A high-hardness Cu-Fe-P alloy strip with high resistance to softening and its preparation method

Abstract

This invention relates to a high-hardness, high-softening-resistance Cu-Fe-P alloy strip and its preparation method. The method includes the following steps: high-temperature aging treatment of Cu-Fe-P alloy base material under a protective atmosphere; then, large-deformation cold rolling with a total deformation of 60%–70%; followed by graded aging; and finally, finished product rolling to obtain a copper alloy strip of the target thickness. The alloy strip prepared by this method has a Vickers hardness of over 170 and a tensile strength ≥580 MPa. Under conditions of 470℃ / 3min, the Vickers hardness stably reaches over 90% of the original hardness. Its comprehensive performance is significantly superior to traditional processes and similar advanced technologies, and it can meet the stringent requirements of the electronics and information industry for the comprehensive performance of copper alloy lead frame materials.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal rolling processing, specifically relating to a high-hardness Cu-Fe-P alloy strip with high resistance to softening and its preparation method. Background Technology

[0002] Leadframe materials are widely used in the electronics and information industry, including 5G communication, IoT, and smartphones. Copper alloys, due to their excellent electrical and thermal conductivity and high strength, are increasingly becoming an indispensable key material for integrated circuits. Copper alloy leadframe materials serve as the carrier of integrated circuit chips and also play a role in electrical conductivity and heat dissipation. They are key components of integrated circuits, and the improvement of integrated circuit performance places higher demands on the comprehensive performance of copper alloy leadframe materials.

[0003] Leadframe materials are characterized by "high strength and high conductivity," and their mechanical properties and resistance to high-temperature softening are key performance indicators. These directly affect the structural stability, electrical connection reliability, and heat dissipation efficiency of semiconductor packaging under soldering and long-term high-temperature operating environments. Therefore, improving the material's resistance to high-temperature softening can further enhance the applicability of alloy end products. Currently, the performance of Cu-Fe-P alloy leadframe materials generally meets the performance indicators in standard GB / T20254.1-2015 "Copper and Copper Alloy Strips for Leadframes": HV≥145, and the Vickers hardness after treatment at 470℃ for 3 minutes should not be less than 80% of the original hardness. While this indicator meets the requirements of traditional packaging processes, it is no longer sufficient to adapt to the trend of integrated circuits continuously developing towards high power, high density, and miniaturization. This invention, through a rational design of the processing method, can effectively improve the hardness and resistance to high-temperature softening of Cu-Fe-P alloy materials without reducing other performance characteristics. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-hardness, high-softening-resistance Cu-Fe-P alloy strip and its preparation method. By controlling the alloy composition and employing a two-step rolling and aging process during the cold working deformation stage, the second phase is fully precipitated, forming a mixed microstructure of high-density dislocations, deformation twins, and nano-precipitates. This improves the alloy's mechanical properties, particularly its hardness and resistance to high-temperature softening. Without compromising other properties, the material's strength and resistance to high-temperature softening are enhanced, thus meeting the comprehensive performance requirements of copper alloy leadframe materials in the electronics and information industry.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for preparing a Cu-Fe-P alloy strip with high hardness and high resistance to softening, comprising the following steps:

[0006] (1) High temperature aging: Under a protective atmosphere, the Cu-Fe-P alloy base material is kept at 480-550℃ for 7-15 hours to allow Fe and P elements to fully precipitate and form strengthening phases;

[0007] (2) Large deformation cold rolling: The base material after step (1) is subjected to multiple passes of large-processing cold deformation rolling, with a total deformation of 60% to 70%;

[0008] (3) Grading and aging: The strip after cold rolling in step (2) is first kept at 300-350℃ for 4-8 hours, and then the temperature is raised to 440-460℃ and kept for 3-6 hours before being taken out of the furnace. Protective gas is used during the heat preservation.

[0009] (4) Finished product rolling: The strip after step (3) is cold rolled with a total deformation of 60% to 70% to obtain copper alloy strip of the target thickness.

[0010] Furthermore, the composition of the Cu-Fe-P alloy base material, by weight percentage, includes: Fe: 2.3-2.5%; P: 0.07-0.09%; Zn: 0.05-0.20%; Sn: 0.01-0.04%; Mg: 0.02-0.09%; Ni: 0.005-0.025%; the balance being copper and unavoidable impurities.

[0011] Furthermore, the thickness of the Cu-Fe-P alloy base material is 1.0~2.0 mm.

[0012] Furthermore, the Cu-Fe-P alloy base material is made from Cu-Fe-P alloy ingots through heating, hot rolling, quenching, and cold working.

