JP5044259B2 - Circuit structure - Google Patents

Description

  The present invention relates to a circuit structure including a bus bar.

Conventionally, the thing of patent document 1 is known as a circuit structure body used for the electrical junction box for vehicles, for example. This is a configuration in which a circuit board and a bus bar are laminated via an adhesive layer, and electronic components are soldered to the circuit board and the bus bar by, for example, a reflow method. This bus bar is generally made of a copper alloy, but for the purpose of preventing surface oxidation and improving solderability, the surface of the base metal is plated with a metal (for example, tin) having excellent oxidation resistance and solder wettability. A layer may be formed.
JP 2003-164039 A

In the case of the above reflow method, the temperature in the reflow furnace is set to a temperature higher than the melting temperature of the solder in order to shorten the soldering time. Then, for example, when a solder having a relatively high melting point is used, the bus bar may be heated to a temperature higher than the melting point of the metal constituting the plating layer, and the plating layer of the bus bar may be melted. In such a case, there is a concern that the adhesive strength between the bus bar and the circuit board becomes insufficient as a result of the adhesive layer floating and air entering between the bus bar and the adhesive layer.
The above problem also occurs when the bus bar and the heat sink are bonded. It also occurs when a bus bar is bonded to an adhesive member such as a circuit board or a heat sink.

  Therefore, for example, it is conceivable to remove the plating layer in the area of the bus bar that is bonded to the circuit board to expose the base material. Then, since the plating layer is not interposed between the base material and the adhesive layer, air does not enter between the base material and the adhesive layer even if the circuit component is heated to a temperature at which the plating layer melts. Thereby, it was expected that sufficient adhesive strength was obtained between the bus bar and the circuit board. However, if the base material is to be exposed in the entire area of the bus bar that is bonded to the circuit board, a large amount of work time is required, resulting in a problem that manufacturing efficiency is lowered.

The present invention has been completed based on the above-described circumstances, and improves the manufacturing efficiency and provides a circuit structure having sufficient adhesive strength between a bus bar and an adhesive member including a circuit board or a heat sink. The purpose is to provide.

  As means for achieving the above object, the invention of claim 1 includes a bus bar in which a tin plating layer is formed on the surface of a metal base material, and an adhesive region provided on at least one surface of the bus bar. An adhesive member bonded via an insulating adhesive layer, wherein a plurality of exposed portions formed by exposing the surface of the base material are spaced apart from each other in the adhesive region of the bus bar. The base material exposure rate, which is the ratio of the projected area of the exposed portion in the direction perpendicular to the plate surface of the bus bar to the projected area of the adhesion region in the direction perpendicular to the plate surface of the bus bar, It is characterized by being 5% or more.

  According to a second aspect of the present invention, in the first aspect, the base material exposure rate is 50% or less.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the base material exposure rate is 20% to 45%.

  According to a fourth aspect of the present invention, there is provided the method according to any one of the first to third aspects, wherein the base material exposure rate is not less than 30% and not more than 40%.

  According to a fifth aspect of the present invention, in the method according to any one of the first to fourth aspects, the exposed portions are formed so as to be arranged at a predetermined pitch interval. .

  A sixth aspect of the present invention is the method according to any one of the first to fifth aspects, wherein the exposed portion is formed with a convex portion protruding from a surface of the base material, and the convex portion. Is made of the base material or an alloy of the base material.

  A seventh aspect of the invention is characterized in that, in the sixth aspect, the convex portion has a substantially annular shape when viewed from the adhesive member side.

  According to an eighth aspect of the present invention, in the apparatus according to any one of the first to seventh aspects, the exposed portion is formed by intermittently irradiating the bus bar with laser light at a predetermined interval. It is characterized by being.

<Invention of Claims 1 to 4>
According to the first to fourth aspects of the present invention, since the exposed portion is exposed from the tin plating layer, the exposed portion and the adhesive layer are directly bonded. Thereby, even if a circuit structure is heated to a temperature at which the tin plating layer melts, air can be prevented from entering between the bus bar and the adhesive member.

  And according to the present invention, the base material exposure rate, which is the ratio of the projected area in the direction perpendicular to the plate surface of the bus bar to the projected area in the direction perpendicular to the plate surface of the bus bar in the adhesion region, It is 5% or more, preferably 50% or less, more preferably 20% or more and 45% or less, and particularly preferably 30% or more and 40% or less.

  When the base material exposure rate is less than 5%, the adhesive strength between the bus bar and the adhesive member decreases. When the base material exposure rate exceeds 50%, the processing time for forming the exposed portion is extended, and thus the manufacturing efficiency is lowered.

