Circuit assembly, connected busbar structure, and electrical junction box

Provided is a circuit assembly that includes a circuit board that has an opening, a plurality of busbars that are laid on one surface side of the circuit board, a coil that has a main portion 16 and a plurality of lead terminals, the lead terminals being connected to the plurality of busbars that are exposed through the opening, and a heatsink that is laid, via an adhesive agent, on surfaces of the plurality of busbars that are opposite to the circuit board. Cut-out portions for evacuating the adhesive agent are formed at edges of the plurality of busbars that are opposite to each other in the opening.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of PCT/JP2015/062074 filed Apr. 21, 2015, which claims priority to Japanese Patent Application JP 2014-097716 filed May 9, 2014; JP 2014-097719 filed May 9, 2014; and JP 2014-097426 filed May 9, 2014.

FIELD OF THE INVENTION

The technique disclosed in the present description relates to a circuit assembly, a connected busbar structure, and an electrical junction box.

BACKGROUND OF THE INVENTION

Conventionally, devices in which a circuit assembly including a circuit board on which various electronic components are mounted is accommodated in a case are known as devices for energizing and de-energizing in-car electric components.

In such devices, the electronic components mounted on the circuit board are small and have superior functionality.

However, these electronic components have a relatively large heat generation, and thus if heat generated by the electronic components stay in the case, there will be a risk that the temperature in the case increases and the performance of the electronic components accommodated in the case decreases.

Accordingly, as an example of various structures for discharging the heat generated by the circuit board or the electronic components, a circuit assembly111as shown inFIG. 7is conceivable that has a configuration in which a heat discharging member130is provided on that surface of a circuit board112that is opposite to the surface on which an electronic component115is provided.

On the other hand, as shown inFIGS. 6 and 7, it is also conceivable that an opening113is formed in a region of the circuit board112that corresponds to the electronic component115, a plurality of busbars120are provided on that surface of the circuit board112that is opposite to the surface on which the electronic component115is provided, and terminals117of the electronic component115are connected to the busbars120exposed through the opening113. By configuring an electric power circuit with the plurality of busbars120, it is possible to flow a high current through the electric power circuit.

However, when the electronic component115is connected to the plurality of busbars120via the opening113formed in the circuit board112, an adhesive agent135for bonding the heat discharging member that is laid (layered) on the surfaces of the busbars120that are opposite to the circuit board112may enter a gap S between adjacent busbars120, and may get into contact with a lower surface of a main portion116of the electronic component115, as shown inFIG. 7. In such a situation, if the adhesive agent135expands due to the heat generated by the circuit board112or the electronic component115, or adversely contracts by being cooled, the electronic component115will be pushed or drawn by the adhesive agent135, possibly causing a connection failure such as a crack in a connection section between the terminal117and the busbar120.

The technique disclosed in the present description was made in view of the above-described circumstances, and it is an object thereof to provide a circuit assembly and an electrical junction box that have high connection reliability.

SUMMARY

According to the technique disclosed in the present description, a circuit assembly includes: a circuit board that has an opening; a plurality of busbars that are laid on one surface side of the circuit board; an electronic component that has a main portion and a plurality of lead terminals, the lead terminals being connected to the plurality of busbars that are exposed through the opening; and a heatsink that is laid, via an adhesive agent, on surfaces of the plurality of busbars that are opposite to the circuit board, and is characterized in that cut-out portions for evacuating the adhesive agent are formed at parts of edges of the plurality of busbars that are opposite to each other in a region of the opening.

According to the technique disclosed in the present description, the adhesive agent that has entered a gap between adjacent busbars in the region of the opening extends broadly and shallowly in the cut-out portions of the busbars, thus preventing the adhesive agent from getting into direct contact with the lower surface of the main portion of the electronic component. Accordingly, even if the adhesive agent expands due to the heat generated in the electronic component or the circuit board, or adversely contracts by being cooled, the electronic component will be prevented from being directly affected thereby, preventing connection sections between the lead terminals and the busbars from being affected. Accordingly, it is possible to achieve a circuit assembly and an electrical junction box that have high connection reliability.

A configuration is also possible in which a pair of the cut-out portions are formed at positions of the plurality of busbars that are opposite to each other in the region of the opening.