[0013] Furthermore, in step (1), the Cu-Fe-P alloy base material is subjected to high-temperature aging treatment in a bell furnace.

[0014] Furthermore, in step (3), the Cu-Fe-P alloy base material undergoes graded aging treatment in a bell furnace.

[0015] The second technical solution proposed in this invention is: a Cu-Fe-P alloy strip with high hardness and high resistance to softening, prepared by the above-mentioned method.

[0016] Furthermore, the prepared high-hardness, high-softening-resistance Cu-Fe-P alloy strip has a Vickers hardness HV≥170, tensile strength≥580 MPa, and after treatment at 470℃ / 3min, the high-temperature softening hardness is not less than 90% of the original hardness.

[0017] The technical principle and beneficial effects of this invention are as follows: 1. This invention forms high-density dislocations and deformation twins through large deformation cold working and finished product rolling cold working; the combination of high-temperature aging and graded aging allows Fe and P to be fully precipitated as second phases to form Fe2P, Fe3P and other nano-precipitates, while Mg and P form Mg3P2 in the form of compounds; the mixed structure of high-density dislocations, deformation twins, nano-precipitates, and compounds formed by this preparation process can effectively improve the strength of the material and improve the mechanical properties of the alloy, especially its hardness and resistance to high-temperature softening.

[0018] 2. Currently, the properties of Cu-Fe-P alloy leadframe materials are generally HV > 145, and after heat treatment at 470℃ for 3 minutes, their hardness is not less than 80% of the original hardness. Through the above preparation process, the tested hardness HV can reach over 170, and the resistance to softening at 470℃ for 3 minutes shows that the Vickers hardness stably reaches over 90% of the original hardness, effectively expanding the applicability of downstream end products.

[0019] 3. The method of the present invention improves product performance through component control and the above-mentioned processing technology, reduces the dependence of current lead frame materials on high-end equipment through high-temperature solid solution + aging strengthening, and facilitates promotion and use. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments, but this should not be construed as limiting the invention in any way.

[0021] This invention uses a Cu-Fe-P alloy ingot after conventional processing as the experimental raw material. The conventional process includes ingot casting, walking beam furnace heating, hot rolling, quenching, and cold rolling. The thickness of the resulting raw material can be 1.0-2.0 mm. After high-temperature aging, large deformation cold rolling, graded aging, and finished product rolling, the high-hardness and high-softening-resistance Cu-Fe-P alloy strip product of this invention is obtained.

[0022] The alloy composition of the Cu-Fe-P alloy ingot, by weight percentage, includes: Fe: 2.3-2.5%; P: 0.07-0.09%; Zn: 0.05-0.20%; Sn: 0.01-0.04%; Mg: 0.02-0.09%; Ni: 0.005-0.025%; the balance being copper and unavoidable impurities.

[0023] The preparation process is described in detail below with different embodiments. Examples 1-4 illustrate the preparation process of the present invention, while Comparative Examples 1-4 are comparative experiments conducted from different perspectives to demonstrate the necessity of the preparation process of the present invention.

[0024] Example 1

[0025] In this embodiment, a 1.5mm thick base material obtained through ingot casting, walking beam furnace heating, hot rolling, quenching, and cold working is used for high-temperature aging, large deformation cold rolling, graded aging, and finished product rolling. The specific process steps are as follows:

[0026] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 550℃, and the protective gas is used for heat preservation for 8 hours. The protective gas is N2+H2.

[0027] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 66.7% to obtain a strip with a thickness of 0.5 mm.

[0028] Step 3, grading and aging: Place the 0.5mm strip into a bell furnace and hold it at 340℃ for 5 hours. Then raise the temperature to 450℃ and hold it for 4 hours before removing it from the furnace. Use a protective gas during the holding process. The protective gas is N2+H2.

[0029] Step 4, Finished product rolling: Roll the 0.5mm thick strip to 0.203mm, with a processing rate of 59.4%.

[0030] Product performance: After the above production process, the produced 0.203mm copper strip has a hardness of HV=175, a tensile strength of 590MPa, and a Vickers hardness of 161 after treatment at 470℃ / 3min. The high-temperature softening hardness reaches 92% of the original hardness.

[0031] Example 2

[0032] In this embodiment, a 1.2mm thick base material obtained through ingot casting, walking beam furnace heating, hot rolling, quenching, and cold working is used for high-temperature aging, large deformation cold rolling, graded aging, and finished product rolling. The specific process steps are as follows:

[0033] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 480℃, and the protective gas is N2+H2 for 15 hours.

