WO2017110136A1 - Electronic component mounting structure, electronic component, and method for forming electronic component mounting structure - Google Patents

Abstract

To provide an electronic component mounting structure having high migration resistance, and high mounting strength with respect to a substrate. Disclosed is an electronic component mounting structure wherein solder fillets 17 connecting land electrodes 6a, 6b and external electrodes 3a, 3b to each other are formed, and furthermore, a coating resin layer 4 having migration suppressing functions is provided. The coating resin layer 4 covers , out of the four side surfaces of an electronic component 1, three side surfaces excluding a side surface facing a main surface of a substrate, and covers a pair of end surfaces of the electronic component 1 together with the external electrodes and the solder fillets 17 , and the coating resin layer 4 is not in contact with a main surface of a substrate 5, or in contact with, merely in the vicinity of the electronic component 1, the main surface of the substrate 5.

Description

Electronic component mounting structure, electronic component and method of forming electronic component mounting structure

The present invention relates to an electronic component mounting structure, and more particularly, to an electronic component mounting structure having high migration resistance and high mounting strength to a substrate.

The present invention also relates to an electronic component suitable for forming the electronic component mounting structure of the present invention described above.

Furthermore, the present invention relates to a method for forming an electronic component mounting structure suitable for forming the electronic component mounting structure of the present invention described above.

Measures against ion migration are an important issue in electronic component mounting structures in which electronic components are mounted on a substrate.

Ion migration (hereinafter abbreviated as “migration”) means that the metal component of one electrode is ionized between the electrodes having a potential difference, moves toward the other electrode, and is deposited between the electrodes by the deposited metal. This is a phenomenon in which the insulation property of the electrode decreases or the electrodes are short-circuited. It is likely to occur under high humidity conditions.

) Various studies have been made on technology for suppressing migration.

For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2014-157951), an external electrode of an electronic component is joined to a land electrode (substrate electrode) of the substrate by soldering, and then the entire substrate together with the electronic component is coated with a coating resin layer (protective layer). A technique for coating with a coating) is disclosed. Specifically, a coating resin layer is formed by supplying a resin with a dispenser onto a substrate on which electronic components are mounted. It is considered that the occurrence of migration is suppressed because the moisture resistance is improved by the coating resin layer.

In Patent Document 2 (Japanese Patent Laid-Open No. 9-167890), a resin component is contained in a solder paste used for reflow soldering, and the resin is deposited on the surface of a solder fillet formed after reflowing. A technique for forming a layer (protective coating) is disclosed. The coating resin layer is considered to suppress the occurrence of migration starting from the solder fret.

Furthermore, Patent Document 3 (Japanese Patent Laid-Open No. 2013-26392) is not intended to suppress migration, but in order to mount a plurality of electronic components in a narrow area on a substrate, external electrodes are not provided. An electronic component is disclosed in which a coating resin layer (insulating layer) made of a heat resistant resin is formed in advance on a pair of formed end surfaces and three side surfaces. The electronic component is disposed on the land electrode of the substrate on which the solder paste is applied with the side surface on which the coating resin layer is not formed facing down, and is mounted by reflow soldering. The coating resin layer prevents a short circuit between the external electrodes of adjacent electronic components mounted at high density, but at the same time, it is considered that migration between the external electrodes of each electronic component is also suppressed.

JP 2014-157951 A JP-A-9-167890 JP 2013-26392 A

The technique disclosed in Patent Document 1 has the following problems because the entire substrate is covered with the coating resin layer together with the electronic components. First, since it is necessary to add one step of coating the entire substrate with the coating resin layer together with the electronic component, there is a problem that the mounting operation of the electronic component becomes complicated and the cost increases. In addition, once the coating resin layer is formed, it is difficult to confirm whether or not the electronic component has been successfully mounted on the substrate, and it is difficult to measure the electrical characteristics of the electronic circuit formed on the substrate. There was a problem. Furthermore, once a coating resin layer is formed, it is difficult to replace electronic components, and even when one electronic component fails, the entire substrate must be discarded along with other electronic components. It was.

Further, the technique disclosed in Patent Document 2 has the following problems because the solder paste used for the reflow solder contains a resin component in advance. First of all, a special solder paste containing a resin component must be prepared. For this purpose, it is necessary to add one process, and it is necessary to manage the produced solder paste, which increases the cost. there were. In addition, the coating resin layer can suppress migration from the solder fillet to the starting point and end point, but it still has the problem that migration from the external electrode of the electronic component, land electrode, etc. to the starting point and end point cannot be suppressed. It was.

Furthermore, in the technique disclosed in Patent Document 3, since the external electrode of the electronic component is covered with a coating resin layer made of a heat-resistant resin during reflow soldering, a solder fillet is not formed, and the substrate and the electronic component There was a problem that the bonding strength with was weak. That is, since no solder fillet is formed, the external electrode of the electronic component is joined to the electrode only on the contact surface with the land electrode, and the electronic component is detached from the substrate only by applying a slight lateral force. There was a problem that.

The present invention has been made in order to solve the above-described conventional problems. As a means for this, the electronic component mounting structure of the present invention has a pair of end faces and four side faces connecting the pair of end faces. An electronic component having an external electrode formed at an end including the end surface; a substrate having a land electrode formed on a main surface; and a solder that joins the land electrode and the external electrode. A solder fillet connecting the land electrode and the external electrode is formed, and further includes a coating resin layer having a migration suppressing function, and the coating resin layer is formed on the main surface of the substrate among the four side surfaces of the electronic component. Covers three side surfaces excluding the opposite side surfaces and covers a pair of end faces of the electronic component together with external electrodes and solder fillets, and the coating resin layer is not in contact with the main surface of the substrate. Or it was assumed to be in contact only in the vicinity of the main surface and the electronic components of the substrate.

It is preferable that the coating resin layer further covers a side surface of the four side surfaces of the electronic component that faces the main surface of the substrate. In this case, the effect of suppressing migration starting from the external electrode or solder fillet of the electronic component by the coating resin layer as the starting point or the ending point becomes higher.

