Red copper strip for IGBT (Insulated Gate Bipolar Translator) copper substrate and processing method thereof

Abstract

The invention discloses a red copper strip for an IGBT copper substrate and a processing method of the red copper strip, and belongs to the technical field of red copper processing. The red copper material is smelted, cast and processed into a cast ingot; heating is conducted in a stepping heating mode, the temperature range is 840-1000 DEG C, hot rolling and face milling are conducted, and a strip with the thickness being 15-20 mm is machined; rough rolling is conducted on the strip, and the strip is machined to be 3.8-4 mm in thickness through 8-pass rolling; annealing and cleaning; the cleaned strip is subjected to two-pass finish rolling, and a strip with the thickness ranging from 2.8 mm to 3.5 mm is formed; and cleaning to obtain the red copper strip for the IGBT copper substrate. The heat treatment, rough rolling and annealing processes in the red copper machining process are improved, the obtained red copper strip for the IGBT copper substrate is good in surface consistency, and the heat conduction performance is improved when the red copper strip is applied to an IGBT module.

Description

Technical Field

[0001] The invention belongs to the technical field of copper alloy processing, and in particular relates to a red copper strip for an IGBT copper substrate and a processing method thereof. Background Art

[0002] In the field of power electronics, IGBT (insulated gate bipolar transistor) is increasingly widely used. It is a high-power power electronic device with the advantages of large input impedance, small on-resistance, high voltage resistance, low power loss, good dynamic performance, fast switching speed, high operating frequency, etc. It is an ideal switching device in the field of power electronics. With the rapid development of IGBT, higher requirements are put forward for its production and processing. As an important component of IGBT, the selection of copper substrate has a vital impact on the performance and reliability of IGBT.

[0003] IGBT copper strip is used as the IGBT copper substrate and is an important heat-conducting component. It has high requirements on the surface quality of the material and should have good surface consistency. The existing process will select the conventional six-pass rolling process in the rough rolling stage when rolling the copper strip. The surface color difference is large, and when the rough rolling mill rolls the bottom, the curling tension is too large, which increases the fit between the material layers and causes adhesion after annealing: when the curling tension is too small, the outer ring of the material will slip during annealing. Therefore, the copper strip prepared by the existing process will have product defects such as bonding points, bruise points, and color differences on the surface, and the surface consistency is poor. These surface problems will affect the welding of the material in subsequent processing. Finally, when it is applied to IGBT, the thermal conductivity will decrease, affecting the normal operation of the entire IGBT module. At present, there is no good solution. Summary of the invention In view of the problems of poor surface consistency and poor thermal conductivity of current copper strips, the present invention provides a copper strip for an IGBT copper substrate and a processing method thereof, improves the surface cleaning, heat treatment, rough rolling and annealing processes in the copper processing process, and the obtained copper strip for the IGBT copper substrate has good surface consistency and improved thermal conductivity when used in an IGBT module.

[0004] The present invention is achieved through the following technical solutions: A method for processing a red copper strip for an IGBT copper substrate comprises the following steps: (1) Melting and casting copper materials to form ingots; (2) Heating by step heating method, the temperature range is 840~1000℃, hot rolling, milling, and processing into strips with a thickness of 15~20mm; (3) Rough rolling the strip to a thickness of 3.8-4 mm through 8 passes; (4) Annealing; (5) Cleaning the surface of the annealed strip; (6) The cleaned strip is subjected to two passes of finish rolling to form a strip with a thickness of 2.8 to 3.5 mm; (7) Cleaning the strip obtained in step (6) to obtain a red copper strip for an IGBT copper substrate.

[0005] Furthermore, in step (2), the hot rolling start temperature is 800-860°C, the final rolling temperature is 600-660°C, and the total hot rolling processing rate is 85-90%. Furthermore, the step-by-step heating method in step (2) is as follows: the step-by-step heating furnace is divided into 10 furnace zones of equal size, each furnace zone can be heated independently, and the temperatures from the first furnace zone to the tenth furnace zone are 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 920°C, 960°C, and 1000°C, respectively.