With the configuration in which the pair of cut-out portions are formed at positions of the plurality of busbars that are opposite to each other in the region of the opening, it is possible to ensure a large area for the gap between the busbars, making it possible to prevent the adhesive agent from getting into contact with the lower surface of the main portion of the electronic component.

Furthermore, the technique disclosed in the present description relates to an electrical junction box in which the circuit assembly is accommodated in a case.

According to the technique disclosed in the present description, it is possible to achieve a circuit assembly or an electrical junction box that have improved connection reliability.

DETAILED DESCRIPTION

An embodiment of a circuit assembly will be described with reference toFIGS. 1 to 5.

An electrical junction box10of the present embodiment is provided with a circuit assembly11including a circuit board12and a heatsink30, and a synthetic resin case40that accommodates the circuit assembly11. Note that in the following description, the upper side ofFIG. 1refers to “front side” or “upper side”, and the lower side ofFIG. 1refers to “rear side” or “lower side”.

As shown inFIG. 1, the circuit assembly11is provided with the circuit board12, coils15(an example of an electronic component) that are arranged on the front surface (upper side ofFIG. 1) of the circuit board12, a plurality of busbars20that are arranged on the rear surface (lower side ofFIG. 1) of the circuit board12, and the heatsink30(seeFIG. 5) that is arranged on the rear surfaces of the busbars20.

The circuit board12is substantially L-shaped, and has, on its front surface, a conductive circuit that is not shown and is achieved by printed wiring.

As shown inFIGS. 1 and 5, each coil15is a surface-mounted coil, and has a main portion16in the shape of a rectangular parallelepiped, and a pair of lead terminals17provided in the vicinity of the edges of two opposing sides of the bottom surface of the main portion16.

The plurality of busbars20are formed by pressing a metal plate into predetermined shapes. The busbars20are substantially rectangular, and are arranged in a predetermined pattern with a gap S between adjacent busbars20. Some busbars20have, on an edge thereof, a connecting piece21that protrudes outward and is formed as one piece with the corresponding busbar20. Each connecting piece21has a bolt mounting hole21A through which a bolt is inserted, and is electrically connected to an external power supply, the bolt (not shown) being inserted through the bolt mounting hole21A and being screwed to a power supply terminal mounted on a vehicle.

The plurality of busbars20are adhered to the rear surface of the circuit board12via an insulating adhesive sheet25. The adhesive sheet25has substantially the same shape as the circuit board12.

As shown inFIG. 1, the circuit board12has openings13for mounting the coils15on the busbars20at positions at which the coils15are arranged. As shown inFIG. 4, a part of each opening13through which the main portion16of the coil15is arranged opens in the shape of a rectangle that is slightly larger than the bottom surface of the main portion16. Furthermore, openings with a small width are formed extending from a pair of edges on which the lead terminals17of the coil15are located.

Furthermore, the adhesive sheet25has, at the positions corresponding to the openings13of the circuit board12, sheet openings26that have substantially the same shape as the openings13and have an opening size slightly larger than that of the openings13(seeFIGS. 1 and 3).

In the region of each opening13of the circuit board12, a pair of the busbars20is partially exposed. The exposed pair of busbars20have, at parts of their opposite edges, cut-out portions22that are cut out in the shape of a rectangle so as to extend the gap S between the adjacent busbars20. In the present embodiment, the cut-out portions22are respectively provided in the pair of busbars20, opposing each other.

The coils15are arranged on the front surface side of the circuit board12, namely, in the regions in which the connection openings13are formed. In the present embodiment, the lead terminals17of the coils15are connected to the surfaces of the busbars20that are exposed through the opening13and the sheet opening26by a well-known method such as soldering.

The heatsink30is arranged on the lower surfaces (rear surfaces) of the busbars20(seeFIG. 5). The heatsink30is a plate-shaped member that is made of a metal material such as aluminum or an aluminum alloy that is excellent in heat conductivity, and has the function to discharge heat generated in the circuit board12and the coils15. The heatsink30is adhered to the rear surface side of the busbars20with, for example, a thermosetting adhesive agent35. The adhesive agent35is an adhesive agent that is insulating and has heat conductivity.

