JP2020088075A - Resin layer forming material and resin layer coated electronic component mounting board - Google Patents

Abstract

To provide a resin layer forming material capable of sealing the unevenness of an electronic component mounting board with excellent followability and capable of accurately suppressing or preventing formation of rust in a metal exposed portion of the electronic component mounting board, and a resin layer coated electronic component mounting board having excellent reliability, in which the unevenness of an electronic component mounting board is covered with the resin layer.SOLUTION: A resin layer forming material according to the present invention is used to form a resin layer 7 that covers an electronic component mounting board 45 including a board 5 and an electronic component 4 mounted on the board 5, and includes a solvent-soluble resin as a main material, and in the formed resin layer 7, when a water vapor permeability of the resin layer 7 is A [g/m/day], and a concentration of ionic impurities contained in the resin layer 7 is B [ppm], the relationship of A×B≤30 is satisfied.SELECTED DRAWING: Figure 1

Description

The present invention relates to a resin layer forming material and a resin layer-covered electronic component mounting board.

Conventionally, in electronic devices such as mobile phones, smartphones, calculators, electronic newspapers, tablet terminals, videophones, and personal computers, for example, electronic component mounting boards on which electronic components such as semiconductor elements, capacitors, and coils are mounted. Although mounted, this electronic component mounting board is sealed with a resin against the irregularities formed by mounting the electronic component for the purpose of preventing contact with external factors such as moisture and dust. Sometimes.

Such resin encapsulation is performed by, for example, arranging the electronic component mounting board in the metal cavity and then injecting a solvent-soluble resin such as urethane resin having high fluidity to cover the electronic component mounting board. A potting method is known in which an electronic component mounting substrate is sealed by forming (see, for example, Patent Document 1).

However, a resin layer formed by the potting method, that is, a resin layer mainly composed of a solvent-soluble resin can make the resin layer follow the irregularities of the electronic component mounting board, In particular, it is not possible to sufficiently suppress the permeation of moisture (water vapor), and in the electronic component mounting board, metal exposed portions such as terminals of the electronic component are rusted, which causes the electronic component mounting board. There was a problem of causing poor conduction in.

JP, 2011-122051, A

An object of the present invention is to seal unevenness of an electronic component mounting board with excellent followability, and to appropriately suppress or prevent the occurrence of rust in a metal exposed portion of the electronic component mounting board. Provided is a resin layer-forming material capable of forming a resin layer capable of forming a resin layer, and a resin layer-covered electronic component mounting board having excellent reliability in which irregularities included in an electronic component mounting board are covered with the resin layer. Especially.

Such an object is achieved by the present invention described in (1) to (10) below.
(1) A resin layer forming material used to form a resin layer covering an electronic component mounting substrate including a substrate and electronic components mounted on the substrate and containing a solvent-soluble resin as a main material. There
The resin layer formed using the resin layer forming material has a water vapor permeability of the resin layer of A [g/m ² /day] and a concentration of ionic impurities contained in the resin layer of B[ ppm], the resin layer forming material is characterized by satisfying the relationship of A·B≦30.

(2) The resin layer-forming material according to (1), wherein the water vapor permeability A is 20 g/m ² /day or less.

(3) The resin layer forming material as described in (1) or (2) above, wherein the concentration B of the ionic impurities is 3.0 ppm or less.

(4) The resin layer according to any one of the above (1) to (3), which satisfies a relationship of B/C≦0.200 when an average thickness of the resin layer to be formed is C [μm]. Forming material.

(5) The resin layer forming material as described in any one of (1) to (4) above, wherein the resin layer has an average thickness of 5 μm or more and 100 μm or less.

(6) The solvent-soluble resin is any one of (1) to (5) above, which is at least one kind of (meth)acrylic resin, polyolefin elastomer, styrene elastomer, polyester resin and urethane resin. Resin layer forming material.

(7) The resin layer forming material further contains a solvent,
The resin layer forming material according to any one of (1) to (6) above, wherein the solvent is at least one of toluene, normal hexane, methyl ethyl ketone, and ethyl acetate.

(8) The resin layer forming material according to any one of (1) to (7), wherein the resin layer forming material has a viscosity at 25° C. of 30 mPa·s or more and 500 mPa·s or less.

