A mold and method for cutting and binding leads of a QFP high pin lead frame

Abstract

The application provides a mold and a method for cutting and binding pins of a QFP high pin lead frame, which solves the technical problems of silver surface abrasion caused by the pressing of a stripper plate and the high cost caused by frequent grinding of a convex mold, and fundamentally eliminates the wire bonding defects caused by abrasion. The mold comprises an upper mold assembly and a lower mold assembly, the upper mold assembly is provided with a stripper plate, a pressing insert mounting hole is formed in the lower surface of the stripper plate, the pressing insert mounting hole corresponds to the pin tip area of the lead frame material belt in the closed mold state, a pressing insert is fixedly installed in the pressing insert mounting hole, and the material of the pressing insert is POM.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, specifically to a mold for cutting and binding leads in a QFP high-pin lead frame. The invention also provides a method for cutting and binding leads in a QFP high-pin lead frame. Background Technology

[0002] The lead frame is a core metal structural component in semiconductor packaging, undertaking critical functions such as chip support, electrical signal transmission, and heat dissipation. Its quality directly determines the reliability and yield of semiconductor devices. QFP (Quad Flat Package), as one of the most widely used packaging forms, has pins extending from four sides, with a maximum number of 64 pins and a pin pitch as small as 0.4mm. It is widely used in high-end chips such as microcontrollers, digital signal processors, and memory.

[0003] QFP high-pin products (pin length to width ratio ≥ 5:1) adopt a standard process flow of "stamping → electroplating → molding". Due to the small cross-sectional area and large length of the pins in high-pin products, resulting in poor rigidity, if the pins are directly cut into independent states during the stamping stage, they are prone to bending and twisting deformation during subsequent roll-up, continuous electroplating, and high-speed molding, leading to product scrap. Therefore, the industry commonly uses a "pin binding" process—retaining connecting ribs (pin bindings) at the pin tips during the stamping stage, connecting all pins into a single unit, significantly improving the strip's resistance to deformation. Before the molding process, a 0.05–0.10 mm thick high-temperature resistant polyimide tape is hot-pressed onto the inner pin area using a tape-applying mold to prevent deformation of the inner pins during subsequent pin binding cutting. The finished lead frame is then obtained through three steps: denting, pin binding cutting, and final cutting.

[0004] Cutting the binding leads is the most critical step in the forming process. Its function is to cut off the binding leads connecting the leads, making the leads independent entities. In this step, the stripper plate also acts as a pressure plate, used to clamp the strip before punching and prevent it from shifting. In traditional mold design, to ensure pressure accuracy and wear resistance, the pressure inserts are made of tungsten carbide (hard alloy). However, in actual production, it has been found that when the tungsten carbide insert clamps the strip, it will slide and rub against the silver plating layer on the lead tips, resulting in obvious black friction marks or damage to the silver layer on the lead tips.

[0005] More seriously, after a certain number of uses, the cutting edge of the punch gradually dulls, and the shearing method for the foot changes from ideal pure shearing to extrusion and tearing. During the return stroke after punching, the burrs generated during the tearing process cause the foot tip to adhere abnormally tightly to the punch sidewall. This causes the punch to move the foot tip upwards, with a displacement of 0.02–0.05 mm. Under the continuous pressure of the stripper plate, the upwardly displaced foot tip experiences intense forced friction and extrusion against the blank holder, drastically increasing the degree of silver surface scratches.

[0006] Silver layer abrasion is one of the most common and difficult defects to resolve in the production of QFP high-pin leadframes. According to industry statistics, this defect causes an average yield loss of approximately 5% to 15%, and for some high-pin-count, fine-pitch products, it can even exceed 20%. Abraded silver layers can lead to insufficient adhesion between the bonding wire and the pin surface during subsequent wire bonding processes, resulting in poor soldering or bonding failure. Furthermore, in high-speed automated bonding equipment, the abnormal surface roughness of the abraded area can easily cause abnormal contact of the bonding wire, resulting in "wire tangling," which interrupts wire bonding and severely reduces production efficiency.

