Lead frame

Abstract

The utility model discloses a lead frame, include: first and second part lead frame. First part lead frame has interior insulating structure, including copper bottom plate with insulating heat conduction layer and surface copper layer. Surface copper layer has chip mounting area. Insulating heat conduction layer forms the electrically insulated connecting structure between copper bottom plate and surface copper layer. The bottom surface of copper bottom plate is radiating surface, and the thickness of copper bottom plate is greater than the thickness of surface copper layer. Second part lead frame includes multiple lead terminals formed by single layer copper alloy, and each lead terminal is welded on the corresponding welding position of surface copper layer and forms the welding fixed structure of first and second part lead frame, and the lead terminal constitutes device support structure and electric connection channel. The utility model can reduce installation complexity and use cost, can provide enough insulating strength and reduce thermal resistance simultaneously, can also be compatible with batch production standard lead frame, realizes batch production under the condition that almost does not need to change tooling.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor devices, and in particular to a lead frame. Background Technology

[0002] Power semiconductor devices can generally be divided into two main categories: discrete devices (single transistors) and power module devices (multi-chip integration). Discrete devices can be further divided into three categories based on their packaging materials: metal packages, ceramic packages, and plastic packages. Among these, plastic packages account for more than 90% of the discrete device market due to their low material cost, simple manufacturing process, and ease of mass production, with a global market size exceeding 300 billion yuan.

[0003] Widely used power transistors, such as TO-3, TO-220, and TO-247, typically consist of a metal leadframe, a power chip, a solder layer, internal bonding aluminum wires, and a molding compound. The metal leadframe is usually made of copper or a copper alloy. The power chip is first soldered to a copper base provided with the leadframe. Figure 1A The diagram shown is a structural diagram of an existing power single transistor using a metal lead frame; as shown... Figure 1B As shown, is Figure 1A The circuit diagram shown is for a single power transistor. Figure 1B The medium-power single transistor 104 uses an IGBT, and its electrodes include a gate (G), an emitter (E), and a collector (C). The back of the power chip 102 is mounted on a copper base plate 101. The front electrode of the power chip 102 is connected to a corresponding terminal 103 via a bonding wire, and the copper base plate 101 is also connected to a terminal 103.

[0004] In the structure shown in Figure 1, due to the conductivity of the copper sheet 101 at the bottom of the chip, the back side of the discrete device, after packaging, is usually referred to as an electrode of the chip. In practical use, it is essential to ensure insulation from the heat sink surface. Therefore, thermally conductive films or ceramic sheets, such as alumina or silicon nitride sheets, are typically used on the back side of the discrete device to provide thermal conductivity and electrical insulation. During installation, a semi-solid thermal paste still needs to be applied to the back side of the insulating thermally conductive sheet to fill the interface gaps and reduce thermal resistance. These additional materials and steps increase the complexity and cost of discrete device installation.

[0005] As an improvement over conventional discrete devices, the bottom copper layer of power chips is replaced with a ceramic copper-clad substrate (DBC), such as alumina (Al2O3), aluminum nitride (AlN), or silicon nitride (Si3N4) ceramic. Utilizing the electrical insulation properties of ceramic substrates, the finished discrete device has an electrically insulated bottom, greatly simplifying installation and use. However, due to the low thermal conductivity and high brittleness of alumina ceramic, the ceramic substrate must maintain a relatively high thickness during the manufacturing process, limiting its ability to reduce thermal resistance. Meanwhile, high-conductivity ceramic substrates such as AlN and Si3N4 are very expensive, also limiting their application in discrete devices. Utility Model Content

[0006] The technical problem to be solved by this utility model is to provide a lead frame that can reduce installation complexity and usage cost, provide sufficient insulation strength while reducing thermal resistance, and be compatible with mass-produced standard lead frames, enabling mass production with almost no tooling changes.

[0007] To solve the above-mentioned technical problems, the lead frame provided by this utility model includes: a first part of the lead frame and a second part of the lead frame.

[0008] The first lead frame has an inner insulation structure, which includes a copper base plate with an insulating and thermally conductive layer and a surface copper layer formed on the top surface of the insulating and thermally conductive layer.

