JP3303224B2 - Soldering method and soldering iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for soldering, for example, a method for soldering electronic parts with high quality.

[0002]

2. Description of the Related Art For example, when assembling an electronic device, it is common to solder various electronic components and wirings to an electronic substrate. However, if O ₂ is present in the working atmosphere, there is a concern that soldering defects may occur.

Therefore, a method of performing soldering in an oxygen-free state by using a high-temperature nitrogen gas atmosphere as a soldering work atmosphere has been put to practical use. For example, the solder bath apparatus is covered with a frame or the like and shut off from the outside to supply high-temperature nitrogen gas, or supply nitrogen gas into a reflow furnace.

[0004]

However, in the conventional soldering method in a nitrogen gas atmosphere, there is a case where a larger nest is formed on the solder adhered to the electronic substrate or the like than in the air. For example, solder H63A at 250 ° C
When soldering in the air, soldering in the air is 2-3 μm
On the other hand, in the conventional soldering in a nitrogen gas atmosphere, the nest was as large as 7 to 8 μm.

[0005] As a result, flux and halogen residues tend to remain in solder nests, and in some cases the quality is lower than that of soldering performed in the air. In addition, halogen residues remaining in the nests oxidize with time, lead oxidation of the soldered parts occurs, leading to poor quality. Particularly recently, from the viewpoint of adverse effects on the environment and the human body, no fluorocarbons and toluene have been completely eliminated. And there is a concern about such a problem of poor quality over time.

Further, in the conventional soldering method in a nitrogen gas atmosphere, there is a problem that the height of the solder is poor compared with the soldering in the air, and it cannot be said that the finish has a good appearance.

Further, in the conventional method of soldering in a nitrogen gas atmosphere, a complete nitrogen gas atmosphere is not used until the completion of a product. Instead, an electronic component is soldered to a mounted electronic board using a soldering iron. When soldering or correcting the soldering of the electronic substrate using a soldering iron, the soldering must be performed in the air, and there is a concern about poor quality due to O ₂ .

In view of the above problems, an object of the present invention is to provide a soldering method capable of soldering electronic parts and the like with high quality and good appearance.

[0009]

The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, in the conventional soldering method, a high-temperature nitrogen gas atmosphere has a relatively high temperature, for example, solder H63.
In the case of A, the temperature is about 250 ° C. to 300 ° C., and since the entire soldering apparatus is in a high-temperature nitrogen gas atmosphere, the solder is completely solidified from a molten state, and it takes a relatively long time until the temperature becomes sufficiently low. As a result of being exposed to a high-temperature nitrogen gas atmosphere and slowly solidifying the solder to the end, it was found that nests inside the soldered solder increased, and that the solder was flattened and had a poor height. Was.

Therefore, the soldering method according to the present invention is characterized in that molten solder is brought into contact with a work to solidify it, or a solder layer formed on the surface of the work is melted and solidified. Soldering in a high-temperature nitrogen gas atmosphere at a temperature at which the molten solder can be slowly cooled makes the molten solder almost hemispherical due to its surface tension. A soldering method, characterized in that molten solder is directionally solidified by cooling to form a fine solidified structure.

According to the present invention, there is provided a method for performing soldering while transferring a work on a transfer conveyor or the like, for example, a soldering method using an automatic soldering device such as a stationary solder bath device, a jet solder bath device, or a nozzle jet solder bath device. If the method is applied to a soldering method using a reflow furnace, the apparatus can be easily constructed, and the effect is great. Of course, a method of performing soldering by raising and lowering a work, for example, a soldering method using a tabletop jet type solder bath apparatus,
Alternatively, the present invention can be applied to a soldering method using a soldering iron.

In order to form a dense and well-soldered solder, the attached molten solder is soldered in a high-temperature nitrogen gas atmosphere that can be slowly cooled with a gentle temperature profile, and immediately before the start of solidification, a low temperature of room temperature or lower. It is important to cool rapidly in a nitrogen gas atmosphere. Therefore, a high-temperature nitrogen gas atmosphere is used at a temperature at which the used solder can be slowly cooled, for example, solder H
In the case of 63A, the temperature is about 20 ° C. higher than the melting point of solder to about 150 ° C. lower than the melting point, that is, 80 ° C. to 250 ° C.
The temperature is in the temperature range of 200C, preferably 200C to 250C. In the case of other solder compositions, the temperature at which the cooling can be performed slowly is determined based on the cooling rate at room temperature. In this case, since the behavior of the molten solder is determined by the time during which the work is exposed to the high-temperature atmosphere, the temperature of the atmosphere can be set to a lower temperature depending on the transfer speed of the work and the size of the high-temperature nitrogen gas atmosphere.

