JP2001237532A - Flux coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux coating method wherein there is no effect exerted on quality as a circuit board, control is simple and a proper amount of flux can be continuously applied on a desired part of the circuit board, so that superior soldering is enabled. SOLUTION: This flux coating method is a method for applying flux whose base material is water on the circuit board 46. By sticking fine particles of the flux on the circuit board at a room temperature or in a dry atmosphere, the diameter of the flux fine particle stuck on the circuit board is set to be at most 30 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux coating method for supplying a flux required for soldering to a desired portion of a circuit board continuously by using a flux based on water.

[0002]

2. Description of the Related Art When an electronic component is mounted on a circuit board by soldering, a flux is applied to the circuit board before soldering and mounting in order to ensure wettability with an electrode portion of the circuit board and perform good soldering. are doing. As the flux, a rosin-based flux or a flux based on water is used. However, it is desirable that the flux does not contain VOC (volatile organic compound) from the viewpoint of impact on the global environment.
A flux based on water is used. The water-based flux is composed only of water and the active ingredient.

FIG. 7 shows a spray fluxer 10 used for continuously applying a flux to a circuit board.
The spray fluxer 10 has an inlet 11 and an outlet 12.
A pair of transport belts 13 running toward the side are provided. The transport belt 13 is driven by a driving device 18 via a driving belt 19.

[0004] A spray nozzle 14 is arranged below the conveyor belt 13. By sending compressed air and flux into the spray nozzle 14, the flux fine particles 15 are sprayed upward from the spray port 14a at the tip. An exhaust port 17 for discharging air inside the apparatus to the outside by an exhaust device (not shown) is formed in the upper surface portion of the spray flexure 10.

FIG. 8 shows the internal structure of the tip of the spray nozzle 14, in which a nozzle 21 is inserted into a nozzle cover 23. Nozzle 21 has a tubular flux passage 2
1 a is formed, and the flux fine particles 15 introduced into the nozzle 21 are jetted from a spray port 14 a having a diameter D at the tip of the nozzle 21. Spray port 14a
Has a diameter D of about 0.5 to 1.0 mm, whereas the particle diameter of the sprayed flux 15 is 30 to 40 mm.
Although it is on the order of μm, the maximum particle size becomes a larger value.

[0006] As shown in FIG. 8, a needle 22 is inserted inside the nozzle 21. The needle 22 is not shown, but is adjusted in the axial direction (up and down) by an adjustment knob.
The width w of the flux passage 21a can be adjusted by this movement. Therefore, it is possible to adjust the spray amount of the flux fine particles 15.

The space between the nozzle cover 23 and the nozzle 21 is
An air passage 23a is formed, and air flows in the air passage 23a in a direction indicated by an arrow. By changing the pressure of the air, the blowing pressure to the flux fine particles 15 changes, so that the blowing angle θ of the sprayed flux fine particles 15 can be adjusted.

In the above-described apparatus, the transport belt 13 is caused to travel by the drive device 18 via the drive belt 19, and the circuit board 16 introduced from the entrance 11 is placed on the transport belt 13 and transported in the direction of the exit 12. I do. When the circuit board 16 passes above the spray nozzle 14 by this conveyance, the flux fine particles 15 are sprayed from the spray nozzle 14 in the form of mist to apply the flux to the circuit board 16.
Then, the circuit board 16 to which the flux has been applied is transported by the transport belt 13 and is carried out from the outlet 12.

However, when a flux based on water is applied using such a spray flexor, the average particle diameter of the flux fine particles 15 is 30 to 4%.
Since the maximum particle diameter is 0 μm and the maximum particle diameter is larger than the above, the fine particles of the flux adhered to the electrode portion of the circuit board 16 may adhere to each other to form water droplets, which may affect the quality of soldering. In particular, in a flux in which water accounts for 90% by weight or more, the attached fine particles become large, and the influence on the soldering quality is remarkable.

