JP2997904B2 - Electronic component soldering method - 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 an electronic component, which is used for soldering and fixing a surface mount type electronic component to a printed circuit board.

[0002]

2. Description of the Related Art Conventionally, mounting a surface mount type electronic component on a printed circuit board is mainly performed by wave soldering,
Reflow soldering has been applied.

[0003] Among them, wave soldering applies an adhesive to a component mounting surface of a printed circuit board with a dispenser.
After temporarily fixing the electronic component to the board surface of the printed board with this adhesive, the solder wave heated and fluidized is brought into contact with the mounting surface of the electronic component, and the external terminals of the electronic component and the conductive pattern of the printed board are brought into contact with each other. Are connected and fixed.

In reflow soldering, paste solder in which solder powder and flux are mixed is applied to the component mounting surface of a printed circuit board by screen printing, and the electronic component is mounted on the board surface of the printed circuit board by contacting the paste solder. After that, the paste solder is melted in a reflow furnace to connect and fix a contact point between an external terminal of the electronic component and a conductive pattern on a printed circuit board.

However, in the wave soldering, the solder is fluidized and used. Therefore, if the conductive pattern of the printed circuit board is formed into a fine circuit, a short circuit is likely to occur due to the formation of a solder bridge between adjacent patterns. The melting of the solder requires heating at about 250 to 270 ° C., and the electronic components applicable from this melting temperature are limited.
In addition, since the molten solder is bulged and adhered in an arc shape due to surface tension, not only the amount of adhered solder increases but also it is difficult to control the film thickness. Further, since the molten solder is stored in a stirrer or a tank, there is a disadvantage that the solder is easily contaminated with time.

[0006] In reflow soldering, since paste solder is printed by screen printing, it is difficult to perform appropriate printing in accordance with fine circuits. In addition, since it is difficult to make the temperature distribution in the reflow furnace uniform, mounting displacement of the electronic component is likely to occur due to the difference in surface tension of the remelted solder depending on the location. The melting of the solder requires a high-temperature heat treatment of about 210 to 240 ° C., and not only does the material cost of the paste solder increase due to the presence of the flux, but also the cost increases.
There are drawbacks such as unavoidable contamination of flux by tar.

[0007]

SUMMARY OF THE INVENTION The present invention provides an excellent electronic component which can be soldered at a low temperature and requires a small amount of solder, and is free from contamination by flux tarnish and can cope with a fine circuit pattern. It is an object of the present invention to provide a soldering method.

[0008]

In a method of soldering an electronic component according to the present invention, an oxide film is removed from a surface of a printed circuit board to which the electronic component is soldered and fixed, and after cleaning, the oxide film is removed. Polybutene is applied as a heat medium to the surface of the plate, and further, dispersion solder in which fine-grained solder is dispersed in liquid polybutene is attached to the surface of the plate. An electronic component that is in contact with the conductive pattern of the printed circuit board is temporarily fixed to the board surface of the printed circuit board with an adhesive, and is subjected to a heat treatment in a low-temperature atmosphere to solder and fix the electronic component to the printed circuit board. ing.

[0009]

In this method for soldering electronic components, an oxide film is removed from the surface of the printed circuit board, which is a contact point between the external terminal of the electronic component and the conductive pattern on the printed circuit board.
An antioxidant polybutene is applied to the board surface of the printed circuit board, and a dispersion solder in which fine-grained solder is dispersed in liquid polybutene is attached to a portion of the board surface to which the polybutene is applied, and then the electronic component Is temporarily fixed on the board surface of the printed circuit board with an adhesive, and the heat treatment is performed in a low-temperature atmosphere, so that the electronic components are soldered and fixed to the printed circuit board with the dispersion solder. Solder can be securely fixed by the amount of solder, the cost associated with soldering can be reduced, there is no contamination due to flux dust, etc.Since the dispersion solder dispersion is fine-grained, soldering to fine circuit patterns Can also be applied.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for soldering electronic parts according to the present invention, polybutene is used as a heat medium. This polybutene (also referred to as “polybutylene”) is a polymer of 1-butene and 2-butene (commercially available from Nippon Oil Co., Ltd.), and although the viscosity varies depending on the molecular weight, it is suitable for the present invention at room temperature. Is about 10000 cps and 190-
It is preferable to have a viscosity of about 10 cps at a temperature of 200 ° C. The polybutene has heat resistance, prevents oxidation of the object to be coated, and can be used stably at a temperature of 190 ° C. or more for a long time, and is therefore also preferable as a heat medium for transmitting the heat of the molten solder to the object to be coated.

