Lead frame structure

Abstract

The utility model discloses a lead frame structure, which comprises at least one chip seat, a plurality of pins distributed around the chip seat, first connecting ribs connected with the corresponding pins, and a plurality of second connecting ribs connected with the first connecting ribs, the surface of the first connecting rib is provided with a raised first rib part which is not contacted with the pin, the surface of the second connecting rib is provided with a raised second rib part, and the first rib part and the second rib part are positioned on the same side surface of the lead frame and are distributed at the periphery of the concave part; through the structure, the strength of the lead frame in the area where the concave part is located can be enhanced, and burrs generated by cutting operation can be reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of a semiconductor packaging process, in particular to a lead frame structure. Background Art

[0002] Quad Flat No-lead Package (QFNP) is an increasingly common trend in chip packaging in the current semiconductor industry. As Figure 1 and Figure 2 shown, the lead frame 10 used for such a packaging structure is only partially drawn in the figure. The lead frame 10 includes at least one chip seat 11, a plurality of pins 12 distributed around the chip seat 11, a first connecting rib 13 connected to the corresponding pins 12, and a second connecting rib 14 connected to the plurality of first connecting ribs 13. Each chip seat 11 and the plurality of pins 12 distributed around it are the basic units of a single semiconductor component. The lead frame 10 is distributed with a plurality of basic units in an array manner. Therefore, the first connecting rib 13 is also connected between two adjacent pins 12. In addition, a recess 15 is formed on the side wall at the junction of the first connecting rib 13 and the second connecting rib 14. The width of the first connecting rib 13 or the second connecting rib 14 is reduced between two adjacent recesses 15. This recess 15 structure is used to reduce burrs generated during the cutting operation after packaging.

[0003] In the early lead frame structure, the thicknesses of the first connecting rib and the second connecting rib are the same as those of the pins. Therefore, two cutting operations must be performed during singulation. Moreover, due to the thick thicknesses of the first connecting rib and the second connecting rib, the cutting depth and accuracy are poor, and the tool wear is also increased. As Figure 1 , 2 shown, for the lead frame used after improvement, the semi-etching process is used to halve the thicknesses of the first connecting rib 13 and the second connecting rib 14. This method helps to reduce tool wear. However, after the thicknesses are both reduced, the strength of the original area where the recess 15 is located is further weakened. Therefore, some lead frames 10 form a rib 16 protruding on the surface of the first connecting rib 13 and connecting two adjacent pins 12. However, this method still cannot increase the strength too much, and it is still easy to deform during packaging processes such as wire bonding. In addition, the rib 16 used for reinforcement is prone to generate burrs during the subsequent cutting operation, and then solder bridging problems occur, resulting in a risk of short circuit in the subsequent finished products. Summary of the Utility Model

[0004] The main object of the present utility model is to provide a lead frame structure. Although the first connecting rib and the second connecting rib with reduced thickness are formed by a semi-etching process and connected to the corresponding pins, the first rib and the second rib protruding from each surface are still retained. The protruding first rib and second rib can increase the strength of the structure, reduce the deformation during packaging processes such as wire bonding, and also reduce the burrs generated during tool cutting.

[0005] To achieve the foregoing object, the present utility model adopts the following technical solutions:

[0006] The present utility model is a lead frame structure, including: at least one chip seat, a plurality of pins distributed around the chip seat, a first connecting rib connected to the corresponding pins, and a second connecting rib connected to the plurality of first connecting ribs, wherein a concave portion is further formed on the side wall at the junction of the first connecting rib and the second connecting rib. The surface of the first connecting rib has a protruding first rib and the first rib does not contact the pin, the surface of the second connecting rib has a protruding second rib, and the first rib and the second rib are on the same side of the lead frame and distributed around the concave portion.

[0007] As one of the preferred embodiments, the first rib and the second rib are adjacent but do not contact.

[0008] As one of the preferred embodiments, the first rib is a strip-shaped protrusion, and the strip distribution direction is the same as that of the first connecting rib. The second rib is a strip-shaped protrusion, and the strip distribution direction is the same as that of the second connecting rib.