The following will describe an example of a method for manufacturing the electrical junction box10according to the present embodiment. First, as shown inFIG. 1, the adhesive sheet25, cut in a predetermined shape, is laid on the lower surface of the circuit board12on whose front surface an electrically conducting path is formed by printed wiring, and the plurality of busbars20arranged in a predetermined pattern are pressed thereto. Accordingly, the circuit board12and the plurality of busbars20are adhered and fixed to each other via the adhesive sheet25. In this state, parts of the upper surfaces of the plurality of busbars20are exposed through the openings13of the circuit board12and the sheet openings26of the adhesive sheet25.

Then, solder is applied to predetermined positions of the circuit board12by screen printing. Then, the coils15are placed at the predetermined positions, and reflow soldering is performed.

Then, the adhesive agent35is applied to the upper surface of the heatsink30, and the circuit board12on which the coils15and the plurality of busbars20are arranged is laid thereon from above. Since, at this time, the pair of cut-out portions22are formed at the edges of the plurality of busbars20that are opposite to each other in the regions of the openings13of the circuit board12, the adhesive agent35that has entered the gaps S between the adjacent busbars20extends broadly and shallowly in the cut-out portions22(seeFIG. 5). Thereafter, the adhesive agent35is cured by application of heat.

Lastly, the circuit board12(circuit assembly11) laid on the heatsink30is accommodated in the case40, and the electrical junction box10is formed.

The following will describe the functions and effects of the electrical junction box10according to the present embodiment. According to the present embodiment, the adhesive agent35that has entered the gap S between adjacent busbars20in the regions of the openings13of the circuit board12extends broadly and shallowly in the cut-out portions22of the busbars20, and is prevented from getting into direct contact with the lower surfaces of the main bodies16of the coils15. Accordingly, even if the adhesive agent35expands due to the heat of the coils15or the circuit board12, or adversely contracts by being cooled, the main bodies16of the coils15are prevented from being directly affected thereby, making it difficult for a connection section between the busbar20and the lead terminal17to be affected. That is, it is possible to achieve a circuit assembly11and an electrical junction box10that have high connection reliability.

A configuration is also possible in which each pair of cut-out portions22are provided at positions of the plurality of busbars20that are opposite to each other in the region of the opening13. Accordingly, it is possible to ensure a large area for the gap between adjacent busbars20, preventing the adhesive agent35from getting into contact with the lower surfaces of the main bodies16of the coils15.

Other Aspects

The technique disclosed by the present description is not limited to the embodiment described in the foregoing description and drawings, and encompasses, for example, the following various aspects.

The foregoing embodiment has a configuration in which the cut-out portions22are provided on both of the pair of busbars20that are exposed through the opening13, but a configuration is also possible in which a cut-out portion22is provided on one of the pair of busbars20.

Furthermore, in the case where the cut-out portions22are provided on both of the pair of busbars20, the cut-out portions22are not necessarily provided at opposite positions, and may be provided at shifted positions. Furthermore, the cut-out portions22are provided in an asymmetric shape.

Furthermore, the positions, shape, and the number of the cut-out portions22are not limited to those of the foregoing embodiment, and may be changed suitably.

The foregoing embodiment has described an example in which the coils15are mounted, but the present invention is applicable to the case where, instead of the coils15, other electronic components such as capacitors or shunt resistors are mounted.

The technique described in the present description relates to another embodiment of a circuit assembly and a connected busbar structure.

Circuit assemblies that include a busbar are conventionally known. JP 2012-235693A describes a circuit assembly that includes a circuit board, and a plurality of busbars that are arranged over the rear surface of the circuit board. The busbars have, at ends thereof, a plurality of tab-shaped terminal sections arranged in parallel. In manufacturing of this circuit assembly, a connected busbar structure is first formed in which the terminal sections of the plurality of busbars are connected to each other by tie bars. The circuit assembly is formed by cutting the tie bars.

However, the configuration in which the tie bars that connect the terminal sections are cut in order to form the circuit assembly needs to ensure such a size that a die for cutting the tie bars can advance between the terminal sections, and may interfere with downsizing of the circuit assembly.

The technique described in the present description was made in view of the above-described circumstances, and it is an object thereof to downsize the circuit assembly.

According to the technique described in the present description, a circuit assembly includes a circuit board that is made of an insulating plate on which an electrically conducting path is formed, and that is provided with a through-hole, and a busbar substrate that is laid on the circuit board, and includes a plurality of busbars made of plate-shaped metal, and cut sections formed by cutting a tie bar connecting the plurality of busbars, wherein the cut sections of the busbar substrate are formed at positions that are contiguous with the through-hole of the circuit board.

