JP5428612B2 - Electronic component mounting structure - Google Patents

Description

  The present invention relates to an electronic component mounting structure.

  Conventionally, as described in Patent Document 1, for example, an electronic component is mounted on a circuit board by being soldered to a land formed on the circuit board.

  A pair of lands are formed on the surface of the circuit board by etching, plating, or printing techniques. On the other hand, a pair of electrodes is formed on the surface of the electronic component by plating or printing technology. By soldering each land and each electrode, a solder part is formed between each land and each electrode. By this solder portion, the land and the electrode are electrically connected.

JP 2004-228444 A

  When a circuit board on which electronic components are mounted as described above is mounted on a vehicle, for example, the circuit board is required to withstand changes in environmental temperature from below freezing to about 100 ° C.

  However, the circuit board and the electronic component have different coefficients of thermal expansion. For this reason, due to a temperature change accompanying a change in the use situation of the vehicle, a thermal stress is generated in the solder portion connecting the circuit board and the electronic component due to a difference in volume change between the circuit board and the electronic component. . When the above temperature change is repeated, cracks are generated and grow in the solder part, and in some cases, the solder part may be broken.

  In particular, a large shear stress is applied to the solder portion located between the land facing the circuit board of the electronic component and the land due to the difference in volume change between the electronic component and the circuit board. . For this reason, there is a concern that cracks are generated and grow from the solder portion located between the opposing surface of the electronic component and the land.

  The present invention has been completed based on the above circumstances, and an object thereof is to provide an electronic component mounting structure in which the occurrence of cracks in a solder portion is suppressed.

The present invention relates to an electronic component mounting structure, in which an electronic component having a thermal expansion coefficient different from that of a land formed on a circuit board and a position corresponding to the land of the circuit board is provided. A component, an electrode formed on a surface opposite to the circuit board of the surface of the electronic component and a surface different from the counter surface, a solder portion that connects the land and the electrode on the different surface, and It is arranged in a region between the facing surface of the electronic component and the land, and restricts the penetration of the heated and melted solder into the region between the facing surface of the electronic component and the land . A regulating portion that does not contact the electrode and the solder portion .

  According to the present invention, intrusion of molten solder is restricted in a region between the facing surface of the electronic component and the land. As a result, no solder exists in the region between the opposing surface of the electronic component and the land. As a result, the occurrence of cracks in the solder due to thermal stress between the facing surface of the electronic component and the land is suppressed.

  In addition, since the restricting portion is arranged in the region between the facing surface of the electronic component and the land, the distance between the electrode formed on a surface different from the facing surface of the electronic component and the land is the facing of the electronic component. Compared to the case where the electrodes and lands formed on the surface are soldered, they are larger. Thereby, the thermal stress applied between the electronic component and the circuit board can be relaxed by the solder portion.

The following configuration is preferable as an embodiment of the present invention.
It is preferable that the restriction portion is provided on the entire facing surface of the electronic component .

  According to said structure, it can control reliably that the melt | dissolved solder permeates between the opposing surface of an electronic component, and a land.

  It is preferable that the restricting portion is in close contact with both the opposing surface of the electronic component and the land.

  According to said structure, it can control more reliably that the melt | dissolved solder permeates between the opposing surface of an electronic component, and a land.

  It is preferable that the restricting portion includes a solder resist layer formed on a surface of the circuit board on which the land is formed.

  According to said structure, since the melt | dissolved solder is excluded by a soldering resist layer, it can suppress reliably that a solder permeates between the opposing surface of an electronic component, and a land.

  The solder resist layer can be formed in the step of applying the solder resist to the circuit board. Thereby, since it is not necessary to provide the process of manufacturing a control part newly, the raise of manufacturing cost can be suppressed.

  It is preferable that the restricting portion is bonded to the facing surface of the electronic component with an adhesive layer.

  According to said structure, the thermal stress which generate | occur | produces between the opposing surface of an electronic component and a land is transmitted to a control part by an adhesive agent, and is absorbed by a control part. Thereby, it can suppress more reliably that a crack generate | occur | produces in a solder part with a thermal stress.

