JP2014127481A - Circuit board, method of producing moisture-proof coating of circuit board, and motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable, inexpensive and compact circuit board, by coating the circuit board using a minimum necessary moisture-proof material.SOLUTION: In coating protection of a circuit board, after pre-heating a circuit board 1, an electrical connection 4 of the circuit board 1 and an electronic component 2 is coated with a solventless moisture-proof coat material 3, and then the moisture-proof coat material 3 is hardened under pressure state. When using a hydrogenated urethane resin as the moisture-proof coat material 3, a highly heat-resistant protection heating of circuit board, resistant even against a reactive substance such as hydrogen sulphide, and also resistant against thermal shock because of flexibility is possible.

Description

  The present invention relates to a method for coating a protective film for preventing deterioration of a circuit board on which electronic components are mounted due to exposure to water or gas, and a mounting structure provided with the protective film.

  Circuit boards used to control electronic devices are corroded by moisture and reactive substances in the ambient gas when used in high-temperature and high-humidity environments or when reactive substances such as sulfur compounds are present in the surroundings. Damaged.

  Circuit boards used in environments where such corrosion may occur should be protected with an insulating resin material on the circuit board surface to prevent exposure to atmospheric gases such as moisture and reactive substances. It corresponds by forming.

  It is important for the protective coating to be formed to prevent the surface exposure of the electrical connection portion of the circuit board, and the cause of the surface exposure of the electrical connection portion must be dealt with. The cause of this is a defect in the protective coating due to the repelling of the insulating resin material due to foreign matters remaining on the circuit board surface, the space between the electronic components, or the air remaining between the electronic component and the substrate escapes when the insulating resin material is cured. This is due to a defect that occurs due to remaining.

  For example, Patent Document 1 and Patent Document 2 provide a potting technique in which a housing for housing a circuit board is provided, and the entire circuit board is sealed using a sealing resin for each electronic component. Is disclosed.

  Further, Patent Document 3 discloses a technique for preventing the circuit board from moisture by using a hot-melt resin that exhibits fluidity only during heating as a sealing resin without a housing that houses the circuit board. .

  Patent Document 4 discloses a technique for moisture-proofing a circuit board by covering a board and electronic components with an insulating moisture-proof sheet.

JP 2006-100370 A Japanese Patent Laid-Open No. 11-103000 JP 2008-244062 A JP 2003-145687 A

  However, as in the techniques described in Patent Document 1 and Patent Document 2, a housing for housing a circuit board is provided, and the housing is provided in a configuration in which the board and electronic components are completely sealed with a sealing resin. There is a problem that the size of the circuit board increases because of the necessity. Furthermore, since it is necessary to completely seal the entire circuit board, there is a strong tendency that the amount of the sealing resin used is excessive, and the problem of high cost is considered.

  In addition, as in the technique described in Patent Document 3, when a hot melt resin that exhibits fluidity only during heating is used as the sealing resin, the adhesion between the hot melt resin and the substrate and the electronic component surface is weak. In addition, the problem of creating a gap at the interface between the hot melt resin and the substrate and the surface of the electronic component due to thermal stress in the use environment is considered.

  In addition, moisture and reactive substances in the air accumulate in this gap, and the original purpose of electrical connection may not serve the purpose of preventing exposure to atmospheric gases such as moisture and reactive substances. Sex is considered.

  Furthermore, since the hot melt resin becomes hard at low temperatures, when the temperature difference in the usage environment of the circuit board is large, a large stress is repeatedly applied to the electrical connection part between the board and the electronic component. The possibility of unstable reliability is considered. Further, since the hot melt resin is applied to the substrate and the electronic component in a state where the hot melt resin is melted at a high temperature at the time of hot melt application, the possibility that the substrate and the electronic component are damaged by the heat of the hot melt resin is also considered.

  And, as in the invention described in Patent Document 4, in the method of coating the substrate and the electronic component with the insulating moisture-proof sheet, the height difference between the substrate surface and the individual electronic components is an allowable range of elongation of the moisture-proof sheet. In the case of a configuration exceeding 1, the problem that it cannot be used is also considered. In addition, when the moisture-proof sheet contracts during use at a high temperature, a stress is always applied to the electrical connection portion between the substrate and the electronic component, so that the possibility that the reliability of the electrical connection portion becomes unstable is also considered. Furthermore, the problem that the cost increases when the moisture-proof sheet is used is also considered.

