JP3933879B2 - Method for preventing oxidation of molten solder in water vapor atmosphere - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention is a method for preventing oxidation of molten solder.To the lawRelated.
[0002]
  like thisAn inert gas such as nitrogen gas is used for the purpose of realizing oxidation prevention. That is, the atmosphere is replaced with an inert gas to form an inert gas atmosphere having a low oxygen concentration, and soldering is performed while preventing oxidation of the solder and the soldered portion in this atmosphere.
[0003]
However, nitrogen gas purchased in a cylinder is expensive and has the problem of increasing running costs. In addition, the PSA type and membrane separation type nitrogen gas generators are also expensive, and there is a problem of increasing the initial cost at the time of introduction.
[0004]
[Prior art]
It is known that molten solder easily oxidizes in the atmosphere, and the oxide of the molten solder formed on the surface reduces the solderability (wettability) of the printed wiring board. In addition, it is known that this oxide is drastically consumed as dross that does not produce added value.
[0005]
Therefore, when soldering a workpiece to be soldered with many electronic components such as a printed wiring board and having many fine soldered parts, soldering must be performed in an inert gas atmosphere with a low oxygen concentration. Has been done. Thereby, generation | occurrence | production of dross can also be prevented (suppressed), ensuring favorable solderability.
[0006]
Examples of techniques for soldering a printed wiring board in such an inert gas atmosphere include, for example, the technique disclosed in Japanese Utility Model Publication No. 57-9010 and the technique disclosed in Japanese Patent No. 2832566. That is, an inert gas such as nitrogen gas is supplied into a chamber covered by a “cover” or “container” to form an inert gas atmosphere having a low oxygen concentration, and soldering is performed in this atmosphere. This is a technology that has been configured.
[0007]
Further, in such an inert gas atmosphere with a low oxygen concentration, oxidation of the soldered portion of the printed wiring board is prevented, and solderability is further improved. In addition, since no oxide is generated on the surface of the molten solder, the fluidity of the molten solder is improved, and the molten solder is reliably supplied to a fine soldered portion, thereby improving the solderability.
[0008]
[Problems to be solved by the invention]
However, since it is necessary to supply nitrogen gas along with the soldering operation, there is a problem of raising the production cost associated with the soldering operation. In addition, the nitrogen gas supplied to the cylinder is expensive, and the PSA type and membrane separation type nitrogen gas generators are also expensive.
[0009]
On the other hand, although it is known that water vapor forms a weak inert atmosphere, there has been a problem that the water promotes oxidation of an object such as a workpiece. In particular, many electronic components have low resistance to moisture, and a specific technique using a water vapor atmosphere for soldering a printed wiring board on which a large number of electronic components are mounted has not been put into practical use.
[0010]
The object of the present invention is to establish a technology for forming an inert atmosphere at low cost to prevent oxidation of workpieces, etc., and to prevent the oxidation of molten solder and improve the solderability of printed wiring boards equipped with a large number of electronic components. It is to be able to realize at running cost.
[0011]
[Means for Solving the Problems]
  The present inventionMolten solder andIt is characterized in that a water vapor atmosphere can be used so as not to oxidize workpieces and electronic parts.
  That is,This is a method for preventing the molten solder from being oxidized by the water vapor atmosphere in which a water vapor atmosphere that does not cause water vapor condensation is formed around the molten solder to prevent oxidation of the molten solder.
[0012]
  When the water vapor condenses, it liquefies and adheres to the workpiece or object to promote oxidation. However, if a water vapor atmosphere is formed so as not to cause condensation of water vapor, it is possible to prevent the workpiece and the object from being oxidized. That is, oxidation of the molten solder can be prevented.
  For this purpose, a supply means for covering the molten solder with a shielding means heated to a temperature equal to or higher than the boiling point of water, maintaining the atmospheric temperature inside the shielding means at a temperature equal to or higher than the boiling point of water, and supplying water vapor to the shielding means An outlet and a discharge port for discharging the atmosphere inside the shielding means to the outside are provided, the pressure inside the shielding means is maintained at atmospheric pressure, and water vapor is supplied from the supply port to the inside of the shielding means. Around molten solder covered with shielding meansIn that atmosphereA steam atmosphere that does not cause condensation of water vapor is formed to prevent oxidation of the molten solder.
[0013]
  Thus, by maintaining the temperature of the shielding means and the atmospheric temperature inside the shielding means at a temperature equal to or higher than the boiling point of water, and further maintaining the pressure inside the shielding means at atmospheric pressure by the discharge port, Even if water vapor is supplied from the supply port to the inside of the shielding means, the water vapor does not condense inside the shielding means. Therefore, it is possible to prevent the molten solder covered by the shielding means from being oxidized..
[0023]
DETAILED DESCRIPTION OF THE INVENTION
  Method for preventing oxidation of molten solder by steam atmosphere according to the present inventionLaw isIt can be implemented in the following example embodiments. The work to be soldered is a printed wiring board on which a large number of electronic components (chip-type electronic components, lead-type electronic components, mechanical components, etc.) are mounted.
