JP2738303B2 - Manufacturing method of electronic component mounted circuit board - 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 of manufacturing an electronic component mounted circuit board having electronic components mounted on a circuit board.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of this type of electronic component mounted circuit board, after applying flux to the circuit board,
The electronic components are soldered, then the flux is removed by cleaning with chlorofluorocarbon, and finally an acrylic moisture-proofing agent is applied and dried. Here, a rosin-based flux is used.

However, the use of water washing has been studied due to the recent movement of defluorocarbons. In this water washing, a hydrophilic (water-soluble) flux such as a polyether-based resin or glycerin is used instead of a hydrophobic flux such as the rosin-based flux.

[0004]

When such a water-soluble flux is washed with water instead of the conventional rosin-based flux, migration between the leads of the electronic components on the circuit board or between the electrodes is caused. This caused a problem that the insulation resistance was reduced. The present invention has been made in view of the above-described problems, and it is an object of the present invention to manufacture an electronic component-mounted circuit board using a water-soluble flux without causing the problems of the occurrence of the migration and a decrease in insulation resistance. I do.

[0005]

The inventor of the present invention has made various studies on the above-mentioned conventional problems. As a result, even after washing with water, a small amount of flux remains on the circuit board. Was found to have occurred. That is, water invades from the outside through the moisture barrier,
This intruded water is absorbed by the remaining flux,
It was determined that a water film was formed, and as a result, migration occurred between the leads or electrodes of the electronic component on the circuit board, and the insulation resistance was reduced.

In order to reduce the amount of moisture permeating the moisture barrier, a study was conducted using a saturated thermoplastic elastomer moisture barrier, which is a low moisture permeable material. Turned out to be. This is because even if a low moisture permeable desiccant is used to reduce the amount of water permeation, the water washing flux is water-soluble, so that even if a small amount remains on the substrate, it will remove moisture. This is because the water is sucked and a water film is formed.

From the above consideration, the present inventor considers that the above phenomenon does not occur if the residual flux is taken into the desiccant and the residual flux is removed from the surface of the circuit board. The use of a desiccant compatible with the flux was studied. As a result, those obtained by adding a rosin ester to a saturated thermoplastic elastomer,
Alternatively, it has been experimentally and theoretically found that a silicone-based moisture barrier has excellent solubility with residual flux.

According to the present invention, which has been made based on the above-described study, a step of applying a water-soluble flux to the surface of a circuit board, and after this application, an electronic component is applied to the circuit board. Soldering step, after this soldering step of washing the flux with water, after this water washing, a moisture-proof agent compatible with the remaining flux,
The method is characterized by comprising a step of coating the surface of the circuit board, and a step of drying the desiccant after applying the desiccant.

According to a second aspect of the present invention, in the first aspect of the invention, the step of applying the desiccant comprises dissolving a resin obtained by adding a rosin-based resin to a saturated thermoplastic elastomer as a base resin in a solvent. It is characterized in that it is a step of applying as a moisture barrier. According to a third aspect of the present invention, in the second aspect of the invention, a styrene-ethylene-butylene-based polymer is used as the saturated thermoplastic elastomer, and a rosin-ester-based resin is used as the rosin-based resin. I have.

According to a fourth aspect of the present invention, in the first aspect of the invention, the step of applying the desiccant is a step of applying a silicone resin as the desiccant. According to a fifth aspect of the present invention, in the fourth aspect, polydimethylsiloxane is used as the silicone resin.

[0011]

According to the first to fifth aspects of the present invention, a water-soluble flux is applied to the surface of a circuit board, and after soldering the electronic components, the flux is removed by washing with water, and the desiccant is removed. After application, it is dried. Here, a moisture-proofing agent having compatibility with the flux remaining after washing with water is used.

Therefore, since the residual hydrophilic flux localized at the interface with the circuit board is taken into the desiccant,
Since a water film layer is not formed due to the absorption of residual flux and the adhesion between the circuit board and the moisture proofing agent is improved, insulation deterioration due to migration can be prevented.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. First, an electronic component mounted circuit board manufactured according to the present invention will be described. FIG. 1 shows a partial cross section thereof. The electronic component 3 is fixed on the circuit board 1 by inserting the pins 2 and soldering.
Is applied to form an electronic component-mounted circuit board. As the mounting of the electronic component 3, a surface mounting type or the like can be used other than such a pin insertion type.

FIG. 2 shows a method of manufacturing the electronic component-mounted circuit board. First, a water-soluble flux for washing with water is applied onto the circuit board 1. As the water-soluble flux, a mixture of a polyether having a terminal alkyl group, methylamine hydrochloride, an organic acid, and isopropyl alcohol as described in JP-A-3-26891 is used. Next, the electronic component 3 is soldered on the circuit board 1. Thereafter, washing is performed using water to remove the flux. After this water washing, a very small amount of flux (polyether resin) remains on the circuit board 1 as a washing residue.