The rapid cooling immediately before the start of solidification of the molten solder may be performed by exposing it to the atmosphere. However, the molten solder releases latent heat upon solidification and simultaneously dissolves O ₂ , H ₂ , CO, etc. in the atmosphere. Therefore, a nitrogen gas atmosphere is used because it causes oxidation, porosity, and oxidation of the solder immediately before solidification is the largest cause of bridges, horns, and glares. The low-temperature nitrogen gas atmosphere is at room temperature, specifically, at a temperature of 25 ° C. or lower, but below the freezing point, for example, −20 ° C. to −30 in order to secure the quenching effect.
It is good also as ° C. When the work surface is exposed to a low-temperature nitrogen gas atmosphere, the molten solder is rapidly cooled from the surface,
It is preferable to spray a low-temperature nitrogen gas on the back surface of the work and rapidly cool the work from the back side, because the quenching effect is promoted and a finer rapidly solidified structure can be obtained.

Although a cylinder or the like may be used as the nitrogen source, the cost increases. Therefore, it is preferable to separate the nitrogen gas from the compressed air by using a nitrogen gas separation device having a built-in hollow separation membrane, and to heat the separated nitrogen gas to a high temperature with a heating feeder to supply it. When a soldering iron is used, there is a heat generating portion such as a heater. Therefore, the nitrogen gas may be heated by utilizing the heat generated by the soldering iron.

It is desirable that the present invention can be easily applied to an existing soldering apparatus, and it is also preferable that the present invention can be applied to various apparatuses using an oxygen-free atmosphere other than the soldering apparatus. Therefore, a nitrogen gas generator that supplies high-temperature nitrogen gas to various devices that use an oxygen-free atmosphere to form a high-temperature nitrogen gas atmosphere, and has a built-in hollow separation membrane to separate nitrogen gas from compressed air It is preferable to provide a nitrogen gas generator provided with an apparatus and a heating supply device for heating and supplying the nitrogen gas from the nitrogen gas separator to a high temperature.

The compressed air may be supplied to a nitrogen gas separator by preparing a dedicated compressor. However, since a compressed air pipe is provided in the factory facility, the compressed air in the pipe is used. Nitrogen gas may be separated. In this case, the compressed air is preferably dry.

When soldering to a work using a soldering iron, after preheating the work soldering site with a high-temperature nitrogen gas,
It is preferable that the soldering is performed by bringing a soldering iron into contact in a high-temperature nitrogen gas atmosphere, and rapid cooling is performed with a low-temperature nitrogen gas immediately before the start of solidification of the molten solder. In this case, low-temperature nitrogen gas is preferably sprayed on the back surface of the work to rapidly cool the work from the back surface. In particular, when an electronic component is soldered later to a mounted electronic board, it is preferable that the mounted component in the vicinity of the soldering site is not affected by heat. In other words, when soldering a work in a retrofit using a soldering iron, high-temperature nitrogen gas is injected around the tip of the soldering iron, and low-temperature nitrogen gas is injected around the tip. At the time of soldering, it is preferable to protect the work and the element near the soldering site from the high-temperature nitrogen gas with the low-temperature nitrogen gas.

The soldering iron used in such a method is preferably constructed as follows. That is, in a soldering iron in which the tip can be heated by the heat generated by the heater incorporated in the iron, the first protective cover is hermetically covered around the heater, and the tip side of the tip is covered with the tip. A first nitrogen gas supply passage is formed by opening to the periphery, a second protective cover is hermetically covered around the first protective cover, and its tip is placed around the tip opening of the first protective cover. Open and second
Forming a nitrogen gas supply passage, supplying nitrogen gas to the first and second nitrogen gas supply passages and supplying high-temperature nitrogen gas around the tip chip and low-temperature nitrogen gas around the high-temperature nitrogen gas. Good.

