TO-94 lead frame and packaging structure thereof

Abstract

The utility model relates to a TO-94 lead frame and a packaging structure thereof, the lead frame comprises an outer frame, a plurality of packaging units are arranged in the outer frame, each packaging unit comprises a base island, a first pin and a second pin, the top end of the second pin is provided with a supporting part, a coining part and an enclosure frame, the supporting part leads the coining part to the base island, the supporting part is provided with a limiting convex part, and the limiting convex part is arranged on the enclosure frame. The limiting protruding part is a protrusion perpendicular to the horizontal plane, the surrounding frame is arranged on the periphery of the coining part in a surrounding mode, a buffering groove is formed between the surrounding frame and the coining part, the two ends of the surrounding frame extend towards the supporting part and are connected with the corresponding sides of the supporting part, and a weak joint is formed at the joint of the surrounding frame and the supporting part. According to the technical scheme of the TO-94 lead frame and the packaging structure thereof, the plastic deformation of the coining part of the second pin can be limited within a certain range without enlarging the distance between the pins and without the help of a coining mold, and the deformation range of the coining part during coining is controllable.

Description

TECHNICAL FIELD

[0001] The utility model relates to power module technical field more specifically, it is TO -94 lead frame and its packaging structure. BACKGROUND

[0002] TO -94 lead frame is a kind of metal frame structure commonly used in small and medium power semiconductor device packaging, usually by copper alloy stamping, using TO standard appearance design, form low cost, good heat dissipation discrete device after injection molding packaging, it is mostly used in consumer electronics and industrial control field.

[0003] TO -94 lead frame is composed of several packaging units, the characteristic of each packaging unit is with 4 pins and center base island, wherein, part pin is independent pin, in this way, with the announcement number for CN204809213U, the patent name "TO -94 power integrated circuit packaging structure" of China is example, it includes multiple independent packaging units, and the packaging unit includes first frame carrier stage, second frame carrier stage, inner lead welding part and lead pin assembly;Lead pin assembly includes first pin, second pin, third pin and fourth pin, first frame carrier stage is connected with first pin, second frame carrier stage is connected with fourth pin, second pin and third pin are arranged in the avoidance area formed between first frame carrier stage and second frame carrier stage, and are fixedly connected with inner lead welding part.

[0004] The top end of pin is formed into precision pressing area by precision pressing, makes surface height planarization, eliminates cutting burr and forms dense metal base, provides ideal interface for subsequent electroplating even adhesion.

[0005] However, traditional precision pressing process has inherent defects, when implementing high-pressure stamping, the material of pin end often produces unexpected plastic deformation, specifically, non-uniform thinning in thickness direction and expansion in radial direction, if the deformation amount exceeds the critical value, it will cause the profile distortion of pin top end, cause adjacent pin interference, and induce micro-cracks to reduce the structural strength of pin, and when executing electroplating process, it will lead to uneven distribution of plating layer, seriously affect product yield, to solve the problems of pin profile deformation interference, crack defects and plating uniformity caused by precision pressing process.

[0006] Conventional solutions include ①using the scheme of expanding the spacing between adjacent pins, although this scheme can improve the above-mentioned process defects to some extent, but inevitably leads to the increase of the overall size of lead frame, and further causes the increase of the volume of packaging module in subsequent packaging process;②using corresponding precision pressing die, the deformation range of precision pressing area is limited by the cavity of precision pressing die, but different specifications of lead frame need to develop matching high-precision die separately, and the die needs to be frequently replaced to adapt to product size changes, leading to long development cycle and high manufacturing cost. The utility model discloses a TO-94 lead frame and packaging structure thereof

[0007] In view of the above, in order to overcome the plastic deformation of the top end of the independent pin of the packaging unit of the existing TO94 lead frame during precision stamping, the conventional method of expanding the pin spacing will cause the increase of the overall size of the lead frame and the increase of the volume of the packaging module, and the use of precision mold has the problems of long research and development cycle and high manufacturing cost, the purpose of the utility model is to provide a TO-94 lead frame and packaging structure thereof without expanding the pin spacing and without the aid of precision mold, the plastic deformation of the precision pressing part of the second pin is limited within a certain range, and the deformation range is controllable during precision pressing.

