Circuit board and its manufacturing method

Abstract

The objective of this invention is to provide a circuit board that enables the connection of conductive components to an additional metal layer via welding. The solution comprises: a circuit pattern 3 disposed on an insulating layer 7; an additional metal layer 9 laminated and bonded to the circuit pattern 3; and a lead frame 11 laminated on the additional metal layer 9 and connected via welding. The combined thickness of the additional metal layer 9 and the circuit pattern 3 in the lamination direction is 1.5 mm to 3.0 mm, and the thickness of the lead frame 11 in the lamination direction is 0.2 mm to 1.2 mm.

Description

Technical Field

[0001] The present invention relates to a circuit board for power components and the like and a method for manufacturing the same. Prior Art

[0002] As a circuit board for high current use for power components and the like, sometimes the thickness of the circuit pattern is partially increased to reduce the thermal resistance. For example, in Patent Document 1, in a portion where an electronic component such as a chip of a power semiconductor is mounted, the circuit pattern stacked upward is used as an additional metal layer and laminated on the circuit pattern. In this additional metal layer, an electronic component is mounted by solder.

[0003] On the other hand, there is a requirement to mount a conductive member such as a lead frame on a circuit board by welding or soldering (laser welding) performed by laser or the like. However, Patent Document 1 assumes that an electronic component is mounted by solder and cannot cope with welding or laser welding at a higher temperature.

[0004] For example, if a conductive member is connected to a circuit pattern by welding, the heat during welding is transferred from the circuit pattern to the interface with the insulating layer of the resin that supports the circuit pattern, and there is a risk of damaging the insulating layer. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2006-319146. Summary of the Invention

[0006] [Problems to be Solved by the Invention]

[0007] The problem to be solved is that it cannot cope if the heat during connection of the conductive member becomes large. [Technical Means for Solving the Problems]

[0008] The present invention provides a circuit board including: a circuit pattern provided on an insulating layer; an additional metal layer laminated and joined to the circuit pattern; and a conductive member laminated and joined to the additional metal layer by welding, wherein the total thickness of the additional metal layer and the circuit pattern in the lamination direction is 1.5 mm to 3.0 mm, and the thickness of the conductive member in the lamination direction is 0.2 mm to 1.2 mm.

[0009] Moreover, the present invention provides a method for manufacturing a circuit board, wherein the circuit board includes: a circuit pattern disposed on an insulating layer; an additional metal layer laminated and joined to the circuit pattern; and a conductive member laminated and joined to the additional metal layer. The total thickness of the additional metal layer and the circuit pattern in the lamination direction is 1.5 mm to 3.0 mm, and the thickness of the conductive member in the lamination direction is 0.2 mm to 1.2 mm. In the method for manufacturing the circuit board, the conductive member is laminated on the additional metal layer and connected by laser welding. [Advantages of the Invention]

[0010] According to the present invention, damage to the insulating layer caused by heat during connection of the conductive member can be suppressed. Brief Explanation of Drawings

[0011] FIG. 1 is a cross-sectional view of a circuit board around the mounting portion of a lead frame according to Embodiment 1 of the present invention. FIG. 2 is a top view of the circuit board of FIG. 1. FIG. 3 is a schematic cross-sectional view of a state where an additional metal layer is ultrasonically joined to a circuit pattern. FIG. 4 is an enlarged cross-sectional view of a portion where a tool pushes against the additional metal layer in FIG. 3. FIG. 5 is a cross-sectional view showing the experimental method of Embodiment 1. FIG. 6 is a graph showing the experimental results of FIG. 5. Embodiment

[0012] By adjusting the thickness of the portion of the circuit pattern where the conductive member is connected in the lamination direction and the thickness of the conductive member in the lamination direction, the object of suppressing damage to the insulating layer caused by heat during connection of the conductive member is achieved.

[0013] The circuit board 1 includes a circuit pattern 3, an additional metal layer 9, and a conductive member 11. The circuit pattern 3 is disposed on the insulating layer 7. The additional metal layer 9 is laminated and joined to the circuit pattern 3. The conductive member 11 is laminated and joined to the additional metal layer 9 by welding.

[0014] The total thickness of the additional metal layer 9 and the circuit pattern 3 in the lamination direction is 1.5 mm to 3.0 mm, and the thickness of the conductive member 11 in the lamination direction is 0.2 mm to 1.2 mm.

