Power chip package support and method of manufacturing a power module

Abstract

The application relates to a preparation method of a power chip packaging support and a power module. The preparation method of the power chip packaging support comprises the following steps: preparing a semi-cured heat-conducting insulating adhesive sheet on a predetermined area of a metal substrate surface; pre-pasting a metal heat-dissipation plate on the heat-conducting insulating adhesive sheet, the metal heat-dissipation plate being recessed to the edge of the heat-conducting insulating adhesive sheet; punching the metal substrate to obtain a lead frame, the lead frame comprising a chip seat and a plurality of pins connected to each other, the heat-conducting insulating adhesive sheet being recessed to the edge of the chip seat; and finally curing the heat-conducting insulating adhesive sheet. The preparation method of the power module comprises the following steps: mounting a chip on the chip seat of the packaging support; placing the packaging support with the mounted chip into an injection mold, and injecting a packaging material to complete the preparation of a packaging body; and punching and removing a connecting strip connected to the plurality of pins. The preparation method can effectively improve the insulation and voltage resistance performance of the packaging support and the power module.

Description

Technical Field

[0001] This invention relates to the field of power chip packaging; more specifically, it relates to a method for preparing a power chip packaging bracket and a power module. Background Technology

[0002] Package holders are a common packaging carrier for power chip packaging. Their typical structure includes a lead frame for power chip mounting and external electrical connection, and a metal heat sink for heat dissipation. The metal heat sink and the chip holder of the lead frame are usually insulated and thermally conductive by a ceramic sheet, which has the disadvantage of high material and production costs.

[0003] Using thermally conductive insulating film for insulation and heat conduction between the metal heat sink and the chip mount is a viable low-cost alternative. However, during actual production and application, the applicant discovered that the packaging bracket and its packaging module using thermally conductive insulating film have poor insulation / voltage withstand performance. Based on in-depth research, the applicant further discovered that the insulation / voltage withstand performance is greatly affected by the manufacturing process, and thus proposed the solution of this invention. Summary of the Invention

[0004] The main objective of this invention is to provide a method for fabricating a power chip packaging bracket, which can obtain a packaging bracket with high insulation and withstand voltage performance at low cost.

[0005] Another object of the present invention is to provide a method for preparing a power module with high insulation / voltage withstand performance at low cost.

[0006] To achieve the aforementioned main objectives, a first aspect of the present invention discloses a method for fabricating a power chip packaging bracket, comprising the following steps: S1, a semi-cured thermally conductive insulating film is formed in a predetermined area on the surface of a metal substrate; S2, a metal heat sink is pre-attached to the thermally conductive insulating film; wherein, when viewed along the thickness direction of the thermally conductive insulating film, the metal heat sink is recessed within the edge of the thermally conductive insulating film; S3, punching the metal substrate to obtain a lead frame; wherein, the lead frame includes a chip holder connected together and multiple pins, and viewed along the thickness direction of the thermally conductive insulating film, the thermally conductive insulating film is recessed within the edge of the chip holder; S4, complete the final curing of the thermally conductive insulating film.

[0007] In the above technical solution, on the one hand, since the thermally conductive insulating film is set to be recessed within the edge of the chip holder, it is not punched during the punching of the metal substrate, thereby preventing or reducing cracks in the thermally conductive insulating film caused by punching force. On the other hand, the thermally conductive insulating film completes its final curing process only after punching. Even if cracks are generated in the thermally conductive insulating film due to the impact of punching force, the cracks can be healed by the molten adhesive during the transition of the thermally conductive insulating film from the semi-cured state to the final cured state. This solves the problem of reduced insulation / voltage withstand performance caused by cracks in the thermally conductive insulating film, and can improve the insulation / voltage withstand performance of the packaging bracket at low cost.

[0008] Furthermore, the metal heat sink is designed to be recessed within the edge of the thermally conductive insulating film, forming a step between the edges of the metal heat sink and the thermally conductive insulating film. This increases the creepage distance between the metal heat sink and the chip mount, thereby further improving the withstand voltage performance.

[0009] According to a specific embodiment of the present invention, step S1 includes: S11, a peelable resist film is attached to the surface of the metal substrate, the resist film having a window that exposes the predetermined area; S12, a fluid-state thermally conductive insulating adhesive is applied inside the window; S13, pre-cur the thermally conductive insulating adhesive to obtain a semi-cured thermally conductive insulating sheet.

