JPH10173333A - Reflow furnace and flux-removing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and completely remove flux, adhering to a low-temperature part by disposing a heater at a part susceptible to adhesion of flux other than a preheating zone and a main heating zone. SOLUTION: A printed board P is transferred through an inlet 14 into a reflow furnace 1 by means of a transfer unit 6 and preheated at a specified temperature in a preheat zone 2. The preheated printed board 1 is transferred to a main heating zone 3 by means of the transfer unit 6. Since the temperature in the main heating zone 3 is high, the flux of solder paste is melted, and oxides and contaminats adhering to a soldering part are removed while being reduced and cleaned off. When the powdery solder of solder paste is melted subsequently, it is spread while being wetted to the soldering part cleaned with the flux. Finally, the printed board P is transferred to a cooling zone 4 and cooled down by means of a cold air blow-out type cooling machine 9 thus solidifying the molten solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow furnace used for soldering printed circuit boards and electronic components, and a method for removing a flux adhered inside the reflow furnace.

[0002]

2. Description of the Related Art As a method of soldering a printed circuit board and an electronic component, there are a troweling method, an immersion method, a reflow method and the like.

[0003] In the ironing method, an operator holds a iron in one hand and a greasy wire solder in the other hand, applies the greasy wire solder to a soldering portion, and then melts the solder with the iron. In this way, soldering is performed. The ironing method is
Not only is there a problem in productivity because soldering must be performed for each soldering part, but also in parts that are densely mounted, soldering cannot be performed because the iron does not enter the narrow soldering part. There was also. Therefore,
The ironing method is suitable for correcting a defect generated by another soldering method or for soldering a special electronic component after soldering by another soldering method.

[0004] The immersion method is a method of soldering a printed board on which electronic components are mounted by an automatic soldering apparatus provided with a fluxer, a preheater, a jet solder bath, a cooler, and the like. This immersion method is very excellent in productivity because a large number of soldered parts on the printed circuit board can be soldered in a single process.
For a surface mount component such as a QFP or SOIC, a bridge is formed in which the solder straddles and adheres between the narrow soldered portions.

[0005] The reflow method is a method in which a solder paste is applied to a soldering portion of a printed board with a printing device or a discharge device, and the printed board is heated in a reflow furnace and soldered. In this reflow method, solder paste is applied only to the soldering part, so that many places can be soldered at once, and even if high-density mounting, bridges do not occur unlike the immersion method. It has excellent features not found in the above soldering method. Therefore,
Most printed circuit boards on which surface mount components are mounted are soldered by the reflow method.

[0006] The solder paste used in the reflow method is:
It is obtained by dissolving solid components such as rosin, thixotropic agent and activator with a solvent to form a paste-like flux and kneading the powdered solder. The solder paste is printed and applied to a printed circuit board with a metal mask or a silk screen, or discharged and applied by a dispenser, and then the electronic component is mounted on the applied portion and the electronic component is temporarily joined by the adhesive force of the solder paste. In this way, the printed circuit board on which the electronic components are mounted is heated and soldered in a reflow furnace including a preheating zone, a main heating zone, and a cooling zone.

[0007] The printed circuit board on which the electronic components are mounted on the solder paste application section is 100 to 15 in the preheating zone.
Preheat to 0 ° C. This preheating volatilizes the solvent in the flux of the solder paste to prevent the solvent from being bumped by the main heating at the high temperature in the next step, and promotes the activation of the flux.

[0008] The pre-heated printed circuit board is conveyed to a main heating zone, where it is heated to a high temperature to melt the solder paste and spread the molten solder to the soldering portion.

[0009] The printed circuit board heated in the main heating zone is then conveyed to a cooling zone, where it is blown with cold air to cool the molten solder to be rapidly solidified. Rapid solidification of the molten solder
This is because, if vibration or impact is applied to the printed circuit board during solidification, the soldered portion may be peeled off or cracks may occur in the solder.

[0010]

However, in the conventional reflow furnace, a large amount of flux adheres to the cooling zone and the entrance and exit. This is because, when the solder paste applied to the printed circuit board is heated in the preheating zone or the main heating zone, the solvent in the flux volatilizes, and solid components such as rosin, thixotropic agent, and rosin evaporate. This is because the flux fume comes into contact with a cooling zone or an entrance / exit which is a relatively low temperature portion other than the preheating zone and the main heating zone, where the flux fume condenses and becomes a solid flux and adheres. .