In order to solve the above-described problem, another electronic component mounting structure according to the present invention includes a pair of end faces and four side faces connecting the pair of end faces, and external electrodes are provided at the ends including the end faces. Comprising a formed electronic component, a substrate having a land electrode formed on the main surface, and a conductive adhesive that joins the land electrode and the external electrode, and further comprising a coating resin layer having a migration suppressing function, The coating resin layer covers the four side surfaces of the electronic component and is not in contact with the main surface of the substrate, or is in contact only with the main surface of the substrate in the vicinity of the electronic component. Note that the land electrode and the external electrode are firmly bonded with a conductive adhesive.

Further, in both the above-described mounting structures of the present invention, it is preferable that the coating resin layer further covers the land electrode. In this case, the migration that makes the land electrode the starting point and the ending point can also be suppressed by the coating resin layer.

In addition, the coating resin layer does not have an opening, and the coating resin layer can completely cover a necessary portion. In this case, the effect of suppressing migration by the coating resin layer is further ensured.

However, an opening may be present in the coating resin layer. Even if there are partial cracks or holes in the coating resin layer, the effect of suppressing migration is exhibited. That is, the distance between the electrodes is greatly involved in the deterioration of the insulating property and the occurrence of a short circuit due to migration, and the distance is more likely to occur and the distance is less likely to occur. Even if there are partial cracks or holes in the coating resin layer, the substantial distance between the electrodes increases through the cracks or holes, so that the occurrence of migration can be suppressed.

The pigment may be contained in the coating resin layer. In this case, deterioration of the resin forming the coating resin layer over time can be prevented, and the occurrence of migration can be suppressed over a long period of time.

The coating resin layer can be formed on the surface of the electronic component in advance, for example.

Also, the electronic component of the present invention is suitable for forming the electronic component mounting structure described above. As a means therefor, the electronic component of the present invention comprises a pair of end faces and four side faces connecting the pair of end faces, and an external electrode is formed at the end including the end faces. A coating resin layer having a suppression function is provided. The coating resin layer covers three of the four side surfaces and covers a pair of end surfaces together with external electrodes. The coating resin layer has a softening point of 90 ° C. As mentioned above, it shall be formed with resin which is 230 degrees C or less. This is because if the softening point of the coating resin layer is lower than 90 ° C., there is a problem that the softened resin flows excessively during mounting and the coating resin layer on the top surface of the electronic component becomes thin. This is because if the softening point of the coating resin layer exceeds 230 ° C., the coating resin layer is not softened at the time of mounting, and there is a problem that good fillet formation by solder cannot be performed.

In the application documents, the softening point of the coating resin layer was measured by a penetration method using a TMA apparatus (Thermomechanical Analysis Apparatus). Details of the measurement method will be described in the “Experiment” column of the “Mode for Carrying Out the Invention”.

Further, another electronic component of the present invention includes a pair of end faces and four side faces connecting the pair of end faces, and an external electrode is formed on an end including the end faces. A coating resin layer having a migration suppressing function is provided. The coating resin layer covers four side surfaces and a pair of end surfaces together with external electrodes. The coating resin layer has a softening point of 90 ° C. or higher and 150 ° C. or lower. It is assumed that it is formed of a resin that is. This is because if the softening point of the coating resin layer is lower than 90 ° C., there is a problem that the softened resin flows excessively during mounting and the coating resin layer on the top surface of the electronic component becomes thin. This is because if the softening point of the coating resin layer exceeds 150 ° C., there is a problem that the coating resin layer is not broken or takes time to break due to heat applied during mounting.

Further, another electronic component of the present invention is an electronic component comprising a pair of end faces and four side faces connecting the pair of end faces, and an external electrode is formed on the end including the end faces, The external electrode is formed such that a part thereof extends to four side surfaces, and further includes a coating resin layer having a migration suppressing function, and the coating resin layer covers three of the four side surfaces together with the external electrode. The remaining one side surface of the four side surfaces is covered except for the portion where the external electrode is formed, and further, a pair of end surfaces are covered together with the external electrode, and the coating resin layer has a softening point of 90 ° C. or higher, It was assumed to be formed of a resin that is 230 ° C. or lower. This is because if the softening point of the coating resin layer is lower than 90 ° C., there is a problem that the softened resin flows excessively during mounting and the coating resin layer on the top surface of the electronic component becomes thin. This is because if the softening point of the coating resin layer exceeds 230 ° C., the coating resin layer is not softened at the time of mounting, and there is a problem that good fillet formation by solder cannot be performed.

Also, the electronic component mounting structure forming method of the present invention is suitable for forming the electronic component mounting structure described above. As a means therefor, a method for forming a mounting structure for an electronic component according to the present invention includes a pair of end faces and four side faces connecting the pair of end faces, and an external electrode is formed at an end including the end faces. A step of preparing an electronic component including a coating resin layer having a migration suppressing function that covers three of the side surfaces and covers a pair of end surfaces together with external electrodes, and a substrate on which a land electrode is formed on the main surface A step of applying a solder paste on the land electrode, and a step of placing electronic parts on the land electrode coated with the solder paste with the side surface not covered with the coating resin facing down. By heating, the solder paste is melted and the molten solder is supplied, and the coating resin layer is softened, and the molten solder is removed from the gap between the external electrode and the coating resin layer. A step of infiltrating, by cooling, solidifying the molten solder is penetrated into the gap between the external electrode and the coating resin layer, it was those with, and forming a solder fillet.

In addition, another electronic component mounting structure forming method of the present invention includes a pair of end faces and four side faces connecting the pair of end faces, and external electrodes are formed on end portions including the end faces. A step of preparing an electronic component including a coating resin layer having a migration suppressing function that covers one side surface and covers a pair of end surfaces together with an external electrode; and a step of preparing a substrate on which a land electrode is formed on the main surface; , A step of applying a solder paste on the land electrode, a step of placing an electronic component on the land electrode on which the solder paste has been applied, and heating to supply the molten solder by melting the solder paste and coating Softens the resin layer, breaks the coating resin layer between the land electrode and the external electrode, and penetrates the molten solder into the gap between the external electrode and the coating resin layer. And that step, by cooling, solidifying the molten solder is penetrated into the gap between the external electrode and the coating resin layer, was those with, and forming a solder fillet.

In the electronic component mounting structure of the present invention, the coating resin layer covers the three side surfaces of the electronic component and the pair of end surfaces of the electronic component together with the external electrode and the solder fillet. In addition, the occurrence of migration with the solder fillet as a starting point or an end point is suppressed. In the electronic component mounting structure of the present invention, the solder fillet for joining the external electrode and the land electrode of the electronic component is formed between the external electrode of the electronic component and the coating resin layer. The bonding strength between the external electrode and the land electrode is high.