(1) Embodiment-1
With reference to FIG. 1 and FIG. 2, Embodiment-1 of this invention is demonstrated. FIG. 1 is a perspective view for explaining the entire soldering apparatus used in Embodiment-1 of the present invention, and FIGS. 2 (a) and 2 (b) are longitudinal sectional views of FIG. In addition, the control system (control part and drive part) of the water supply pump in FIG. 2A is a view showing a longitudinal section of FIG. 1, while FIG. 2B is a view showing another example of the attachment of the antioxidant chamber.
[0024]
That is, the molten solder 2 heated and melted by a heater (not shown) is accommodated in a solder tank 1 made of, for example, a stainless steel member, and the molten solder 2 is pumped by a motor 3 (a joint 4 and a pump shaft 5). The pump is rotated through the suction port 7 and supplied to the blow body 8, and the molten solder 2 is jetted from the blow port 9 to form a jet wave 10. The temperature of the molten solder 2 is usually around 250 ° C.
[0025]
On the other hand, as a shielding means for covering the liquid surface of the molten solder 2, an antioxidant chamber 11 is provided to cover a region where the pump shaft 5 is in contact with the liquid surface of the molten solder 2, and the skirt portion 12 of the antioxidant chamber 11 is connected to the molten solder. 2 (see FIG. 2 (a)), and the pump shaft 5 is configured to be fitted to the pump shaft insertion hole 13 through which the antioxidant chamber 11 is inserted, leaving a slight gap. Thus, the pump shaft 5 is configured to shield the region in contact with the liquid surface of the molten solder 2.
[0026]
A water vapor supply pipe 14 for supplying water vapor from the supply port 17 into the oxidation prevention chamber 11 is connected to the oxidation prevention chamber 11, and a water vapor discharge port 15 is provided at the periphery below the oxidation prevention chamber 11. The water vapor supply pipe 14 is covered with a heat insulating material 16 that prevents the temperature of the water vapor from decreasing.
[0027]
On the other hand, a water vapor generation chamber 18 similarly made of a stainless steel member or the like is provided in close contact with the solder tank 1 made of a stainless steel material or the like for containing the molten solder 2, and the water stored in the water tank 19. Is supplied to the water vapor generation chamber 18 through a water supply pipe 21 by a water supply pump 20. In addition, the control part 22 (computer system etc.) and the drive part 23 (electric power drive circuit) which drive the water supply pump 20 become the predetermined | prescribed predetermined fixed flow volume with which the flow volume of the water supplied by this water supply pump 20 is predetermined. It is comprised as mentioned above and is selected according to the kind of water supply pump 20 to be used.
[0028]
When the water vapor supply device 25 is configured as described above, the water vapor generation chamber 18 provided in close contact with the solder bath 1 is heated to a temperature equivalent to that of the molten solder 2, that is, a temperature of about 250 ° C. The water supplied to 18 boils in the water vapor generation chamber 18 to generate water vapor. The flow path forming plate 24 provided in the water vapor generation chamber 18 is a member for completely heating (about 250 ° C.) and supplying the water vapor generated in the meandering flow path. Is supplied to the antioxidant chamber 11 through the steam supply pipe 14.
[0029]
The inner diameter of the steam supply pipe 14 is selected to be sufficiently large with respect to the steam supply flow rate, and is selected to such an extent that no pressure loss occurs with the steam supply. That is, the water vapor supplied from the water vapor generation chamber 18 is supplied to the oxidation prevention chamber 11 at a pressure approximately equal to the atmospheric pressure, and then discharged from the discharge port 15.
[0030]
In this case, the oxidation prevention chamber 11 in which the skirt portion 12 is immersed in the molten solder 2 is maintained at a temperature of about 250 ° C. equivalent to the molten solder 2. That is, the atmospheric temperature in the antioxidant chamber 11 is about 250 ° C. and the temperature of water vapor supplied into the acid prevention chamber 11 is about 250 ° C. The water vapor pressure does not drop rapidly.
[0031]
Accordingly, a water vapor atmosphere having a low oxygen concentration is formed in the oxidation prevention chamber 11, and water vapor condensation does not occur in the water vapor atmosphere, so that the oxidation of the molten solder 2 covered with the oxidation prevention chamber 11 is prevented. Will be able to.
[0032]
As a result, the molten solder 2 and the atmosphere are agitated in a region where the rotating pump shaft 5, the liquid surface of the molten solder 2 and the atmosphere on the liquid surface are in contact with each other. Significant progress will be suppressed.
[0033]
Moreover, since the gas used to form the low oxygen concentration atmosphere is water vapor and the raw material is water, it is possible to form an atmosphere with a low oxygen concentration at any time and anywhere at a very low cost.
[0034]
Incidentally, it has been confirmed that the oxygen concentration in the antioxidant chamber 11 can be reduced to about 20 ppm by the water vapor atmosphere. In addition, the amount of oxide of molten solder 2 generated by continuous operation for 36 hours is drastically reduced to about 1/30 of the amount of oxide generated in the atmosphere, and an inert gas such as nitrogen gas is supplied to reduce the oxygen concentration. Compared to the case where the atmosphere is formed, the result is inferior.