[0008] In order to achieve the above purpose, the technical solution of the utility model is:

[0009] A TO-94 lead frame, comprising an outer frame, a plurality of packaging units arranged inside the outer frame, the packaging unit comprising a base island, a first pin and a second pin, the two ends of the first pin are connected to the outer frame and the base island respectively, the second pin is an independent pin, the bottom end of which is connected to the outer frame, and the top end of which extends to the base island, the first pin and the second pin are connected in series through a connecting rib, the top end of the second pin has a support part, a precision pressing part and a surrounding frame, the support part guides the precision pressing part to the base island, and the support part has a limiting protrusion, the limiting protrusion is a protrusion perpendicular to the horizontal plane, the surrounding frame is arranged around the outer periphery of the precision pressing part and forms a buffer groove between the surrounding frame and the precision pressing part, the two ends of the surrounding frame extend to the support part and are connected to the corresponding side of the support part, and a weak joint is formed at the joint of the surrounding frame and the support part.

[0010] Preferably, the thickness of the surrounding frame is smaller than that of the precision pressing part.

[0011] Preferably, the outer edge of the surrounding frame is provided with a avoiding opening.

[0012] Preferably, the center axes of the avoiding openings of the adjacent surrounding frames are staggered on the radial plane of the surrounding frame.

[0013] Preferably, the weak joint comprises a sink, and the sink is distributed on the lateral joint position of the surrounding frame and the support part.

[0014] Preferably, the weak joint further comprises a fracture zone, the fracture zone is located on the top joint position of the surrounding frame and the support part, and is arranged along the width direction of the surrounding frame and communicates with the sink.

[0015] Preferably, the cross-sectional shape of the fracture zone is triangular.

[0016] Preferably, the outer wall of the limiting protrusion is provided with a glue injection hole, and the glue injection hole penetrates through at least two side walls of the limiting protrusion.

[0017] The packaging structure comprises the TO-94 lead frame, and further comprises a plastic sealing shell, wherein the inside of the plastic sealing shell is provided with a receiving cavity corresponding to the limiting protrusion, the receiving cavity is matched with the shape of the limiting protrusion, and the limiting protrusion is embedded in the receiving cavity.

[0018] Compared with the prior art, the packaging structure has the advantages that:

[0019] The top end of the second pin in the TO-94 lead frame has a support part, a precision pressing part and a frame, the frame surrounds the outer periphery of the precision pressing part and is spaced apart from the precision pressing part, a hollow buffer groove is formed between the frame and the outer edge of the precision pressing part, the precision pressing part produces plastic deformation under high pressure, specifically, the thickness direction is thinned and the radial direction is expanded, the buffer groove provides a space for the deformation of the precision pressing part, the frame forms a deformation constraint boundary, the plastic deformation of the precision pressing part is controlled within the space range defined by the buffer groove, the deformation of the precision pressing part is controllable during precision pressing, the interference risk caused by the deformation of adjacent second pins is eliminated, the generation of micro cracks is reduced, the structural strength of the pin is improved, the thickness distribution of the plating layer is uniform during the subsequent electroplating process, in addition, the technical defect that the distance between adjacent second pins must be increased in the traditional solution is overcome, thereby maintaining the compactness of the overall structure of the lead frame, meeting the miniaturization requirement of the packaging module, and the entire precision pressing process does not depend on the cooperation of high-precision molds, significantly shortens the research and development cycle, and reduces the manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the overall structure of the TO-94 lead frame of the utility model;

[0021] Figure 2 is a schematic diagram of the overall structure of one of the packaging units of the TO-94 lead frame of the utility model (after precision pressing and frame cutting);

[0022] Figure 3 is a schematic diagram of the overall structure of one of the packaging units of the TO-94 lead frame of the utility model (before precision pressing);