According to the technique described in the present description, a connected busbar structure includes a tie bar that connects a plurality of busbars made of plate-shaped metal such that the busbars can be cut, the connected busbar structure serving as a busbar substrate by being laid on a circuit board made of an insulating plate on which an electrically conducting path is formed and cutting the tie bar, wherein the tie bar is formed at a position that is contiguous with a through-hole formed in the circuit board.

According to the foregoing configuration, in manufacturing of the circuit assembly, it is possible to form the cut sections by cutting the tie bar using a die through the through-hole of the circuit board. Accordingly, the busbars that are connected to each other by a tie bar on the inside of the circuit board are not necessarily connected by a tie bar on the outside of the circuit board, and thus it is possible to reduce the number of the tie bars on the outside of the circuit board. Accordingly, it is possible to reduce the area of the portion of the busbar substrate that ensures such a size that a die for cutting the tie bar on the outside of the circuit board can advance. Accordingly, it is possible to downsize the circuit assembly.

The following aspects are preferable as aspects of the foregoing configuration.

Each busbar that has a cut section has a terminal section that is connectable to the outside, and the terminal sections are bent in the vicinity of an edge of the circuit board.

In a configuration in which, for example, terminal sections of a plurality of busbars are connected to each other by tie bars, and the tie bars are cut at the time of manufacturing of the circuit assembly, when the terminal sections are subjected to bending, it is efficient to perform cutting the tie bar and bending the terminal sections at the same time. However, when cutting the tie bar and bending the terminal sections are performed at the same time, it is not possible to bend the terminal sections in the vicinity of the edge of the circuit board since such a size that a die for cutting the tie bar can advance is ensured on the base end side of the terminal sections. In this case, there is the problem that the length of the terminal sections increases and downsizing of the circuit assembly is not possible.

By forming the cut sections at positions that are contiguous with a through-hole of the circuit board, the terminal sections can be bent in the vicinity of the edge of the circuit board, making it possible to reduce the length of the terminal sections and to downsize the circuit assembly.

An electronic component that has lead terminals to be connected to the busbars is provided, and the lead terminals are connected to the busbars having the cut sections through the through-hole.

Accordingly, since the through-hole of the circuit board through which a die or the like is passed when cutting the tie bars can be used for the connection of the electronic components, it is possible to increase the density of arrangement of the electronic components. Accordingly, it is possible to downsize the circuit assembly.

According to the technique described in the present description, it is possible to downsize the circuit assembly.

Hereinafter, Embodiment 2 will be described with reference toFIGS. 8 to 14.

A circuit assembly210may be arranged on a power supplying path between, for example, a power supply such as a battery of a vehicle such as an electric automobile, and a load constituted by an in-car electric component such as a lamp or a wiper, and may be used as, for example, a DC-DC converter, or an inverter.

As shown inFIG. 8, the circuit assembly210includes a circuit board211that is made of an insulating plate on which an electrically conducting path is formed, a busbar substrate213that is made of plate-shaped metal and is laid on the circuit board211, and electronic components226A to226D that are connected to the circuit board211and the busbar substrate213.

The electronic components226A to226D include switching elements226A made of a FET (Field Effect Transistor), shunt resistors226B, coils226C, capacitors226D, and the like, and include lead terminals227that are connected to the electrically conducting path of the circuit board211or to busbars214by soldering. The lead terminals227of the coils226C are L-shaped, and are arranged so as to extend along the bottom and side surfaces of the rectangular parallelepiped-shaped main portion.

The circuit board211is made of an insulating plate made of an insulating material on which an electrically conducting path made of a copper foil (not shown) is printed and wired, and is adhered to the busbar substrate213via an adhesive sheet224, as shown inFIG. 9. This circuit board211has a plurality of through-holes212A and212B that are formed through the circuit board211. The plurality of through-holes212A and212B include the plurality of component insertion holes212A through which the electronic components226A to226D are inserted, and the plurality of terminal insertion holes212B through which a plurality of terminals (not shown) of other circuits are inserted.

The component insertion holes212A have a shape and size that correspond to the shape and size on the bottom surface side of the electronic components226A to226D, and are rectangular shaped so that one or multiple electronic components226A to226D can be inserted therethrough. The component insertion holes212A through which the coils226C and the capacitors226D are inserted are formed so as to have such a size that the outer circumferences on the bottom side of coils226C and the capacitors226D fit therein, and have cut-out portions218that are cut out conforming to the positions of the lead terminals227. Solder fillets for soldering the lead terminals227are respectively formed on the inside of the cut-out portions218.

