Preparation method of copper alloy for lead frame with multi-scale precipitation phase

Abstract

A method for preparing a copper alloy for a lead frame with a multi-scale precipitation phase belongs to the technical field of high-performance copper alloy lead frame material preparation. The invention provides a heat treatment process for a Cu-Ni-Co-Si alloy strip with high strength and high hardness and containing multi-scale precipitation phases inside, and the alloy composition prepared is: Ni: 1.8%-3.0%, Co: 0.7%-1.5%, Si: 0.6%-0.72%, and the balance is Cu. Under the premise of ensuring the reasonable processing rate and dimensional uniformity of the pre-treatment process, the heat treatment process of rapid cooling and high and low temperature cycle aging adopted by the invention effectively regulates the size gradient and precipitation degree of the nano-scale (Ni, Co)2Si precipitation phase, so that the precipitation phase is uniformly dispersed in multiple scales, and a Cu-Ni-Co-Si alloy strip with good matching of tensile strength and electrical conductivity is obtained, which meets the performance requirements of the lead frame material.

Description

Technical Field

[0001] The invention relates to the field of preparation of high-performance copper alloy lead frame materials, and in particular to a method for preparing a copper alloy with multi-scale precipitation phase reinforcement, so that the copper alloy has excellent mechanical properties and good electrical conductivity. Background Art

[0002] Cu-Ni-Co-Si alloy is widely used in the preparation of integrated circuit lead frames due to its excellent mechanical properties and good electrical and thermal conductivity. It undertakes multiple functions such as carrying chips, connecting circuits and releasing heat. With the rapid development of the electronic information industry in recent years, integrated circuits are constantly upgrading to centralization, high density and high reliability, and people have put forward higher requirements on the performance of lead frame materials. How to obtain higher strength and conductivity has become a hot spot in the development of this field.

[0003] Cu-Ni-Co-Si alloy is a precipitation-strengthened copper alloy, and its good service performance mainly comes from work hardening and precipitation strengthening. During the preparation process, the alloy introduces high-density dislocations through cold deformation to form a dislocation substructure. In the subsequent aging process, the dislocations interact with the precipitated hard (Ni, Co)2Si phase, which greatly improves the mechanical properties of the alloy. The electrical conductivity of the alloy is mainly affected by lattice scattering, impurity scattering (second phase) and defect scattering (dislocations), which often forms a mutually restrictive relationship with the strength of the alloy. Therefore, how to achieve a good balance between high strength and high conductivity is the key to the preparation of high-performance Cu-Ni-Co-Si alloy. Based on the specific composition of the alloy, improving the traditional deformation heat treatment process and controlling the size and distribution of the precipitated phase during the aging process have become effective ways to improve the service performance of the alloy.

[0004] Based on the above content, designing the deformation heat treatment process for specific alloy components and developing the Cu-Ni-Co-Si alloy preparation technology with multi-scale precipitation phases with high aging precipitation stability have become urgent problems to be solved. Summary of the invention

[0005] In view of the problem that the existing deformation heat treatment process of Cu-Ni-Co-Si alloy cannot fully exert the mechanical properties and electrical conductivity of the material, the present invention proposes a new heat treatment process for specific components, namely, the alloy is subjected to alternating cycle treatment at high temperature (aging temperature, 450℃~500℃) and low temperature (liquid nitrogen, -196℃), and the precipitation behavior of the (Ni,Co)2Si phase of the alloy during the aging process is regulated by rapid cooling and rapid heating, and finally a Cu-Ni-Co-Si alloy plate and strip with multi-scale precipitation phases is obtained, which has higher strength and conductivity than the existing Cu-Ni-Co-Si alloys.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase, including but not limited to the following steps:

[0008] Step 1: Melting of alloy:

[0009] Step 1.1 Ingredients: copper busbar, nickel plate, cobalt particles and silicon particles are used as raw materials, which are cut and ultrasonically cleaned, and then dried; the materials are calculated by mass fraction, and the alloy composition is Ni: 1.8%-3.0%, Co: 0.7%-1.5%, Si: 0.6%-0.72%, and the balance is Cu. The three elements Ni, Co and Si in the copper alloy meet the following conditions: (a) 2.0≤Ni / Co≤3.0; (b) 4.1≤(Ni+Co) / Si≤6.3, and the proportion is made; the purity of the copper busbar is ≥99.5%, and the purity of the nickel plate, silicon particles and cobalt particles is ≥99.9%;