[0010] In the above technical solution, the coating area of ​​the thermally conductive insulating adhesive is defined by the adhesive resist film. The adhesive resist film can be peeled off after the thermally conductive insulating adhesive is semi-cured or fully cured, which has the advantage of simple manufacturing process.

[0011] Preferably, there is a gap of at least 0.1 mm between the thermally conductive insulating film and the edge of the chip holder, which is more conducive to reducing the impact of the punching force on the thermally conductive insulating film during the punching of the metal substrate.

[0012] Preferably, there is a gap of at least 0.3 mm between the edge of the metal heat sink and the edge of the thermally conductive insulating film, so as to provide a larger creepage distance between the metal heat sink and the chip holder and achieve better withstand voltage performance.

[0013] Preferably, the metal substrate is a copper substrate with a thickness of 0.5 mm to 1.0 mm.

[0014] Preferably, the metal heat sink is a copper heat sink with a thickness of 1.0mm to 2.0mm.

[0015] Preferably, the thickness of the thermally conductive insulating film is 0.1mm to 0.2mm to achieve a better balance between thermal conductivity and insulation.

[0016] Preferably, the thermally conductive insulating film contains ceramic filler, and the thermal conductivity of the thermally conductive insulating film is above 5 W / m·K.

[0017] Optionally, the chip holder, the thermally conductive insulating film, and the metal heat sink are provided with interconnected clearance holes or clearance grooves.

[0018] To achieve the aforementioned objective, a second aspect of the present invention discloses a method for manufacturing a power module, comprising the following steps: The packaging bracket is fabricated according to the aforementioned method for preparing the power chip packaging bracket; A power chip is mounted on the chip socket of the packaging bracket; The package holder with the power chip installed is placed into the injection mold, and the packaging material is injected to complete the packaging body; wherein, the metal heat sink has a heat dissipation surface exposed from the package body; The connecting strip that connects the multiple pins is removed by punching.

[0019] The above-described method for fabricating power modules, employing the aforementioned chip packaging bracket fabrication method, enables the low-cost production of power modules with insulation and withstand voltage properties. The heat dissipation surface of the metal heat sink can be connected to an external heat sink, thereby achieving rapid heat dissipation of the power chip.

[0020] Furthermore, the injection mold includes an upper mold and a lower mold. The upper mold has pressing parts on opposite sides of its inner cavity. During the injection molding process, the opposite sides of the chip holder are pressed together by the pressing parts, so that the metal heat sink is tightly attached to the bottom wall of the lower mold.

[0021] In the above technical solution, the metal heat sink is tightly attached to the bottom wall of the lower mold during injection molding, preventing the encapsulating adhesive from flowing onto the heat dissipation surface of the metal heat sink. This helps to fully expose the heat dissipation surface of the metal heat sink and also eliminates the need for grinding and removing the adhesive from the heat dissipation surface of the metal heat sink, simplifying the manufacturing process of the power module.

[0022] To more clearly illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the fabrication process of the power chip packaging bracket in Example 1.

[0024] Figure 2 This is a schematic diagram of the process for fabricating a thermally conductive insulating film on the surface of a metal substrate in Example 1.

[0025] Figure 3 This is a schematic diagram of the fabrication process of the power chip packaging bracket in Example 1.

[0026] Figure 4 This is a first-view structural schematic diagram of the power chip packaging bracket in Embodiment 1.

[0027] Figure 5 This is a second-view structural schematic diagram of the power chip packaging bracket in Embodiment 1.

[0028] Figure 6 This is a schematic diagram of the structure after the power chip is installed on the packaging bracket in Example 2.

[0029] Figure 7 This is a first-view three-dimensional structural diagram of the power module in Embodiment 2.

[0030] Figure 8 This is a second-view three-dimensional structural diagram of the power module in Embodiment 2.

[0031] Figure 9 This is a front structural diagram of the power module in Example 2.

[0032] Figure 10 yes Figure 9 Schematic diagram of the BB cross-section structure.

[0033] Figure 11 This is a bottom view of the upper mold structure of the injection mold in Example 2.

[0034] Figure 12 This is a schematic diagram of the planar structure of the power chip packaging bracket in Example 3. Detailed Implementation

[0035] Many specific details are set forth in the following description in conjunction with specific embodiments in order to provide a full understanding of the invention. However, it should be understood that the following specific embodiments and detailed description are for illustrative purposes only and do not limit the scope of protection of the invention.