[0019]

According to the present invention, since the soldering is performed in a high-temperature nitrogen gas atmosphere in which the molten solder is slowly cooled, the molten solder is in a favorable bulging state due to its surface tension. Take the shape. In addition, since the molten solder is rapidly cooled in a low-temperature nitrogen gas atmosphere at room temperature or lower immediately before the solidification of the molten solder, the distance between the liquidus and solidus of the molten solder is substantially reduced. And the solder can be made into a finely solidified structure.

As a result, there is no scatter of solder balls, bridges or solder, and it is dense, has very few segregation of Pb and Sn and has very few pores, has excellent heat shock resistance, and has high quality non-oxidizing and non-cleaning with good build. Can be soldered.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific examples shown in the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention, which is an example applied to a nozzle jet type solder bath apparatus. In the figure, a jet nozzle 11 is provided in a solder tank 10, and a jet pump P is built in the solder tank 10, and molten solder (solder H63A) 12 in the solder tank 10 is jetted upward and an electronic substrate (workpiece) is formed. 2) The residual molten solder 12 after the jet flow is brought into contact with and adhered to W to be collected in the solder bath 10. An electronic board W on which a conveyor 13 is disposed above the solder tank 10 and on which electronic components are mounted
Can be conveyed, and thus a nozzle jet type solder bath apparatus is constituted.

A first frame 14 is provided between the solder tank 10 and the conveyor 13 so as to surround the upper surface of the solder tank 10, and a second frame 15 is provided in front of the first frame 14 in the conveying direction. An opening or a gap is provided at the upper ends of the two frame members 14 and 15 so that the electronic substrate W can be transported. In the first area A, a second area B in front of the work transport direction is partitioned from the outside by the second frame 15.

Reference numeral 16 denotes a compressor having a drier function for supplying compressed air, 17 denotes a nitrogen gas separation device having a built-in hollow separation membrane for separating nitrogen gas from compressed air, 1
Reference numeral 8 denotes the temperature of the nitrogen gas from the nitrogen gas separator 17 at 200 ° C.
A heating / supplying machine which is heated to 250 ° C. and supplied into the first frame body 14 to form a high-temperature nitrogen gas atmosphere, and 19 cools the nitrogen gas from the nitrogen gas separator 17 to −20 ° C. to −30 ° C. And a cooling / supplying device for supplying the low-temperature nitrogen gas atmosphere by supplying it into the second frame 13.

Next, a soldering method will be described. When the electronic substrate W on which the electronic components are mounted is transported by the transport conveyor 13 and reaches the solder tank 10, molten solder 12 is jetted from the jet nozzle 11 of the solder tank 10. In a high-temperature nitrogen gas atmosphere (see the temperature characteristic a in FIG. 2), the molten solder 12 contacts and adheres to a predetermined location.

When the electronic substrate W is further conveyed and separated from the jet of the molten solder 12 of the jet nozzle 11, the electronic substrate W is conveyed in the high temperature nitrogen gas atmosphere at 250 ° C. in the first area A. Then, the molten solder 12 attached to the electronic substrate W is gradually cooled to approximately 250 ° C. as shown by the temperature characteristic “b” in FIG. 2, and becomes a substantially hemispherical shape having a desired shape due to its surface tension.

When the electronic substrate W exits the high-temperature nitrogen gas atmosphere in the first region A, the temperature of the next second region B is changed from -20.degree.
It is transported in a low-temperature nitrogen atmosphere at a temperature of ° C. (see temperature characteristic c in FIG. 2). Then, the molten solder 12 of the electronic substrate W is rapidly cooled as shown by the temperature characteristic d in FIG. As a result, the molten solder 12 is given directional solidification in which the distance between the liquidus line and the solidus line is substantially reduced, and dendrites and free crystals do not develop. The solidification of the solder 12 is completed. When the solidification of the solder of the electronic substrate W is completed and the substrate exits the low-temperature nitrogen gas atmosphere in the second region B, the electronic substrate W is exposed to a room temperature atmosphere, and the temperature of the solder rises to room temperature.