[0010] Step 1.2 Melting: Place the copper bar in step 1.1 in a crucible in a melting furnace and melt it at 1150°C-1200°C. After the copper bar is completely melted, add the nickel plate, silicon particles and cobalt particles in the above ingredients, continue to heat to 1350°C-1400°C, stir thoroughly after the alloy is completely melted, and keep warm for 20min-40min to obtain a uniform Cu-Ni-Co-Si melt;

[0011] Alternatively, the copper bar, nickel plate, cobalt particles and silicon particles in step 1.2 are placed in a crucible in a smelting furnace and smelted until the alloy is completely melted to obtain a Cu-Ni-Co-Si melt;

[0012] Step 1.3: pouring: pouring the uniform melt obtained in step 1.2, controlling the furnace temperature to be 1150°C to 1200°C, and then air-cooling to room temperature to obtain an alloy ingot;

[0013] When the smelting furnace used in step 1.2 is a non-vacuum smelting furnace, the melt is degassed by passing an inert gas before pouring;

[0014] Step 2: Deformation and heat treatment of the alloy:

[0015] Step 2.1 homogenization annealing: the alloy ingot obtained in the above step 1.3 is subjected to homogenization annealing treatment at 900°C-975°C, and the alloy ingot is subjected to heat preservation treatment, with a heating rate of 5°C / min-10°C / min and a heat preservation time of 2h-4h; then cooled to room temperature by water cooling to obtain an annealed alloy; wherein the annealed alloy is a supersaturated solid solution with uniform microstructure;

[0016] Step 2.2 Hot rolling: The annealed alloy obtained in step 2.1 is kept at a temperature range of 900°C to 975°C for 30 min to 60 min, and then hot rolled with a deformation amount of 60% to 90%. The deformation amount of each pass is 10% to 15% of the initial thickness, and the processing rate is 0.01s -1 ~0.1s -1 After each rolling, the hot rolled slab needs to be returned to the furnace for 5-10 minutes of heat preservation; then cooled to obtain the hot rolled slab; the cooling method is water cooling;

[0017] Step 2.3 Solid solution: The hot-rolled slab obtained in the above step 2.2 is placed in a heat treatment furnace for heat preservation treatment at a temperature of 900°C-975°C, a heating rate of 5°C / min-10°C / min, and a heat preservation time of 1h-4h; then cooled by water cooling to obtain a recrystallized structure in a supersaturated solid solution state;

[0018] Step 2.4 Milling: The alloy after the solution treatment in step 2.3 is subjected to surface milling treatment, with a single-side milling thickness of 0.5 mm to 1 mm and a single-side milling thickness of 1 mm to 2 mm, so as to remove oxides and heat treatment defects on the alloy surface;

[0019] Step 2.5 Cold rolling: The solid solution alloy treated by milling in step 2.4 is subjected to cold rolling deformation, with a cold rolling deformation of 80%-90%, a deformation of 10%-15% per pass, and a processing rate of 0.01s -1 ~0.1s -1 , and obtain a cold-rolled sheet;

[0020] Step 2.6 Aging: The cold-rolled sheet is subjected to a cycle of heating-insulating-cooling-standing treatment, and then water-cooled to room temperature after high-temperature insulation treatment to obtain a copper alloy for lead frames with excellent comprehensive properties.

[0021] Furthermore, the ultrasonic cleaning in step 1.1 is ultrasonic cleaning in water at room temperature until there is no grease on the surface of the raw material; the drying temperature is 40°C~70°C, and the drying time is 1h~2h.

[0022] Furthermore, the smelting furnace in step 1.2 is a vacuum induction melting furnace or a non-vacuum induction melting furnace.

[0023] Furthermore, in step 2.6, when the cold-rolled sheet undergoes a cycle of heating-keeping-cooling-standing, the initial heating rate is 5°C / min~10°C / min.

[0024] The heating-keeping-cooling-standing process is specifically as follows: heating to 450°C-500°C, keeping the temperature in a heat treatment furnace for 60min-120min, rapidly cooling with a low-temperature liquid refrigerant, and then standing for 20h-24h; the number of cycles is 1-2 times.