[0009] The surface copper layer has a chip mounting area.

[0010] The insulating and thermally conductive layer forms an electrically insulating connection structure between the copper base plate and the surface copper layer.

[0011] The bottom surface of the copper base plate is a heat dissipation surface, and the insulating heat-conducting layer and the copper base plate form a heat conduction channel between the bottom surface of the surface copper layer and the heat dissipation surface; the thickness of the copper base plate is greater than the thickness of the surface copper layer.

[0012] The second lead frame includes multiple lead terminals formed of a single layer of copper alloy; each lead terminal is welded to a corresponding welding position on the surface copper layer to form a structure in which the first lead frame and the second lead frame are welded and fixed together, and the lead terminals constitute the device support structure and the electrical connection channel between the internal chip and the external circuit.

[0013] A further improvement is that, on a plane perpendicular to the thickness, the insulating thermally conductive layer and the copper base plate both have a first planar structure of the same size and are aligned, and the surface copper layer has a second planar structure, the edge of the second planar structure being located inside the edge of the first planar structure and forming a stepped structure at the edge of the second planar structure.

[0014] A further improvement is that the distance between the edge of the second planar structure and the edge of the first planar structure is not less than 0.5 mm.

[0015] A further improvement is that one second part of the lead frame is simultaneously welded to one or more first part of the lead frame; the second part of the lead frame includes one or more lead terminal groups, each of the lead terminal groups includes multiple lead terminals, and the lead terminal groups correspond one-to-one with the first part of the lead frame.

[0016] A further improvement is that the welding structure between the lead terminal and the surface copper layer includes an ultrasonic welding structure and a laser welding structure.

[0017] A further improvement is that the thickness of the copper base plate is 1.5mm to 3mm; and the thickness of the surface copper layer is 0.1mm to 0.5mm.

[0018] The thickness of the insulating and thermally conductive layer is 100μm to 250μm.

[0019] A further improvement is that the thickness of the copper base plate is 2mm; and the thickness of the surface copper layer is 0.3mm.

[0020] The thickness of the insulating and thermally conductive layer is 150 μm.

[0021] A further improvement is that the material of the copper base plate includes C10300 pure copper; the material of the surface copper layer is C10300 pure copper.

[0022] A further improvement is that the insulating and thermally conductive layer is made of a material with a thermal conductivity greater than or equal to 15 W / mK, and the peel strength between the insulating and thermally conductive layer and the surface copper layer is greater than or equal to 15 N / cm.

[0023] A further improvement is that the insulating thermally conductive layer has an insulation strength of greater than or equal to 2.5kV AC for 60s.

[0024] A further improvement is that the copper alloy of the second part of the lead frame includes a copper alloy of type C19400 or a copper alloy with a conductivity of 80% or higher.

[0025] A further improvement is that the surface copper layer includes one or more of the chip mounting areas, and the surface copper layer also has an electrical connection pattern for a circuit topology for connecting multiple chips.

[0026] A further improvement is that the lead frame is compatible with TO series devices.

[0027] A further improvement is that the TO series devices include the TO-247 device and the TO-247plus device.

[0028] This utility model's lead frame includes a first lead frame and a second lead frame. The first lead frame has an internal insulation structure formed by stacking three layers: a copper base plate, an insulating and heat-conducting layer, and a surface copper layer. The back of the copper base serves as a heat dissipation surface and is electrically insulated from the top surface copper layer. This reduces installation complexity and usage costs. For example, the heat sink can be directly installed on the heat dissipation surface without the need for additional materials or steps.

[0029] The first part of the lead frame and the second part of the lead frame are set separately in this utility model. The materials of the first part of the lead frame can be set independently. Both the copper base plate and the insulating and heat-conducting layer can be formed of materials with good thermal conductivity. For example, the copper base plate can be made of C10300 pure copper with a thermal conductivity higher than 380W / mK, and the insulating and heat-conducting layer can be made of materials with a thermal conductivity equal to or equal to 15W / mK. At the same time, the insulating and heat-conducting layer can also provide an insulation strength greater than 4kV AC for 60 seconds. Therefore, this utility model can provide sufficient insulation strength and reduce thermal resistance at the same time.

