Circuit board and method for manufacturing circuit board

Abstract

A method for manufacturing a circuit board and a circuit board according to the present invention comprises one aspect in which the circuit board has a pad to which an electrode of an electronic component is electrically connected by soldering, a solder joint portion in the connection between the pad and the electrode of the electronic component is connected by a portion of an electrode on a side surface of the electronic component and an electrode on a lower surface of the electronic component, and a solder inflow suppression portion that is formed using a resist is provided immediately below the electrode on the lower surface. It is thereby possible to suppress cracking from propagating in the solder portion for electrically connecting the electronic component to the pad.

Description

Circuit board and method for manufacturing the circuit board

[0001] The present invention relates to a circuit board and a method for manufacturing a circuit board.

[0002] The circuit board of Patent Document 1 is a circuit board on which an electronic component sealed with resin in a substantially rectangular parallelepiped shape is soldered and mounted, and the electronic component comprises a planar pad electrode formed on the bottom surface of the sealing body and having an anchor hole through which the resin passes on the underside of one end of the sealing body, and a lead electrode drawn out from the side surface of the other end of the sealing body and whose tip is located below the electrode surface of the pad electrode, and the circuit board is characterized in that it has a non-solder-wettable portion that connects the portion of the land on which the pad electrode is mounted that faces the anchor hole and the portion on which the pad electrode is not mounted.

[0003] Japanese Patent Application Laid-Open No. 2007-012850

[0004] However, when an electronic component having electrodes that are externally connected to the side and underside of a sealing body is mounted by soldering the electrodes to pads on a circuit board, cracks tend to develop in the solder that has flowed to the underside of the electronic component, potentially reducing the reliability of the electrical connection.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a circuit board and a method for manufacturing the circuit board that can prevent cracks from progressing in the solder joints that electrically connect electronic components to pads.

[0006] In one aspect of the circuit board according to the present invention, the solder joint between the pad and the electrode of the electronic component is connected by a part of the electrode on the side surface and the electrode on the bottom surface of the electronic component, and a solder inflow prevention portion is provided directly below the electrode on the bottom surface. Also, in one aspect of the method for manufacturing a circuit board according to the present invention, the circuit board has a pad to which the electrode of the electronic component is electrically connected by solder joint and a via arranged in the pad, and the manufacturing method includes a step of applying a resist to form a solder inflow prevention portion using the resist to prevent solder from inflowing into the via.

[0007] According to the present invention, it is possible to prevent cracks from progressing in the solder joints that electrically connect the electronic component to the pads.

[0008] FIG. 1 is a plan view showing a first embodiment of a circuit board according to the present invention. FIG. 2 is a cross-sectional view (cross-sectional view of the X-X plane of FIG. 1 ) showing the first embodiment of a circuit board according to the present invention. FIG. 3 is a process diagram showing a method for manufacturing a circuit board of the first embodiment. FIG. 4 is a cross-sectional view (cross-sectional view of the X-X plane of FIG. 4 ) showing the second embodiment of a circuit board according to the present invention. FIG. 5 is a cross-sectional view (cross-sectional view of the X-X plane of FIG. 6 ) showing the third embodiment of a circuit board according to the present invention. FIG. 6 is a cross-sectional view (cross-sectional view of the X-X plane of FIG. 8 ) showing the fourth embodiment of a circuit board according to the present invention. FIG. 7 is a cross-sectional view (cross-sectional view of the X-X plane of FIG. 10 ) showing the fourth embodiment of a circuit board according to the present invention. FIG. 8 is a cross-sectional view (cross-sectional view of the X-X plane of FIG. 10 ) showing the fifth embodiment of a circuit board according to the present invention.

[0009] A circuit board and a method for manufacturing the circuit board according to an embodiment of the present invention will be described in detail below. The circuit board according to the embodiment of the present invention constitutes, for example, an electronic control unit mounted on a vehicle.