The adhesive sheet224has substantially the same shape as the circuit board211, an insulating adhesive agent is applied to it, and has through holes225at positions corresponding to the through-holes212A and212B.

The busbar substrate213is made of metal such as copper or a copper alloy, and has the plurality of plate-shaped busbars214that are shaped in accordance with the shape of the electrically conducting path. The plurality of busbars214have terminal sections215that are obtained by bending portions arranged outside the outer circumference of the circuit board211in the shape of an L or a crank. Each terminal section215is to be connected to an external terminal, and is formed with a width and thickness that depend on the electric power.

Before assembling the circuit assembly210, by punching a rectangular metal plate, the busbar substrate213is formed into a connected busbar structure221that includes the plurality of busbars214, a frame body216arranged around the plurality of busbars214, inner tie bars220A (an example of the “tie bars”) for connecting the plurality of busbars214, and outer tie bars220B for connecting the busbars214and the frame body216. The frame body216of the connected busbar structure221has, at four corners thereof, holding holes217for holding the position of the connected busbar structure221that are formed through the frame body216.

The inner tie bars220A are arranged inward of the outer circumference of the circuit board211so as to connect the plurality of busbars214, and are arranged below the component insertion holes212A of the circuit board211through which the coils226C are inserted (positions that are contiguous with the through-holes), as shown inFIGS. 10 and 11. By cutting the inner tie bars220A before the electronic components226A to226D are mounted, cut sections222, which are cut end surfaces of the inner tie bars220A, are formed, as shown inFIGS. 12 and 13. That is, in the state in which the busbar substrate213is assembled into the circuit assembly210, the busbar substrate213includes the cut sections222, which are formed by cutting the inner tie bars220A. The cut sections222are the cut end surfaces of the inner tie bars220A that are cut by a die, and the side surfaces of the busbars214are cut in a step-like manner with a predetermined size.

The outer tie bars220B are arranged outward of the outer circumference of the circuit board211so as to connect the busbars214and the frame body216, and are cut after the electronic components226A to226D are mounted. When the outer tie bars220B are cut by a die, the terminal sections215of the busbars214are bent at the same time. The cut end surfaces of the outer tie bars220B are formed smoothly along the outer circumference of the busbars214and the terminal sections215.

The following will describe a method for manufacturing the circuit assembly210.

As shown inFIG. 9, the connected busbar structure221is formed by punching a metal plate, the adhesive sheet224and the circuit board211are laid on the connected busbar structure221at a predetermined position thereof, and the circuit board211is fixed to the connected busbar structure221(FIG. 10). In this state, the inner tie bars220A that connect adjacent busbars214are exposed through the component insertion holes212A of the circuit board211.

Then, the inner tie bars220A are cut using a die, and the cut sections222are formed (FIG. 12). Then, the lead terminals227of the electronic components226A to226D are connected to the circuit board211and the busbars214by, for example, reflow soldering (FIG. 14).

Also, the frame body216is separated by cutting the outer tie bars220B using a die and bending the terminal sections215at the same time, and the circuit assembly210is formed (FIG. 8).

A heat discharging member made of a metal material such as an aluminum alloy that has high heat conductivity is laid on this circuit assembly210, for example, the lower surfaces of the busbars214, via an insulating adhesive agent. Then, the circuit assembly210is disposed in a case made of a synthetic resin, and is then installed as an electrical junction box in a vehicle.

According to the present embodiment, the following functions and effects are achieved.

According to the present embodiment, at the time of manufacturing the circuit assembly210, the cut sections222can be formed by cutting the inner tie bars220A (tie bars) using a die through the component insertion holes212A (through-holes) of the circuit board211. Accordingly, as compared to the case where cut sections are formed only on the outside of the circuit board211, the busbars214whose cut sections222are formed on the inside of the circuit board211do not necessarily have a cut section on the outside of the circuit board211. Accordingly, the number of the outer tie bars220B can be reduced, thus making it possible to reduce the area of the portion of the busbar substrate213for which such a size on the outside of the circuit board211is ensured that a die for cutting a tie bar can advance. Accordingly, it is possible to downsize the circuit assembly210.