[0035]
In another example shown in FIG. 2B, the skirt portion 12 of the antioxidant chamber 11 is configured to have a gap slightly away from the liquid surface of the molten solder 2, and this gap is formed in the antioxidant chamber 11. It is the example comprised as the discharge port 15 of the inside atmosphere.
[0036]
Therefore, since the oxidation prevention chamber 11 is not heated from the molten solder 2, the plate heater 26 is provided on the upper wall of the oxidation prevention chamber 11 so as to heat it.
[0037]
In this example, the temperature of the antioxidant chamber 11 can be adjusted by adjusting the power supplied to the plate heater 26. As a result, the atmospheric temperature in the antioxidant chamber 11 can also be adjusted, but this atmospheric temperature is also affected by the temperature of the molten solder 2.
[0038]
In the above example, a heater (not shown) used as a heating source for the water vapor generation chamber 18 for generating water vapor is used to hold the solder in a molten state by being immersed in the solder bath 1 itself, that is, the molten solder 2. However, a special heater may be provided for generating water vapor.
[0039]
That is, the steam generation chamber 18 may be provided independently of the solder bath 1 and the steam generation chamber 18 may be provided with a dedicated heater for steam generation and further for steam heating. In this case, there is an advantage that the temperature of the generated water vapor can be arbitrarily adjusted and controlled, but the cost slightly increases.
[0040]
The most important thing is to avoid creating an atmosphere in the antioxidant chamber 11 that causes condensation of water vapor. For this purpose, the pressure of the steam atmosphere in the steam supply path and the oxidation prevention chamber 11 should not be lowered rapidly or its temperature should not be lowered rapidly. This is because when the water vapor condenses, an atmosphere in which the water vapor is atomized or dew-dropped is formed, and an atmosphere that promotes oxidation is formed on the contrary by the adhesion of water.
[0041]
Therefore, in the example shown in FIG. 2B, the temperature of the antioxidant chamber 11 heated by the plate heater 26 may be set higher than the temperature of the water vapor supplied into the antioxidant chamber 11. In addition, the thickness of the water vapor supply pipe 14 that connects the water vapor generation chamber 18 and the oxidation prevention chamber 11 is made large so that pressure loss does not occur with the supply of water vapor. Further, the steam supply pipe 14 is configured to be covered with a heat insulating material so that the temperature of the steam supply pipe 14 does not decrease.
[0042]
In the example shown in FIG. 1 and FIGS. 2A and 2B, the thickness of the water vapor supply pipe 14 and the size of the discharge port 15 provided in the antioxidant chamber 11 are sufficiently increased with respect to the water vapor supply flow rate. There is no pressure loss that causes condensation of water vapor in the flow path. That is, the pressure of each part is configured to be approximately atmospheric pressure.
(2) Embodiment-2
Embodiment-2 of this invention is demonstrated with reference to FIG. 3 and FIG. 3 is a perspective view for explaining the entire soldering apparatus used in Embodiment-2 of the present invention, and FIG. 4 is a view showing a longitudinal section of FIG. 2 and the inside of the antioxidant chamber. (A) is a figure which shows the longitudinal cross-section of FIG. 3, FIG.4 (b) is the perspective view which cut | disconnected some antioxidant chambers and showed the mode of the inside.
[0043]
In addition, the control system (control part and drive part) of the water supply pump in FIG. 3 is drawn with the block diagram.
[0044]
This embodiment example-2 is an example in which the technique for preventing oxidation of molten solder in a steam atmosphere according to the present invention is used in the technique of Japanese Patent Application Laid-Open No. 2000-277903, but soldering for forming the jet wave 10 of the molten solder 2 In the point which is an apparatus, it is the same as that of Embodiment-1.
[0045]
The difference from the first embodiment is that the motor 31 for driving the pump 30 can be provided on the lower side of the solder bath 1. That is, a pipe 32 that communicates between the bath bottom 1a of the solder bath 1 and the liquid level of the molten solder 2 is provided as a waste body of the molten solder 2, and the hollow pump shaft 34 is provided on the pipe 32 through the drive shaft 33. And a pump 30 provided on the hollow pump shaft 34 is rotationally driven.
[0046]
And in order to prevent the oxidation of the molten solder 2 which is easy to generate | occur | produce in the area | region where the hollow pump shaft 34, the liquid level of the molten solder 2, and air | atmosphere contact similarly to the example 1 of embodiment, the antioxidant which covers the said area | region A chamber 28 is provided.
[0047]
The antioxidant chamber 28 has a skirt portion 29 immersed in the molten solder 2 and is connected to a water vapor supply pipe 14 covered with a heat insulating material 16 for supplying water vapor into the antioxidant chamber 28. It is. The hollow pump shaft 34 that appears on the liquid surface of the molten solder 2 is provided with a through hole 35, and the space between the pipe 32 and the drive shaft 33, which is a discharge body for the molten solder 2, is provided. The solder tank 1 communicates with the space below the tank bottom 1a. That is, the opening between the bath bottom 1a of the solder bath 1 and the drive shaft 33 becomes the discharge port 36 of the water vapor atmosphere.
