Lead frame structure and packaging method

Abstract

The invention provides a lead frame structure and a packaging method, and the lead frame structure comprises a lead frame, a plurality of transverse connecting ribs disposed on the lead frame, and a plurality of longitudinal connecting ribs perpendicular to the transverse connecting ribs. The transverse connecting ribs and the longitudinal connecting ribs divide the lead frame into a plurality of lead frame unit groups, each lead frame unit group comprises at least two transversely adjacent lead frame units, and each lead frame unit comprises a base island and a pin which is arranged on the longitudinal side of the base island and is separated from the base island; the pins of the same group of lead frame units share one common connecting rib, the two ends of the common connecting rib are respectively connected with the longitudinal connecting ribs, and the part, close to the longitudinal connecting ribs, of the common connecting rib bends and protrudes upwards, so that the plane where the pins are located is higher than the plane where the base islands are located. The lead frame structure can be compatible with various packaging modes.

Description

Technical Field

[0001] The invention relates to the field of integrated circuit packaging, in particular to a lead frame structure and a packaging method using the lead frame structure. Background Art

[0002] In the field of power devices, there is a package called LFPAK, which originated abroad and has been around for 20 years. Figure 1 As shown in FIG. 1 , the assembly process of the LFPAK package is as follows: first, the chip 130 is welded on the base island 110 of the lead frame 100, and then the buckle 120 and the copper clip 140 of the lead frame 100 are used for assembly positioning to complete the assembly, and then the lead frame 100 is plastic-encapsulated with a plastic encapsulation body 150, and finally the ribs are cut and the pins are bent. The characteristic of the product is that the bent pins can absorb stress after the PCB board is installed to avoid cracking of the plastic encapsulation body.

[0003] Disadvantages of the LFPAK packaging structure in the prior art: 1. The copper clip 140 and the lead frame 100 are restricted in position in the X and Y directions by the buckle 120. Due to the processing errors of various components, the buckle fails: interference mismatching will cause the copper clip to fail to be fixed, and the product cannot be injection molded and scrapped; excessive freedom will cause the encapsulation injection mold to press the pins or the rib cutting mold to cut the pins; 2. Since the structure adopts the integrated design of copper clip 140 and pin, the copper clip is directly above the lead frame base island after assembly, which means that this structure can only be used for copper clip type packaging, and cannot be used for low-cost aluminum ribbon bonding packaging on the market.

[0004] 3. Since this structure uses a snap-on design to fix the relative position of the copper clip and the lead frame, the snap-on design area wastes material and frame area, resulting in a relatively high unit price for this product. Summary of the invention

[0005] The object of the present invention is to provide a lead frame structure compatible with multiple packaging methods and a packaging method using the lead frame structure.

[0006] In an embodiment of the present invention, a lead frame structure is provided, which includes a lead frame and a plurality of transverse ribs arranged on the lead frame and a plurality of longitudinal ribs perpendicular to the transverse ribs, the transverse ribs and the longitudinal ribs divide the lead frame into a plurality of lead frame unit groups, each lead frame unit group includes at least two transversely adjacent lead frame units, each lead frame unit includes a base island, pins arranged on a longitudinal side of the base island and separated from the base island, the pins of the same group of lead frame units share a common rib, the two ends of the common rib are respectively connected to the longitudinal ribs, and the portion of the common rib close to the longitudinal ribs is bent and protruded upward, so that the plane where the pins are located is higher than the plane where the base island is located.

[0007] In the embodiment of the present invention, the height of the plane where the pins are located is equal to the height of the top surface of the chip after the chip is welded to the base island.

[0008] In the embodiment of the present invention, the tip ends of the plurality of pins are pre-cut and disconnected from the frame body.

[0009] In the embodiment of the present invention, one transverse side of the base island is connected to the longitudinal connecting ribs via a transverse support rod, and the other transverse side of the base island is connected to a T-shaped support rod, and the T-shaped support rod is connected to the transverse connecting ribs.

[0010] In an embodiment of the present invention, a packaging method of the lead frame structure is provided, which includes: Soldering the chip onto the base island; Welding a copper clip on the chip and the pin so that the chip and the pin are electrically connected through the copper clip; Injection molding packaging, plastic-encapsulating the chip, the pins and the copper clip, and tinning the exposed parts after plastic encapsulation; Electroplating: tinning the exposed portion of the pin; Cut the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

[0011] In an embodiment of the present invention, another packaging method of the lead frame structure is provided, which includes: Soldering the chip onto the base island; Bonding an aluminum ribbon and a copper wire to the chip and the pin, so that the chip and the source pin are electrically connected through the aluminum ribbon, and the chip and the gate pin are electrically connected through the copper wire; Injection molding packaging, plastic-sealing the chip, the pins, the aluminum tape and the copper wire, and tinning the exposed parts after plastic sealing; Cut the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

