Low-stress copper-cobalt-nickel-silicon alloy and preparation method and application thereof

Abstract

The invention relates to a low-stress copper-cobalt-nickel-silicon alloy and a preparation method and application thereof. The low-stress copper-cobalt-nickel-silicon alloy comprises 0.5 wt%-1.0 wt% of Ni, 0.005 wt%-0.4 wt% of Co, 0.1 wt%-0.3 wt% of Si, 0.05 wt%-0.4 wt% of Sn, 0.01 wt%-0.02 wt% of P, 0.05 wt%-0.3 wt% of Zn and the balance Cu and inevitable trace impurities. The preparation method of the low-stress copper-cobalt-nickel-silicon alloy comprises the steps of burdening, smelting, casting, hot rolling, rough rolling, primary annealing, intermediate rolling, aging heat treatment, finished product rolling and secondary annealing. The preparation method comprises the following steps: proportioning and smelting according to the mass percent of each element of the copper alloy; the aging heat treatment is stepped aging heat treatment, heating is conducted to 200-350 DEG C, heat preservation is conducted for 1-2 h, then heating is conducted to 400-500 DEG C, and heat preservation is conducted for 10-12 h.

Description

Technical Field

[0001] This invention belongs to the field of copper alloys, specifically relating to a copper-cobalt-nickel-silicon alloy, its preparation method, and its application. Background Technology

[0002] With the rapid development and iteration of consumer electronics, the components of these electronic devices are becoming increasingly miniaturized, more powerful, and more reliable. Consequently, the semiconductor lead frames of mobile phones and laptops are developing towards miniaturization, high density, finer lead spacing, and more pins. Traditional cemented carbide stamping lead frames can no longer meet the requirements for fine-pitch lead frames. However, etching processes can achieve the production of lead frames with the highest density and the most pins. Therefore, the application prospects of etching forming for lead frames are broad.

[0003] Copper alloy leadframes are core structural components of semiconductors, primarily providing mechanical support for the chip, transmitting signals / power, and aiding in heat dissipation. Therefore, copper alloy leadframes possess high strength, excellent thermal conductivity, and high-temperature resistance. Meanwhile, the copper strip used for leadframe etching places higher demands on the product's board shape and residual stress. Currently, customers have higher requirements for etched copper strips: tensile strength ≥580MPa, conductivity ≥55%, board shape accuracy ≤3I, etching warpage ≤0.08mm, and high-temperature softening resistance—meaning the alloy retains more than 85% of its original hardness and strength after holding at 450℃ for 1 hour. Currently, the lead frame uses C19400 iron bronze strip, whose alloy composition is Fe: 2.1-2.6 wt%, Zn: 0.05-0.20 wt%, P: 0.015-0.015 wt%, Pb≤0.03 wt%, with the balance being Cu. Its tensile strength is <550MPa, the product's plate shape is ≤10I, and the etching warpage is 0.15-0.30mm. Domestically produced iron bronze for etching cannot yet meet the new product requirements put forward by customers in terms of tensile strength, plate shape, residual stress, and resistance to high-temperature softening. Therefore, the strength, plate shape, residual stress, and resistance to high-temperature softening of existing copper alloy strips for etching lead frames need further improvement.

[0004] CN101151385A discloses a Cu-Ni-Si-Co-Cr copper alloy for electronic components, containing Ni: 0.5-2.5 wt%, Co: 0.5-2.5 wt%, Si: 0.3-1.2 wt%, Cr: 0.09-0.5 wt%, with the remainder being copper and unavoidable impurities. In this alloy composition, ([Ni+Co] / Si) is 4-5, and (Ni / Co) is 0.5-2. However, the Ni, Co, and Si contents are too high, causing the material's conductivity to fall below 55% IACS. Because Sn and P are not added, the formation and precipitation of the second phase are not promoted during the aging process, resulting in coarse precipitates, high internal stress in the alloy, and unqualified warpage measurements after etching.

[0005] Cu-Ni-Si alloys (so-called Corson alloys) have attracted attention as materials with a superior balance between strength and electrical conductivity. In this alloy system, for example, through processes based on solution treatment, cold rolling, aging treatment, cold finishing, and low-temperature annealing, it is possible to obtain sheet metal with a yield strength of over 700 MPa while maintaining high electrical conductivity (30–50% IACS). However, further increasing the strength of this alloy system is not necessarily easy.

[0006] Given the shortcomings of the existing technologies, there is an urgent need to design alloy composition and process parameters to prepare copper alloys with high strength, excellent resistance to high-temperature softening, good electrical conductivity, excellent plate shape, and minimal residual stress, while ensuring the conductivity of the alloy. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a low-stress copper-cobalt-nickel-silicon alloy, which is composed of the following components by weight percentage: Ni: 0.5-1.0 wt%, Co: 0.005-0.4 wt%, Si: 0.1-0.3 wt%, Sn: 0.05-0.4 wt%, P: 0.01-0.02 wt%, Zn: 0.05-0.3 wt%, with the balance being Cu and unavoidable trace impurities; The (Ni+Co) / Si mass ratio is 4.5-5.5. "wt%" refers to the weight percentage, where Ni is 0.05-1.00 wt%, for example, 0.06 wt%, 0.07 wt%, 0.75 wt%, 0.80 wt%, 0.85 wt%, 0.90 wt%, which is the percentage of the weight of Ni element in the weight of the copper-cobalt-nickel-silicon alloy.

[0008] The Co content is 0.005-0.4 wt%, for example, 0.005 wt%, 0.006 wt%, 0.009 wt%, 0.095 wt%, 0.100 wt%, 0.125 wt%, 0.200 wt%, 0.350 wt%, 0.385 wt%, which represents the percentage of the weight of Co in the copper-cobalt-nickel-silicon alloy.