[0009] As one of the preferred embodiments, the first rib and the second rib are both strip-shaped protrusions, and the strip distribution directions are both the same as that of the second connecting rib.

[0010] As one of the preferred embodiments, there are several first ribs symmetrically distributed on the surfaces of the first connecting ribs on both sides of the second connecting rib.

[0011] As one of the preferred embodiments, the second rib is distributed in a long strip protruding shape on the surface of the first connecting rib and also connects the plurality of second connecting ribs.

[0012] As one of the preferred embodiments, the second rib is distributed in a long strip protruding shape on the surface of the first connecting rib and also connects the plurality of second connecting ribs.

[0013] As one of the preferred embodiments, the first rib and the second rib are connected and in an L-shaped protruding shape, and each first rib or second rib is located between two adjacent concave portions.

[0014] As one of the preferred embodiments, the first rib is connected to the second rib and is in the shape of a T-shaped protrusion, and each of the first ribs or the second ribs is located between two adjacent recesses.

[0015] As one of the preferred embodiments, at the end of the encapsulation operation, the lead frame will first remove the encapsulation colloid distributed and coated on the lead frame by laser cutting, so that the vertical wall surfaces of the pins, the first connecting rib and the second connecting rib are exposed.

[0016] As one of the preferred embodiments, at the end of the encapsulation operation, the lead frame will remove the second connecting rib through a cutting operation, and the cutting area of this cutting operation also covers the distribution area of the first rib.

[0017] Compared with the prior art, the lead frame structure of the present utility model forms the protruding first ribs and the second ribs on the same side surface of the first connecting rib and the second connecting rib, and is distributed around the recesses. In this way, not only the strength of the area where the recesses are located is increased, but also the overall strength of the lead frame is increased, reducing the deformation of packaging processes such as wire bonding. In addition, since the first rib is not connected to the pin, the subsequent cutting operation after encapsulation can first use laser cutting to accurately control the depth dimension and flat surface of the stepped structure. And because no tool is used in this step, it can reduce the generation of burrs and also reduce the subsequent problem of solder bridging. Finally, when singulating, only a tool is used for one-time cutting, which can also reduce the loss of the singulating tool, so the service life of the tool is increased. Description of the Drawings

[0018] Figure 1 It is a perspective view of a conventional lead frame.

[0019] Figure 2 It is a partial enlarged view of a conventional lead frame.

[0020] Figure 3 It is a perspective view of the first embodiment of the lead frame of the present utility model.

[0021] Figure 4 It is a partial enlarged view of the first embodiment of the lead frame of the present utility model.

[0022] Figure 5 It is a partial enlarged view of the second embodiment of the lead frame of the present utility model.

[0023] Figure 6 It is a partial enlarged view of the third embodiment of the lead frame of the present utility model.

[0024] Figure 7 It is a partial enlarged view of the fourth embodiment of the lead frame of the present utility model.

[0025] Figure 8It is a partially enlarged view of the fifth embodiment of the lead frame of the present utility model.

[0026] Figure 9 It is a bottom view of the encapsulated lead frame of the present utility model.

[0027] Figure 10 It is a schematic diagram of laser cutting of the encapsulated lead frame of the present utility model.

[0028] Figure 11 It is a schematic plan view of the encapsulated lead frame of the present utility model after singulation.

[0029] Main reference numeral description:

[0030] 10: Lead frame 11: Chip seat

[0031] 12: Pin 13: First connecting rib

[0032] 14: Second connecting rib 15: Recess

[0033] 16: Rib 20: Lead frame

[0034] 21: Chip seat 22: Pin

[0035] 23: First connecting rib 24: Second connecting rib

[0036] 25: Recess 26: First rib

[0037] 27: Second rib 30: Encapsulation colloid

[0038] 50: Semiconductor component. Detailed implementation manners

[0039] Next, the technical solution of the present utility model will be clearly and completely described in conjunction with specific embodiments and the accompanying drawings. It should be noted that when a component is referred to as being "mounted on or fixed to" another component, it means that it can be directly on the other component or there may also be an intermediate component. When a component is considered to be "connected" to another component, it means that it can be directly connected to the other component or there may be an intermediate component at the same time. In the illustrated embodiments, directions such as up, down, left, right, front, and back are relative and are used to explain the relative structures and movements of different components in this case. When the components are in the positions shown in the figures, these representations are appropriate. However, if the description of the component positions changes, then it is considered that these representations will also change accordingly.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this utility model belongs. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit this utility model. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0041] As Figure 3 and Figure 4 shown, the figures are a perspective view and a partial enlarged view of the lead frame structure of this utility model. The lead frame 20 of this utility model is made of metal and includes at least one chip seat 21, several pins 22 distributed around the chip seat 21, a first connecting rib 23 connected to the corresponding pins 22, and a second connecting rib 24 connected to a plurality of first connecting ribs 23. The thickness of the first connecting rib 23 and the second connecting rib 24 is less than the thickness of the pins 22. In this embodiment, the thickness is only one-half of the thickness of the pins 22. In addition, the first connecting rib 23 is also connected between two corresponding pins 22. A concave portion 25 is formed on the side wall at the junction of the first connecting rib 23 and the second connecting rib 24. In this example, concave portions 25 with reduced dimensions are formed at the four corners of the junction of the first connecting rib 23 and the second connecting rib 24. The adjacent two concave portions 25 reduce the width of the first connecting rib 23 or the second connecting rib 24 at that location. The purpose of the concave portion 25 is to reduce burrs generated during the cutting operation after encapsulation.

[0042] In the traditional lead frame, the metal strength is likely to be reduced at the distribution areas of multiple concave portions. To improve this phenomenon, the key point of this design of this utility model is that: there is a raised first rib portion 26 on the surface of the first connecting rib 23 and the first rib portion 26 does not contact the pins 22. There is a raised second rib portion 27 on the surface of the second connecting rib 24. The first rib portion 26 and the second rib portion 27 are on the same side of the lead frame 20 and are distributed around the concave portion 25, thereby increasing the strength of the distribution area of the concave portion 25 and reducing the deformation of packaging processes such as wire bonding. Also, due to the existence of the first rib portion 26 and the second rib portion 27, the strength of the first connecting rib 23 and the second connecting rib 24 is increased, synchronously increasing the strength of the overall lead frame 20. In addition, the pins 22 are only connected to the first connecting rib 23 and the first rib portion 26 does not contact them. Therefore, the depth dimension and flat surface of the stepped structure can be precisely controlled by laser cutting first. Thus, during subsequent electroplating of the tin layer and singulation operation, burr generation and solder bridging problems can be reduced. In addition, the second connecting rib 24 of the lead frame 20 of this utility model will be removed during the final singulation operation. The cutting area of this cutting operation also covers all the distribution areas of the first rib portion 26 and most of the first connecting rib 23.

[0043] The metal lead frame 20 of this utility model forms the first connecting rib 23 and the second connecting rib 24 by semi-etching, and the first rib portion 26 and the second rib portion 27 are retained on the corresponding surfaces during the etching operation. AsFigure 4 As shown in the figure, in the first embodiment of the present utility model, although the first rib 26 and the second rib 27 are adjacent to each other, they do not contact each other. The first rib 26 is a strip-shaped protrusion, and the strip distribution direction is the same as that of the first connecting rib 23. The second rib 27 is also a strip-shaped protrusion, and the strip distribution direction is the same as that of the second connecting rib 24.

[0044] As Figure 5 Shown is a partially enlarged view of the second embodiment of the lead frame of the present utility model. In this embodiment, most of the structures of the lead frame 20 are the same as those of the above embodiment. The main structure is still that the first rib 26 with a protrusion is on the surface of the first connecting rib 23 and the first rib 26 does not contact the lead 22. The second rib 27 with a protrusion is on the surface of the second connecting rib 24. The difference is that although the first rib 26 is a strip-shaped protrusion, the strip distribution direction is the same as that of the second connecting rib 24. In this embodiment, there are several first ribs 26 symmetrically distributed on both sides of the second connecting rib 24 on the surface of the first connecting rib 23. Additionally, at least one first rib 26 is located in the area with the minimum width of the first connecting rib 23. There are recesses 25 on both symmetric positions on both sides of the second rib 27, thereby preventing the recesses 25 from deforming during processes such as wire bonding, and also increasing the overall strength of the lead frame 20 and reducing the loss of the singulation tool.