[0048]
The means for supplying water vapor at a desired constant flow rate (water vapor generation chamber 18, water supply pump 20, water supply pipe 21, water tank 19, control unit 23 and drive unit 22 of water supply pump 20) This is the same as Embodiment-1.
[0049]
Accordingly, as in the first embodiment, a water vapor atmosphere that does not cause condensation can be formed in the antioxidant chamber 28, and the oxidation of the molten solder 2 covered by the antioxidant chamber 28 is prevented. Will be able to. That is, since a water vapor atmosphere with a low oxygen concentration is formed in the oxidation prevention chamber 28 and no water vapor condensation occurs in the water vapor atmosphere, oxidation of the molten solder 2 covered with the oxidation prevention chamber 28 is prevented. Will be able to.
[0050]
As a result, the molten solder 2 and the atmosphere are agitated in a region where the rotating hollow pump shaft 34 and the liquid surface of the molten solder 2 are in contact with the atmosphere on the liquid surface, thereby oxidizing the molten solder 2 generated thereby. The remarkable progress of will be suppressed.
[0051]
Moreover, since the gas used to form the low oxygen concentration atmosphere is water vapor and the raw material is water, it is possible to form an atmosphere with a low oxygen concentration at any time and anywhere at a very low cost.
(3) Embodiment-3
Embodiment 3 of the present invention will be described with reference to FIG. FIG. 5 is a view showing a soldering system for explaining the embodiment example 3. FIG. 5 (a) is a side sectional view of the soldering system, and the water vapor generation system and the exhaust system are drawn as symbol diagrams. FIG.5 (b) is a figure which shows the cross section of the conveyance conveyor of a solder tank upper part.
[0052]
This Embodiment-3 is a soldering system having a soldering device 40, a preheating device 41, and a transfer conveyor 42 as the main components. A low oxygen concentration water vapor atmosphere is used in the soldering process in which the soldering device 40 is provided. 1 is an example of a soldering system configured to form.
[0053]
As the soldering device 40, the soldering device shown in the above-described Embodiment-1 and Embodiment-2 can be used. The preheating device 41 is provided with a preheating heater 44 for heating the printed wiring board 43 which is a work to be soldered by infrared rays, hot air or the like, and the upper surface of the printed wiring board 43 in FIG. Is also provided with a reflector 45 for heating sufficiently.
[0054]
The conveyer 42 is provided in two parallel strips and is configured to hold both side ends of the printed wiring board 43, and includes a preheating process in which the preheating device 41 is provided and a soldering process in which the soldering device 40 is provided. These are means for transporting the printed wiring board 43 sequentially in the direction of arrow A, and have the same configuration as that of a commonly used transport conveyor. That is, it is a mechanism in which both side ends of the printed wiring board 43 are held and conveyed by holding claws 48 provided on a chain 47 that is guided by the conveyor frame 46 and rotates.
[0055]
In order to form a low oxygen concentration water vapor atmosphere in the soldering process, the soldering apparatus 40 is covered with an antioxidant chamber 49. The antioxidant chamber 49 is provided with a carry-in port 50 and a carry-out port 51 through which the transport conveyor 42 passes, and the skirt portion 52 is immersed in the molten solder 2 of the soldering device 40.
[0056]
A plate heater 53 is provided on the upper wall of the oxidation prevention chamber 49. The purpose of the plate heater 53 is the same as that of the plate heater 26 used in FIG. 2 (b), whereby the temperature of the large antioxidant chamber 49 that is easily cooled is maintained at a temperature equal to or higher than the boiling point of water. Or it is kept at the same temperature as the molten solder 2. That is, even if the skirt portion 52 is immersed in the molten solder 2, the oxidation chamber 49 is large, so that the temperature is lowered at the upper portion and it is difficult to maintain the temperature above the boiling point of water. It is.
[0057]
On the other hand, a sheathed heater 54 is provided in the conveyor frame 46 of the conveyor 42 passing through the antioxidant chamber 49, particularly in the area of the soldering device 40, and the temperature of the conveyor 42 is maintained in the antioxidant chamber 49. The temperature is higher than the boiling point of water (for example, 100 ° C. or a temperature equivalent to that of the molten solder 2). The sheathed heater 54 may be provided over the entire length of the transport conveyor 42.
[0058]
In this way, the plate heater 53 is provided in the oxidation prevention chamber 49 and the sheath heater 54 is provided in the transfer conveyor 42 and heated, so that the atmospheric temperature in the oxidation prevention chamber 49, the transfer conveyer 42 and the oxidation prevention chamber 49 is reduced to water. It becomes possible to maintain the temperature above the boiling point (for example, 100 ° C. or a temperature equivalent to the molten solder 2). The heaters 53 and 54 are configured so as to have the same temperature as possible by a temperature control device (not shown) so that unnecessary thermal convection of the atmosphere and condensation of water vapor do not occur in the oxidation prevention chamber 49. This is desirable.