[0025] The low-temperature liquid refrigerant is liquid nitrogen at -196°C.

[0026] The copper alloy plate and strip has a thickness of 0.5 mm to 2 mm.

[0027] The copper alloy has the characteristics of work hardening, with a fibrous deformation structure inside and accompanied by dislocation proliferation.

[0028] The copper alloy has the characteristics of an aging precipitation-strengthened alloy and contains hard (Ni, Co)2Si nano-reinforced phases of different sizes.

[0029] The (Ni, Co)2Si reinforcement phases of different scales in the copper alloy form complex interactions with dislocations. The precipitated phases of different scales preferentially nucleate and grow at locations with high dislocation density. At high temperatures, the precipitated phases hinder the release of dislocations to form dislocation entanglements or multiply dislocations (dislocation loops) there.

[0030] The alloy heat treatment process plays a particularly critical role in the alloy aging precipitation behavior. It plays the following three roles in the alloy: 1. It makes the strengthening phase in the alloy present multiple scales; 2. It promotes the full precipitation of the strengthening phase in the alloy; 3. It makes the dislocation defects in the alloy interact with the strengthening phase.

[0031] The key technical point of the present invention is that the present invention fully forms a multi-scale uniformly dispersed (Ni, Co)2Si precipitation phase by controlling the number of aging cycles and adjusting the temperature coordination of combined aging. The alloy strip after cold rolling and aging treatment is affected by the interaction between the internal precipitation phase and dislocation, thereby obtaining ideal comprehensive performance.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention adjusts the nucleation and precipitation degree of the (Ni, Co)2Si phase in the alloy by introducing a combined aging process in the temperature range of 450°C to 500°C and 1 to 2 times of rapid cooling to -196°C on the basis of conventional aging steps.

[0034] 2. Affected by the rapid cooling cycle aging proposed in the present invention, the size of the precipitated phase is directly related to the number of cycles, resulting in the precipitated phase presenting a state of uniform distribution of multiple scales, thereby obtaining a more sufficient precipitation strengthening effect.

[0035] 3. The combined rapid cooling cycle aging process proposed in the present invention obtains a Cu-Ni-Co-Si alloy strip with higher hardness, strength and good electrical conductivity, providing more options for the production of lead frame copper alloy strips. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The scanning electron micrographs of the multi-scale precipitation phases at different cycle numbers in Example 4 of the present invention are shown; (a) to (c) are the results obtained under the conditions of 0, 1, and 2 cycles, respectively.

[0037] Figure 2 2 are transmission electron micrographs of the two rapid cooling cycles in Examples 3 and 4 of the present invention; wherein (a) and (b) are for Example 3, and (c) is for Example 4, showing the multi-scale precipitate size and distribution, and the interaction between dislocations and precipitates. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0039] In this embodiment, copper bars (purity ≥ 99.95%), nickel plates (purity ≥ 99.95%), high-purity cobalt particles (purity ≥ 99.95%), and high-purity silicon particles (purity ≥ 99.95%) are selected as raw materials.

[0040] Embodiment 1:

[0041] The finished lead frame copper alloy material is prepared by a single rapid cooling cycle aging at 450°C as follows:

[0042] Step 1: Melting of alloy.

[0043] Step 1.1. Cut the copper busbar into strips with a width of less than 30 mm and remove the surface grease by ultrasonic cleaning at room temperature. Weigh the materials according to the mass percentage of Ni 1.8%, Co 0.7%, Si 0.6%, and the balance Cu, weigh 2 kg of copper busbar, nickel plate, high-purity cobalt particles, and high-purity silicon particles. Dry the raw materials in a drying oven at a drying temperature of 60°C and a drying time of 2 hours.

[0044] Step 1.2. Place the dried copper bar, nickel plate, silicon particles and cobalt particles in a crucible in a medium frequency vacuum induction melting furnace. Close the furnace chamber and start evacuating the vacuum until the vacuum in the furnace chamber reaches 1×10 -2 Pa, stop vacuuming and backwash argon to 0.06MPa. Turn on the medium frequency power supply to start melting. Raise the temperature to 1350℃, and after the copper bar, nickel plate, silicon particles and cobalt particles in the crucible are completely melted, keep the temperature for 40 minutes to obtain Cu-Ni-Co-Si melt.

