WO2010143379A1 - Method of producing electronic component mounting structure, and electronic component mounting structure - Google Patents

Abstract

Disclosed is a method of producing an electronic component mounting structure, provided with a mounting step of mounting an electronic component on a circuit board by soldering terminals connected to the electronic component to electrodes formed on a circuit board surface, a coating step of coating a liquid state curable resin composition so as to cover the soldered section on the surface of the circuit board surface formed by soldering, said liquid state curable resin composition including a curable resin and a foaming agent, a curing step of forming a cured resin by curing the liquid state curable resin composition at a temperature lower than the temperature at which the foaming agent foams, and a foaming step which causes a foaming agent to foam by heating at least a portion of the cured resin.

Description

Electronic component mounting structure manufacturing method and electronic component mounting structure

The present invention relates to an electronic component mounting structure manufacturing method and an electronic component mounting structure. Specifically, the present invention relates to a method for manufacturing an electronic component mounting structure capable of controlling the thickness of a cured resin that protects an electronic component mounted on a circuit board surface.

Conventionally, to protect electronic components mounted on the circuit board surface from moisture, gas, dust, impact, etc., overcoating that covers the electronic components with a cured resin such as epoxy resin, polyurethane, silicone resin, acrylic resin, etc. The law is known.

In addition, in order to reinforce the solder joint of the electronic component mounting structure formed by mounting the electronic component on the circuit board surface by flip chip connection, a resin is formed in the gap formed between the circuit board surface and the electronic component. An underfill method for filling a cured product is also known.

Patent Document 1 discloses a sealing resin composition containing a curable resin and a foaming agent. The encapsulating resin composition disclosed in Patent Document 1 is an underfill resin composition that allows an electronic component mounted on a circuit board surface to be easily removed and repaired (repaired). Specifically, the sealing resin composition is underfilled and cured at the solder joint between the circuit board and the electronic component flip-chip connected to the surface thereof. And when removing the electronic component mounted in the circuit board, a foaming agent is foamed by heating to the temperature at which the foaming agent in resin cured material foams. The strength of the cured resin is reduced by foaming of the foaming agent, and the mounted electronic component can be easily removed by melting the solder.

In addition, an electronic component mounted on a circuit board accommodated in a portable electronic device may be disconnected or damaged by an impact or the like. In order to suppress such damage due to disconnection, etc., a protective coating made of a cured resin is formed for the purpose of reinforcement on parts that are relatively susceptible to damage such as joints between the circuit board surface and electronic components. The method of doing is also known. As an example, an electronic component mounting structure 50 obtained by mounting an electronic component 52 including an IC (Integrated Circuit) package 60 and lead terminals 61 on a circuit board 13 as shown in FIG. 3 will be described. The electronic component 52 is inserted into the through hole H1 formed in the circuit board 13 from the front surface of the circuit board 13 and then soldered to the circuit (not shown) formed on the back surface of the circuit board 13 using the solder 55. It is implemented by attaching. And the resin cured material 53 which is a protective film is formed in the surface of the solder | pewter 55 and the lead terminal 61 soldered. As shown in FIG. 3, it is easy to form a cured resin 53 having a uniform thickness and an appropriately thick thickness in the flat region (R1) of the electronic component 52. On the other hand, in the region (R2) of the tip portion of the lead terminal 61 and the edge portion (R3) of the electronic component 52, a cured resin 53 having a uniform thickness and an appropriately thick thickness can be formed due to the influence of the interfacial tension or the like. Have difficulty. Therefore, the film thickness of the cured resin 53 in such a region tends to be thin. As a result, there is a possibility that the insulation characteristics and the like due to the cured resin 53 are reduced in the thin portion of the cured resin 53. For example, when the film thickness of the cured resin 53 formed at the tip portion of the lead terminal 61 becomes thin, current may leak from the thin portion. Such current leakage is particularly likely to occur in a high temperature and high humidity environment.
In order to solve such a problem, after forming the resin cured product 53 in a region such as the tip portion (R2) of the lead terminal 61 or a region such as the edge portion (R3) of the electronic component 52, another A method of increasing the film thickness by overlapping the cured resin products is also conceivable. However, it is difficult to form a film at a pinpoint in a fine region such as a tip portion or an edge portion of a lead terminal in a separate process, and productivity is reduced due to an increase in processes. Furthermore, when another resin cured product is stacked, the weight increases accordingly, which is not preferable from the viewpoint of weight reduction.
JP 2007-131820 A

