. In this heating zone, the first 4 zones are preheating zones and the following 3 zones are reflow zones (peak heating zones). In this reflow zone, the circuit board cream solder is melted. Two cooling zones are provided after the reflow zone. After the solder is melted, the circuit board is cooled and carried out from the furnace exit side.
Depending on the reflow furnace, the number of heating zones and cooling zones is different, and the number of preheating zones and reflow zones in the heating zones is also different.

While moving in the preheating zone, the circuit board is preheated and the flux contained in the cream solder is activated as described above. The fully preheated circuit board moves to the reflow zone where it is further heated to the temperature required for solder melting.
The circuit board in which the solder is melted is cooled in the cooling zone. The cooled circuit board is carried out from the exit side of the furnace. A labyrinth is provided on the exit side in the same manner as the entry side to prevent intrusion of outside air.

Next, the hot air heating method of the reflow furnace will be described with reference to FIG.
FIG. 2 is a cross-sectional view taken along line BB in FIG. In the figure, reference numeral 1 denotes a cross-section of the furnace outer structure (shell). The shell is covered with a heat insulating material (not shown). This is to prevent heat exchange between the outside air and the nitrogen gas in the furnace.
2 is a circuit board. The conveyor rails 3a and 3b are moved by the chain conveyor toward the front in the direction perpendicular to the paper surface.
The conveyance rail includes a fixed conveyance rail 3a and a movable conveyance rail 3b. The movable conveyance rail 3b has a structure that moves in the width direction (left-right direction in FIG. 2) according to the size of the circuit board to be conveyed.
5 is a chamber. This is an enclosure provided to separate the nitrogen gas absorbed by the circulation fan 8 and the heating nitrogen gas heated by the heater 10 after heating the circuit board 2.
Reference numeral 11 denotes a blowout panel. The blowing panel is provided with a number of blowing nozzles 6 for blowing out nitrogen gas heated by the heater 10. The circuit board 2 is heated by the nitrogen gas jet (E) heated from the spray nozzle 6 colliding with the circuit board 2. As described above, this collision jet type has the advantage of high heat transfer coefficient and excellent heating capability.
Reference numeral 12 denotes a sealing device. This sealing device 12 prevents outside air from entering the reflow furnace.
15 is the piping of the blowing nozzle according to the present invention. In the present embodiment, as described above, piping is provided from the furnace inlet toward the center of the furnace, and a blowing nozzle (not shown) is provided at the tip of the predetermined zone.

Next, the movement of nitrogen gas in the furnace will be described with reference to FIG.
The in-furnace nitrogen gas is sucked from the lower part by the circulation fan 8 driven by the motor 9 and blown out from both sides of the circulation fan 8 as indicated by a symbol D in the figure. Further, new nitrogen gas is blown from a nitrogen gas filling port (not shown). The newly blown nitrogen gas and the nitrogen gas blown from the circulation fan 8 are heated by the electric heater 10.
A flow D of nitrogen gas heated to a predetermined temperature is sprayed from the spray nozzle 6 toward the circuit board 2. E shows the flow of nitrogen gas at this time.
A device having the same structure as the above-described nitrogen gas spraying device is also provided on the lower side of the circuit board.

  The nitrogen gas that has heated the circuit board is sucked from the suction port 7, blown out again to both sides of the circulation fan 8 by the circulation fan 8, and heated by the heater 10. The nitrogen gas having a lowered temperature and the hot nitrogen gas blown out from the circulator before being sucked are isolated by the chamber 5.

With reference to FIG. 3, an example of installation of the nozzle and the nozzle of the blow nozzle according to the present invention will be described.
In the figure, the left side is the furnace inlet, and the right side is the furnace outlet. The labyrinth described above is provided at the entrance and exit. Reference numerals 3a and 3b denote transport rails for transporting a circuit board (not shown) from the inlet toward the outlet. The inner 3a is a fixed conveyance rail.
3b is a movable conveyance rail. Depending on the size of the circuit board, the movable conveyance rail 3b moves in the vertical direction in FIG. 3 to adjust the width between the conveyance rails.
FIG. 3a shows an example in which a blowout nozzle pipe 15 is installed from the entrance of the furnace toward the center of the furnace. In this example, one pipe is piped along the fixed transport rail 3a, and the other pipe is piped along the movable transport rail 3b. That is, when the movable transfer rail 3b moves, the piping piped along the transfer rail 3b also moves in the furnace width direction, and the blowing position of the nitrogen gas blown from the blowing nozzle attached to the tip of the piping also changes.