[0007] To address this long-standing industry problem, those skilled in the art have made numerous attempts and improvements, but none have achieved the desired results: 1. Surface treatment solutions for tungsten steel: These include mirror polishing, matte sandblasting, and nitriding. These solutions can only change the microstructure of the tungsten steel surface and cannot change its inherent high hardness and high coefficient of friction; the wear phenomenon is hardly reduced. 2. Blanking and Avoidance Solution for Pressing Position: The pressing position of the unloading plate is cut out and moved backward so that the pressing surface avoids the silver surface area of ​​the lead tip. Although this solution can avoid direct pressing friction, it will cause the lead tip to lose effective restraint, resulting in obvious upward deformation during punching and stripping. The deformation can reach more than 0.05mm, causing new lead coplanarity defects, which will further reduce the yield. 3. Other hard material solutions: Experiment with using other hard materials such as ceramics and high-speed steel to fabricate the press-fit inserts. These materials have coefficients of friction similar to, or even higher than, tungsten steel, and the wear problem remains unresolved. 4. Coating solution: Deposit a DLC (diamond-like carbon) coating on the surface of the tungsten carbide insert. Although the DLC coating can reduce the coefficient of friction, the adhesion between the coating and the substrate is poor, and it is easy to peel off under repeated pressing and friction. The service life is only 10,000 to 20,000 cycles. Moreover, the coating process is complex and costly, making it difficult to apply on a large scale. 5. Elastic Material Solution: Attempts were made to use elastic materials such as rubber and silicone to manufacture the pressing inserts. However, these materials have too low hardness to provide sufficient pressing force, and their wear resistance is extremely poor, resulting in a service life of less than 1000 cycles, making them completely unsuitable for industrial production. 6. PEEK Material Solution: PEEK (polyetheretherketone) is a high-performance engineering plastic with high strength and wear resistance. While using PEEK to manufacture pressed inserts reduces wear, approximately 7% of products still exhibit slight wear, resulting in a yield rate of only around 93%, which is insufficient for high-end products. Furthermore, PEEK material costs 5-8 times more than POM, making its cost-effectiveness poor.

[0008] Furthermore, regarding the problem of dull punches causing the tip to shift upwards and exacerbate wear, the only current industry solution is frequent grinding of the cutting punch. This requires stopping the machine every 3,000 to 5,000 cycles for re-grinding to restore the cutting edge's sharpness, thereby reducing the upward displacement of the tip and indirectly alleviating wear. However, frequent grinding not only fails to fundamentally eliminate wear but also severely shortens the punch's lifespan, increasing mold maintenance costs and downtime. It is estimated that mold maintenance costs resulting from this measure account for more than 15% of total production costs.

[0009] For a long time, a deep-rooted technical bias has existed in this field: that blanking inserts must be made of high-hardness, high-wear-resistance cemented carbide materials, otherwise they cannot withstand the huge blanking forces and frequent friction during the punching process, leading to a decrease in blanking accuracy and rapid wear of the inserts. Therefore, no one has ever considered using low-hardness engineering plastics to make blanking inserts for the foot-cutting process. Summary of the Invention

[0010] To address the aforementioned problems, this invention provides a mold for cutting and binding feet of QFP high-pin lead frames. It solves the technical problems of silver surface abrasion caused by stripper plate pressing and excessive cost caused by frequent grinding of punches, fundamentally eliminating wire tying defects caused by abrasion.

[0011] A mold for cutting the binding feet of a QFP high-foot lead frame is characterized in that: it includes an upper mold assembly and a lower mold assembly, the upper mold assembly is provided with a stripper plate, the lower surface of the stripper plate is provided with a pressure insert mounting hole, the pressure insert mounting hole corresponds to the tip area of ​​the lead frame strip in the mold closed state, a pressure insert is fixedly installed in the pressure insert mounting hole, and the pressure insert is made of POM.

