Method for removing burrs on cutting channel of lead frame through electrolysis

Abstract

The invention provides a method for removing burrs on a cutting channel of a lead frame through electrolysis. The method comprises the steps that S1, a transparent UV protection film is pasted on the cutting face of the lead frame; s2, carrying out primary cutting on the lead frame pasted with the UV protection film to form steps with wettability side wings; s3, taking the lead frame subjected to primary cutting as an anode, and putting the anode into an electrolysis device for electrolysis; s4, after electrolysis is finished, UV illumination treatment is conducted on the cutting face of the lead frame, then the UV protection film is bonded through a bonding film, and separation of the UV protection film and the lead frame is achieved by removing the bonding film; and S5, electroplating tinning and secondary cutting are carried out on the lead frame. According to the invention, the problem that burrs are easily generated on the cutting channel of the lead frame in the two-step cutting process of the wettability flank product is solved.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor integrated circuit packaging and relates to a method for removing burrs from cutting paths of a lead frame by electrolysis. Background Art

[0002] To meet the needs of SMT automated assembly and testing of automotive components, wettable flank technology has attracted more and more attention. At present, the industry mainly uses a two-step cutting separation method to separate wettable flank products. The specific technical solution is as follows: (1) Use a film laminating machine to apply UV film to the front of the lead frame after plastic sealing, and the edge of the UV film is attached to the ring; (2) Use a cutting machine to place the ring on the stage, and use a pre-designed wide knife to cut along the cutting path on the back of the lead frame to form a step of the wettable flank; (3) Use a UV irradiator to remove the UV film on the front of the frame; (4) Electroplating tin is applied to the frame after one-step cutting; (5) Repeat the above steps (1)-(3) for the electroplated frame for a second cutting, in which a narrow knife is used for cutting, and finally the product separation is completed.

[0003] The main problem with the above technical method is that the first cut is a partial cut of the product, and there are a large number of burrs of varying lengths on the surface of the cut path, with a burr length of about 100-200μm. The presence of these burrs will cause the product after the second cut to fail to meet the inspection standard, and even cause a short circuit between the pins, thereby reducing the product yield. Conventional deburring methods cannot effectively solve this type of tiny burrs while ensuring the functional integrity of the device. Summary of the invention

[0004] In order to solve the above problems of the prior art, the present invention provides a method for electrolytically removing burrs from the cutting paths of a lead frame, which solves the problem that burrs are easily generated on the cutting paths of the lead frame during the two-step cutting process of wettable flank products.

[0005] The present invention is achieved through the following technical solutions: A method for electrolytically removing burrs from a lead frame cutting path, comprising: S1, pasting a transparent UV protective film on the cut surface of the lead frame; S2, cutting the lead frame with the UV protective film attached to form a step of wettable flanks; S3, placing the lead frame cut once as an anode in an electrolysis device for electrolysis; S4, after the electrolysis is completed, the cut surface of the lead frame is subjected to UV light treatment, and then the UV protective film is adhered to the UV protective film with an adhesive film, and the UV protective film is separated from the lead frame by peeling off the adhesive film; S5, electroplating tin and secondary cutting are performed on the lead frame.

[0006] Preferably, in S3, the cathode used in electrolysis is a copper rod.

[0007] Preferably, in S3, the electrolyte used for electrolysis is a CuSO4 solution.

[0008] Furthermore, the electrolyte temperature is room temperature.

[0009] Preferably, in S3, the current intensity used for electrolysis is 10-12A.

[0010] Preferably, in S3, the electrolysis time is 10-15 s.

[0011] Preferably, in S4, the UV light treatment time is 10-20s.

[0012] Preferably, in S4, the adhesive film is a UV film or a transparent tape.

[0013] Preferably, in S4, the size of the burrs in the cut lines of the lead frame is within 50 μm.

[0014] Preferably, before S1, a UV film is attached to the front of the lead frame, with the edge of the UV film attached to the Ring; after S2 and before S3, the UV film is treated with UV light to release the stickiness, and the lead frame is removed from the Ring.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention pastes a transparent UV protective film on the cut surface of the lead frame before the first cutting, which plays a role in isolating the electrolyte. After the first cutting, the lead frame is placed in an electrolysis device, and the burrs are preferentially oxidized and removed because they protrude from the surface. The remaining area of ​​the lead frame still retains the original structure because the UV protective film is attached to the surface. The lead frame after electrolysis is irradiated with ultraviolet light to release the stickiness of the UV protective film. The UV protective film is quickly removed from the cut surface of the lead frame through the adhesive film to avoid scratching the chip. The method can effectively remove the burrs in the cutting path after the lead frame is cut once, thereby exposing the plastic package under the burrs, effectively avoiding short circuits of the device after the second cutting, and improving the product yield. It is simple to operate and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1This is a schematic diagram of the lead frame cutting surface film and one-time cutting.