(9) An electronic component mounting board, and the resin layer that covers at least the electronic component and is formed using the resin layer forming material according to any one of claims 1 to 8. Characteristic resin layer coated electronic component mounting board.

(10) The resin layer-covered electronic component mounting board according to (9), wherein the board is a printed wiring board.

According to the present invention, the resin layer that covers the electronic component mounting substrate including the substrate and the electronic components mounted on the substrate is mainly composed of the solvent-soluble resin. As a result, in the resin layer-covered electronic component mounting board, the resin layer covers the irregularities formed by mounting the electronic component on the board in a state in which the resin layer follows with excellent followability.

Further, in the resin layer-covered electronic component mounting board, the resin layer composed mainly of the solvent-soluble resin covers the electronic component mounting board including the substrate and the electronic component, and the water vapor permeability of the resin layer is A When the concentration is [g/m ² /day] and the concentration of the ionic impurities contained in the resin layer is B [ppm], the relationship of A·B≦30 is satisfied. Thereby, it can be said that the moisture (water vapor) permeability in the resin layer is appropriately suppressed, and the contact with the ionic impurities is appropriately suppressed in the resin layer even if the moisture (water vapor) permeates. .. Therefore, when the resin layer-covered electronic component mounting substrate is applied to, for example, a water meter, an outdoor unit included in an air conditioner, a solar power generation system, or a signal provided to an electronic device arranged outdoors such as a traffic light, It is possible to accurately prevent water vapor from reaching the electronic components of the layer-covered electronic component mounting board, and to accurately suppress contact with the ionic impurities in the resin layer even if moisture permeates. be able to. Therefore, it is possible to properly suppress the occurrence of the conduction failure in the electronic component mounting board due to the generation of rust on the metal exposed portion such as the terminal included in the electronic component. As a result, the resin layer-covered electronic component mounting board has excellent reliability.

1 is a vertical cross-sectional view showing an embodiment of a resin layer-covered electronic component mounting board of the present invention. FIG. 6 is a vertical cross-sectional view for explaining the method of manufacturing the resin layer-covered electronic component mounting board shown in FIG. 1.

Hereinafter, a resin layer forming material and a resin layer-covered electronic component mounting board of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

First, prior to describing the resin layer-forming material of the present invention, a resin layer-covered electronic component mounting board (resin layer-coated substrate of the present invention) including a resin layer formed using the resin layer-forming material of the present invention The electronic component mounting board) will be described.

<Resin layer coated electronic component mounting board>
FIG. 1 is a longitudinal sectional view showing an embodiment of a resin layer-covered electronic component mounting board of the present invention. In the following description, for convenience of explanation, the upper side in FIG. 1 is referred to as “upper” and the lower side is referred to as “lower”.

The resin layer-covered electronic component mounting substrate 50 includes an electronic component mounting substrate 45 including the substrate 5 and the electronic component 4, and a resin layer 7 that covers at least a part of the substrate 5 and the electronic component 4. .. In the resin layer-covered electronic component mounting board 50, the resin layer 7 is formed by using the resin layer forming material of the present invention, and is composed mainly of a solvent-soluble resin, and the water vapor permeation of the resin layer 7 is performed. When the degree is A [g/m ² /day] and the concentration of the ionic impurities contained in the resin layer 7 is B [ppm], the relationship A·B≦30 is satisfied.

In the resin layer-covered electronic component mounting board 50 having such a configuration, the resin layer 7 that covers at least a part of the substrate 5 and the electronic component 4 is composed of a solvent-soluble resin as a main material in the present invention as described above. ing. As a result, in the resin layer-covered electronic component mounting board 50, the resin layer 7 covers the irregularities 6 formed by mounting the electronic component 4 on the board 5 in a state in which the resin layer 7 follows with excellent followability. It has become a thing.