[0012] Its further features are: The upper mold assembly also includes an upper mold base, an upper backing plate punch fixing base, an ejector plate base, and a cutting and binding punch; the lower mold assembly includes a concave plate and a lower mold base, and the upper mold assembly and the lower mold assembly are connected by guide pillars for guidance and limiting. POM (Polyoxymethylene) is divided into two types: homopolymer POM and copolymer POM. Homopolymer POM has higher strength and hardness, but poorer thermal stability and chemical resistance. Copolymer POM has good thermal stability, low water absorption, and excellent dimensional stability, making it more suitable for precision mold parts. The pressing insert is made of copolymer POM material with a density of 1.41–1.42 g / cm³. 3 The coefficient of dynamic friction with steel is 0.15 to 0.35, and the water absorption rate is 0.22% to 0.25%. Under the temperature and humidity environment of the stamping workshop, the dimensional change is minimal, which can ensure long-term stable pressing accuracy. To further reduce the coefficient of friction and improve self-lubricating performance, the pressure insert is made of lubricated modified POM material. The lubricating modification component is selected from silicone oil or polytetrafluoroethylene (PTFE). After modification, the dynamic friction coefficient of POM against steel can be reduced to 0.15-0.20, resulting in better anti-wear effect. The pressing working surface of the pressing insert corresponds perfectly to the silver surface area of ​​the tip of the lead frame strip in the vertical projection, and the shape of the pressing working surface of the pressing insert matches the shape of the tip area, thereby ensuring uniform force during pressing and avoiding silver layer damage caused by local stress concentration. The Rockwell hardness of the blank holder is in the range of M80-R120, and the flexural modulus is 2500-3000MPa. This hardness and modulus range can provide sufficient blanking force to ensure that the lead frame strip does not shift during the punching process, and also has a certain degree of flexible buffering effect to absorb the impact force generated by the upward displacement of the punch tip during the return stroke and reduce friction. The pressure insert is fixed in the pressure insert mounting hole of the unloading plate by screw connection or press fit. The screw connection method is easy to disassemble and replace, while the press fit method has a simple structure and high positioning accuracy. It can be selected according to actual production needs. The pressure working surface of the pressure insert is recessed by 0.05 to 0.08 mm relative to the unloading plate surface, preferably 0.05 to 0.06 mm. This recess design is another key innovation of the present invention: In multi-product co-molding production, there are slight differences in the thickness of the strip and the height of the leads of different products. If the working surface of the insert is flush with the unloading plate surface, ineffective pressure will occur when switching products, causing copper and silver slag to adhere to the insert surface, which will scratch the silver surface of subsequent products. On the other hand, if the recess is too large, the pressure force will be insufficient and the foot tip cannot be effectively restrained. The recess range of 0.05 to 0.08 mm can ensure that there is enough pressure on the foot tip when the foot-binding punch moves upward after cutting, and can also avoid ineffective pressure and slag adhesion problems after switching to another product. A method for cutting and binding feet of QFP high-pin lead frames is characterized in that: in the foot cutting and binding step of the molding process, a pressure insert made of polyoxymethylene (POM) material is used to press and position the silver surface area of ​​the lead frame material strip at the tip, thereby preventing friction black marks from being generated in the silver surface area at the tip during the pressing process of the stripper plate; and, by setting the pressing working surface of the pressure insert to be recessed relative to the stripper plate surface, ineffective pressing and copper and silver slag adhesion are avoided during the co-molding production of multiple products.

[0013] The core technical principle of this invention lies in: Low friction and self-lubricating properties: POM material has an extremely low coefficient of friction and excellent self-lubricating properties. Its dynamic friction coefficient with steel is only 0.15 to 0.35, which is much lower than that of tungsten steel (0.4 to 0.6). Even when the upward displacement of the punch tip increases after the punch is blunted, the friction between POM and the silver plating layer is still very small. It will not generate enough frictional heat and shear force to damage the silver layer, thus fundamentally eliminating silver surface scratches. Flexible buffering effect: POM has a hardness much lower than tungsten steel and has a certain degree of elasticity and flexibility. When the punch returns and the tip moves upward, the POM insert will produce a small elastic deformation to absorb the displacement and avoid rigid forced friction between the hard insert and the tip of the lead frame strip. Breaking the chain reaction: In existing solutions, punch dulling → tip moving upward → increased wear is a vicious cycle that can only be broken by frequently grinding the punch. However, the POM material blanking insert of this invention can still maintain excellent anti-wear effect after the punch is dulled, thereby breaking this chain reaction and greatly reducing the dependence on the sharpness of the punch cutting edge.

