Method for reducing surface chromatic aberration of copper strip of lead frame

Abstract

The invention provides a method for reducing the surface chromatic aberration of a copper strip of a lead frame. The method mainly comprises the procedures of pre-finish rolling, online annealing, washing treatment and finished product rolling. When pre-finish rolling is carried out, the total machining rate is 50%-75%, the roughness Ra of an adopted roller is 0.15-0.25 micron, 4-8 passes are adopted for rolling, and the single-pass machining rate is 15%-30%. And during online annealing, the annealing temperature is controlled to be 580-650 DEG C, and the annealing time is 7-100 s. And during brushing treatment, acid pickling is firstly carried out, then a grinding brush of 1000-4000 meshes is used for surface treatment, and the reduction rate of the grinding brush is 5%-30%. And finally, when a finished product is rolled, the total machining rate is 30%-78%, 1-5 passes are adopted for rolling, and a smooth roller with the roughness Ra smaller than 0.08 microns is used for rolling in the last pass. By controlling the processes of pre-finish rolling, on-line annealing, washing treatment, finished product rolling and the like, the color difference on the surface of the copper strip can be eliminated or reduced, so that the uniformity of the electroplated surface is improved.

Description

Technical Field

[0001] The present invention relates to the field of the surface quality of copper materials, and specifically to a method for reducing the surface color difference of copper strips for lead frames. Background Art

[0002] Lead frame materials are widely used in fields such as integrated circuits and electronic connectors, and have high strength, high conductivity, low thermal expansion, excellent electroplating and stamping properties, etc. With the development of lead frame materials in the industry, stricter requirements are put forward for the surface of copper materials. During the production process, color difference stripe defects often appear on the surface of the strip, which are irregular distributions of light and dark, or continuous strip-shaped dark stripes. The dark stripes are consistent with the extension direction of the strip. The strip with stripes will show a blackened color after electroplating. Therefore, to improve the quality of strip products, it is necessary to eliminate the surface color difference, thereby improving the quality of the electroplated products.

[0003] Currently, the common surface treatment methods mainly use brush grinding to control the surface quality. In the prior art, the main production process of copper strips is: face milling after hot rolling - primary rolling - soft annealing - acid and alkali washing - pre-finishing rolling - annealing in an air-cushion furnace - finishing rolling of the finished product - cleaning and grinding. Among them, the surface quality of the material mainly depends on the cleaning and grinding process. The surface defects of the material are eliminated by a high-precision grinding brush. This process has extremely strict requirements for the quality of the brush. After brushing, the surface brush marks and roughness are required to be uniform. Currently, most of the brush types that meet the grinding requirements use imported grinding brushes, with high usage costs and short service cycles. After the grinding brush is worn, it is easy to form brush marks of different depths on the surface of the finished strip. The surface quality of the products of the client is basically controlled by finished product slitting and screening. Summary of the Invention

[0004] In order to solve the surface color difference of copper strips for lead frames, through analysis and research, it is found that the color difference stripe defects are generated during the rolling process, and controlling the generation of color difference involves surface control in multiple rolling processes; the present invention provides a method for reducing the surface color difference of copper strips for lead frames to eliminate or reduce the surface color difference of copper strips, thereby improving the uniformity of the surface after electroplating. The process of the mother strip after pickling treatment during the processing of existing frame materials in processes such as pre-finishing rolling, online annealing, brushing treatment, and finished product rolling is controlled to achieve the reduction or elimination of the surface color difference of the strip.

[0005] In order to achieve the above object, the specific solution adopted by the present invention is as follows: A method for reducing the surface color difference of copper strips for lead frames mainly includes the following steps: Step 1, pre-finishing rolling: The total processing rate is 50 - 75%, the roughness Ra of the rolling rolls used is 0.15 - 0.25 μm, 4 - 8 passes of rolling are adopted, and the single-pass processing rate is 15% - 30%; Step 2, Online annealing: The annealing temperature is controlled at 580 - 650 °C, and the annealing time is 7 - 100 s; Step 3, Washing treatment: First, pickling is carried out, and then a grinding brush with 1000 - 4000 meshes is used for surface treatment, and the reduction rate of the grinding brush is 5% - 30%; Step 4, Finished product rolling: The total processing rate is 30% - 78%, and 1 - 5 passes of rolling are adopted. Among them, in the last pass, a bright roll with a surface roughness Ra less than 0.08 μm is used for rolling.

[0006] Further, in Step 4, when 2 - 5 passes of rolling are adopted, in the first 1 - 4 passes, a rough roll with a surface roughness Ra of 0.1 - 0.15 μm is used for rolling.

[0007] Further, in Step 3, when pickling, an aqueous sulfuric acid solution with an acid concentration of 5% - 15% is used.

[0008] Further, in Step 3, the grinding brush is an abrasive brush with the bristle material being alumina or silicon carbide.