[0015] In this case, the respective thicknesses of the additional metal layer 9 and the circuit pattern 3 can be arbitrarily set as long as their total is 1.5 mm to 3.0 mm. As an embodiment, the thickness of the additional metal layer 9 in the stacking direction can be set to 0.7 mm to 2.7 mm, and the thickness of the circuit pattern 3 in the stacking direction can be set to 0.3 mm to 0.8 mm.

[0016] The manufacturing method of the circuit board 1 is to stack the conductive members 11 and connect them to the additional metal layer 9 by laser welding.

[0017] In one embodiment, the manufacturing method of the circuit board 1 can stack the additional metal layer 9 on the circuit pattern 3, and press the tool T against the connection surface 12 of the additional metal layer 9 to perform ultrasonic vibration for bonding. In this case, the conductive members 11 can be stacked and connected to the surface 12 of the additional metal layer 9 that has been bonded to the circuit pattern 3 by laser welding. [Example 1]

[0018] [Circuit board] FIG. 1 is a cross-sectional view of a circuit board showing the periphery of the mounting portion of a lead frame according to Example 1 of the present invention. FIG. 2 is a top view of the circuit board of FIG. 1.

[0019] The circuit board 1 in FIGS. 1 and 2 is a circuit board for high current such as a power element. The circuit board 1 is a metal substrate circuit board, which includes: a metal substrate 5, an insulating layer 7, a circuit pattern 3, an additional metal layer 9, and a lead frame 11 as a conductive member.

[0020] The metal substrate 5 is formed of a plate-like body made of metal. In addition, the shape of the metal substrate 5 can be appropriately set, and a heat sink shape can also be adopted.

[0021] The material of the metal substrate 5 can be, for example, a single metal or alloy such as aluminum, iron, copper, or stainless steel, and it doesn't matter whether it has flexibility or not. The metal substrate 5 can also further include a non-metal such as carbon. And the metal substrate 5 can also include aluminum composite with carbon. Moreover, the metal substrate 5 can have a single-layer structure or a multi-layer structure.

[0022] The thickness of the metal substrate 5 can be appropriately set, for example, to 2.0 mm. The metal substrate 5 has a high thermal conductivity. For example, the thermal conductivity of copper is 370 - 400 W·m - 1·K - 1, that of aluminum is 190 - 220 W·m - 1·K - 1, and that of iron is 60 - 80 W·m - 1·K - 1.

[0023] The insulating layer 7 is laminated on the metal substrate 5 and formed into a plate shape. The insulating layer 7 not only serves to electrically insulate the circuit pattern 3 from the metal substrate 5 but also serves as an adhesive for bonding them to each other. Therefore, a resin is generally used for the insulating layer 7. The thickness of the insulating layer 7 can be appropriately set, for example, to 0.13 mm.

[0024] The insulating layer 7 of this embodiment can be composed of an epoxy resin, a cyanate resin, etc. In the epoxy resin, for example, an amine-based hardener, a phenol-based hardener, an acid anhydride-based hardener, or an imidazole-based hardener is combined. In the cyanate resin, for example, dicyandiamide or a phenol resin is combined as a hardener. Also, the insulating layer 7 can be composed of a thermoplastic resin, that is, a liquid crystal polymer such as a wholly aromatic polyester or other thermoplastic resins.

[0025] The insulating layer 7 preferably further contains an inorganic filler. As the inorganic filler contained in the insulating layer 7, those having excellent electrical insulation and high thermal conductivity are preferred, and examples include alumina, silica, aluminum nitride, boron nitride, silicon nitride, magnesium oxide, etc., and it is preferred to use one or more selected from these.

[0026] The filling rate of the inorganic filler in the insulating layer 7 can be appropriately set according to the type of the inorganic filler. For example, based on the entire volume of the resin contained in the insulating layer 7, it is preferably 85% by volume or less, more preferably 30 - 85% by volume.

[0027] The insulating layer 7 can further contain, for example, a coupling agent, a dispersant, etc. In addition, an insulating sheet in a semi-cured state can also be used as the insulating layer 7.

[0028] The circuit pattern 3 is provided on the insulating layer 7. Thereby, the circuit pattern 3 is provided on an insulating substrate having the insulating layer 7 on the metal substrate 5. This circuit pattern 3 is a plate-like body or a thin sheet and is formed into a predetermined pattern by etching the conductor 3a.

[0029] The thickness of the circuit pattern 3 in this embodiment is 0.3 mm to 0.8 mm, and is formed of, for example, a conductor for the circuit, that is, copper material, with a thickness of 0.5 mm. Except for the laminated portion of the additional metal layer 9, the remaining thickness of the circuit pattern 3 is fixed. However, the thickness of the circuit pattern 3 can also vary.