[0045] As Figure 6 Shown is a partially enlarged view of the third embodiment of the lead frame of the present utility model. In this embodiment, most of the structures of the lead frame 20 are the same as those of the first embodiment. The main structure is still that the first rib 26 with a protrusion is on the surface of the first connecting rib 23 and the first rib 26 does not contact the lead 22. The second rib 27 with a protrusion is on the surface of the second connecting rib 24. The first rib 26 is a strip-shaped protrusion, and the strip distribution direction is the same as that of the first connecting rib 23. The difference is that the second rib 27 is distributed on the surface of the second connecting rib 24 in a long strip protrusion shape and also connects to a plurality of first connecting ribs 23. In this way, the length of the protrusion of the second rib 27 is longer, and it can also achieve the purpose of preventing the recesses 25 from deforming during processes such as wire bonding, and also increasing the overall strength of the lead frame 20 and reducing the loss of the singulation tool.

[0046] As Figure 7 Shown is a partially enlarged view of the fourth embodiment of the lead frame of the present utility model. In this embodiment, most of the structures of the lead frame 20 are the same as those of the first embodiment. The main structure is still that the first rib 26 with a protrusion is on the surface of the first connecting rib 23 and the first rib 26 does not contact the lead 22. The second rib 27 with a protrusion is on the surface of the second connecting rib 24. The difference is that the first rib 26 and the second rib 27 are connected to form an L-shaped rib. In this embodiment, there are four groups of L-shaped ribs formed, distributed in an equiangular ring shape, so that each first rib 26 or second rib 27 is located between two adjacent recesses 25 to increase the strength of the distribution area of the recesses 25.

[0047] AsFigure 8 As shown, it is a partially enlarged view of the fifth embodiment of the lead frame of the present utility model. In this embodiment, most of the structures of the lead frame 20 are the same as those of the first embodiment. The main structure is still that the first rib portion 26 with protrusions is formed on the surface of the first connecting rib 23 and the first rib portion 26 does not contact the lead 22, and the second rib portion 27 with protrusions is formed on the surface of the second connecting rib 24. The difference is that the first rib portion 26 and the second rib portion 27 are connected to each other and form a T-shaped rib portion. In this embodiment, two sets of T-shaped rib portions are formed and are symmetrically distributed. Each of the first rib portion 26 or the second rib portion 27 is located between two adjacent recesses 25, so as to increase the strength of the distribution area of the recesses 25.

[0048] Next, an explanation will be made on the singulation operation performed on the lead frame 20 of the present utility model after die bonding, wire bonding, and encapsulation. As Figure 9 shown, it is a bottom view of the encapsulated lead frame. The area indicated by the central imaginary line in the figure is the final forming area of a single semiconductor component 50. In this figure, the encapsulation colloid 30 has been coated on the lead frame 20. The chip seat 21 of the lead frame 20 is provided with a chip and has been wire-bonded and electrically connected to the corresponding lead 22. This part is the same as the prior art and will not be described again. In the figure, because the encapsulation colloid 30 has been encapsulated above the lead frame 20, only the chip seat 21, the lead 22, the first rib portion 26, and the second rib portion 27 are exposed on the bottom surface of the lead frame 20.

[0049] As Figure 10 shown, since the first rib portion 26 in the present utility model is not connected to the lead 22, the encapsulation colloid 30 covering the first connecting rib 23 and the second connecting rib 24 can be removed by laser cutting in the present utility model. Laser cutting can restore the vertical wall surface of the lead 22, the surfaces of the first connecting rib 23 and the second connecting rib 24 to the smooth flatness during the etching operation. Compared with the existing structure, because the first cutting must be performed with a tool, its depth accuracy and flatness are both worse than those of the present utility model. Then electroplating can be carried out to form a tin layer on the exposed surfaces everywhere, such as the surfaces of the chip seat 21, the lead 22, the first connecting rib 23, and the second connecting rib 24.