[0023] Figure 4 is a schematic diagram of the local structure of the top end of the second pin of the packaging unit of the TO-94 lead frame of the utility model before precision pressing (the arrow is the plastic deformation direction of the precision pressing part during subsequent precision pressing);

[0024] Figure 5 is a schematic diagram of the local cross-sectional structure of the precision pressing part of the second pin and the frame of the packaging unit of the TO-94 lead frame of the utility model in a side view state;

[0025] Figure 6 is an enlarged structure schematic diagram of A of the utility model Figure 3 ;

[0026] Figure 7 is a partial sectional structure schematic diagram of the second pin supporting part of the TO-94 lead frame packaging unit of the utility model;

[0027] Figure 8 is a sectional structure schematic diagram of the packaging module with the TO-94 lead frame of the utility model;

[0028] Figure 9 is the B part enlarged structure schematic diagram of the utility model Figure 8 .

[0029] As shown in the figure:

[0030] 100, outer frame; 200, packaging unit; 21, base island; 22, first pin; 23, second pin; 231, supporting part; 231a, limiting convex part; 231b, glue injection hole; 232, fine pressing part; 233, surrounding frame; 233a, avoiding opening; 234, buffer groove; 235, weak knot; 235a, sink opening; 235b, fracture zone; 24, connecting rib; 300, plastic packaging shell; 31, accommodating cavity. Specific implementation

[0031] In order to make the purpose, technical scheme and advantage of the present application more clear, the technical scheme in the present application and how the technical scheme in the present application solves the above technical problems will be described clearly and completely below in specific examples and combined with the drawings in the present application. Obviously, the described examples are part of the examples of the present application, not all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] In the description of the present application, it should be explained that, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or indirect connection through intermediate medium, or the internal communication of two elements or the interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation to the present application.

[0034] The terms "first", "second", "third", "fourth", and the like in the description and in the claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the use of the so-called positive coordinates, where appropriate, can be interchanged, such that the embodiments described herein could be carried out in sequences other than the ones shown or described herein.

[0035] In the embodiments of the present application, the words "exemplary" and "for example" are used to mean example, by way of illustration or demonstration. Any embodiment or design scheme described as "exemplary" or "for example" in the present application should not be construed as being more preferred or having more advantages than other embodiments or design schemes. Rather, the use of "exemplary" or "for example" is intended to present the relevant concept in a specific manner.

[0036] As mentioned in the background, the TO-94 lead frame is composed of a plurality of packaging units 200, each packaging unit 200 corresponds to a 4-pin and center base island 21, the pin includes an independent pin, the top of the independent pin is formed into a precision pressing area through a precision pressing process, the surface of the precision pressing area is flattened compared to other parts of the pin, and the cutting burr is eliminated to form a dense metal base, which provides an ideal interface for uniform adhesion of subsequent electroplating. However, the traditional precision pressing process has inherent defects. When high-pressure stamping is performed, the material at the end of the pin often produces unintended plastic deformation, which is specifically manifested as non-uniform thinning in the thickness direction and uncontrollable expansion in the radial direction, causing distortion of the top end profile of the pin. If the deformation exceeds a critical value, it will cause interference between adjacent pins and induce micro cracks to reduce the structural strength of the pin. At the same time, when the electroplating process is performed, it will lead to uneven distribution of the plating layer, which seriously affects the product yield. In view of the above problems, the conventional solutions include using a scheme to expand the spacing between adjacent pins or using a precision pressing die to form a precision pressing area. However, the increase of the spacing between adjacent pins will inevitably lead to an increase in the overall size of the lead frame, which in turn causes an increase in the volume of the packaging module in the subsequent packaging process. In addition, the precision pressing die needs to be developed separately according to different specifications of the lead frame, which is difficult to adapt to changes in product size and will lead to a long research and development cycle and a significant increase in manufacturing cost.