  The present invention solves the above considerations and problems. After preheating the substrate and the electrical connection portion of the electronic component, a solvent-free moisture-proof coating material is applied, and the moisture-proof coating material is added. An object of the present invention is to provide a highly reliable, inexpensive and small circuit board with a minimum necessary moisture-proof coating material by coating by a method of curing under pressure.

A first invention is a circuit board having a substrate, an electronic component disposed on a mounting surface of the substrate, and a moisture-proof coating layer covering the substrate and the electronic component.
The moisture-proof coating layer is a cured product of a solvent-free moisture-proof coating material, and on the surface of the substrate and the electronic component, a moisture-proof coating layer covering portion that covers the surface of the substrate and the electronic component with the cured product, A circuit board having the substrate and a moisture-proof coating layer uncovered portion where the surface of the electronic component is exposed, and having a moisture-proof coating layer containing bubbles between the mounting surface side of the electronic component and the substrate. .

  A second invention is the circuit board according to the first invention, wherein the moisture-proof coating layer is a cured product obtained by curing a solventless moisture-proof coating material while being pressurized.

  According to a third aspect of the present invention, in the circuit board according to the first aspect, the moisture-proof coat layer is a cured product obtained by increasing the temperature of the circuit board and curing the solvent-free moisture-proof coat material while pressing it. It is a substrate.

  A fourth invention is the circuit board according to the first to third inventions, wherein the material of the moisture-proof coat is urethane.

  5th invention is a motor containing the circuit board of 1st-4th invention.

6th invention mounts an electronic component on the mounting surface of a board | substrate, provides a moisture-proof coating layer by apply | coating and hardening a moisture-proof coating material to the electronic component mounting board | substrate with which the said electronic component was mounted,
On the surface of the substrate and the electronic component, a moisture-proof coating layer coating portion that covers the surface of the substrate and the electronic component with the moisture-proof coating layer, and a moisture-proof coating layer that is not exposed to the surface of the substrate and the electronic component A circuit board and a moisture-proof coat layer containing bubbles between the mounting surface side of the electronic component and the substrate.

  According to a seventh aspect of the present invention, there is provided a method for manufacturing a moisture-proof coat on a circuit board according to the sixth invention, wherein the moisture-proof coat layer is formed by curing a solvent-free moisture-proof coat material while being pressurized. Is the method.

  According to an eighth aspect of the present invention, there is provided the method for manufacturing a moisture-proof coating on a circuit board according to the sixth aspect, wherein the moisture-proof coating layer is cured while increasing the temperature of the circuit board and pressurizing a solvent-free moisture-proof coating material. Is a method of manufacturing a moisture-proof coating on a circuit board provided.

  A ninth invention is a method for manufacturing a moisture-proof coat on a circuit board according to the sixth to eighth inventions, wherein the material of the moisture-proof coat is urethane.

  According to the circuit board and the processing method thereof of the present invention, after preheating the board and the electrical connection part of the electronic component, the solvent-free moisture-proof coating material is applied and the moisture-proof coating material is cured under pressure. By applying the coating method, it is possible to provide a reliable, inexpensive and small circuit board with the minimum necessary moisture-proof coating material, which has a great industrial value.

The figure which shows the coating method process of the moisture-proof coating of the circuit board of this invention Schematic sectional view of the circuit board of the present invention The figure which shows the coating method process of the moisture-proof coating of the conventional circuit board Schematic sectional view of a conventional circuit board Graph showing the relationship between temperature and viscosity of moisture-proof coating materials

  The present invention will be described below with reference to the drawings and tables. In addition, this invention is not limited by the following examples.

  FIG. 1 is a diagram showing a method of coating a moisture-proof coating on a circuit board according to the present invention. In STEP 1 in FIG. 1, the substrate 1 is warmed before the moisture-proof coating material 3 is applied.