The present invention relates to an electronic component mounting structure capable of easily controlling the thickness of a protective coating when an electronic component mounted on a circuit board surface is coated with a curable resin composition containing a foaming agent. It aims at providing the manufacturing method of.

One aspect of the present invention is to mount an electronic component on a circuit board by soldering a terminal connected to the electronic component to an electrode formed on the surface of the circuit board, and a circuit formed by soldering. An application step of applying a liquid curable resin composition containing a curable resin and a foaming agent so as to cover a solder joint on the substrate surface, and a temperature lower than the temperature at which the foaming agent foams the liquid curable resin composition An electronic component mounting structure manufacturing method comprising: a curing step of forming a resin cured product by curing at a temperature; and a foaming step of foaming a foaming agent by heating at least a part of the resin cured product.
Another aspect of the present invention is an electronic component mounting structure including a circuit board and at least one electronic component mounted by soldering on an electrode formed on the surface of the circuit board. The portion is covered with a resin cured product, and the resin cured product is a cured product of a curable resin composition containing a foaming agent and a curable resin, and at least a part of the foaming agent of the resin cured product is foamed. An electronic component mounting structure.
Another aspect of the present invention is an electronic component mounting structure including a circuit board and at least one electronic component mounted on the first surface of the circuit board. The electronic component includes an electronic component body and an electronic component. It has a plurality of lead terminals for mounting through holes connected to the component body, and the circuit board is provided around the through holes on the surface of the second surface and the plurality of through holes that penetrate from the first surface to the second surface. Each lead terminal is inserted into each through-hole and soldered to the circuit, and the soldered portion of the surface of the second surface and its periphery are covered with a cured resin. The resin cured product is a cured product of a curable resin composition containing a foaming agent and a curable resin, and at least a part of the foaming agent of the resin cured product is foamed. It is.

According to the present invention, it is possible to easily control the film thickness of the cured resin that covers the joint portion of the electronic component mounted on the circuit board.

The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

It is a schematic cross section for demonstrating the mounting process of the manufacturing method of the electronic component mounting structure 10 of this embodiment. It is a schematic cross section for demonstrating the application | coating process of the manufacturing method of the electronic component mounting structure 10 of this embodiment. It is a schematic cross section for demonstrating the hardening process of the manufacturing method of the electronic component mounting structure 10 of this embodiment. It is a schematic cross section for demonstrating the foaming process of the manufacturing method of the electronic component mounting structure 10 of this embodiment. It is a longitudinal cross-sectional view which shows typically the structure of the electronic component mounting structure 20 for demonstrating the effect of the manufacturing method of the electronic component mounting structure of this embodiment. It is a longitudinal cross-sectional view which shows typically the structure of the conventional electronic component mounting structure 50 which coat | covered the electronic component mounted in the circuit board with the protective film which consists of resin hardened | cured material.

First, the liquid curable resin composition used for the manufacturing method of the electronic component mounting structure according to the present embodiment will be described in detail.
The liquid curable resin composition is a curable resin composition that is liquid at room temperature and contains a curable resin and a foaming agent. The curable resin composition which is liquid at normal temperature is a composition containing a foaming agent as a main component of a solvent-free liquid resin or a resin varnish obtained by dissolving a solid resin at normal temperature in a solvent. It is.
Specific examples of the curable resin include a thermosetting resin, a photocurable resin, and an electron beam curable resin. As such a curable resin, a conventionally known curable resin is used, and specifically, formed from a resin component such as a silicone resin, polyurethane, acrylic resin, polyolefin, epoxy resin, or the like. . Among these, a thermosetting silicone resin, a thermosetting polyolefin, and the like are particularly preferable from the viewpoint that the foaming state can be easily controlled in the foaming process described later.