After that, a desiccant 4 is applied to the surface of the circuit board 1. As shown in FIG. 3, the desiccant 4 can be obtained by adding a rosin-based resin using a saturated thermoplastic elastomer as a base resin and dissolving it in a solvent (xylene and toluene). Here, as the resin composition, the base resin is mixed at a ratio of 80 to 60 (preferably 70) wt%, and the rosin-based resin is mixed at a ratio of 20 to 40 (preferably 30) wt%. Note that, specifically, a styrene-ethylene-butylene-based polymer is used as the saturated thermoplastic elastomer. In addition, styrene-ethylene-propylene-based, styrene-ethylene-based, and styrene-based polymers having the same polarity can be used. Also,
Specifically, a rosin ester resin is used as the rosin resin.

In addition, in addition to the above, as the moisture-proofing agent 4, FIG.
As shown in the above, a silicone resin can be used. Specifically, polydimethylsiloxane is used as the silicone resin. In addition, polymethylethylsiloxane or polymethylphenylsiloxane having the same basic structure can be used.

As a method of applying the moisture proofing agent 4, a dipping method, a potting method, a brush coating method, a spraying method, or the like can be used, and the method can be appropriately selected according to the shape of the circuit board 1. After the application of the desiccant 4, the desiccant 4 is dried. The drying conditions are such that a stable moisture-proof film can be formed.

Next, the mechanism by which the cleaning residue is taken into the desiccant 4 by applying the desiccant 4 will be described. At the stage of performing the water cleaning, the cleaning residue 5 remains on the circuit board 1 (FIG. 4A). This washing residue 5
Is dissolved and removed from the surface of the circuit board 1 by the application of the desiccant 4 and is dissolved in the desiccant 4 (FIG. 4).
(B)). Thereafter, when the desiccant 4 is dried, the cleaning residue 5 is taken into the solidified desiccant 4 (FIG. 4C). As a result, there is no cleaning residue 5 at the interface.

FIG. 5 shows the results of the condensation cycle test.
The moisture proofing agent was evaluated based on the migration generation length with respect to the number of cycles in which the dew condensation state was repeated. When a conventional acrylic-based desiccant is used as the desiccant, migration occurs remarkably with a relatively small number of cycles, and the insulation resistance is short-circuited. No outbreak was seen.

Therefore, according to this embodiment, since there is no washing residue which is a hydrophilic resin localized at the interface, the temperature,
Under the dew condensation, there is no gap due to the formation of a water film layer due to the absorption of water from the cleaning residue, so that a decrease in insulation resistance can be prevented. Furthermore, since the adhesion between the circuit board 1 and the desiccant 4 is improved, the movement of ionic components in the cleaning residue is eliminated, and the insulation deterioration due to migration or the like in the circuit board on which electronic components, board wiring, etc. are present is reduced. Can be eliminated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electronic component mounted circuit board manufactured by a manufacturing method of the present invention.

FIG. 2 is a process chart showing a manufacturing method of the present invention.

FIG. 3 is a diagram showing chemical names and structures of a moisture-proofing agent and the like used in the present invention.

FIG. 4 is a view for explaining a mechanism by which a cleaning residue is taken into the desiccant by applying the desiccant.

FIG. 5 is a diagram showing the results of a condensation cycle test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Circuit board 3 Electronic component 4 Moisture-proof film

Claims (5)

(57) [Claims] A step of applying a water-soluble flux to the surface of a circuit board; a step of soldering an electronic component to the circuit board after the application; and a step of washing the flux with water after the soldering. Electronic component mounting, comprising: a step of applying a desiccant compatible with the remaining flux to the surface of the circuit board after washing with water; and a step of drying the desiccant after applying the desiccant. A method for manufacturing a circuit board. 2. The step of applying the desiccant is a step of dissolving a resin obtained by adding a rosin-based resin to a saturated thermoplastic elastomer as a base resin in a solvent and applying the resultant as a desiccant. 2. The method for manufacturing an electronic component mounted circuit board according to claim 1. 3. The electronic component-mounted circuit board according to claim 2, wherein a styrene / ethylene / butylene-based polymer is used as the saturated thermoplastic elastomer, and a rosin-ester-based resin is used as the rosin-based resin. Production method. 4. The method according to claim 1, wherein the step of applying the desiccant is a step of applying a silicone resin as the desiccant. 5. The method according to claim 4, wherein polydimethylsiloxane is used as the silicone resin.