[0014] Compared with the prior art, the present invention has the following significant advantages: 1. Completely eliminate silver surface scratches: POM's low coefficient of friction and self-lubricating properties fundamentally solve the problem of friction and scratches on the silver plating layer caused by tungsten steel materials, increasing the product appearance yield from 85%–95% in traditional solutions to over 99.5%; 2. Significantly extended punch life: By breaking the chain reaction of punch dulling and increased wear, the number of punches that do not require grinding is increased from 3,000-5,000 to over 50,000, reducing mold maintenance costs by over 90%, while also significantly reducing downtime and improving production efficiency; 3. Eliminate wire tying defects: The wire tying rate is reduced from 3% to 8% in traditional solutions to below 0.1%, which significantly improves the yield and efficiency of subsequent packaging processes; 4. Simple structure and low cost: It only requires replacing the traditional tungsten carbide insert with a POM insert, without making any changes to other parts of the mold; the price of POM material is only about 1 / 10 of that of tungsten carbide, and it is easy to process, with the cost of a single insert being less than 10 yuan; 5. Easy to replace and maintain: After the POM material pressure insert wears out, it can be replaced within 10 minutes without the need for professional mold repair personnel; 6. Solve the problem of slag adhesion in common molds: The recessed design of the pressing working surface effectively avoids ineffective pressing and copper and silver slag adhesion during the production of multiple products in common molds, thus improving the versatility of the mold. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the overall structure of the mold of the present invention; Figure 2 is a schematic diagram of the lead frame strip structure; Figure 3 is an enlarged schematic diagram of one unit in Figure 2, and also shows the bottom view of the press insert; Figure 4 is an assembly cross-sectional view of the pressure insert and the unloading plate according to a specific embodiment of the present invention, and the recess amount of the pressure working surface is marked. Figure 5 is a schematic diagram of the process of cutting the foot using the mold of the present invention, which shows the contact state between the foot tip and the blank holder during punching and return stroke. The names corresponding to the serial numbers in the diagram are as follows: 1-Upper mold base; 2-Upper backing plate; 3-Punch fixing plate; 4-Ejector plate base; 5-Ejector plate; 51-Pressure insert mounting hole; 6-Cutting foot punch; 7-Pressure insert; 71-Pressure working surface; 8-Leader frame strip; 81-Pin; 82-Binding foot; 83-Feet; 9-Diaphragm plate; 10-Lower mold base; 11-Guide post. Detailed Implementation

[0016] A mold for cutting lead-binding pins for QFP high-pin lead frames, see Figures 1-5 It includes: an upper mold assembly and a lower mold assembly; The upper mold assembly includes an upper mold base 1, an upper backing plate 2, a punch fixing base 3, a stripper plate base 4, a stripper plate 5, and a foot-cutting punch 6. The lower surface of the stripper plate 5 is provided with a pressure insert mounting hole 51, which corresponds to the tip 83 area of ​​the lead wire frame strip 8 in the mold-closed state. A pressure insert 7 is fixedly installed within the pressure insert mounting hole 51. The material of the pressure insert 7 is POM. The lower mold assembly includes a concave mold plate 9 and a lower mold base 10; The upper mold assembly and the lower mold assembly are connected by guide posts 11 for guidance and limiting.

[0017] In specific implementation, the pressing insert 7 is made of copolymerized polyoxymethylene material with a density of 1.41–1.42 g / cm³. 3 The coefficient of dynamic friction with steel is 0.15 to 0.35, and the water absorption rate is 0.22% to 0.25%. Under the temperature and humidity environment of the stamping workshop, the dimensional change is minimal, which can ensure long-term stable pressing accuracy. In specific implementation, the pressure insert 7 can be made of lubricated modified POM material. The lubricating modification component is selected from silicone oil or polytetrafluoroethylene (PTFE). After modification, the dynamic friction coefficient of POM against steel can be reduced to 0.15 to 0.20, and the anti-wear effect is better.

