JPH0832214A - Production of circuit board for mounting electronic device - Google Patents

Abstract

PURPOSE:To prevent migration without lowering the insulating resistance by cleaning off the flux after soldering, coating a circuit board with a moisture- proof agent compatible with the residual flux, and then drying the moisture- proof agent. CONSTITUTION:A circuit board 1 is coated with a water soluble flux for water cleaning. An electronic device 3 is then soldered onto the circuit board 1. Subsequently, it is cleaned with water thus removing the flux. After finishing the water cleaning, the trace of flux is left as a residue on the surface of the circuit board 1. The circuit board 1 is then coated with a moisture-proof agent 4 which is eventually dried. Consequently, the residue 5 is taken into the solidified moisture-proof agent 4 and disappears from the surface of the circuit board 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for manufacturing an electronic component mounting circuit board in which electronic components are mounted on a circuit board.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of this kind of electronic component mounted circuit board, after applying flux to the circuit board,
Electronic parts are soldered, then the flux is removed by washing with chlorofluorocarbon, and finally an acrylic moisture barrier is applied and dried. Here, a rosin-based flux is used as the flux.

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

[0004]

When such a water-soluble flux is replaced with a conventional rosin-based flux for washing with water, migration occurs between leads or electrodes of electronic parts on a circuit board. However, there was a problem that the insulation resistance was lowered. The present invention has been made in view of the above problems, and an object of the present invention is to manufacture an electronic component-mounted circuit board using a water-soluble flux without causing the problems such as the occurrence of migration and a decrease in insulation resistance. To do.

[0005]

The inventors of the present invention have made various studies on the above-mentioned conventional problems. As a result, a slight amount of flux remains on the circuit board even after washing with water. I found out that this happened. That is, water invades from the outside through the moisture-proof agent,
This invaded water is absorbed by the residual flux,
It was judged 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 decreased.

Therefore, in order to reduce the amount of moisture that permeates the moisture-proofing agent, a study was conducted using a moisture-proofing agent of a saturated thermoplastic elastomer which is a low moisture-permeable material, and it was improved to some extent, but migration still occurred. It turned out that This is because even if the amount of permeation of water is reduced by using a moisture-proofing agent having a low moisture permeability, the water cleaning flux is water-soluble, so even if a small amount remains on the substrate, it will absorb moisture. This is because it sucks and forms a film of water.

From the above consideration, the inventor of the present application considers that the above phenomenon will not occur if the residual flux is taken into the moistureproofing agent and the residual flux is removed from the surface of the circuit board, and the water-soluble property The use of a moisture barrier that is compatible with the flux was investigated. As a result, saturated thermoplastic elastomer with rosin ester added,
Alternatively, it has been experimentally and theoretically found that the silicone-based moistureproofing agent has excellent solubility with the residual flux.

According to the present invention based on the above-mentioned study, as described in claim 1, a step of applying a water-soluble flux on the surface of the circuit board, and after this application, electronic parts are mounted on the circuit board. A step of soldering, a step of washing the flux with water after the soldering, and a moistureproof agent having compatibility with the residual flux after the water washing,
The method is characterized by including a step of applying to the surface of the circuit board and a step of drying the moistureproof agent after applying the moistureproof agent.

According to a second aspect of the present invention, in the step of applying the moisture-proofing agent according to the first aspect of the invention, a saturated thermoplastic elastomer is used as a base resin to which a rosin-based resin is added, which is dissolved in a solvent. It is characterized in that it is a step of applying as the moistureproof agent. According to the invention of claim 3, in the invention of claim 2, a styrene / ethylene / butylene polymer is used as the saturated thermoplastic elastomer, and a rosin ester resin is used as the rosin resin. There is.

The invention according to claim 4 is characterized in that, in the invention according to claim 1, the step of applying the moistureproof agent is a step of applying a silicone resin as the moistureproof agent. A fifth aspect of the invention is characterized in that, in the fourth aspect of the invention, polydimethylsiloxane is used as the silicone resin.

[0011]

According to the invention described in claims 1 to 5, the water-soluble flux is applied to the surface of the circuit board, the electronic component is soldered, and then the flux is removed by washing with water to remove the moisture-proofing agent. After application, it is dried. Here, as the moisture preventive agent, one having compatibility with the flux remaining after washing with water is used.

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

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, an electronic component mounting 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, and the moistureproof agent 4 is applied to the entire surface of the circuit board 1.
Is applied to form an electronic component mounting circuit board. For mounting the electronic component 3, a surface mount type or the like can be used in addition to the pin insertion type.