As the thermosetting resin, a resin that can be cured at a temperature lower than the gas generation temperature of the foaming agent, which will be described later, is preferable because it can suppress foaming during thermosetting. Specifically, for example, a resin that can be cured at a temperature that is 10 ° C. or more lower than the gas generation temperature of the foaming agent, and further 20 ° C. or more is preferable. Specifically, it is preferably a low temperature curable thermosetting resin that is cured at a low temperature such as room temperature to 100 ° C., and further room temperature to 80 ° C. In such a case, the thermosetting resin can be cured while being suppressed from foaming by heating to a curing temperature lower than the gas generation temperature of the foaming agent.
In order to foam the foaming agent in the resin cured product, it is preferable that the thermosetting resin to be used has elasticity even after curing. Specifically, it is preferable that the glass transition point (Tg) of the cured resin is lower than the foaming temperature. Specifically, for example, the cured resin preferably has a Tg of 100 ° C. or lower.

As the foaming agent, an organic decomposable foaming agent capable of generating gas by heating to a predetermined temperature and foaming the resin cured product is used. Specific examples of such a foaming agent include, for example, azodicarbonamide (gas generation temperature: about 208 ° C., the same applies hereinafter), N, N′-dinitrosopentamethylenetetramine (about 205 ° C.), 4,4′- Oxybis (benzenesulfonylhydrazide) (about 159 ° C.), sodium bicarbonate (about 150 ° C.), barium azodicarboxylate (about 245 ° C.), acetone-paratoluenesulfonyl hydrazone (about 135 ° C.), paratoluenesulfonyl semicarbazide (about 220 ° C.) ° C), and mixtures thereof.

The gas generation temperature of the foaming agent can be measured using, for example, a differential scanning calorimeter (DSC). Specifically, a predetermined amount of foaming agent is weighed as a sample, and the thermal behavior of the foaming agent when the weighed foaming agent is heated at a predetermined temperature increase rate is measured by DSC. Usually, an endothermic peak is observed in the curve indicating the relationship between the endothermic amount and the temperature. Here, the temperature at which the endothermic amount is maximum is the gas generation temperature.

Such an organic decomposable foaming agent generates foaming gas, specifically, for example, nitrogen gas (N ₂ ), carbon dioxide gas (CO ₂ ), etc. by decomposing at a predetermined temperature. The gas generation temperature is not particularly limited, but is preferably a temperature that does not exceed the melting point of the solder used for mounting the electronic component, and specifically, for example, 110 to 210 ° C., more preferably 120 to 180 ° C. It is preferable that it is the range of these.

The content of the foaming agent in the liquid curable resin composition is 0.05 to 45% by mass, more preferably 1 to 40% by mass, particularly 5%, based on the total amount of the liquid thermosetting resin and the foaming agent. It is preferably ˜25 mass. When the content ratio of the foaming agent in the liquid curable resin composition is too high, the content ratio of the curable resin is relatively decreased, and thus the properties such as adhesion of the obtained resin cured product tend to be decreased. There is. On the other hand, when the content of the foaming agent in the liquid curable resin composition is too low, the resin cured product tends not to be sufficiently thick due to foaming.

The liquid curable resin composition may contain an additive as necessary. Specific examples of additives include, for example, curing catalysts, foam stabilizers, emulsifiers, flame retardants (phosphorus compounds, halogen compounds, etc.), antioxidants, anti-aging agents, ultraviolet absorbers, plasticizers, fillers (talc) Clay, calcium carbonate, silica powder, alumina, carbon black, titanium oxide, iron oxide, etc.), dyes, pigments and the like. You may use an additive individually by 1 type or in combination of 2 or more types.