Further, in the mounting structure of another electronic component of the present invention, since the coating resin layer covers the four side surfaces of the electronic component, the occurrence of migration using the external electrode of the electronic component or the solder fillet as the starting point or the ending point occurs. Is suppressed. Note that the land electrode and the external electrode are firmly bonded by a conductive adhesive.

Moreover, according to the electronic component of the present invention, the mounting structure of the electronic component of the present invention can be easily formed.

Further, according to the method for forming an electronic component mounting structure of the present invention, the electronic component mounting structure of the present invention can be easily formed.

1A to 1C are perspective views showing steps performed in the method for forming the electronic component mounting structure 100 according to the first embodiment. 1A to 1C are used in the method for forming the electronic component mounting structure 200 according to the second embodiment. FIGS. 2D to 2F are continuations of FIG. 1C, and are perspective views showing steps performed in the method for forming the mounting structure 100, respectively. 2D to 2F are used in the method for forming the electronic component mounting structure 200 according to the second embodiment. 2 is a perspective view showing an example of a method for applying a coating resin to the electronic component 1. FIG. 4A and 4B are SEM photographs showing a cross section of the mounting structure 100. FIG. However, FIG. 4A shows a 90 × magnification, and FIG. 4B shows a 800 × magnification. FIG. 5A is a cross-sectional view showing an electronic component mounting structure 300 according to the third embodiment. FIG. 5B is a cross-sectional view showing an electronic component mounting structure 400 according to the fourth embodiment. FIGS. 6A to 6C show steps performed in the method of forming the electronic component mounting structure 500 according to the fifth embodiment. FIG. 6A is a perspective view, and FIG. , (C) is a sectional view. FIGS. 7A to 7C are cross-sectional views showing steps performed in the method of forming the electronic component mounting structure 600 according to the sixth embodiment. FIGS. 8A to 8C are cross-sectional views showing steps performed in the method of forming the electronic component mounting structure 700 according to the seventh embodiment.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

Each embodiment shows an embodiment of the present invention by way of example, and the present invention is not limited to the content of the embodiment. Moreover, it is also possible to implement combining the content described in different embodiment, and the implementation content in that case is also included in this invention. Further, the drawings are for helping understanding of the embodiment, and may not be drawn strictly. For example, a drawn component or a dimensional ratio between the components may not match the dimensional ratio described in the specification. In addition, the constituent elements described in the specification may be omitted in the drawings or may be drawn with the number omitted.

[First Embodiment]
1A to 1C and FIGS. 2D to 2F show a method of forming an electronic component mounting structure 100 according to the first embodiment. However, FIGS. 1A to 1C are perspective views showing steps performed in the forming method. FIGS. 2D to 2F are continuations of FIG. 1C, and are cross-sectional views showing steps performed in the formation method. 2D to 2F, the external appearance is shown instead of a cross section of a component main body 2 and external electrodes 3a and 3b of the electronic component 1 described later for the sake of clarity.

First, as shown in FIG. 1A, an electronic component 1 is prepared. In the present embodiment, an NTC thermistor widely distributed as a general-purpose product was prepared as the electronic component 1.

The electronic component (NTC thermistor) 1 includes a component body 2. The component body 2 includes a pair of end surfaces 2a and 2b and four side surfaces 2c, 2d, 2e, and 2f that connect the end surfaces 2a and 2b. The component body 2 is made of a semiconductor ceramic that exhibits negative resistance temperature characteristics. Although not shown, the component main body 2 has a laminated structure composed of a plurality of layers, and internal electrodes are formed between specific layers. The internal electrode contains, for example, Ag—Pd as a main component.

External electrodes 3 a and 3 b are formed at the end of the component body 2. In the present embodiment, the external electrode 3a is formed in a cap shape on the end surface 2a of the component body 2 and the four side surfaces 2c to 2f surrounding the end surface 2a. Similarly, the external electrode 3b is formed in a cap shape on the end surface 2b of the component body 2 and the four side surfaces 2c to 2f surrounding the end surface 2b. However, the external electrode 3a is not necessarily formed in a cap shape, and may be formed at least on the end surface 2a of the component main body 2. Similarly, the external electrode 3b is not necessarily formed in a cap shape, and may be formed at least on the end surface 2b of the component main body 2.

In the present embodiment, the external electrodes 3a and 3b are each formed in a multilayer structure of three layers (not shown). The first layer is composed of a baked electrode layer mainly composed of Ag. The second layer is composed of a plating electrode layer containing Ni as a main component. The third layer is composed of a plating electrode layer containing Sn as a main component. However, the structure of the external electrodes 3a and 3b is arbitrary and is not limited to the above. For example, a baked electrode layer mainly composed of Pd or a baked electrode layer mainly composed of Ag—Pd may be used instead of the baked electrode layer mainly composed of Ag. Alternatively, the plating electrode layer mainly containing Ni in the second layer and the plating electrode layer mainly containing Sn in the third layer may be omitted.

Next, a coating resin is attached to the end surfaces 2a and 2b of the component body 2 and three side surfaces 2c, 2d and 2e among the four side surfaces 2c to 2f, as indicated by arrows in FIG. A coating resin layer 4 is formed as shown in FIG. The coating resin layer 4 is formed on the external electrodes 3a and 3b.

The coating resin layer 4 is for suppressing the microphones having the external electrodes 3a and 3b, a solder fillet 17 (to be described later) and the like as starting points and ending points. Since the microphone is easily generated under a high humidity condition, it can be said that the coating resin layer 4 has a migration suppressing function as long as at least the moisture resistance is improved.

In addition, improving the moisture resistance refers to a state in which the coating resin layer 4 suppresses the generation of water droplets on the migration starting and ending electrodes and fillets.

The coating resin layer 4 needs to be softened by heat during reflow soldering. That is, the coating resin layer 4 is softened by heat during reflow soldering, and a solder fillet 17 is formed between the external electrodes 3a and 3b and the coating resin layer 4 to improve the bonding strength. There is a need.