[0030] The second part of this utility model, the lead frame, is used to separately set the lead terminals. In this way, the lead terminals can be made of copper alloy. The copper alloy provides sufficient mechanical strength to realize the device support structure. At the same time, the conductivity of the copper alloy can also realize the electrical connection channel between the internal chip and the external circuit. Under the premise of meeting the insulation gap requirements, the high current lead terminals of the device can also be made by increasing the thickness and width, thereby reducing the internal resistance and reducing the loss of the lead terminals. Furthermore, by using lead terminal materials with a conductivity of 80% IACS or higher, the application range can be further expanded.

[0031] The first part of the lead frame and the second part of the lead frame are fixed together by welding between the lead terminals and the surface copper layer. This makes it compatible with standard lead frames for mass production, enabling mass production with almost no changes to the tooling. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0033] Figure 1A This is a structural diagram of an existing power single tube that uses a metal lead frame;

[0034] Figure 1B yes Figure 1A The circuit diagram of the single power transistor is shown below;

[0035] Figure 2This is a cross-sectional structural diagram of the lead frame according to an embodiment of the present invention;

[0036] Figure 3A This is a perspective view of the first part of the lead frame when the lead frame of this utility model is applied to a standard TO-247 discrete device;

[0037] Figure 3B This is an overall structural diagram of the lead frame of this utility model embodiment when applied to a standard TO-247 discrete device;

[0038] Figure 4A This is an overall structural diagram of the lead frame of this utility model embodiment when applied to a standard TO-247plus discrete device;

[0039] Figure 4B yes Figure 4A The diagram shows the overall structure after the chip is mounted. Detailed Implementation

[0040] like Figure 2 The diagram shown is a cross-sectional view of the lead frame according to an embodiment of the present invention. The lead frame according to the present invention includes: a first part of the lead frame 301 and a second part of the lead frame 305.

[0041] The first lead frame 301 has an inner insulation structure, which includes a copper base plate 302 with an insulating and thermally conductive layer 303 and a surface copper layer 304 formed on the top surface of the insulating and thermally conductive layer 303.

[0042] The surface copper layer 304 has a chip mounting area.

[0043] The insulating and thermally conductive layer 303 forms an electrically insulating connection structure between the copper base plate 302 and the surface copper layer 304.

[0044] The bottom surface of the copper base plate 302 is a heat dissipation surface. The insulating thermally conductive layer 303 and the copper base plate 302 form a heat conduction channel between the bottom surface of the surface copper layer 304 and the heat dissipation surface. The thickness of the copper base plate 302 is greater than the thickness of the surface copper layer 304. The heat dissipation surface allows for direct mounting of heat sinks, simplifying the manufacturing process.

[0045] The second part of the lead frame 305 includes a plurality of lead terminals 306 formed of a single layer of copper alloy. Figure 2Only a cross-sectional structure of one of the lead terminals 306 is shown. Each lead terminal 306 is welded to a corresponding welding position on the surface copper layer 304, forming a structure in which the first part of the lead frame 301 and the second part of the lead frame 305 are welded and fixed together. The lead terminals constitute the device support structure and the electrical connection channel between the internal chip and the external circuit. The specific structure of the second part of the lead frame 305 is set according to the actual application. Please refer to the application... Figure 3B The second part of the lead frame 305a shown is Figure 4A The second part of the lead frame 305b is shown.

[0046] In this embodiment, on a plane perpendicular to the thickness, the insulating thermally conductive layer 303 and the copper base plate 302 both have first planar structures of the same size and are aligned. The surface copper layer 304 has a second planar structure, the edge of which is located inside the edge of the first planar structure and forms a stepped structure at the edge of the second planar structure. In some embodiments, the distance between the edge of the second planar structure and the edge of the first planar structure is not less than 0.5 mm.