[0010] 1 and 2 are diagrams showing a portion of a circuit board 10 according to the first aspect on which an electronic component 20 is mounted, with Fig. 1 being a plan view seen from the top surface of the circuit board 10 (in other words, the mounting surface on which the electronic component 20 is mounted), and Fig. 2 being a cross-sectional view taken along the X-X plane shown in Fig. 1. The electronic component 20 is mounted on the top surface of the circuit board 10 by soldering.

[0011] Electronic component 20 is a chip capacitor or the like that is sealed with resin in a substantially rectangular parallelepiped shape and has electrodes 21 that are externally connected to the ends of the sealing body. The bottom surface of the sealing body is the surface that faces the mounting surface of circuit board 10, and the side surface of the sealing body is the surface that is perpendicular to the mounting surface of circuit board 10. Electrode 21 is provided continuously from the top surface of one end of the sealing body, across the side surface, and to the bottom surface. Hereinafter, the electrode on the side surface of the sealing body will be referred to as side electrode 21A, and the electrode on the bottom surface of the sealing body will be referred to as bottom electrode 21B.

[0012] The circuit board 10 has a multilayer circuit in which insulating layers and conductor wiring layers are alternately stacked, with the conductor wiring layers electrically connected by vias 30, and pads 40 for electrically connecting the electronic components 20 to the multilayer circuit by solder bonding. The vias 30 are arranged within the pads 40. In other words, the circuit board 10 has a so-called pad-on-via structure.

[0013] Resist 60 is applied to the portions of circuit board 10 that are not in contact with pad 40. Solder joints 50 between pad 40 and electrode 21 of electronic component 20 are formed by connecting side electrode 21A and a portion of bottom electrode 21B. Vias 30 are disposed within pad 40 directly below bottom electrode 21B.

[0014] Furthermore, a solder-flow prevention portion 70 is formed on the pad 40 directly below the lower-surface electrode 21B to prevent molten solder from flowing onto the underside of the electronic component 20 during the reflow process in which solder paste is melted in a high-temperature furnace for soldering. The solder-flow prevention portion 70 is formed by applying a strip-shaped resist 60 to the pad 40 so that it protrudes above the pad 40. In other words, the solder-flow prevention portion 70 forms a wall on the pad 40, thereby preventing the solder from flowing beyond the solder-flow prevention portion 70.

[0015] Here, solder-flow prevention portion 70 is formed in a horseshoe shape with the open end on the side farther from fillet (in other words, side electrode 21A), and is arranged so that horseshoe-shaped solder-flow prevention portion 70 surrounds the opening of via 30. In other words, solder-flow prevention portion 70 is provided on the fillet side away from the opening of via 30 arranged in pad 40, and prevents solder from flowing into via 30 arranged in pad 40 directly below lower electrode 21B.

[0016] Cracks tend to grow in the solder that has flowed to the underside of electronic component 20. Furthermore, when via 30 is disposed in pad 40 directly below underside electrode 21B, the flux contained in the substrate or solder, or the moisture absorbed by the substrate or solder, evaporates during the reflow process, generating gas in via 30. This gas may then flow toward the fillet and cause voids (in other words, cavities) in solder joint 50. If a crack that has grown in the solder that has flowed to the underside of electronic component 20 connects with a void in the fillet, the growth of the crack is accelerated, and the reliability of the electrical connection of electronic component 20 is impaired.

[0017] Therefore, the solder flow prevention portion 70 prevents solder from flowing into the underside of the electronic component 20 and the vias 30, where cracks are likely to develop, and also prevents gas generated in the vias 30 from flowing toward the fillet. This prevents the occurrence of solder cracks on the underside of the electronic component 20 and the occurrence of voids in the fillets, thereby increasing the reliability of the electrical connection of the electronic component 20.

[0018] The solder flow prevention portion 70 reduces the amount of solder flowing onto the underside of the electronic component 20, reducing the solder joints 50 at the underside electrodes 21B of the electronic component 20, but still ensures sufficient durability. Gas generated in the vias 30 escapes from the open end of the horseshoe-shaped solder flow prevention portion 70 in the opposite direction to the side toward the fillet. The solder flow prevention portion 70 can be provided regardless of whether or not via fill plating is applied to fill the interior of the vias 30, and provides the same effects regardless of whether or not via fill plating is applied.