  Moreover, when the base material exposure rate is 20% or more, the adhesive strength between the bus bar and the adhesive member is further improved, and when it is 45% or less, the processing time can be shortened.

  Furthermore, if the base material exposure rate is 30% or more and 40% or less, even if the adhesive strength between the bus bar and the adhesive member varies, the minimum value of the dispersed adhesive strength has sufficient strength. Is particularly preferred.

<Invention of Claim 5>
According to the invention of claim 5, since the exposed portions are formed in a state of being arranged with a predetermined pitch interval, the stress applied to each exposed portion can be made uniform. Thereby, since the stress added to each exposed part can be disperse | distributed, the adhesive strength of a bus-bar and an adhesive member can be improved further.

<Invention of Claim 6>
According to invention of Claim 6, since the convex part protrudes in the adhesive member side, the adhesive strength of a bus-bar and an adhesive member improves because a convex part and the contact bonding layer adhere | attach firmly.

<Invention of Claim 7>
As described above, since the adhesive strength between the bus bar and the adhesive member can be improved by providing the convex portion, if the ratio of the convex portion in the exposed portion is increased, the adhesive strength between the bus bar and the adhesive member is improved. It becomes possible. According to invention of Claim 7, the convex part has comprised the substantially cyclic | annular form seeing from the adhesion member side. This makes it possible to efficiently form the convex portions and increase the proportion of the convex portions in the exposed portion, so that the adhesive strength between the bus bar and the adhesive member can be improved.

<Invention of Claim 8>
According to the invention of claim 8, the convex portion can be formed by a simple technique of irradiating laser light.

  An embodiment in which a circuit structure 10 according to the present invention is applied to an electrical junction box will be described with reference to FIGS. The electrical connection box 11 is used by being mounted on an automobile or the like. The electrical junction box 11 is provided between a battery (not shown) and electrical components (not shown) such as a headlamp and a wiper, and distributes and supplies power supplied from the battery to each electrical component. Controls such as switching of power supply. 1 and 2 are a perspective view and a cross-sectional view of the electrical junction box 11 in the present embodiment.

  As shown in FIG. 2, the electrical junction box 11 includes a circuit structure 10 and a case 12 that houses the circuit structure 10. As shown in FIG. 3, the circuit structure 10 is a circuit in which the bus bar 15 and a bonding region 34 formed on the surface (the upper surface in FIG. 3) of the bus bar 15 are bonded via an insulating bonding layer 14A. A substrate (an example of the adhesive member of the present invention) 13, an electronic component 16 (for example, a relay) mounted on the front surface side (the upper surface side in FIG. 4) of the circuit board 13, and the rear surface (the lower surface in FIG. 3) of the bus bar 15 ) And a heat radiating plate (an example of the adhesive member of the present invention) 23 adhered to the adhesive region 34 via an insulating adhesive layer 14B.

  Conductive paths (not shown) are formed in a predetermined pattern on the surface (the upper surface in FIG. 2) of the circuit board 13 by a printed wiring technique. An opening 17 is formed in the circuit board 13 at a predetermined position. The bus bar 15 is exposed in the opening 17, and the lead 18 of the electronic component 16 is accommodated in the opening 17 in the bus bar 15, and the lead of the electronic component 16 is made of, for example, Pb-free solder (not shown). The electronic component 16 and the bus bar 15 are electrically connected by being connected to 18 by soldering.

  The bus bar 15 bonded to the back surface of the circuit board 13 is formed by bending a metal plate excellent in conductivity into a predetermined shape, thereby forming a power circuit. As shown in FIG. 3, a fuse terminal 19 for inserting and connecting a connection part of an electrical component such as a fuse (not shown), for example, at the edge on the right back side in FIG. 3 of each bus bar 15. And a tab portion 21 that is inserted into a second connector housing 20 to be described later and functions as a terminal fitting of the connector.

  The heat radiating plate 23 is made of metal (for example, alumite-treated aluminum surface), is substantially similar to the circuit board 13 and is slightly larger than the circuit board 13 (see FIG. 3). ), And a plate-like bracket 23B extending in a step shape from the right end edge in FIG. The electrical junction box 11 of the present embodiment is fixed to the vehicle body by a bolt (not shown) through the bracket 23B.

  As shown in FIG. 2, the case 12 that houses the circuit structure 10 is assembled so as to block the opening on the surface side (the side opposite to the heat dissipation plate 23) of the frame body 22 and the frame body 22. And a cover 24. A heat radiating plate 23 is fixed to the frame 22 so as to close the opening on the back side.