That is, the flux fine particles sprayed from the spray nozzle 14 and adhered to the electrode portion of the circuit board 16 are uniformly distributed on the electrode portion at the moment of the adhesion, but water accounts for 90% by weight or more. In the flux, since the latent heat of vaporization of water is large, the moisture in the flux fine particles hardly evaporates, and the flux fine particles remain on the electrode portion in a state containing a large amount of water. In addition, since water has a large surface tension, fine particles containing a large amount of water are more likely to adhere to fine particles sprayed later or fine particles adjacent to the fine particles, and quickly become water droplets. The water droplets are scattered on the electrode portion of the circuit board. In addition, the flux particles that have become water droplets are:
Further, the moisture is less likely to evaporate. Then, when soldering is performed in a state containing such moisture, the moisture remaining without evaporating impairs the flux action, and causes soldering failure such as non-wetting of the solder and unsoldering. Furthermore, even if moisture evaporates immediately before soldering, good semicircularity cannot be obtained because the active component remains intermittently on the electrodes of the circuit board.

Japanese Patent Application Laid-Open No. Hei 8-229674 has been proposed to solve such a problem. This method quickly evaporates the moisture of the adhered flux fine particles and forms a continuous active ingredient film.
Using a spray nozzle heated to 100 to 250 ° C., a flux based on water is sprayed on the circuit board. Further, the circuit board is heated to about 100 ° C. in advance, and a flux containing water as a base material is sprayed on the heated circuit board.

[0012]

However, the method disclosed in Japanese Patent Application Laid-Open No. Hei 8-229674 has the following problems.

(1) In the heating of the spray nozzle, when the flux passes through the spray nozzle, the flux is also heated, so that the activation of the flux is promoted, and the active component in the flux is reduced to oxygen or flux in the atmosphere. Reacts with water contained in water, and its activity ability is reduced. As a result, the effect of the flux cannot be sufficiently exerted, and soldering failure may occur.

(2) The circuit board and electronic components are thermally damaged by the heat load of heating the circuit board. That is, if the heating temperature of the circuit board is too high, thermal damage to the circuit board and electronic components increases, and in some cases, they are damaged.

(3) If the heating of the circuit board is insufficient, it takes time to evaporate the moisture contained in the flux, so that the probability that the fine particles attached to the electrode portion of the circuit board adhere to each other and become water droplets increases. In addition, there is an increased risk that a film formed by the active component in the flux is intermittently formed on the surface of the circuit board. As a result, the quality of soldering may become unstable.

(4) In order to heat the spray nozzle and the circuit board, it is necessary to sufficiently control the temperatures of these. For example, if the temperature of the spray nozzle is higher than a predetermined temperature, the moisture in the flux evaporates too much and the flux concentration becomes high, and as a result, the nozzle tends to be clogged. On the other hand, when the temperature of the spray nozzle is lower than the predetermined temperature, the particle diameter of the flux fine particles does not decrease, and it takes time for the moisture in the flux to evaporate. For this reason, the flux fine particles adhere to each other and become large particles, so that a coating of the active component of the continuous flux cannot be formed, and as a result, poor soldering tends to occur.

As described above, in the conventional method of heating the circuit board and the spray nozzle to evaporate the moisture in the flux to form a continuous coating of the active component, the soldering quality due to the decrease in the active power of the flux is reduced. Not only in terms of quality, such as deterioration, adverse effects on circuit boards and electronic components, instability of solderability when temperature control is inadequate, and an increase in the number of nozzle maintenance, but also in terms of productivity. Have a problem.

The present invention has been made in consideration of such conventional problems, and does not affect the quality of the circuit board, is easy to manage, and has an appropriate amount at a desired position on the circuit board. It is an object of the present invention to provide a method of applying a flux that can apply a suitable flux to a continuous ladle, thereby enabling a good semicircle.

[0019]

In order to achieve the above object, the invention of claim 1 is a method of applying a water-based flux to a circuit board, the method comprising applying fine particles of the flux to a circuit board at room temperature. It is characterized in that the diameter of the flux fine particles adhered to the circuit board is reduced to 30 μm or less by being adhered to the substrate.