[0059]
Further, the temperature of the water vapor supplied from the water vapor generation chamber 18 rapidly decreases in the supply process and in the oxidation prevention chamber 49, or the pressure of the water vapor supplied from the water vapor generation chamber 18 decreases in the supply process and the oxidation prevention chamber. In order to prevent the water vapor from condensing in the water vapor atmosphere formed in the antioxidant chamber 49, it is necessary to prevent the water from being rapidly lowered in the water 49. This is the same as the matter described in the first embodiment and the second embodiment.
[0060]
On the other hand, the configuration of the water vapor supply device 25 is the same as that of the embodiment-1 and the embodiment-2, and the water vapor generation chamber 18 is provided in close contact with the solder bath 2, and is provided in the solder bath 2. Water is heated by heat conduction from the molten solder 2 heated by a heater (not shown) to generate water vapor, and the water vapor is heated.
[0061]
The water vapor generation chamber 18 is stored in a water tank 19, a water supply pump 20, a drive unit 23 and a control unit 22 that drive and control the water supply pump 20, and a water tank 19 so that a predetermined flow rate of water per unit time can be supplied. And water 55.
[0062]
On the other hand, the water vapor generated in the water vapor generation chamber 18 is supplied into the oxidation prevention chamber 49 by the water vapor supply pipe 14 which is kept warm by the heat insulating material 16, and below the transport conveyor 42, that is, near the jet wave 10 of the molten solder 2. It is supplied from a water vapor supply port housing 56 provided toward the soldered surface side of the wiring board 43.
[0063]
The water vapor supplied to the antioxidant chamber 49 flows out and is discharged from the carry-in port 50 and the carry-out port 51 provided in the antioxidant chamber 49. Therefore, an exhaust hood 58 connected to an exhaust fan 57 is provided in the vicinity of the carry-in port 50 and the carry-out port 51, and the water vapor atmosphere discharged from the carry-in port 50 and the carry-out port 51 is removed from the exhaust hood 58. It is a mechanism to exhaust through.
[0064]
A neutralization filter 59 is provided in the exhaust hood 58. As the neutralization filter 59, a normal particle filter such as a filter made of a porous member or a filter formed by a bent flow path can be used. The neutralizing filter 59 is attached or coated with an alkaline material such as lime, and neutralizes the acidic substance in the atmosphere captured by the exhaust hood 58. Acts as follows.
[0065]
By configuring the soldering system as described above, it becomes possible to form a water vapor atmosphere having a low oxygen concentration that does not cause water vapor condensation in the antioxidant chamber 49. Of course, no condensation of water vapor occurs in the oxidation prevention chamber 49 or the transport conveyor 42.
[0066]
For example, when the temperature of the molten solder 2 is 250 ° C., the temperature of the antioxidant chamber 49 and the temperature of the transfer conveyor 42 are kept at about 150 ° C., and the atmospheric temperature in the antioxidant chamber 49 is also about 120 to 200 ° C. And water vapor at about 110 to 200 ° C. may be supplied. Further, since the size of the carry-in port 50 and the carry-out port 51 of the oxidation prevention chamber 49 is large enough to pass through the transfer conveyor 42, the pressure in the oxidation prevention chamber 49 is maintained at substantially the same pressure as the atmospheric pressure. The
[0067]
When the printed wiring board 43, which is a work to be soldered, is to be soldered, the printed wiring board 43 is first heated by the preheating device 41. The preheating temperature of the printed wiring board 43 is changed to water. The heating temperature is set so that it is heated to a temperature not lower than the boiling point, for example, a temperature of about 110 ° C. to 150 ° C. and carried into the oxidation prevention chamber 49. That is, the heating temperature is set by adjusting the temperature of the preheating heater 44 of the preheating device 41. In this case, the temperature of the electronic component mounted on the printed wiring board 43 is also heated to a temperature equal to or higher than the boiling point of water before being carried into the oxidation prevention chamber 49.
[0068]
Thus, by organizing the soldering system and the soldering process, the printed wiring board 43 in the low oxygen concentration water vapor atmosphere does not occur in the printed wiring board 43 carried into the oxidation prevention chamber 49 without causing water vapor condensation. And the jet wave 10 of the molten solder 2 are brought into contact with each other, and the printed wiring board 43 can be soldered. That is, soldering can be performed in an atmosphere having a low oxygen concentration without causing condensation of water vapor in a soldering process in which the printed wiring board 43 and the jet wave 10 of the molten solder 2 are in contact with each other.
[0069]
Therefore, good wettability soldering can be performed in a state where oxidation of the molten solder 2 is suppressed. That is, soldering with excellent solderability can be performed. Moreover, since the raw material for forming the low oxygen concentration atmosphere is water, it can be realized anytime and anywhere at low cost.
[0070]
By the way, the soldering surface of the printed wiring board 43 that is the work to be soldered, that is, the lower surface in contact with the jet wave 10 of the molten solder 2 is preliminarily coated with flux in order to improve solderability. . This flux vaporizes or generates fumes when it comes into contact with the jet wave 10 of the molten solder 2, but is guided to the exhaust hood 58 together with the water vapor atmosphere discharged from the carry-in port 50 and the carry-out port 51 of the antioxidant chamber 49. Exhausted.