  The frame body 22 is made of an insulating material such as a synthetic resin, and is configured by combining two parts of the frame main body 22A and the auxiliary frame body 22B. The circuit body 10 extends over the entire circumference along the periphery of the circuit board 13. It is formed so as to surround continuously. The auxiliary frame body 22B and the frame body 22A, that is, the frame body 22 are fixed to the surface of the heat sink 23 by an adhesive layer (not shown).

  Further, the first connector housing 25 is assembled on the right side of FIG. 2 in the frame body 22, and the second connector housing 20 is assembled on the left side of FIG. 2. Both connector housings 20, 25 are opened leftward in FIG. 2. is doing.

  As shown in FIG. 4, the bus bar 15 has a tin plating layer 27 formed on both front and back surfaces of a metal base material 26. The tin plating layer 27 can improve solder wettability between the lead 18 of the electronic component 16 and the bus bar 15. Further, it is possible to reduce the contact resistance between the fuse terminal 19 and the tab portion 21 and an electrical component such as a fuse connected thereto. In the present embodiment, the thickness dimension of the tin plating layer 27 formed on both the front and back surfaces of the base material 26 is 1 μm to 2 μm (thickness only on one surface).

  As the base material 26, any metal can be used as long as it is a conductive metal, and copper or a copper alloy is preferable because it is excellent in conductivity. As the copper alloy, a copper alloy containing one or more selected from tin, chromium, zinc, silicon, nickel, phosphorus, iron and the like can be used.

  The tin plating layer 27 can be formed by a known means such as an electroless plating method, an electroplating method, or a method of immersing the base material 26 in a molten metal.

  Now, on the surface of the bus bar 15, exposed portions 31 where the tin plating layer 27 is peeled off and the surface of the base material 26 is exposed are formed with a predetermined pitch interval (for example, 70 μm to 360 μm). (See FIG. 5). Although not shown in detail on the back surface of the bus bar 15, similarly to the surface of the bus bar 15, exposed portions 31 where the surface of the base material 26 is exposed are formed with a predetermined pitch interval. Yes. The exposed portion 31 has a substantially circular shape when viewed from the circuit board 13 side or the heat sink 23 side.

As shown in FIG. 7, the exposed portion 31 is formed with a convex portion 30 protruding from the surface of the base material 26 toward the circuit board 13 or the heat sink 23. Metal protrusion 30 which constitutes the base material 26 (copper or copper alloy), or consists of the metal constituting the base material 26 alloy (e.g. _Cu 6 Sn ₅ or the like). The convex portion 30 is formed in a substantially annular shape in the vicinity of the outer edge portion of the exposed portion 31 when viewed from the circuit board 13 side or the heat sink 23 side, and the exposed portion 31 has a crater shape as a whole. On the outside of the exposed portion 31, an alloy layer 32 made of an alloy of metal and tin (for example, Cu ₆ Sn ₅ or the like) forming the base material 26 is formed so as to surround the exposed portion 31. A tin plating layer 27 is formed on the outer side of the alloy layer 32.

  The diameter of the exposed portion 31 in the present embodiment is, for example, about 60 μm. Further, the convex portion 30 in the present embodiment is formed in the vicinity of the outer edge portion of the exposed portion 31 in a substantially annular shape having an outer diameter dimension of about 60 μm and an inner diameter dimension of about 40 μm. Moreover, the protrusion dimension from the surface of the base material 26 of the convex part 30 in this embodiment is about 5 micrometers, for example.

  When the electronic component 16 is soldered to the circuit board 15 by the reflow method as in this embodiment, the temperature in the reflow furnace is set to a temperature higher than the melting temperature of the solder in order to shorten the soldering time. Has been. Then, when a solder having a relatively high melting point, such as Pb-free solder, is used, the bus bar 15 is heated to a temperature higher than the melting point of the tin plating layer 27, and the tin plating layer 27 of the bus bar 15 is melted. May end up. In such a case, the adhesive layers 14A and B float and air enters between the bus bar 15 and the adhesive layers 14A and B. As a result, the adhesive strength between the bus bar 15 and the circuit board 13 or the bus bar 15 and the heat sink 23 There is a concern that the adhesive strength of the resin becomes insufficient.

  According to the present embodiment, since the exposed portion 31 is exposed from the tin plating layer 27, the exposed portion 31 and the adhesive layers 14A and 14B are directly bonded. Thereby, even if the circuit structure 10 is heated to a temperature at which the tin plating layer 27 is melted, air can be prevented from entering between the bus bar 15 and the adhesive layers 14A and 14B. As a result, the adhesive strength between the bus bar 15 and the circuit board 13 and the adhesive strength between the bus bar 15 and the heat sink 23 can be improved.