[0037] As shown in Figure 1 Based on this, the present application provides a TO-94 lead frame, which includes an outer frame 100, the inside of the outer frame 100 has a plurality of packaging units 200, the packaging units 200 are divided into two rows and arranged in sequence along the length direction of the outer frame 100, the number of packaging units 200 in each row is an even number, and in this case, a TO-94 lead frame including 12 packaging units 200 in each row is taken as an example. The outer frame 100 provides support for each packaging unit 200 and maintains the mechanical strength of the entire lead frame.

[0038] As shown in Figure 2 andFigure 3 As shown, the packaging unit 200 is composed of the base island 21, the first pin 22 and the second pin 23, the surface of the base island 21 is formed with a metal plating layer through an electroplating process, the plating layer is preferably a silver layer or a nickel-containing composite layer, which is configured according to the requirements of the welding process, and provides a metallurgical bonding interface required for welding for the chip, ensures the welding strength and has good heat conduction performance, the number of the first pin 22 is 1, in this embodiment, the two ends of the first pin 22 are defined as the first end and the second end respectively, the first end is the bottom end fixedly connected to the outer frame 100, and the second end is the top end extending to the base island 21 and connected thereto, which provides support and positioning for the base island 21, so that the base island 21 is kept in the internal space defined by the outer frame 100, and the relative position accuracy with the outer frame 100 is ensured, and the packaging requirements are met.

[0039] As shown in Figure 2 and Figure 3 The second pin 23 is an independent pin, and the number is 3, the second pin 23 has a first end and a second end distributed along the length direction thereof, and the first end and the second end constitute two end portions of the second pin 23 respectively, in order to distinguish from the end portion definition of the first pin 22, in this embodiment, the first end of the second pin 23 is defined as the bottom end, which refers to the end portion connected to the outer frame 100, and the second end is defined as the top end, which refers to the end portion extending to the base island 21, so as to be independent of the definition of the end portion of the first pin 22 but keep consistent with the structural logic;

[0040] As shown in Figure 2 to Figure 4As shown, the top end of the second pin 23, i.e. the second end of the second pin 23 has a support part 231, a precision pressing part 232 and a surrounding frame 233, the support part 231 is directly connected to the main body part of the second pin 23, which is an axial extension of the main body part of the second pin 23, the precision pressing part 232 is used to bear the precision pressing load, which is connected to the side of the support part 231 away from the main body part of the second pin 23, the precision pressing part 232 is directed to the base island 21 through the support part 231, the support part 231 has a limiting protrusion 231a, which is a protrusion perpendicular to the horizontal plane, thereby increasing the wall thickness dimension of the support part 231, thereby compensating for the loss of structural strength of the precision pressing part 232 due to thickness thinning during precision pressing, the surrounding frame 233 surrounds the outer periphery of the precision pressing part 232 and is spaced apart from the precision pressing part 232, the hollow buffer groove 234 is formed between the outer edge of the surrounding frame 233 and the precision pressing part 232, the two ends of the surrounding frame 233 extend towards the support part 231 and form a bend at the position opposite to the support part 231, which is connected to the corresponding side of the support part 231, so that the end of the buffer groove 234 is closed, when the second end of the second pin 23 is precision pressed, the precision pressing part 232 plastically deforms under high pressure, which is manifested as thickness thinning and radial expansion, the buffer groove 234 provides space for the deformation of the precision pressing part 232, and the surrounding frame 233 constitutes a deformation constraint boundary, which controls the plastic deformation of the precision pressing part 232 within the spatial range defined by the buffer groove 234, ensuring that the deformation of the precision pressing part 232 is controllable during precision pressing, eliminating the risk of interference between adjacent second pins 23 due to deformation, reducing the generation of micro cracks, improving the structural strength of the pin, ensuring uniform thickness distribution of the plating layer during subsequent electroplating process, in addition, it overcomes the technical defect that the distance between adjacent second pins 23 must be increased in the traditional solution, thereby maintaining the compactness of the overall structure of the lead frame, meeting the miniaturization needs of the packaging module, and the entire precision pressing process does not rely on the cooperation of high-precision molds, significantly shortening the development cycle and reducing manufacturing costs;