In the resin layer-covered electronic component mounting board 50, the resin layer 7 composed mainly of a solvent-soluble resin covers the electronic component mounting board 45 including the substrate 5 and the electronic component 4, and the resin layer 7 The water vapor permeability of A is set to A [g/m ² /day] and the concentration of the ionic impurities contained in the resin layer 7 is set to B [ppm], the relationship of A·B≦30 is satisfied. Thereby, the permeability of moisture (water vapor) in the resin layer 7 is appropriately suppressed, and the contact of the resin layer 7 with ionic impurities is appropriately suppressed even if the moisture (water vapor) permeates. Can be said. Therefore, when the resin layer-covered electronic component mounting substrate 50 is applied to, for example, a water meter, an outdoor unit included in an air conditioner, a solar power generation system, or a signal device provided in an electronic device arranged outdoors, It is possible to properly prevent water vapor from reaching the electronic component 4 provided in the resin layer-covered electronic component mounting board 50, and to prevent contact with ionic impurities in the resin layer 7 even if moisture permeates. It can be controlled accurately. Therefore, it is possible to properly suppress the occurrence of conduction failure in the electronic component mounting board 45, which is caused by the generation of rust on a metal exposed portion such as a terminal included in the electronic component 4. As a result, the resin layer-covered electronic component mounting board 50 has excellent reliability.

As described above, the resin layer-covered electronic component mounting board 50 includes the electronic component mounting board 45 and the resin layer 7. Hereinafter, each of these parts constituting the resin layer-covered electronic component mounting board 50 will be sequentially described.

<< Electronic component mounting board 45 >>
As shown in FIG. 1, the electronic component mounting board 45 includes a substrate 5 and an electronic component 4 mounted (placed) on the substrate 5. The electronic component mounting board 45 includes the substrate 5 By mounting the electronic component 4 on the upper portion, the convex portion 61 is formed on the substrate 5 so as to correspond to the position where the electronic component 4 is mounted, and is formed corresponding to the position between the electronic components 4. Concavities and convexities 6 composed of concave portions 62 are formed.

The substrate 5 is not particularly limited, but examples thereof include a printed wiring board and the like, and examples of the electronic component 4 include semiconductor elements, capacitors, coils, connectors and resistors.

<<Resin layer 7>>
The resin layer 7 covers at least a part of the substrate 5 and the electronic component 4 included in the electronic component mounting substrate 45, and in the present embodiment, the upper surface of the substrate 5 on which the electronic component 4 is mounted (on one side). The surface 6 covers almost the entire surface, so that when the electronic component 4 is mounted on the substrate 5, the projections and depressions 6 formed by the projections 61 and the depressions 62 are covered.

The resin layer 7 is composed of a solvent-soluble resin as a main material, and as described in detail in a method of sealing the electronic component mounting substrate 45 described later, the solvent-soluble resin and a solvent (organic It is provided by supplying a liquid material containing a solvent) to the upper surface side of the substrate 5 on which the electronic component 4 is mounted, and then drying and solidifying the liquid material. Therefore, the resin layer 7 can be covered with the resin layer 7 following the unevenness 6 formed by mounting the electronic component 4 on the substrate 5 with excellent followability. In particular, the substrate 5 is provided with an opening and/or a through hole for exposing an electrode (metal exposed portion; not shown) for electrically connecting with the electronic component 4. The resin layer 7 can be formed with excellent compactness up to the holes.

Further, the resin layer 7 composed mainly of a solvent-soluble resin covers the upper surface of the substrate 5 on which the electronic component 4 is mounted, and the resin layer 7 has a water vapor permeability of A [g/g/g]. m ² /day] and the concentration of the ionic impurities (Cl ⁻ ) contained in the resin layer 7 is B [ppm], the relationship of A·B≦30 is satisfied.

As a result, it is possible to properly prevent the water vapor from reaching the electronic component 4 (particularly, the metal exposed portion such as the terminal) included in the resin layer-covered electronic component mounting board 50 via the resin layer 7, Moreover, even if moisture (water vapor) permeates the electronic component 4 through the resin layer 7, the contact between the water vapor and the ionic impurities in the resin layer 7 can be appropriately suppressed.

The solvent-soluble resin satisfies the relationship that the water vapor permeability A [g/m ² /day] of the resin layer 7 and the concentration B [ppm] of the ionic impurities contained in the resin layer 7 are A·B≦30. The type is selected so as to obtain, for example, polyimide resin, polyamideimide resin, fluorinated aromatic polymer, (meth)acrylic resin, polyamide resin, aramid resin, polysulfone resin, polyolefin elastomer, cycloolefin polymer. Examples thereof include polyolefin resins, styrene elastomers, polyester resins, epoxy resins, urethane resins, phenol resins, and the like, and one or more of these can be used in combination. Among these, at least one of (meth)acrylic resin, polyolefin elastomer, styrene elastomer, polyester resin and urethane resin is preferable. Thereby, the resin layer 7 can be formed with excellent adhesion to the substrate 5 and the electronic component 4, and the resin layer 7 can surely satisfy the relationship of A·B≦30.