  Further, the convex portion 30 formed on the front surface side of the bus bar 15 protrudes toward the circuit board 13, and the convex portion 30 formed on the back surface side of the bus bar 15 protrudes toward the heat radiating plate 23 side. Thereby, since the convex part 30 and adhesive layer 14A, B adhere | attach firmly, the adhesive strength between the bus-bar 15 and the circuit board 13 and the bus-bar 15 and the heat sink 23 improves.

  Furthermore, since the convex portion 30 has a substantially annular shape when viewed from the circuit board side 13 and the heat radiating plate 23 side, the bonding strength between the bus bar 15 and the circuit board 13 and the bonding strength between the bus bar 15 and the heat radiating plate 23 are increased. This can be further improved.

  Further, in the present embodiment, the base material exposure rate, which is the ratio of the projected area of the exposed portion 31 in the direction perpendicular to the plate surface of the bus bar 15 to the projected area of the adhesion region 34 in the direction perpendicular to the plate surface of the bus bar. Is 5% or more, preferably 50% or less, more preferably 20% or more and 45% or less, and particularly preferably 30% or more and 40% or less. If it is less than 5%, the adhesive strength between the bus bar 15 and the circuit board 13 or the adhesive strength between the bus bar 15 and the heat sink 23 is lowered. On the other hand, when the base material exposure rate is increased, the adhesive strength is also increased. However, if the base material exposure rate exceeds 50%, the processing time for forming the exposed portion 31 is extended. Production efficiency for forming is reduced.

  The base material exposure rate is preferably 20% or more, since the adhesive strength between the bus bar and the adhesive member is further improved, and it is preferably 45% or less because the processing time can be shortened.

  Furthermore, when the base material exposure rate is 30% or more and 40% or less, even if the adhesive strength between the bus bar and the adhesive member varies, it is particularly preferable because the minimum value of variation has sufficient strength. .

  The base material exposure rate can be calculated, for example, as follows. First, SEM (scanning electron microscope) photographs of the front and back surfaces of the bus bar 15 are taken from a direction perpendicular to the plate surface of the bus bar 15. Accordingly, the SEM photograph is an image obtained by projecting the front and back surfaces of the bus bar 15 in a direction perpendicular to the plate surface of the bus bar. In this SEM photograph, the center of the exposed portion 31 having a substantially circular shape is set as a lattice point, and the area of the minimum rectangle formed by the lattice point is calculated. As described above, since the exposed portions 31 are arranged at a predetermined pitch interval, the square area can be easily calculated from the pitch interval. FIG. 8 illustrates a calculation method in the case where the minimum quadrangle is rectangular. The centers A, B, C, and D of the substantially annular portion of the exposed portion 31 are set as lattice points A, B, C, and D, and the area of the quadrilateral ABCD formed by the lattice points A, B, C, and D is the center A. It is calculated by the product of the pitch interval L1 between -B and the pitch interval L2 between the centers A and C.

  In the SEM photograph, the area of the exposed portion 31 located in the region surrounded by the above-described quadrilateral ABCD is calculated by approximating the exposed portion 31 to a circle and obtaining the area. The reason is as follows. Since the square ABCD is rectangular, the internal angle of each vertex is 90 °, which is a quarter of 360 °. Thereby, each exposed part 31 centering on the lattice points A, B, C, and D is in a state in which each quarter region is surrounded by the rectangle ABCD. For this reason, the area of the exposed portion 31 located in the region surrounded by the quadrilateral ABCD is equal to the area of one exposed portion 31.

  The base material exposure rate can be calculated by multiplying 100 by dividing the area of the exposed portion 31 by the square area. As described above, when the exposed portions 31 are formed with a predetermined pitch interval, only one of the smallest quadrilateral ABCD formed by the lattice points A, B, C, and D is exposed. By calculating the area of the portion 31 and the area of the square ABCD, the base material exposure rate can be calculated easily.

  Then, the manufacturing method of the electrical junction box 11 which concerns on this embodiment is demonstrated. First, the tin plating layer 27 is formed on both the front and back surfaces of the plate-like base material 26 made of a copper alloy by electroplating.

  The exposed portion 31 is formed by intermittently irradiating the adhesive region of the bus bar 15 on which the tin plating layer 27 is formed with a predetermined pitch interval with laser light.

  The laser beam is not particularly limited, and for example, a Yb fiber laser, a carbon dioxide laser, a YAG laser, or the like can be used. As the laser beam irradiation device, a pulse oscillation type is preferable, and for example, a laser marking device can be suitably used.