[0047] A second lead frame 305 is simultaneously welded to one or more first lead frames 301; the second lead frame 305 includes one or more lead terminal groups, each lead terminal group including multiple lead terminals 306, and each lead terminal group corresponds one-to-one with the first lead frame 301. The lead terminal groups are also applicable to... Figure 3B The lead terminal group 308a shown is Figure 4A The lead terminal group 308b shown is illustrated.

[0048] In this embodiment, the welding structure between the lead terminal 306 and the surface copper layer 304 is an ultrasonic welding structure. In other embodiments, the welding structure between the lead terminal 306 and the surface copper layer 304 can also be a laser welding structure.

[0049] In some embodiments, the thickness of the copper base plate 302 is 1.5mm to 3mm; preferably, the thickness of the copper base plate 302 is 2mm.

[0050] The thickness of the surface copper layer 304 is 0.1 mm to 0.5 mm. Preferably, the thickness of the surface copper layer 304 is 0.3 mm.

[0051] The thickness of the insulating and thermally conductive layer 303 is 100μm to 250μm. Preferably, the thickness of the insulating and thermally conductive layer 303 is 150μm.

[0052] In some embodiments, the material of the copper base plate 302 includes C10300 pure copper, which has good thermal conductivity, such as above 380W / mK, which is much higher than the thermal conductivity of copper alloy materials used in existing conventional lead frames, such as C19400 copper alloy at 260W / mK.

[0053] In some embodiments, the surface copper layer 304 is made of C10300 pure copper, which has a conductivity close to 100% IACS and can provide the lowest device internal resistance.

[0054] In some embodiments, the insulating thermally conductive layer 303 is made of a material with a thermal conductivity greater than or equal to 15 W / mK and the peel strength between the insulating thermally conductive layer 303 and the surface copper layer 304 is greater than or equal to 15 N / cm.

[0055] The insulating and thermally conductive layer 303 has an insulation strength of greater than or equal to 2.5kV AC for 60s.

[0056] In some embodiments, the copper alloy of the second lead frame 305 includes a C19400 copper alloy. Compared to pure copper, the C19400 copper alloy has greater mechanical strength and can provide sufficient mounting strength. Using the C19400 copper alloy to form the lead terminal 306 can reduce deformation and damage during device handling and provide sufficient support for the device position during installation and use.

[0057] In some embodiments, the copper alloy of the second lead frame 305 can also be a copper alloy with a conductivity of 80% IACS or higher. Since the lead terminal 306 is the connection channel between the internal chip and the external circuitry, especially for power devices, the high current of the chip must pass through the channel provided by the lead terminal 306. Therefore, the higher the conductivity of the lead terminal 306 material, the lower the internal resistance of the terminal, the less the loss, and the lower the terminal heat generation. Therefore, under the premise of meeting the insulation gap requirements, the high-current lead terminals of the device can further reduce internal resistance and lead terminal losses by increasing the thickness and width design. The conductivity of C19400 copper alloy can only reach about 50% IACS. For high-current devices, its internal resistance is high, and the heat generation is significant, limiting high-power applications. Lead terminal materials with a conductivity of 80% IACS or higher can further expand the application scope of this invention. Alternatively, a copper alloy with a conductivity of 80% IACS or higher can be used.

[0058] In this embodiment, the surface copper layer 304 includes one or more chip mounting areas, and the surface copper layer 304 also has an electrical connection pattern for a circuit topology for connecting multiple chips.

[0059] In this embodiment, the lead frame is compatible with TO series devices. The TO series devices include the TO-247 device and the TO-247plus device.

[0060] This utility model embodiment of the lead frame includes a first part of the lead frame 301 and a second part of the lead frame 305. The first part of the lead frame 301 has an internal insulation structure formed by stacking three layers, namely a copper base plate 302, an insulating and heat-conducting layer 303, and a surface copper layer 304. The back side of the copper base serves as a heat dissipation surface and is electrically insulated from the top surface copper layer 304. This can reduce the complexity of installation and the cost of use. For example, the heat sink can be directly installed on the heat dissipation surface without the need to coat additional materials or add extra steps.