[0019] 3 is a diagram showing steps 1 to 5 of the method for manufacturing the circuit board 10 shown in FIGS. 1 and 2. In step 1, a resist application step is performed in which a resist 60 is applied to the pad 40 directly below the bottom electrode 21B of the electronic component 20, thereby forming a solder flow prevention portion 70 that prevents solder from flowing onto the bottom surface of the electronic component 20. In more detail, when a via 30 is disposed within the pad 40 directly below the bottom electrode 21B, the solder flow prevention portion 70 is formed by the resist 60 on the fillet side outside the opening of the via 30 disposed in this pad 40, separating the fillet side from the via 30 side.

[0020] In the second step, solder paste is printed on the pads 40. The solder paste is printed so that it is higher than the solder flow prevention portion 70. It is also preferable to avoid solder adhering to the vias 30 as much as possible, so the solder paste is not printed within the area surrounded by the solder flow prevention portion 70. In the third step, the electronic component 20 is mounted so that the electrodes 21 are positioned on the solder paste.

[0021] In the fourth step, a reflow process is performed to melt the solder paste. During this reflow process, as the solder melts and the electronic component 20 begins to sink, the solder flows out toward the via 30 from the gap between the underside of the electronic component 20 and the solder flow prevention portion 70. However, the provision of the solder flow prevention portion 70 limits the amount of solder flowing out toward the via 30, and also sufficiently reduces the amount of solder that enters the via 30. Furthermore, gas generated within the via 30 escapes from the area surrounded by the solder flow prevention portion 70 toward the side opposite the solder paste.

[0022] The fifth step shows the state in the reflow step where the electronic component 20 has completely sunk and the solder begins to solidify with the underside of the electronic component 20 in contact with the solder inflow prevention portion 70. At this time, the contact between the underside of the electronic component 20 and the solder inflow prevention portion 70 prevents the solder from flowing over the solder inflow prevention portion 70 into the via 30, and also prevents the solder that has entered the via 30 from returning to the fillet side. Furthermore, the gas generated within the via 30 continues to escape from the area surrounded by the solder inflow prevention portion 70 toward the side opposite the solder paste.

[0023] Even if vias 30 are not arranged in pads 40 directly below bottom electrodes 21B of electronic component 20, providing solder-flow prevention portion 70 can prevent solder cracks from occurring on the bottom surface of electronic component 20, thereby improving the reliability of the electrical connection of electronic component 20. Figures 4 and 5 are diagrams showing a case where solder-flow prevention portion 70 is provided on circuit board 10 where vias 30 are not arranged in pads 40 directly below bottom electrodes 21B of electronic component 20, with Figure 4 being a plan view seen from the top of circuit board 10 and Figure 5 being a cross-sectional view of plane X-X shown in Figure 4.

[0024] The circuit board 10 of the second embodiment shown in Figures 4 and 5 differs from the circuit board 10 of the first embodiment shown in Figures 1 and 2 only in that it does not have vias 30. In the circuit board 10 shown in Figures 4 and 5, the provision of solder flow prevention portion 70 prevents solder from flowing to the underside of electronic component 20, where solder cracks are likely to occur, thereby preventing a decrease in connection reliability due to cracks.

[0025] Furthermore, the solder-flow prevention portion 70 provided on the circuit board 10 in which the via 30 is disposed in the pad 40 directly below the lower-surface electrode 21B of the electronic component 20 is not limited to a structure in which it is provided on the fillet side away from the opening of the via 30. Figures 6 and 7 are diagrams showing a third embodiment of the solder-flow prevention portion 70, where Figure 6 is a plan view seen from the top surface of the circuit board 10 and Figure 7 is a cross-sectional view of the X-X plane shown in Figure 6.

[0026] 6 and 7 , the solder-flow prevention portion 70 is provided so as to fill the via 30 with resist 60. In this circuit board 10, the via 30 is filled with the solder-flow prevention portion 70, which prevents gas from being generated in the via 30 and flowing toward the fillet, thereby preventing voids from being generated in the fillet and accelerating the propagation of solder cracks that lead to voids.