  As shown in FIG. 6, a tin plating layer 27 is formed on the surface of the base material 26 of the bus bar 15 in a state before irradiation with laser light (indicated by a wavy arrow in the figure). When this bus bar 15 is irradiated with laser light, the tin plating layer 27 and the base material 26 are melted and scattered. Then, as shown in FIG. 7, the exposed portion 31 from which the tin plating layer 27 is peeled and the surface of the base material 26 is exposed, and the convex portion 30 protruding from the surface of the base material 26 inside the exposed portion 31, An alloy layer 32 made of an alloy of tin and copper is formed outside the exposed portion 31. A tin plating layer 27 remains on the outside of the alloy layer 32.

  The plate material is punched and formed by pressing, and the bus bar 15 is formed by bending it into a predetermined shape.

  Next, the bus bar 15 is bonded to the back surface side (the lower surface side in FIG. 4) of the circuit board 13 via the adhesive layer 14A. The adhesive layer 14A may be, for example, an adhesive sheet made of a resin film coated with an adhesive on both sides, or may be coated with an adhesive on the back surface of the circuit board 13 or the surface of the bus bar 15 (upper surface side in FIG. 4). Good. Then, the laminated body of the circuit board 13 and the bus bar 15 is pressed. This pressing step may be a heating press or a press at room temperature.

  Subsequently, the heat radiating plate 23 is bonded to the rear surface side of the bus bar 15 (the lower surface side in FIG. 4) via the adhesive layer 14B. As described above, the adhesive layer 14B may be, for example, an adhesive sheet made of a resin film in which an adhesive is applied on both sides, and the adhesive on the back surface of the bus bar 15 or the surface of the heat sink 23 (upper surface side in FIG. 4). May be applied. Then, the laminated body of the circuit board 13, the bus bar 15, and the heat sink 23 is pressed. This pressing step may be a heating press or a press at room temperature.

  Next, on the predetermined positions of the circuit board 13 and the bus bar 15, for example, a screen-printing technique is applied, for example, creamy Pb-free solder (so-called cream solder) having a melting temperature of 210 ° C. to 240 ° C. To do. Thereafter, the electronic component 16 is placed on the circuit board 13 so that the lead 18 of the electronic component 16 and the region coated with Pb-free solder are aligned. In this state, the circuit component 10 is housed in a reflow furnace (not shown), heated to a temperature at which the Pb-free solder is melted, and then cooled, so that the circuit board 13 and the bus bar 15 and the electronic component 16 are soldered. To do. In the reflow oven, the circuit structure is heated for about 10 seconds at a peak temperature of 250-260 ° C.

  Next, the frame body 22A and the auxiliary frame body 22B are assembled to the heat sink 23 from the circuit component 10 side, and the auxiliary frame body 22B and the heat sink 23, and the auxiliary frame body 22B and the frame body 22A are bonded to each other. The frame 22 is formed by fixing with an agent (not shown).

  In this way, the frame body 22 that surrounds the circuit board 13 over the entire circumference is configured, and after the heat sink 23 that covers the circuit board 13 and the bus bar 15 from the back side is fixed to the frame body 22, A filling material (not shown) that covers the entire circuit board 13 and the contact portion between the circuit board 13 and the electronic component 16 is injected into the recess formed by the heat sink 23. As a result, it is possible to prevent water from entering the conductive portion of the circuit board 13, the bus bar 15, and the electronic component 16 and interference of foreign matter.

  Then, the second connector housing 20 is assembled to the frame main body 22A, and the second connector housing 20 and the frame main body 22A are locked in an assembled state by screws.

  Thereafter, the first connector housing 25 is assembled to the auxiliary frame body 22B, and finally the cover 24 is attached.

(Evaluation of adhesive strength between bus bar and circuit board)
A model experiment on the adhesive strength between the bus bar 15 and the circuit board 13 was performed below. As a result of this model experiment, it was confirmed that the adhesive strength between the bus bar 15 and the circuit board 13 is improved by forming the exposed portion 31 on the bus bar 15.

<Test piece 1-1>
A tin plating layer having a thickness of 1 μm to 2 μm was formed on a copper plate (corresponding to the base material according to the present invention) having a width of 25 mm, a length of 80 mm, and a thickness of 0.64 mm by electroplating. Of one end of the copper plate, an area having a width of 25 mm and a length of 25 mm is used as an adhesion area, and a laser beam is intermittently applied to the adhesion area at a pitch interval of 70 μm × 90 μm using a Yb fiber laser device. Irradiated. Thereby, the exposed part which the tin plating layer peeled and the surface of the copper plate exposed was formed. The exposed portion was formed with a substantially annular convex portion when viewed from the direction perpendicular to the plate surface of the copper plate. It took 131 seconds to process one copper plate.

  When measured with a length measuring microscope, the protruding dimension of the convex part from the copper plate was 5 μm.