[0009] The Si content is 0.1-0.3 wt%, for example, 0.1 wt%, 0.02 wt%, 0.15 wt%, 0.18 wt%, 0.20 wt%, 0.24 wt%, 0.28 wt%, which is the percentage of the weight of Si element in the weight of the copper-cobalt-nickel-silicon alloy.

[0010] The Sn content is 0.05-0.4 wt%, for example, 0.05 wt%, 0.08 wt%, 0.11 wt%, 0.15 wt%, 0.20 wt%, 0.24 wt%, 0.30 wt%, 0.35 wt%, 0.39 wt%, which is the percentage of the weight of Sn in the copper-cobalt-nickel-silicon alloy.

[0011] The P is 0.01-0.02 wt%, for example, 0.01 wt%, 0.012 wt%, 0.018 wt%, 0.02 wt%, which is the percentage of the weight of the P element in the weight of the copper-cobalt-nickel-silicon alloy.

[0012] The Zn content is 0.05-0.3 wt%, for example, 0.05 wt%, 0.08 wt%, 0.09 wt%, 0.10 wt%, 0.18 wt%, 0.25 wt%, 0.27 wt%, which is the percentage of the weight of Zn element in the weight of the copper-cobalt-nickel-silicon alloy.

[0013] Preferably, the weight percentages of each component in the copper-cobalt-nickel-silicon alloy are: Ni: 0.8 wt%, Co: 0.2 wt%, Si: 0.2 wt%, Sn: 0.15 wt%, P: 0.015 wt%, Zn: 0.1 wt%, with the balance being Cu and unavoidable trace impurities.

[0014] In this invention, the low-stress copper-cobalt-nickel-silicon alloy includes a second phase, which includes a Ni3Si phase, and the average diameter of the second phase is ≤0.2μm.

[0015] In this invention, the second phase further includes the (Co, Ni)2Si phase.

[0016] In this invention, the second phase is diffusely distributed, and the number of second phase particles precipitated per unit area of ​​tissue is ≥1000 / μm.2 .

[0017] In this invention, the copper-cobalt-nickel-silicon alloy has a conductivity ≥55% IACS, a tensile strength ≥580 MPa, a plate shape ≤3I, and an etching warpage ≤0.08 mm.

[0018] In this invention, the residual stress of the copper-cobalt-nickel-silicon alloy is represented by etching warpage.

[0019] In this invention, the copper-cobalt-nickel-silicon alloy exhibits a stress relaxation rate of ≤10% and a high-temperature softening resistance of ≥85% after holding at 120℃ with an initial stress of 50% of the yield strength for 1000 hours.

[0020] Preferably, the conductivity is 60-65% IACS.

[0021] Preferably, the tensile strength is 600-700 MPa.

[0022] Preferably, the plate shape is 0.5-2I.

[0023] Preferably, the residual stress, i.e. the etching warpage, is 0.01-0.05 mm.

[0024] Preferably, the stress relaxation rate is 4-7%.

[0025] Preferably, the high-temperature softening resistance is 90-95%.

[0026] Adding trace amounts of zinc (Zn) can lower the solution temperatures of Ni, Co, and Si in the alloy and accelerate the precipitation rate of the second phase during the formation process. Simultaneously, Zn improves the weldability of this copper alloy, primarily by lowering the required welding temperature and increasing the fluidity of the molten and semi-solid weld pool, making it easier for the molten metal to fill the weld gaps and improving weld quality. The effect of Zn is significant above 0.05%, but exceeding 0.3% severely reduces the alloy's conductivity. Therefore, a Zn content controlled within the range of 0.05-0.3% is optimal.

[0027] Adding trace amounts of Sn allows it to synergistically interact with Ni, Co, and Si to promote the precipitation of the second phase, forming finer and more stable dispersed precipitates such as Ni3Si and (Co, Ni)2Si. Simultaneously, tin forms an α-phase solid solution with the copper matrix, strengthening the copper alloy matrix and improving its elasticity and wear resistance. A Sn content of 0.05% or higher effectively promotes the precipitation of the second phase while improving elasticity and wear resistance. However, levels exceeding 0.4% significantly reduce the conductivity of the copper alloy; therefore, a Sn content controlled within the range of 0.05-0.4% is optimal.

[0028] By adding Ni, Co, and Si elements, Ni, Co, and Si form second-phase strengthening phases Ni3Si and (Co, Ni)2Si during aging heat treatment. Through the "dispersion strengthening" effect, the hardness, strength, electrical conductivity, and high-temperature softening resistance of the alloy are greatly improved.

[0029] Adding trace amounts of phosphorus (P) allows it to react with oxygen during the casting process, effectively deoxidizing and purifying the melt, reducing gases and impurities, improving ingot quality, and preventing defects such as porosity and cracks. Simultaneously, P inhibits grain growth during heat treatment, refining the grains and thus improving the alloy's strength and plasticity. However, when the phosphorus content exceeds a certain value, excess phosphorus tends to segregate at grain boundaries and form brittle phosphides with cobalt and nickel, reducing the amount of cobalt and nickel available to form silicides, decreasing the distribution and morphology of existing precipitates, and consequently reducing the alloy's conductivity and performance. Conversely, too low a phosphorus content fails to deoxidize and purify the melt; therefore, a phosphorus content of 0.01-0.02% is preferred.

[0030] In this invention, the copper alloy contains 0.5-1.0 wt% Ni, 0.005-0.4 wt% Co, and 0.1-0.3 wt% Si, with a (Ni+Co) / Si mass ratio of 4.5-5.5. When the (Ni+Co) / Si mass ratio is too high, the excess Ni or Co fails to form a second-phase reinforcing phase with Si, instead remaining dissolved in the matrix. Simultaneously, it fails to form a large number of fine, uniform second-phase reinforcing phases, thus reducing the alloy's conductivity and strength. If the (Ni+Co) / Si mass ratio is too low, the Si content is excessive. Excess Si easily forms coarse, brittle silicides (such as Cu3Si or elemental Si), significantly reducing the alloy's plasticity, increasing the risk of cold-working cracking, and simultaneously reducing the alloy's strength and conductivity.