As a result, very high quality and high quality soldering can be obtained with good quality, little residue of halogens is left, deterioration of soldering with the lapse of time can be prevented, and recent chlorofluorocarbons and toluene are completely eliminated. Electronic component mounting technology can be provided. In addition, the flux attached to the back surface of the electronic substrate W is also rapidly cooled together with the molten solder 12 and shrunk largely to make it crisp without stickiness, as if it were coated with varnish and dried, so that the insulation can be improved. .

The electronic components mounted on the electronic substrate W come into contact with the molten solder 12 at a temperature of 250 ° C. or more during soldering,
Although there is a concern about the adverse effects of heat conduction, rapid cooling immediately after soldering can mitigate the effects of heat, and quenching from high to low temperatures can provide an aging effect due to temperature differences, resulting in inspection quality. Can be expected to improve.

By the way, it is proposed that the molten solder 12 be solidified densely by immediately quenching in a low-temperature nitrogen atmosphere immediately after soldering. In this case, a solder icicle, a bridge or a solder ball is formed, and the soldering is performed. Of poor quality. On the other hand, in the present method, since the high-temperature molten solder 12 is rapidly cooled in a state where a desired bulge is formed by slow cooling, no icing, bridges or solder balls of such solder are formed.

Further, soldering can be performed with good soldering, which cannot be performed by using a solder wringer, a bridge, or a solder ball. As a result, the amount of solder scum is reduced, and a great effect is obtained in terms of working environment and manufacturing cost.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention applied to a soldering iron, and the same reference numerals as those in FIG. 1 denote the same or corresponding parts. In the figure, a tip is provided at a tip of a soldering iron 23, and a nitrogen gas supply pipe 25 is attached to the soldering iron 23 by a mounting rod 24, and the nitrogen gas supply pipe 25 supplies a low-temperature nitrogen gas toward the tip. It is supposed to. A nitrogen gas heating pipe 27 is wound around a portion of the soldering iron 23 with a built-in heater, and the nitrogen gas heating pipe 27 heats the nitrogen gas and supplies it to the tip chip. The nitrogen gas from the nitrogen gas separator 17 is switched by a switching valve 20 to a nitrogen gas supply pipe 25 and a nitrogen gas heating pipe 27 and supplied.

In the case of soldering, a solder wire is sent through a solder wire supply pipe as usual, and the solder wire is melted by a soldering iron 23 and soldered to the electronic substrate W. At this time, when the air compressor 16 is operated to compress the air, the air is sent to the nitrogen gas separator 17 to separate the nitrogen gas from the compressed air, and the separated nitrogen gas is passed through the switching valve 20 to the nitrogen gas heating pipe. 27 and the soldering iron 23
Is heated to a predetermined temperature, for example, 200 ° C. to 250 ° C. in the heating portion, and is discharged near the tip of the soldering iron 23;
A small area D of a high-temperature nitrogen gas atmosphere is formed in front of the soldering iron 23, and soldering is performed in the high-temperature nitrogen gas atmosphere D.

When the soldering iron 23 is separated from the electronic substrate W, the molten solder attached to the electronic substrate W becomes a hot nitrogen gas atmosphere D
And gradually rises in a substantially hemispherical shape due to the surface tension. Immediately before the start of solidification of the molten solder attached to the electronic substrate W, the switching valve 20 switches the supply of the nitrogen gas to the nitrogen gas supply pipe 25. Then, the hemispherical molten solder is exposed to a low-temperature nitrogen gas atmosphere and quenched, so that high-quality soldering that is dense and well-filled can be performed.

Further, since the high-temperature nitrogen gas is discharged to the tip end side of the soldering iron 23, it is also possible to adopt a method of preheating the soldering site and then contacting the chip to perform soldering.

As a result, the solder flux can be preheated to activate and prevent the flux from scattering, so that a smooth and good soldering operation can be performed. In addition, the chip of the high-temperature soldering iron 23 contacts the electronic substrate W. Before heating the electronic substrate W,
As a result, it is possible to prevent a local and rapid rise in temperature (heat shock) of the electronic substrate W to prevent thermal destruction of the electronic components, and further to preheat the flux, the electronic substrate, and the supplied solder wires, resulting in the heat of the solder layer. Intermittent brittleness can be prevented.