  An SEM (scanning electron microscope) photograph of the adhesion region was taken from a direction perpendicular to the copper plate surface. In this SEM photograph, the center of the exposed portion having a substantially circular shape was defined as a lattice point, and the area of the minimum rectangle formed by the lattice point was calculated. Referring to FIG. 8, the following calculation was performed from the pitch interval described above, assuming that L1 is 70 μm and L2 is 90 μm.

  Next, the radius R of the outer edge portion of the exposed portion was measured to be 30 μm from the SEM photograph.

From the above values, the base material exposure rate was calculated to be 44.9% by the following formula.
(((30 μm) ^ 2 × π / (70 μm × 90 μm)) × 100

  On the other hand, an insulating substrate made of epoxy resin and having a thickness of 1.5 mm (corresponding to the circuit board according to the present invention) is cut into a width of 25 mm and a length of 100 mm, and one end of this insulating substrate has a width of 25 mm, A region having a length of 12.5 mm was defined as a bonding region.

  Thereafter, a known thermosetting resin (adhesive) is applied to the bonding area of the copper plate, the bonding area of the insulating substrate is laminated, and according to the curing conditions of the thermosetting resin, a predetermined temperature, a predetermined pressure, a predetermined The pressing process was performed over time, and the copper plate and the insulating substrate were bonded.

  Subsequently, assuming heating at the time of reflow soldering, the test piece was housed in a heating furnace and heated at a peak temperature of 250 ° C. to 260 ° C. for about 10 seconds.

  A tensile shear test was performed on the three test pieces 1-1 produced as described above, and the tensile shear stress was measured. The tensile rate at this time should be at least 10 mm / sec in the measurement test as long as at least a difference in tensile shear stress between test pieces described later can be observed. The average value of the tensile shear stress of the three test pieces was calculated, and the result is shown in Table 1.

<Test pieces 1-2 to 1-8>
Test pieces 1-2 to 1-8 were produced in the same manner as the test piece 1-1 except that the exposed portion was formed by irradiating the bonding area of the copper plate with laser light at the pitch interval shown in Table 1. A tensile shear test was performed. The results are shown in Table 1.

<Test piece 1-9>
A test piece 1-9 was prepared and a tensile shear test was performed in the same manner as the test piece 1-1 except that the laser beam was irradiated to the bonding area of the copper plate with a mesh pattern having a mesh interval of 0.4 mm (400 μm). It was. The results are shown in Table 1.

In addition, the base material exposure rate of the test piece 1-9 was calculated with 27.8% from the following formula | equation.
100 × (((400 μm) ^ 2- (400 μm-60 μm) ^ 2) / (400 μm ^ 2))
In the above formula, 60 μm means the processing width of the mesh formed by irradiating the laser beam.

<Test pieces 1-10 to 1-13>
Test pieces 1-10 to 1-13 were prepared in the same manner as the test pieces 1-9, except that the copper plate was exposed by irradiating the adhesion region with laser light at a mesh interval shown in Table 1. A test was conducted. The results are shown in Table 1.

<Specimen 1-14>
A test piece 1-14 was produced in the same manner as the test piece 1-1 except that the adhesion region was not irradiated with laser light, and a tensile shear test was performed. The results are shown in Table 1.

(result)
The shear strength of the test piece 1-14 was 2.9 MPa, which was significantly lower than the shear strength (11.61 MPa to 6.78 MPa) of the test pieces 1-1 to 1-8 in which the exposed portions were formed. This is considered to be due to the following reason.

  When the test piece is heated, the tin plating layer having a melting point of 232 ° C. melts. Thereby, an adhesive agent will be in the state which floated with respect to the copper plate. For this reason, in the test piece 1-14, it is thought that air entered between the copper plate and the adhesive and the adhesive strength was lowered.

  On the other hand, in the test pieces 1-1 to 1-8 in which the exposed portion is formed, the exposed portion and the adhesive are directly bonded to each other, so that the tin plating layer can be prevented from being melted and entering air. Furthermore, since the convex portion and the adhesive are firmly bonded, the adhesive strength is further improved.

  Moreover, when the test piece 1-2 (base material exposure rate 34.9%) and the test piece 1-10 (base material exposure rate 36.0%), which are substantially the same base material exposure rate, are compared, In the test piece 1-2 in which the exposed portion is formed with an interval, the shear strength is 12.09 MPa, whereas in the test piece 1-10 in which the copper plate is exposed by irradiating the laser beam with a mesh pattern, 8.92 MPa. It was low. Similarly, test piece 1-3 (base material exposure rate 26.2%, shear strength 11.07 MPa) is compared with test piece 1-11 (base material exposure rate 27.8%, shear strength 4.07 MPa). In this case, the shear strength of the test piece 1-11 irradiated with the laser beam with the mesh pattern was low. Also when test piece 1-6 (base material exposure rate 10.7%, shear strength 7.14 MPa) and test piece 1-13 (base material exposure rate 11.6%, shear strength 1.23 MPa) were compared. It is the same. The reason for this is not necessarily clear, but is considered as follows.