[0036] Example 1

[0037] Example 1 relates to a method for fabricating a power chip packaging bracket. For example... Figure 1 and Figure 3 As shown, the preparation method of the packaging bracket in Example 1 includes the following steps S1 to S4: S1, a semi-cured thermally conductive insulating film 120 is prepared in a predetermined area on the surface of the metal substrate 100; S2, a metal heat sink 130 is pre-attached on the thermally conductive insulating film 120; S3, the metal substrate 100 is punched to obtain a lead frame 110 with a chip holder 111 and multiple pins 112; S4, the final curing of the thermally conductive insulating film 120 is completed.

[0038] Specifically, such as Figure 2 and Figure 3As shown, step S1 includes the following steps S11 to S13: S11, attaching a peelable resist film 400 to the surface of the metal substrate 100; S12, coating a fluid thermally conductive insulating adhesive within the window 410 of the resist film 400; S13, pre-curing the thermally conductive insulating adhesive. In this invention, the metal substrate 100 can be a copper substrate (bare copper plate) with a thickness of 0.5mm to 1.0mm (e.g., 0.6mm), and the resist film 400 can be a TPX resist film, which has good temperature resistance and peelability.

[0039] refer to Figure 3 As shown in step S11, the resist film 400 adhered to the surface of the metal substrate 100 in step S11 has a window 410 exposing a predetermined area of ​​the surface of the metal substrate 100, i.e., the window 410 is adapted to the shape of the thermally conductive insulating film 120. In step S12, the coating of the thermally conductive insulating adhesive can refer to the screen printing method commonly used in the circuit board industry. A perforated plate (with perforations forming in the area corresponding to the window 410 to allow the thermally conductive insulating adhesive to pass through) is used to uniformly coat the thermally conductive insulating adhesive within the window 410 to improve the thickness uniformity of the thermally conductive insulating adhesive. In step S13, the thermally conductive insulating adhesive can be pre-baked to achieve its transformation from a fluid state to a semi-cured state, thereby obtaining a semi-cured thermally conductive insulating film 120.

[0040] The resist film 400 can be peeled off after pre-curing in step S13 (e.g.) Figure 3 As shown in b), the film can also be peeled off after the metal heat sink 130 is pre-attached in step S2 or after final curing in step S4. Peeling off the resist film 400 after step S13 or S2 is more convenient, while peeling it off after step S4 allows for more precise definition of the shape of the thermally conductive insulating film 120.

[0041] In this invention, the metal heat sink 130 can be a copper heat sink with a thickness of 1.0mm to 2.0mm (e.g., 1.3mm). During the pre-attachment step S2, appropriate pressure and temperature can be applied to the metal heat sink 130 (e.g., by using a heated mounting head to adsorb the metal heat sink 130 to complete the pre-attachment process), so that the metal heat sink 130 is initially fixed on the thermally conductive insulating film 120.

[0042] like Figure 3As shown in Figure c, when viewed along the thickness direction of the thermally conductive insulating film 120, the metal heat sink 130 is located within the outer contour of the thermally conductive insulating film 120, and there is a gap between the metal heat sink 130 and the edge of the thermally conductive insulating film 120; that is, the metal heat sink 130 is set to be recessed within the edge of the thermally conductive insulating film 120 to increase the creepage distance between the metal heat sink 130 and the chip holder 111 and improve the withstand voltage performance. Preferably, the gap L1 between the metal heat sink 130 and the edge of the thermally conductive insulating film 120 is at least 0.3 mm, more specifically it can be 0.3 mm to 0.5 mm, for example 0.4 mm.

[0043] like Figure 3 As shown in d, the lead frame 110 obtained by punching in step S3 includes a chip holder 111 and a plurality of pins 112 connected together. Viewed along the thickness direction of the thermally conductive insulating film 120, the thermally conductive insulating film 120 is located within the outer contour of the chip holder 111, and there is a gap between the thermally conductive insulating film 120 and the edge of the chip holder 111; that is, the thermally conductive insulating film 120 is recessed within the edge of the chip holder 111. Because the thermally conductive insulating film 120 is designed to be recessed within the edge of the chip holder 111, the thermally conductive insulating film 120 is not punched during the punching of the metal substrate 100, thereby preventing or reducing defects such as cracks in the thermally conductive insulating film 120 caused by punching force. Preferably, the gap L2 between the thermally conductive insulating film 120 and the edge of the chip holder 111 is at least 0.1 mm.