[0006] Furthermore, in step (3), the single-pass processing rate is not higher than 20%, and the pass processing rate decreases successively.

[0007] Furthermore, the curling tension of the last pass of rough rolling in step (3) is 26KN±1KN, which can achieve a suitable fit between material layers, avoid material slippage, and avoid the generation of bruise points.

[0008] Furthermore, the annealing conditions in step (4) are 500-600°C for 4-6 hours, 350-400°C for 8-10 hours, and 400-450°C for 4-6 hours.

[0009] Furthermore, in step (6), the single pass processing rate of the finishing rolling is 8-20%.

[0010] Furthermore, the copper material described in step (1) is low-oxygen copper with a copper content of more than 99% and an oxygen content of less than 30 ppm.

[0011] In the present invention, the red copper strip for IGBT copper substrate is obtained by processing using the above method.

[0012] Beneficial effects achieved by the present invention: The present invention uses a step-by-step non-uniform heat treatment method to heat treat the copper alloy, controls the heating rate from slow to fast, reduces the structural segregation during material solidification, obtains a uniform and fine microstructure, and is beneficial to enhancing the refinement effect of internal grains during subsequent rough rolling deformation.

[0013] The present invention improves the traditional six-pass rolling to eight-pass rolling. With the increase of the number of passes, the grain refinement effect is better. In the repeated rolling deformation process, the internal grains of copper are continuously broken, elongated and recrystallized and refined. The microstructure of the copper strip is made more uniform and fine, which is conducive to improving the mechanical properties such as strength and hardness of the material, and will also have a positive impact on its subsequent processing formability (such as stamping, bending, etc.), reducing the probability of defects such as cracks; and more rolling passes make the process of gradual release and redistribution of internal stress in the copper strip more sufficient and uniform, reducing stress concentration, and the internal residual stress of the finished product is in a relatively more reasonable and uniform state, thereby reducing the possibility of deformation caused by stress release during subsequent storage, transportation or further processing. In addition, eight-pass rolling can better eliminate some tiny surface defects such as protrusions and wrinkles, making the surface of the copper strip smoother and flatter. For products that require subsequent surface treatment (such as plating) or are directly used in occasions with high appearance requirements, the quality is more guaranteed. By increasing the number of passes, the rolling process is refined, and the probability of surface scratches, cracks and other defects caused by excessive single-pass reduction is reduced. The overall quality of the copper strip surface is improved, the defective rate is reduced, and the product yield is increased.

[0014] The improvement of the annealing process of the present invention improves the residual stress distribution of the alloy material, effectively controls the processing version, and improves the tensile strength and high temperature resistance of the alloy material by controlling the rough rolling deformation and annealing temperature. DETAILED DESCRIPTION

[0015] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention.

[0016] Example 1 (1) Smelting and casting low-oxygen copper with a copper content of more than 99% and an oxygen content of less than 30 ppm to form ingots; (2) The walking-beam heating furnace is divided into 10 furnace zones of equal size, each furnace zone can be heated independently, and the temperatures from the first furnace zone to the tenth furnace zone are 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 920°C, 960°C, and 1000°C, respectively. The ingot in step (1) is added to the walking-beam heating furnace, heated by a walking-beam heating method, and the temperature range is 840-1000°C. It is hot rolled and milled to form a strip with a thickness of 16.0 mm; (3) rough rolling the strip to a thickness of 3.95 mm through 8 passes; First pass: material thickness 16.0mm→12.88mm; Second pass: material thickness 12.88mm→10.50mm; The third pass: material thickness 10.50mm→8.66mm; Fourth pass: material thickness 8.66mm→7.23mm; Fifth pass: material thickness 7.23mm→6.11mm; The sixth pass: material thickness 6.11mm→5.22mm; The seventh pass: material thickness 5.22mm→4.52mm; Pass 8: Material thickness 4.52mm→3.95mm; (4) Annealing: Annealing conditions are 560°C for 5 h, 380°C for 8 h, and 430°C for 5 h; (5) Clean the surface of the annealed strip; add 500mm wide and 30 micron thick lining paper between the material layers to avoid friction and collision between the layers and the formation of bruise points; (6) The cleaned strip is subjected to two passes of finish rolling, 3.95 mm → 3.36 mm → 3.0 mm, to form a strip with a thickness of 3.0 mm; (7) The strip obtained in step (6) is cleaned again to obtain a red copper strip for an IGBT copper substrate.