[0009] Further, in Step 1, the object of pre - finishing rolling is the mother strip after pickling treatment.

[0010] Beneficial effects: (1) In the present invention, by controlling the roughness of the rolling rolls during the pre - finishing rolling and the finished product rolling processes, where the roughness Ra of the rolling rolls is controlled at 0.15 - 0.25 μm during the pre - finishing rolling process, while ensuring the rolling efficiency, the scratches and damages on the surface of the copper strip are minimized as much as possible. During the finished product rolling process, two types of rolling rolls are adopted. The rough roll can effectively reduce the occurrence of strip slipping during the rolling process, thereby reducing the generation of color difference. The bright roll is a low - roughness roll, which can meet the basic requirement of the industry for the surface roughness of the copper alloy material for lead frames ≤0.08 μm.

[0011] (2) Online annealing can eliminate the internal stress and hardening phenomenon generated during the pre - finishing rolling process of the copper strip, thereby restoring its plasticity and toughness. By controlling the annealing temperature and time, the structure and properties of the copper strip can be further ensured to be uniform.

[0012] (3) In the present invention, pickling is carried out on the annealed material, which is beneficial to removing the oxidation on the surface of the copper material. And for the surface of the copper material after acid corrosion, after being washed and treated with a grinding brush, the surface layer of the copper material can be removed, thereby further reducing the surface color difference, attached dirt, etc. of the copper material; generally, there will be brush marks when a brush grinds the surface of the strip. Due to the bridging characteristics of the copper strip during the rolling and stretching process, after matching the reduction rate of the brush and the processing rate, the surface brush marks can be basically eliminated.

[0013] (4) In the present invention, the requirements for the grinding brush during the washing treatment process are relatively low, and an ordinary abrasive brush made of alumina or silicon carbide can be used.

[0014] (5) The method of the present invention can effectively improve the surface quality of the product, reduce the production cost, and is convenient for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a picture of the surface of the copper strip obtained in Example 1 magnified 10 times.

[0016] Figure 2 It is a picture of the surface of the copper strip obtained in Example 1 magnified 10 times after electroplating the copper strip. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1 A method for solving the surface color difference of the copper strip of the lead frame includes the following steps: Using a QFe2.5 alloy mother strip with a width of 650 mm and a thickness of 1.2 mm after annealing and pickling, the base material is subjected to pre-finishing rolling, online annealing, washing treatment, and finished rolling. The specific process parameters are as follows: Step 1, pre-finishing rolling: The total rolling reduction rate is 71.7%. The roughness Ra of the rolling rolls used is 0.25 μm, and it is rolled in 5 passes. The pass distribution is: 1.2 - 0.87 - 0.65 - 0.49 - 0.38 - 0.3; Step 2, online annealing: The 0.3 mm strip after rolling is subjected to online annealing, and the annealing system is 600 °C for 50 s; Step 3, washing treatment: Pickling is carried out using a sulfuric acid aqueous solution with an acid concentration of 10%. After pickling, the surface is brushed using a 2000-mesh grinding brush, and the brush pressing rate is 20%; Step 4, finished rolling: The total rolling reduction rate is 57.6%; it is rolled in 3 passes. The pass distribution is: 0.3 - 0.22 - 0.165 - 0.127. Among them, the first two passes use rough rolls with a roughness Ra of 0.15 μm, and the last pass uses a smooth roll with a roughness Ra of 0.065 μm.

[0019] After the above production process, the magnified picture of the surface of the 0.127 mm copper strip produced is as shown in Figure 1 shown, and the picture after electroplating is as shown in Figure 2 shown, from Figure 1 and Figure 2It can be seen that there is basically no color difference on the surface of the copper strip. The surface roughness of the strip is 0.07μm, meeting the requirements for use as lead frame material.

[0020] Example 2 Use a QFe2.5 alloy mother strip with a width of 650mm and a thickness of 1.5mm that has been annealed and pickled. Perform pre-finishing rolling, online annealing, washing treatment, and finish rolling on the base material. The specific process parameters are as follows: Step 1, pre-finishing rolling: The total rolling reduction is 66.7%. The roughness Ra of the rolling rolls used is 0.15. Four passes of rolling are performed, and the pass distribution is: 1.5 - 1.12 - 0.85 - 0.65 - 0.5; Step 2, online annealing: Perform online annealing on the 0.5mm strip after rolling. The annealing regime is 600°C for 100s; Step 3, washing treatment: Pickle with a sulfuric acid aqueous solution with an acid concentration of 15%. After pickling, use a 1000-mesh abrasive brush for surface brushing, and the brush pressing rate is 30%; Step 4, finish rolling: The total rolling reduction is 57.6%; Five passes of rolling are performed, and the pass distribution is: 0.5 - 0.4 - 0.28 - 0.21 - 0.15 - 0.11. For the first four passes of rolling, use rough rolls with a roughness Ra of 0.1μm. Change the rolls for the last pass and use a finishing roll with a roughness Ra of 0.08μm.