The solvent (solvent) contained in the resin layer-forming material of the present invention used when forming the resin layer 7 is appropriately selected according to the type of the solvent-soluble resin contained therein. , Methyl ethyl ketone, methyl isobutyl ketone, DIBK (diisobutyl ketone), cyclohexanone, DAA (diacetone alcohol) and other ketones, benzene, xylene, toluene and other aromatic hydrocarbons, normal hexane and other linear alkanes, methyl Alcohols, alcohols such as ethyl alcohol, isopropyl alcohol, n-butyl alcohol, etc., cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, BCSA (butyrocellosolve acetate), NMP (N-methyl). 2-pyrrolidone), THF (tetrahydrofuran), DMF (dimethylformamide), DBE (dibasic acid ester), EEP (ethyl 3-ethoxypropionate), ethyl acetate, DMC (dimethyl carbonate), and the like. One or more of them can be used, and among them, at least one of toluene, normal hexane, methyl ethyl ketone and ethyl acetate is preferable. Thereby, the solvent-soluble resin can be more uniformly dissolved in the resin layer forming material. In addition, such a solvent may be a single solvent or a mixed solvent.

Here, if the water vapor permeability A [g/m ² /day] of the resin layer 7 and the concentration B [ppm] of the ionic impurities contained in the resin layer 7 satisfy the relationship of A·B≦30. It is good, but it is preferable to satisfy the relationship of A·B≦15, and it is more preferable to satisfy the relationship of A·B≦4. Thereby, the effect obtained by setting the sizes of A and B can be more remarkably exhibited.

Further, the water vapor permeability A is preferably 20 g/m ² /day or less, more preferably 5 g/m ² /day or less. As a result, it is possible to more appropriately prevent the water vapor from reaching the electronic component 4 (particularly, a metal exposed portion such as a terminal) included in the resin layer-covered electronic component mounting board 50 via the resin layer 7. ..

Furthermore, the concentration B of the ionic impurities contained in the resin layer 7 is preferably 3.0 ppm or less, and more preferably 1.5 ppm or less. Thereby, even if moisture (water vapor) permeates the electronic component 4 through the resin layer 7, the contact between the water vapor and the ionic impurities in the resin layer 7 can be suppressed more accurately.

The ionic impurities contained in the resin layer 7 include, for example, halide ions such as F ⁻ , Cl ⁻ and Br ⁻ , NH 4 ^+, etc., and the total concentration B of them satisfies the above relationship. However, the concentration of Cl ⁻ (chloride ion) may be set as the concentration B of the ionic impurities so as to satisfy the above relationship. Cl ⁻ (chloride ion) is most likely to be contained as an ionic impurity in the resin layer 7. Therefore, by controlling the concentration of Cl ⁻ (chloride ion) as the concentration B, the relationship of A·B≦4 can be satisfied, and further, the effect obtained by setting the concentration B to 3.0 ppm or less can be obtained. , Can be surely demonstrated.

When the average thickness of the resin layer 7 is C [μm], the relationship B/C with the concentration B of the ionic impurities contained in the resin layer 7 may satisfy B/C≦0.200. It is more preferable that B/C≦0.030 is satisfied. Thereby, even if moisture (water vapor) permeates the electronic component 4 through the resin layer 7, the contact between the water vapor and the ionic impurities in the resin layer 7 can be suppressed more accurately.

Furthermore, the average thickness of the resin layer 7 is preferably 5 μm or more and 100 μm or less, and more preferably 30 μm or more and 50 μm or less. As a result, it is possible to more appropriately prevent the water vapor from reaching the electronic component 4 (particularly, a metal exposed portion such as a terminal) included in the resin layer-covered electronic component mounting board 50 via the resin layer 7. ..

<Method for manufacturing resin layer-covered electronic component mounting board 50>
Next, a manufacturing method for manufacturing the resin layer-covered electronic component mounting board 50 described above, that is, a method of sealing the electronic component mounting board 45 using the resin layer 7 will be described.