[0031] Secondly, this invention provides a method for preparing a low-stress copper-cobalt-nickel-silicon alloy. The prepared copper alloy exhibits high strength, excellent resistance to high-temperature softening, good electrical conductivity, excellent plate shape, and minimal residual stress. The process flow of the preparation method includes batching, smelting, casting, hot rolling, rough rolling, first annealing, intermediate rolling, aging heat treatment, finished product rolling, and second annealing.

[0032] In this invention, the batching and smelting steps are as follows: Electrolytic copper is added to a smelting furnace and heated to melt. The molten metal in the furnace is then tightly covered with dry charcoal. The temperature is then raised to 1300-1380℃, and pure nickel, silicon, cobalt, zinc, and tin are added according to the composition ratio. After 20-50 minutes, slag is skimmed off, and a covering agent is used to cover the molten copper. Simultaneously, a copper-phosphorus master alloy is added according to the ratio. After holding at this temperature for 20-50 minutes, the temperature of the molten copper is adjusted, and casting begins.

[0033] In this invention, preferably, the charcoal covering thickness is 100mm-120mm.

[0034] In this invention, preferably, the covering agent is a mixture of cryolite and sodium carbonate.

[0035] In this invention, preferably, the cryolite and sodium carbonate are mixed in a ratio of 1:0.9-1.2.

[0036] In this invention, preferably, the cryolite and sodium carbonate are mixed in a 1:1 ratio.

[0037] In this invention, preferably, the covering agent has a coverage thickness of 80-100 mm.

[0038] In this invention, preferably, after adding a copper-phosphorus master alloy, the temperature is adjusted to 1250-1350℃.

[0039] In this invention, the casting is a semi-continuous casting process, specifically including a casting temperature of 1250-1350℃ and a casting speed of 60-75mm / min.

[0040] In this invention, preferably, the casting process is a red ingot casting process.

[0041] In this invention, preferably, the crystallizer is protected by a pure argon gas shield during the casting process to isolate it from air. Preferably, the pressure of the argon gas is 0.008-0.012 MPa.

[0042] In this invention, preferably, the flow rate of the argon gas is 50-60 mL / min.

[0043] In this invention, the primary cooling water pressure is 0.5-0.7 MPa, the inlet water temperature is 26-30℃, the outlet water temperature is 40-50℃, the ingot exiting the crystallizer temperature is controlled at 700℃-850℃, and the ingot is cooled by immersion in a water tank at a distance of 2000-2500mm from the crystallizer, with the water temperature in the tank being 38-45℃. The ingot casting specifications are 180*630mm*8000mm.

[0044] In this invention, the hot rolling process includes hot rolling and final rolling with online water cooling and quenching.

[0045] In this invention, the hot rolling process involves heating the ingot to 800-1000℃, preferably 850-950℃, and holding it at that temperature for 1-2 hours.

[0046] In this invention, the hot rolling speed is 150-250 m / min, preferably 200-250 m / min.

[0047] In this invention, the hot rolling refers to high-temperature rapid hot rolling.

[0048] In this invention, the final rolling temperature is 700-780℃.

[0049] In this invention, after final rolling, online water-cooling quenching is used to reduce the temperature to 50-100℃.

[0050] In this invention, online water-cooling quenching is performed within 10 seconds after final rolling.

[0051] In this invention, the alloy thickness obtained after hot rolling is 12.5±0.5mm, and the width after widening is 650±5mm.

[0052] In this invention, the surface is milled after hot rolling.

[0053] In this invention, the milling amount on one side is 0.5-0.8 mm, and the thickness after milling is 11±0.5 mm.

[0054] In this invention, the alloy is rough rolled after milling, and the rough rolling has a machining rate of 80-98%.

[0055] In this invention, the alloy is trimmed after rough rolling.

[0056] In this invention, the cutting edge is a single-sided cut of 7-8mm, and the width after cutting is 635±0.5mm.

[0057] In this invention, the first annealing is solution gas cushion furnace annealing.

[0058] In this invention, the first annealing is high-temperature rapid solution gas cushion furnace annealing.

[0059] The solution-bonded air cushion furnace annealing adopts a single-sheet unfolding air cushion furnace annealing, with an annealing temperature of 800-850℃ and an annealing speed of 20-50m / min.

[0060] In the solution-cooled gas cushion furnace annealing process, the heating section of the gas cushion furnace is 10-14m long, the air-cooling section is 2-4m long, and the water-cooling section is 2-4m long. After passing through the water-cooling section, the temperature of the copper billet drops to below 20-50℃.

[0061] In the air cushion furnace, the protective gas contains 2-4% H2 (by volume) and the balance is nitrogen.

[0062] In this invention, after the first annealing, the average grain size of the alloy microstructure is 1-5 μm.

[0063] In this invention, after the first annealing, the alloy has a hardness of 85-100HV, a tensile strength of 360-400MPa, an elongation of 45-55%, and an electrical conductivity of 20-28%IACS.

[0064] In this invention, the intermediate rolling mill has a processing rate of 30-80%; preferably, the processing rate is 45-75%.

[0065] In this invention, the aging heat treatment is a stepped aging heat treatment.

[0066] The stepped aging heat treatment includes heating the furnace to 200-350℃, preferably 280-320℃, and holding it at that temperature for 1-2 hours.

[0067] The aging heat treatment involves holding the temperature at a certain level, then raising the temperature to 400-500℃, preferably 420-460℃, and holding for 10-12 hours.