Furthermore, the electronic components226A to226D that have the lead terminals227to be connected to the busbars214are provided, and the lead terminals227are connected to the busbars214having the cut section222via the component insertion holes212A (through-holes).

Accordingly, since the through-holes of the circuit board211through which a die is to be passed when cutting the inner tie bars220A can be used for connection of the electronic components226C, it is possible to increase the density of arrangement of the electronic components226A to226D. Accordingly, it is possible to downsize the circuit assembly210.

Hereinafter, another embodiment of a circuit assembly and an electrical junction box will be described with reference toFIGS. 15 to 18.

As shown inFIG. 15, the embodiment of a circuit assembly and an electrical junction box relates to an embodiment in which the connected busbar structure221in which the busbars214are connected to each other by inner tie bars237do not have a cut section in their terminal sections and are not connected by outer tie bars. Descriptions of the same configurations as those of the foregoing embodiments will be omitted.

As shown in comparative examples ofFIGS. 17 and 18, the terminal sections231of the plurality of busbars232are connected to each other by the outer tie bars230, and in the case where the outer tie bars230are cut and the terminal sections231are bent during manufacturing the circuit assembly210, it is efficient to cut the outer tie bars230and bend the terminal sections231at the same. However, when cutting the outer tie bars230and bending the terminal sections231are performed at the same, it is not possible to bend the terminal sections231in the vicinity of the edge of the circuit board211since such a size L is ensured on the base end side of the terminal sections231that the die for cutting the outer tie bars230can advance, and the terminal sections231are bent at positions apart from the edge of the circuit board211by the size L. In this case, there is the problem that the need of the size L increases the length of the terminal sections231and makes it impossible to downsize the circuit assembly.

According to the present embodiment, as shown inFIGS. 15 and 16, the plurality of adjacent busbars236are connected to each other by the inner tie bars237, and terminal sections235(that are not connected by outer tie bars220B) are formed on the busbars236connected by the inner tie bars237. Since the inner tie bars220are arranged below the component insertion holes212A (positions that are contiguous with the through-holes), cut sections240obtained by cutting the inner tie bars220A are also arranged below the component insertion hole212A.

Since the outer tie bars do not need to be cut in order to form the terminal sections238, it is not necessary to ensure such a size from the edge of the circuit board211that the die for cutting the outer tie bars can advance. Accordingly, it is possible to bend the terminal sections238in the vicinity of the edge of the circuit board211, eliminating the need of increasing the length of the terminal sections238for the bending of the terminal sections238. It is therefore possible to downsize the circuit assembly.

Other Aspects

The technique described in the present description is not limited to the embodiments described with reference to the foregoing description and drawings, and the technical scope of the technique described in the present description may encompass, for example, the following aspects:

(1) The positions and the number of the inner tie bars220A are not limited to the positions and the number of the foregoing embodiment. Furthermore, it is possible to form a suitable number of the cut sections222at suitable positions according to the inner tie bars220A.
(2) The cut sections222and240may not necessarily have a shape in which sides of the busbars are cut out. For example, the cut sections may be formed so as to be co-planar with sides of the busbars.
(3) The circuit board may have, in addition to the component insertion holes212A, through-holes for cutting the cut sections222and240using a die.

The technique described in the present description relates to another embodiment of a circuit assembly and an electrical junction box.

Circuit assemblies that include various types of electronic components, a circuit board, and busbars that are laid on the circuit board are conventionally known (see, for example, JP 2013-99071A). In such circuit assemblies, various types of electronic components are connected by a method such as soldering.

Examples of the electronic components to be connected to the circuit assembly include a relay and a shunt resistor. Since among such electronic components, the shunt resistor is entirely made of a metal material, if the busbars are soldered, the solder433wets and extends (expands), and may reach a resistor section432, as shown inFIG. 24. In such a case, there is the problem that an inappropriate shape of the soldered section may cause the solder crack due to thermal impulse of a cooling/heating cycle, resulting in a reduction in electrical connection reliability.

It is an object of the technique described in the present description to enhance the electrical connection reliability of a circuit assembly that includes a shunt resistor.

According to the technique described in the present description, a circuit assembly includes a circuit board that has an opening, busbars that are laid on one surface side of the circuit board, and a shunt resistor that has connection terminal sections that are connected to the busbars in the opening of the circuit board by soldering, and a resistor section that is contiguous to the connection terminal sections, wherein solder fillets that connect the shunt resistor and the busbars are formed closer to the connection terminal sections than to the resistor section.

