QFN packaging structure with electromagnetic shielding function and preparation method thereof

Abstract

The invention provides a QFN (Quad Flat No-lead) packaging structure with an electromagnetic shielding function and a preparation method thereof. The packaging structure comprises a metal frame, a chip, a plastic packaging part, an electromagnetic shielding metal layer and a conductive metal column, the plastic package part wraps the chip, the conductive metal columns and the front and side surfaces of the metal frame, the side surfaces of the end parts of the metal pins far away from the base islands are exposed, and the tops of the conductive metal columns are exposed; the electromagnetic shielding metal layer covers the front surface and the side surface of the plastic packaging part and is conducted with the top of the conductive metal column, so that electromagnetic shielding of the packaging structure is realized; and the electromagnetic shielding metal layer does not cover the side surface of the end part of the exposed metal pin. The metal layer conformal shielding technology is adopted, the electromagnetic shielding metal layer is formed by conducting metal layer sputtering on the surface of the plastic packaging part, the conductive metal columns attached to the front faces of the grounding pins are conducted with the electromagnetic shielding layer, signal isolation between the packaging structure and external electronic elements and the environment is achieved, and the electromagnetic shielding capacity of the electronic chip is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, and more specifically to a QFN packaging structure with electromagnetic shielding function and its preparation method. Background Technology

[0002] With the increasing prevalence of electronic products in the field of high-frequency communication signals, electronic chips need to have stronger electromagnetic shielding capabilities to prevent electromagnetic interference between the chip and external components and the environment.

[0003] Existing QFN package structures employ a metal shielding cover to achieve electromagnetic shielding between the chip and components, or between chips. This involves placing a cover with an electromagnetic shielding layer on the surface of the package frame, covering the chip and the pins of the QFN package structure. The electromagnetic shielding layer contacts of the cover are electrically connected to the ground pin, thus achieving an electromagnetically shielded QFN package structure. While this package structure achieves shielding, it occupies a large space and is costly.

[0004] The ideal solution is a conformal shielding structure with an electromagnetic shielding metal layer. However, in existing packaging processes for shielded packages, substrate packaging is the most common method to achieve this function. However, substrate processing is costly, has low reliability, and poor thermal conductivity. Furthermore, while conformal shielding with a metal layer can reduce electromagnetic interference, it has limitations. It requires no exposed metal leads on the sides of the chip package, with only ground terminals remaining to facilitate communication with the electromagnetic shielding metal layer. In existing QFN package structures, because the side leads are exposed, directly sputtering the electromagnetic shielding metal layer to create the electromagnetic shielding structure would lead to short circuits. Another approach is to add an insulating layer to the outside of the QFN package leads to prevent short circuits between the leads and the electromagnetic shielding layer. However, this increases the complexity of the insulating layer fabrication, and after fabrication, it must ensure that the insulating layer exposes the ground pin so that the electromagnetic shielding layer is grounded through the ground pin, thus achieving electromagnetic shielding in the QFN package structure. This packaging structure is more complex, increases manufacturing costs, and the additional insulating layer also affects the thermal conductivity of the package structure.

[0005] Therefore, a new QFN package structure needs to be designed that can achieve electromagnetic shielding, avoid pin short circuits, and meet the overall performance requirements of the package. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a QFN package structure with electromagnetic shielding and its fabrication method, effectively preventing pin short circuits and improving the overall performance of the package structure.

[0007] On one hand, this invention discloses a method for fabricating a QFN packaging structure with electromagnetic shielding function, the method comprising the following steps: S1. Prepare a metal frame. The surface of the metal frame is provided with base islands and multiple metal pins. The base islands are used to mount chips. The metal pins include functional pins and ground pins. The metal pins are used to electrically connect to the chips. The ground pins are electrically connected to conductive metal pillars on the front. S2. After electrically connecting a conductive metal post to the front of the grounding pin, mount the chip on the surface of the base island; the chip is electrically connected to the metal pin. S3. Use molding compound to mold the front of the metal frame to form a molding part. The molding part covers the front and sides of the chip, conductive metal pillars and metal frame, and is cut into individual products. Among them, the ends of the metal pins away from the base island of the individual products are exposed, and the tops of the conductive metal pillars are exposed. S4. Mount the bottom of the plastic seal of a single product into the adhesive film, so that the exposed metal pin ends at the bottom of the plastic seal are completely covered by the adhesive film. S5. Sputter an electromagnetic shielding metal layer on the front and side of the encapsulation part. The electromagnetic shielding metal layer is connected to the top of the conductive metal pillar to achieve electromagnetic shielding of the encapsulation structure. After sputtering the electromagnetic shielding metal layer, remove the adhesive film so that the electromagnetic shielding metal layer does not cover the end sides of the exposed metal pins.