[0018] Figure 2 Schematic diagram of the cutting path morphology after one cutting.

[0019] Figure 3 Schematic diagram of the electrolysis device.

[0020] Figure 4 Schematic diagram of removing the UV protective film from the cut surface of the lead frame for adhesive film.

[0021] Figure 5 Schematic diagram of the cutting path morphology after electrolytic deburring.

[0022] Figure 6 This is the morphology of the cutting path before and after electrolysis in Example 1.

[0023] In the figure: 1-SAW knife, 2-UV protective film, 3-plastic package, 4-lead frame, 5-pin, 6-heat sink, 7-burr, 8-cutting path, 9-secondary cutting line, 10-DC power supply, 11-clip, 12-fixed bracket, 13-electrolyte, 14-cathode. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0026] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0027] The method for electrolytically removing burrs from a lead frame cutting path of the present invention comprises the following contents: (1) Apply UV film to the cut surface of the lead frame before cutting Before the first cut, a protective film needs to be pasted on the back of the lead frame, i.e. the cutting surface. Considering that the cutting path can be seen through the protective film during subsequent cutting, a transparent protective film needs to be selected to ensure the visibility of the cutting path of the lead frame after the film is pasted. Considering the removal of the protective film after electrolysis, a transparent UV protective film is selected as the protective film. The viscosity of the protective film can be reduced by ultraviolet light irradiation, making it easy to remove. The main function of the film is to isolate the electrolyte from the area of ​​the lead frame other than the cutting path to avoid electrolysis from destroying the original structure. The cutting path is exposed due to the first cut and can fully contact with the electrolyte.

[0028] (2) Electrolytic method to remove burrs on cutting paths The lead frame after the first cutting is placed as the anode in the electrolysis device, the copper rod is used as the cathode, and the electrolyte is CuSO4 solution. The burrs on the cutting path protrude from the surface of the plastic package in the cutting path, and the current density is most concentrated during electrolysis, so they are preferentially oxidized and removed. The burrs can be removed in a targeted manner by adjusting the current size and the power-on time, thereby avoiding short circuits between the product pins due to burrs after the second cutting. The lead frame attached by the UV film will not contact the electrolyte and will retain its original structure.

[0029] (3) How to remove the UV protective film Place the lead frame after electrolysis in a UV irradiator, irradiate the UV protective film with UV to remove the stickiness of the UV protective film, then place it on an anti-static workbench, cover the protective film with an adhesive film, and peel off the adhesive film to quickly remove the UV protective film to avoid scratching the chip.

[0030] Based on this, the method for electrolytically removing burrs from the cutting path of a lead frame according to the present invention specifically comprises the following steps: S1, before cutting the lead frame once, a transparent UV protective film 2 with visible cutting path is pasted on the back side of the lead frame, i.e., the cutting surface; Figure 1 As shown, the lead frame 4 has a plastic package 3 and pins 5.

[0031] S2, using SAW knife 1 to cut the lead frame with UV protective film attached along the cutting path 8, forming a step of wettable flanks, and the UV protective film on the cutting surface of the lead frame is cut into independent parts; at the same time, burrs 7 ( Figure 2 ), the burrs extend to the surface of the plastic package and cover the plastic package. If the burrs are not processed, the pins will short-circuit due to the burrs after the second cutting, resulting in defective products; S3, the lead frame 4 is placed in an electrolytic device as an anode for electrolysis. The burr 7 is preferentially electrolytically oxidized because it protrudes from the surface. At this time, the plastic package on the surface of the cutting path is completely exposed. The electrolytic device is as follows: Figure 3 As shown, two clips 11 are fixed on the fixed bracket 12, and the two clips 11 are respectively clamped with the anode and the cathode 14 and connected to the DC power supply 10, and the electrolytic device is filled with electrolyte 13; S4, UV irradiation is performed on the cut surface of the lead frame to remove the stickiness of the residual UV protective film. The UV irradiation time is 10-20s. The UV protective film is adhered with an adhesive film, and the UV protective film is separated from the lead frame by peeling off the adhesive film. Figure 4 ); S5, electroplating tinning and secondary cutting are performed, and the secondary cutting line 9 is located inside the primary cutting line to achieve product separation.