When a flux based on water is applied to a circuit board by a conventional method, since the flux fine particles adhering to the circuit board are not restricted, the diameter of the flux fine particles to be sprayed becomes large and this adheres to the circuit board. .
In addition, since the latent heat of vaporization of water is large, the moisture in the fine particles having a large particle diameter is difficult to evaporate, and when the fine particles are continuously sprayed with insufficient water evaporation, the particles adhere to each other, It becomes larger flux particles. Since the surface tension of water is large and the circuit board is hydrophobic, the flux particles that have increased due to close contact do not spread out but spread as water droplets on the circuit board. Flux particles scattered as water droplets are more difficult to evaporate. When soldering is performed in a state where the flux contains a large amount of moisture, the remaining moisture has an adverse effect on the flux action, resulting in poor soldering. what if,
Even if the soldering is performed in a state where the moisture is completely evaporated, the active component of the flux is intermittently present in a spot-like manner, so that it is not possible to perform a good soldering.

On the other hand, when a flux having a smaller particle diameter can be applied to the circuit board, the evaporation time of water becomes faster, and the fine flux particles do not adhere to each other to form larger particles. An appropriate amount of flux can be continuously applied to a desired portion of the substrate, a continuous film of the active component of the flux can be formed, and good soldering can be performed.

From the above viewpoint, the present inventors have studied the relationship between the particles when the flux fine particles adhere to the circuit board and the evaporation time. As the particle diameter becomes smaller, the evaporation time becomes shorter. Was found.
When this relation was further pursued, when the diameter of the flux fine particles attached to the circuit board was set to 30 μm or less at room temperature of 40 ° C. or less, the flux fine particles attached to the circuit board adhered to each other to become large particles. It has previously been found that the water in the particles evaporates, thereby continuously forming the active component of the flux on the circuit board.

According to the first aspect of the present invention, the flux is applied to the circuit board at room temperature. Therefore, compared to the conventional method in which the nozzle or the circuit board is heated and applied, the activity of the flux is not reduced by heating. Form a continuous and uniform flux coating on the circuit board without damaging the circuit board, without forming active flux components on the circuit board intermittently, and without causing nozzle clogging it can. Thereby, good soldering can be performed.

According to a second aspect of the present invention, in the first aspect, the flux is applied to the circuit board in a dry atmosphere.

In the present invention, since the application of the flux to the circuit board is performed in a dry atmosphere, the evaporation of the fine particles adhering to the circuit board can be further accelerated, and the weight of the active ingredient dissolved in the water of the base material can be increased. % Can be lowered. Therefore, even when the flux is applied by a plurality of nozzles a plurality of times, the flux fine particles do not adhere to each other at all, and a continuous and uniform coating of the flux can be formed on the circuit board. Becomes possible. Here, the dry atmosphere means that the humidity at room temperature is 40%.
It shows the following atmosphere.

[0026]

(Embodiment 1) Setting of flux application conditions in this embodiment will be described. In order to set conditions under which the fine flux particles adhering to the electrodes of the circuit board do not adhere to each other to form water droplets, 2
Under an environment of 5 ° C./60% RH, adipic acid (HOOC (CH ₂ ) ₄ ) was placed on a copper plate made of the same material as the electrodes of the circuit board.
A flux based on water consisting of 2% by weight (COOH) and the balance distilled water was sprayed at a distance of 50 mm from the copper plate using a spray nozzle having a nozzle diameter of 0.2 mm. Here, a nozzle diameter of 0.2 mm is used as the spray nozzle.
Since it occupies 8% by weight, the risk of clogging of the nozzle is extremely small, and the flux can be easily sprayed even with a nozzle diameter of 0.2 mm.

Under these conditions, the flux is applied to the copper plate while changing the spray amount and the particle size of the flux, and the image of the state in which the flux adheres to the copper plate is magnified and displayed with a microscope through a video camera. By recording the video and slow-playing or stopping it, the state of the time change of the adhesion and evaporation of the flux was observed. As a result, it was found that when the spray pressure was 0.1 MPa and the spray amount was 0.15 cc / min or less per square centimeter, the flux particles adhering to the copper plate evaporated quickly without adhering to each other.