In general, the flow of nitrogen gas in the furnace varies depending on the size of the circuit board and the presence or absence of the circuit board. This is because the flow of nitrogen gas blown from the spray nozzle hits the circuit board and is reflected.
The circuit board moves on a transport rail in the reflow furnace. As the circuit board moves, the circuit board may or may not exist in each zone in the reflow furnace.
As described with reference to FIG. 2, the flow E of nitrogen gas blown from the spray nozzle 6 is reflected from the circuit board 2 when the circuit board 2 is present, and then sucked from the upper suction port 7 and there is no circuit board. Advances as it is and is sucked into the lower suction port 7 on the opposite side. Since the flow of nitrogen gas in the furnace changes depending on the position of the circuit board 2 in this way, the blowing nozzle that suppresses the flow of nitrogen gas in the furnace also changes the location where the nitrogen gas is blown out due to the difference in the width between the conveyance rails. It is necessary to let

  In addition, in the case where an anti-blowing nozzle according to the present invention is provided in an existing reflow furnace, a method for piping along a fixed or movable conveyance rail does not require any new equipment, and refurbishment of the reflow furnace can be reduced. There is an advantage.

FIG. 3 shows an installation example of the blowing nozzle according to the present invention.
FIG. 3A shows an example in which a blowing nozzle pipe 15 is installed from the inlet of the reflow furnace toward the center of the furnace. A similar configuration may be provided by piping from the furnace outlet toward the center as shown in FIG.
Moreover, it is also possible to blow out nitrogen gas in the direction opposite to the piping direction by making the blowing nozzle attached to the head of the piping into a U-shaped tube.

  Usually, it is most effective to provide this blow nozzle near the boundary between the preheating zone and the heating zone, but depending on the structure of the furnace, it may be more effective if it is provided in other parts.

FIG. 4 shows various forms of the blowout nozzle according to the present invention.
4A and 4B are blowout nozzles for blowing out nitrogen gas in the same direction as the piping. In a reflow furnace in which the flow of nitrogen gas in the furnace is directed from the exit side of the furnace to the entry side, when the blow nozzle piping is installed from the exit of the furnace toward the center of the furnace, or the flow is discharged from the entry side. It is effective when piping from the furnace inlet when facing the side.
Whether the route of the piping pipe is from the furnace inlet or the outlet is to obtain a preheating effect due to the passing zone when nitrogen gas flows in the piping pipe.
The U-shaped tubular blowing nozzle shown in FIGS. 4C and 4D is effective when blowing nitrogen gas in the direction opposite to the piping direction. Nitrogen gas flows in the pipe 15 from the furnace inlet toward the center of the furnace, the nitrogen gas in the pipe is preheated in the preheating zone and the heating zone, and toward the furnace inlet side at the boundary between the reflow zone and the cooling zone. That is, it is suitable for blowing nitrogen gas in the direction opposite to the piping direction.

The blowing nozzles shown in FIGS. 5 (a) and 5 (b) are effective when blowing nitrogen gas toward the lower side of the circuit board. This type of nozzle is suitable when there is a possibility that the nitrogen gas may hit the circuit board and cool the circuit board when nitrogen gas is blown in the horizontal direction due to restrictions on piping.
5C, 5D, and 5E are types in which one nozzle is provided in one pipe. This is suitable for increasing or decreasing the nitrogen gas blowing amount in the furnace width direction or changing the blowing direction according to the size of the circuit board.
It is also possible to provide a branch valve in the pipe and change the nitrogen gas blowing amount and direction for each of a plurality of nozzles attached to the pipe.

FIG. 6A shows piping that is effective when nitrogen gas is blown out in a plurality of zones. For example, when nitrogen gas is blown out at the boundary between the preheating zone, the heating zone, and the cooling zone. Similarly, it is also possible to provide a branch valve in the pipe and change the nitrogen gas blowing amount for each of a plurality of nozzles attached to the pipe.
The above piping method is particularly effective when the present invention is added to an existing furnace, but the same piping structure can be obtained even in a new furnace.
FIG. 6B is an example of piping in a case where a blowing nozzle device is previously provided between a plurality of zones in a newly installed reflow furnace.
Three nozzles are provided in the width direction at the boundary of the residual heat zone, reflow zone, and cooling zone, respectively in the inlet side direction and outlet side direction, depending on the flow direction of nitrogen gas in the furnace and the size of the circuit board, respectively. Adjust the nozzle blowout amount.
The piping method and nozzle shape described above are examples, and various blowout nozzles can be applied depending on the structure of the furnace, the size of the circuit board, and the like.