  According to the present invention, it is possible to suppress the occurrence of cracks in the solder portion.

Schematic sectional view showing a mounting structure of an electronic component according to Embodiment 1 Schematic plan view showing the mounting structure of electronic components Schematic sectional view showing the process of forming lands on the surface of the circuit board Schematic sectional view showing the process of forming a solder resist layer on the surface of the circuit board Schematic sectional view showing the process of forming a synthetic resin layer on the surface of the circuit board Schematic cross-sectional view showing the state where electronic parts are bonded to the synthetic resin layer Schematic sectional view showing the mounting structure of the electronic component according to the second embodiment Schematic sectional view showing the mounting structure of the electronic component according to the third embodiment Schematic plan view showing a mounting structure of an electronic component according to Embodiment 4

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, a pair of lands 11 made of copper foil are formed at a predetermined interval on the surface (upper surface in FIG. 1) of a circuit board 10 made of insulating synthetic resin by a printed wiring technique. Has been. As shown in FIG. 2, the land 11 has a rectangular shape.

  As shown in FIG. 2, the surface of the circuit board 10 has a rectangular shape so as to cover a region on the inner side in the left-right direction in FIG. 2 and a region located between the pair of lands 11 in the pair of lands 11. A formed solder resist layer 12 (corresponding to the restricting portion 19 described in the claims) is formed. The solder resist layer 12 covers a substantially half region of each land 11 on the inner side in the left-right direction in FIG. The solder resist layer 12 is in close contact with the surface of the circuit board 10 and the land 11. The solder resist layer 12 is formed by a known method such as silk screen printing. In the present embodiment, the thickness dimension of the solder resist layer 12 is, for example, 30 μm.

  An insulating synthetic resin layer 13 (corresponding to the restricting portion 19 described in the claims) is formed so as to overlap above the solder resist layer 12 in FIG. The synthetic resin layer 13 is formed by a known method such as silk screen printing. As the synthetic resin, any resin such as a thermosetting resin or a thermoplastic resin can be used as necessary. In the present embodiment, the thickness dimension of the synthetic resin layer 13 is set to 20 μm, for example.

  On the upper surface of the synthetic resin layer 13 in FIG. 1, an electronic component 14 having a thermal expansion coefficient different from that of the circuit board 10 is bonded via an insulating adhesive layer 15. For example, a thermosetting resin can be used as the adhesive. The adhesive layer 15 is formed so as to cover the facing surface 16 of the electronic component 14 that faces the circuit board 10. Further, the synthetic resin layer 13 is in close contact with the facing surface 16 of the electronic component 10 via the adhesive layer 15.

  The electronic component 14 has a rectangular parallelepiped shape. On the surface of the electronic component 14, an electrode 17 made of, for example, a metal foil formed by plating is formed at positions near both ends in the left-right direction in FIG. The electrode 17 is formed on the surface 16 of the electronic component 14 on the facing surface 16 where the electronic component 14 and the circuit board 10 face each other and on a surface 25 different from the facing surface 16. Note that the surface 25 different from the facing surface 16 refers to the upper surface 20, the left and right end surfaces 21 and 22, the side surface 23 located on the front side of the paper surface, and the side surface 24 located on the back side of the paper surface in FIG.

  As the electronic component 14, for example, any element such as a chip resistor, a ceramic capacitor, or a semiconductor chip can be used as necessary.

  The electronic component 14 is arranged on the circuit board 10 in such a posture that the electrodes 17 are positioned above the lands 11.

  As shown in FIG. 2, the solder resist layer 12 and the synthetic resin layer 13 described above cover the opposing surface 16 of the electronic component 14 and further cover a larger area than the opposing surface 16 of the electronic component 14. Is formed on the surface.

  Solder portions 18 that electrically connect the electrodes 17 of the electronic component 14 and the lands 11 are formed at the left and right ends of the electronic component 14 in FIG. As described above, since the facing surface 16 of the electronic component 14 is covered with the solder resist layer 12 and the synthetic resin layer 13, molten solder is formed in a region between the facing surface 16 of the electronic component 14 and the land 11. Intrusion is regulated. Accordingly, the electrode 17 provided on the facing surface 16 among the electrodes 17 of the electronic component 14 is not in contact with the solder portion 18. The solder portion 18 is in contact with the electrode 17 formed on the surface 25 different from the facing surface 16 among the electrodes 17 of the electronic component 14.