Then, spraying was performed under the above conditions, and the particle size of the flux fine particles adhering to the copper plate and the evaporation time of water in the particles were measured a plurality of times. As a result, the particle diameter was 30 μm.
It was found that there were no flux fine particles exceeding m, and the water evaporation time was less than 1 second. FIG. 1 is a graph of this result.

As shown in FIG. 1, when the diameter of the flux fine particles is 30 μm, water evaporates in about 1 second, and the diameter becomes 10 μm.
In the case of the fine particles of m, they evaporate in less than 0.2 seconds. On the other hand, when the diameter of the flux fine particles exceeds 30 μm, the evaporation time exceeds 1 second, and when the diameter of the flash fine particles further increases, the above observation shows that the fine particles of the flux adhere to each other and become large. Time becomes extremely long. When the diameter of the flux fine particles reached 40 μm, it was found that immediately after that, the adhesion of the flux fine particles became large, and the evaporation time became too long to show, so that a continuous and uniform coating of the flux was not formed.

In the above observation, the diameter when the fine particles of the flux adhered to the circuit board was measured. However, since the diameter of the fine particles of the flux varies, the "fine particle diameter of the flux is not The phrase “not exceeding 30 μm” means that the maximum value does not exceed 30 μm in the range of variation.

FIG. 2 shows a spray fluxer 40 which is a flux coating device used in this embodiment. Coating room 3
9, the entrance 41 and the exit 42 of the circuit board 46
A pair of transport belts 43 running from the entrance 41 side to the exit 42 side are arranged inside. The transport belt 43 is driven by a drive device 48 via a drive belt 49.

Below the conveyor belt 43, a circuit board 46 is provided.
Spray nozzles 4 for spraying flux against
41 and 442 are arranged. The reason for using two spray nozzles is to surely form a continuous flux active component coating on the circuit board 46, and the number of spray nozzles is not limited. Therefore, one spray nozzle may be used when the active ingredient of the continuous flux can be applied reliably, and three spray nozzles may be used when the active ingredient of the continuous flux cannot be applied even with two nozzles. It may be above. These spray nozzles 441, 4
Reference numeral 42 denotes a transport belt 43 by a moving unit (not shown).
It is possible to reciprocate at an arbitrary speed in the belt width direction. The spray nozzle 44 used here
Reference numerals 1 and 442 are the same type as the spray nozzles used for setting the above-described application conditions.

Compressed air and flux are fed into the spray nozzles 441 and 442, and the flux fine particles 45 are sprayed from the spray ports 441a and 442a at the tips of the spray nozzles 441 and 442. The coating chamber 39
An exhaust port 47 for exhausting the internal air to the outside by an exhaust device (not shown) is opened on the upper surface of the.

FIG. 3 shows the details of the tip of the spray nozzle 441. The tip of the spray nozzle 442 has the same shape as the spray nozzle 441. FIG.
Then, the left half thereof shows a cross section.

The spray nozzle 441 has a nozzle 51, and the inside of the nozzle 51 is provided with a tubular flux passage 5.
It is 3. The tip of the nozzle 51 has a diameter D (D =
The nozzle 52 is inserted into the flux passage 52. The needle 52 can be freely moved in the axial direction (vertical direction) of the nozzle 51 by an adjustment knob (not shown). The movement of the needle 52 changes the width w of the flux passage 53, so that the spray amount of the flux fine particles 45 can be adjusted.

In the spray fluxer 40, the drive belt 48 drives the transport belt 43 via the drive belt 49 from the entrance 41 to the exit 42. Then, the circuit board 46 introduced from the entrance 41 is placed on the traveling conveyor belt 43 and transported in the direction of the exit 42. When the circuit board 46 passes above the spray nozzle 441 by this conveyance, the spray nozzle 441
The flux 45 sprayed from the spray port 441 a is applied to the lower surface of the circuit board 46. Spray nozzle 44
1 is a conveyor belt 43 according to the board width of the circuit board 46.
The flux particles 45 are sprayed while repeating the reciprocating movement in the belt width direction, so that the entire lower surface of the circuit board 46 can be coated with the flux.