[0008] In some embodiments, in step S4, the adhesive film is pre-attached onto a temporary metal carrier plate, and then the bottom of the encapsulation part is attached to the adhesive film. Appropriate pressure is applied to the encapsulation part, and the depth of embedding of the adhesive film is such that the end side of the exposed metal pin at the bottom of the encapsulation part is completely wrapped by the adhesive film, so as to prevent the electromagnetic shielding metal layer sputtered later from conducting with the metal pin and causing a short circuit.

[0009] In some embodiments, in step S5, the electromagnetic shielding metal layer includes a first layer, a second layer, and a third layer from bottom to top. The first layer is a seed layer, the second layer is an electromagnetic shielding metal material layer, and the third layer is a stainless steel protective layer. The first layer increases the bonding force between the electromagnetic shielding metal material and the encapsulation part; the second layer realizes the electromagnetic shielding function of the encapsulation structure; and the third layer prevents the oxidation of the electromagnetic shielding metal material, while also giving the encapsulation structure a good appearance and better printing quality.

[0010] In some implementations, the first layer is a stainless steel layer, and the second layer is a copper layer with a thickness of 3-9 μm.

[0011] In some implementations, the electromagnetic shielding metal layer is prepared by magnetron sputtering.

[0012] In some implementations, the chip is electrically connected to the metal pins via metal bonding wires, which are also encapsulated in a plastic package.

[0013] In some embodiments, the conductive metal pillar is a copper pillar with a diameter of 0.1-0.3 mm.

[0014] On the other hand, the present invention also discloses a QFN package structure with electromagnetic shielding function, which is made by the above-mentioned preparation method. The package structure includes a metal frame, a chip, a molding compound, an electromagnetic shielding metal layer, and conductive metal pillars. The metal frame includes a base island and multiple metal pins. The base island is used to mount the chip, and the metal pins include functional pins and ground pins. The metal pins are electrically connected to the chip, and the ground pins are electrically connected to a conductive metal pillar on the front. The molding compound covers the front and sides of the chip, conductive metal pillars, and metal frame, with the ends of the metal pins furthest from the base island exposed and the tops of the conductive metal pillars exposed. An electromagnetic shielding metal layer covers the front and sides of the encapsulation portion and is connected to the top of the conductive metal pillars to achieve electromagnetic shielding of the encapsulation structure; the electromagnetic shielding metal layer does not cover the ends and sides of the exposed metal pins.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The QFN package structure disclosed in this invention has a simple overall structure and adopts conformal metal layer shielding technology. An electromagnetic shielding metal layer is formed by sputtering a metal layer on the surface of the plastic package. The electromagnetic shielding layer is connected by a conductive metal pillar mounted on the front of the ground pin, thereby achieving signal isolation between the package structure and external electronic components and improving the electromagnetic shielding capability of the electronic chip.

[0016] The QFN package structure disclosed in this invention uses a high-temperature resistant adhesive film to fix and protect the packaged product, ensuring that the exposed metal pins at the bottom of the molded portion are completely wrapped by the adhesive film. This prevents short circuits caused by the sputtered electromagnetic shielding metal layer conducting with the metal pins. Subsequently, combined with the metal layer sputtering process, a compact and reliable electromagnetic shielding structure is formed, improving the overall performance and stability of the package. It also effectively solves the pin short circuit problem caused by exposed side pins in existing QFN structures, ensuring the normal function of the package.

[0017] The QFN package structure disclosed in this invention does not require modifications to existing metal frames or pins during fabrication. It achieves grounding of the electromagnetic shielding metal layer simply by cleverly placing conductive metal pillars between the grounding pin and the electromagnetic shielding metal layer. The process is simple and facilitates mass production. Furthermore, during fabrication, an innovative adhesive film is used to protect the sides of the metal pins, effectively preventing short circuits caused by the sputtered electromagnetic shielding metal layer conducting with the metal pins. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the QFN package structure in this invention; Figure 2 This is a schematic diagram of the metal frame structure; Figure 3 This is a schematic diagram of the cross-sectional structure of the metal frame; Figure 4 for Figure 3 A schematic diagram of a structure in which a conductive metal pillar is attached to the surface of the grounding pin; Figure 5 for Figure 4 A schematic diagram of a structure in which chips are mounted on the surface of the base island; Figure 6 for Figure 5 A schematic diagram of the proof structure; Figure 7 This is a schematic diagram of the structure after plastic sealing; Figure 8 A schematic diagram illustrating the structure for cutting into individual encapsulated products; Figure 9 A schematic diagram of a structure for mounting adhesive film on the bottom of a plastic-encapsulated product; Figure 10 This is a schematic diagram of the structure of a plastic-sealed product with an embedded film component at the bottom after pressure is applied. Figure 11 In order to be in Figure 10 The diagram shows a schematic of the sputtered electromagnetic shielding metal layer in the structure shown.