As the dispersion solder, one obtained by dispersing fine-grained molten solder having an average particle diameter of 10 μm in liquid polybutene is used. This dispersion solder is obtained by adding a solder composition to a liquid polybutene at a weight ratio of 50% by volume or less based on polybutene. If the added amount of the solder composition is large, it is difficult to atomize the solder. Therefore, to obtain a dispersion solder in which molten solder having an average particle diameter of 10 μm is dispersed in liquid polybutene, the solder composition may be added in an amount of 5 Vol% or less. The suspension of the solder composition and the liquid polybutene is heated to 190 ° C. or higher, preferably 19 ° C., in a nitrogen gas or argon gas atmosphere.
The solder is melted by heating to 0 to 200 ° C. and stirred by a homogenizer to obtain a dispersion solder in which the molten solder is uniformly dispersed in liquid polybutene. As the homogenizer, an ultra-high-speed homogenizer (for example, manufactured by Polytron Co., Ltd.) was used, and the above-described suspension was used for 19 hours.
5000 to 30,000 times under a temperature condition of 0 to 200 ° C. /
Stir for a minute. In order to obtain a powder having an average particle diameter of 10 μm by this stirring, the treatment may be performed at 10,000 times / minute or more for about 1 to 5 minutes. When the molten solder is dispersed in the liquid polybutene, the molten solder is not immediately cooled by spraying, which will be described later, so that the molten solder can be attached to the contact point between the electronic component and the printed circuit board in a molten state.

In order to solder an electronic component using the heat medium and the dispersion solder, first, an oxide film is removed from a surface of a printed circuit board to which the electronic component is soldered and fixed, and then a cleaning process is performed. Thereafter, as shown in FIG. 1, a liquid polybutene 2 is applied to the portion of the printed circuit board 1 from which the oxide film has been removed, in order to prevent reoxidation. The polybutene 2 may When toward the plate surface of the printed circuit board 1 by using a dispenser D ₁ injects applied in a dot pattern, the magnitude of the pressure applied to the liquid surface, because it controls the coating amount of the application time of pressure It can be applied properly even in a fine place.

After the application of the polybutene 2, the printed circuit board 1 is made to correspond to the application position of the polybutene 2 as shown in FIG.
The dispersion solder 3 is sprayed on the plate surface.

As shown in FIG. 3, the solder spraying apparatus includes a homogenizer tank 10 containing a solder / polybutene suspension, and a mechanism for injecting the dispersion solder 3 formed in the homogenizer tank 10. Can be used. The solder bath of the homogenizer tank 10 is sealed and placed in an inert atmosphere. However, even if the solder bath is placed in the atmosphere, the oxidation of the solder can be prevented because polybutene substantially blocks the solder from the air. The inside of the homogenizer tank 10 is maintained at a temperature that keeps the solder in a molten state by a heater (not shown). Further, a homogenizer 11 is provided in the homogenizer tank 10, and a dispersion solder 3 in which fine-grained molten solder is dispersed in polybutene is prepared by stirring the suspension of solder and polybutene with the blades 12 of the homogenizer 11. I do. Nitrogen gas is introduced from the nitrogen tank 13 into the inside of the homogenizer tank 10 to prevent oxidation of the solder. In addition, the dispersion solder 3 obtained in the homogenizer tank 10 is used.
Can be guided by a heat-resistant pump 14 to a solder bath 17 through conduits 15 and 16 and sprayed from a spray nozzle 18 onto the printed circuit board 1. Nitrogen gas is preferably introduced into the solder bath 17 from a nitrogen tank 24 to prevent oxidation of the solder, and the remaining dispersion solder 3 is returned to the return line 19.
And returns to the bottom of the homogenizer tank 10. The conduit through which the dispersion solder 3 flows is preferably kept warm or heated, and the bath, bath, conduit, and nozzle are preferably made of stainless steel. The amount of the solder adhered on the printed circuit board can be set to an appropriate amount by determining the concentration of the dispersion solder, the flow rate and the contact time. In addition, a solder concentration meter 20 utilizing, for example, light transmission or the like is provided in the conduit 15 so that the concentration of the dispersion solder can be monitored. The detected concentration is converted into an electric signal and compared with the limit concentration in the comparator 21. When a shortage of solder occurs, the control valve 23 of the solder tank 22 is used.
Can be opened and solder can be supplied.