[0071]
On the other hand, if halogen is contained in the flux, the vaporized or fumed halogen is discharged from the carry-in port 50 and the carry-out port 51 of the oxidation prevention chamber 49 and then melts into the condensed water vapor due to the temperature drop. This produces acidic mist and dew drops. The acidic mist droplets and dew droplets are captured by a neutralization filter 59 provided in the exhaust hood 58 and neutralized with an alkaline neutralizer. Therefore, the atmosphere exhausted by the exhaust fan 57 does not affect the environment.
(4) Embodiment-4
With reference to FIG. 6, Embodiment-4 of this invention is demonstrated. FIG. 6 is a diagram illustrating another soldering system, and shows a side sectional view of the soldering system. In addition, the steam generation system and the exhaust system are drawn as symbol diagrams in the same manner as in Embodiment-3 shown in FIG.
[0072]
The difference between the soldering system of the embodiment-4 and the soldering system of the embodiment-3 is that the preheating unit including the preheating device 41 is covered with the oxidation prevention chamber 49. In connection with this, it is provided that a sheathed heater 54 for heating the conveyor 42 is provided over the entire length of the transport conveyor 42, and that the water vapor condenses in the antioxidant chamber 49 on the printed wiring board 43 carried into the antioxidant chamber 49. In order to prevent this, the anti-condensation heating device 61 for the printed wiring board 43 is provided in front of the carry-in port 50 of the antioxidant chamber 49, and the printed wiring board 43 carried out from the carry-out port 51 of the antioxidant chamber 49 is dried. This is because a drying accelerating device 62 is provided.
[0073]
Further, in the oxidation prevention chamber 49, a water vapor supply port housing 56 is provided in the preheating device 41 so that water vapor is supplied also to the preheating process section. The suppression plate 63 provided in the antioxidant chamber 49 is a member for forming a so-called labyrinth flow path to suppress unnecessary atmospheric flow in the antioxidant chamber 49.
[0074]
As described above, by accommodating the preheating step and the soldering step in the oxidation prevention chamber 49, the atmosphere in the oxidation prevention chamber 49 is also heated by the preheating heater 44 of the preheating device 41. However, there is a temperature drop due to the increase in the size of the antioxidant chamber 49. Therefore, in this example, the plate heaters 53 are provided at two locations of the antioxidant chamber 49 so that the entire antioxidant chamber 49 can be maintained at a temperature equal to or higher than the boiling point of water.
[0075]
Since the preheating heater 44 is usually heated to a temperature of 200 ° C. or higher, it is not necessary to provide a separate heating means for preventing the condensation of water vapor. Therefore, the temperature of the atmosphere in the oxidation prevention chamber 49, the transfer conveyor 42, the preheating heater 44, and the oxidation prevention chamber 49 can be kept above the boiling point of water. In addition, about this temperature, the temperature range (for example, about 120 to 200 degreeC) as illustrated in the said Example-3 is practical.
[0076]
Therefore, as in Embodiment-1 and Embodiment-2, the water vapor generation chamber 18 and its supply system and the oxidation prevention chamber 49 do not cause a rapid decrease in the water vapor pressure or a rapid decrease in the water vapor temperature. In addition, it is possible to form a water vapor atmosphere having a low oxygen concentration that does not cause water vapor condensation in the oxidation prevention chamber 49.
[0077]
On the other hand, an anti-condensation heating device 61 provided with a heater 65 with a carry-in conveyor 64 sandwiched in the chamber 66 is provided in front of the carry-in port 50 of the anti-oxidation chamber 49, and the printed wiring board 43 as the work to be soldered is placed in the water It is configured to be heated into the oxidation prevention chamber 49 after being heated to the boiling point or higher. Therefore, no condensation of water vapor occurs on the printed wiring board 43 in the antioxidant chamber 49.
[0078]
The printed wiring board 43 is heated to, for example, about 150 ° C. by the preheating heater 44, and then the soldered surface is brought into contact with the jet wave 10 of the molten solder 2 to be soldered. Since these processes are performed in a water vapor atmosphere having a low oxygen concentration, a soldering environment similar to that in a low oxygen concentration atmosphere to which an inert gas such as nitrogen gas is supplied can be obtained. That is, it is possible to perform soldering without oxidation of the soldered portions of the molten solder 2 and the printed wiring board 43, that is, soldering with good wettability. In addition, since the raw material of water vapor forming the low oxygen concentration atmosphere is water, it can be realized at any cost anywhere.
[0079]
In this way, the soldering operation of the printed wiring board 43 is performed in an atmosphere that does not cause condensation of water vapor, and is performed in such a manner that no condensation of water vapor occurs on the printed wiring board 43 as well. However, a three-dimensional shape is formed on the printed wiring board 43 due to the shape and size of electronic components (not shown) mounted on the printed wiring board 43, and a water vapor atmosphere remains in the corner. If it is unloaded from the unloading port 51 of the oxidation prevention chamber 49, water vapor may be condensed on the printed wiring board 43 thereafter.
