QFN (Quad Flat No-lead) lead frame, preparation method thereof and QFN packaging structure

Abstract

The invention provides a QFN lead frame, a preparation method thereof and a QFN packaging structure, in the QFN lead frame, planar pins are arranged at four corners of the front surface of a frame unit, empennage pins are bent to be perpendicular to the front surface of the frame unit, and the planar pins and the empennage pins form a semi-surrounding structure for each corner of the frame unit. According to the QFN lead frame disclosed by the invention, the stress is dispersed through the semi-surrounding structure, and the cracking and collapse risks are reduced. The planar pin also provides an additional solderable surface, so that the molten solder is easier to wet and attach, and the risk of pseudo soldering or refusing soldering is reduced. According to the QFN packaging structure, by using the QFN lead frame with the semi-surrounding structure on the periphery, the packaging structural strength is enhanced, the packaging four-corner structure is effectively prevented from being broken, and the overall stability of the packaging structure is improved. Because the plane pin and the empennage pin are not wrapped by the molding compound, the QFN packaging structure can dissipate heat through the plane pin and the empennage pin.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor packaging, and in particular relates to a QFN lead frame, a preparation method thereof, and a QFN packaging structure. Background Art

[0002] The lead frame, as the chip carrier of the integrated circuit, is a key structural component that uses bonding materials to achieve electrical connection between the internal circuit lead ends of the chip and the external leads to form an electrical circuit. It acts as a bridge connecting to external wires and is also the main way to dissipate heat inside the chip.

[0003] The traditional QFN package structure uses a conventional lead frame as the main structure. After packaging, the package structure will completely seal the lead frame in the plastic package. The heat dissipation channel is relatively single, and it mainly relies on the back of the base island located in the center of the bottom of the package for heat dissipation. The heat dissipation speed is slow, which makes it difficult to meet the growing heat dissipation needs and will also affect the service life of the product.

[0004] In addition, the four corners of the QFN package structure are areas where PCB stress is concentrated (such as thermal expansion or mechanical vibration), so the structure in the four corners is prone to collapse and cracking.

[0005] Therefore, a new packaging structure is urgently needed to solve these problems, improve the heat dissipation performance of the QFN packaging structure, and increase the strength of the packaging structure and the stability of welding. Summary of the Invention

[0006] The object of the present invention is to provide a QFN lead frame and a QFN package structure that enhance the overall structural strength, effectively prevent the collapse of the package four corner structures, and improve stability.

[0007] In a first aspect, the present invention discloses a method for preparing a QFN lead frame, the method comprising the following steps: S1. Provide a metal substrate, arrange a plurality of frame units in an array on the metal substrate, and use a chemical etching process to form base islands and pins on the front surface of the metal substrate, with the pins being provided at the edges of the frame units. While forming the base islands and pins, provide pins at the four corners of the frame units, including planar pins and tail pins. S2. Stamping and cutting the metal substrate to form an independent QFN lead frame, with the planar pins arranged at the four corners of the front of the frame unit; the tail pins are bent perpendicular to the front of the frame unit, and the planar pins and the tail pins form a semi-enclosed structure for each corner of the frame unit.

[0008] In a second aspect, the present invention also provides a QFN lead frame prepared using the above method, which includes a plurality of frame units arranged in an array on a metal substrate, wherein the frame unit includes a base island and pins arranged on the front side of the frame unit, and the pins are arranged at the edges of the frame unit.

[0009] The QFN lead frame also includes pins arranged at the four corners of the frame unit, and the pins include planar pins and tail pins. The planar pins are arranged at the four corners of the front of the frame unit, and the tail pins are bent perpendicular to the front of the frame unit. The planar pins and tail pins form a semi-enclosed structure for each corner of the frame unit.

[0010] Preferably, the frame unit, the plane pins and the tail wing pins are integrally formed.

[0011] Preferably, the tail fin pin includes a first tail fin and a second tail fin of the same structure, and the first tail fin and the second tail fin are vertically connected.

[0012] Preferably, the end edges of the plane pins and the tail wing pins are both arc-shaped.

[0013] In a third aspect, the present invention discloses a QFN packaging structure, which includes the above-mentioned QFN lead frame, and also includes a semiconductor chip and a plastic packaging part. The semiconductor chip is mounted on the base island of the QFN lead frame, and the semiconductor chip is electrically connected to the pins through leads. The plastic packaging part covers the semiconductor chip and the leads, and the planar pins and tail wing pins surround the four corners of the QFN packaging structure.

[0014] Preferably, the semiconductor chip is electrically connected to the planar pins.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The QFN leadframe disclosed in this invention forms a semi-enclosed structure around each corner of the frame unit using flat pins and tail pins, distributing stress and reducing the risk of cracking and collapse. The flat pins also provide additional solderable surface, making it easier for molten solder to wet and adhere, reducing the risk of cold solder joints or solder rejection.