Whether or not the coating resin layer 4 is softened by heat during reflow soldering and a good solder fillet 17 is formed at the joint and the good coating resin layer 4 can be maintained, mainly, It depends on the softening point of the resin constituting the coating resin layer 4 and the amount of solder supplied. The softening point of the coating resin can be adjusted by the type of the resin as the main component, the ratio of the resin as the main component to the total amount including the solvent to be dispersed (concentration of the resin as the main component), etc. it can. *

The conditions under which a good solder fillet 17 is formed and the good coating resin layer 4 can be maintained will be described in the “Experiment” section described later.

In this embodiment, an epoxy resin having a softening point of 230 ° C. is used as the resin that is the main component of the coating resin. The softening point was measured by a penetration method using a TMA apparatus (Thermomechanical analysis apparatus). Details of the measurement method will be described in the “Experiment” section described later. As the solvent, thinner mainly composed of MEK (methyl ethyl ketone) was used, and the concentration of the epoxy resin was set to 10%. However, the concentration of the epoxy resin can be adjusted as appropriate. Instead of the epoxy resin, an acrylic melamine resin, a polyester resin, an acrylic urethane resin, an acrylate resin, a silicon acrylate resin, an epoxy acrylate resin, a phenol resin, an acrylic silicon resin, or the like may be used. Moreover, the kind of solvent can also be changed suitably. In this embodiment, a small amount of pigment is added to the coating resin for the purpose of suppressing deterioration of the resin over time.

The formation of the coating resin layer 4 is performed, for example, by arranging a plurality of electronic components 1 on a base 50 and spraying the above-described coating resin using a spray device 60 as shown in FIG. Note that an adhesive layer 51 is formed on the surface of the base 50 and is in close contact with the bottom surface (side surface 2 f) of the component body 2, so that the coating resin layer 4 is not formed on the side surface 2 f of the component body 2.

In this embodiment, the coating resin layer 4 has a thickness of 5 to 15 μm.

In parallel with the preparation of the electronic component 1, the substrate 5 is prepared as shown in FIG. The substrate 5 is made of resin or ceramics.

A pair of land electrodes 6 a and 6 b are formed on the main surface of the substrate 5. In the present embodiment, the land electrodes 6a and 6b are formed in a multilayer structure in which a plating electrode layer mainly composed of Sn is formed on a main electrode layer mainly composed of Cu, although not shown. In the present embodiment, the thickness of the main electrode layer is 18 μm, and the thickness of the plating electrode layer is about 1 μm. Next, as shown in FIG. 2D, the solder paste 7 is applied (printed) to the land electrodes 6a and 6b. In this embodiment, the solder paste 7 is composed mainly of SnAgCu solder. In this embodiment, the application thickness of the solder paste 7 is 150 μm.

Next, as shown in FIG. 2E, the electronic component 1 is arranged on the land electrodes 6a and 6b to which the solder paste 7 is applied. The electronic component 1 is arranged with the side surface 2f of the component main body 2 on which the coating resin layer 4 is not formed facing down. As a result, the external electrode 3a of the electronic component 1 contacts the solder paste 7 applied on the land electrode 6a, and the external electrode 3b contacts the solder paste 7 applied on the land electrode 6b.

Next, the substrate 5 on which the electronic component 1 is arranged is heated at 265 ° C. for 20 seconds.

As a result, the solder paste 7 is melted, molten solder (not shown) is supplied onto the land electrodes 6a and 6b, and the coating resin layer 4 formed on the electronic component 1 is softened. Then, the molten solder penetrates into the gap between the external electrodes 3a and 3b and the coating resin layer 4 due to surface tension.

Next, the substrate 5 on which the electronic component 1 is arranged is naturally cooled to solidify the molten solder, thereby forming a solder fillet 17 as shown in FIG. The coating resin layer 4 that has been softened by natural cooling also recovers its original hardness.

The solder fillet 17 firmly joins the external electrodes 3a and 3b to the land electrodes 6a and 6b. The solder fillet 17 is covered with the coating resin layer 4.

Thus, the mounting structure 100 according to the first embodiment is completed. 4A and 4B show SEM photographs of a cross section of the mounting structure 100. FIG. However, FIG. 4A shows a 90 × magnification, and FIG. 4B shows a 800 × magnification.

When 50 electronic component mounting structures 100 of the present embodiment were created, it was confirmed that 50 solder fillets 17 were formed, and the reproducibility was high.

In the mounting structure 100 of the present embodiment, since the external electrodes 3a, 3b and the solder fillet 17 are covered with the coating resin layer 4, the occurrence of migration with the external electrodes 3a, 3b and the solder fillet 17 as starting points and ending points is generated. Is suppressed.

In the mounting structure 100 of the present embodiment, the external electrodes 3a and 3b are firmly joined to the land electrodes 6a and 6b by the solder fillet 17.

[Second Embodiment]
In the first embodiment, the mounting structure 100 is formed using an NTC thermistor as the electronic component 1. In the second embodiment, the type of electronic component is changed, and the mounting structure 200 is formed by the same method as in the first embodiment. In the description of the second embodiment, description will be made with reference to FIGS. 1A to 1C and FIGS. 2D to 2F of the first embodiment.

In the second embodiment, as shown in FIG. 1A, a multilayer ceramic capacitor that is widely distributed as a general-purpose product is prepared as the electronic component 11.

The electronic component 11 made of a multilayer ceramic capacitor has the same external shape as the electronic component 1 made of the NTC thermistor of the first embodiment. That is, the electronic component 11 has a component body 2 having a pair of end surfaces 2a and 2b and four side surfaces 2c, 2d, 2e, and 2f that connect the end surfaces 2a and 2b. The component body 2 is made of dielectric ceramics whose main component is barium titanate or the like. Although not shown, the component main body 2 has a laminated structure composed of a plurality of layers, and internal electrodes are formed between the layers. The internal electrode contains, for example, Cu, Ni, Ag, Pd or the like as a main component.

External electrodes 3 a and 3 b are formed at the end of the component body 2. Although not shown, the external electrodes 3a and 3b are each formed in a multilayer structure of three layers. The first layer is composed of a baked electrode layer mainly composed of Cu. The second layer is composed of a plating electrode layer containing Ni as a main component. The third layer is composed of a plating electrode layer containing Sn as a main component.

Next, a coating resin is attached to the end surfaces 2a and 2b of the component body 2 and three side surfaces 2c, 2d and 2e among the four side surfaces 2c to 2f, as indicated by arrows in FIG. A coating resin layer 4 is formed as shown in FIG.