[0034] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 66.7% to obtain a strip with a thickness of 0.4 mm;

[0035] Step 3, grading and aging: Place the 0.4mm strip into a bell furnace and hold it at 350℃ for 4 hours. Then raise the temperature to 460℃ and hold it for 4 hours before removing it from the furnace. Use a protective gas during the holding process. The protective gas is N2+H2.

[0036] Step 4, Finished product rolling: Roll the 0.4mm thick strip to 0.127mm, with a processing rate of 68.25%.

[0037] Product performance: After the above production process, the produced 0.127mm copper strip has a hardness HV=173, a tensile strength of 588MPa, and a Vickers hardness of 163 after treatment at 470℃ for 3min. The high-temperature softening hardness reaches 94% of the original hardness.

[0038] Example 3

[0039] In this embodiment, a 1.0 mm thick base material obtained through ingot casting, walking beam furnace heating, hot rolling, quenching, and cold working is used for high-temperature aging, large deformation cold rolling, graded aging, and finished product rolling. The specific process steps are as follows:

[0040] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 500℃, and the protective gas is N2+H2 for 12 hours.

[0041] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 70% to obtain a strip with a thickness of 0.3mm.

[0042] Step 3, grading and aging: The 0.3mm strip is placed in a bell furnace and held at 300℃ for 6 hours. Then the temperature is increased to 440℃ and held for 4 hours before being removed from the furnace. A protective gas, N2+H2, is used during the holding process.

[0043] Step 4, Finished product rolling: Roll the 0.3mm thick strip to 0.11mm, with a processing rate of 63.3%.

[0044] Product performance: After the above production process, the produced 0.11mm copper strip has a hardness of HV=175, a tensile strength of 582MPa, and a Vickers hardness of 159 after treatment at 470℃ for 3min. The high-temperature softening hardness reaches 91% of the original hardness.

[0045] Example 4

[0046] In this embodiment, a 2.0 mm thick base material obtained through ingot casting, walking beam furnace heating, hot rolling, quenching, and cold working is used for high-temperature aging, large deformation cold rolling, graded aging, and finished product rolling. The specific process steps are as follows:

[0047] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 530℃, and the protective gas is used for heat preservation for 10 hours. The protective gas is N2+H2.

[0048] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 62.5% to obtain a strip with a thickness of 0.75mm;

[0049] Step 3, grading and aging: Place the 0.75mm strip into a bell furnace and hold it at 350℃ for 6 hours. Then raise the temperature to 460℃ and hold it for 4 hours before removing it from the furnace. Use a protective gas, N2+H2, during the holding process.

[0050] Step 4, Finished product rolling: Roll the 0.75mm thick strip to 0.3mm, with a processing rate of 60%.

[0051] Product performance: After the above production process, the produced 0.75mm copper strip has a hardness of HV=174, a tensile strength of 588MPa, and a Vickers hardness of 158 after treatment at 470℃ for 3min. The high-temperature softening hardness reaches 91% of the original hardness.

[0052] The following are comparative test examples.

[0053] Comparative Example 1

[0054] Comparative Example 1 uses the same alloy composition as Examples 1-4. The preparation process does not involve graded aging; it uses only a general aging method. A 2.0 mm thick base material obtained through ingot casting, walking beam furnace heating, hot rolling, quenching, and cold working is used for high-temperature aging, large-deformation cold rolling, general low-temperature aging, and final rolling. Specific process parameters are as follows:

[0055] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 530℃, and the protective gas is used for heat preservation for 10 hours. The protective gas is N2+H2.

[0056] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 62.5% to obtain a strip with a thickness of 0.75mm;

[0057] Step 3, general low temperature aging: Put the 0.75mm strip into the bell furnace and keep it at 460℃ for 4 hours before taking it out of the furnace. Use a protective gas during the heat preservation. The protective gas is N2+H2.

[0058] Step 4: Finished product rolling: Roll the 0.75mm thick strip to 0.3mm.

[0059] Product Performance and Analysis: After the above production processes, the produced 0.3mm copper strip has a hardness HV=156 and a tensile strength of 540MPa. After treatment at 470℃ for 3min, its Vickers hardness is 140, and the high-temperature softening hardness reaches 88.5% of the original hardness, which does not meet the performance indicators required by this invention. The reason is that this example lacks a graded aging process, and the Fe atoms dissolved in the alloy did not form precipitated strengthening phases as much as possible, thus failing to meet the performance indicators required by the preparation process of this invention.