  The upper surface of the solder part 18 is formed so as to incline downward as it goes outward in the left-right direction from the electrodes 17 formed on both edges in the left-right direction in FIG.

  In addition, as solder which comprises the solder part 18, arbitrary solders, such as lead free solder, can be used as needed.

  Next, a method for mounting the electronic component 14 will be described. First, as shown in FIG. 3, a pair of lands 11 made of copper foil are formed on the surface of the circuit board 10 by a printed wiring technique. The pair of lands 11 are formed at a predetermined interval.

  Next, as shown in FIG. 4, a step of applying a solder resist to a region different from the region to be soldered on the surface of the circuit board 10 by screen printing is performed. At the same time, as shown in FIG. 2, a solder resist layer is formed so as to cover a region located between the pair of lands 11 and a substantially half region located in the left-right direction in FIG. 2 of the pair of lands 11. 12 is formed.

  Next, as shown in FIG. 5, the synthetic resin layer 13 is formed by screen printing so as to overlap the upper surface of the solder resist layer 12 in FIG. The restriction portion 19 is formed by the solder resist layer 12 and the synthetic resin layer 13 described above.

  Next, as shown in FIG. 6, an adhesive layer 15 made of a thermosetting resin is applied to the upper surface of the synthetic resin layer 13 in FIG. The electronic component 14 is placed on the adhesive layer 15 in a posture in which the electrodes 17 of the electronic component 14 are positioned above the lands 11 in FIG.

  Subsequently, the circuit board 10 on which the electronic component 14 is placed is heated in a heating furnace (not shown) (150 ° C. for 120 seconds in this embodiment) to cure the adhesive. Thus, the electronic component 14 is bonded to the upper surface of the synthetic resin layer 13 in FIG.

Next, a rosin-based post flux is applied to the surface of the land 11. Subsequently, the circuit board 10 to which the electronic component 14 is bonded is preheated (140 ° C. in this embodiment), and molten solder (Sn ₃ Ag _0.5 Cu solder heated to 255 ° C. in this embodiment). Is brought into contact with the electrode 17 of the electronic component 14 and the land 11 of the circuit board 10 for a predetermined time (in this embodiment, 5 seconds). The solder in the molten state is restricted from entering the region between the facing surface 16 of the electronic component 14 and the land 11 by the solder resist layer 12 and the synthetic resin layer 13. Thereafter, the solder is solidified. As a result, a solder portion 18 is formed between the electrode 17 of the electronic component 14 and the land 11.

  Next, the operation and effect of this embodiment will be described. When the circuit board 10 on which the electronic component 14 is mounted is mounted on a vehicle, for example, the circuit board 10 is required to withstand changes in environmental temperature from below freezing to about 100 ° C.

  However, the circuit board 10 and the electronic component 14 have different coefficients of thermal expansion. For this reason, a thermal stress is generated in the solder portion 18 that connects the circuit board 10 and the electronic component 14 due to a temperature change accompanying a change in the vehicle usage. When the above temperature change is repeated, cracks are generated and grow in the solder portion 18, and there is a concern that the solder portion 18 may break in some cases.

  In particular, in the solder part 18 located between the opposing surface 16 of the electronic component 14 facing the circuit board 10 and the land 11, the difference is caused by the difference in thermal expansion coefficient between the electronic component 14 and the circuit board 10. Thus, a large shear stress is applied. For this reason, there is a concern that cracks are generated and grow from the solder portion 18 located between the facing surface 16 of the electronic component 14 and the land 11.

  In view of the above points, in the present embodiment, the restricting portion 19 is formed in the region between the facing surface 16 of the electronic component 14 and the land 11 to restrict the intrusion of the heat-melted solder. Thereby, according to this embodiment, the penetration | invasion of the melt | dissolved solder is controlled in the area | region between the opposing surface 16 of the electronic component 14, and the land 11. FIG. As a result, due to the thermal stress applied to both the circuit board 10 and the electronic component 14 due to the difference in thermal expansion coefficient between the circuit board 10 and the electronic component 14, between the facing surface 16 of the electronic component 14 and the land 11. It is possible to prevent the solder from cracking.