[0021] After the above production processes, the 0.11mm copper strip produced has no color difference on its surface, and the surface roughness of the strip is 0.08μm, meeting the requirements for use as lead frame material.

[0022] Example 3 Use a QFe2.5 alloy mother strip with a width of 650mm and a thickness of 0.8mm that has been annealed and pickled. Perform pre-finishing rolling, online annealing, washing treatment, and finish rolling on the base material. The specific process parameters are as follows: Step 1, pre-finishing rolling: The total rolling reduction is 50%. The roughness Ra of the rolling rolls used is 0.18μm. Four passes of rolling are performed, and the pass distribution is: 0.8 - 0.68 - 0.57 - 0.48 - 0.4; Step 2, online annealing: Perform online annealing on the 0.4mm strip after rolling. The annealing regime is 600°C for 70s; Step 3, washing treatment: Pickle with a sulfuric acid aqueous solution with an acid concentration of 5%. After pickling, use a 4000-mesh abrasive brush for surface brushing, and the brush pressing rate is 5%; Step 4, finish rolling: The total rolling reduction is 30%; One pass of rolling, 0.4 - 0.28, is performed using a finishing roll with a roughness Ra of 0.06μm for rolling.

[0023] After the above production process, the surface of the produced 0.28 mm copper strip has no color difference, and the surface roughness of the strip is 0.063 μm, meeting the requirements for use as lead frame material.

[0024] Example 4 Use a QFe2.5 alloy mother strip with a width of 650 mm and a thickness of 2.0 mm that has been annealed and pickled. Perform pre-finishing rolling, online annealing, brushing treatment, and finish rolling on the mother strip. The specific process steps are as follows: Step 1, pre-finishing rolling: The total rolling reduction is 75%. The roughness Ra of the rolling rolls used is 0.2 μm. 8 passes of rolling are used, and the pass distribution is: 2.0 - 1.7 - 1.4 - 1.1 - 0.88 - 0.72 - 0.6 - 0.5 - 0.38; Step 2, online annealing: Perform online annealing on the 0.38 mm strip after rolling. The annealing regime is 600 °C for 65 s; Step 3, brushing treatment: Use a sulfuric acid aqueous solution with an acid concentration of 15% for pickling. After pickling, use a 2000-mesh abrasive brush for surface brushing, and the brush pressing rate is 20%; Step 4, finish rolling: The total rolling reduction is 60%; 3 passes of rolling are used, and the pass distribution is: 0.38 - 0.3 - 0.24 - 0.152. Among them, for the first 1 - 4 passes, a rough roll with a roughness Ra of 0.12 μm is used for rolling, and for the last pass, a smooth roll with a roughness Ra less than 0.062 μm is used for rolling.

[0025] After the above production process, the surface of the produced 0.152 mm copper strip has no color difference, and the surface roughness of the strip is 0.063 μm, meeting the requirements for use as lead frame material.

[0026] The above is only the preferred embodiments of the present invention, and it does not impose any form of limitation on the present invention. Any equivalent transformation or modification made according to the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for reducing the surface color difference of copper strips of lead frames, characterized in that, It mainly includes the following steps: Step 1, pre-finishing rolling: The total processing rate is 50 - 75%, the roughness Ra of the rolling rolls used is 0.15 - 0.25 μm, 4 - 8 passes of rolling are adopted, and the processing rate per pass is 15% - 30%; Step 2, in-line annealing: The annealing temperature is controlled at 580 - 650 °C, and the annealing time is 7 - 100 s; Step 3, washing treatment: First, pickling is carried out, and then surface treatment is carried out using a grinding brush with 1000 - 4000 mesh, and the reduction rate of the grinding brush is 5% - 30%; Step 4, finishing rolling: The total processing rate is 30% - 78%, 1 - 5 passes of rolling are adopted, and among them, in the last pass, a finishing roll with a roughness Ra less than 0.08 μm is used for rolling.

2. The method for reducing the surface color difference of the copper strip of the lead frame according to claim 1, characterized in that, In Step 4, when 2 - 5 passes of rolling are adopted, in the first 1 - 4 passes, a rough roll with a roughness Ra of 0.1 - 0.15 μm is used for rolling.

3. A method for reducing the surface color difference of the copper strip of a lead frame according to claim 1, characterized in that, In Step 3, a sulfuric acid aqueous solution with an acid concentration of 5% - 15% is used for pickling.

4. A method for reducing the surface color difference of the copper strip of the lead frame according to claim 1, characterized in that, In Step 3, the grinding brush is an abrasive brush with the bristle material being alumina or silicon carbide.

5. A method for reducing the surface color difference of the copper strip of a lead frame according to claim 1, characterized in that, The object of pre-finishing rolling in Step 1 is the mother tape after pickling treatment.

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