[0019] Label Explanation: Metal frame A; base island 1; metal pin 2; functional pin 201; ground pin 202; end side of metal pin 203; conductive metal pillar 3; top of conductive metal pillar 301; chip 4; encapsulation part 7; film part 8; metal carrier plate 9; electromagnetic shielding metal layer 10. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] This invention discloses a method such as Figure 1 The QFN package structure shown has electromagnetic shielding function. The package structure includes a metal frame A, a chip 4, a molding compound 7, an electromagnetic shielding metal layer 10, and conductive metal pillars 3.

[0022] The QFN packaging structure with electromagnetic shielding function disclosed in this invention has a simple overall structure, high reliability and high performance, and can achieve large-scale stable production.

[0023] This invention also discloses a method for preparing the above-mentioned QFN packaging structure, which includes the following steps: S1. Prepare a metal frame A. The surface of the metal frame A is provided with a base island 1 and multiple metal pins 2. The base island 1 is used to mount the chip 4. The metal pins 2 include functional pins 201 and ground pins 202. The metal pins 2 are used to electrically connect with the chip 4. The ground pins 202 are electrically connected to conductive metal pillars 3 on the front side. S2. After electrically connecting the conductive metal post 3 to the front of the grounding pin 202, the chip 4 is mounted on the surface of the base island 1; the chip 4 is electrically connected to the metal pin 2. S3. The front side of the metal frame A is molded with molding compound to form a molding part 7. The molding part 7 covers the chip 4, the conductive metal pillar 3 and the front and side sides of the metal frame A, and is cut into individual products. Among them, the end side 203 of the metal pins away from the base island 1 of the individual products is exposed, and the top 301 of the conductive metal pillar is exposed. S4. The bottom of the single product encapsulation part 7 is attached to the adhesive film part 8 so that the exposed metal pin end side 203 at the bottom of the encapsulation part 7 is completely wrapped by the adhesive film part 8. S5. Sputter an electromagnetic shielding metal layer 10 on the front and side of the encapsulation part 7. The electromagnetic shielding metal layer 10 is connected to the top 301 of the conductive metal pillar to achieve electromagnetic shielding of the encapsulation structure. After sputtering the electromagnetic shielding metal layer 10, remove the adhesive film 8 so that the electromagnetic shielding metal layer 10 does not cover the end side 203 of the exposed metal pin.

[0024] Specifically, the structural diagram of metal frame A is as follows: Figure 2 and Figure 3 As shown, it includes an array of base islands 1 and multiple metal pins 2, with base islands 1 and metal pins 2 disposed on the same plane; the metal pins 2 are distributed around the four sides of base islands 1. Base islands 1 are used to mount chips 4, and the metal pins 2 include functional pins 201 and ground pins 202. The metal pins 2 are electrically connected to chips 4, and the ground pins 202 are electrically connected to conductive metal pillars 3 on their front side.

[0025] The metal frame A is made of copper, and the common width of the metal pin 2 is 0.2-0.4mm.

[0026] Conductive metal pillars 3 can be mounted on the front side of ground pin 202 using SMT technology. Figure 3 The schematic diagram of the structure in which the conductive metal pillar 3 is attached is shown below. Figure 4 As shown.

[0027] The conductive metal pillar 3 in this invention is a copper pillar with a diameter of 0.1-0.3 mm. Other metals with good conductivity can also be used to prepare the conductive metal pillar 3. The height of the conductive metal pillar 3 is adjusted according to the overall thickness of the packaging structure. Generally, it is 50-100 μm lower than the thickness of the molding compound 7. The metal pillar can be soldered to the grounding pin 202 using solder paste.