[0041] As shown in Figure 4 and Figure 6 As shown, the junction of the surrounding frame 233 and the support part 231 has a weak section 235, which can be understood as a mechanically weakened area formed by local thinning or width reduction of the connection between the surrounding frame 233 and the support part 231, the weak section 235 makes the surrounding frame 233 easy to separate from the support part 231 by cutting or breaking, so that the surrounding frame 233 can be quickly separated from the support part 231 by mechanical cutting or breaking during the packaging process, avoiding spatial interference of the surrounding frame 233 during subsequent packaging;

[0042] As shown in Figure 2 and Figure 3As shown, the first pin 22 and each of the second pins 23 are connected to each other by a connecting rib 24. The connecting rib 24 extends along the length of the outer frame 100, connecting each package unit 200 in series and fixing it inside the outer frame 100.

[0043] like Figure 5 As shown, further, in order to protect the frame 233 from high-pressure impact during the fine pressing process, in one embodiment, the thickness of the frame 233 is less than that of the fine pressing part 232, thereby forming a thickness gradient between the fine pressing part 232 and the frame 233. By utilizing this thickness difference, it is ensured that the pressure load is accurately applied to the fine pressing part 232 during the fine pressing process, and the frame 233 in the non-fine pressing area is prevented from undergoing plastic deformation and occupying the space corresponding to the buffer groove 234.

[0044] like Figure 3 and Figure 4 As shown, further, during the precision pressing process, in order to address the issue of slight plastic deformation caused by the high-pressure impact on the frame 233, in one real-time mode, a clearance opening 233a is provided on the outer edge of the frame 233. The central axes of adjacent clearance openings 233a are staggered on the radial plane of the frame 233. The shape of the clearance openings 233a includes, but is not limited to, geometric features such as arcs and rectangles. It can be understood that the parts of the frame 233 on both sides of the clearance opening 233a protrude towards the adjacent frame 233 relative to the clearance opening 233a. Through the staggered clearance openings 233a, when the high-pressure load is applied to the frame 233 during the precision pressing process, the protruding parts preferentially undergo directional plastic deformation towards the clearance opening 233a area of ​​the adjacent frame 233. At the same time, the main body of the frame 233 synchronously undergoes compensating deformation towards the interior of the clearance opening 233a, thereby effectively controlling the deformation direction of the frame 233 and preventing interference between adjacent frames 233 during plastic deformation.

[0045] like Figure 4 and Figure 6 As shown, the weak section 235 includes a countersunk opening 235a. In this embodiment, the countersunk openings 235a are symmetrically distributed on the lateral joint of the frame 233 and the support 231. The width of the joint is reasonably reduced by the countersunk openings 235a. When the joint is subjected to shear load, a stress concentration area is formed at the countersunk openings 235a, causing the frame 233 to break along this position, realizing rapid separation from the support 231 and avoiding spatial interference caused by the frame 233 during subsequent encapsulation.

[0046] like Figure 4 and Figure 6As shown, the weak joint 235 also includes a fracture zone 235b located on the joint between the frame 233 and the top of the support portion 231 and arranged along the width direction of the frame 233, and in communication with the sink 235a distributed on both sides. The fracture zone is a weak connection area formed on the joint between the frame 233 and the support portion 231, which can effectively concentrate stress and promote the directional fracture of the frame 233 along the fracture zone 235b when the joint is subjected to shear load, thereby achieving the rapid and controllable separation of the frame 233 and the support portion 231 and significantly improving the fracture response speed.

[0047] Further, the cross-sectional shape of the fracture zone 235b is triangular, and when the joint between the support portion 231 and the frame 233 is subjected to shear load, stress is concentrated at the bottom area of the fracture zone 235b, thereby accelerating the initiation of fracture and improving the fracture response speed.