As described above, the present invention is particularly effective in the reflow furnace that mainly heats the upper and lower portions of the circuit board by the hot air impingement jet method.
As conventional techniques, there are various methods for blowing nitrogen gas from the inlet or outlet of a reflow furnace to prevent the flow of nitrogen gas in the reflow furnace. However, as described above, in a recent mainstream reflow furnace where a strong nitrogen gas flow is generated in each zone in the vertical direction, the nitrogen gas blown from the inlet or the outlet flows in each zone in the vertical direction. However, it played the role of so-called multiple air curtains and could not control the flow of nitrogen gas in the center of the furnace.

  By providing a furnace gas flow rate measuring device, such as an orifice tube, at the furnace inlet and outlet, when a flow occurs, the atmospheric gas is blown out by the blowing nozzle according to the present invention in a direction to cancel the flow direction. Thus, the flow in the furnace can be controlled. Further, by controlling the flow in the furnace, it is possible to prevent the flux from adhering to the in-furnace apparatus over a wide range.

  Even in a conventional type reflow furnace in which a hot air blowing nozzle is provided above the circuit board and an infrared heater is provided below the circuit board, the flow in the furnace can be controlled by the blowing nozzle according to the present invention. This is because the flow of the nitrogen gas in the furnace can be controlled more efficiently than the method of blowing the nitrogen gas at the entrance and exit of the furnace by blowing the nitrogen gas directly to the place where the flow occurs in the furnace.

(Second Embodiment)
In the second embodiment of the present invention, temperature measuring devices (reference numeral 16 in FIG. 2), for example, thermocouples, are installed at a plurality of locations in the furnace, and the temperature in the furnace in each zone is measured. This is a reflow furnace that controls the blowing direction and blowing amount of nitrogen gas from the blowing nozzle in accordance with the temperature change in the furnace.

FIG. 7A shows the furnace temperature distribution from the furnace inlet to the outlet. The vertical axis represents the furnace temperature, and the horizontal axis represents the furnace zone.
In the reflow furnace shown in FIG. 7, four preheating zones, three reflow zones, and two cooling zones are provided.
The outside air temperature at the furnace entrance is Ta. The furnace temperature rises sequentially in the four preheating zones. Further heating is performed in the reflow zone, and the temperature is increased until the surface of the circuit board exceeds the melting point Tb of the cream solder. After the solder is melted in the reflow zone, the furnace temperature decreases in the two cooling zones.

As the flow of nitrogen gas occurs in the furnace, the temperature distribution in the furnace changes accordingly. The dotted line in FIG. 7B shows the furnace temperature distribution when nitrogen gas flows from the inlet to the outlet of the furnace. When the nitrogen gas in the high-temperature reflow zone slightly flows toward the cooling zone, the furnace temperature in the reflow zone decreases and the furnace temperature in the cooling zone increases.
Conversely, when a flow of nitrogen gas is generated from the furnace outlet to the inlet, the temperature distribution indicated by the dotted line in FIG.

  The flow of the nitrogen gas in the furnace is detected based on the change in the temperature distribution, and the nitrogen gas is blown out from the blowing nozzle according to the present invention in the direction opposite to the flow direction of the nitrogen gas. Flow can be controlled.

The specific control method of the nitrogen blowing amount accompanying the change in the furnace temperature distribution is, for example, according to the following procedure.
1. Periodically measure the furnace temperature in multiple zones in the furnace. For example, the temperature inside the furnace is measured by a thermocouple. A thermometer may be installed in each zone, but temperature changes at the boundary between the preheating zone and the reflow zone and at the boundary between the reflow zone and the cooling zone are particularly important.
2. When the furnace temperature changes to a certain value or more, it is determined whether the nitrogen gas is flowing toward the entrance side or the exit side from the change in each furnace temperature. When the temperature at the boundary between the preheating zone and the reflow zone decreases and the temperature at the boundary between the reflow zone and the cooling zone increases, the flow of nitrogen gas from the inlet side to the outlet side occurs in the furnace. Can be detected. Among the three reflow zones, the flow of nitrogen gas between the zones can be detected based on the respective temperature changes.
3. A small amount of nitrogen gas is blown out from the blowing nozzle in the direction opposite to the flow direction of the nitrogen gas in the furnace.
4). Thereafter, when it is detected from the temperature change in the furnace at each position that the flow has stopped, the blowing of nitrogen gas from the blowing nozzle is stopped. There is also a method of controlling the nitrogen outflow from the blowout nozzle more finely.