[0061] In this embodiment of the present invention, the first lead frame 301 and the second lead frame 305 are separately provided. The material of the first lead frame 301 can be set independently. Both the copper base plate 302 and the insulating and thermally conductive layer 303 can be formed of materials with good thermal conductivity. For example, the copper base plate 302 can be made of C10300 pure copper with a thermal conductivity higher than 380W / mK, and the insulating and thermally conductive layer 303 can be made of a material with a thermal conductivity equal to or equal to 15W / mK. At the same time, the insulating and thermally conductive layer 303 can also provide an insulation strength greater than 4kV AC for 60sec. Therefore, this embodiment of the present invention can provide sufficient insulation strength while reducing thermal resistance.

[0062] The second part of this utility model embodiment, the lead frame 305, is used to separately set the lead terminals 306. In this way, the material of the lead terminals 306 can be independently made of copper alloy. The copper alloy provides sufficient mechanical strength to realize the device support structure. At the same time, the conductivity of the copper alloy can also realize the electrical connection channel between the internal chip and the external circuit. Under the premise of meeting the insulation gap requirements, the high current lead terminals 306 of the device can also be made by increasing the thickness and width, thereby reducing the internal resistance and the loss of the lead terminals 306. Furthermore, by using the lead terminal 306 material with a conductivity of 80% IACS or higher, the application range can be further expanded.

[0063] In this embodiment of the utility model, the first part of the lead frame 301 and the second part of the lead frame 305 are fixed together by welding between the lead terminal 306 and the surface copper layer 304. This makes it compatible with standard lead frames for mass production, enabling mass production with almost no need to change the tooling.

[0064] This utility model embodiment realizes a lead frame structure with a built-in base plate insulation and heat-conducting layer, which is compatible with the standard lead frame for mass production, and can achieve mass production with almost no change to the tooling.

[0065] In this embodiment of the invention, unlike existing traditional integrated leadframes, the copper base plate 302 is made of C10300 pure copper, with a thermal conductivity higher than 380 W / mK, far exceeding the thermal conductivity of copper alloy materials used in traditional leadframes, such as C19400 copper alloy at 260 W / mK. Therefore, the structure of this embodiment of the invention can reduce the thermal resistance from the chip to the bottom surface of the device compared to existing traditional packaging, and improve the chip's current output capability under the same operating conditions.

[0066] In this embodiment of the invention, the thickness of the intermediate insulating and thermally conductive layer 303 ranges from 100 micrometers to 250 micrometers, and the thermal conductivity ranges from 8 W / mK to 30 W / mK. The insulating and thermally conductive layer with a thickness of 150 micrometers and a thermal conductivity of 15 W / mK has an equivalent thermal resistance that is 46% lower than that of a 380-micrometer-thick alumina ceramic copper-clad substrate. Simultaneously, the insulating and thermally conductive layer 303 provides an insulation strength greater than 4 kV AC for 60 seconds, ensuring safe operating conditions for the device.

[0067] In this embodiment of the invention, the surface copper layer 304 is a chip mounting copper layer, made of C10300 pure copper, with a conductivity close to 100% IACS, providing the lowest possible device internal resistance. The thickness of the surface copper layer 304 ranges from 0.1 mm to 0.5 mm, typically 0.3 mm, and allows for pattern design, providing more circuit topologies beyond single transistors. Through its design in conjunction with the lead frame of the second part, it enables more functional semiconductor devices, such as half-bridges and chopper circuits. The surface copper layer 304 and the intermediate insulating and thermally conductive layer 303 maintain a high interface peel strength of 15 N / cm, ensuring the process conditions for electrical connection with the lead terminals 306 of the second part of the lead frame, and ensuring the device's lifespan and reliability during use.

[0068] In this embodiment of the invention, the two lead frame structures are joined into a single unit through a welding process. Ultrasonic welding is an effective method for achieving electrical connection between the lead terminal 306 and the surface copper layer 304 of the base plate. Unlike existing standard lead frames, in this embodiment of the invention, due to the presence of the insulating and heat-conducting layer 303, the lead terminal 306 remains insulated from the copper base plate 302 after welding. Other embodiments may also employ laser welding. Laser welding allows for precise control of the weld point position and quality, achieving high-precision welding. Furthermore, due to its shorter welding time, compared to ultrasonic welding, it requires less tooling, has higher welding efficiency, and is more suitable for mass production, thus reducing the cost of the lead frame.