Since the polybutene 2 is preliminarily applied to the area where the dispersion solder 3 is sprayed, oxidation of the area is prevented, and the adhesion of the polybutene to the dispersion solder 3 can be ensured. This adhesion amount is 10
It can be set freely within the range of about 100 μm, and since the solder itself is covered and protected by polybutene, it does not oxidize.

After the process of attaching the dispersion solder 3, a cleaning process is performed. Thereafter, as shown in FIG. 4, a liquid adhesive 4 for temporarily fixing the electronic component to the surface of the printed circuit board 1 is used.
Is applied. Well the use of dispenser D ₂ also when the adhesive 4 is applied, can be attached even to the ball pasty fine location by spraying in the same manner as polybutene 2 described above.

With the adhesive 4, as shown in FIG. 5, the external terminals of the electronic component 5 are positioned at positions corresponding to contact points with the conductive pattern of the printed circuit board 1 on which the polybutene 2 and the dispersion solder 3 are applied. The part 5 is temporarily fixed.

Thereafter, the printed circuit board 1 on which the electronic components 5 are temporarily fixed is sent to a reflow furnace in a nitrogen gas atmosphere and subjected to a heat treatment. At the time of heating, the melting temperature of the solder is 190 to 200 ° C. because the polybutene 2 and the polybutene component in the dispersion solder 3 act as a heat medium.
It can be set to a low temperature. The fine solder in the dispersion solder 3 is melted and hardened by this heat treatment, so that the electronic component 5 is firmly fixed to the plate surface of the printed circuit board 1.

[0019]

As described above, according to the method for soldering electronic components according to the present invention, (1) Before the dispersion solder is sprayed, the oxide film is removed and the soldered portion is cleaned. Since oxidation is prevented by applying polybutene, dispersion solder in which fine-grained molten solder is dispersed in polybutene can be securely attached. (2) Since polybutene is used as a heat medium, the soldering temperature is 1
Soldering can be performed at a temperature as low as about 90 to 200 ° C. (3) Since the solder is dispersed in the polybutene, it does not come into direct contact with the atmosphere or other atmospheres, so that oxidation can be prevented, so that no solder failure occurs. (4) The dispersion solder has an average particle diameter of several μm to several tens μm, for example, about 10 μm, and has a low ratio of solder / polybutene, so that it can be attached in a state close to electroplating. The thickness of the solder can be freely controlled within a range of about 10 to 100 μm, and even if the circuit pattern is fine, it is possible to avoid the occurrence of a solder bridge between the patterns. (5) Since the dispersion solder does not need to contain a flux, it is possible to prevent the electronic components and the printed circuit board from being contaminated with the resin.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a step of applying polybutene in a method according to the present invention.

FIG. 2 is an explanatory view showing a soldering step in the method according to the present invention.

FIG. 3 is an explanatory view showing an example of a soldering device that can be used in the method according to the present invention.

FIG. 4 is an explanatory view showing a step of applying an adhesive for temporarily fixing electronic components in the method according to the present invention.

FIG. 5 is an explanatory view showing a mounting process of an electronic component in the method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Polybutene 3 Dispersion solder 4 Adhesive 5 Electronic component

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-27891 (JP, A) JP-A-57-167665 (JP, A) JP-A 63-6195 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H05K 3/34

Claims (1)

(57) [Claims] 1. A board surface of a printed circuit board to which an electronic component is soldered and fixed is subjected to an oxide film removal treatment and a washing treatment, and then polybutene is applied as a heat medium to the board surface portion.
Further, a dispersion solder in which fine-grained solder is dispersed in liquid polybutene is attached to the surface of the plate, and then the electronic component in which the external terminal is in contact with the conductive pattern of the printed circuit board using the surface of the plate as a contact point. A method of soldering an electronic component, comprising: temporarily fixing the electronic component to a surface of a printed circuit board with an adhesive; and performing a heat treatment in a low-temperature atmosphere to solder and fix the electronic component to the printed circuit board.