  By heating the substrate 1, the viscosity of the moisture-proof coating material 3 applied in STEP 2 decreases, and the moisture-proof coating material 3 easily enters the gap between the substrate 1 and the electronic component 2 and the gap between the electronic components 2. The electrical connection portion 4 between the substrate 1 and the electronic component 2 can be covered by the amount. Thus, the part coat | covered with the moisture-proof coating material 3 is a moisture-proof coating layer coating | coated part. In addition, by heating the substrate 1, it is possible to remove moisture on the substrate 1, which is one of the defect factors when applying the moisture-proof coating material 3.

  The temperature of the substrate 1 is preferably a temperature that does not damage the electronic component 2 or the electrical connection portion 4 of the electronic component, and that does not generate spring in the moisture-proof coating material 3.

  Further, the moisture-proof coating material 3 applied in STEP 2 is applied using a solvent-free moisture-proof coating material, and when the moisture-proof coating material 3 is cured in STEP 3 in a pressurized environment, the moisture-proof coating material of STEP 2 is used. It is possible to perform defoaming and miniaturization of bubbles generated in the coating step 3.

  Thus, it is not necessary to apply the moisture-proof coat to the top portion of the electrolytic capacitor or the portion not related to the electrical connection where the substrate wiring is not applied, and the coating without defects can be realized by applying only the necessary portion.

  As a result, as shown in FIG. 2, a highly reliable, inexpensive, and small circuit board free from defects such as bubbles can be formed in the electrical connection portion 4, and electrical connection can be made from atmospheric gases such as moisture and reactive substances. It is possible to prevent the portion 4 from being exposed and causing problems such as disconnection and short circuit.

  The pressurizing condition is a pressure at which the bubbles 6 in the moisture-proof coating material and the electronic component surface residual bubbles 7 can be removed by pressurization, and any pressure that does not destroy the electronic component 2 may be used. In this case, the generated bubbles are only the residual bubbles 5 under the electronic component, and it is possible to prevent the electrical connection portion 4 from being exposed and causing problems such as disconnection and short circuit.

  However, as shown in FIG. 3, in the conventional potting method, as shown in FIG. 4, the bubbles 6 in the moisture-proof coating material, the residual bubbles 7 on the electronic component surface, and the residual bubbles 5 below the electronic component are prominent. Since it is necessary to cover the entire electronic component 2 with the moisture-proof coating material 3 in order to ensure the performance, the housing 8 is necessary, the circuit board itself becomes large and heavy, and the cost increases.

  In the present embodiment, the moisture-proof coating material 3 is applied in a state where the substrate 1 is set to 80 ° C., and thus the viscosity of the moisture-proof coating material 3 is adjusted to the initial state as shown in FIG. It becomes possible to apply to the substrate 1 in a low viscosity state of 1/6 or less, and the electronic component 2 and the electrical connection portion 4 are not damaged by thermal stress.

  Furthermore, it becomes possible to remove moisture on the substrate surface, and at the time of applying the moisture-proof coating material 3, generation of bubbles 6 in the moisture-proof coating material, residual bubbles 7 on the electronic component surface, and residual bubbles 5 under the electronic component can be suppressed. .

  Further, since the moisture-proof coating material 3 uses a solvent-free urethane resin, new bubbles generated by the evaporation of the solvent during the curing are not generated. Therefore, after the moisture-proof coating material 3 is cured, the bubbles 6 in the moisture-proof coating material, the residual bubbles 7 on the electronic component surface, and the residual bubbles 5 below the electronic component are generated after the moisture-proof coating material 3 is cured. If measures are taken not to remain on the surface, a highly reliable protective film can be formed.

  For this purpose, the moisture-proof coating material 3 is cured under a pressurized environment. When the moisture-proof coating material 3 is applied to the substrate 1 and the electronic component 2 and placed in the pressure device, a part of the substrate 1 or the electronic By having at least one part of the part 2 not having the moisture-proof coating material 3 attached thereto, the moisture-proof coating material 3 can be easily conveyed to the pressure device in an uncured state. In the present embodiment, by providing a moisture-proof coating non-coated area 9 which is a moisture-proof coating layer non-coated portion at the end of the substrate 1 or the top of the electronic component 2, it is possible to grab that portion and move it to the pressurizing device. Met.