In addition, since the solder and the flux can be preheated with the high-temperature nitrogen gas, the amount of heat stored in the chip of the soldering iron 23 is small, and even if the tip of the chip is extremely small, the soldering can be performed with a sufficient amount of heat. Means that low-temperature soldering can be achieved. Furthermore, since the chip of the soldering iron 23 is in a non-oxidizing atmosphere, the oxidation of the chip is prevented, the wettability of the molten solder can be improved, and the life of the chip can be improved.

When a high-temperature nitrogen gas atmosphere is used only for preheating, air or a mixed gas of nitrogen gas and air can be used instead of nitrogen gas.

[Third Embodiment] FIG. 4 shows a third embodiment of the present invention applied to a soldering iron. In the present embodiment, the soldering iron 50 includes a iron part 51 and a grip part 52,
A heater (for example, a round bar-shaped alumina nitride heater) 53 is built in the iron portion 51, a tip of the heater 53 is inserted into a hole of the chip holder 54, and a tip 55 is fixed to a tip of the chip holder 54. The heat generated by the built-in heater 53 is transmitted to the tip chip 55 so that the tip chip 55 is heated.

The rear end of the heater 53 is inserted and held in a central hole of a holder 56 built in the tip of the grip 52, and a temperature sensor (not shown) is attached. The holder 56 has a plurality of nitrogen gas supply holes 57.
, 58 ... are formed in a double annular shape inside and outside, and the holder 56 is connected to the tip of a nitrogen gas supply pipe 59 inserted into the grip portion 52.
The rear end of 9 leads to the above-mentioned nitrogen gas separator.

A first protective cover 60 is air-tightly fixed to the tip of the grip portion 52.
0 covers the periphery of the heater 53 and extends to the distal end with a predetermined gap, for example, 1 mm, between the heater 53 and the tip holder. The distal end is communicated with a plurality of communication holes around the distal tip 55, Thus, the first nitrogen gas supply passage 61 is formed.

Further, a second protective cover 62 is fixed to the tip of the grip portion 52 outside the first protective cover 60, and the second protective cover 62 extends around the first protective cover 60 by a predetermined distance. A gap, e.g., a gap of 2 mm, is airtightly covered and extends to the front end side.
0, and a plurality of communication holes near the front end of the first tip 55 are formed.
, And a low-temperature nitrogen gas 66 is supplied around the high-temperature nitrogen gas.

Next, the method of use will be described. When soldering is performed afterwards using the soldering iron of the present embodiment, first, the heater 53 of the soldering iron 50 is energized to heat the tip chip 55 to 280 ° C. to 380 ° C., while the nitrogen of the soldering iron 50 is heated. The gas supply pipe 59 has a pressure of 1.0 to 5.0 kg / c.
m ² , flow rate 4 liter / min, purity 99-99.9%
Of nitrogen gas. Then, the nitrogen gas passing through the first nitrogen gas supply passage 61 generates 20
Heated to 0 ° C. to 250 ° C., the volume is nearly doubled, and the nitrogen gas passing through the second nitrogen gas supply passage 63 is discharged forward at room temperature. The flow rate and pressure of the nitrogen gas can be adjusted by setting the inner diameter and the number of the nitrogen gas supply holes 57 and 58 of the holder 56.

When the preparation is completed, high-temperature nitrogen gas 64 is sprayed onto the soldering portion of the substrate for 2 to 5 seconds to preheat the soldering portion, thereby activating low residue flux at the soldering portion. Can be Also,
When the O ₂ concentration is 5 ppm or less, fluxless soldering is possible. In this case, the substrates and electronic components around the soldering site are exposed to the atmosphere of the low-temperature nitrogen gas 65, so that the surrounding substrates and electronic components are not affected by heat.

Next, in about 0.3 to 0.8 seconds, the tip 55 is brought into contact with the soldering site and heated to supply a flux-free thread solder, and the soldering is performed in an atmosphere of high-temperature nitrogen gas 64. A portion of molten solder is formed at the site. Next, the tip chip 55 is separated from the soldering portion, and the molten solder is exposed to the atmosphere of the low-temperature nitrogen gas 65, while rapidly cooling by blowing a nitrogen gas at room temperature from the back surface of the substrate.