[0060] Comparative Example 2

[0061] This comparative example uses the same alloy composition as Examples 1-4 and employs a general Cu-Fe-P alloy strip processing method; that is, a base material with a thickness of 2.0 mm is obtained through ingot casting, walking beam furnace heating, hot rolling, quenching, and cold working, and then prepared using a high-temperature aging, large deformation cold rolling, softening annealing, and finished product rolling process. The specific process parameters are as follows:

[0062] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 550℃, and the protective gas is used for heat preservation for 10 hours. The protective gas is N2+H2.

[0063] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 62.5% to obtain a strip with a thickness of 0.75mm;

[0064] Step 3, softening annealing: Anneal the 0.75mm strip in an air cushion furnace at 600℃ and an annealing speed of 12m / min. Use a protective gas, N2+H2, during annealing.

[0065] Step 4: Finished product rolling: Roll the 0.75mm thick strip to 0.3mm.

[0066] Product Performance and Analysis: After the above production processes, the produced 0.3mm copper strip has a hardness HV=152 and a tensile strength of 535MPa. After treatment at 470℃ for 3min, its Vickers hardness is 126, and the high-temperature softening hardness reaches 83% of the original hardness, which does not meet the performance indicators required by this invention. The reason is that the softening annealing process temperature in step three causes the Fe strengthening phase and Mg3P2 compound to dissolve back into the copper matrix, thereby affecting the overall amount of strengthening phase precipitation and impacting the overall performance indicators.

[0067] Comparative Example 3

[0068] This comparative example uses an ingot of grade TFe2.5, with an alloy composition including: Fe: 2.1-2.6%; P: 0.015-0.15%; Zn: 0.05-0.2%; the balance being copper and unavoidable impurities. The processing method described in Examples 1-4, i.e., ingot casting-walking furnace heating-hot rolling-quenching-cold working, yields a base material with a thickness of 1.5 mm. Then, following the method of this invention, it undergoes high-temperature aging-large deformation cold rolling-graded aging-finished product rolling. Specific process parameters are as follows:

[0069] Step 1, High-temperature aging: Aging treatment is carried out using a bell furnace at 500℃, and the protective gas is used for heat preservation for 10 hours. The protective gas is N2+H2.

[0070] Step 2, large deformation cold rolling: The surface of the material after high temperature aging is cleaned, and then rolled with a large processing rate of 66.7% to obtain a strip with a thickness of 0.5 mm.

[0071] Step 3, grading and aging: Place the 0.5mm strip into a bell furnace and hold it at 340℃ for 5 hours, then raise the temperature to 450℃ and hold it for 4 hours before removing it from the furnace. Use a protective gas during the holding process, which is N2+H2.

[0072] Step 4: Finished product rolling: Roll the 0.5mm thick strip to 0.203mm;

[0073] Product Performance and Analysis: After the above production processes, the produced 0.203mm copper strip has a hardness HV=153 and a tensile strength of 545MPa. After treatment at 470℃ for 3min, its Vickers hardness is 127, and the high-temperature softening hardness reaches 83% of the original hardness. Therefore, without compositional control, the performance indicators described in the preparation process of this invention cannot be achieved. This is because the composition of a typical Cu-Fe-P alloy frame, after the above processing, has reached its limit in terms of improving material strength.

[0074] This invention increases the P content by adding Mg, which adds a Mg3P2 strengthening phase compared to the aging precipitates of general Cu-Fe-P alloys. Sn exists in the copper alloy in solid solution, improving the strength and heat resistance of the material, thereby enhancing the overall material performance.

[0075] Comparative Example 4

[0076] This comparative example uses the same alloy composition as Examples 1-4. The preparation process is hot rolling-milling-primary rolling-solution treatment-one-cold rolling-pre-aging-reversion heat treatment-cold rolling and aging. The specific process parameters are as follows:

[0077] Step 1, Hot rolling: The copper alloy ingot is heated, hot rolled, and then quenched to a thickness of 16.5 mm.

[0078] Step 2, Milling: Mill the hot-rolled copper alloy to remove the oxide layer, leaving a thickness of 15mm.

[0079] Step 3, Preliminary rolling: The milled copper alloy is pre-rolled to 2.0 mm;

[0080] Step 4, Solution treatment: The copper alloy after initial rolling is subjected to high-temperature online solution treatment. The heating temperature is 960℃, the flow rate is 4m / min, and the cooling medium is nitrogen or ammonia decomposition gas.

[0081] Step 5, One-time cold rolling: The solution-treated copper alloy is cold-rolled to 0.8mm in one pass, with a processing rate of 60%.