[0069] The embodiments of this application are further described below with reference to specific applications:

[0070] like Figure 3A The image shown is a perspective view of the first part of the lead frame when the lead frame of this utility model is applied to a standard TO-247 discrete device. The first part of the lead frame is marked with 301a, and the copper base plate is marked with 302a. The copper base plate 302a is made of C10300 pure copper and has a thickness of 2mm.

[0071] The insulation and thermal conductive layer, marked 303a, has a thickness of 175 micrometers, a thermal conductivity of ≥15 W / mK, and an insulation withstand voltage of ≥4.0 kV AC for 60 seconds. The specific parameters of the insulation and thermal conductive layer 303a can be set as needed; for example, it can also be set to: a thickness of 150 micrometers, a thermal conductivity of ≥15 W / mK, and an insulation withstand voltage of >2.5 kV AC for 60 seconds.

[0072] The dimensions of the insulating and thermally conductive layer 303a are the same as those of the bottom copper layer, i.e., the copper base plate 302a.

[0073] The surface copper layer marked 304a is made of C10300 pure copper and has a thickness of 0.3 mm. The size of the surface copper layer 304a is 0.5 mm smaller than that of the insulating and thermally conductive layer 303a, providing a stepped structure. After molding, it can provide better insulation withstand voltage between the surface copper layer 304a and the bottom copper layer, improving the reliability of the device.

[0074] like Figure 3B The diagram shown is an overall structural diagram of the lead frame when applied to a standard TO-247 discrete device according to an embodiment of this utility model. The second part of the lead frame, marked 305a, includes multiple lead terminal groups 308a, each of which includes multiple lead terminals. These lead terminals are individually marked 306a. Each lead terminal group 308a corresponds one-to-one with the first part of the lead frame 301a. The lead terminals 306a are further secured with copper alloy reinforcing bars.

[0075] like Figure 4A The figure shown is an overall structural diagram of the lead frame when applied to a standard TO-247plus discrete device according to an embodiment of this utility model. Figure 4B yes Figure 4A The diagram shows the overall structure after the chip is mounted. Figure 4A In the middle, the first part of the lead frame is marked with 301b, and the copper base plate is marked with 302b. The copper base plate 302b is made of C10300 pure copper with a thickness of 2mm.

[0076] The thickness of the insulating and thermally conductive layer, marked 303b, is 150 micrometers, with a thermal conductivity of >= 15 W / mK and an insulation withstand voltage of >= 2.5 kV AC for 60 seconds.

[0077] The dimensions of the insulating and thermally conductive layer 303b are the same as those of the bottom copper layer, i.e., the copper base plate 302b.

[0078] The surface copper layer marked 304b is made of C10300 pure copper and has a thickness of 0.3 mm. The size of the surface copper layer 304b is 0.5 mm smaller than that of the insulating and thermally conductive layer 303b, providing a stepped structure. After molding, it can provide better insulation withstand voltage between the surface copper layer 304b and the bottom copper layer, improving the reliability of the device.

[0079] The first part of the lead frame 301a is also provided with mounting holes 307.

[0080] The second part of the lead frame, marked 305b, includes multiple lead terminal groups 308b, each of which includes multiple lead terminals. These lead terminals are individually marked 306b. Each lead terminal group 308b corresponds one-to-one with the first part of the lead frame 301b. The lead terminals 306b are also secured with copper alloy reinforcing bars. It can be seen that the left-side lead terminal 306b of the second part of the lead frame 308b is welded to the surface copper layer 304b of the base plate, thus achieving a connection.