[0016] The QFN package structure disclosed in the present invention enhances the structural strength of the package by using a QFN lead frame with a semi-enclosed structure on all sides, effectively prevents the collapse of the four corner structures of the package, and improves the overall stability of the package structure.

[0017] After packaging, the QFN package structure disclosed in this invention does not encapsulate the planar pins and tail pins with the plastic encapsulation compound. This allows the QFN package structure to dissipate heat through these pins. This invention changes the traditional chip heat dissipation method, enabling the chip to exchange heat with the outside world through the pins, significantly improving the chip's heat dissipation performance and resolving the problem of poor heat dissipation efficiency in traditional packaging methods.

[0018] The QFN lead frame disclosed in the present invention has a simple structure, is easy to mass-produce, has good cost-effectiveness, and ensures high-quality output of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the QFN lead frame in Example 1 of the present invention; Figure 2 Schematic diagram of the structure of the pins in Example 1; Figure 3 Schematic diagram of the semi-enclosed structure in Example 1; Figure 4 This is a schematic diagram of the structure in which the ends of the pins are curved in Example 1; Figure 5 This is another structural diagram of Example 1 in which the ends of the pins are curved; Figure 6 Schematic diagram of the QFN package structure in Example 2; Figure 7 The QFN package structure in Example 2 adopts Figure 4 A schematic structural diagram of the lead frame shown; Figure 8 The QFN package structure in Example 2 adopts Figure 5 Schematic diagram of the structure of the lead frame shown.

[0020] Reference numerals: frame unit 1 , base island 2 , pin 3 , pin 4 , plane pin 40 , tail pin 41 , arc 42 , first tail 410 , second tail 411 , semi-enclosed structure A. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings.

[0022] Example 1 like Figure 1 As shown, this embodiment provides a QFN lead frame and a preparation method thereof, specifically, the QFN lead frame is manufactured by a process combining etching and stamping.

[0023] The present invention discloses a method for preparing a QFN lead frame, which comprises the following steps: S1. Provide a metal substrate, arrange multiple frame units 1 in an array on the metal substrate, and use a chemical etching process to form base islands 2 and pins 3 on the front surface of the metal substrate. The pins 3 are arranged at the edges of the frame units 1. While forming the base islands 2 and pins 3, pins 4 are respectively provided at the four corners of the frame units 1. The pins 4 include a plane pin 40 and a tail pin 41. S2. Stamp and cut the metal substrate to form an independent QFN lead frame, and the planar pins 40 are arranged at the four corners of the front of the frame unit 1; the tail pins 41 are bent perpendicular to the front of the frame unit 1, and the planar pins 40 and the tail pins 41 form a semi-enclosed structure for each corner of the frame unit 1.

[0024] In this embodiment, a plurality of frame units 1 are arranged in an array on a metal substrate. The array structure is not shown in the figure, and only the frame unit 1 is described. Figures 1 to 3 As shown, a base island 2 and pins 3 are formed on the front of the frame unit 1 , and the pins 3 are arranged at the edges of the frame unit 1 .

[0025] The chemical etching process mentioned in this embodiment forms the base island 2 and lead 3 on the front of the frame unit 1. This process is prior art and is briefly described here. The lead frame forming process mainly develops a production process (taking the mechanical template electroplating process as an example): frame design, etching mold creation, raw material pre-cleaning, dry film pressing, exposure, development, etching, film stripping, dry film pressing, exposure, development, silver plating, film stripping, stamping, cutting, and packaging. A stamping process is added to the etched lead frame production process. The matching stamping tool is created according to the design. The lead frame is silver-plated and then stamped to complete the production.

[0026] During the manufacturing process of the QFN lead frame, while forming the pins 3, pins 4 are also formed at the four corners of the frame unit 1, namely the flat pins 40 and the tail pins 41. The flat pins 40 are set at the four corners of the front of the frame unit 1, while the tail pins 41 are retained during the stamping and cutting stages when the unnecessary metal substrate is cut. The stamping process bends the tail pins 41 so that they are perpendicular to the front of the frame unit 1. In this way, the flat pins 40 and the tail pins 41 can form a semi-enclosed structure A at each corner of the frame unit 1, as shown in FIG. Figure 3 shown.

[0027] In this embodiment, the frame unit 1, the planar pins 40 and the tail pins 41 are integrally formed in the manufacturing process of the QFN lead frame. The process is simple and controllable, easy to mass produce, and has good cost-effectiveness, while ensuring high-quality output of the product.

[0028] In a specific implementation, in order to better surround the four corners of the QFN lead frame, the tail pins 41 are set to be the first tail 410 and the second tail 411 with the same structure, as shown in FIG. Figure 2 、 Figure 3 As shown, the first and second fins 410, 411 are symmetrically arranged along the diagonal lines of the lead frame. After bending, the first and second fins 410, 411 are vertically connected and, together with the flat pins 40, form a semi-enclosed structure A around the four corners of the QFN lead frame. This structure disperses stress and reduces the risk of cracking and collapse. The flat pins 40 and fin pins 41 also provide additional solderable surface, making it easier for molten solder to wet and adhere, reducing the risk of cold solder joints or solder rejection.