Subsequently, the circuit board 46 is connected to the spray nozzle 4
The flux fine particles 45 sprayed from the spray port 442a of the spray nozzle 442 when passing above the
Is applied to the lower surface of the circuit board 46. The spray nozzle 442 sprays the fine particles 45 while repeating the reciprocating movement of the conveyor belt 43 in the belt width direction in accordance with the width of the circuit board 46.
Is applied to the entire lower surface of the substrate. Therefore, in addition to the flux application by the spray nozzle 441, the flux application by the spray nozzle 442 is performed on the circuit board 46. After this application, the circuit board 46 is transported by the transport belt 43 and is discharged from the outlet 42. As described above, an appropriate amount of flux is applied to the circuit board 46, and a film of the active component of the continuous flux can be formed.

In this embodiment, the spray conditions of the flux 45 are a spray pressure of 0.1 MPa and a spray amount is 0.12 cc / min per square centimeter. The distance L between the circuit board 46 and the spray nozzles 441 and 442 is set to 5
It was set to 0 mm. The transfer speed of the circuit board 46 is 1 m per minute
The distance between the spray nozzles 441 and 442 was set to 5 cm. Under such conditions, the circuit board 46 was transported by the transport belt 43, and a flux containing water as a base material consisting of 2% by weight of adipic acid and the balance of distilled water was applied to the circuit board 46.

By setting the transport speed of the circuit board 46 at 1 m per minute and the interval between the spray nozzles 441 and 442 at 5 cm, the flux fine particles sprayed from the spray nozzle 441 finally adhere to the circuit board 46. After that, a time interval of 1 second or more is required until the flux fine particles sprayed from the next spray nozzle 442 first adhere to the circuit board 46. Therefore, the diameter of the flux fine particles sprayed from the spray nozzle 441 and adhering to the circuit board 46 does not exceed 30 μm, and after the moisture is completely evaporated within one second, the circuit board 46 is re-spun by the next spray nozzle 442. Flux particles adhere to the surface. Therefore, the flux fine particles do not adhere to each other to form large particles.

In this embodiment, after the flux was applied as described above, the surface of the electrode portion of the circuit board 46 was observed under magnification. As a result, it was confirmed that adipic acid as an active ingredient remained as a continuous body on the surface of the electrode portion.

Further, the following method was used to quantitatively prove that adipic acid was a continuum on the surface of the electrode. In the method of the prior art, the solder is not wetted at the time of soldering because a continuous coating of the active component of the flux is not formed. When this fact is taken in reverse, if the wettability of the solder is good, it means that the coating of the active component of the flux was continuously formed. Then, by directly evaluating the wettability of the solder, it was proved that the coating of the flux with adipic acid was continuously formed. As a method for evaluating the wettability of the solder, a meniscus test method (meniscograph) was used.

The meniscus test method is a test method for measuring a temporal change in wetting when a test piece is immersed in molten solder at a constant depth, speed, and time interval. In this method, as shown in FIG. 4, the wettability can be determined by measuring the zero cross time (t) from a curve that records the temporal change of the wetting obtained during the test.
The zero cross time (t) means that after the test piece comes into contact with the molten solder, the wet portion of the test piece wets up to the surface of the solder bath (that is, the buoyancy of the test piece and the surface tension of the molten solder become equilibrium). Time). That is, the test piece having better wettability has a zero cross time (t).
Becomes smaller. In order to obtain good wettability of the test piece, it is necessary that the flux is continuously applied to the test piece. If the flux is applied continuously to the test piece, the zero cross time ( The value of t) becomes smaller.