[0018] In specific implementation, the pressing working surface 71 of the pressing insert 7 and the silver surface area of ​​the foot tip 83 of the lead frame strip 8 are completely corresponding in vertical projection, and the shape of the pressing working surface 71 of the pressing insert 7 matches the shape of the foot tip 83 area, thereby ensuring uniform force during pressing and avoiding silver layer damage caused by local stress concentration. The Rockwell hardness of the blank holder 7 is in the range of M80-R120, and the flexural modulus is 2500-3000MPa. This hardness and modulus range can provide sufficient blank holder force to ensure that the lead frame material 8 does not shift during the punching process, and also has a certain degree of flexible buffering effect, which can absorb the impact force generated by the upward displacement of the tip 83 during the return stroke of the punch and reduce friction.

[0019] The pressure insert 7 is fixed in the pressure insert mounting hole 51 of the unloading plate by means of screw connection or press fit. The screw connection method is easy to disassemble and replace, while the press fit method has a simple structure and high positioning accuracy, and can be selected according to actual production needs.

[0020] In specific implementation, the recessed amount M of the pressing working surface 71 of the pressing insert 7 relative to the unloading plate surface is 0.05~0.08mm, and most preferably 0.05~0.06mm. This recessed amount design is another key innovation of the present invention: In the production of multiple products using a common mold, there are slight differences in the thickness of the strip and the height of the leads of different products. If the working surface 71 of the insert is flush with the surface of the unloading plate 5, ineffective pressing will occur when switching products, causing copper slag and silver slag to adhere to the surface of the insert, which will scratch the silver surface of subsequent products; while if the recessed amount M is too large, it will result in insufficient pressing force and inability to effectively restrain the foot tip; the recessed amount range of 0.05~0.08mm can ensure that there is sufficient pressing amount for the foot tip 83 when the foot binding punch moves upward after cutting, and can also avoid ineffective pressing and slag adhesion problems after switching to another product; A method for cutting and binding leads for QFP high-pin lead frames: In the lead-binding step of the molding process, a pressure insert 7 made of polyoxymethylene (POM) material is used to press and position the silver surface area of ​​the lead frame material strip 8's tip 83, thereby preventing friction black marks from being generated on the silver surface area of ​​the tip 83 during the pressing process of the stripper plate 5; and by setting the pressing working surface 71 of the pressure insert 7 to be recessed relative to the lower surface of the stripper plate 5, ineffective pressing and copper and silver slag adhesion during the co-molding production of multiple products are avoided.

[0021] Specific Implementation Example 1: This example is a 128-pin QFP product. The pin pitch of the 128-pin QFP product is 0.4mm, the pin width is 0.16mm, the copper alloy substrate thickness is 0.127mm, and it is ring-plated with silver with a silver layer thickness of 2.0~5.0μm.

[0022] The manufacturing process of the 128-pin QFP product is as follows: stamping (including pin forming) → roll electroplating silver → inner pin tape bonding (hot pressing 0.07mm high temperature resistant polyimide tape at 180±10℃) → forming (denting → pin cutting → cutting).

[0023] The mold structure is shown in Figures 1 to 5, including an upper mold assembly and a lower mold assembly. The upper mold assembly includes, from top to bottom, an upper mold base 1, an upper backing plate 2, a punch fixing plate 3, a stripper plate base 4, and a stripper plate 5. The lower mold assembly includes, from top to bottom, a concave mold plate 9 and a lower mold base 10. The foot-cutting punch 6 is fixed to the punch fixing plate 3, and its lower end passes through the through hole of the stripper plate 5. The concave mold plate 9 is provided with a die cutting edge that mates with the foot-cutting punch 6.

[0024] The unloading plate 5 has a pressing insert mounting hole 51 at the silver surface area of ​​the tip 83 of the corresponding lead frame strip 8. The pressing insert 7 is fixed in the pressing insert mounting hole 51 by an internal hex screw. The pressing working surface 71 of the pressing insert 7 corresponds completely to the silver surface area of ​​the tip 83 in vertical projection, and the profile matches the shape of the tip area.