[0081] Figure 4B This is the state before chip mounting, ultrasonic bonding, and injection molding. It can be seen that IGBT chips 401 and FRD chips 402 are mounted in each of the first part of the lead frame 301b. The back sides of both IGBT chips 401 and FRD chips 402 are connected to the left-side lead terminal 306b via contact with the bottom surface copper layer 304b. The emitter of IGBT chip 401 and the front electrode of FRD chip 402 are connected to the middle lead terminal 306b via emitter bonding wire 403a. The gate of IGBT chip 401 is connected to the right-side lead terminal 306b via gate bonding wire 403b.

[0082] The present invention has been described in detail above through specific embodiments, but these are not intended to limit the present invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A lead frame, characterized in that, include: First part of the lead frame and second part of the lead frame; The first lead frame has an inner insulation structure, which includes a copper base plate with an insulating and thermally conductive layer and a surface copper layer formed on the top surface of the insulating and thermally conductive layer. The surface copper layer has a chip mounting area; The insulating and thermally conductive layer forms an electrically insulating connection structure between the copper base plate and the surface copper layer; The bottom surface of the copper base plate is a heat dissipation surface, and the insulating heat-conducting layer and the copper base plate form a heat conduction channel between the bottom surface of the surface copper layer and the heat dissipation surface; the thickness of the copper base plate is greater than the thickness of the surface copper layer. The second lead frame includes multiple lead terminals formed of a single layer of copper alloy; each lead terminal is welded to a corresponding welding position on the surface copper layer to form a structure in which the first lead frame and the second lead frame are welded and fixed together, and the lead terminals constitute the device support structure and the electrical connection channel between the internal chip and the external circuit.

2. The lead frame as described in claim 1, characterized in that: On a plane perpendicular to the thickness, the insulating thermally conductive layer and the copper base plate both have a first planar structure of the same size and are aligned. The surface copper layer has a second planar structure, the edge of the second planar structure is located inside the edge of the first planar structure and forms a stepped structure at the edge of the second planar structure.

3. The lead frame as described in claim 2, characterized in that: The distance between the edge of the second planar structure and the edge of the first planar structure is not less than 0.5 mm.

4. The lead frame as described in claim 1, characterized in that: A second part of the lead frame is simultaneously welded to one or more first part of the lead frame; the second part of the lead frame includes one or more lead terminal groups, each of the lead terminal groups includes multiple lead terminals, and the lead terminal groups correspond one-to-one with the first part of the lead frame.

5. The lead frame as described in claim 1, characterized in that: The welding structure between the lead terminal and the surface copper layer includes ultrasonic welding structure and laser welding structure.

6. The lead frame as described in claim 1, characterized in that: The thickness of the copper base plate is 1.5mm to 3mm; the thickness of the surface copper layer is 0.1mm to 0.5mm. The thickness of the insulating and thermally conductive layer is 100μm to 250μm.

7. The lead frame as described in claim 6, characterized in that: The thickness of the copper base plate is 2mm; the thickness of the surface copper layer is 0.3mm. The thickness of the insulating and thermally conductive layer is 150 μm.

8. The lead frame as described in claim 1, characterized in that: The material of the copper base plate includes C10300 pure copper; the material of the surface copper layer is C10300 pure copper.

9. The lead frame as described in claim 8, characterized in that: The insulating and thermally conductive layer is made of a material with a thermal conductivity greater than or equal to 15 W / mK, and the peel strength between the insulating and thermally conductive layer and the surface copper layer is greater than or equal to 15 N / cm.

10. The lead frame as described in claim 9, characterized in that: The insulating and thermally conductive layer has an insulation strength of greater than or equal to 2.5 kVAC for 60 seconds.

11. The lead frame as described in claim 1, characterized in that: The copper alloy of the second part of the lead frame includes a copper alloy of type C19400 or a copper alloy with a conductivity of 80% IACS or higher.

12. The lead frame as described in claim 1, characterized in that: The surface copper layer includes one or more chip mounting areas, and the surface copper layer also has an electrical connection pattern for a circuit topology for connecting multiple chips.

13. The lead frame as described in claim 1, characterized in that: The lead frame is compatible with TO series devices.

14. The lead frame as described in claim 13, characterized in that: The TO series devices include the TO-247 device and the TO-247plus device.

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