[0048] As shown in Figure 7 The outer wall of the limiting protrusion 231a is provided with a glue injection hole 231b, which is in communication with at least two side walls of the limiting protrusion 231a. In the subsequent packaging process, the glue liquid passes through the glue injection hole 231b, and after the glue liquid is solidified, it forms an interlock with the limiting protrusion 231a, thereby enhancing the bonding strength of the limiting protrusion 231a and the entire second pin 23 with the packaging material.

[0049] As shown in Figure 8 and Figure 9 In addition, the application provides a packaging structure, which comprises the lead frame described above, and further comprises a plastic package shell 300. The plastic package shell 300 has a receiving cavity 31 corresponding to the limiting protrusion 231a in the interior. The receiving cavity 31 matches the shape of the limiting protrusion 231a, and the limiting protrusion 231a is embedded in the receiving cavity 31. In the embedded state, the limiting protrusion 231a and the receiving cavity 31 form an interlock, which effectively limits the axial, radial displacement and deflection of the pin in the plastic package shell 300, ensures that the second pin 23 and the plastic package shell 300 remain stable for a long time, and prevents the second pin 23 from separating in a mechanical vibration environment after packaging.

[0050] It should be understood that the various forms of the flow shown above can be reordered, added or deleted steps. For example, the steps described in the present application can be executed in parallel, in sequence or in different order, as long as the desired results of the technical solutions of the present application can be achieved, which is not limited herein.

[0051] The above embodiments and descriptions described only illustrate the principles and the best embodiments of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed application.

Claims

1. A TO-94 lead frame, comprising an outer frame (100), wherein a plurality of packaging units (200) are arranged inside the outer frame (100), the packaging unit (200) comprising a base island (21), a first pin (22) and a second pin (23), wherein the two ends of the first pin (22) are respectively connected to the outer frame (100) and the base island (21), the second pin (23) is an independent pin, the bottom end of which is connected to the outer frame (100) and the top end of which extends toward the base island (21), the first pin (22) and the second pin (23) are connected in series by a connecting rib (24), characterized in that, The top of the second pin (23) has a support portion (231), a pressing portion (232), and a frame (233). The support portion (231) leads the pressing portion (232) toward the base island (21). The support portion (231) has a limiting protrusion (231a), which is a protrusion perpendicular to the horizontal plane. The frame (233) surrounds the outer periphery of the pressing portion (232) and forms a buffer groove with the pressing portion (232). The two ends of the frame (233) extend toward the support portion (231) and are connected to the corresponding side of the support portion (231). A weak joint (235) is formed at the joint between the frame (233) and the support portion (231).

2. A TO-94 lead frame according to claim 1, characterized in that, The thickness of the frame (233) is less than that of the precision pressing part (232).

3. A TO-94 lead frame according to claim 1, characterized in that, An avoidance opening (233a) is provided on the outer edge of the frame (233).

4. A TO-94 lead frame according to claim 3, characterized in that, The central axes of the clearance openings (233a) on opposite sides of the adjacent frame (233) are staggered on the radial plane of the frame (233).

5. A TO-94 lead frame according to claim 1, characterized in that, The weak section (235) includes a countersunk (235a), which is located at the lateral joint of the frame (233) and the support (231).

6. A TO-94 lead frame according to claim 5, characterized in that, The weak section (235) also includes a fracture zone (235b), which is located at the top joint of the frame (233) and the support (231), and is arranged along the width direction of the frame (233) and communicates with the countersunk opening (235a).

7. A TO-94 lead frame according to claim 6, characterized in that, The cross-sectional shape of the fault zone (235b) is triangular.

8. A TO-94 lead frame according to claim 1, characterized in that, An injection hole (231b) is provided on the outer wall of the limiting protrusion (231a), and the injection hole (231b) is connected to at least two side walls of the limiting protrusion (231a).

9. A packaging structure comprising the TO-94 lead frame of any one of claims 1 to 8, characterized in that, It also includes a plastic encapsulated housing (300), the interior of which has a receiving cavity (31) corresponding to the limiting protrusion (231a), the shape of the receiving cavity (31) matching that of the limiting protrusion (231a), and the limiting protrusion (231a) being embedded in the receiving cavity (31).

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