Furthermore, according to the technique described in the present description, an electrical junction box includes the above-described circuit assembly, and a case in which the circuit assembly is accommodated.

In the technique described in the present description, the solder fillets that connect the shunt resistor and the busbars are formed closer to the terminal sections of the shunt resistor than to the resistor section thereof, and thus a designed resistance value can be obtained.

If, as shown inFIG. 24, the solder433wets and extends to the resistor section432of the shunt resistor, and fills up the space between the resistor section432and the busbars420, there will be a risk that a solder crack is likely to occur due to thermal impulse of a cooling/heating cycle. However, according to the technique described in the present description, the solder fillets that connect the shunt resistor and the busbars are formed closer to the terminal sections of the shunt resistor than to the resistor section thereof, and thus solder that fills up the space between the resistor section and the busbar is not likely to be formed, and a solder crack is not likely to occur even under the thermal impulse of a cooling/heating cycle, improving electrical connection reliability.

The technique described in the present description may have the following configurations:

Cut-out portions are formed in areas of the busbars that overlap the resistor section of the shunt resistor, and ends of the cut-out portions may be set to be closer to the connection terminal sections than to the resistor section.

By making such a configuration, the busbars are cut out to the vicinity of the connection terminal sections of the shunt resistor, and thus it is possible to reliably prevent the solder from wetting and extending to the resistor section.

According to the technique described in the present description, it is possible to improve the electrical connection reliability of a circuit assembly including a shunt resistor.

Hereinafter, the electrical junction box10including the circuit assembly11according to Embodiment 4 will be described with reference toFIGS. 19 to 23.

An electrical junction box310of the present embodiment is provided with a circuit assembly311that includes a circuit board313and busbars320, and a case312that is made of a synthetic resin and in which the circuit assembly311is accommodated. Note that in the following description, the upper side ofFIG. 23refers to “front side” or “upper side”, and the lower side ofFIG. 23refers to “rear side” or “lower side”.

As shown inFIGS. 19 and 21, the circuit assembly311includes the circuit board313, shunt resistors330arranged on the front surface (upper side of theFIG. 21) of the circuit board313, and a plurality of busbars320that are adhered to the rear surface (lower side ofFIG. 21) of the circuit board313via an adhesive sheet315.

The circuit board313is substantially L-shaped in a top view, and has, on its front surface, an electrically conducting path that is not shown and is achieved by printed wiring.

The circuit board313has, at positions at which the shunt resistors330are arranged, openings314each for connecting two shunt resistors330to the busbars320. As shown inFIG. 22, each opening314is open in the shape of a rectangle, and the two shunt resistors330are arranged such there is a gap G1between the two shunt resistors330and the edges of the opening.

The adhesive sheet315is made of an insulating material, and has substantially the same shape and size as those of the circuit board313. As shown inFIG. 22, the adhesive sheet315has, at positions that correspond to the openings314of the circuit board313, sheet openings316that are each larger than the circumference of the opening314of the circuit board313.

The plurality of busbars320are formed by pressing a metal plate into predetermined shapes. The busbars320are arranged in a predetermined pattern with a gap G2between adjacent busbars320. Some of the plurality of busbars320have a bolt insertion hole321through which a bolt is to be inserted, and are connected to an external power supply via the bolt.

Of the plurality of busbars320, the busbars320to which the shunt resistors330are connected have cut out portions that are dimensioned so as to conform to the resistor sections332of the shunt resistors330(hereinafter, referred to as “cut-out portions322”). As shown inFIG. 22, the cut-out portions322are provided by cutting rectangles from two busbars320. The cut-out portions322are contiguous with (communicate with) the gaps G2between the two busbars320.

As shown inFIG. 23, ends322A of the cut-out portions322that are formed in the busbars320to which the shunt resistors330are connected are set to be closer to the connection terminal sections331of the shunt resistors330than to the resistor sections332thereof, and the cut-out portions322are provided entirely over the sections that overlap the resistor sections332.

The shunt resistors330are arranged in the openings314of the circuit board313, and are connected to the busbars320by soldering. In the present embodiment, two shunt resistors330are provided for each opening314of the circuit board313.