[0032] The cathode used in the electrolysis of the present invention is a copper rod, the electrolyte is a CuSO4 solution at room temperature, the current intensity is 10-12A, and the electrolysis time is 10-15s.

[0033] like Figure 5 As shown, the burrs on the surface of the cutting path after electrolysis are basically removed, exposing the complete plastic package structure. After secondary cutting, there is a plastic package gap between the pins to avoid short circuit.

[0034] In the embodiment of the present invention, the adhesive film is specifically a UV film, and the brands of the UV film and the UV protective film are both SLIONTEC, model 6360-95.

[0035] Example 1 For the QFN20L-3×3×0.75 package type, wettable flank product processing is performed. The chip size is 1.0mm×1.0mm, the flank pin thickness is 0.203mm, and the one-time cutting width is 0.44mm. The specific implementation steps are as follows: Step 1: Use a film laminating machine to stick a UV film on the front of the lead frame, with the edge of the UV film attached to the Ring; Step 2: Use a film laminating machine to apply a transparent UV protective film on the back side of the lead frame, i.e. the cutting surface, to ensure the visibility of the cutting path of the lead frame after laminating; Step 3: Use a cutting machine to place the Ring on the stage, and use a 0.44mm SAW knife to make a cut along the cutting path on the back of the lead frame, with a cutting depth of 0.15mm to form a step of the wettable flank. It was observed that the length of the burr in the cutting path after one cut was 100-200μm; Step 4: Use a UV light machine to remove the stickiness of the UV film on the front of the lead frame through ultraviolet light, and remove the lead frame from the Ring; Step 5: Place the lead frame cut once as the anode in the electrolysis device, the cathode is a copper rod, the electrolyte is a CuSO4 solution, the electrolyte temperature is room temperature, the current intensity is 10A, the electrolysis time is 10s, turn off the DC power supply, and the electrolysis is completed; Step 6: Use a UV irradiator to remove the bonding between the UV protective film on the back of the lead frame and the lead frame through ultraviolet light, and the irradiation time is 15 seconds; Step 7: Use manual film sticking to stick the adhesive film to the surface of the UV protective film after ultraviolet light irradiation, and gently press it to achieve effective contact between the adhesive film and the UV protective film; Step 8: Manually remove the adhesive film. The bonding force between the adhesive film and the UV protective film is greater than the bonding force between the UV protective film and the lead frame. When removing the adhesive film, the UV protective film on the surface of the lead frame is also removed. Observe the lead frame after the film is removed. The plastic package structure in the cutting path is completely exposed on the surface, and the burrs are controlled within 50μm.

[0036] Step 9: Carry out subsequent electroplating tinning and secondary cutting processes. The width of the secondary cutting is 0.3mm to achieve complete separation of the products.

[0037] Example 2 For the QFN32L-4×4×0.55 package type, wettable flank product processing is performed. The chip size is 1.02mm×1.5mm, the flank pin thickness is 0.15mm, and the one-time cutting width is 0.40mm. The specific implementation steps are as follows: Step 1: Use a film laminating machine to stick a UV film on the front of the lead frame, with the edge of the UV film attached to the Ring; Step 2: Use a film laminating machine to apply a transparent UV protective film on the back side of the lead frame, i.e. the cutting surface, to ensure the visibility of the cutting path of the lead frame after laminating; Step 3: Use a cutting machine to place the Ring on the stage, and use a 0.40mm SAW knife to make a cut along the cutting path on the back of the frame, with a cutting depth of 0.10mm to form a step of the wettable flank. It was observed that the length of the burr in the cutting path after one cut was 120-150μm; Step 4: Use a UV light machine to remove the stickiness of the UV film through ultraviolet light and remove the lead frame from the Ring; Step 5: Place the lead frame cut once as the anode in the electrolysis device, the cathode is a copper rod, the electrolyte is a CuSO4 solution, the electrolyte temperature is room temperature, the current intensity is 12A, the electrolysis time is 10s, turn off the DC power supply, and the electrolysis is completed; Step 6: Use a UV light machine to remove the bonding effect between the UV protective film and the lead frame by ultraviolet light for 15 seconds; Step 7: Use manual film sticking to stick the adhesive film to the surface of the UV protective film after ultraviolet light irradiation, and gently press it to achieve effective contact between the adhesive film and the UV protective film; Step 8: Manually remove the adhesive film. The bonding force between the adhesive film and the UV protective film is greater than the bonding force between the UV protective film and the lead frame. When removing the adhesive film, the UV protective film on the surface of the lead frame is also removed. Observe the frame after the film is removed. The plastic package structure in the cutting path is completely exposed on the surface, and the burrs are controlled within 50μm.