[0044] The number of pins 112 can be designed according to the package requirements of the power chip. In this embodiment, there are four pins 112, one of which is (e.g., ...) Figure 4 and Figure 5 The first pin 112a) shown is connected to the chip socket 111, and the four pins are connected by a connecting strip 113. The number of pins 112 can also be designed to be three or other numbers.

[0045] In step S4, hot pressing or baking methods can be used to achieve the final / complete curing of the thermally conductive insulating film 120, while simultaneously ensuring a reliable fixed connection of the metal heat sink 130. Preferably, the thickness of the thermally conductive insulating film 120 is 0.1mm~0.2mm (referring to the thickness of the thermally conductive insulating film 120 in the final bracket product).

[0046] In this invention, the thermal conductivity of the thermally conductive insulating film 120 is preferably above 5 W / m·K. Such a thermally conductive insulating film 120 requires the use of ceramic fillers to achieve high thermal conductivity and insulation. However, for thermally conductive insulating films 120 containing ceramic fillers, the presence of the ceramic fillers gives the thermally conductive insulating film 120 ceramic-like properties, making it more susceptible to the effects of punching forces.

[0047] In this embodiment, the lead frame 110 is manufactured using a low-cost punching process. The thermally conductive insulating film 120 completes its final curing process only after the punching step. Even if the thermally conductive insulating film 120 develops cracks due to the punching force, these cracks can be healed by the molten adhesive when the thermally conductive insulating film 120 changes from a semi-cured state to a final cured state. This solves the problem of reduced insulation / voltage withstand performance caused by cracks in the thermally conductive insulating film 120, and improves the insulation / voltage withstand performance of the encapsulation bracket at a low cost.

[0048] Furthermore, such as Figures 3 to 5 As shown, the chip holder 111 has a first U-shaped clearance groove 114, the thermally conductive insulating film 120 has a second U-shaped clearance groove 121, and the metal heat sink 130 has a third U-shaped clearance groove 131. The clearance grooves are interconnected and their openings face the same side. Their positions are designed to allow the mounting holes of the power module (see Embodiment 2) to pass through them. The U-shaped clearance groove design helps reduce material usage. Furthermore, the U-shaped rather than circular clearance groove on the thermally conductive insulating film 120 makes the adhesion and peeling of the resist film 400 more convenient.

[0049] Example 2

[0050] Example 2 relates to a method for preparing a power module, comprising the following steps: preparing a package bracket according to the preparation method of Example 1; installing a power chip 200 on the chip socket 111 of the package bracket / lead frame 110; placing the package bracket with the power chip 200 installed into an injection mold and injecting packaging material to complete the preparation of the package 300; and punching out the connecting strip 113 that connects multiple pins 112.

[0051] In this invention, the power chip 200 can be an IGBT chip or a MOSFET chip, such as a SiC MOSFET chip. The power chip 200 has electrodes on its front and back sides, for example, a drain on the back side and a source and gate on the front side. Specifically, as shown... Figure 6 As shown, the back of the power chip 200 is mounted on the chip socket 111, and the electrodes on the back are electrically connected to the chip socket 111. The electrodes on the front of the power chip 200 are electrically connected to the corresponding pins 112 via wires 201.

[0052] like Figures 7 to 10 As shown, the chip socket 111, power chip 200, wires 201, and metal heat sink 130 are all housed within the package 300, with pins 112 extending from one side of the package 300. The metal heat sink 130 has a heat dissipation surface 132 exposed from the package 300, which can be connected to an external heat sink to achieve rapid heat dissipation of the power chip 200. The package 300 has mounting holes 301 for mounting and securing the power module.

[0053] The injection mold for manufacturing the package 300 includes an upper mold and a lower mold. During injection molding, the package holder with the power chip installed is first placed in the lower mold. When the upper and lower molds are closed, a mold cavity that matches the shape of the package 300 is formed. Injecting encapsulation material into the mold cavity produces the package 300. Preferably, as follows... Figure 11 As shown, pressing portions 510 are provided on opposite sides of the inner cavity of the upper mold 500. During the injection molding process, the opposite sides of the chip holder 111 are pressed together by the pressing portions 510, so that the metal heat sink 130 / heat dissipation surface 132 is tightly attached to the bottom wall of the lower mold, thereby preventing the encapsulation material / encapsulation adhesive from flowing to the heat dissipation surface 132 of the metal heat sink 130. Furthermore, the upper mold 500 is also provided with a core post 520, which is used to form the mounting hole 301.