  As described above, since the adhesive strength between the bus bar and the adhesive member can be improved by providing the convex portion, if the ratio of the convex portion in the exposed portion is increased, the adhesive strength between the bus bar and the adhesive member is improved. It becomes possible. In the present embodiment, since the convex portion has a substantially annular shape, the convex portion can be formed more efficiently than in the case where laser light is irradiated with a mesh pattern. As a result, since the ratio of the convex part in an exposed part can be enlarged, it is thought that the adhesive strength of a bus-bar and an adhesive member can be improved.

  Test pieces 1-1 to 1-8 having a base material exposure rate of 5% or more have a shear strength of 6.78 MPa or more, and have sufficient adhesive strength even when heated to a melting point of tin or higher. Further, since the base material exposure rate is 50% or less, the processing time is 131 seconds or less, and the production efficiency can be improved. When test piece 1-2 (shear strength 12.09 MPa) showing similar values of shear strength and test piece 1-9 (shear strength 12.2 MPa) are compared, processing time is 113 s for test piece 1-2. On the other hand, it is 290 s for the test piece 1-9, and it can be seen that the processing time can be shortened by the present invention.

  Furthermore, the test pieces 1-3 to 1-2 having a base material exposure rate of 20% or more and 45% or less have a significantly improved shear strength of 11.07 MPa to 12.09 MPa.

  Furthermore, the test piece 1-2 whose base material exposure rate is 30% or more and 40% or less shows the highest shear strength of 12.09 MPa, which is particularly preferable.

  Moreover, in the test piece 1-1, the minimum value of shear strength was 10.93 MPa among three test pieces. Moreover, in the test piece 1-3, the minimum value of shear strength was 10.43 MPa among three test pieces. On the other hand, in the test piece 1-2, among the three test pieces, the minimum shear strength was 11.66 MPa, indicating a sufficient strength. Thus, even when the shear strength varies, the minimum value of the shear strength shows a sufficient strength, which is particularly preferable.

(Evaluation of bond strength between bus bar and heat sink)
Subsequently, a model experiment was conducted on the adhesive strength between the bus bar and the heat sink. As a result of this model experiment, it was confirmed that the adhesion strength between the bus bar and the heat sink is improved by forming the exposed portion on the bus bar.

<Test specimen 2-1>
An anodized plate having a thickness of 2.0 mm (the surface of the aluminum plate is anodized and corresponds to a heat sink according to the present invention) is cut into a width of 25 mm and a length of 100 mm, and one end of the anodized plate Among the portions, an area having a width of 25 mm and a length of 12.5 mm was defined as an adhesion area. A test piece 2-1 was prepared in the same manner as the test piece 1-1 except that this alumite plate was bonded to a copper plate, and a tensile shear test was performed. The results are summarized in Table 2.

<Test pieces 2-2 to 2-6>
Test pieces 2-2 to 2-6 were prepared in the same manner as for the test pieces 2-1, except that the exposed portions were formed by irradiating the bonding area of the copper plate with laser light at the pitch intervals shown in Table 2. A tensile shear test was performed. The results are shown in Table 2.

<Test piece 2-7>
A test piece 2-7 was prepared in the same manner as the test piece 1-14 except that the above-described anodized plate was bonded to a copper plate, and a tensile shear test was performed. The results are shown in Table 2.

(result)
In the test piece 2-6 whose base material exposure rate is 2.9%, the shear strength is 2.0 MPa, and the shear of the test pieces 2-1 to 2-5 whose base material exposure rate is 5% or more and 50% or less It was low compared with the strength (3.6 MPa to 5.6 MPa). As a result, it was found that the base material exposure rate should be 5% or more.

  Moreover, the test piece 2-1 (base material exposure rate 34.9%) whose base material exposure rate is 30% or more and 40% or less shows a high shear strength of 5.6 MPa, and is particularly preferable.

  As described above, according to the present embodiment, since the exposed portion is exposed from the tin plating layer, the exposed portion and the adhesive layer are directly bonded. Thereby, even if a circuit structure is heated to a temperature at which the tin plating layer melts, air can be prevented from entering between the bus bar and the adhesive member.

  Moreover, since said convex part protrudes to the adhesive member side, a convex part and an adhesive layer adhere | attach firmly. Thereby, the bus bar and the adhesive member can be firmly bonded.