FIG. 2 is a vertical cross-sectional view for explaining a method of manufacturing the resin layer-covered electronic component mounting board shown in FIG.

The method of manufacturing the resin layer-covered electronic component mounting board 50 of the present embodiment includes a coating step of coating the substrate 5 and the electronic component 4 included in the electronic component mounting board 45 with the resin layer 7. Hereinafter, this coating step will be described.

(Coating process)
First, as shown in FIG. 2A, an electronic component mounting substrate 45 including a substrate 5 and an electronic component 4 mounted on the upper surface (one surface) of the substrate 5 is prepared.

Then, almost the entire upper surface side of the electronic component mounting board 45, that is, the substrate 5 and the electronic component 4 exposed on the upper surface side of the electronic component mounting board 45 are formed by a resin layer 7 composed mainly of a solvent-soluble resin. Cover (see FIG. 2B).

The resin layer 7 covering the substrate 5 and the electronic component 4 is made of a liquid material (a resin layer forming material of the present invention) containing a solvent-soluble resin and a solvent (organic solvent) in which the solvent-soluble resin is soluble. Supplying to the upper surface side of the substrate 5 on which the component 4 is mounted, and drying and solidifying the liquid material after the substrate 5 exposed on the upper surface side of the substrate 5 and the electronic component 4 are covered with this liquid material. Provided by. Since the resin layer 7 is provided by drying and solidifying the liquid material in a state where the substrate 5 and the electronic component 4 are coated with such a liquid material, the electronic component 4 is mounted on the substrate 5. The resin layer 7 is formed in a state of following the unevenness 6 thus formed with excellent followability.

Further, the board 5 (printed wiring board) is provided with an opening and/or a through hole for exposing an electrode (not shown) for electrically connecting to the electronic component 4, but as described above, By supplying the material (material for forming a resin layer of the present invention) in a liquid state and then drying and solidifying the resin layer 7 to form the resin layer 7, the resin layer 7 can be excellently formed up to these openings and through holes. It can be formed with high density.

As a method of supplying the liquid material to the upper surface side of the substrate 5 on which the electronic component 4 is mounted, for example, a method of immersing the electronic component mounting substrate 45 in the liquid material (immersion method), an upper surface side of the electronic component mounting substrate 45 Examples thereof include a method of showering (spraying) the liquid material (spraying method) and a method of applying the liquid material to the upper surface side of the electronic component mounting substrate 45 (coating method). Among them, the spraying method or the coating method is used. Is preferred. According to the spraying method or the coating method, the liquid material can be selectively supplied to the upper surface side of the electronic component mounting substrate 45 relatively easily.

Further, this liquid material (material for forming a resin layer) preferably has a viscosity at 25° C. of 30 mPa·s or more and 500 mPa·s or less, and more preferably 100 mPa·s or more and 350 mPa·s or less. As a result, the resin layer 7 can be formed with higher density up to the opening and the through hole.

The content of the solvent-soluble resin in the liquid material is not particularly limited, but is preferably 5 wt% or more and 60 wt% or less, and more preferably 10 wt% or more and 30 wt% or less. As a result, the resin layer 7 having the above-mentioned average thickness can be formed relatively easily, and the viscosity of the liquid material at 25° C. can be reliably set within the above range.

Through the coating process as described above, the resin layer-covered electronic component mounting substrate 50 in which the substrate 5 and the electronic component 4 are coated with the resin layer 7 can be obtained.

Although the resin layer forming material and the resin layer-covered electronic component mounting board of the present invention have been described above, the present invention is not limited to these.

For example, in the above-described embodiment, a case has been described in which a resin layer is formed on almost the entire upper surface side of the substrate and the entire substrate and electronic components exposed on the upper surface side of the substrate are covered with the resin layer. The resin layer is not limited, and may cover a part of the substrate and the electronic component on the upper surface side of the substrate.

Further, the resin layer may be formed so as to cover almost the entire lower surface of the substrate or a part thereof. Further, when the resin layer covers substantially the entire lower surface side or a part of the lower surface side of the substrate, an electronic component covered with the resin layer may be mounted on the lower surface side of the substrate.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited thereto.