FIG. 2 shows a method of manufacturing the above electronic component mounted circuit board. First, a water-soluble flux for cleaning water is applied onto the circuit board 1. As the water-soluble flux, a mixture of a terminal alkyl group polyether, methylamine hydrochloride, an organic acid and isopropyl alcohol as described in JP-A-3-268891 is used. Next, the electronic component 3 is soldered on the circuit board 1. Then, the flux is removed by washing with water. After this water cleaning, a very small amount of flux (polyether resin) remains on the circuit board 1 as a cleaning residue.

Thereafter, the moistureproof agent 4 is applied to the surface of the circuit board 1. As shown in FIG. 3, the moistureproof agent 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 in a ratio of 80 to 60 (preferably 70) wt% and the rosin resin is mixed in a ratio of 20 to 40 (preferably 30) wt%. As the saturated thermoplastic elastomer, specifically, a styrene / ethylene / butylene polymer is used. Other than that, styrene / ethylene / propylene type, styrene / ethylene type, and styrene type polymers having the same polarity as that can be used. Also,
A rosin ester resin is specifically used as the rosin resin.

Further, in addition to the above, as the moistureproof agent 4, FIG.
As shown in, a silicone resin can be used. As the silicone-based resin, specifically, polydimethylsiloxane is used. Other than that, polymethylethyl siloxane or polymethylphenyl siloxane having the same basic structure as that can be used.

As the coating method of the moistureproofing agent 4, a dipping method, a potting method, a brush coating method, a spray-on method or the like can be used, and the method can be appropriately selected depending on the shape of the circuit board 1. After applying the moistureproof agent 4, the moistureproof agent 4 is dried. This drying condition is set so that a stable moisture-proof film can be formed.

Next, the mechanism by which the cleaning residue is incorporated into the moistureproof agent 4 by applying the moistureproof agent 4 will be described. At the stage of cleaning with water, the cleaning residue 5 remains on the circuit board 1 (FIG. 4A). This wash residue 5
Is dissolved and removed from the surface of the circuit board 1 by applying the moisture-proofing agent 4, and is dissolved in the moisture-proofing agent 4 (FIG. 4).
(B)). After that, when the moistureproof agent 4 is dried, the cleaning residue 5 is in a state of being taken into the solidified moistureproof agent 4 (FIG. 4C). As a result, the cleaning residue 5 is removed from the interface.

FIG. 5 shows the result of the condensation cycle test.
The moistureproofing agent was evaluated by the migration generation length with respect to the number of cycles of repeating the condensation state. When a conventional acrylic moisture-proofing agent is used as the moisture-proofing agent, migration occurs remarkably in a relatively small number of cycles, and the insulation resistance is short-circuited. No outbreak was observed.

Therefore, according to this embodiment, since the cleaning residue, which is the hydrophilic resin localized at the interface, is eliminated, the temperature,
Under dew condensation, the gap due to the formation of the water film layer due to the absorption of the cleaning residue is eliminated, and the reduction of the insulation resistance can be prevented. Furthermore, since the adhesion between the circuit board 1 and the moisture-proofing agent 4 is improved, the migration of ionic components in the cleaning residue is eliminated, and the insulation deterioration due to migration or the like is reduced in the circuit board having electronic components, board wiring, etc. It can be lost.

[Brief description of drawings]

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

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

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

FIG. 4 is a diagram illustrating a mechanism in which a cleaning residue is incorporated into a moistureproofing agent by applying the moistureproofing agent.

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

[Explanation of symbols] 1 circuit board 3 electronic component 4 moisture-proof film

Claims (5)

[Claims] 1. 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. After washing with water, a step of applying a moisture barrier agent compatible with the residual flux to the surface of the circuit board, and a step of drying the moisture barrier agent after applying the moisture barrier agent are mounted. Circuit board manufacturing method. 2. The step of applying the moisture-proofing agent is a step of dissolving a saturated thermoplastic elastomer with a rosin-based resin as a base resin in a solvent and applying the solution as the moisture-proofing agent. 1. A method for manufacturing an electronic component-mounted circuit board according to 1. 3. The electronic component mounted circuit board according to claim 2, wherein a styrene / ethylene / butylene polymer is used as the saturated thermoplastic elastomer, and a rosin ester resin is used as the rosin resin. Production method. 4. The method for manufacturing an electronic component mounted circuit board according to claim 1, wherein the step of applying the moistureproof agent is a step of applying a silicone resin as the moistureproof agent. 5. The method of manufacturing an electronic component mounted circuit board according to claim 4, wherein polydimethylsiloxane is used as the silicone resin.