  On the other hand, the distance between the electrode 17 formed on the surface 25 different from the facing surface 16 of the electronic component 14 and the land 11 is such that the electrode 17 formed on the facing surface 16 of the electronic component 14 and the land 11 are connected. It is larger than that. Thereby, the thermal stress applied between the electronic component 14 and the circuit board 10 is relieved by the solder portion 18.

  In the present embodiment, since the facing surface 16 of the electronic component 14 is covered with the restricting portion 19, it is ensured that molten solder enters between the facing surface 16 of the electronic component 14 and the land 11. Can be regulated.

  Furthermore, in the present embodiment, the restricting portion 19 is in close contact with both the opposing surface 16 and the land 11 of the electronic component 14 via the adhesive layer 15, and thus the opposing surface 16 of the electronic component 14 and the land 11 are in close contact. It is possible to more reliably regulate the intrusion of molten solder between the two.

  In addition, according to the present embodiment, the restricting portion 19 includes the solder resist layer 12. Since this solder resist layer 12 eliminates molten solder, it is possible to reliably prevent the molten solder from entering between the opposing surface 16 of the electronic component 14 and the land 11.

  Furthermore, according to this embodiment, the upper surface of the synthetic resin layer 13 and the facing surface 16 of the electronic component 14 are bonded by the adhesive layer 15. Thereby, the thermal stress generated between the opposing surface 16 of the electronic component 14 and the land 11 is transmitted to the synthetic resin layer 13 and the solder resist layer 12 by the adhesive, and is caused by the synthetic resin layer 13 and the solder resist layer 12. Absorbed. Thereby, it can suppress more reliably that a crack generate | occur | produces in the solder part 18 with a thermal stress.

  In addition, according to the present embodiment, since the restricting portion 19 including the solder resist layer 12 is provided on the circuit board 10, the restricting portion 19 can also be formed in the step of applying the solder resist to the circuit board 10. it can. Thereby, since it is not necessary to provide the process of manufacturing the control part 19 newly, the raise of manufacturing cost can be suppressed.

  Further, since the thermal expansion coefficient of the circuit board 10 is different from the thermal expansion coefficient of the land 11, there is a concern that the circuit board 10 and the land 11 are peeled off due to a temperature change. In view of the above points, according to the present embodiment, the solder resist layer 12 covers substantially half of the land 11 on the inner side in the left-right direction in FIG. Thereby, it can suppress that the area | region covered with the soldering resist layer 12 among the edge of the land 11 peels from the circuit board 10. FIG.

<Embodiment 2>
Next, Embodiment 2 of the present invention will be described with reference to FIG. In the present embodiment, the electronic component 14 is soldered to the land 11 while being placed on the upper surface of the synthetic resin layer 13 in FIG. Since the configuration other than the above is substantially the same as that of the first embodiment, the same configuration is denoted by the same reference numeral, and redundant description is omitted.

  According to this embodiment, the process of applying an adhesive and the process of curing the adhesive can be omitted.

<Embodiment 3>
Next, Embodiment 3 of the present invention will be described with reference to FIG. In the present embodiment, the distance between the pair of lands 11 formed on the circuit board 10 is set to be approximately the same as the length of the electronic component 14 in the left-right direction in FIG.

  On the surface of the circuit board 10, a solder resist layer 12 is formed in a region located between the pair of lands 11. An electronic component 14 is bonded to the upper surface of the solder resist layer 12 in FIG.

  Since the configuration other than the above is substantially the same as that of the first embodiment, the same configuration is denoted by the same reference numeral, and redundant description is omitted.

  According to this embodiment, the process of forming the synthetic resin layer 13 can be omitted.

<Embodiment 4>
Next, a fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, the synthetic resin layer 13 is formed on the surface of the circuit board 10 with an interval in the vertical direction in FIG. Each synthetic resin layer 13 is formed so as to straddle the pair of lands 11.