(Example 1)
<Preparation of liquid material for forming resin layer>
In order to prepare a liquid material for forming a resin layer, a solvent-soluble resin that constitutes the resin layer to be formed, and an organic solvent (solvent) that dissolves this solvent-soluble resin Prepared.

That is, a styrene-based elastomer (“PPET 1505SG” manufactured by Toagosei Co., Ltd.) was prepared as a solvent-soluble resin.
In addition, toluene was prepared as an organic solvent.

Next, SIBS was dissolved in toluene to prepare a liquid material having a SIBS content of 10 wt %.

<Manufacture of resin layer coated electronic component mounting board>
First, an arbitrary electronic component mounting substrate is prepared, and then the prepared liquid material is supplied to the upper surface side of the substrate on which the electronic component is mounted, and then dried and solidified, so that the upper surface side of the electronic component mounting substrate 45 is provided. A resin layer 7 was formed to cover the exposed substrate 5 and electronic component 4. As a result, the resin layer-covered electronic component mounting substrate of Example 1 in which the substrate and the electronic component were coated with the resin layer 7 was obtained.
The average thickness (μm) of the formed resin layer 7 was 20 μm.

The concentration B of the ionic impurities (Cl ⁻ ) in the resin layer 7 was 1.97 ppm when measured using a capillary electrophoresis apparatus (“Agilent 7100 CE” manufactured by Agilent Technologies).

Further, a resin layer 7 having an average thickness of 35 μm was formed, and the water vapor permeability A of the resin layer 7 was measured according to the following procedure in accordance with JIS Z 0208. The result was 15.0 g/m ² /day. Met.

That is, regarding the water vapor transmission rate A of the resin layer 7, first, calcium chloride was added to the metal cup, and then the edge portion was fixed with a wax while the metal cup was covered with the resin layer 7. Next, after weighing the initial weight of this product, it was stored in a built-in chamber at 40° C. and 90% RH for 1 week. Then, the weight was measured after weighing for 1 week, and the weight was calculated based on the weight increase obtained from the difference between the weight and the initial weight.

(Example 2)
A resin layer-covered electronic component mounting board of Example 2 was obtained in the same manner as in Example 1 except that the resin layer was formed by changing the average thickness to 40 μm.

(Example 3)
A styrene-isobutylene-styrene triblock copolymer (SIBS, manufactured by Kaneka, "SIBSTAR 062T") was prepared in place of the styrene elastomer (PPET 1505SG), and the average thickness of the resin layer formed was changed to 40 μm. A resin layer-covered electronic component mounting board of Example 3 was obtained in the same manner as in Example 1.

(Example 4)
A styrene-isobutylene-styrene triblock copolymer (SIBS, manufactured by Kaneka, "SIBSTAR 072T") was prepared in place of the styrene elastomer (PPET 1505SG), and the average thickness of the resin layer to be formed was changed to 40 μm. A resin layer-covered electronic component mounting board of Example 4 was obtained in the same manner as in Example 1.

(Comparative Example 1)
A resin layer-covered electronic component mounting board of Comparative Example 1 was obtained in the same manner as in Example 1 except that the resin layer was formed by changing the average thickness to 10 μm.

(Comparative example 2)
In place of the styrene elastomer (PPET 1505SG), a polyolefin resin (“Humiseal 1B51NS” manufactured by Air Brown) was prepared, and the average thickness of the resin layer to be formed was changed to 30 μm. Similarly, a resin layer-covered electronic component mounting board of Comparative Example 2 was obtained.

<Evaluation test>
With respect to the resin layer-covered electronic component mounting boards produced in each of the examples and each of the comparative examples, the shape followability was evaluated. Hereinafter, these evaluation methods will be described.

<< Shape conformability >>
The shape following property was evaluated as follows.
That is, with respect to the resin layer-covered electronic component mounting boards produced in each of the examples and each of the comparative examples, judgment was made based on the following evaluation criteria depending on the presence or absence of voids in the coated unevenness. The presence or absence of voids was observed using a microscope.

The respective symbols are as follows, and ◯ was passed and × was not passed.
⊚: The bottom of the step is covered in a filled state ○: Although a slight void is formed at the bottom of the step,
It can be said that the coating is filled up to almost the bottom of the step. ×: Covered with a clear void formed at the bottom of the step.