[0038] Step 9: Carry out subsequent electroplating tinning and secondary cutting processes. The width of the secondary cutting is 0.3mm to achieve complete separation of the products.

[0039] Embodiment 3: For the QFN24L-5×5×0.75 package type, wettable flank product processing is performed. The chip size is 1.8mm×1.8mm, the flank pin thickness is 0.203mm, and the one-time cutting width is 0.46mm. The specific implementation steps are as follows: Step 1: Use a film laminating machine to stick a UV film on the front of the lead frame, with the edge of the UV film attached to the Ring; Step 2: Use a film laminating machine to apply a transparent UV protective film on the back side of the lead frame, i.e. the cutting surface, to ensure the visibility of the cutting path of the lead frame after laminating; Step 3: Use a cutting machine to place the Ring on the stage, and use a 0.46mm SAW knife to make a cut along the cutting path on the back of the frame, with a cutting depth of 0.12mm to form a step of the wettable flank. It was observed that the length of the burr in the cutting path after one cut was 150-200μm; Step 4: Use a UV light machine to remove the stickiness of the UV film through ultraviolet light and remove the lead frame from the Ring; Step 5: Place the lead frame cut once as the anode in the electrolysis device, the cathode is a copper rod, the electrolyte is a CuSO4 solution, the electrolyte temperature is room temperature, the current intensity is 12A, the electrolysis time is 15s, turn off the DC power supply, and the electrolysis is completed; Step 6: Use a UV light machine to remove the bonding effect between the UV protective film and the lead frame by ultraviolet light for 15 seconds; Step 7: Use manual film sticking to stick the adhesive film to the surface of the UV protective film after ultraviolet light irradiation, and gently press it to achieve effective contact between the adhesive film and the UV protective film; Step 8: Manually remove the adhesive film. The bonding force between the adhesive film and the UV protective film is greater than the bonding force between the UV protective film and the lead frame. When removing the adhesive film, the UV protective film on the surface of the lead frame is also removed. Observe the frame after the film is removed. The plastic package structure in the cutting path is completely exposed on the surface, and the burrs are controlled within 50μm.

[0040] Step 9: Carry out subsequent electroplating tinning and secondary cutting processes. The width of the secondary cutting is 0.3mm to achieve complete separation of the products.

[0041] In Example 1, the cutting path picture before electrolysis is as follows Figure 6 As shown in (a), it can be seen that there are a lot of burrs on the cutting path; the cutting path after electrolysis is shown in Figure 6 As shown in (b), it can be seen that after electrolysis, the burrs on the cutting path are basically removed and the surface is relatively smooth.

[0042] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for electrolytically removing burrs from lead frame cutting paths, It is characterized in that include: S1, pasting a transparent UV protective film on the cut surface of the lead frame; S2, cutting the lead frame with the UV protective film attached to form a step of wettable flanks; S3, placing the lead frame cut once as an anode in an electrolysis device for electrolysis; S4, after the electrolysis is completed, the cut surface of the lead frame is subjected to UV light treatment, and then the UV protective film is adhered to the UV protective film with an adhesive film, and the UV protective film is separated from the lead frame by peeling off the adhesive film; S5, electroplating tin and secondary cutting are performed on the lead frame.

2. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S3, the cathode used in electrolysis is a copper rod.

3. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S3, the electrolyte used for electrolysis is CuSO 4 Solution.

4. The method for electrolytically removing burrs from lead frame cutting paths according to claim 3, It is characterized in that The electrolyte temperature is room temperature.

5. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S3, the current intensity used for electrolysis is 10-12A.

6. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S3, the electrolysis time is 10-15s.

7. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S4, the UV light treatment time is 10-20s.

8. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S4, the adhesive film is a UV film or a transparent tape.

9. The method for electrolytically removing burrs from lead frame cutting paths according to claim 1, It is characterized in that In S4, the burr size in the lead frame cutting path is obtained to be within 50 μm.

10. The method for electrolytically removing burrs from lead frame cut lines according to claim 1, It is characterized in that Before S1, a UV film is attached to the front of the lead frame, and the edge of the UV film is attached to the ring; after S2 and before S3, the UV film is treated with UV light to release the stickiness, and the lead frame is removed from the ring.

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