In this embodiment, an acrylic melamine resin having a softening point of 120 ° C. is used as the resin that is the main component of the coating resin. The solvent used was thinner mainly composed of xylene, and the concentration of the acrylic melamine resin was 10%. In the present embodiment, a small amount of pigment is added to the coating resin for the purpose of suppressing deterioration of the resin over time.

In this embodiment, the coating resin layer 4 has a thickness of 5 to 15 μm.

Next, as shown in FIG. 2D, the solder paste 7 is applied (printed) to the land electrodes 6a and 6b. In this embodiment, the solder paste 7 is composed mainly of SnAgCu solder. In the present embodiment, the application thickness of the solder paste 7 is 100 μm.

Next, as shown in FIG. 2E, the electronic component 11 is placed on the land electrodes 6a and 6b to which the solder paste 7 is applied.

Next, the substrate 5 on which the electronic component 1 is arranged is heated at 265 ° C. for 20 seconds. As a result, the solder paste 7 is melted, molten solder (not shown) is supplied onto the land electrodes 6a and 6b, and the coating resin layer 4 formed on the electronic component 11 is softened. Then, the molten solder penetrates into the gap between the external electrodes 3a and 3b and the coating resin layer 4 due to surface tension.

Next, by naturally cooling the substrate 5 on which the electronic component 11 is arranged, the molten solder is solidified to form a solder fillet 17 as shown in FIG. 2 (F), and the mounting structure according to the second embodiment Complete 200.

Also in the mounting structure 200 of the second embodiment, since the external electrodes 3a, 3b and the solder fillet 17 are covered with the coating resin layer 4, migration using the external electrodes 3a, 3b and the solder fillet 17 as starting points and end points is performed. Occurrence is suppressed.

Also in the mounting structure 200 of the present embodiment, the external electrodes 3a and 3b are firmly joined to the land electrodes 6a and 6b by the solder fillet 17.

[Experiment]
In the mounting structures 100 and 200 according to the first embodiment and the second embodiment, it is possible to maintain a good coating resin layer 4 in which a good solder fillet 17 is formed at the joint and migration can be suppressed. In order to clarify the conditions, the following experiment was performed.

Using the electronic component 11 made of the multilayer ceramic capacitor used in the second embodiment, coating resin is applied to the end surfaces 2a and 2b of the component body 2 and the three side surfaces 2c, 2d and 2e of the four side surfaces 2c to 2f. The samples according to Examples 1 to 8 were prepared by attaching them. Each sample differs in at least one of the material of the resin used as the main component of the coating resin layer 4 and the softening point. For comparison, a sample according to Comparative Example 1 in which the coating resin layer 4 was not formed was prepared. Table 1 shows the material and softening point of the resin as the main component of the coating resin layer 4 of each sample.

In Examples 1 to 8, any one of acrylic melamine resin, polyester resin, acrylic silicon resin, and acrylic urethane resin was used as the main component of the coating resin layer 4.

In Examples 1 to 8, the softening point of the resin as the main component of the coating resin layer 4 was set to 70 ° C. or higher and 330 ° C. or lower. The softening point can be adjusted by the type of the resin as the main component, the concentration of the resin as the main component, and the like. *

The softening point was measured by a penetration method using a TMA apparatus (Thermomechanical-Analysis apparatus) after forming the coating resin layer 4 on the component body 2. More specifically, using a TMA device manufactured by Rigaku Corporation, product number: TP-8, a probe probe is brought into contact with the coating resin layer 4 of each sample with a load of 1 gf, and the measurement environment temperature is changed from room temperature to 350. The temperature was raised to 10 ° C. at a rate of 10 ° C./min, and the temperature at which the coating resin layer 4 was deflected by 15% with respect to the film thickness by the needle probe was defined as the softening point of the resin constituting the coating resin layer 4.

Using the samples according to Examples 1 to 8, the mounting structure 200 was formed by the method according to the second embodiment. That is, the solder paste 7 was applied (printed) to the land electrodes 6a and 6b, each sample was placed thereon, and heated at 265 ° C. for 20 seconds. Moreover, the mounting structure was formed with the same method using the sample concerning a comparative example.

In all the samples according to Examples 1 to 8, solder fillets 17 were formed. However, the height of the solder fillet 17 was different for each sample. Table 1 shows the height of the solder fillet 17 of each sample as a percentage of the height of the solder fillet of Comparative Example 1 (without the coating resin layer 4). There are some exceptions, but the lower the softening point of the resin as the main component, the higher the height of the solder fillet 17 tends to be.

Also, the adhesion strength of the samples according to Examples 1 to 8 was measured. The measurement of the fixing strength is performed by shearing the component main body 2 of the mounted electronic component 11 from the lateral direction with a pressing jig at a height less than ¼ of the thickness of the component main body 2, and required for breaking. The load was defined as the fixing strength. Similarly, the fixing strength (N) of the sample according to Comparative Example 1 was measured. Table 1 shows the fixing strength of each sample.

Furthermore, after the samples according to Examples 1 to 8 and Comparative Example 1 were placed under conditions where minute condensation occurred, the occurrence rate of migration was examined. Specifically, first, the sample was placed on a variable temperature stage and then housed in a tank having a temperature of 25 ° C. and a humidity of 50%. With the voltage of 50 V applied to the sample, first, the temperature of the variable stage was raised to 35 ° C., and the sample was dried. Subsequently, while the voltage of 50 V was applied to the sample, the temperature of the variable temperature stage was lowered to 0 ° C., and the sample was cooled for 1 hour. As a result, minute condensation occurred on the outer periphery of the sample. After 1 hour, the sample was taken out from the tank and examined for the occurrence of migration. Table 1 shows the migration rate of each sample. The number of parameters of each sample was 50. The migration occurrence rate of Comparative Example 1 without the coating resin layer 4 was 96%. On the other hand, the migration occurrence rate in Examples 1 to 8 was 4% to 44%.

．Evaluation for each sample was performed. A case where the fixing strength was 10 N or more and the migration rate was improved to 12% or less was evaluated as good (◯). As a result, Examples 1, 2, 3, 5, and 8 were good. On the other hand, in Examples 4, 6, and 7, the migration occurrence rate was improved, but the degree of improvement was insufficient and did not become good. In Examples 6 and 7, the fixing strength was insufficient.