Furthermore, the water vapor permeability (barrier) was evaluated using the resin layer 7 in the resin layer-covered electronic component mounting boards of the examples and the comparative examples. The evaluation method will be described below.

<<Water vapor permeability (barrier) (whether rust is generated on the copper foil)>>
Prepare a substrate coated with copper foil, then, each of the liquid material prepared in each Example and each Comparative Example, respectively, by supplying to the upper surface side of the substrate coated with copper foil and then dried and solidified, A resin layer covering the substrate and the copper foil was formed. The average thickness of the resin layer to be formed was the same as the average thickness of the resin layer provided in the resin layer-covered electronic component mounting boards of Examples and Comparative Examples corresponding to each.

Then, the resin layers covering the substrate and the copper foil, which correspond to the examples and the comparative examples, were immersed in hot water at 80° C. for 240 hours, and the copper foils after 24 hours and after 240 hours, respectively. The presence or absence of rust was observed and judged based on the following evaluation criteria. The presence or absence of rust was observed with a microscope from the resin layer side.

Each symbol is as follows, and ⊚ or ◯ was accepted, and × was rejected.
⊚: No rust was found on the copper foil even after 240 hours. ◯: No rust was found on the copper foil after 24 hours.
Occurrence of rust is observed after 240 hours. X: Clear rust is observed after 24 hours in the copper foil.

As is clear from Table 1, in the resin layer-covered electronic component mounting board of each example, since the resin layer is composed mainly of the solvent-soluble resin, the electronic component can be formed without forming a void at the bottom of the recess. It was possible to coat the mounting substrate. Further, in the resin layer-covered electronic component mounting boards of the respective examples, the resin layer composed mainly of the solvent-soluble resin satisfies the relationship of A·B≦30 to prevent rust in the copper foil. The results showed that the occurrence could be properly suppressed.

On the other hand, in the resin layer-covered electronic component mounting substrate of each comparative example, it was possible to coat the electronic component mounting substrate without creating a void at the bottom of the recess, but a solvent-soluble resin was used. The resin layer formed as the main material cannot satisfy the relationship of A/B≦30, and A/B>30. Due to this, rust occurs in the copper foil after 24 hours. The results are shown.

4 electronic component 5 substrate 6 unevenness 7 resin layer 45 electronic component mounting substrate 50 resin layer coated electronic component mounting substrate 61 convex portion 62 concave portion

Claims (10)

A substrate and a resin layer forming material used to form a resin layer covering an electronic component mounting substrate including an electronic component mounted on the substrate, the resin layer forming material containing a solvent-soluble resin as a main material,
The resin layer formed using the resin layer forming material has a water vapor permeability of the resin layer of A [g/m ² /day] and a concentration of ionic impurities contained in the resin layer of B[ ppm], the resin layer forming material is characterized by satisfying the relationship of A·B≦30. The resin layer forming material according to claim 1, wherein the water vapor permeability A is 20 g/m ² /day or less. The resin layer forming material according to claim 1, wherein the concentration B of the ionic impurities is 3.0 ppm or less. The resin layer forming material according to any one of claims 1 to 3, which satisfies a relationship of B/C ≤ 0.200 when an average thickness of the resin layer to be formed is C [µm]. The resin layer forming material according to claim 1, wherein the resin layer has an average thickness of 5 μm or more and 100 μm or less. The resin layer formation according to any one of claims 1 to 5, wherein the solvent-soluble resin is at least one of (meth)acrylic resin, polyolefin elastomer, styrene elastomer, polyester resin, and urethane resin. Materials. The resin layer forming material further contains a solvent,
The resin layer forming material according to any one of claims 1 to 6, wherein the solvent is at least one selected from the group consisting of toluene, normal hexane, methyl ethyl ketone, and ethyl acetate. The resin layer forming material according to claim 1, wherein the resin layer forming material has a viscosity at 25° C. of 30 mPa·s or more and 500 mPa·s or less. It has the said electronic component mounting substrate, and the said resin layer which coat|covers at least the said electronic component formed using the resin layer forming material of any one of Claim 1 thru|or 8. Resin layer coated electronic component mounting board. The resin layer-covered electronic component mounting board according to claim 9, wherein the board is a printed wiring board.

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