[0068] In this invention, after the aging heat treatment, the grain size of the microstructure is 0.5-3 μm.

[0069] In this invention, after the aging heat treatment, second phase particles are precipitated.

[0070] In this invention, the second phase is a Ni3Si strengthening phase.

[0071] In this invention, preferably, the second phase further includes a (Co, Ni)2Si phase.

[0072] In this invention, the average diameter of the second phase particles is ≤0.2μm.

[0073] In this invention, preferably, the average diameter of the second phase particles is 0.045-0.15 μm.

[0074] In this invention, the second phase is diffusely distributed, and the number of second reinforcing phase particles precipitated per unit area of ​​the tissue is ≥1000 / μm. 2 .

[0075] In this invention, the number of particles in the second reinforcing phase is 1500-3000 per μm. 2 .

[0076] In this invention, after the aging heat treatment, the alloy is cleaned and dried.

[0077] In this invention, the cleaned and dried alloy is rolled into a finished product, and the finished product rolling has a processing rate of 30-40%.

[0078] After the finished product is rolled, the alloy is cleaned and dried.

[0079] In this invention, the cleaned and dried alloy is subjected to tension bending straightening using a 23-roll tension bending straightening method. The straightening elongation is 0.15-0.3%, and the straightening tension is 220-280 N / mm. 2 .

[0080] In this invention, the alloy after bending and straightening is subjected to a second annealing, which is an online stress-relief furnace annealing.

[0081] In this invention, the online stress-relief annealing is performed using a single-sheet unfolding air cushion furnace, with an annealing temperature of 400-500℃, preferably 420-460℃.

[0082] In this invention, the tension of the copper strip in the air cushion furnace during the second annealing is 180-260 N / mm. 2 Annealing speed is 60-100 m / min, and the protective gas is 2-4% (by volume) H2 and the balance nitrogen.

[0083] In this invention, the alloy finished product is slitting and packaged after the second annealing.

[0084] In this invention, the cleaning process includes degreasing and acid washing.

[0085] In this invention, the degreasing is performed using an aqueous sodium hydroxide solution; the acid washing is performed using sulfuric acid; preferably, the sulfuric acid concentration is 120-150 g / L.

[0086] In this invention, the drying process uses an oven with a temperature of 75–95°C.

[0087] In this invention, the copper-cobalt-nickel-silicon alloy undergoes hot rolling and a first annealing, which greatly improves the solid solubility of the alloy. This allows the Ni, Co, and Si elements in the copper alloy microstructure to be dissolved in the α matrix to the maximum extent, providing favorable conditions for the strengthening and dispersion precipitation of the second phase during subsequent aging heat treatment. In other words, it increases the precipitation motive force of the second phase during subsequent aging heat treatment, which is conducive to the full precipitation and refinement of the second phase during subsequent aging heat treatment, thereby further improving the strength, high-temperature softening resistance, bending properties, and electrical conductivity of the alloy material.

[0088] In this invention, the stepped aging heat treatment employs this microstructure-controlled stepped aging process, resulting in a grain size ≤3μm. This ensures the sufficient precipitation of the second-phase Ni3Si and (Co, Ni)2Si reinforcing phases, while maintaining an conductivity above 55% IACS. Furthermore, this process results in an average diameter of less than 200 nm for the precipitated reinforcing second phases, with approximately 1000 particles / μm per unit area. 2 The above achieves the optimal effect of second-phase dispersion strengthening, greatly improving the material's strength, conductivity, and resistance to high-temperature softening.

[0089] In this invention, the second annealing equipment is a tension-straightening air-cushion annealing furnace. The annealing temperature is controlled within the aging temperature range, and the annealing speed and tension are coordinated to release internal stress in the textured structure after high processing rate, reduce distortion energy during processing, and ensure that the volume ratio of dislocation clusters in the material structure is ≤10%. Simultaneously, the internal stress in the material structure is completely released, ensuring that the processing internal stress inside the copper alloy is released after annealing, further improving the plate shape. If the annealing temperature is too low or the speed is too high, the dislocations formed during cold working of the copper alloy will not be fully recovered, and the volume ratio of dislocation clusters in the material structure will be >10%, resulting in insufficient residual internal stress in the copper alloy. If the stress-relief annealing temperature is too high or the speed is too low, the grain structure grows after recrystallization of the cold-worked copper alloy structure, leading to a significant decrease in alloy strength, failing to meet the requirement of greater than 580 MPa.

[0090] In this invention, the material structure dislocation clusters refer to the dense dislocation aggregation regions formed when the material is subjected to external forces, heat treatment, etc., dispersed individual dislocations attract and entangle with each other.

[0091] In this invention, the second annealing, namely stress-relief annealing, increases tension control, which can further release the internal stress from cold working and improve the sheet shape during the annealing process, ensuring that the sheet shape accuracy is ≤3I. At this time, the unit tension needs to reach more than 30% of the material's tensile strength, i.e., a unit tension of 180-260 N / mm. 2 However, if the tension is too high, the alloy strip will generate new local internal stress during stress relief annealing, which will make it impossible to reduce the cold working internal stress of the alloy to the required range.

[0092] Thirdly, the present invention also provides the application of the aforementioned low-stress copper-cobalt-nickel-silicon alloy in lead frames. The copper-cobalt-nickel-silicon alloy of the present invention possesses high strength, excellent resistance to high-temperature softening, good electrical conductivity, excellent plate shape, and minimal residual stress, making it suitable for applications requiring lead frame etching, etc.

[0093] The copper-cobalt-nickel-silicon alloy provided by this invention has a warpage of ≤0.08mm after etching in the lead frame; Preferably, the etching warpage is 0.01-0.05 mm.

[0094] In this invention, etching warpage refers to the degree of deviation between the actual shape of a component and the ideal plane (or designed curved surface) after etching, and is a key indicator for measuring the geometric accuracy of etched parts. Warpage is usually expressed as the ratio of "maximum deviation / component size".