[0017] Example 2 (1) Smelting and casting low-oxygen copper with a copper content of more than 99% and an oxygen content of less than 30 ppm to form ingots; (2) The walking-beam heating furnace is divided into 10 furnace zones of equal size, each furnace zone can be heated independently, and the temperatures from the first furnace zone to the tenth furnace zone are 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 920°C, 960°C, and 1000°C, respectively. The ingot in step (1) is added to the walking-beam heating furnace, heated by a walking-beam heating method, and the temperature range is 840-1000°C. It is hot rolled and milled to form a strip with a thickness of 18 mm. (3) rough rolling the strip to a thickness of 3.77 mm through 8 passes; First pass: material thickness 18.0mm→14.49mm; Second pass: material thickness 14.49mm→11.74mm; The third pass: material thickness 11.74mm→9.57mm; Fourth pass: material thickness 9.57mm→7.84mm; Fifth pass: material thickness 7.84mm→6.47mm; The sixth pass: material thickness 6.47mm→5.37mm; The seventh pass: material thickness 5.37mm→4.48mm; Pass 8: Material thickness 4.48mm→3.77mm; (4) Annealing: Annealing conditions are 590°C for 4 h, 390°C for 10 h, and 450°C for 6 h; (5) Clean the surface of the annealed strip; add 500mm wide and 30 micron thick lining paper between the material layers to avoid friction and collision between the layers and the formation of bruise points; (6) The cleaned strip is subjected to two passes of finish rolling, 3.77 mm → 3.24 mm → 3.0 mm, to form a strip with a thickness of 3.0 mm; (7) The strip obtained in step (6) is cleaned again to obtain a red copper strip for an IGBT copper substrate.

[0018] Example 3 (1) Smelting and casting low-oxygen copper with a copper content of more than 99% and an oxygen content of less than 30 ppm to form ingots; (2) The walking-beam heating furnace is divided into 10 furnace zones of equal size, each furnace zone can be heated independently, and the temperatures from the first furnace zone to the tenth furnace zone are 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 920°C, 960°C, and 1000°C, respectively. The ingot in step (1) is added to the walking-beam heating furnace, heated by a walking-beam heating method, and the temperature range is 840-1000°C. It is hot rolled and milled to be processed into a strip with a thickness of 16 mm; (3) rough rolling the strip to a thickness of 3.96 mm through 8 passes; First pass: material thickness 16.0mm→13.12mm; Second pass: material thickness 13.12mm→10.82mm; The third pass: material thickness 10.82mm→9.0mm; Fourth pass: material thickness 9.0mm→7.50mm; Fifth pass: material thickness 7.50mm→6.30mm; The sixth pass: material thickness 6.30mm→5.32mm; The seventh pass: material thickness 5.32mm→4.55mm; Pass 8: Material thickness 4.55mm→3.96mm; (4) Annealing: Annealing conditions are 520°C for 6 h, 360°C for 8 h, and 420°C for 6 h; (5) Clean the surface of the annealed strip; add 500mm wide and 30 micron thick lining paper between the material layers to avoid friction and collision between the layers and the formation of bruise points; (6) The cleaned strip is subjected to two passes of finish rolling, 3.96 mm → 3.36 mm → 3.0 mm, to form a strip with a thickness of 3.0 mm; (7) The strip obtained in step (6) is cleaned again to obtain a red copper strip for an IGBT copper substrate.