In Examples 1, 2, 3, 5, and 8, which were all good, the softening point of the resin as the main component was in the range of 90 ° C. or higher and 230 ° C. or lower. On the other hand, in Examples 4, 6, and 7, which were not good, the softening point of the resin as the main component was outside the range of 90 ° C. or higher and 230 ° C. or lower. From the above, if the softening point of the resin as the main component is in the range of 90 ° C. or higher and 230 ° C. or lower, a good solder fillet 17 is formed at the joint, and the occurrence of migration can be suppressed. It was found that a good coating resin layer 4 can be maintained.

[Third Embodiment]
FIG. 5A shows a mounting structure 300 for an electronic component (NTC thermistor / multilayer ceramic capacitor) according to the third embodiment. However, FIG. 5A is a cross-sectional view of the mounting structure 300. In FIG. 5A, for the sake of clarity, an external appearance is shown instead of a cross section of a component main body 2 and external electrodes 3a and 3b of an electronic component 1 (11) described later.

In the third embodiment, the mounting structure 300 is formed by both the electronic component 1 made of an NTC thermistor and the electronic component 11 made of a multilayer ceramic capacitor.

In the electronic component mounting structures 100 and 200 according to the first embodiment and the second embodiment, the coating resin layer 4 is formed on the side surface 2f (side surface opposite to the substrate 5) of the component body 2 of the electronic component 1 (11). Not formed. On the other hand, in the electronic component mounting structure 300 according to the third embodiment, the coating resin layer 14 is also formed on the side surface 2f of the component main body 2 as indicated by an arrow in FIG.

The mounting structure 300 according to the third embodiment is formed by a method similar to that of the electronic component mounting structures 100 and 200 according to the first and second embodiments. That is, also in the third embodiment, the coating resin is previously attached to the end surfaces 2a, 2b of the component body 2 of the electronic component 1 (11) and the three side surfaces 2c, 2d, 2e except the side surface 2f. Layer 14 was formed.

However, in the third embodiment, the type of resin that is the main component of the coating resin, the type of solvent in which the resin is dispersed, the concentration of the resin, the thickness of the coating resin layer 14, the temperature at which reflow soldering is performed, and the like are adjusted. By doing so, the coating resin layer 14 formed on the side surfaces 2c and 2e of the component main body 2 is melted by heat at the time of performing reflow soldering, flows to the side surface 2f of the component main body 2, and covers the side surface 2f. I did it.

In the mounting structure 300, since the coating resin layer 14 also covers the side surface 2 f facing the main surface of the substrate 5 of the component body 2, the external electrodes 3 a and 3 b and the solder fillet 17 by the coating resin layer 14 are used as starting points and end points. The effect of suppressing migration is higher.

[Fourth Embodiment]
FIG. 5B shows a mounting structure 400 of the electronic component (NTC thermistor / multilayer ceramic capacitor) according to the fourth embodiment. However, FIG. 5B is a cross-sectional view of the mounting structure 300. In FIG. 5B, for the sake of clarity, an external appearance is shown instead of a cross section of a component main body 2 and external electrodes 3a and 3b of an electronic component 1 (11) described later.

In the fourth embodiment, the mounting structure 400 is formed by both the electronic component 1 made of an NTC thermistor and the electronic component 11 made of a multilayer ceramic capacitor.

In the electronic component mounting structures 100 and 200 according to the first and second embodiments, the coating resin layer 4 did not cover the land electrodes 6a and 6b. In contrast, in the electronic component mounting structure 400 according to the fourth embodiment, the coating resin layer 24 covers the land electrodes 6a and 6b as shown by arrows in FIG. 5B.

The mounting structure 400 according to the fourth embodiment is formed by a method similar to that of the electronic component mounting structures 100 and 200 according to the first and second embodiments. That is, also in the fourth embodiment, the coating resin layer 24 is formed in advance by attaching the coating resin to the end surfaces 2a and 2b and the three side surfaces 2c, 2d and 2e of the component body 2 of the electronic component 1 (11). did.

However, in the fourth embodiment, the type of resin that is the main component of the coating resin, the type of solvent in which the resin is dispersed, the concentration of the resin, the thickness of the coating resin layer 24, the temperature at which reflow soldering is performed, and the like are adjusted. By doing so, the coating resin layer 24 melted by the heat during the reflow soldering flowed to the land electrodes 6a and 6b so as to cover the land electrodes 6a and 6b.

In the mounting structure 400, since the coating resin layer 24 covers the land electrodes 6a and 6b, in addition to the migration starting from the external electrodes 3a and 3b and the solder fillet 17 as the starting point and ending point, the land electrodes 6a and 6b are used as starting points and Migration to the end point is suppressed by the coating resin layer 24.

[Fifth Embodiment]
6A to 6C show a method for forming a mounting structure 500 for an electronic component (NTC thermistor / multilayer ceramic capacitor) according to the fifth embodiment. However, FIGS. 6A to 6C show steps performed in the forming method, FIG. 6A is a perspective view, and FIGS. 6B and 6C are cross-sectional views. 6B and 6C, the external appearance is shown in place of the cross section of the component main body 2 and the external electrodes 3a and 3b of the electronic component 1 (11) for easy viewing.

In the fifth embodiment, the mounting structure 500 is formed by both the electronic component 1 made of an NTC thermistor and the electronic component 11 made of a multilayer ceramic capacitor.

In the method for forming the mounting structure 500 according to the fifth embodiment, the method for forming the electronic component mounting structures 100 and 200 according to the first and second embodiments is changed. Hereinafter, a method for forming the mounting structure 400 will be described with emphasis on the changed part.

First, as shown in FIG. 6A, an electronic component 1 (11) is prepared. The electronic component 1 (11) includes a component main body 2, and the component main body 2 includes a pair of end surfaces 2a and 2b and four side surfaces 2c, 2d, 2e, and 2f that connect the end surfaces 2a and 2b. External electrodes 3 a and 3 b are formed at the end of the component body 2.

Next, a coating resin is adhered to the entire surface of the component body 2 on which the external electrodes 3a and 3b are formed, as indicated by arrows in FIG. That is, in the first embodiment and the second embodiment, the coating resin is attached to the end faces 2a, 2b of the component body 2 and the three side faces 2c, 2d, 2e of the four side faces 2c to 2f. In the fifth embodiment, the coating resin is adhered to the entire surface of the component main body 2 including the side surface 2f (side surface facing the substrate 5).