[0082] Step 6, Pre-aging: The copper alloy after one cold rolling is subjected to pre-aging treatment at a temperature of 500℃ for 10 hours.

[0083] Step 7, Regression Heat Treatment: The pre-aged copper alloy is subjected to regression heat treatment at a temperature of 600℃ and a holding time of 5 minutes.

[0084] Step 8, Cold Rolling and Aging:

[0085] a. Cold rolling: The 0.8mm strip after step seven is cold rolled on a finishing mill to a thickness of 0.34mm, with a processing rate of 57.5%;

[0086] b. Single aging: Aging is carried out once in a bell-shaped furnace at an aging temperature of 450℃ for 5 hours;

[0087] c. Cold rolling: After cold rolling on a finishing mill, the strip thickness is 0.18 mm, and the deformation is 47%;

[0088] d. Secondary aging: Secondary aging is carried out in a bell-shaped furnace at an aging temperature of 400℃ for 4 hours;

[0089] e. Final rolling: Final rolling is performed on the finishing mill, with a thickness of 0.11 mm and a total deformation of 38.9%.

[0090] Product Performance and Analysis: After the above production processes, the produced 0.11mm copper strip has a hardness HV=161 and a tensile strength of 555MPa. After treatment at 470℃ for 3min, its Vickers hardness is 140, and the high-temperature softening hardness reaches 87% of the original hardness, which does not meet the performance indicators required by this invention.

[0091] Based on the above preparation process, the solution treatment in step four is beneficial to improving the overall performance of the alloy, but it requires a specific high-temperature air cushion furnace. The reversion heat treatment in step seven will also cause some of the second phase to dissolve back, thus affecting the improvement of the material's comprehensive performance after the subsequent rolling process. Furthermore, the initial rolling process requires at least four cold workings, resulting in a large overall processing rate and a thin final product thickness, with a thickness of 0.203 mm or more. The high-temperature solution treatment thickness in step four needs to be controlled above 3.0 mm, which places high demands on existing equipment and is not suitable for industrial production.

[0092] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific implementation of the present invention with reference to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims.

Claims

1. A method for preparing a Cu-Fe-P alloy strip with high hardness and high resistance to softening, characterized in that, Includes the following steps: (1) High temperature aging: Under a protective atmosphere, the Cu-Fe-P alloy base material is kept at 480-550℃ for 7-15 hours to allow Fe and P elements to fully precipitate and form strengthening phases; (2) Large deformation cold rolling: The base material after step (1) is subjected to multiple passes of large-processing cold deformation rolling, with a total deformation of 60% to 70%; (3) Grading and aging: The strip after cold rolling in step (2) is first kept at 300-350℃ for 4-8 hours, and then the temperature is raised to 440-460℃ and kept for 3-6 hours before being taken out of the furnace. Protective gas is used during the heat preservation. (4) Finished product rolling: The strip after step (3) is cold rolled with a total deformation of 60% to 70% to obtain copper alloy strip of the target thickness; The composition of the Cu-Fe-P alloy base material, by weight percentage, includes: Fe: 2.3-2.5%; P: 0.07-0.09%; Zn: 0.05-0.20%; Sn: 0.01-0.04%; Mg: 0.02-0.09%; Ni: 0.005-0.025%; the balance being copper and unavoidable impurities. The Cu-Fe-P alloy base material is made from Cu-Fe-P alloy ingots through heating, hot rolling, quenching, and cold working.

2. The method for preparing the high-hardness, high-softening-resistance Cu-Fe-P alloy strip according to claim 1, characterized in that, The thickness of the Cu-Fe-P alloy base material is 1.0~2.0 mm.

3. The method for preparing the high-hardness, high-softening-resistance Cu-Fe-P alloy strip according to claim 1, characterized in that, In step (1), the Cu-Fe-P alloy base material is subjected to high-temperature aging treatment in a bell furnace.

4. The method for preparing the high-hardness, high-softening-resistance Cu-Fe-P alloy strip according to claim 1, characterized in that, In step (3), the Cu-Fe-P alloy base material is subjected to graded aging treatment in a bell furnace.

5. A high-hardness Cu-Fe-P alloy strip with high resistance to softening, prepared by the method described in any one of claims 1 to 4.

6. The high-hardness, high-softening-resistance Cu-Fe-P alloy strip according to claim 5, characterized in that, Its Vickers hardness HV≥170, tensile strength≥580 MPa, and after treatment at 470℃ / 3min, the high-temperature softening hardness is not less than 90% of the original hardness.