The liquid curable resin composition can be prepared by uniformly mixing a liquid curable resin and a foaming agent and defoaming. The liquid curable resin composition may contain a diluent in order to adjust its viscosity. When a diluent is used, the content of the diluent is preferably 40 to 90% by mass, more preferably 50 to 80% by mass, from the viewpoints of handleability, coating properties, leveling properties, and the like.
The solution viscosity of the liquid curable resin composition is preferably 1000 to 100 mPa · sec, more preferably 400 to 200 mPa · sec. In the case of such a solution viscosity, since it can be applied as an overcoat material for covering the surface of an electronic component or as an underfill material for flip chip mounting, the overcoat material and the underfill material can be applied in a single process. The material can be applied simultaneously. The solution viscosity is a value measured by a method based on the drop time of the viscosity cup.

Next, a method for manufacturing an electronic component mounting structure using the liquid curable resin composition as described above will be described in detail with reference to FIGS. 1A to 1D.
The manufacturing method of the electronic component mounting structure according to the present embodiment includes a mounting step of mounting the electronic component on the circuit board by soldering a terminal connected to the electronic component to an electrode formed on the surface of the circuit board. Applying a liquid curable resin composition containing a curable resin and a foaming agent to cover the solder joints on the circuit board surface formed by soldering, and foaming the liquid curable resin composition A curing step of forming a resin cured product by curing at a temperature lower than the temperature at which the agent foams, and a foaming step of foaming the foaming agent by heating at least a part of the resin cured product.
For example, as shown in FIG. 1A, the mounting process for mounting electronic components on the surface of the circuit board includes electronic components 2a, 1a, 1b, 1c at predetermined positions on the surface of the circuit board 3, which are mounting areas. This is a process of mounting by soldering and joining the terminals 2b and 2c.
The electronic component 2a is an IC package, and the electrode 7 formed on the surface thereof is connected to the electrode 1a formed on the surface of the circuit board by wire bonding with a wire W. The electronic component 2b is an IC package, and an unillustrated electrode formed on the back surface is connected to the electrode 1b formed on the surface of the circuit board by flip-chip mounting with solder bumps s1. The electronic component 2c is a connector, and a plurality of lead terminals L for mounting through holes are inserted into through holes H2 formed on the circuit board, and each lead terminal L is soldered to the electrode 1c formed on the back surface thereof. They are connected by mounting through holes.

Specific examples of circuit boards include various printed boards including rigid boards and flexible boards. A rigid substrate uses a known circuit forming method such as a photoresist method on the surface of a substrate obtained by laminating a plurality of prepregs impregnated with a curable resin such as an epoxy resin on a fiber base material and heating and pressing. A printed wiring board on which a circuit made of copper foil or the like is formed. The flexible substrate is formed by forming a circuit on the surface of a heat-resistant resin film such as a polyimide film.

Specific examples of electronic components that can be used in the method for manufacturing an electronic component mounting structure according to this embodiment include various IC packages, various resistors, various light emitting diodes, various capacitors, various connectors, and the like. The number of electronic components mounted on the circuit board surface may be one or more. Usually, a plurality of packages are mounted depending on the application.

The method for mounting electronic components on the circuit board surface is not particularly limited, and a known surface mounting method or through-hole mounting method can be used. Specific examples include the following. Examples thereof include wire bonding connection in which a plurality of electrodes 7 formed on the surface of the electronic component 2a and an electrode 1a formed on the surface of the circuit board 3 are connected by thin wires such as gold wires. Also, a plurality of protruding solder bumps s1 formed on electrodes (not shown) formed on the surface of the electronic component 2b are placed on the electrodes 1b formed on the surface of the circuit board 3 so as to correspond to the solder bumps s1, The flip chip mounting which joins by passing through a reflow furnace is mentioned. Further, the lead terminals L of the electronic component 2c having a plurality of lead terminals L for mounting through holes are inserted into the through holes H2 formed on the circuit board, and each lead terminal L is soldered to the electrode 1c formed on the back surface thereof. Through-hole mounting to be attached.