  Next, after applying the moisture-proof coating material 3 to the substrate 1 and holding it under a pressure of 2.5 atm until curing is completed, the bubbles 6 in the moisture-proof coating material and the bubbles 7 remaining on the electronic component surface are retained. It can be easily removed. Further, by curing the moisture-proof coating material 3 in the pressurizing device, the remaining bubbles are only in the residual bubbles under the electronic component 5, and the volume of the residual bubbles under the electronic component 5 is reduced in inverse proportion to the pressurized pressure. And remains under the electronic component 2 without being deposited in the moisture-proof coating material during curing.

  As a result, it is possible to prevent the electrical connection portion 4 from being exposed after curing and causing problems such as disconnection and short circuit. When the pressure applied during pressure curing is 4 atm or less, electronic parts such as electrolytic capacitors are not damaged.

  And as shown in Table 1, by using a hydrogenated urethane resin for the moisture-proof coating material 3, it has high heat resistance, is resistant to reactive substances such as hydrogen sulfide, and is flexible. Circuit boards that are resistant to thermal shock, and can be used in high-temperature environments such as car engine rooms and manufacturing plants, and in harsh environments with high concentrations of reactive substances. A usable circuit board can be provided.

  The field of use of the present invention relates to a method of coating a protective film for preventing deterioration of a circuit board on which an electronic component is mounted due to exposure to water or gas, and a mounting structure provided with the protective film. It can be particularly preferably used for a motor having a severe use environment such as in a factory or a car engine room.

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Electronic component 3 Moisture-proof coating material 4 Electrical connection part 5 Residual bubble under electronic component 6 Air bubble in moisture-proof coating material 7 Residual bubble on the surface of electronic component 8 Case 9 Moisture-proof coating non-application area

Claims (9)

In a circuit board having a substrate, an electronic component disposed on a mounting surface of the substrate, and a moisture-proof coating layer covering the substrate and the electronic component,
The moisture-proof coating layer is a cured product of a solvent-free moisture-proof coating material, and on the surface of the substrate and the electronic component, a moisture-proof coating layer covering portion that covers the surface of the substrate and the electronic component with the cured product, A circuit board having the moisture-proof coating layer uncovered portion where the surface of the substrate and the electronic component is exposed, and a moisture-proof coating layer containing bubbles between the mounting surface side of the electronic component and the substrate. 2. The circuit board according to claim 1, wherein the moisture-proof coating layer is a cured product obtained by curing a solventless moisture-proof coating material while being pressurized. The circuit board according to claim 1, wherein the moisture-proof coating layer is a cured product obtained by curing the solvent-proof moisture-proof coating material while pressurizing the temperature of the circuit board. 4. The circuit board according to claim 1, wherein the moisture-proof coat is made of urethane. A motor comprising the circuit board according to claim 1. An electronic component is mounted on the mounting surface of the substrate, and a moisture-proof coating layer is provided by applying and curing a moisture-proof coating material on the electronic component mounting substrate on which the electronic component is mounted,
On the surface of the substrate and the electronic component, a moisture-proof coating layer coating portion that covers the surface of the substrate and the electronic component with the moisture-proof coating layer, and a moisture-proof coating layer that is not exposed to the surface of the substrate and the electronic component And a moisture-proof coating method for a circuit board in which a moisture-proof coating layer containing bubbles is provided between the mounting surface side of the electronic component and the substrate. 7. The method for producing a moisture-proof coat on a circuit board according to claim 6, wherein the moisture-proof coat layer is formed by curing a solvent-free moisture-proof coat material while being pressurized. 7. The method for producing a moisture-proof coat on a circuit board according to claim 6, wherein the moisture-proof coat layer is a circuit board provided by curing the solvent-proof moisture-proof coating material while increasing the temperature of the circuit board and pressurizing the solvent-free moisture-proof coat material. A method for manufacturing a moisture-proof coat. 9. The method for manufacturing a moisture-proof coat on a circuit board according to claim 6, wherein the moisture-proof coat is made of urethane.

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