[0095] In this invention, residual stress refers to the internal stress field of a component under natural conditions with no external load and uniform temperature, which is in a state of self-equilibrium.

[0096] In this invention, after the etching process is completed, the component is removed from the etching solution environment, and the temperature gradually returns to uniformity, but the redistribution of residual stress does not stop. At this time, the component will achieve a new equilibrium state of internal stress through elastic deformation or slight plastic deformation, and the warping shape will stabilize accordingly. If the total residual stress exceeds the yield strength of the material, "permanent warping" will occur; if the stress does not exceed the yield strength, the warping can be partially alleviated through elastic recovery.

[0097] Compared with the prior art, the beneficial effects of this invention are as follows: This invention promotes the precipitation of the second strengthening phases Ni3Si and (Co, Ni)2Si during aging heat treatment by controlling the contents of Ni, Co, Si, Sn, Zn, and P. At the same time, it refines the second strengthening phases and ensures that the strengthening phases are uniformly dispersed on the matrix, thereby maximizing the strengthening effect of the second phase precipitation, improving the hardness, strength, and conductivity of the material, and also enhancing the high-temperature softening resistance and stress relaxation resistance of copper-cobalt-nickel-silicon alloys.

[0098] The hot rolling and annealing processes of this invention significantly improve the solid solubility of the alloy, maximizing the dissolution of Ni, Co, and Si elements in the copper alloy microstructure within the α matrix. This increases the precipitation potential of the second phase during subsequent aging heat treatment, facilitating the full precipitation and refinement of the second phase during this process. Consequently, it further enhances the strength, resistance to high-temperature softening, bending performance, and electrical conductivity of the alloy material. Through stretch bending straightening and online stress-relief furnace annealing, the straightening process improves the plate shape, while the online stress-relief furnace annealing process reduces distortion energy during microstructure processing, ensuring that the product's plate shape accuracy is ≤3I and the etching warpage is ≤0.08mm. Detailed Implementation

[0099] Those skilled in the art can refer to the content of this document and appropriately replace and / or modify the process parameters to achieve the desired results. However, it should be particularly noted that all similar replacements and / or modifications are obvious to those skilled in the art and are considered to be included in this invention. The products and preparation methods described in this invention have been described through preferred examples, and those skilled in the art can obviously modify or appropriately change and combine the products and preparation methods described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0100] Unless otherwise defined, the technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention pertains. This invention uses the methods and materials described herein; however, other suitable methods and materials known in the art may also be used. The materials, methods, and examples described herein are illustrative only and are not intended to be limiting. All publications, patent applications, patent cases, provisional applications, database entries, and other references mentioned herein are incorporated herein by reference in their entirety. In case of conflict, the definitions included in this specification shall prevail.

[0101] Unless otherwise stated, all percentages, parts, proportions, etc. are by weight; other statements include, but are not limited to, “wt%” meaning weight percentage, “mol%” meaning mole percentage, and “vol%” meaning volume percentage.

[0102] When quantities, concentrations, or other numerical values ​​or parameters are given as ranges, preferred ranges, or a series of upper and lower preferred values, it should be understood that they specifically disclose all ranges formed by any pair of values ​​of any larger or preferred range limit and any smaller or preferred range limit, regardless of whether the ranges are disclosed separately. For example, when describing a range of “1 to 5 (1-5)”, the described range should be understood to include ranges such as “1 to 4 (1-4)”, “1 to 3 (1-3)”, “1 to 2 (1-2)”, “1 to 2 (1-2) and 4 to 5 (4-5)”, “1 to 3 (1-3) and 5”, etc. Unless otherwise stated, where numerical ranges are described herein, the ranges are intended to include the range endpoints as well as all integers and fractions within that range.

[0103] When the term “about” is used to describe the endpoint of a numerical value or range, the disclosure should be understood to include the specific value or endpoint referred to.

[0104] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive "or" rather than an exclusive "or". For example, any of the following conditions apply to condition A "or" B: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist).

[0105] Furthermore, the indefinite articles “a” and “an” preceding the elements or components of the invention are intended to indicate that the number of times the said element or component appears (i.e., occurs) is not limited. Therefore, “a” or “an” should be understood to include one or at least one, and unless the quantity is explicitly stated to be singular, the singular form of the elements or components also includes the plural case.

[0106] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, the phrase "comprising an element defined as..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0107] Unless otherwise specified, the materials, methods, and examples described herein are exemplary and not limiting. While similar or equivalent methods and materials can be used to implement or test the invention, suitable methods and materials are described herein.

[0108] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0109] This invention selects 6 examples and 9 comparative examples for illustration. The mass percentage of the alloy chemical composition of each example and comparative example is shown in Table 1. The details of the key process operation parameters are shown in Table 2, and the details of the alloy performance test data are shown in Table 3. The preparation process of the copper-cobalt-nickel-silicon alloys in the 6 examples and 9 comparative examples is as follows: batching and melting → semi-continuous casting → high-temperature rapid hot rolling + final rolling and online water cooling quenching → milling → rough rolling → trimming → high-temperature rapid solution gas cushion furnace annealing → intermediate rolling → stepped aging heat treatment → cleaning → finished product rolling → cleaning → 23-roll tension straightening → online stress relief furnace annealing → finished product slitting and packaging.

[0110] 1) Batching and Smelting: Electrolytic copper is added to the smelting furnace and heated to melt. The molten copper in the furnace must be tightly covered with dry charcoal, and no copper liquid should be exposed to the air. Then, the temperature is raised to 1300~1380℃, and pure nickel, silicon, cobalt, zinc and tin are added according to the composition ratio. After 20-50 minutes, slag is skimmed off, and a covering agent of cryolite and sodium carbonate in a 1:1 ratio is used for covering, with a covering thickness of 80-100mm. At the same time, copper-phosphorus master alloy is added according to the ratio. After holding at this temperature for 20-50 minutes, the temperature of the molten copper is adjusted to 1250-1350℃ to begin casting.