[0080]
Therefore, in order to prevent this, a drying accelerating device 62 is provided in the vicinity of the carry-out port 51 of the oxidation prevention chamber 49, and for example, air for accelerating drying toward the printed wiring board 43 carried out from the carry-out port 51. It is configured to spray. As this air, dry air or hot air with low humidity is suitable. That is, by blowing dry air or hot air on a carry-out conveyor 67 provided at the carry-out port 51 with a fan 69 provided with a heater 68, the water vapor atmosphere remaining in the corner of the printed wiring board 43 is blown off simultaneously. Even a small amount of remaining water can be immediately dried.
(5) Embodiment-5
With reference to FIG. 7, the soldering system of Embodiment-5 of this invention is demonstrated. FIG. 5 is a view for explaining another soldering system, and shows a side sectional view of the soldering system. In addition, the steam generation system and the exhaust system are drawn with symbol diagrams in the same manner as in Embodiment-3 of FIG.
[0081]
This embodiment example-5 is an example in which the technique of the present invention is applied to a reflow soldering apparatus. The difference from a conventional reflow soldering apparatus using nitrogen gas or the like is that a neutralizing filter 78 is used as a flux fume removal filter and that a condensation prevention heating apparatus 61 is provided upstream of the carry-in port 50 of the furnace body 71. And that a drying promoting device 62 similar to that of the fourth embodiment is provided in the vicinity of the carry-out port 51 of the furnace body 71. Of course, a water vapor generating device 25 for forming a low oxygen concentration atmosphere is provided. The heating furnace 71 also serves as an oxidation prevention chamber.
[0082]
This reflow soldering apparatus includes a preheating process part 72 and a reflow process part 73 inside a heating furnace 71, and the preheating process part 72 is further composed of a temperature raising part 74 and a temperature equalizing part 75. ing. Each process is provided with heating means 76 for heating the printed wiring board 43 as a work to be soldered.
[0083]
Although this heating means 76 is provided facing the upper and lower sides of the conveyor 42 that conveys the printed wiring board 43, that is, both surfaces of the printed wiring board 43, the heating means 76 is provided with the heating means 76 provided only on the upper side or the lower side. There is also.
[0084]
As the heating means 76, a hot wire heating means such as infrared rays, a hot air heating means for blowing a hot air atmosphere, a heating means using both hot wire heating and hot air heating, etc. are widely used. In FIG. 7, the specific configuration of the heating means is omitted and not shown.
[0085]
Usually, the printed wiring board 43 is heated to about 150 ° C. in the preheating process section 72, and then the printed wiring board 43 is heated to about 210 to 250 ° C. in the reflow process section 73. Soldering is performed by melting previously supplied solder (not shown). Therefore, the temperature of the atmosphere in the furnace body 71 of the reflow soldering apparatus, the conveyance conveyor 42, and the furnace body 71 is hold | maintained at about 150-250 degreeC at least.
[0086]
However, a temperature drop may occur in a part of the furnace body 71, the carry-in entrance 50 part or the carry-out exit 51 part of the transport conveyor 42, and there is a possibility that water vapor condenses in the part. In such a case, as in each of the above-described embodiments, the portion is provided with a heating means so that the temperature is equal to or higher than the boiling point of water.
[0087]
Further, since the length of the steam supply pipe 14 for supplying steam to each heating chamber of the furnace body 71 is increased, a heater (not shown) is provided not only on the heat insulating material 16 but also on the steam supply pipe 14 itself. It is good to comprise so that it may be covered with the heat insulating material 16. The steam generation chamber 18 is provided with a heater (not shown) for heating. As this heater, an electric heater is suitable because of its excellent temperature controllability and the like. However, you may comprise so that water vapor | steam may be generated using the heating by a thermal power. In this case, the water vapor generation cost can be reduced.
[0088]
In this embodiment example-5, the printed wiring board 43, which is a work to be soldered, is first heated to a temperature not lower than the boiling point of water (for example, 110 ° C. or higher) while being conveyed by the carry-in conveyor 64 in the condensation prevention heating device 61. Then, it is transported to a preheating step part 72 (temperature raising part 74 and temperature equalizing part 75) in the furnace body 71 and heated to a temperature of about 150 ° C., for example. Then, it is conveyed to the reflow process part 73, is heated at about 210-250 degreeC, for example, and reflow soldering is performed.
[0089]
Each of these process parts, that is, the preheating process part 72 and the reflow process part 73 are performed in a low oxygen concentration water vapor atmosphere, and can perform reflow soldering with excellent wettability without oxidation of the solder or soldered part. . Moreover, since the raw material for water vapor is water, soldering can be performed in a low oxygen concentration atmosphere at any time and anywhere at low cost.
[0090]
Then, by blowing dry air or hot air to the printed wiring board 43 conveyed from the carry-out port 51 of the furnace body 71 by the drying accelerating device 62, the water vapor atmosphere remaining in the corner of the printed wiring board 43 is blown off. At the same time, any remaining moisture can be dried immediately.
[0091]
Further, water vapor, gasified flux (flux gas) and flux fume discharged from the carry-in port 50 and the carry-out port 51 of the furnace body 71 are captured by the exhaust hood 58 and exhausted. In this case, even if the flux contains halogen, it is captured and neutralized by the neutralization filter 59, so that the atmosphere exhausted by the exhaust fan 57 does not adversely affect the environment.