Each shunt resistor330includes a connection terminal sections331connected to the busbars320, and a resistor section332that is contiguous to the connection terminal sections331. As shown inFIG. 23, the resistor section332of each shunt resistor330forms a flat surface protruding upward. InFIG. 23, the resistor section332is provided in a region R between two dotted lines. The connection terminal sections331are respectively provided contiguously to both ends of the resistor section332of the shunt resistor330.

In the present embodiment, the solder fillets333that connect the shunt resistors330and the busbars320are formed closer to the connection terminal sections331of the shunt resistors330than to the resistor sections332thereof.

Method for Manufacturing Electrical Junction Box310

Hereinafter, an example of a method for manufacturing the electrical junction box310according to the present embodiment will be described.

The adhesive sheet315that is cut in a predetermined shape is laid on the lower surface of the circuit board313on whose front surface an electrically conducting path is formed by printed wiring, and the plurality of busbars320arranged in a predetermined pattern are pressed thereto. Accordingly, the circuit board313and the plurality of busbars320are adhered and fixed to each other via the adhesive sheet315, and as shown inFIG. 20, some of the busbars320are exposed through the openings314of the circuit board313and the sheet openings316of the adhesive sheet315.

Then, by applying solder to predetermined positions of the circuit board313, placing two shunt resistors330on the busbars320that are exposed through each opening314of the circuit board313, and putting the assembly into a reflow oven so that it is subjected to soldering, it is possible to obtain the circuit assembly311. In this circuit assembly311, as shown inFIG. 23, the solder fillets333that connect the shunt resistors330and the busbars320are formed closer to the connection terminal sections331than to the resistor section332.

The circuit assembly311obtained in this manner is accommodated in the case312, and thereby the electrical junction box310of the present embodiment can be obtained.

Functions and Effects of the Present Embodiment

Hereinafter, the functions and effects of the present embodiment will be described.

If, as with the conventional example shown inFIG. 24, the solder433that connects the shunt resistor430and the busbars420wets and extends to not only the connection terminal sections431but also to the resistor section432, and is formed so as to fill up the spaces between the resistor section432and the busbars420, an inappropriate shape of the soldered section may cause a solder crack due to thermal impulse of a cooling/heating cycle. InFIG. 24, the reference numeral411denotes a circuit assembly, the reference numeral413denotes a circuit board, the reference numeral414denotes an opening of the circuit board, the reference numeral415denotes an adhesive sheet that connects the circuit board and the busbars, and the reference numeral416denotes a sheet opening.

In contrast, in the present embodiment, the solder fillets333that connect the shunt resistors330and the busbars320are formed in an appropriate shape at positions closer to the terminal sections of the shunt resistors330than to the resistor sections thereof.

According to the present embodiment, it is thus possible to obtain a designed resistance value. Furthermore, according to the present embodiment, since the solder fillets that connect the shunt resistors330and the busbars320are not likely to fill up the space between the resistor sections332of the shunt resistors and the busbars320, a solder crack is not likely to occur even under the thermal impulse of a cooling/heating cycle, improving electrical connection reliability.

Moreover, according to the present embodiment, the cut-out portions322are provided entirely over the sections of the busbars320that overlap the resistor sections332of the shunt resistors330, the terminals322A of the cut-out portions322are set closer to the connection terminal sections331than to the resistor sections332, and thus the busbars320are cut out to the vicinity of the connection terminal sections331of the shunt resistors330, making it possible to prevent the solder from wetting and extending to the resistor sections332reliably.

Other Aspects

The technique described in the present description is not limited to the embodiment described with reference to the foregoing description and drawings, and the technical scope of the technique described in the present description may encompass, for example, the following aspects:

(1) In the foregoing embodiment, a circuit assembly311that does not include a heatsink is described, but a heatsink may be provided on the surfaces of the busbars320that are opposite to the circuit board side.

(2) The foregoing embodiment has described an example in which the cut-out portions322are provided entirely over the sections of the busbar320that overlap the resistor sections332of the shunt resistors330, and the ends322A of the cut-out portions322are set closer to the connection terminal sections331than to the resistor sections332, but the present invention is not limited to this. The busbar may partially remain in the section that overlaps the resistor section of the shunt resistor.
(3) The foregoing embodiment has described an example in which two shunt resistors330are provided, but the present invention is not limited to this, and one or three of more shunt resistors330may be provided.