[0030] In addition, the circuit pattern 3 can also be formed of aluminum or the like. Also, the circuit pattern 3 can be attached to the metal substrate 5隔着 an insulating layer 7 without etching by previously forming it by stamping or cutting.

[0031] In the circuit pattern 3 of this embodiment, other components, that is, a lead frame 11, are connected. In the portion of the circuit pattern 3 where the lead frame 11 is connected, an additional metal layer 9 is laminated and joined, and is formed thicker in part.

[0032] The additional metal layer 9 is formed in a plate shape. The additional metal layer 9 in this embodiment is formed of copper and can also be constituted by other conductors for the circuit, such as aluminum. The planar shape of the additional metal layer 9 is, for example, a square with a side length of 10 mm. However, the planar shape of the additional metal layer 9 can be arbitrarily set.

[0033] The thickness of the additional metal layer 9 in the lamination direction is 0.7 mm to 2.7 mm. In this embodiment, the thickness of the additional metal layer 9 in the lamination direction is greater than the thickness of the circuit pattern 3 in the lamination direction, but it can also be smaller than the thickness of the circuit pattern 3 in the lamination direction. This additional metal layer 9 has a fixed thickness. The total thickness of the circuit pattern 3 and the additional metal layer 9 is 1.5 mm to 3.0 mm.

[0034] The additional metal layer 9 has a bonding surface 10 formed by the bottom surface facing the circuit pattern 3 on one side in the lamination direction, and a connection surface 12 formed by the surface facing the lead frame 11 on the other side.

[0035] The bonding surface 10 is bonded entirely within the range facing the circuit pattern 3 in the lamination direction. The bonding is performed by ultrasonic welding. The connection surface 12 is the portion that connects the lead frame 11 by a bonding performed by laser welding. This connection surface 12 is provided with uneven portions 17. The uneven portions 17 are provided on the connection surface 12. In this embodiment, the uneven portions 17 are provided on the entire surface of the connection surface 12. By the entire surface, it only needs to be a substantially entire surface, and also includes the case where a part or all of the outer peripheral region of the connection surface 12 is flat.

[0036] This uneven portion 17 is formed by a tool uneven portion 15 (described later in FIG. 5) of a tool T for vibration transmission (described later in FIG. 5). The tool T is used to join an additional metal layer 9 to the circuit pattern 3 by ultrasonic vibration in the plane direction.

[0037] This uneven portion 17 can have various planar shapes and cross-sectional shapes. However, regardless of the shape, it has an engaging recess 17a and an engaging projection 17b. The interval between the engaging recess 17a and the engaging projection 17b is set fixedly and regularly, but it can also be set randomly.

[0038] The engaging recess 17a of the uneven portion 17 is formed in a quadrangular shape in plan view and in an inverted quadrangular pyramid shape in cross section. The shape of the engaging recess 17a of the uneven portion 17 is not particularly limited, and it can also be a recess formed by a curved surface. The uneven portion 17 including the engaging recess 17a and the engaging projection 17b is an indentation of the tool uneven portion 15 described later, and can be made into an appropriate shape according to the shape of the tool uneven portion 15.

[0039] The lead frame 11 is connected to the connection surface 12 in the stacking direction by laser welding. The lead frame 11 is in the shape of a rectangular plate and is appropriately bent, etc. This lead frame 11 is pulled out from the connection surface 12 to the side in the direction crossing the stacking direction. The lead frame 11 has a gap in the crossing direction between it and the uneven portion 17 except for the pulled-out portion. The thickness of the lead frame 11 in the stacking direction is 0.2 mm to 1.2 mm. The material of the lead frame 11 is copper, iron, an alloy of these, etc.

[0040] In addition, the shape of the lead frame 11 can be set arbitrarily. And the conductive member connected to the connection surface 12 is not limited to the lead frame 11, and can also be other conductive materials.

[0041] [Method for manufacturing a circuit board] FIG. 3 is a schematic cross-sectional view of the state where an additional metal layer 9 is ultrasonically joined to the circuit pattern 3 of Example 1. FIG. 4 is an enlarged cross-sectional view of the portion where the tool T in FIG. 3 pushes against the additional metal layer 9.