[0025] This mold is designed for two products. Initial testing revealed that if the working surface 71 of the insert is flush with the bottom surface of the stripper plate 5, ineffective material pressing occurs with each opening and closing during product switching, resulting in the adhesion of copper and silver slag. Therefore, the insert was machined to reduce its surface area, making the working surface 71 recessed by 0.05mm relative to the bottom surface of the stripper plate 5.

[0026] The press-fit insert 7 is made of Polyplastics POM M90-44 copolymer polyoxymethylene (POM) from Japan, with the following performance parameters: density 1.41 g / cm³. 3Tensile strength 60MPa, flexural modulus 2580MPa, Rockwell hardness M80, coefficient of dynamic friction against steel 0.15, water absorption 0.22%, heat distortion temperature 110℃ (1.82MPa).

[0027] The working cycle of the mold is as follows: Mold closing stage: The upper mold assembly moves downward, the stripper plate 5 first contacts the lead frame strip 8, and the pressure insert 7 presses the silver surface area of ​​the tip 83 with a low coefficient of friction and flexible buffer. Punching stage: After the stripper plate 5 is fully clamped, the foot-cutting punch 6 extends and cooperates with the cutting edge of the die plate 9 to cut off the foot 82; during this process, the POM flexible contact surface of the pressure insert 7 can effectively absorb the impact force generated by the upward displacement of the foot tip 83 when the punch returns, and reduce friction; Mold opening stage: The upper mold assembly moves upward, and the stripper plate 5 is kept in a pressed state under the action of spring force, so that the lead frame strip 8 is separated from the punch. Then the pressure insert 7 is removed from the lead frame strip 8, completing one work cycle.

[0028] Mass production tests show that when using the traditional tungsten carbide insert solution, the cutting edge of the punch begins to dull after 3,000 punching cycles, and the wear phenomenon is significantly aggravated, requiring machine shutdown for grinding and repair. After using the POM material blanking insert of this invention, after 50,000 continuous punching cycles, there are no wear marks on the silver surface of the tip, and the appearance yield is stable at over 99.6%. Wire bonding verification shows that the wire breakage rate is reduced to below 0.08%. The number of punches that do not require grinding reaches 52,000 cycles, the mold maintenance cost is reduced by 92%, the service life of the blanking insert is about 150,000 cycles (wear amount 0.02mm), and the replacement time is about 8 minutes.

[0029] Specific Embodiment Two: This embodiment is for a 100-pin QFP product. The 100-pin QFP product has a pin pitch of 0.6mm, a pin width of 0.2mm, a copper alloy substrate thickness of 0.127mm, and is fully silver-plated with a silver layer thickness of 2.0~5.0μm. The process flow is the same as in Specific Embodiment One.

[0030] The mold structure is basically the same as in Specific Embodiment 1. The pressure insert 7 is made of POM material modified with PTFE lubrication, which has a coefficient of dynamic friction with steel of 0.16, a Rockwell hardness of M85, and a flexural modulus of 2650MPa. The working surface of the pressure insert is recessed by 0.06mm relative to the surface of the unloading plate.

[0031] Mass production tests show that after 55,000 continuous punching cycles, the silver surface of the toe is free of scratches, with an appearance yield of 99.5%; the wire breakage rate is 0.07%; and the number of punch cycles that do not require grinding reaches 51,000.

[0032] Specific Implementation Example 3: This example is for a 64-pin QFP product. The 64-pin QFP product has a pin pitch of 0.8mm, a pin width of 0.33mm, a copper alloy substrate thickness of 0.152mm, and is fully silver-plated with a silver layer thickness of 2.5~7.0μm. The process flow is the same as in Specific Implementation Example 1.

[0033] The mold structure is basically the same as in Specific Embodiment 1. The pressing insert 7 is made of DuPont POM 100P homopolymer polyoxymethylene, with a density of 1.42 g / cm³. 3 It has a Rockwell hardness of R120, a flexural modulus of 2950 MPa, and a coefficient of dynamic friction against steel of 0.30. The pressure working surface 71 of the pressure insert 7 is recessed by 0.08 mm relative to the lower surface of the unloading plate 5.