[0019] Comparative Example 1 Compared with Example 1, the rough rolling in step (3) of Comparative Example 1 was performed for 6 passes (original process) to a thickness of 3.95 mm, specifically: First pass: material thickness 16.0 mm → 13 mm; Second pass: material thickness 13mm→10mm; The third pass: material thickness 10mm→7.8mm; Fourth pass: material thickness 7.8mm→6mm; The fifth pass: material thickness 6mm→4.9mm; The sixth pass: material thickness 4.9mm→3.95mm; The other steps are the same as those in Example 1 to obtain a 3.0 mm copper strip.

[0020] Comparative Example 2 Compared with Example 1, the step (4) of Comparative Example 2 is annealing; the annealing condition is 430° C. for 10 h; The other steps are the same as those in Example 1 to obtain a 3.0 mm copper strip.

[0021] Comparative Example 3 Compared with Example 1, in Comparative Example 3, step (2): the walking beam heating furnace is divided into 10 furnace zones of equal size, each furnace zone can be heated independently, and the temperatures from the first furnace zone to the tenth furnace zone are 840° C., 858° C., 876° C., 894° C., 912° C., 930° C., 948° C., 966° C., 984° C., and 1000° C., respectively, and the strip is hot rolled and milled to be processed into a strip with a thickness of 16 mm; The other steps are the same as those in Example 1 to obtain a 3.0 mm copper strip.

[0022] Performance Test: The copper strips prepared in Examples 1 to 3 of the present invention have smooth surfaces, no product defects such as bruises and color differences, and good surface consistency, while the copper strip prepared in Comparative Example 1 has a small number of tiny protrusions and wrinkles on the surface, and has slight color differences. The tensile strength, hardness, thermal conductivity and electrical conductivity of the copper strips prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested, and the results are shown in Table 1 below: Table 1 Performance of the copper strips prepared in Examples 1 to 3 and Comparative Examples 1 to 3 As can be seen from Table 1, the present invention controls the hot working, rough rolling processing rate and annealing process after rough rolling, so that the copper strip prepared has higher tensile strength and hardness, and good thermal and electrical conductivity, and has good application in IGBT modules.

Claims

1. A method for processing a copper strip for an IGBT copper substrate, characterized in that: The following steps are involved: (1) Melting and casting copper materials to form ingots; (2) Heating by step heating method, the temperature range is 840~1000℃, hot rolling, milling, and processing into strips with a thickness of 15~20mm; (3) Rough rolling the strip to a thickness of 3.8-4 mm through 8 passes; (4) Annealing; (5) Cleaning the surface of the annealed strip; (6) The cleaned strip is subjected to two passes of finish rolling to form a strip with a thickness of 2.8 to 3.5 mm; (7) Cleaning the strip obtained in step (6) to obtain a red copper strip for an IGBT copper substrate.

2. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: In step (2), the hot rolling start temperature is 800-860°C, the final rolling temperature is 600-660°C, and the total hot rolling processing rate is 85-90%.

3. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: The step-by-step heating method in step (2) is as follows: the step-by-step heating furnace is divided into 10 furnace zones of equal size, each furnace zone can be heated independently, and the temperatures from the first furnace zone to the tenth furnace zone are 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 920°C, 960°C, and 1000°C, respectively.

4. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: In step (3), the single-pass processing rate is not higher than 20%, and the pass processing rate decreases successively.

5. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: The curling tension of the last pass of rough rolling in step (3) is 26KN±1KN. It can achieve the appropriate fit between material layers, prevent material slippage and avoid the generation of bruise points.

6. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: The annealing conditions in step (4) are 500-600°C for 4-6 hours, 350-400°C for 8-10 hours, and 400-450°C for 4-6 hours.

7. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: The single pass processing rate of the finishing rolling in step (6) is 8-20%.

8. The method for processing the red copper strip for IGBT copper substrate according to claim 1, characterized in that: The copper material described in step (1) is low-oxygen copper with a copper content of more than 99% and an oxygen content of less than 30 ppm.

9. A red copper strip for IGBT copper substrate obtained by processing according to the method of any one of claims 1 to 8.

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