In this embodiment, the conditions shown in Table 1 are set when performing the meniscus test method, and 50 × 10 × 0.5 (thickness) mm is set so that the test can be easily performed under these conditions.
The copper plate (see FIG. 5) was used as a test piece and quantitatively evaluated by measuring a zero cross time (t). In this case, since the meniscus test method does not have a standardized clear standard and it is difficult to evaluate the absolute value, a reference value is set in advance, and evaluation is performed by a comparison test with that value. For reference, a sample was also prepared by a coating method according to a conventional technique and evaluated.

[0044]

[Table 1]

In order to set a reference value in the evaluation, a test piece in which a continuous film of adipic acid was surely formed on the surface of a copper plate was used as a reference sample, and the test piece was prepared by the following method. First, a reference sample on which a continuous film of adipic acid was reliably formed was prepared by the following procedure using a conventional flux not using water as a base material.

(1) Adipic acid was dissolved in IPA (isopropyl alcohol) to prepare an IPA solution of adipic acid. The ratio is 2% by weight of adipic acid and 98% by weight of IPA. (2) A copper plate as a reference sample was immersed in this IPA solution of adipic acid for several seconds and pulled up. (3) After lifting, IPA has a small surface tension and spreads on the surface of the copper plate, and because of its high volatility, it spontaneously evaporates within a few seconds. Was done.

According to the above-mentioned methods (1) to (3), a coating film of adipic acid can be reliably and continuously formed on the surface of the copper plate. The reference sample to which the IPA solution of adipic acid was applied in this manner was subjected to a meniscus test within 5 seconds after application of the solution, and a zero cross time (T _BASE ) as a parameter indicating the meniscus was measured, and this value was used as a reference value. .

Here, when a continuous film of adipic acid is formed on the test piece to which the flux is applied, the zero cross time (t) of the sample is t ≒ T
_BASE . Conversely, when a continuous film of adipic acid has not been formed, the zero cross time (t) of the sample is t≫T _BASE .

Hereinafter, the contents of the meniscus test and the results thereof will be described. Using the spray fluxer of FIG. 2 and the flux application method according to the present embodiment, first, an appropriate amount of a flux based on water was applied to the surface A of the test piece shown in FIG. Subsequently, the flux was applied to surface B corresponding to the back side of surface A within several seconds. A meniscus test was performed within 5 seconds after application on the B side, and a zero cross time was measured. The test piece prepared by this method is referred to as “Sample 1”
The zero cross time of Sample 1 was set to (t ₁ ). On the other hand, using the spray fluxer shown in FIG. 7, a test piece obtained by applying a water-based flux in the same procedure as that of the sample 1 and measuring the zero-cross time by the method of the prior art was referred to as “sample 2”. And the zero cross time of Sample 2 was (t ₂ ).

Table 2 and FIG. 6 show the measurement results of the zero cross times of the reference sample, sample 1 and sample 2 by the meniscus test.
Shown in Compared to Sample 1 zero cross time (t ₁₎ the zero crossing time of the reference sample (the test piece was applied with a method according to the embodiment) (T _BASE), sample 1, an average value of zero cross time (t ₁₎ 1.29 seconds,
The average value of the zero cross time (T _BASE ) of the reference sample is almost the same as 1.04 seconds, and therefore, t ₁ ≒
T _BASE is established. Therefore, it can be inferred that a continuous film of adipic acid was formed.

Similarly, comparing the zero cross time (t ₂ ) of sample ₂ (the test piece coated by the method according to the prior art) with the zero cross time (T _BASE ) of the reference sample, sample 2 has a zero cross time (t ₁ ). Has an average value of 2.98 seconds, which is higher than the average value of the reference sample zero-cross time (T _BASE ) of 1.04 seconds.
₂ ≫T _BASE . Therefore, it can be inferred that a continuous film of adipic acid was not formed.

[0052]

[Table 2]

From the above two results, in the flux coating method according to the present embodiment, the water-based flux can form a continuous film of adipic acid at the same level as the IPA-based flux. There was found. This is because (a) the flux fine particles adhere to the electrode portion of the circuit board, and (b) the moisture contained in the attached flux evaporates quickly, whereby the flux is condensed.
(C) The actions (a) to (c) in which only the adipic acid as the active ingredient remains are repeated without the flux fine particles adhering to each other, and as a result, the adipic acid continuous on the circuit board is formed. This is because a coating was formed.