[0034] Mass production tests show that after 48,000 continuous punching cycles, the silver surface of the 83mm tip is free of scratches, with an appearance yield of 99.7%; the wire breakage rate is 0.09%; and the number of punches that do not require grinding reaches 49,000 cycles.

[0035] Material selection and surface treatment comparison of the press-fit insert: To verify the superiority of the present invention, we conducted comparative tests on various existing technical solutions and materials. The test conditions were the same as in specific embodiment one, and the results are shown in the table below:

[0036] The low yield of the blanking solution for the material pressing position is mainly due to the non-compliance of coplanarity caused by the upward deformation of the pins.

[0037] As can be clearly seen from the table above, the POM insert solution of the present invention is far superior to all other solutions in terms of appearance yield, wire bonding rate and punch life, while the cost is extremely low and the cost-effectiveness is extremely high.

[0038] Of particular note is that when the punch has been punched 50,000 times, the cutting edge has become noticeably dull. Using a traditional tungsten carbide insert solution, the wear yield at this point drops below 60%. However, using the POM insert solution of this invention, the yield remains above 99.5%. This fully demonstrates that this invention can effectively break the chain reaction between punch dulling and accelerated wear, which is impossible with existing technologies.

[0039] In the text, POM is translated into Chinese as engineering plastic (polyoxymethylene).

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0041] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A mold for cutting lead-binding feet in QFP high-pin lead frames, characterized in that: It includes an upper mold assembly and a lower mold assembly. The upper mold assembly is provided with a stripper plate. The lower surface of the stripper plate is provided with a pressure insert mounting hole. The pressure insert mounting hole corresponds to the tip area of ​​the lead frame strip in the mold closed state. A pressure insert is fixedly installed in the pressure insert mounting hole. The material of the pressure insert is POM.

2. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 1, characterized in that: The upper mold assembly also includes an upper mold base, an upper backing plate punch fixing seat, an unloading plate seat, and a cutting and binding punch; the lower mold assembly includes a concave plate and a lower mold base, and the upper mold assembly and the lower mold assembly are connected by guide posts for guidance and limiting.

3. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 1, characterized in that: The press-fit insert is made of copolymerized polyoxymethylene material with a density of 1.41–1.42 g / cm³. 3 The coefficient of dynamic friction with steel is 0.15 to 0.35, and the water absorption rate is 0.22% to 0.25%.

4. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 1, characterized in that: The pressure insert is made of lubricated modified POM material. The lubricating modification component is selected from silicone oil or polytetrafluoroethylene. After modification, the dynamic friction coefficient of POM against steel can be reduced to 0.15 to 0.

20.

5. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 1, characterized in that: The pressing working surface of the pressing insert corresponds perfectly to the silver surface area of ​​the toe of the lead frame strip in vertical projection, and the shape of the pressing working surface of the pressing insert matches the shape of the toe area.

6. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 3, characterized in that: The Rockwell hardness of the pressed insert is in the range of M80-R120, and the flexural modulus is 2500-3000 MPa.

7. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 1, characterized in that: The pressure insert is fixed in the pressure insert mounting hole of the unloading plate by screw connection or press fitting.

8. A mold for cutting lead-binding feet in a QFP high-pin lead frame according to claim 1, characterized in that: The pressing working surface of the pressing insert is recessed by 0.05 to 0.08 mm relative to the surface of the unloading plate.

9. A method for cutting lead-binding pins for QFP high-pin lead frames, comprising using a mold for cutting lead-binding pins for QFP high-pin lead frames as described in any one of claims 1-8, characterized in that: In the foot-cutting step of the molding process, a pressure insert made of polyoxymethylene (POM) material is used to press and position the silver surface area of ​​the lead frame strip to the tip, thereby preventing friction black marks from being generated in the silver surface area of ​​the tip during the pressing process of the stripper plate. In addition, by setting the pressing working surface of the pressure insert to be recessed relative to the stripper plate surface, ineffective pressing and copper and silver slag adhesion are avoided when multiple products are produced in the same mold.

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