The adhesion of the coating resin to the entire surface of the component body 2 is performed by immersing the component body 2 on which the external electrodes 3a and 3b are formed in the coating resin. However, as in the first embodiment, the base 50 and the spray device 60 shown in FIG. 3 are used, the component body 2 is turned upside down in the middle, and the coating resin is attached to the entire surface of the component body 2. Also good.

Alternatively, the coating resin may be attached to the entire surface of the component body 2 by putting a plurality of component bodies 2 in a rotary barrel and spraying the coating resin on the component body 2 while rotating the barrel. .

Note that the coating resin used in the fifth embodiment is not the same as the coating resin used in the first embodiment and the second embodiment, and lowers the softening point of the coating resin and reduces the thickness of the coating resin. Such changes have been made.

Next, as shown in FIG. 6B, the electronic component 1 (11) having the coating resin layer 34 formed on the entire surface of the component body 2 is replaced with the land electrode 6a to which the solder paste 7 of the substrate 5 is applied. 6b.

Next, the substrate 5 on which the electronic component 1 (11) is arranged is heated at 265 ° C. for 20 seconds.

As a result, the solder paste 7 is melted and molten solder is supplied, the coating resin layer 34 is softened, and the contact surface of the coating resin layer 34 with the solder paste 7 is broken. Then, from the broken portion of the coating resin layer 34, the molten solder penetrates into the gap between the external electrodes 3 a and 3 b and the coating resin layer 4 due to surface tension.

Next, the substrate 5 on which the electronic component 1 (11) is placed is naturally cooled to solidify the molten solder, thereby forming a solder fillet 17 as shown in FIG. 6 (C). The coating resin layer 34 that has been softened by natural cooling also recovers its original hardness.

As described above, the mounting structure 500 according to the fifth embodiment is completed.

[Sixth Embodiment]
7A to 7C show a method for forming a mounting structure 600 for an electronic component (NTC thermistor / multilayer ceramic capacitor) according to the sixth embodiment. However, FIGS. 7A to 7C are cross-sectional views showing steps performed in the forming method. 7A to 7C, the external appearance is shown instead of the cross-sections of the component main body 2 and the external electrodes 3a and 3b of the electronic component 1 for easy viewing.

In the sixth embodiment, the mounting structure 600 is formed by both the electronic component 1 made of an NTC thermistor and the electronic component 11 made of a multilayer ceramic capacitor.

The sixth embodiment is modified from the fifth embodiment.

Also in the sixth embodiment, as in the fifth embodiment, first, the coating resin layer 34 is adhered to the entire surface of the component body 2 of the electronic component 1 (11).

Next, in the sixth embodiment, as shown in FIG. 7A, the coating resin layer 34 on the external electrodes 3a and 3b is formed only on the side surface 2f of the component body 2 (side surface facing the substrate 5). Peel off by polishing or laser irradiation.

Next, as shown in FIG. 7B, the electronic component 1 is disposed on the land electrodes 6a and 6b to which the solder paste 7 is applied, with the side surface 2f opposed to the substrate 5.

Next, by heating at 265 ° C. for 20 seconds, the electronic component 1 is bonded to the substrate 5 as shown in FIG. The solder paste 7 forms a solder fillet 17. As described above, the mounting structure 600 according to the fifth embodiment is completed.

In the mounting structure 600 according to the sixth embodiment, since the coating resin layer 34 on the external electrodes 3a and 3b on the side surface 2f of the component body 2 is peeled in advance, the coating resin layer 34 is removed by heating at the time of soldering. There is no need to break, and it can be implemented smoothly. Note that the softening temperature of the coating resin 34 layer may be higher than that in the fifth embodiment.

In the mounting structure 600 according to the sixth embodiment, since the side surface 2f of the component main body 2 is covered with the coating resin layer 34, the migration suppressing function is also good.

[Seventh Embodiment]
8A to 8C show a method for forming a mounting structure 700 for an electronic component (NTC thermistor / multilayer ceramic capacitor) according to the seventh embodiment. However, FIGS. 8A to 8C are cross-sectional views showing steps performed in the formation method. 8A to 8C, the external appearance is shown instead of the cross-sections of the component main body 2 and the external electrodes 3a and 3b of the electronic component 1 for easy viewing.

In the seventh embodiment, the mounting structure 700 is formed by both the electronic component 1 made of an NTC thermistor and the electronic component 11 made of a multilayer ceramic capacitor.

In the seventh embodiment, the sixth embodiment is further modified. Specifically, in the sixth embodiment, solder is used to join the electronic component 1 (11) to the substrate 5, but in the seventh embodiment, a conductive adhesive is used instead of the solder.

First, the coating resin layer 34 is adhered to the entire surface of the component body 2 of the electronic component 1 (11).

Next, as shown in FIG. 8A, the coating resin layer 34 on the external electrodes 3a and 3b is peeled off by polishing or laser irradiation only on the side surface 2f of the component body 2 (side surface opposite to the substrate 5). . Next, as shown in FIG. 8B, the electronic component 1 is placed on the land electrodes 6a and 6b coated with the conductive adhesive 57 with the side surface 2f facing the substrate 5. Next, heating is performed at a predetermined temperature, and the electronic component 1 is bonded to the substrate 5 with the conductive adhesive 57 as shown in FIG. As described above, the mounting structure 700 according to the seventh embodiment is completed. In the seventh embodiment, no fillet is formed, but the electronic component 1 (11) is firmly bonded to the substrate 5 by the conductive adhesive 57.

The mounting structures 100 to 700 according to the first to seventh embodiments and the forming methods thereof have been described above. However, the present invention is not limited to the above-described contents, and various modifications can be made in accordance with the gist of the invention.

For example, in the first to seventh embodiments, the NTC thermistor is used as the electronic component 1 and the multilayer ceramic capacitor is used as the electronic component 11. However, the types of the electronic components 1 and 11 are limited to the NTC thermistor and the multilayer ceramic capacitor. Absent. For example, a resistor, an inductor, a PTC thermistor, another type of capacitor, or the like may be used.

In the electronic components 1 and 11, an internal electrode (not shown) is formed inside the component body 2, but the internal electrode is not essential in the present invention.