As described above, according to this embodiment,
At room temperature, in order to set the application conditions so that the diameter of the flux fine particles when adhering to the circuit board does not exceed 30 μm,
Moisture evaporates in a short time from the flux fine particles attached to the circuit board, and the flux fine particles do not adhere to each other. As a result, a continuous flux active component film is formed on the circuit board, and the wettability of the solder is reduced. And good soldering can be performed.

In this embodiment, the case where the temperature is 25 ° C. has been described. However, if the room temperature is 40 ° C. or less, it is possible to apply a flux having good solderability. On the other hand, when the temperature exceeds 40 ° C., there is a problem such as a clogged nozzle. Further, in this embodiment, as the application conditions, the spray pressure is 0.1 MPa and the distance between the circuit board and the spray nozzle is 50 mm. However, if the flux application amount is 0.15 cc / min or less per square centimeter, the application is performed. The condition does not matter.

(Embodiment 2) In this embodiment, the spray fluxer shown in FIG. 2 is installed in a dry environment at a temperature of 25 ° C. and a humidity of 30% RH. After setting the conditions, a flux containing water as a base material is applied to the circuit board, and the same as in Embodiment 1,
An image of the flux fine particles adhering to the circuit board enlarged and displayed by a microscope was recorded by a video camera, and the state of the change of the adhesion and evaporation of the flux fine particles was observed by slow reproduction or stationary. As a result, no change was observed in the diameter of the flux fine particles immediately after the attachment, but it was found that the evaporation time of water was shorter than the evaporation time shown in FIG.

Thereafter, the surface of the electrode portion on the circuit board was enlarged and observed. As a result, as in the first embodiment, adipic acid as an active ingredient remained as a continuous body on the surface of the electrode portion. I was able to confirm that I was there.

Further, in order to quantitatively prove that a continuous adipic acid film was formed, the first embodiment was used.
A meniscus test was performed and evaluated in the same manner as described above. As a result, almost the same results as in the first embodiment were obtained. As a result, it was found that a continuous coating film of adipic acid can be formed by applying the flux fine particles to the circuit board in a dry atmosphere.

[0059]

According to the first aspect of the present invention, a coating of the active component of the flux can be continuously formed on the circuit board. Therefore, damage to the electronic components and uneven coating due to a decrease in the activity of the flux can be achieved. Can be prevented, and good solderability can be obtained. In addition, since heating means is not required, equipment for coating can be simplified.

According to the second aspect of the present invention, since the flux fine particles adhere to the circuit board in a dry atmosphere, the evaporation speed of the attached fine particles is increased, and more fine particles adhere to the circuit board. be able to. Therefore,
In addition to the effect of the first aspect, it is possible to obtain a film of the active ingredient of the flux at an early stage.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between a particle diameter and an evaporation time in Embodiment 1.

FIG. 2 is a cross-sectional view of a spray fluxer used for flux application according to the embodiment.

FIG. 3 is a partially cutaway perspective view of a spray nozzle.

FIG. 4 is a measurement graph of a meniscus test.

FIG. 5 is a perspective view of a test piece.

FIG. 6 is a characteristic diagram of a meniscus test result in the first embodiment.

FIG. 7 is a sectional view of a conventional spray fluxer.

FIG. 8 is a sectional view of a spray nozzle used for a conventional spray fluxer.

Claims (2)

[Claims] 1. A method of applying a flux containing water as a base material to a circuit board, wherein the flux fine particles adhere to the circuit board at room temperature to reduce the diameter of the flux fine particles attached to the circuit board to 30 μm. A flux coating method characterized by the following. 2. A method for applying a flux to the circuit board, comprising:
The flux coating method according to claim 1, wherein the flux coating is performed in a dry atmosphere.