[0050] As Figure 11As shown, the lead frame 20 is completely cut off using a cutting tool. At this time, the second connecting rib 24 and the second rib portion 27 thereon, most of the first connecting rib 23 and all the first rib portions 26 thereon, and all the encapsulated encapsulation colloid 30 are simultaneously removed, thereby forming an individual semiconductor component 50. Only the chip seat 21, several pins 22 distributed around it, and a small part of the first connecting rib 23 are left at the bottom of the semiconductor component 50. Since the first cutting of the present utility model uses a laser, there is no burr generation, and subsequent electroplating will not have tin adhering to the burr surface, causing the problem of tin connection between adjacent pins 22. Therefore, when completely cutting off, due to the relationship of the concave portion 25, it is not easy to have the problem of tin being stretched and diffused to cause a short circuit of tin connection, thereby making the yield of the finished product higher.

[0051] In summary, the lead frame structure of the present utility model forms the raised first rib portion 26 and the second rib portion 27 on the first connecting rib 23 and the second connecting rib 24 of each lead frame 20. And because the first rib portion 26 or the second rib portion 27 is located between two adjacent concave portions 25, thereby increasing the strength of the lead frame 20 in the distribution area of the concave portion 25, avoiding deformation during packaging operations such as wire bonding, and being able to increase the strength of the overall lead frame. In the subsequent singulation operation after packaging, first cut with a laser, and then cut off at one time, so that the accuracy of singulation can be maintained, burrs can be avoided, the problem of tin bridging can be reduced, and the tool loss can also be reduced by only one cut.

[0052] The above are only the preferred embodiments of the present utility model and are not used to limit the scope of the embodiments of the present utility model. That is, all equivalent changes and modifications made within the scope of the present utility model are covered by the protection scope of the present utility model.

Claims

1. A lead frame structure, comprising: At least one chip seat, a plurality of pins distributed around the chip seat, a first connecting rib connected to the corresponding pins, and a second connecting rib connected to the plurality of the first connecting ribs, wherein the first connecting rib and the second connecting rib also form a recessed portion at the side wall where they are connected, characterized in that: the surface of the first connecting rib has a raised first rib and the first rib does not contact the pins, the surface of the second connecting rib has a raised second rib, the first rib and the second rib are located on the same side of the lead frame and are distributed around the recessed portion.

2. The lead frame structure according to claim 1, characterized in that: The first rib portion and the second rib portion are adjacent to each other but not in contact with each other.

3. The lead frame structure according to claim 2, characterized in that: The first rib is protruding in strip shape, and the strip distribution direction is the same as that of the first connecting rib. The second rib is protruding in strip shape, and the strip distribution direction is the same as that of the second connecting rib.

4. The lead frame structure according to claim 2, characterized in that: The first rib and the second rib are both strip-shaped protrusions, and the strip distribution direction is the same as that of the second connecting rib.

5. The lead frame structure according to claim 4, characterized in that: The first ribs have a plurality of first ribs symmetrically distributed on the surface of the first connecting rib on both sides of the second connecting rib.

6. The lead frame structure according to claim 2, wherein: The second ribs are distributed on the surface of the first connecting ribs in the shape of long protrusions and are also connected to a plurality of the second connecting ribs.

7. The lead frame structure according to claim 1, wherein: The first rib is connected to the second rib and is in an L-shaped protrusion. Each of the first rib or the second rib is located between two adjacent recesses.

8. The lead frame structure according to claim 1, wherein: The first rib is connected to the second rib and is in a T-shaped protrusion. Each first rib or second rib is located between two adjacent recesses.

9. The lead frame structure according to any one of claims 1 to 8, characterized in that: At the end of the packaging operation, the lead frame is firstly cut by laser to remove the packaging colloid distributed and coated on the lead frame, so that the vertical wall surface of the lead, the first connecting rib and the second connecting rib are exposed.

10. The lead frame structure according to any one of claims 1 to 8, characterized in that: The lead frame will be cut off at the end of the packaging operation to remove the second connecting rib, and the cutting area of ​​this cutting operation also covers the first rib distribution area.

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