[0042] As shown in FIGS. 3 and 4, the tool T is used in this manufacturing method. In addition, FIG. 3 shows an example where a tool T of 12 mm square, which is larger than this, is used for an additional metal layer 9 of 10 mm square. A tool T smaller than the additional metal layer 9 can also be used.

[0043] In the cross-sectional shape, the tool T is provided with tool uneven portions 15 corresponding to the uneven portions 17. In the tool uneven portions 15, the tool concave portion 15a and the tool convex portion 15b are formed corresponding to the engaging convex portion 17b and the engaging concave portion 17a of the uneven portion 17.

[0044] In the manufacturing method of this embodiment using the tool T, an additional metal layer 9 is laminated on the circuit pattern 3, and the tool T is pressed against the connection surface 12 of the additional metal layer 9 and ultrasonic vibration is applied. Thereby, by the transmission of ultrasonic vibration, the additional metal layer 9 is joined to the circuit pattern 3. This joining is performed on the entire joining surface 10 where the additional metal layer 9 corresponds to the portion of the tool T pressed against the connection surface 12 in the lamination direction.

[0045] In this embodiment, by pressing the tool T, uneven portions 17 are formed on the connection surface 12 of the additional metal layer 9 corresponding to the tool uneven portions 15.

[0046] After joining the additional metal layer 9 to the circuit pattern 3 in this way, as shown in FIGS. 1 and 2, the lead frame 11 is connected to the connection surface 12 of the additional metal layer 9. This connection is made by placing the connected portion 14 of the lead frame 11 on the connection surface 12 of the additional metal layer 9. In this state, a laser is irradiated from the connected portion 14 of the lead frame 11 to perform welding of the lead frame 11 and the additional metal layer 9.

[0047] At this time, the laser intensity is in accordance with the thickness of the lead frame 11. That is, the laser intensity is such that the lead frame 11 with a thickness of 0.2 mm to 1.2 mm is melted to an extent that it can be joined to the additional metal layer 9 thereunder. The laser intensity is changed according to the material of the conductive material such as the lead frame 11, for example, the laser absorption rate or melting point of the material.

[0048] Based on this setting of the laser intensity, the heat during welding is dispersed by the additional metal layer 9 with a thickness of 1.5 mm to 3.0 mm and the circuit pattern 3, suppressing the influence on the insulating layer 7. In addition, the heat dispersibility varies depending on the materials of the additional metal layer 9 and the circuit pattern 3, such as the thermal conductivity of the materials.

[0049] [Experimental results] FIG. 5 is a cross-sectional view showing the experimental method of Example 1. As shown in FIG. 5, in the experiment, the additional metal layer 9 was previously joined to the entire front surface of the circuit pattern 3 with the joining surface 10, and the lead frame 11 was laminated on the connection surface 12 of the additional metal layer 9, and welding was performed by irradiation with the laser L.

[0050] Measure the temperature of the back surface of the circuit pattern 3 at this time in the part TC corresponding to the laser irradiation part. The back surface of the circuit pattern 3 is the surface located on the opposite side of the surface of the lead frame 11 irradiated with the laser in the stacking direction.

[0051] The material of the lead frame 11 is copper, and the thicknesses are set to 0.2 mm, 0.5 mm, and 1.0 mm. The materials of the circuit pattern 3 and the additional metal layer 9 are set to copper. The total thickness of the circuit pattern 3 and the additional metal layer 9 is set to 0.5 mm to 3.0 mm. Also, the intensity of the laser varies to 500 W, 750 W, and 1300 W according to the thickness of the lead frame 11, and the melting amount of the additional metal layer 9 is set to 0.2 mm ± 0.1 mm.

[0052] FIG. 6 is a graph showing the experimental results of FIG. 5. The vertical axis is the peak temperature of the back surface of the circuit pattern 3 (circuit back peak temperature), and the horizontal axis is the total thickness of the circuit pattern 3 and the additional metal layer 9 (total circuit thickness). In FIG. 6, 0.2 mm 500 W means that the thickness of the lead frame 11 is 0.2 mm and the intensity of the laser is 500 W. The same applies to 0.5 mm 750 W and 1.0 mm 1300 W.