[0092]
Further, the flux gas (gasified flux) and flux fumes generated in the furnace body 71 are removed by providing a neutralizing filter 78 in the flux recovery filter 77 so that the flux fumes do not stay in the furnace body 71. It is configured. The reason why the neutralizing filter 78 is used here is to prevent the flux from becoming acidic when the trapped flux contains halogen and eroding the flux recovery system.
[0093]
The flux recovery filter 77 includes a neutralization filter 78, a circulation fan 79, a suction port housing 80, a discharge port housing 81, a circulation pipe 83 covered with a heat insulating material 82, and a filter chamber 84. Then, the atmosphere in the heating chamber of the reflow process section 73 where a large amount of gasified flux and flux fumes are generated is circulated to remove flux fumes that are likely to adhere to the furnace body 71, the conveyor 42, the printed wiring board 43 and the like. , Forming a pollution-free atmosphere.
[0094]
【The invention's effect】
  As described above, the method for preventing oxidation of molten solder in the water vapor atmosphere of the present inventionTo the lawAccording to this, there is no need to obtain expensive inert gas from a cylinder or the like, or to provide an expensive inert gas generator such as a nitrogen gas generator. Can be formed at low cost.
[0095]
Moreover, the problem that oxidation is caused by moisture even in a low oxygen concentration atmosphere because of the water vapor atmosphere has been solved by forming the atmosphere so as not to condense the water vapor. In addition, by preheating the printed wiring board, the problem of water vapor condensation in the printed wiring board, which is the work to be soldered, is solved, and soldering work in a water vapor atmosphere of the printed wiring board that is vulnerable to moisture becomes possible. It was.
[0096]
As described above, according to the present invention, a low oxygen concentration atmosphere (low oxygen concentration water vapor atmosphere) can be formed at any time and anywhere to prevent oxidation of molten solder, or to oxidize a soldered portion of a printed wiring board. This makes it possible to perform soldering with good quality and excellent wettability.
[0097]
That is, waste due to oxidation of the molten solder can be suppressed and a good quality soldering operation can be realized at low cost.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view for explaining the whole of a soldering apparatus used in embodiment example-1 of the present invention.
FIG. 2 is a view showing a longitudinal section of FIG.
FIG. 3 is a perspective view for explaining the entire soldering apparatus used in Embodiment-2 of the present invention.
4 is a view showing a longitudinal section of FIG. 3 and the inside of an antioxidant chamber. FIG.
FIG. 5 is a view showing a soldering system for explaining an embodiment-3 of the present invention.
FIG. 6 is a diagram for explaining another soldering system;
FIG. 7 is a diagram for explaining another soldering system;
[Explanation of symbols]
1 Solder bath
1a Tank bottom
2 Molten solder
3 Motor
4 Fitting
5 Pump shaft
6 Pump
7 Suction port
8 Blowhole
9 Air outlet
10 Jet wave
11 Antioxidation chamber
12 Skirt
13 Pump shaft insertion hole
14 Steam supply pipe
15 outlet
16 Insulation material
17 Supply port
18 Steam generation chamber
19 Water tank
20 Water supply pump
21 Water supply pipe
22 Control unit
23 Drive unit
24 flow path forming plate
25 Water vapor supply device
26 Plate heater
28 Antioxidation chamber
29 Skirt
30 pumps
31 motor
32 pipes
33 Drive shaft
34 Hollow pump shaft
35 Through-hole
36 outlet
37 screws
40 Soldering equipment
41 Preheating device
42 Conveyor
43 Printed wiring board
44 Preheating heater
45 Reflector
46 Conveyor frame
47 chain
48 Holding claws
49 Antioxidation chamber
50 carry-in entrance
51 Unloading port
52 Skirt
53 Plate heater
54 Seeds heater
55 water
56 Water vapor supply port housing
57 fans
58 exhaust hood
59 Neutralization filter
61 Pseudo-shrinkage preventing heating device
62 Drying promotion device
63 Deterrent plate
64 Carry-in conveyor
65 Heater
66 chambers
67 Unloading conveyor
68 Heater
69 fans
71 Furnace
72 Preheating process section
73 Reflow Process Department
74 Temperature riser
75 Soaking section
76 Heating means
77 Flux recovery filter
78 Neutralization filter
79 Circulation fan
80 Suction port housing
81 Discharge port housing
82 Thermal insulation
83 Circulation pipe
84 Filter chamber

Claims (1)

A supply port for covering the molten solder by a shielding means heated to a temperature equal to or higher than the boiling point of water, maintaining the atmospheric temperature inside the shielding means at a temperature equal to or higher than the boiling point of water, and supplying water vapor to the inside of the shielding means; An outlet for discharging the atmosphere inside the shielding means to the outside is provided to maintain the pressure inside the shielding means at atmospheric pressure, and water vapor is supplied from the supply port to the inside of the shielding means to the shielding means. A method for preventing oxidation of molten solder in a water vapor atmosphere, characterized by forming a water vapor atmosphere that does not cause vapor condensation in the atmosphere around the covered molten solder to prevent oxidation of the molten solder.

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