Then, the heat of the molten solder is rapidly absorbed into the surroundings, and the molten solder is rapidly cooled as a whole, and fine quenched crystals, fine columnar crystals, and fine free crystals are formed. The columnar crystals are likely to generate grain boundaries containing impurities and gases in parallel with the crystal columns, and the molten solder is formed by applying a high-temperature nitrogen gas 65 pressure of 1.0 to 5.0 kg / cm ^{2 to the} free crystal flux gas or impurity gas. To release gas and eliminate bubbles and gas holes. The pressurized high-temperature nitrogen gas 6
By means of 5, the dendrites can be filled under pressure with the molten solder melt, thereby preventing micro and macro porosity (porosity) and providing a dense crystal structure.

Accordingly, the entire molten solder is quenched to substantially reduce the distance between the liquidus and solidus of the molten solder, exert a pressurizing effect, and achieve macroscopic segregation (Pb, Sn).
And the like, and dendrites, layered structure, nucleated structure, etc. of micro segregation are reduced to obtain a solidified solder having a fine crystal structure with few impurities and gas.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing temperature characteristics for explaining the soldering method of FIG. 1;

FIG. 3 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a third embodiment of the present invention.

[Description of Signs] 17 Nitrogen gas separator 18 Heating and supplying device 23 Soldering iron 25 Nitrogen gas supply pipe. 27 Nitrogen gas heating pipe 50
Soldering iron 51 Iron part 53 Heater 55 Tip 60 First protective cover 61 First nitrogen gas supply passage 62 Second protective cover 63 Second nitrogen gas supply passage 65 High temperature nitrogen gas 66 Low temperature nitrogen gas D High temperature Nitrogen gas atmosphere W Electronic substrate (work)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-231160 (JP, A) JP-A-4-262628 (JP, A) JP-A-4-309457 (JP, A) JP-A-6-261 244548 (JP, A) JP-A-6-21640 (JP, A) JP-A-59-151492 (JP, A) JP-A-6-151032 (JP, A) JP-A-6-334326 (JP, A) JP-A-6-315766 (JP, A) JP-A-6-70962 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 3/34 B23K 31/02 B23K 3/02

Claims (5)

(57) [Claims] 1. A method of contacting and adhering molten solder to a work to solidify it, or melting and solidifying a solder layer formed on the surface of the work to perform soldering. Is at room temperature
By performing soldering in a high-temperature nitrogen gas atmosphere at a lower temperature than the molten solder that can be slowly cooled based on the cooling rate, the molten solder is made almost hemispherical with its surface tension, and the molten solder is solidified A soldering method characterized by rapidly cooling in a low-temperature nitrogen gas atmosphere at room temperature or lower immediately before the start to directionally solidify the entire molten solder to form a fine solidified structure. 2. The soldering method according to claim 1, wherein a low-temperature nitrogen gas is blown onto the back surface of the work when the rapid cooling is started, so that the work back surface is also rapidly cooled. 3. When soldering a work using a soldering iron, after preheating a soldering portion of the work with a high-temperature nitrogen gas, the soldering is performed by contacting the soldering iron in a high-temperature nitrogen gas atmosphere. 3. The soldering method according to claim 1, wherein the molten solder is rapidly cooled with a low-temperature nitrogen gas. 4. When soldering a workpiece by post-installation using a soldering iron, a high-temperature nitrogen gas is sprayed around a tip of the soldering iron and a low-temperature nitrogen gas is sprayed around the tip. 4. The soldering method according to claim 3, wherein the work and the element near the soldering portion are protected from the high-temperature nitrogen gas by the low-temperature nitrogen gas during the preheating and the soldering. 5. A soldering iron in which a tip chip can be heated by heat generated by a heater built in the iron portion, the first protection cover is hermetically covered around the heater, and the tip side is covered. A first nitrogen gas supply passage is formed around the tip tip to form a first nitrogen gas supply passage. The second protection cover is hermetically covered around the first protection cover, and the tip of the second protection cover is opened at the tip of the first protection cover. To form a second nitrogen gas supply passage, and supply nitrogen gas to the first and second nitrogen gas supply passages to supply a high-temperature nitrogen gas around the tip chip and a high-temperature nitrogen gas around the high-temperature nitrogen gas. A soldering iron characterized by supplying a low-temperature nitrogen gas.