[0028] Install chip 4 to Figure 4 In the structure shown, the structure is as follows Figure 5 and Figure 6 As shown. The pads 5 of chip 4 are electrically connected to the metal pins 2. Specifically, the functional pads 501 and functional pins 201 of chip 4 are electrically connected via metal bonding wires 6, and the ground pads 502 and ground pins 202 of chip 4 are electrically connected via metal bonding wires 6. The metal bonding wires 6 are subsequently encapsulated by the molding compound 7.

[0029] After chip 4 is electrically connected to metal pin 2, as follows Figure 7 and Figure 8 As shown, the encapsulation structure is encapsulated using molding compound to form the encapsulation part 7. The encapsulation part 7 covers the front and sides of the chip 4, the conductive metal pillar 3, and the metal frame A. After encapsulation, the packaged product is cut into a single package, and the top surface of the encapsulation part 7 is ground to expose the top 301 of the conductive metal pillar and the side 203 of the metal pins away from the base island 1.

[0030] This invention employs conformal metal layer shielding technology. By sputtering a metal layer on the surface of the encapsulation portion 7 to form an electromagnetic shielding metal layer 10, and by connecting the conductive metal pillar 3 mounted on the front side of the grounding pin 202 to the electromagnetic shielding layer, signal isolation between the encapsulation structure and external electronic components is achieved, thereby improving the electromagnetic shielding capability of the encapsulation structure.

[0031] like Figure 9 and Figure 10 As shown, before sputtering the electromagnetic shielding metal layer 10, the bottom of the encapsulation part 7 is first attached to the adhesive film 8 so that the end side 203 of the exposed metal pin at the bottom of the encapsulation part 7 is completely wrapped by the adhesive film 8, so as to prevent the sputtered electromagnetic shielding metal layer 10 from conducting with the metal pin 2 and causing a short circuit; the adhesive film 8 is removed after sputtering the electromagnetic shielding metal layer 10.

[0032] The adhesive film 8 is a high-temperature resistant adhesive film. The adhesive film 8 is pre-attached onto a temporary metal carrier plate 9, and then the bottom of the plastic seal 7 is attached to the adhesive film 8, forming a... Figure 9 The structure shown; then, appropriate pressure is applied to the encapsulation portion 7, and the depth of the embedded film 8 is such that the end side 203 of the exposed metal pin at the bottom of the encapsulation portion 7 is completely wrapped by the film 8, forming a structure as shown. Figure 10 The structure shown effectively prevents a short circuit caused by the subsequent sputtering of the electromagnetic shielding metal layer 10 and the metal pin 2. Then, the electromagnetic shielding metal layer 10 is sputtered using existing magnetron sputtering technology to form the structure shown. Figure 11 The structure shown is formed after sputtering of the electromagnetic shielding metal layer 10, followed by removal of the temporary metal carrier plate 9 and the adhesive film 8. Figure 1 The packaging structure shown.

[0033] The QFN packaging structure disclosed in this invention uses a high-temperature resistant adhesive film 8 to fix and protect the packaged product, so that the exposed metal pin end side 203 at the bottom of the molding compound 7 is completely wrapped by the adhesive film 8, preventing short circuits caused by the sputtered electromagnetic shielding metal layer 10 conducting with the metal pin 2; then, combined with the metal layer sputtering process, a compact and reliable electromagnetic shielding structure is formed, which improves the overall performance and stability of the package; it also effectively solves the pin short circuit problem caused by the exposed side pins in the existing QFN structure, ensuring the normal function of the package.

[0034] The electromagnetic shielding metal layer 10 covers the front and sides of the encapsulation portion 7 and is in communication with the top 301 of the conductive metal pillar, thereby achieving electromagnetic shielding of the encapsulation structure; the electromagnetic shielding metal layer 10 does not cover the end sides 203 of the exposed metal pins.

[0035] The electromagnetic shielding metal layer 10 is prepared by magnetron sputtering.

[0036] The electromagnetic shielding metal layer 10 in this invention includes a first layer, a second layer, and a third layer from bottom to top. The first layer is a seed layer, the second layer is an electromagnetic shielding metal material layer, and the third layer is a stainless steel protective layer. The first layer increases the bonding force between the electromagnetic shielding metal material and the encapsulation part 7. The second layer realizes the electromagnetic shielding function of the encapsulation structure. The third layer prevents the oxidation of the electromagnetic shielding metal material and at the same time makes the encapsulation structure present a good appearance and better printing quality.