[0111] 2) Semi-continuous casting: The copper molten metal is cast at a temperature controlled at 1250-1350℃, with a casting speed of 60-75 mm / min, using a red ingot casting process. During casting, the crystallizer is protected by a pure argon gas shield to isolate it from air. The argon gas pressure inside the crystallizer is 0.008-0.012 MPa, and the flow rate is 50-60 mL / min. For the red ingot casting process: the primary cooling water pressure is 0.5-0.7 MPa, the inlet temperature is 26-30℃, and the outlet temperature does not exceed 40℃. The ingot temperature exiting the crystallizer is controlled at 700℃-850℃. The ingot is then cooled by immersion in a water tank at a temperature of 38-45℃ when it is 2000-2500 mm from the crystallizer. The ingot casting dimensions are 180*630mm*8000mm.

[0112] 3) High-temperature rapid hot rolling + final rolling online water cooling and quenching: The ingot is heated to 850℃-950℃ and held at that temperature for 1-2 hours. Then, hot rolling begins at a speed of 200-250 m / min, ensuring the final rolling temperature is above 700℃. Simultaneously, online water quenching is performed within 10 seconds of the final rolling to reduce the copper strip temperature to below 100℃. The thickness after hot rolling is 12.5±0.5 mm, and the width after widening is 650±5 mm.

[0113] 4) Milling: The milling amount on one side is 0.5-0.8mm, and the thickness after milling is 11±0.5mm.

[0114] 5) Rough rolling: The rough rolling processing rate is controlled at 80-98%.

[0115] 6) Edge trimming: 7-8mm on one side, resulting in a width of 635±0.5mm after trimming. 7) High-Temperature Rapid Solution Annealing in an Air Cushion Furnace: A single-sheet unfolding air cushion furnace is used for annealing at a temperature of 800-850℃ and a speed of 20-50 m / min. The heating section of the air cushion furnace is 10-14 m long, the air-cooling section is 2-4 m long, and the water-cooling section is 2-4 m long. After the water-cooling section, the copper billet temperature drops below 50℃. The protective gas in the air cushion furnace contains 2-4% H2 (by volume) and the balance is nitrogen. After solution annealing, the average grain size of the strip is controlled within 5 μm, the strip hardness is 85-100 HV, the tensile strength is 360-400 MPa, the elongation is 45-55%, and the conductivity is 20-28% IACS.

[0116] 8) Intermediate rolling: The processing rate is controlled at 45-75%.

[0117] 9) Stepped aging heat treatment: First, heat the furnace to 280-320℃ and hold for 1-2 hours. Then, raise the temperature to 420-460℃ and hold for 10-12 hours. After heat treatment, the grain size of the microstructure is less than 3μm, and the average diameter of the precipitated second-phase Ni3Si and (Co, Ni)2Si reinforcing phase particles is less than 200 nm, with the number of second-phase reinforcing phase particles precipitated per unit area of ​​the microstructure being 1000 particles / μm. 2 above.

[0118] 10) Cleaning: Degreasing with sodium hydroxide aqueous solution. Acid washing with sulfuric acid concentration of 120-150 g / L. Cleaning and drying in an oven at 75-95℃.

[0119] 11) Finished product rolling: The processing rate is controlled at 30-40%.

[0120] 12) Cleaning: Degreasing with sodium hydroxide aqueous solution. Acid washing with sulfuric acid concentration of 120-150 g / L. Cleaning and drying in an oven at 75-95℃.

[0121] 13) 23-roll tension straightening: straightening elongation is 0.15-0.3%, and straightening tension is 220-280 N / mm. 2 .

[0122] 14) Online stress-relief furnace annealing: Single-sheet unfolded air cushion furnace annealing is adopted, with an annealing temperature of 420-460℃ and a copper strip tension of 180-260 N / mm inside the air cushion furnace. 2 Annealing rate is 60-100 m / min, and the protective gas contains 2-4% H2 and the balance is nitrogen.

[0123] The difference between Comparative Example 1 and Example 4 is that no Co element was added to the alloy elements.

[0124] The difference between Comparative Example 2 and Example 4 is that the (Ni+Co) / Si mass ratio in the alloying elements is less than 4.5, i.e., Si: 0.3 wt%. The difference between Comparative Example 3 and Example 4 is that the P content in the alloying elements is 0.1 wt%.

[0125] The difference between Comparative Example 4 and Example 4 is that in step 7), solution annealing is performed in an air cushion furnace. A single-sheet unfolding air cushion furnace is used for annealing at a temperature of 600°C and a speed of 25 m / min.

[0126] The difference between Comparative Example 5 and Example 4 is that step 9) is not a stepped aging heat treatment. Step 9) heat treatment was performed without stepped aging heat treatment. The temperature was raised to 295°C and held for 11 hours.

[0127] The difference between Comparative Example 6 and Example 4 is that: 14) Online stress-relief furnace annealing. A single-sheet unfolded air cushion furnace was used for annealing at a temperature of 300°C, with a copper strip tension of 240 N / mm inside the furnace. 2 Annealing speed 80m / min.

[0128] The difference between Comparative Example 7 and Example 4 is that step 9) is a stepped aging heat treatment. In step 9) heat treatment, the second stage annealing temperature is 520°C, and the holding time is 11 hours.

[0129] The difference between Comparative Example 8 and Example 4 is that the Ni content is 1.8 wt%, the Co content is 1.0 wt%, the Si content is 0.8 wt%, the (Ni+Co) / Si mass ratio is 3.5, and Sn, P and Zn are not added.