Next, an application process for applying a liquid curable resin composition containing a foaming agent so as to cover a solder joint on the surface of the circuit board formed by soldering will be described.
For example, as shown in FIG. 1B, the coating process is performed to form a resin joint that protects the solder joint formed by soldering the circuit board 3 and the electronic components 2a, 2b, and 2c. It is the process of apply | coating the liquid curable resin composition 4 containing a foaming agent so that it may coat | cover. At this time, by applying the liquid curable resin composition 4 so as to embed the electronic components 2a, 2b, 2c mounted on the surface of the circuit board 3, the liquid curable resin composition 4 is cured. A cured resin for protecting the electronic components 2a, 2b, 2c from the external environment can be formed at the same time. Note that the flip-chip-mounted electronic component 2b is further filled with the liquid curable resin composition 4 in the gap v between the electronic component 2b and the circuit board 3 in this step, so that an underfill material for flip-chip connection is used. Is also supplied. Thereby, the overcoat material and the underfill material are simultaneously applied to the electronic component 2b in one process. The application method of the liquid curable resin composition is not particularly limited, and specific examples include an application method using a dispenser (discharge device). Further, in order to protect the soldered lead terminal L of the electronic component 2c mounted with the through hole, the liquid curable resin composition 4 is applied to the solder joint portion on the back surface of the circuit board 3 to thereby prevent the through hole. A film made of a cured resin can also be formed at the joint between the electronic component 2c and the electrode 1c by mounting.

The coating amount of the liquid curable resin composition is not particularly limited. Specifically, for example, it is preferably 10 to 80 μm, more preferably 20 to 50 μm. When applied to such a thickness, in the foaming process after curing, the flat part is 20 to 160 μm, further 40 to 100 μm, the edge part of the electronic component or the tip part of the lead terminal is 10 to 40 μm, and A film of a cured resin film having a thickness as large as 20 to 30 μm can be obtained.

Next, a curing process for forming a resin cured product by curing the liquid curable resin composition applied as described above at a temperature at which the foaming agent does not foam will be described.
For example, as shown in FIG. 1C, in this step, each of the solder joints of the electronic components 2a, 2b, 2c mounted on the surface of the circuit board 3, the outer surfaces of the electronic components 2a, 2b, 2c, and the surface of the circuit board 3 is provided. The cured resin 5 is formed by curing the liquid curable resin composition 4 covering the periphery of the electronic component mounting region at a temperature at which the foaming agent does not foam. When the liquid curable resin composition 4 contains a thermosetting resin, the curing is performed at a temperature not higher than the gas generation temperature at which the foaming agent does not foam. Moreover, when the liquid curable resin composition 4 contains a photocurable resin, a sufficient amount of light for photocuring is irradiated. Furthermore, when the liquid curable resin composition 4 contains an electron beam curable resin, an electron beam sufficient for electron beam curing is irradiated. By such a method, the applied liquid curable resin composition 4 is cured, and a cured resin product 5 is formed.

Next, a foaming process for foaming the foaming agent by heating at least a part of the cured resin product 5 formed as described above will be described.