(Experimental result)
The results of experiments conducted by the inventors are shown in FIG. FIG. 10 shows the result of confirming the effect of the steering mechanism according to the present invention using a nitrogen-type reflow furnace.
The nitrogen-type reflow furnace used in this experiment is a type of reflow furnace having 12 heating zones and 2 cooling zones in which the upper and lower portions of the circuit board are heated with hot air.
In this experiment, a blowing nozzle for blowing nitrogen gas toward the furnace inlet was provided at the tip of the pipe arranged from the furnace outlet side toward the furnace center. This pipe is installed along the movable conveyance rail (reference numeral 3b in FIG. 3) so that the position where nitrogen gas is blown out changes in accordance with the variation in the width between the conveyance rails.
It was measured how the oxygen concentration in the furnace changes depending on the size of the circuit board, that is, the fluctuation of the width between the conveyance rails.
While changing the nitrogen outflow with a nitrogen supply source pressure of 0.5 MPa and a hot air frequency of 35 Hz, the effect was observed in the furnace oxygen concentration. As a result, the result shown in FIG. 10 was obtained.

The oxygen concentration in each furnace was measured by changing the width of the conveying rail from 100 mm to 250 mm without using the blowing nozzle, that is, without blowing nitrogen gas from the blowing nozzle. At this time, the outflow amount of nitrogen in the reflow furnace was 200 L / min in total.
As a result, the oxygen concentration in the furnace was 1000 ppm or more regardless of the width of the transport rail. Specific numerical values are omitted. Incidentally, the oxygen concentration in the outside air is 200,000 ppm.

Next, with the total nitrogen flow rate in the furnace kept at 200 L / min, 20 L / min of nitrogen was blown out from the blowing nozzle according to the present invention in the direction opposite to the flow direction of the nitrogen gas in the furnace. The blowing nozzle was installed on the inlet side of the tenth zone. That is, before the reflow zone where the solder is melted (on the preheating zone side).
In this case, the in-furnace oxygen concentration at each conveyance rail width was 150, 225, and 215 ppm, respectively, at conveyance rail widths of 100, 150, and 250 mm (see FIG. 10). Although there was some variation, the value was generally from 150 ppm to 225 ppm.
Compared to the case where the in-furnace nitrogen flow rate was also 200 L / min, the use of the blowout nozzle decreased the in-furnace oxygen concentration, which was 1000 ppm or more, to about 200 ppm. Nitrogen gas was blown out from the blow nozzle toward the entrance side of the furnace, so that the flow of nitrogen gas flowing from the entrance side to the exit side in the furnace was suppressed, and accordingly, intrusion of outside air from the furnace inlet was prevented. This indicates that the low oxygen concentration in the furnace could be realized.

Furthermore, in order to obtain the in-furnace oxygen concentration similar to the above without using the blowing nozzle, an experiment was conducted to determine how much the total nitrogen flow rate in the furnace is necessary.
That is, by increasing the amount of new nitrogen blown in each zone and increasing the pressure of nitrogen gas in the reflow furnace, intrusion of outside air is prevented, and the oxygen concentration in the furnace decreases accordingly.
As a result of the experiment, when the total nitrogen flow rate was increased to 250 L / min, the stable values of the in-furnace oxygen concentration were 127, 214, and 215 ppm in the widths of the conveyance rails of 100, 150, and 250 mm, respectively. Although there was some variation, the value was approximately from 150 ppm to 225 ppm (see FIG. 10), and an in-furnace oxygen concentration substantially equal to the above could be obtained.
That is, it was found that the nitrogen flow rate for obtaining an equivalent furnace oxygen concentration can be reduced from 250 L / min to 200 L / min by using the blowout nozzle of the present invention.

  From this experimental result, it is possible to suppress the flow of nitrogen gas just by blowing a small amount of nitrogen gas (20 L / min in this experiment) from the blowing nozzle in the direction to cancel the flow of nitrogen gas in the furnace, and as a result, good It was confirmed that a high furnace oxygen concentration could be realized.

FIG. 1 is an overall view of a reflow furnace according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of the reflow furnace according to the first embodiment of the present invention. FIG. 3 is a plan view of the furnace representing an installation example of the blowing nozzle according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating an example of the blowing nozzle according to the first embodiment of the present invention. FIG. 5 is a diagram illustrating an example of the blowing nozzle according to the first embodiment of the present invention. FIG. 6 is a diagram illustrating an example of the blowing nozzle according to the first embodiment of the present invention. FIG. 7 is a distribution diagram of the atmospheric temperature in the furnace according to the second embodiment of the present invention. FIG. 8 is an overall view of a reflow furnace according to the prior art. FIG. 9 is a sectional view of a conventional reflow furnace. FIG. 10 is a table showing experimental results according to the first embodiment of the present invention.