[0029] like Figure 4 and Figure 5 As shown, when the pin 4 does not need to be electrically connected to the chip or to prevent the pin from occupying too much area, the end edges of the plane pin 40 and the tail pin 41 are both curved 42 ( Figure 5 Not shown, refer to Figure 4 In this way, the plane pin 40 and the tail pin 41 are not likely to cause a short circuit. Figure 5 The dotted part in the middle will be cut off later.

[0030] Example 2 This embodiment discloses a QFN package structure, which includes the QFN lead frame described in Example 1. Figures 6 to 8 As shown, it is a QFN package structure encapsulated using an independent frame unit 1. Figure 6 The QFN package structure shown is a Figure 1 The lead frame shown, Figure 7 The QFN package structure shown is a Figure 4 The lead frame shown, Figure 8 The QFN package structure shown is a Figure 5 lead frame shown.

[0031] The QFN packaging structure also includes a semiconductor chip and a plastic encapsulation part (the semiconductor chip and the plastic encapsulation part are not the focus of this embodiment and are not shown in the figure). The semiconductor chip is mounted on the base island 2 of the QFN lead frame. The semiconductor chip is electrically connected to the pins 3 through leads, and the plastic encapsulation part covers the semiconductor chip and the leads. The main production process of the QFN packaging structure is: chip mounting, wire bonding, encapsulation mold coating, encapsulation, film tearing, tinning, cutting, and packaging. The specific process of the QFN packaging structure in this embodiment can refer to the process in the prior art. The difference is that in this embodiment, the plane pins 40 and the tail pins 41 surround the four corners of the QFN packaging structure.

[0032] The semiconductor chip is electrically connected to the planar pins 40. As shown in the figure, the planar pins 40 also provide additional solderable surfaces, making it easier for molten solder to wet and adhere, thereby reducing the risk of cold solder joints or solder rejection.

[0033] The QFN package structure uses a QFN lead frame with a semi-enclosed structure A on all sides, which enhances the structural strength of the package, effectively prevents the collapse of the four corners of the package, and improves the overall stability of the package structure.

[0034] After the QFN package is encapsulated, the flat pins 40 and the tail pins 41 are not covered by the plastic packaging material. The QFN package structure can dissipate heat through the flat pins 40 and the tail pins 41. This changes the heat dissipation method of traditional chips, allowing the chip to exchange heat with the outside world through pins 4, significantly improving the chip's heat dissipation performance and solving the problem of poor heat dissipation efficiency in traditional packaging methods.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a QFN lead frame, characterized in that: The method comprises the following steps: S1. Provide a metal substrate, arrange a plurality of frame units in an array on the metal substrate, and use a chemical etching process to form base islands and pins on the front surface of the metal substrate, with the pins being provided at the edges of the frame units. While forming the base islands and pins, provide pins at the four corners of the frame units, including planar pins and tail pins. S2. Stamping and cutting the metal substrate to form an independent QFN lead frame, with the planar pins arranged at the four corners of the front of the frame unit; the tail pins are bent perpendicular to the front of the frame unit, and the planar pins and the tail pins form a semi-enclosed structure for each corner of the frame unit.

2. A QFN lead frame, prepared according to the method of claim 1, comprising a plurality of frame units arranged in an array on a metal substrate, the frame units comprising a base island and leads provided on the front surface of the frame units, the leads provided at the edges of the frame units, characterized in that: It also includes pins arranged at the four corners of the frame unit, the pins including plane pins and tail pins, the plane pins are arranged at the four corners of the front of the frame unit; the tail pins are perpendicular to the front of the frame unit after being bent, and the plane pins and tail pins form a semi-enclosed structure for each corner of the frame unit.

3. The QFN lead frame according to claim 2, wherein: The frame unit, the plane tube pins and the tail tube pins are integrally formed.

4. The QFN lead frame according to claim 3, wherein: The tail fin pin includes a first tail fin and a second tail fin of the same structure, and the first tail fin and the second tail fin are vertically connected.

5. The QFN lead frame according to claim 4, wherein: The end edges of the plane tube pins and the tail wing tube pins are both arc-shaped.

6. A QFN package structure comprising the QFN lead frame according to any one of claims 2 to 5, characterized in that: It also includes a semiconductor chip and a plastic packaging part. The semiconductor chip is mounted on the base island of the QFN lead frame. The semiconductor chip is electrically connected to the pins through leads. The plastic packaging part covers the semiconductor chip and the leads. The plane pins and tail pins surround the four corners of the QFN packaging structure.

7. The QFN package structure according to claim 6, wherein: The semiconductor chip is electrically connected to the plane pins.

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