[0027] 8 and 9 are diagrams showing a fourth aspect of the solder-flow prevention portion 70, where Fig. 8 is a plan view seen from the top surface of the circuit board 10 and Fig. 9 is a cross-sectional view of the X-X plane shown in Fig. 8. In the circuit board 10 of the fourth aspect shown in Fig. 8 and Fig. 9, the solder-flow prevention portion 70 is provided so as to fill the via 30 and to prevent solder from flowing onto the underside of the electronic component 20.

[0028] 8 and 9 fills the via 30 with resist 60, and further, a disk-shaped portion formed of resist 60 is laminated on the pad 40 so as to cover the opening of the via 30. The solder-flow prevention portion 70 prevents the occurrence of voids due to the via 30, and also prevents solder from flowing onto the underside of the electronic component 20, where cracks are likely to occur, thereby preventing solder cracks from connecting to voids and accelerating the progression of the cracks.

[0029] 10 and 11 are diagrams showing a fifth embodiment of the solder-flow prevention portion 70, where FIG. 10 is a plan view of the circuit board 10 from above, and FIG. 11 is a cross-sectional view of the X-X plane shown in FIG. 10. In the circuit board 10 of the fifth embodiment shown in FIGS. 10 and 11, the solder-flow prevention portion 70 fills half of the space on the fillet side of the hole of the via 30 and is provided so as to surround the periphery of the opening of the via 30 in a horseshoe shape. By partially filling the via 30, the solder-flow prevention portion 70 can prevent the generation of voids due to the via 30 while allowing gas generated within the via 30 to escape to the opposite fillet side. Furthermore, the solder is prevented from flowing to the underside of the electronic component 20, which is prone to cracking, and can prevent solder cracks from connecting to voids and accelerating the propagation of the cracks.

[0030] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0031] For example, the solder inflow prevention portion 70 is not limited to being formed by the resist 60, and for example, a string-like member or the like may be adhered to the pad 40 to function as the solder inflow prevention portion 70. Furthermore, the solder inflow prevention portion 70 may be formed of a plurality of members provided separately at a plurality of locations.

[0032] REFERENCE SIGNS LIST 10...circuit board, 20...electronic component, 21A...side electrode, 21B...bottom electrode, 30...via, 40...pad, 50...solder joint portion, 60...resist, 70...solder flow prevention portion

Claims

1. A circuit board on which an electronic component having electrodes externally connected to the side and bottom surfaces of an encapsulant is mounted by soldering, the circuit board having pads to which the electrodes of the electronic component are electrically connected by soldering, the solder joints connecting the pads to the electrodes of the electronic component are connected by part of the electrodes on the side and bottom surfaces of the electronic component, and a solder flow prevention section is provided directly below the electrodes on the bottom surface.

2. A circuit board according to claim 1, wherein the solder flow prevention portion prevents solder from flowing onto the underside of the electronic component.

3. The circuit board according to claim 1, wherein the solder flow prevention portion is formed of a resist.

4. The circuit board according to claim 1, wherein a via is disposed in the pad located directly below the electrode on the bottom surface of the electronic component.

5. A circuit board according to claim 4, wherein the solder inflow prevention portion is provided regardless of whether or not via fill plating is performed to fill the interior of the via arranged in the pad.

6. A circuit board according to claim 4, wherein the solder flow prevention portion prevents solder from flowing into the via arranged in the pad.

7. A circuit board according to claim 6, wherein the solder inflow prevention portion is provided so as to fill the interior of the via arranged in the pad.

8. A circuit board according to claim 6, wherein the solder flow prevention portion is provided on the fillet side away from the opening of the via arranged in the pad.

9. A method for manufacturing a circuit board in which an electronic component having electrodes externally connected to the side and bottom surfaces of a sealing body is mounted by soldering, the circuit board having pads to which the electrodes of the electronic component are electrically connected by soldering, and vias arranged in the pads, the manufacturing method including a resist application step of applying resist, the resist application step including a step of forming, with resist, a solder inflow prevention portion that prevents solder from flowing into the vias arranged in the pads.

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