JP2997905B2 - 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 the method of soldering an electronic component according to the present invention, the electronic component is temporarily fixed on a printed circuit board in advance, and a contact point between an external terminal of the electronic component and a conductive pattern on the printed circuit board. After the oxide film is removed, polybutene is applied as a heat medium to the contact point, and then dispersion solder in which fine-grained molten solder is dispersed in polybutene is sprayed at the contact point where the polybutene is applied. In addition, the electronic component is soldered and fixed to a printed circuit board.

[0009]

In this method of soldering electronic parts, the coating is performed after removing the oxide film at the contact points between the external terminals of the electronic parts and the conductive patterns of the printed circuit board using polybutene which can be prevented from being oxidized as a heat medium. Spraying dispersion solder in which fine-grained molten solder is dispersed in polybutene at the contact points and connecting and fixing the external terminals of the electronic component and the conductive pattern of the printed board with this dispersion solder, lowering the soldering temperature It can be securely fixed with a small amount of solder, can reduce the cost associated with soldering, does not contaminate with flux, etc., and can be applied to soldering of fine-grained fine circuit patterns with molten solder of dispersion solder. be able to.

[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, the electronic component 1 is temporarily fixed to a printed board 2 with an adhesive 3, and external terminals of the electronic component 1 and printed terminals are printed. After removing the oxide film from at least the contact portion of the conductive pattern of the substrate 2 and then cleaning, the liquid polybutene 4 is applied as a heat medium to the contact portion where the oxide film has been removed to prevent re-oxidation. This polybutene 4 is preferably spray-coated in a dot shape toward the plate surface of the printed circuit board 2 by using a dispenser D as shown in FIG. 1, and it depends on the magnitude of the pressure applied to the liquid surface and the pressure application time. Since the amount of application can be controlled, it can be applied even to a fine place.

After the application of the polybutene, the electronic component 1 temporarily fixed to the printed circuit board 2 as shown in FIG. 2 is subjected to a soldering process by spraying a dispersion solder from an injection nozzle of a soldering device described later.

As a soldering device, as shown in FIG. 3, a homogenizer tank 10 containing a solder / polybutene suspension is used.
And a mechanism having a mechanism for injecting the dispersion solder 5 created 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 homogenizer tank 10
Is maintained at a temperature that keeps the solder in a molten state by a heater (not shown). The homogenizer tank 10 is provided with a homogenizer 11.
The suspension of the solder and the polybutene is agitated by the one blade 12, thereby producing the dispersion solder 5 in which the fine-grained molten solder is dispersed in the polybutene. Nitrogen gas is introduced from the nitrogen tank 13 into the inside of the homogenizer tank 10 to prevent oxidation of the solder. Further, the dispersion solder 5 obtained in the homogenizer tank 10 is guided to the solder bath 17 via the pipes 15 and 16 by the heat-resistant pump 14, and can be sprayed on the printed board 2 from the injection nozzle 18. By introducing nitrogen gas into the solder bath 17 preferably from a nitrogen tank 24, oxidation of the solder is prevented,
The excess dispersion solder 5 returns to the bottom of the homogenizer tank 10 via the return line 19. The conduit through which the dispersion solder 5 flows may be kept warm or heated.
As the material of the tank, bath, pipe, and nozzle, it is preferable to use stainless steel lining. 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 concentration detection is converted into an electric signal and compared with the limit concentration in the comparator 21. When the solder is insufficient, the control valve 23 of the solder tank 22 is opened to supply the solder.

Since the polybutene 4 is applied in advance to the sprayed portion of the dispersion solder 5, oxidation of the sprayed portion is prevented, and the dispersion solder 5 containing the molten solder is reliably formed by the adhesive force between the polybutenes. By attaching, the contact point between the external terminal of the electronic component and the conductive pattern on the printed circuit board can be soldered and fixed with high accuracy. The amount of adhesion can be freely set within a range of about 10 to 100 μm. Further, since the solder pile itself is covered and protected by polybutene, it can be prevented from being oxidized. After this soldering, a series of soldering steps can be completed by performing a cleaning process.

[0016]

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.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-278809 (JP, A) JP-A-57-167665 (JP, A) JP-A 1-222791 (JP, A) JP-A-3- 116994 (JP, A) Japanese Utility Model 63-6195 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 3/34

Claims (1)

(57) [Claims] An electronic component is temporarily fixed on a printed circuit board in advance, and a contact point between an external terminal of the electronic component and a conductive pattern on the printed circuit board is subjected to an oxide film removing treatment. Then, a dispersion solder in which fine-grained molten solder is dispersed in the polybutene is sprayed onto the contact points where the polybutene is applied, so that the electronic component is soldered and fixed to the printed circuit board. An electronic component soldering method characterized by the above-mentioned.