  Although not shown in detail, a solder resist layer 12 is formed on the lower surface of the synthetic resin layer 13 (the back surface in the direction passing through the paper surface in FIG. 9). The solder resist layer 12 is also formed with a space in the vertical direction in FIG. 9 and is formed so as to straddle the pair of lands 11.

  Since the configuration other than the above is substantially the same as that of the first embodiment, the same configuration is denoted by the same reference numeral, and redundant description is omitted.

  Next, a method for mounting the electronic component 14 according to the present embodiment will be described. In the present embodiment, after the land 11 is formed on the surface of the circuit board 10, a step of applying a solder resist to an area of the circuit board 10 different from the area to be soldered is performed by screen printing. At the same time, as shown in FIG. 9, the solder resist layer 12 is formed so that each solder resist layer 12 straddles each land 11 with an interval in the vertical direction in FIG. 9.

  Next, the synthetic resin layer 13 is formed by screen printing so as to overlap the upper surface of the solder resist layer 12.

Next, rosin-based post flux is applied to the surface of the circuit board 10. Subsequently, a solder paste (Sn ₃ Ag _0.5 Cu solder in this embodiment) is printed on the upper surface of the land 11 by screen printing.

  Next, on the upper surface of the synthetic resin layer 13, the electronic component 14 is disposed above each land 11 in a posture in which each electrode 17 of the electronic component 14 is located.

  Subsequently, the circuit board 10 on which the electronic component 14 is placed is heated in a reflow furnace under a nitrogen atmosphere (245 ° C. in the present embodiment) to melt the solder paste. Thereafter, the solder is solidified. As a result, a solder portion 18 is formed between the electrode 17 of the electronic component 14 and the land 11.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the present embodiment, the restricting portion 19 is configured to be provided on the circuit board 10, but is not limited thereto. For example, by attaching an insulating film so as to cover the facing surface 16 of the electronic component 14. The restricting portion 19 may be formed. Furthermore, the insulating film may be bonded to the circuit board 10 via an adhesive layer.
(2) In the present embodiment, the restricting portion 19 includes the solder resist layer 12, but the restricting portion 19 may not include the solder resist layer 12.
(3) The step of forming the solder resist layer 12 may be performed in any step different from the step of applying the solder resist to a region different from the region to be soldered on the surface of the circuit board 10.
(4) The mounting structure of the electronic component 14 according to the present embodiment can be applied not only to the circuit board 10 mounted on the vehicle but also to any circuit board 10 as necessary.
(5) The thickness dimension of the solder resist layer 12 and the thickness dimension of the synthetic resin layer 13 can be arbitrarily set as necessary.

DESCRIPTION OF SYMBOLS 10 ... Circuit board 11 ... Land 12 ... Solder resist layer (regulation part 19)
13 ... Synthetic resin layer (regulator 19)
DESCRIPTION OF SYMBOLS 14 ... Electronic component 15 ... Adhesive layer 17 ... Electrode 18 ... Solder part 19 ... Restriction part

Claims (5)

A land formed on the circuit board; an electronic component disposed at a position corresponding to the land of the circuit board and having a different coefficient of thermal expansion from the circuit board; and the circuit board among the surfaces of the electronic component An electrode formed on a surface opposite to the counter surface and a surface different from the counter surface, a solder part connecting the land and the electrode on the different surface, and a region between the surface facing the electronic component and the land A restricting portion that is disposed on the electronic component and restricts intrusion of the solder melted into the region between the facing surface and the land of the electronic component so that the electrode on the facing surface does not contact the solder portion ; Electronic component mounting structure with The electronic component mounting structure according to claim 1 , wherein the restriction portion is provided on the entire facing surface of the electronic component. The electronic component mounting structure according to claim 1, wherein the restricting portion is in close contact with both the opposing surface of the electronic component and the land. 4. The electronic component mounting structure according to claim 1, wherein the restricting portion includes a solder resist layer formed on a surface of the circuit board on which the land is formed. 5. The electronic component mounting structure according to any one of claims 1 to 4, wherein the restricting portion is bonded to an opposing surface of the electronic component with an adhesive layer .

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