[0037] In practice, the first layer is a stainless steel layer, and the second layer is a copper layer with a thickness of 3-9 μm. The copper layer serves as a functional layer, and its thickness can be controlled to adjust the shielding effect. A multi-layer electromagnetic shielding metal layer sputtering technology (stainless steel layer-copper layer-stainless steel layer) is employed to form a stable and reliable electromagnetic shielding structure. This achieves signal isolation between the packaged structure and external electronic components and the environment, improving the electromagnetic shielding capability of the electronic chip and enhancing the overall performance of the packaged structure.

[0038] The above descriptions are merely some embodiments of the present invention. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for fabricating a QFN packaging structure with electromagnetic shielding function, characterized in that, The preparation method includes the following steps: S1. Prepare a metal frame. The surface of the metal frame is provided with base islands and multiple metal pins. The base islands are used to mount chips. The metal pins include functional pins and ground pins. The metal pins are used to electrically connect to the chips. The ground pins are electrically connected to conductive metal pillars on the front. S2. After electrically connecting a conductive metal post to the front of the grounding pin, mount the chip on the surface of the base island; the chip is electrically connected to the metal pin. S3. Use molding compound to mold the front of the metal frame to form a molding part. The molding part covers the front and sides of the chip, conductive metal pillars and metal frame, and is cut into individual products. Among them, the ends of the metal pins away from the base island of the individual products are exposed, and the tops of the conductive metal pillars are exposed. S4. Mount the bottom of the plastic seal of a single product into the adhesive film, so that the exposed metal pin ends at the bottom of the plastic seal are completely covered by the adhesive film. S5. Sputter an electromagnetic shielding metal layer on the front and side of the encapsulation part. The electromagnetic shielding metal layer is connected to the top of the conductive metal pillar to achieve electromagnetic shielding of the encapsulation structure. After sputtering the electromagnetic shielding metal layer, remove the adhesive film so that the electromagnetic shielding metal layer does not cover the end sides of the exposed metal pins.

2. The preparation method according to claim 1, characterized in that, In step S4, the adhesive film is pre-attached onto a temporary metal carrier plate, and then the bottom of the encapsulation part is attached to the adhesive film. Appropriate pressure is applied to the encapsulation part, and the depth of embedding of the adhesive film is such that the side of the exposed metal pin at the bottom of the encapsulation part is completely covered by the adhesive film to prevent the electromagnetic shielding metal layer sputtered later from conducting with the metal pin and causing a short circuit.

3. The preparation method according to claim 1, characterized in that, In step S5, the electromagnetic shielding metal layer includes a first layer, a second layer, and a third layer from bottom to top. The first layer is a seed layer, the second layer is an electromagnetic shielding metal material layer, and the third layer is a stainless steel protective layer. The first layer increases the bonding force between the electromagnetic shielding metal material and the encapsulation part; the second layer realizes the electromagnetic shielding function of the encapsulation structure; and the third layer prevents the oxidation of the electromagnetic shielding metal material, while also giving the encapsulation structure a good appearance and good printing quality.

4. The preparation method according to claim 3, characterized in that, The first layer is a stainless steel layer, and the second layer is a copper layer with a thickness of 3-9 μm.

5. The preparation method according to claim 4, characterized in that, The electromagnetic shielding metal layer is prepared by magnetron sputtering.

6. The preparation method according to claim 5, characterized in that, The chip is electrically connected to the metal pins via metal bonding wires, which are also encapsulated in a plastic package.

7. The preparation method according to claim 1, characterized in that, The conductive metal pillar is a copper pillar with a diameter of 0.1-0.3 mm.

8. A QFN package structure with electromagnetic shielding function, manufactured using the preparation method according to any one of claims 1-7, characterized in that, The packaging structure includes a metal frame, a chip, a molding compound, an electromagnetic shielding metal layer, and conductive metal pillars. The metal frame includes a base island and multiple metal pins. The base island is used to mount chips. The metal pins include functional pins and ground pins. The metal pins are electrically connected to the chips. The ground pins are electrically connected to conductive metal pillars on their front side. The encapsulation covers the front and side surfaces of the chip, conductive metal pillars, and metal frame, wherein the ends of the metal pins furthest from the base island are exposed, and the tops of the conductive metal pillars are exposed. The electromagnetic shielding metal layer covers the front and sides of the encapsulation portion and is connected to the top of the conductive metal pillars to achieve electromagnetic shielding of the encapsulation structure; the electromagnetic shielding metal layer does not cover the ends and sides of the exposed metal pins.

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