As described above, the flux adheres to a relatively low temperature portion, and if the flux accumulates, the flux may drop onto the printed circuit board during reflow. When the flux falls on the printed circuit board, the electronic component is destroyed or its appearance is deteriorated. In addition, if the flux adheres to the rotating part of the cooler of the reflow furnace or the transfer device, the function of the cooler or the transfer device is impaired.

In the conventional reflow furnace, when a large amount of flux adheres to the cooling zone or the entrance and exit, after the soldering operation is completed, the operator cools down the reflow furnace sufficiently and cuts it off with a tool such as a knife or cutout. It is a thing. However, the work of shaving off the flux adhering to the inside of the reflow furnace having a complicated structure is very troublesome and cannot be completely shaved. An object of the present invention is to provide a reflow furnace capable of easily and completely removing a flux attached to a low-temperature portion and a method for removing the flux of the reflow furnace.

[0013]

SUMMARY OF THE INVENTION The present inventor has determined that the flux which has been vaporized and condensed becomes more easily flowable than the flux residue after soldering when heated again because of the presence of the solvent. The present invention has been completed by focusing attention.

The present invention provides a reflow furnace comprising a preheating zone for preheating a printed board, a main heating zone for heating the printed board to a temperature higher than the melting temperature of solder, and a cooling zone for cooling the printed board after soldering.
It is a reflow furnace characterized by installing a heater in a place where flux easily adheres in places other than the preheating zone and the main heating zone, and when the printed circuit board is not soldered in the reflow furnace, A flux removal method for a reflow furnace, comprising heating a flux attached to a low temperature part of the reflow furnace to 150 to 250 ° C. to melt the flux, and receiving the melted flux in a lower container.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the reflow furnace of the present invention, heaters are installed at locations where the temperature does not rise relatively high during reflow, and where flux is likely to adhere, such as a cooling zone or an entrance of a reflow oven. .

In the flux removing method of the present invention, the portion where the flux adheres is heated to 150 to 250 ° C.
If the temperature is lower than 150 ° C., the adhered flux does not flow. However, if the temperature is higher than 250 ° C., the flux is carbonized, so that the flux sticks.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view of the reflow furnace of the present invention.

The reflow furnace 1 comprises a preheating zone 2, a main heating zone 3, and a cooling zone 4, and the preheating zone 2
In the upper and lower portions of the main heating zone 3, a plurality of hot air blowout type heaters 5 are provided. A transport device 6 travels from the preheating zone 2 toward the cooling zone 4 between the hot air blowout type heaters installed at the upper and lower portions.

The hot air blowout type heater is a heater in which a crossfa fan 7 is attached to a box, and an electric heater 8 is disposed inside the box. The electric heater 8 of the hot air blowout type heater 5 is energized to
When the is rotated, gas blown from both sides of the box is sucked into the center of the box as shown in the figure. The gas sucked into the box is heated by the electric heater 8 in the box, becomes hot air, and is blown out from both sides of the box again. Therefore, the hot air blown from the hot air blowout type heater 5 hits the printed circuit board P conveyed by the conveying device 6 and uniformly heats the printed circuit board. The hot air that has heated the printed circuit board returns from the center of the box to the box again. The hot-air blowout type heater is not the gist of the present invention, so that the detailed description is omitted.
In the reflow furnace of the present invention, the heater for heating the printed circuit board is not limited to the hot air blowout type heater, but may be any heater.

In the lower part of the cooling zone 4, a cool air blow-off type cooler 9 is provided. The cool air blow-off type cooler includes:
It has the same structure as the above-described hot-air blowout type heater, except that the box is not provided with an electric heater, and a flux reservoir 10 is formed at the lower part instead.

A reflector 11 is provided above the cooling zone, and an electric heater 12 is provided on the reflector.

At appropriate places in the reflow furnace, supply pipes 13 for supplying nitrogen gas into the furnace are provided, so that the atmosphere in the furnace can be made inert during soldering.