[0130] The difference between Comparative Example 9 and Example 4 is that the Ni content is 2.0 wt%, the Co content is 1.2 wt%, the Si content is 0.8 wt%, the Cr content is 0.2 wt%, the (Ni+Co) / Si mass ratio is 4, and Sn, P and Zn are not added.

[0131] Mechanical property testing: The room temperature tensile test was conducted on an electronic universal mechanical property testing machine in accordance with GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Room temperature test method. A 20 mm wide specimen with a head was used, and the tensile speed was 5 mm / min.

[0132] Hardness testing: The test was conducted in accordance with the requirements of GB / T 4340.0-2009 Metallic Materials Vickers Hardness Test - Part 1: Test Method. The test strip size was 30mm × 30mm, the load was 1 kg, and the loading time was 15 s.

[0133] Conductivity testing was conducted in accordance with GB / T 3048.2-2007 Electrical Performance Test Methods for Wires and Cables Part 2: Resistivity Test for Metallic Materials, and expressed as %IACS.

[0134] Grain size analysis of the metallographic structure was performed according to the intercept method in GB / T 6394-2007 "Method for Determination of Average Grain Size of Metals". The grain size was measured in photographs taken under a 5000x metallographic microscope. The sample width was 10 mm and the length was 10 mm.

[0135] High-temperature softening resistance test: After holding at 450℃ for 1 hour, the strength and hardness were tested and calculated.

[0136] Tensile strength test: The room temperature tensile test was conducted on an electronic universal mechanical performance testing machine in accordance with GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Room temperature test method. The test specimen was dumbbell-shaped, the width of the tensile specimen was 20 mm, and the tensile speed was 5 mm / min.

[0137] Panel shape test: Panel shape testing uses online automatic panel shape testing equipment.

[0138] Stress relaxation resistance test: The stress relaxation resistance test requires 120℃, initial stress of 50% of yield strength, and 1000h heat preservation, and then the stress relaxation rate is calculated.

[0139] The size and distribution of the precipitated phase particles in the alloy were analyzed using field emission scanning electron microscopy.

[0140] Composition analysis: The laboratory direct-reading spectrometer was used to perform composition analysis according to the standard "YS / T 482-2022 Analysis Methods for Copper and Copper Alloys: Spark Discharge Atomic Emission Spectrometry".

[0141] Metallographic photographs were taken using a metallographic microscope.

[0142] The area content of recrystallized structures and dislocation clusters was measured using transmission electron microscopy.

[0143] Warpage was tested on the copper alloys obtained in the examples and comparative examples after etching: a strip sample with a length of 250 mm and a width of 70 mm was taken and the warpage was measured after etching.

[0144] Table 1 Chemical composition (wt%) of the embodiments and comparative examples of the present invention

[0145]

[0146] Table 2 Key process parameter control of embodiments and comparative examples of the present invention

[0147]

[0148] Table 3. Organization and performance of embodiments and comparative examples of the present invention.

[0149] Comparative analysis of the embodiments and comparative examples demonstrates that the chemical composition and processing technology of the present invention have a significant impact on the performance of the strip. The above embodiments and comparative examples were analyzed for conductivity, hardness, tensile strength, resistance to high-temperature softening, resistance to stress relaxation, elemental analysis, morphology and distribution of second-phase particles, metallographic photographs, and warpage measurements after etching.

[0150] Comparative Example 1 shows that when Co is not added, the amount of aging precipitates per unit area is small, and because Co is not added, the (Ni+Co) / Si mass ratio is less than 4.5. The excess Si is dissolved in the matrix structure, resulting in low hardness, tensile strength and conductivity of the strip, which does not meet the strength requirements of the connector matrix material.

[0151] As shown in Comparative Example 2, when the mass ratio of (Ni+Co) / Si in the alloying elements is less than 4.5, excess Si elements that do not form solid solutions in the matrix structure are greatly reduced, significantly decreasing the conductivity of the alloy.

[0152] As shown in Comparative Example 3, when the P content in the alloying elements is 0.1 wt%, P is excessively dissolved in the matrix structure, which greatly reduces the conductivity of the alloy.

[0153] Comparative Example 4 shows that when the solution-treated gas cushion furnace was used for annealing, a high-temperature solution treatment was not employed; instead, an annealing temperature of 600℃ and an annealing rate of 25 m / min were used. This solution temperature was too low, resulting in incomplete dissolution of Ni, Co, and Si alloying elements into the alloy matrix. Consequently, the aging precipitation was incomplete, and the precipitated phases were large in diameter and few in number. Ultimately, this led to the aged alloy failing to meet standards in terms of strength, conductivity, resistance to high-temperature softening, resistance to stress relaxation, and warpage measured after etching.

[0154] Comparative Example 5 shows that when step aging heat treatment was not used, but instead heating to 295℃ and holding for 11 hours, this heat treatment did not meet the conditions for complete precipitation during aging of the alloy. As a result, the Ni, Co, and Si dissolved in the alloy did not precipitate completely, and therefore the conductivity, strength, and high-temperature softening resistance were not significantly improved.

[0155] Comparative Example 6 shows that when annealing is performed in an online stress-relief furnace at an annealing temperature of 300℃, the copper strip tension inside the air cushion furnace is 240 N / mm. 2 The annealing rate was 80 m / min. The stress-relief annealing temperature was too low, failing to reach the recovery temperature of the alloy's grain structure. This retained the dislocation clusters from the cold-worked state, and the internal stress was not effectively released. Consequently, the stress relaxation resistance and the warpage measured after etching were both substandard.

[0156] As shown in Comparative Example 7, in step 9), the second stage annealing temperature in the stepped aging heat treatment is 520℃, and the holding time is 11h. The temperature of the second stage of stepped aging is too high, resulting in over-aging. The precipitated phases after aging grow significantly, while the unaged precipitated phases are fine and dispersed, thus greatly reducing the strength, high-temperature resistance, and high-temperature softness of the alloy, making it unqualified.