For example, as shown in FIG. 1D, in the foaming step, the region of the resin cured product 5 formed in the curing step is heated by heating the region surrounded by the broken line B, which is the portion where the film thickness is desired to be increased. The foaming agent contained in the product 5 foams to form pores 6, and the cured resin product 5 forms a foamed structure. Thereby, the electronic component mounting structure 10 is formed. The film thickness of the cured resin 5 is increased by the pressure of the gas when forming the pores 6. In this way, when only the portion of the resin cured product 5 to be thickened is selectively heated, a thick coating such as a portion to be reinforced, specifically, a corner portion of an electronic component or a tip portion of a lead terminal. A thick protective film can be easily formed even on a portion where it is difficult to form. This allows thicker film to be applied in a single step without applying thickening by coating in a separate process on the part that you want to reinforce, or where you want to form a thick-film protective coating such as the tip of a lead terminal. The part can be formed.
Here, the effect of the manufacturing method of this embodiment will be described more specifically. 2, the electronic component mounting structure 20 obtained by mounting the electronic component 52 including the IC package 60 and the lead terminal 61 on the circuit board 13 as shown in FIG. 2 is taken as an example. This will be described in detail in comparison with the component mounting structure 50.
In the electronic component mounting structure 20, the thickness of the cured resin 12 that is a protective coating is greater than the thickness of the cured resin 53 that is the protective coating of the conventional electronic component mounting structure 50 shown in FIG. 3. It is the same except that. In the electronic component mounting structure 20, the thickness of the cured resin 12 formed in the region of the tip portion of the lead terminal 61 and the edge portion of the electronic component 52 is increased by foaming the cured resin 12. . Thereby, the thickness of the region that tends to preferentially become thin due to the influence of the interfacial tension of the liquid curable resin composition after application is increased. Thus, the film thickness of the resin cured product 12 can be controlled by heating the portion where the film thickness is desired to be increased after curing. According to such a method, it is not necessary to secure a thick film by stacking another protective film. In order to heat only the predetermined portion, for example, a heater having a relatively small heating element is brought close to the upper portion of the predetermined portion to directly heat the predetermined portion, or air heated by the heater is sprayed onto the predetermined portion. The method of heating is used.

It is preferable that the heating temperature in the foaming step is equal to or higher than the gas generation temperature of the foaming agent and does not exceed the melting point of the solder used for joining the electronic component and the circuit board. Specifically, for example, it is preferably in the range of 110 to 210 ° C., more preferably 120 to 180 ° C. The heating time is appropriately adjusted depending on the target foaming ratio, and is preferably in the range of, for example, 1 to 10 minutes, and more preferably 3 to 7 minutes. Note that the foaming state can be controlled by changing the heating temperature and the heating time. And the higher the expansion ratio, the thicker the resin cured product. The resin cured product after foaming is 20 to 100 μm at the flat part, and further 20 to 95 μm at the flat part, depending on the film thickness of the resin cured product before foaming. Is preferably 20 to 40 μm, more preferably 20 to 35 μm.
The change in the apparent volume before and after the foaming process of the resin cured product of the foamed part is that the apparent volume after the foaming process is about 2 to 8 times, further about 3 to 5 times the apparent volume before the foaming process. preferable.

In addition, in this embodiment, although the case where only the part which wants to thicken the film thickness of a resin cured material was selectively heated was demonstrated in detail, you may heat the whole resin cured material. When heating the entire cured resin, the circuit board on which the cured resin is formed may be placed in a heating furnace or the like set at a predetermined temperature for a predetermined time. In such a case, the film thickness of the entire formed resin cured product is increased by the foaming process.

EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited to a following example.
[Examples 1 to 8]
(Preparation of liquid curable resin composition)
In this example, as the liquid thermosetting resin, a solvent-free liquid silicone resin (trade name: SE-9187L manufactured by Toray Dow Corning Co., Ltd., hereinafter also referred to as Resin A), or a diluent (dedicated thinner 904 ( Solid polyolefin (trade name: Humiseal 1B51NS manufactured by Chase Inc., hereinafter also referred to as resin B) dissolved in (trade name)) was used. In the resin B solution, the blending ratio of the solid polyolefin and the diluent was 1: 1 (weight ratio).
Then, a solution of resin A or resin B and a foaming agent (4,4′-oxybis (benzenesulfonylhydrazide; gas generation temperature of about 170 ° C.)) are mixed at a ratio shown in Table 1 and subjected to defoaming treatment. A liquid curable resin composition was prepared, and the content ratio of the foaming agent in Table 1 is the weight ratio of the foaming agent to the total amount of the curable resin (in terms of solid content) and the foaming agent.