[0012] Compared with the prior art, the lead frame structure of the present invention is adopted, each lead frame unit group includes at least two laterally adjacent lead frame units, each lead frame unit includes a base island, and a pin arranged on a longitudinal side of the base island and separated from the base island, the pins of the same group of lead frame units share a common connecting rib, the two ends of the common connecting rib are respectively connected to the longitudinal connecting rib, and the part of the common connecting rib close to the longitudinal connecting rib is bent and protruded upward, so that the plane where the pins are located is higher than the plane where the base island is located, so that after the chip is installed, the plane where the chip is located is aligned with the plane where the chip is located. The height of the plane where the pins are located is flush, which is convenient for directly welding copper clips or bonding aluminum strips and copper wires, thereby supporting two different packaging methods; in addition, since the tip ends of the multiple pins are pre-cut and disconnected from the frame body, the tip end surfaces of the pins will also be covered with tin during electroplating, thereby enhancing the bonding strength between the packaged product and the PCB board; support rods are arranged on the left and right sides of the base island, so that the mold can press the support rods during plastic sealing to prevent glue overflow from the exposed base island surface; there is no need to use a buckle to fix the copper clip, which saves frame area and material, thereby supporting the formation of more lead frame units in a frame of the same size. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention is a schematic diagram of a process of packaging using a lead frame of the prior art.

[0014] Figure 2 It is a schematic diagram of the overall structure of the lead frame structure of an embodiment of the present invention.

[0015] Figure 3 It is a partial structural schematic diagram of a lead frame structure according to an embodiment of the present invention.

[0016] Figure 4 yes Figure 3 Schematic diagram of the cross section along line AA.

[0017] Figure 5 The present invention is a schematic diagram of a packaging process using a lead frame structure according to an embodiment of the present invention.

[0018] Figure 6 It is another schematic diagram of a packaging process using the lead frame structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] The implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0021] like Figure 2 and Figure 3 As shown, in an embodiment of the present invention, a lead frame structure is provided, which includes a lead frame 200 and a plurality of transverse connecting ribs 210 arranged on the lead frame 200 and a plurality of longitudinal connecting ribs 220 perpendicular to the transverse connecting ribs. The transverse connecting ribs 210 and the longitudinal connecting ribs 220 separate the lead frame into a plurality of lead frame unit groups 230. Each lead frame unit group 230 includes two laterally adjacent lead frame units 240. It should be noted that, in other embodiments of the present invention, each lead frame unit group 230 may include three or more laterally adjacent lead frame units 240, and the specific number is determined according to actual needs, and the present invention does not limit this.

[0022] Each lead frame unit 240 includes a base island 241 and a plurality of pins 242 disposed on one longitudinal side of the base island 241 and separated from the base island 241. The pins 242 of the same group of lead frame units share a common connecting rib 243, and both ends of the common connecting rib 243 are connected to the longitudinal connecting rib 220 respectively.

[0023] like Figure 4 As shown, the portion of the common connecting rib 243 near the longitudinal connecting rib 220 is bent and raised upward, so that the plane where the pins 242 are located is higher than the plane where the base island 241 is located. Specifically, by setting the amplitude of the bending and raising, the height of the plane where the pins 242 are located is equal to the height of the top surface of the chip after the base island 241 is welded to the chip, so that when welding the copper clip or bonding the aluminum ribbon, the contact surface of the copper clip / aluminum ribbon and the chip surface and the pins 242 are on the same plane, so as to achieve a more reliable electrical connection.

[0024] Furthermore, in the embodiment of the present invention, the tip ends 2421 of the plurality of pins 242 are pre-cut and disconnected from the frame body. This arrangement allows the plurality of pins 242 to be suspended in the air, and only the common connecting rib 243 needs to be bent to achieve the upward movement of the plane where the pins 242 are located, so as to facilitate the overall upward movement of the pins 242. Furthermore, in the tinning process after the chip is plastic-sealed, since the tip ends 2421 of the plurality of pins 242 are pre-cut and exposed, the tip ends 2421 will also be tinned, which can enhance the bonding strength between the packaged product and the PCB board.

[0025] In the embodiment of the present invention, one side of the base island 241 is connected to the longitudinal connecting rib 220 via a transverse support rod 244, and the other side of the base island 241 is connected to a T-shaped support rod 245, and the T-shaped support rod 245 is connected to the transverse connecting rib 210. In this way, support rods are provided on both sides of the base island 241, so that the plastic molding mold can press the support rods to prevent glue overflow from the exposed base island surface during plastic molding.