[0157] Comparative Example 8 shows that the alloy composition contains 1.8 wt% Ni, 1.0 wt% Co, and 0.8 wt% Si, with a (Ni+Co) / Si mass ratio of 3.5. No Sn, P, or Zn were added. The excessively high Ni, Co, and Si content reduced the material's electrical conductivity, failing to reach 55% IACS. Furthermore, the absence of Sn and P during aging did not promote the formation and precipitation of the second phase, resulting in coarse precipitates that further reduced the alloy's conductivity. The presence of these coarse second precipitates also led to high internal stress in the alloy, causing the warpage measurement after etching to fail.

[0158] Comparative Example 9 shows that the Ni content is 2.0 wt%, Co content is 1.2 wt%, Si content is 0.8 wt%, Cr content is 0.2 wt%, and the (Ni+Co) / Si mass ratio is 4. No Sn, P, or Zn were added. Similar to Comparative Example 8, the high Ni, Co, and Si content leads to reduced electrical conductivity, failing to reach 55% IACS. Furthermore, the absence of Sn and P during aging does not promote the formation and precipitation of the second phase, resulting in coarse precipitates that further reduce the alloy's conductivity. The presence of these coarse second precipitates also leads to high internal stress in the alloy, causing the warpage measurement after etching to fail.

[0159] As can be seen from Table 3, the alloys provided in Examples 1-6 of the present invention have suitable hardness, tensile strength, electrical conductivity, resistance to high temperature softening, resistance to stress relaxation, second-phase particle morphology, and warpage measured after etching.

Claims

1. A low-stress copper-cobalt-nickel-silicon alloy, characterized in that, The copper-cobalt-nickel-silicon alloy is composed of the following components in weight percentage: Ni: 0.5-1.0 wt%, Co: 0.005-0.4 wt%, Si: 0.1-0.3 wt%, Sn: 0.05-0.4 wt%, P: 0.01-0.02 wt%, Zn: 0.05-0.3 wt%, with the balance being Cu and unavoidable trace impurities; The mass ratio of (Ni+Co) / Si in the copper-cobalt-nickel-silicon alloy is 4.5-5.5; The copper-cobalt-nickel-silicon alloy includes a second phase, which includes a Ni3Si phase, and the average diameter of the second phase is ≤0.2μm.

2. The low-stress copper-cobalt-nickel-silicon alloy according to claim 1, characterized in that, The second phase also includes the (Co, Ni)2Si phase.

3. The low-stress copper-cobalt-nickel-silicon alloy according to claim 1, characterized in that, The second phase is diffusely distributed, and the number of second phase particles precipitated per unit area of ​​tissue is ≥1000 / μm. 2 .

4. The low-stress copper-cobalt-nickel-silicon alloy according to claim 1, characterized in that, The copper-cobalt-nickel-silicon alloy has a conductivity ≥50% IACS, a tensile strength ≥580 MPa, a plate shape ≤3I, and an etching warpage ≤0.08 mm.

5. The low-stress copper-cobalt-nickel-silicon alloy according to claim 1, characterized in that, The copper-cobalt-nickel-silicon alloy exhibits a stress relaxation rate of ≤10% and a high-temperature softening resistance of ≥85% after holding at 120℃ with an initial stress of 50% of the yield strength for 1000 hours.

6. The method for preparing a low-stress copper-cobalt-nickel-silicon alloy according to any one of claims 1-5, characterized in that, The process flow of the preparation method includes batching, smelting → casting → hot rolling → rough rolling → first annealing → intermediate rolling → aging heat treatment → finished product rolling → second annealing.

7. The method for preparing a low-stress copper-cobalt-nickel-silicon alloy according to claim 6, characterized in that, The hot rolling process includes hot rolling and final rolling with online water cooling and quenching. The hot rolling temperature is 800℃-1000℃ and the rolling speed is 150-250m / min. Preferably, the hot rolling temperature is 850-950℃; Preferably, the hot rolling speed is 200-250 m / min; The hot rolling process is followed by final rolling and online water cooling quenching. The final rolling temperature is 700-780℃, and the final rolling is followed by online water cooling quenching. Preferably, the final binding temperature is 700-750℃; Preferably, online water-cooling quenching is performed within 10 seconds after final clamping; Preferably, during the online water-cooling quenching, the alloy temperature is reduced to 50-100℃.

8. The method for preparing a low-stress copper-cobalt-nickel-silicon alloy according to claim 6, characterized in that, The first annealing is solution annealing in an air cushion furnace, with an annealing temperature of 750-900℃ and an annealing rate of 20-50m / min; Preferably, after the first annealing, the average grain size of the alloy microstructure is ≤5μm; Preferably, after the first annealing, the alloy has a hardness of 85-100 HV, a tensile strength of 360-400 MPa, an elongation of 45-55%, and an electrical conductivity of 20-28% IACS. The second annealing is an online stress-relief furnace annealing, with an annealing temperature of 380-500℃ and an annealing speed of 60-100m / min.

9. The method for preparing a low-stress copper-cobalt-nickel-silicon alloy according to claim 6, characterized in that, The intermediate rolling mill has a processing rate of 45-75%. The aging heat treatment is a stepped aging heat treatment, which first heats to 200-350℃ and holds for 1-2 hours, and then heats to 400-500℃ and holds for 10-12 hours.

10. The application of a low-stress copper-cobalt-nickel-silicon alloy according to any one of claims 1-5 or a copper-cobalt-nickel-silicon alloy prepared by the preparation method according to any one of claims 6-9 in a lead frame; Preferably, the warpage of the copper-cobalt-nickel-silicon alloy after etching the lead frame is ≤0.08mm.

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