(Mounting electronic components on circuit boards)
An IC package having a length of 10 mm, a width of 10 mm, and a height of 5 mm provided with a metal lead terminal portion was mounted on an FR-4 type circuit board using a mounter, and mounted using a reflow furnace having a maximum temperature of 240 ° C. Note that solder of Sn-3Ag-0.5Cu (melting point: 217-219 ° C.) was used for bonding.

(Coating process, curing process and foaming process)
A liquid curable resin composition was applied using a dispenser around the outer surface of the IC package, the joint, and the area where the IC package was mounted on the surface of the circuit board so as to embed the IC package mounted on the circuit board. . As shown in Table 1, in Examples 1, 2, 5, and 7, resin A was used as the curable resin, and in Examples 3, 4, 6, and 8, resin B was used.
And the resin hardened | cured material was formed by heating the circuit board with which the liquid curable resin composition was apply | coated for 60 minutes with the heating furnace set to 40 degreeC. Next, the foaming agent in the cured resin was foamed by heating the circuit board on which the cured resin was formed in a heating furnace set at 170 ° C. for 5 minutes. In this manner, the electronic component mounting structures A to H in which the IC package was mounted on the main surface of the circuit board and the IC package was covered with the foamed cured product were obtained.

(Evaluation)
The obtained electronic component mounting structures A to H were evaluated by the following methods.
[Change in film thickness]
In manufacturing the electronic component mounting structures A to H, the film thickness before and after the foaming process was measured. The film thickness of the cured product was measured at two locations, a flat portion of the circuit board and an edge portion of the IC package.

[Edge insulation]
Regarding the electronic component mounting structures A to H, generation of smoke when a water droplet was dropped while a direct current of 50 V was applied to the cured product formed at the edge portion of the IC package was visually confirmed.

[Adhesion]
A cross-cut tape peeling test was performed on the cured products formed on the electronic component mounting structures A to H. Specifically, a film made of a resin cured product on a flat portion of a circuit board was cut out on a grid having 100 grids of 1 mm × 1 mm square using a cutter knife and a cutter guide. Then, after the cellophane tape was strongly pressure-bonded to the area cut out in the grid of the coating, the number of peeling of the grid when the tape edge was rapidly peeled off at an angle of 45 ° was counted.

As shown in Table 1, in any of Examples 1 to 8, after sealing with a resin cured product composed of a liquid resin composition containing a foaming agent, the foaming agent is foamed to form a film before the foaming step. The film thickness after the foaming process increased more than the thickness.
In Examples 1 to 4 using the liquid resin composition having a foaming agent content of 1 to 40% by mass, the film thickness of the cured product at the edge portion is 20 μm or more by foaming the foaming agent in the cured product. It was a thick one. Therefore, the insulating property of the edge portion was particularly excellent. On the other hand, in Examples 5 and 6 using the liquid resin composition having a foaming agent content of 0.01% by mass, the film thickness of the edge portion did not increase. Therefore, the insulating property of the edge part was slightly inferior. Moreover, in Example 7 and Example 8 using the liquid resin composition whose foaming agent content rate is 50 mass%, since the increase rate of the film thickness of an edge part is high, the insulation of the edge part was excellent. However, since the content of the foaming agent was too high, the adhesion was slightly lowered.

According to the method for manufacturing an electronic component mounting structure of the present invention, the thickness can be easily controlled in the case of forming a protective film that protects the joint between the circuit board and the electronic component. By using such a manufacturing method, a protective film having a high protective property can be formed by an easy process. Therefore, it is useful for protecting an electronic component mounting structure obtained by mounting electronic components such as an IC package, a resistor, a light emitting diode, a capacitor, and a connector on the circuit board.