[0053] As shown in FIG. 6, when the thickness of the lead frame 11 is 0.2 mm to 1.2 mm (the laser intensity varies according to the thickness of the lead frame 11), and the total thickness of the additional metal layer 9 and the circuit pattern 3 in the stacking direction is 1.5 mm to 3.0 mm, damage to the insulating layer 7 can be suppressed. The circuit back peak temperature becomes 105° C. or higher, which damages the insulating layer 7, when the total circuit thickness is less than 1.5 mm. On the other hand, when the total circuit thickness is 1.5 mm or more, the circuit back peak temperature is in the range that does not damage the insulating layer 7 up to the upper limit of the total thickness, that is, 3.0 mm. In addition, if the total thickness exceeds 3.0 mm, it will cause problems such as an increase in size, difficulty in ultrasonic bonding, and a tendency for the suppression of the back surface temperature to saturate, and the influence of material thermal resistance becomes large. Therefore, the upper limit of the total thickness is set to 3.0 mm.

[0054] The insulating layer 7 is formed of a liquid crystal polymer and contains boron nitride and alumina. The insulating layer 7 has differences in degree depending on the heat-resistant temperature of the resin, but if the circuit back peak temperature becomes around 100° C., it will be damaged considerably. Also, the additional metal layer 9 and the circuit pattern 3 are formed of copper as described above. However, the range of the total thickness does not change significantly due to the materials used for the insulating layer 7 of the circuit board 1, the circuit pattern 3, and the additional metal layer 9.

[0055] The circuit board 1 manufactured in this way joins the lead frame 11 to the additional metal layer 9, etc. by laser welding, and even when the heat rises during the joining of the lead frame 11, a high-quality circuit board that suppresses damage to the insulating layer 7 can be completed.

[0056] 1: Circuit board 3: Circuit pattern 3a: Conductor 5: Metal substrate 7: Insulating layer 9: Additional metal layer 10: Joining surface 11: Lead frame (conductive member) 12: Connection surface (surface) 14: Connected part 15: Tool uneven part 15a: Tool concave part 15b: Tool convex part 17: Uneven part 17a: Engaging concave part 17b: Engaging convex part L: Laser T: Tool TC: Portion corresponding to the laser irradiation portion

Claims

1. A circuit board comprising: a circuit pattern disposed on an insulating layer made of resin; an additional metal layer laminated and bonded to the circuit pattern; and a conductive member laminated and bonded to the additional metal layer, wherein the additional metal layer has a bonding surface opposite to the circuit pattern on one side of the lamination direction and a connecting surface opposite to the conductive member on the other side of the lamination direction, wherein the bonding surface of the additional metal layer is entirely bonded in the area facing the circuit pattern in the lamination direction, wherein the combined thickness of the additional metal layer and the circuit pattern in the lamination direction is 1.5 mm to 3.0 mm, and the thickness of the conductive member in the lamination direction is 0.2 mm to 1.2 mm, wherein when the conductive member is bonded to the additional metal layer, the temperature of the back side of the circuit pattern is below a predetermined temperature capable of suppressing damage to the insulating layer made of resin.

2. The circuit board as described in claim 1, wherein, The thickness of the aforementioned additional metal layer in the aforementioned lamination direction is 0.7 mm to 2.7 mm, and the thickness of the aforementioned circuit pattern in the aforementioned lamination direction is 0.3 mm to 0.8 mm.

3. A method for manufacturing a circuit board, the circuit board comprising: a circuit pattern disposed on an insulating layer made of resin; an additional metal layer laminated and bonded to the circuit pattern; and a conductive member laminated and bonded to the additional metal layer, wherein the additional metal layer has a bonding surface opposite to the circuit pattern on one side of the lamination direction and a connecting surface opposite to the conductive member on the other side of the lamination direction, the bonding surface of the additional metal layer is entirely bonded within the area facing the circuit pattern in the lamination direction, the combined thickness of the additional metal layer and the circuit pattern in the lamination direction is 1.5 mm to 3.0 mm, and the thickness of the conductive member in the lamination direction is 0.2 mm to 1.2 mm. In the method for manufacturing the circuit board, The aforementioned conductive component is deposited on the aforementioned additional metal layer and connected by laser welding. When the aforementioned conductive component is bonded to the aforementioned additional metal layer, the temperature of the back side of the aforementioned circuit pattern is set below a predetermined temperature that can suppress damage to the aforementioned insulating layer made of resin.

4. A method for manufacturing a circuit board as described in claim 3, wherein, The aforementioned additional metal layer is deposited on the aforementioned circuit pattern; a tool is pressed onto the surface of the aforementioned additional metal layer and ultrasonic vibration is applied to bond the aforementioned additional metal layer to the aforementioned circuit pattern; and the aforementioned conductive member is deposited on the aforementioned surface of the aforementioned additional metal layer that has been bonded to the aforementioned circuit pattern and connected by laser welding.

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