  According to the present invention, the base material exposure is a ratio of the projected area of the exposed portion in the direction perpendicular to the plate surface of the bus bar to the projected area of the adhesion region in the direction perpendicular to the plate surface of the bus bar. The rate is 5% or more, preferably 50% or less, more preferably 20% or more and 45% or less, and particularly preferably 30% or more and 40% or less. When the base material exposure rate is less than 5%, the adhesive strength between the bus bar and the adhesive member decreases. When the base material exposure rate exceeds 50%, the processing time for forming the exposed portion is extended, and thus the manufacturing efficiency is lowered.

  Furthermore, since the convex portion has a substantially annular shape when viewed from the adhesive member side, the adhesive strength between the bus bar and the adhesive member is further improved.

  Further, since the exposed portions are formed in a state of being arranged with a predetermined pitch interval, the stress applied to each exposed portion can be made uniform. Thereby, since the stress added to each exposed part can be disperse | distributed, the adhesive strength of a bus-bar and an adhesive member can be improved further.

  The exposed portion can be formed by a simple method of irradiating laser light.

<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 exposed portions 31 are formed with a predetermined pitch interval. However, the present invention is not limited to this, and for example, a large shear is generated between the bus bar 15 and the adhesive layers 14A and 14B. In the region where the stress is generated, the interval between the exposed portions 31 may be made denser than other regions. As described above, as long as a plurality of the exposed portions 31 are provided at a predetermined interval, the exposed portions 31 may not be arranged at equal pitch intervals.
(2) The base material exposure rate may be calculated by analyzing an SEM photograph of the bus bar 15 by a known method.

(3) In the present embodiment, the circuit board 13 is bonded to one surface of the bus bar 15 and the heat dissipation plate 23 is bonded to the other surface. It is good also as a structure to which the circuit board 13 or the heat sink 23 is adhere | attached only on one side.
(4) In the present embodiment, each exposed portion 31 has a substantially circular shape, but is not limited thereto, and may be a substantially elliptical shape or a substantially oval shape as long as they are formed with a space therebetween. However, it may take any shape such as a polygonal shape such as a triangle or a quadrangle. Moreover, all the exposed parts 31 may not be the same shape.
(5) In the present embodiment, the convex portion 30 has a substantially annular shape, but is not limited thereto, and may have an approximately elliptical shape or an arbitrary shape such as a polygonal shape such as a triangle or a quadrangle. Moreover, not all the convex parts 30 may be the same shape.

The perspective view of the electrical junction box concerning this embodiment Side view of electrical junction box Partially enlarged perspective view of circuit structure Partial enlarged cross-sectional schematic diagram of the circuit structure Schematic plan view showing the arrangement of the exposed parts on the bus bar Cross-sectional schematic diagram showing the state of laser light irradiation Cross-sectional schematic diagram showing the structure of the convex part Plane schematic diagram showing how to calculate the base material exposure rate

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Circuit structure 13 ... Circuit board (adhesive member)
14A, B ... Adhesive layer 15 ... Bus bar 23 ... Heat sink (adhesive member)
26 ... Base material 27 ... Tin plating layer 30 ... Convex part 31 ... Exposed part 34 ... Adhesion area

Claims (9)

A circuit configuration comprising a bus bar in which a tin plating layer is formed on the surface of a metal base material, and an adhesive member bonded to an adhesive region provided on at least one surface of the bus bar via an insulating adhesive layer Body,
In the adhesion region of the bus bar, a plurality of exposed portions formed by exposing the surface of the base material are formed at intervals,
The base material exposure rate, which is the ratio of the projected area of the exposed portion in the direction perpendicular to the plate surface of the bus bar to the projected area of the adhesive region in the direction perpendicular to the plate surface of the bus bar, is 5% or more. A circuit structure characterized by that. The circuit component according to claim 1, wherein the base material exposure rate is 50% or less. 3. The circuit structure according to claim 1, wherein the base material exposure rate is 20% or more and 45% or less. 4. 4. The circuit structure according to claim 1, wherein the base material exposure rate is 30% or more and 40% or less. 5. 5. The circuit structure according to claim 1, wherein the exposed portions are formed to be arranged with a predetermined pitch interval therebetween. 6. The exposed portion is formed with a convex portion protruding from the surface of the base material, and the convex portion is made of the base material or an alloy of the base material. The circuit structure according to any one of the above items. The circuit structure according to claim 6, wherein the convex portion has a substantially annular shape when viewed from the adhesive member side. The circuit structure according to any one of claims 1 to 7, wherein the exposed portion is formed by intermittently irradiating the bus bar with laser light at a predetermined interval. . The circuit structure according to claim 1, wherein the adhesive member is at least one of a circuit board and a heat sink.

Images