[0054] like Figure 7 and Figure 9 As shown, the package 300 obtained by the above injection molding method has a groove 302 on its side, and part of the side of the chip holder 111 is exposed from the groove 302. To improve safety, preferably, insulating glue can be applied inside the groove 302 after injection molding of the package 300 to cover the part of the chip holder 111 exposed from the groove 302. The connecting strip 113 connecting multiple pins 112 is punched off after injection molding to obtain the finished power module.

[0055] Example 3

[0056] like Figure 12 As shown, the only difference between Embodiment 3 and Embodiment 1 is that the shape of the chip socket 111 in Embodiment 3 is different, and the U-shaped clearance groove 114 on the chip socket 111 in Embodiment 1 is modified into a circular clearance hole 115, which helps to enhance the structural strength of the chip socket 111.

[0057] Although the present invention has been described above by way of embodiments, the above embodiments are only used to exemplify possible implementations of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions or changes made by those skilled in the art in accordance with the present invention should also be covered by the scope of protection defined by the claims of the present invention.

Claims

1. A method for fabricating a power chip packaging bracket, characterized in that... The steps include the following: S1, a semi-cured thermally conductive insulating film is formed in a predetermined area on the surface of a metal substrate; S2, a metal heat sink is pre-attached to the thermally conductive insulating film; wherein, when viewed along the thickness direction of the thermally conductive insulating film, the metal heat sink is recessed within the edge of the thermally conductive insulating film; S3, punching the metal substrate to obtain a lead frame; wherein, the lead frame includes a chip holder connected together and multiple pins, and viewed along the thickness direction of the thermally conductive insulating film, the thermally conductive insulating film is recessed within the edge of the chip holder; S4, complete the final curing of the thermally conductive insulating film; Step S1 includes: S11, a peelable resist film is attached to the surface of the metal substrate, the resist film having a window that exposes the predetermined area; S12, a fluid-state thermally conductive insulating adhesive is applied inside the window; S13, pre-cur the thermally conductive insulating adhesive to obtain a semi-cured thermally conductive insulating sheet.

2. The method for preparing the power chip packaging bracket according to claim 1, characterized in that: The thermally conductive insulating film has a gap of at least 0.1 mm between it and the edge of the chip holder, and the metal heat sink has a gap of at least 0.3 mm between it and the edge of the thermally conductive insulating film.

3. The method for preparing the power chip packaging bracket according to claim 1, characterized in that: The metal substrate is a copper substrate with a thickness of 0.5 mm to 1.0 mm.

4. The method for preparing the power chip packaging bracket according to claim 1, characterized in that: The metal heat sink is a copper heat sink with a thickness of 1.0mm to 2.0mm.

5. The method for preparing a power chip packaging bracket according to claim 1, characterized in that: The thickness of the thermally conductive insulating film is 0.1mm~0.2mm.

6. The method for preparing a power chip packaging bracket according to claim 1, characterized in that: The thermally conductive insulating film contains ceramic filler, and the thermal conductivity of the thermally conductive insulating film is above 5 W / m·K.

7. The method for preparing a power chip packaging bracket according to claim 1, characterized in that: The chip holder, the thermally conductive insulating film, and the metal heat sink are provided with interconnected clearance holes or clearance grooves.

8. A method for fabricating a power module, characterized in that... The steps include the following: The encapsulation bracket is prepared according to the preparation method of any one of claims 1-7; A power chip is mounted on the chip socket of the packaging bracket; The package holder with the power chip installed is placed into the injection mold, and the packaging material is injected to complete the packaging body; wherein, the metal heat sink has a heat dissipation surface exposed from the package body; The connecting strip that connects the multiple pins is removed by punching.

9. The method for preparing a power module according to claim 8, characterized in that: The injection mold includes an upper mold and a lower mold. The upper mold has pressing parts on opposite sides of its inner cavity. During the injection process, the opposite sides of the chip holder are pressed together by the pressing parts, so that the metal heat sink is tightly attached to the bottom wall of the lower mold.

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