An inlet 14 is formed behind the preheating zone 2 of the reflow furnace 1, and an outlet 15 is formed ahead of the cooling zone 4. These inlets and outlets are provided with measures to prevent outside air from entering. The measures to prevent outside air intrusion are to reduce the oxygen concentration by installing a large number of resistors 16 on the upper and lower parts, so that the inside gas flows out but the outside air does not enter. The entrance 14, 1
The electric heaters 17 may be provided also in the upper part of 5 and the flux reservoir 18 may be provided in the lower part.

Next, a method of soldering a printed circuit board in the above-mentioned reflow furnace and a method of removing a flux adhered in the furnace will be described.

The printed circuit board P is transferred by the transfer device 6 from the entrance 14 into the reflow furnace 1. The printed circuit board P is first preheated to a predetermined temperature in the preheating zone 2. At this time, the solder paste applied to the printed circuit board P is also heated, and the solvent in the solder paste flux volatilizes.
The volatilized solvent flows toward the inlet 14 together with the nitrogen gas supplied from the supply pipe 13 into the furnace. When soldering,
Since the inlet 14 is not heated, the temperature of the portion constituting the inlet and the resistor 16 is low. When the volatilized solvent comes into contact with this low temperature part, the solvent condenses,
Become attached.

The printed circuit board P after the preheating is sent to the main heating zone 3 by the transfer device 6. The temperature of the main heating zone 3 is high. When entering the main heating zone, first, the flux of the solder paste melts, spreads to the soldering part, reduces and removes oxides and dirt attached to the soldering part, and cleans. To Thereafter, when the powder solder of the solder paste is melted, the solder spreads on the soldered portion cleaned with the flux. At this time, since the main heating zone is at a high temperature, part of the solder paste flux is vaporized to become flux fume and drifts in the furnace. This flux fume enters the inlet 1 together with the nitrogen gas supplied into the furnace.
4, flows in the direction of the outlet 15 and the cooling zone 4, but the inlet and the outlet and the cooling zone are condensed and adhered here because the temperature is low.

The printed circuit board P in which the solder melted in the main heating zone 3 spreads on the soldering portion is spread on the cooling zone 4
The solder cooled by the cool air blow-off type cooler 9 solidifies, and the soldering is completed.

After a large number of printed circuit boards have been soldered in this way and the work on that day has been completed, the power supply to the electric heater 8 and the crossfa fan 7 in the preheating zone 2 and the main heating zone 3 is cut off. The electric heater 12 disposed in the cooling zone 4 and the electric heater 17 disposed at the inlet 14 and the outlet 15 are energized to heat these electric heaters. Then, the cooling zone and the entrance are heated. The temperature at this time is 150 to 250 ° C. When the temperature of the cooling zone or the inlet / outlet reaches a predetermined temperature, the flux adhering thereto melts, flows and drops downward. Since the flux reservoirs 10 and 18 are provided in the cooling zone and the lower part of the entrance and exit, the flowing flux accumulates in the flux reservoir. The flux accumulated in the flux reservoir is scraped off with a spatula and transferred to another container.

[0029]

As described above, according to the present invention, since the electric heater is installed in a portion where the temperature does not rise during soldering and the flux fume is easily condensed and adhered, when the electric heater is heated, The adhered flux melts and flows, facilitating removal of the flux. Further, the flux removing method of the present invention has an excellent effect of easily removing the flux that has conventionally taken a great deal of time to remove from the furnace.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a reflow furnace of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflow furnace 2 Preheating zone 3 Main heating zone 4 Cooling zone 5 Hot air blowout type heater 9 Cold air blowout type cooler 10, 18 Flux reservoir 12, 17 Electric heater 14 Inlet 15 Outlet

Claims (4)

[Claims] 1. A preheating zone in a reflow furnace comprising a preheating zone for preheating a printed circuit board, a main heating zone for heating the printed circuit board to a temperature equal to or higher than a melting temperature of solder, and a cooling zone for cooling the printed circuit board after soldering. A reflow furnace characterized in that a heater is installed in a place where flux easily adheres to a place other than the main heating zone. 2. The reflow furnace according to claim 1, wherein the heater is provided in a cooling zone. 3. The reflow furnace according to claim 1, wherein the heater is provided at an inlet and / or an outlet. 4. When the printed circuit board is not soldered in the reflow furnace, the flux attached to the low temperature part of the reflow furnace is heated to 150 to 250 ° C. to melt the flux, and the molten flux is melted in the lower part. A flux removal method for a reflow furnace, wherein the flux is received in a container.