Explanation of symbols

1: Shell (outer structure)
2: Circuit board 3: Transfer device 3a: Fixed transfer rail 3b: Movable transfer rail 4: Reflow furnace chamber
5: Chamber 6: Blowing nozzle 7: Suction port 8: Circulating fan 9: Fan motor 10: Heater 11: Blowing panel 12: Sealing device 15: Blowing nozzle 16: Temperature measuring device 23: Peak heating zone 25: Infrared heater 29: Hot air circulator 102: circuit board 103: transfer device 109: fan motor 110: electric heater 117: preheating zone 119: intermediate heating zone 123: peak heating zone 125: infrared panel heater 129: hot air circulator 135: cooling zone

Claims (13)

A reflow furnace for heating a circuit board conveyed by a conveying device,
A circulation fan that circulates atmospheric gas,
A heater for heating the atmospheric gas;
A spray nozzle for spraying the atmosphere gas heated by the heater on the circuit board;
A suction port for sucking the atmospheric gas in the reflow furnace;
A steering mechanism that blows out the atmospheric gas in the same or opposite direction as the conveyance direction of the circuit board,
An apparatus for reducing nitrogen gas consumption in a reflow furnace. The apparatus for reducing consumption of reflow furnace nitrogen gas according to claim 1, wherein the atmosphere gas is an inert gas such as nitrogen, and the reflow furnace is filled with the inert gas. 3. The reflow furnace nitrogen gas consumption according to claim 1, wherein the steering mechanism includes at least one blowout nozzle disposed at one or a plurality of locations in a preheating zone, a heating zone, or a cooling zone in the reflow furnace. Quantity reduction device. The at least 1 blowing nozzle is attached to 1 or several piping arrange | positioned toward the center part of the said reflow furnace from the said reflow furnace entrance or exit side, The 1 thru | or 3 characterized by the above-mentioned. The reflow furnace nitrogen gas consumption reduction apparatus as described in any one of these. The apparatus according to claim 4, wherein the pipe is disposed along a movable transport rail and / or a fixed transport rail of the reflow furnace. The blowing nozzle is a U-shaped shape, and the piping is the blowing nozzle that blows out atmospheric gas in a direction opposite to a direction from the reflow furnace entry side or exit side toward the reflow furnace center. The reflow furnace nitrogen gas consumption reduction device according to any one of claims 3 to 5. The reflow furnace is further provided with one or a plurality of temperature measuring devices in the reflow furnace, and the ambient gas blowing direction and the blowing amount of the steering mechanism are determined by a change in measured temperature in the reflow furnace of the temperature measuring device. The apparatus for reducing nitrogen gas consumption of a reflow furnace according to any one of claims 1 to 6, comprising an apparatus for controlling. A reflow furnace for heating a circuit board conveyed by a conveying device,
Circulate the atmospheric gas with a circulation fan,
The atmospheric gas is heated by a heater,
Spraying the atmosphere gas heated by the heater from the spray nozzle to the circuit board,
The atmospheric gas in the reflow furnace is sucked from the suction port,
A reflow furnace for controlling the flow of the atmospheric gas in the reflow furnace by changing a blowing direction and a blowing amount of the atmospheric gas by a steering mechanism in the same direction as or in the opposite direction to the conveying direction of the circuit board. Nitrogen gas consumption reduction method. The heating method according to claim 8, further comprising:
Based on a temperature change in the reflow furnace from a temperature measuring device in the reflow furnace disposed in the reflow furnace, the flow direction of the atmospheric gas is detected, and the direction in which the flow is cancelled is detected. A method for reducing nitrogen gas consumption in a reflow furnace, wherein the flow of the atmosphere gas in the reflow furnace is controlled by controlling the direction and amount of the atmosphere gas blown by a steering mechanism. The steering mechanism comprises at least one outlet nozzle disposed at one or a plurality of locations in a preheating zone, a heating zone, or a cooling zone in the reflow furnace. The reflow furnace nitrogen gas consumption reduction method according to any one of the above. The blowout nozzle is provided with at least one blowout nozzle attached to one or a plurality of pipes arranged from the entry or exit side of the reflow furnace toward the center of the reflow furnace. The method for reducing a reflow furnace nitrogen gas consumption according to any one of claims 8 to 10. The reflow furnace nitrogen gas consumption according to any one of claims 8 to 11, wherein the pipe is disposed along a movable transport rail and / or a fixed transport rail of the reflow furnace. Reduction method. The blowout nozzle is a blowout nozzle that is U-shaped and allows the piping to blow out atmospheric gas in a direction opposite to the direction from the reflow furnace entry side or exit side toward the reflow furnace center. The method for reducing a reflow furnace nitrogen gas consumption amount according to any one of claims 8 to 12.

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