The components of the coating resin that form the coating resin layers 4, 14, 24, and 34 are also arbitrary, and are not limited to the above-described contents.

Further, in the first to seventh embodiments, the coating resin layers 4, 14, 24, 34 completely covered the necessary portions and there were no cracks or holes, but the coating resin layers 4, 14, 24, Even if there is a partial crack or hole in 34, the occurrence of migration can be suppressed.

Further, the materials and structures of the external electrodes 3a and 3b and the land electrodes 6a and 6b are arbitrary, and are not limited to the above-described contents.

Furthermore, the material and applied film thickness of the solder paste 7 and the conductive adhesive 57 are arbitrary, and are not limited to those described above.

1 ... Electronic component (NTC thermistor)
11 ... Electronic components (multilayer ceramic capacitors)
2 ... Component body 2a, 2b ... End face 2c, 2d, 2e, 2f ... Side face 3a, 3b ... External electrode 4, 14, 24, 34 ... Coating resin layer 5 ... Substrate 6a, 6b ... land electrode 7 ... solder paste 17 ... solder fillet 57 ... conductive adhesive 50 ... base 51 ... adhesive layer 60 ... spray device 100, 200, 300, 400, 500, 600, 700... Electronic component mounting structure

Claims (13)

1. An electronic component comprising a pair of end faces and four side faces connecting the pair of end faces, and an external electrode formed on an end including the end faces;
   A substrate having land electrodes formed on the main surface;
   A solder for joining the land electrode and the external electrode;
   The electronic component mounting structure in which a solder fillet connecting at least the land electrode and the external electrode is formed by the solder,
   Furthermore, a coating resin layer having a migration suppression function is provided,
   The coating resin layer covers three side surfaces of the four side surfaces of the electronic component other than the side surface facing the main surface of the substrate, and the pair of end surfaces of the electronic component are connected to the external electrode. And covering with the solder fillet,
   The electronic component mounting structure, wherein the coating resin layer is not in contact with the main surface of the substrate, or is in contact with the main surface of the substrate only in the vicinity of the electronic component.
2. 2. The electronic component mounting structure according to claim 1, wherein the coating resin layer further covers a side surface of the four side surfaces of the electronic component that faces the main surface of the substrate.
3. An electronic component comprising a pair of end faces and four side faces connecting the pair of end faces, and an external electrode formed on an end including the end faces;
   A substrate having land electrodes formed on the main surface;
   A mounting structure comprising a conductive adhesive for joining the land electrode and the external electrode,
   Furthermore, a coating resin layer having a migration suppression function is provided,
   The coating resin layer covers the four side surfaces of the electronic component and is not in contact with the main surface of the substrate, or is in contact with the main surface of the substrate only in the vicinity of the electronic component. Component mounting structure.
4. The electronic component mounting structure according to any one of claims 1 to 3, wherein the coating resin layer further covers the land electrode.
5. The mounting structure for an electronic component according to any one of claims 1 to 4, wherein there is no opening in the coating resin layer.
6. The mounting structure for an electronic component according to any one of claims 1 to 4, wherein an opening is present in the coating resin layer.
7. The electronic component mounting structure according to any one of claims 1 to 6, wherein a pigment is contained in the coating resin layer.
8. The electronic component mounting structure according to any one of claims 1 to 7, wherein the coating resin layer is formed in advance on a surface of the electronic component.
9. An electronic component comprising a pair of end faces and four side faces connecting the pair of end faces, wherein an external electrode is formed at an end including the end faces,
   Furthermore, a coating resin layer having a migration suppression function is provided,
   The coating resin layer covers three side surfaces of the four side surfaces, and covers the pair of end surfaces together with the external electrodes,
   An electronic component in which the coating resin layer is formed of a resin having a softening point of 90 ° C or higher and 230 ° C or lower.
10. An electronic component comprising a pair of end faces and four side faces connecting the pair of end faces, wherein an external electrode is formed at an end including the end faces,
    Furthermore, a coating resin layer having a migration suppression function is provided,
    The coating resin layer covers the four side surfaces, and covers the pair of end surfaces together with the external electrodes,
    An electronic component in which the coating resin layer is formed of a resin having a softening point of 90 ° C or higher and 150 ° C or lower.
11. An electronic component comprising a pair of end faces and four side faces connecting the pair of end faces, wherein an external electrode is formed at an end including the end faces,
    The external electrode is formed such that a part thereof extends to the four side surfaces,
    Furthermore, a coating resin layer having a migration suppression function is provided,
    The coating resin layer covers three side surfaces of the four side surfaces together with the external electrode, covers the remaining one side surface of the four side surfaces except for a portion where the external electrode is formed, Covering the pair of end faces together with the external electrodes;
    An electronic component in which the coating resin layer is formed of a resin having a softening point of 90 ° C or higher and 230 ° C or lower.
12. A pair of end faces and four side faces connecting the pair of end faces; an external electrode is formed at an end including the end faces; covers three of the four side faces; and Preparing an electronic component including a coating resin layer having a migration suppressing function that covers a pair of end faces together with the external electrode;
    Preparing a substrate having a land electrode formed on the main surface;
    Applying a solder paste on the land electrode;
    Placing the electronic component on the land electrode to which the solder paste is applied, with the side surface not covered with the coating resin facing down;
    Heating and supplying the molten solder by melting the solder paste, softening the coating resin layer, and infiltrating the molten solder into the gap between the external electrode and the coating resin layer;
    And a step of solidifying the molten solder that has penetrated into the gap between the external electrode and the coating resin layer to form a solder fillet by cooling.
13. A pair of end faces and four side faces connecting the pair of end faces, an external electrode is formed at an end including the end faces, covers the four side faces, and the pair of end faces are connected to the external side. A step of preparing an electronic component including a coating resin layer having a migration suppression function that covers the electrode,
    Preparing a substrate having a land electrode formed on the main surface;
    Applying a solder paste on the land electrode;
    Placing the electronic component on the land electrode coated with the solder paste;
    By heating, the solder paste is melted to supply molten solder, the coating resin layer is softened, and the coating resin layer between the land electrode and the external electrode is broken, and the molten solder is Infiltrating the gap between the external electrode and the coating resin layer;
    And a step of solidifying the molten solder that has penetrated into the gap between the external electrode and the coating resin layer to form a solder fillet by cooling.

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