DESCRIPTION OF SYMBOLS 1a, 1b, 1c ... Electrode formed on the circuit board surface 2a, 2b, 2c, 52 ... Electronic component 3, 13 ... Circuit board 4 ... Liquid curable resin composition 5, 12, 53 ... Resin hardened material 6 ... Pore 7 ... Electrode formed on electronic component 10 ... Circuit board 20, 50 ... Electronic component mounting structure 55 ... Solder 60 ... IC package 61 ... Lead terminal,
v: Gap between electronic component 2b and circuit board 3 H1, H2: Through hole

Claims (12)

A mounting step of mounting the electronic component on the circuit board by soldering a terminal connected to the electronic component to the electrode formed on the surface of the circuit board;
An application step of applying a liquid curable resin composition containing a curable resin and a foaming agent so as to cover a solder joint on the surface of the circuit board formed by the soldering;
A curing step of forming a resin cured product by curing the liquid curable resin composition at a temperature lower than a temperature at which the foaming agent foams;
And a foaming step of foaming the foaming agent by heating at least a part of the cured resin product. 2. The method of manufacturing an electronic component mounting structure according to claim 1, wherein the mounting step is a step of surface mounting the electronic component on an electrode formed on the surface of the circuit board. The surface mounting is a step of flip-chip mounting the electronic component on an electrode formed on the surface of the circuit board;
In the coating step, the outer surface of the electronic component and the periphery of the solder joint are integrally covered, and the liquid curable resin composition is filled so as to fill a gap between the electronic component and the circuit board. The method for manufacturing an electronic component mounting structure according to claim 2, wherein the electronic component mounting structure is applied. 2. The method of manufacturing an electronic component mounting structure according to claim 1, wherein the mounting step is a step of mounting the electronic component on an electrode formed on the surface of the circuit board through-hole. 2. The method of manufacturing an electronic component mounting structure according to claim 1, wherein the liquid curable resin is a thermosetting resin that can be cured at a temperature lower by 20 ° C. or more than a foaming temperature of the foaming agent. 2. The method for manufacturing an electronic component mounting structure according to claim 1, wherein the thickness of the curable resin foamed by heating after the foaming step is 20 μm or more. The content of the foaming agent contained in the liquid curable resin composition is in the range of 0.05 to 45% by mass with respect to the total amount of the curable resin and the foaming agent. Manufacturing method of electronic component mounting structure. An electronic component mounting structure including a circuit board and at least one electronic component mounted on the circuit board by soldering,
The soldered part is coated with a cured resin,
The resin cured product is a cured product of a curable resin composition containing a foaming agent and a curable resin,
An electronic component mounting structure, wherein a foaming agent of at least a part of the cured resin is foamed. The electronic component is mounted by flip chip mounting on an electrode formed on the surface of the circuit board,
The electronic component mounting structure according to claim 8, wherein the cured resin is further filled in a gap formed between the electronic component and the circuit board. 9. The electronic component mounting structure according to claim 8, wherein the electronic component is connected by wire bonding to an electrode formed on a surface of the circuit board. The electronic component mounting structure according to claim 8, wherein the electronic component is through-hole mounted on an electrode formed on a surface of the circuit board. An electronic component mounting structure including a circuit board and at least one electronic component mounted on the first surface of the circuit board,
The electronic component has an electronic component main body and a plurality of lead terminals for mounting through holes connected to the electronic component main body, and the circuit board has a plurality of through holes penetrating from the first surface to the second surface, and the first A circuit provided around each through-hole on the surface of two surfaces;
Each lead terminal is inserted into each through-hole and soldered to the circuit,
The soldered portion of the surface of the second surface and its periphery are coated with a resin cured product,
The resin cured product is a cured product of a curable resin composition containing a foaming agent and a curable resin,
An electronic component mounting structure, wherein a foaming agent of at least a part of the cured resin is foamed.

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