[0026] like Figure 5 As shown, in an embodiment of the present invention, a packaging method using the lead frame structure is also provided, which comprises the following steps: Soldering the chip 300 onto the base island 241; Soldering a copper clip 400 on the chip 300 and the pin 242 so that the chip 300 and the pin 242 are electrically connected through the copper clip 400; Injection molding packaging, plastic-encapsulating the chip 300, the pins 242 and the copper clip 400, and tinning the exposed parts after plastic encapsulation; Cut the ribs of the lead frame after plastic encapsulation to separate each plastic encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

[0027] like Figure 6 As shown, in an embodiment of the present invention, another packaging method using the above lead frame structure is also provided, which includes the following steps: Soldering the chip 300 onto the base island 241; Bonding an aluminum ribbon 500 and a copper wire 600 on the chip 300 and the pin 242, so that the chip 300 and the source pin 242 are electrically connected through the aluminum ribbon 500, and the chip 300 and the gate pin 242 are electrically connected through the copper wire 600; Injection molding packaging, plastic-encapsulating the chip 300, the pins 242, the aluminum tape 500, and the copper wire 600, and tinning the exposed parts after plastic encapsulation; Cut the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

[0028] In summary, the lead frame structure of the present invention is adopted, each lead frame unit group includes at least two laterally adjacent lead frame units, each lead frame unit includes a base island, and a pin arranged on a longitudinal side of the base island and separated from the base island, and the pins of the same group of lead frame units share a common connecting rib, and the two ends of the common connecting rib are respectively connected to the longitudinal connecting rib, and the part of the common connecting rib close to the longitudinal connecting rib is bent and protruded upward, so that the plane where the pins are located is higher than the plane where the base island is located, so that after the chip is installed, the plane where the chip is located is aligned with the pins. The height of the plane is flush, which is convenient for directly welding copper clips or bonding aluminum strips and copper wires, thereby supporting two different packaging methods; in addition, since the tip ends of the multiple pins are pre-cut and disconnected from the frame body, the tip ends of the pins will also be covered with tin during electroplating, thereby enhancing the bonding strength between the packaged product and the PCB board; support rods are arranged on the left and right sides of the base island, so that the mold can press the support rods to prevent glue overflow from the exposed base island surface during plastic sealing; there is no need to use a buckle to fix the copper clip, which saves frame area and material, thereby supporting the formation of more lead frame units in a frame of the same size.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lead frame structure, characterized in that: The invention comprises a lead frame and a plurality of transverse connecting ribs arranged on the lead frame and a plurality of longitudinal connecting ribs perpendicular to the transverse connecting ribs, wherein the transverse connecting ribs and the longitudinal connecting ribs separate the lead frame into a plurality of lead frame unit groups, each lead frame unit group comprises at least two transversely adjacent lead frame units, each lead frame unit comprises a base island and pins arranged on a longitudinal side of the base island and separated from the base island, the pins of the same group of lead frame units share a common connecting rib, the two ends of the common connecting rib are respectively connected to the longitudinal connecting ribs, and the portion of the common connecting rib close to the longitudinal connecting ribs is bent and protruded upwards, so that the plane where the pins are located is higher than the plane where the base island is located.

2. The lead frame structure according to claim 1, characterized in that: The height of the plane where the pins are located is equal to the height of the top surface of the chip after the base island is welded to the chip.

3. The lead frame structure according to claim 1, characterized in that: The tip ends of the plurality of pins are pre-cut and disconnected from the frame body.

4. The lead frame structure according to claim 1, wherein: One transverse side of the base island is connected to the longitudinal connecting ribs via a transverse support rod, and the other transverse side of the base island is connected to a T-shaped support rod, and the T-shaped support rod is connected to the transverse connecting ribs.

5. A packaging method using the lead frame structure according to any one of claims 1 to 4, characterized in that: include: Soldering the chip onto the base island; Welding a copper clip on the chip and the pin so that the chip and the pin are electrically connected through the copper clip; Injection molding packaging, plastic-encapsulating the chip, the pins and the copper clip, and tinning the exposed parts after plastic encapsulation; Electroplating: tinning the exposed portion of the pin; Cut the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

6. A packaging method using the lead frame structure according to any one of claims 1 to 4, characterized in that: include: Soldering the chip onto the base island; Bonding an aluminum ribbon and a copper wire to the chip and the pin, so that the chip and the source pin are electrically connected through the aluminum ribbon, and the chip and the gate pin are electrically connected through the copper wire; Injection molding packaging, plastic-sealing the chip, the pins, the aluminum tape and the copper wire, and tinning the exposed parts after plastic sealing; Cut the lead frame after injection molding to separate each plastic-encapsulated chip and each pin of the chip; The pins of the chip are bent and formed.

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