[0045] Step 1.3. When the melt temperature drops to 1200°C, the melt is uniformly poured into a crucible to obtain an ingot (50×55×103 mm).

[0046] Step 2: Deformation heat treatment before aging.

[0047] Step 2.1. The alloy ingot obtained in step 1.3 is placed in a box-type heat treatment furnace for homogenization treatment, and the ingot is heated to 950°C at a rate of 10°C / min. After being kept warm for 2 hours, it is water-cooled to obtain a supersaturated solid solution with uniform composition.

[0048] Step 2.2. The alloy is kept at 950°C for 30 minutes, and hot rolled to a thickness of 5 mm, and then immediately water-cooled to obtain a slab; wherein the total deformation of the hot rolling is 60%, and the processing rate is 0.1s -1 The pressing amount of a single pass is 10% of the initial thickness, and the steel is returned to the furnace and kept warm for 5 minutes after each pass.

[0049] Step 2.3. After drying the slab, place it in a box-type heat treatment furnace for solution treatment. The temperature is raised from room temperature to 950°C at a rate of 10°C / min in the furnace. After keeping it for 2 hours, it is water-cooled to obtain a plate with a uniform supersaturated solid solution.

[0050] Step 2.4. Mill the solution treated plate to remove surface oxides and heat treatment defects. The surface milling depth is 1 mm and the side milling depth is 2 mm.

[0051] Step 2.5. The milled plate is cold rolled to obtain a plate strip with a thickness of 1.8 mm; the total deformation of the cold rolling is 90%, the pressure of a single pass is 10%-15%, and the processing rate is 0.1s -1 .

[0052] Step 2.6. 450℃ one-time rapid cooling cycle aging: Place the plate and strip material obtained in step 2.5 in a box-type heat treatment furnace, and heat the material to 450℃ at a rate of 10℃ / min. After keeping warm for 120 minutes, immediately place it in liquid nitrogen and quickly cool it to -196℃ for 24 hours. After taking the plate and strip material out of the liquid nitrogen, immediately place it in a box-type heat treatment furnace at a temperature of 450℃ and continue to keep warm for 120 minutes, and then immediately place it in water for rapid cooling to obtain the finished lead frame copper alloy material. The hardness, tensile strength and conductivity of the finished lead frame copper alloy material prepared in this embodiment were tested, and the results are shown in Table 1.

[0053] Embodiment 2:

[0054] The finished lead frame copper alloy material is prepared by a combined rapid cooling cycle aging at 450°C and 500°C as follows:

[0055] Step 1: Melting of alloy.

[0056] Step 1.1. Cut the copper busbar into strips with a width of less than 30 mm and remove the surface grease by ultrasonic cleaning at room temperature. Weigh the materials according to the mass percentage of Ni 3.0%, Co 1.5%, Si 0.72%, and the balance Cu, weigh 2 kg of copper busbar, nickel plate, high-purity cobalt particles, and high-purity silicon particles. Dry the raw materials in a drying oven at a drying temperature of 70°C and a drying time of 1 hour.

[0057] Step 1.2. Place the dried copper bar, nickel plate, silicon particles and cobalt particles in a crucible in a medium frequency vacuum induction melting furnace. Close the furnace chamber and start evacuating the vacuum until the vacuum in the furnace chamber reaches 1×10 -2 Pa, stop vacuuming and backwash argon to 0.06MPa. Turn on the medium frequency power supply to start melting. Raise the temperature to 1400℃, and after the raw materials in the crucible are completely melted, continue to raise the temperature to 1400℃ and keep it for 30 minutes to obtain Cu-Ni-Co-Si melt.

[0058] Step 1.3. When the melt temperature drops to 1200°C, the melt is uniformly poured into a crucible to obtain an ingot (50×55×103 mm).

[0059] Step 2: Deformation heat treatment before aging.

[0060] Step 2.1. The alloy ingot obtained in step 1.3 is placed in a box-type heat treatment furnace for homogenization treatment, and the ingot is heated to 900°C at a rate of 5°C / min. After being kept warm for 4 hours, it is water-cooled to obtain a supersaturated solid solution with uniform composition.

[0061] Step 2.2. The alloy is kept at 900°C for 60 minutes and hot rolled to a thickness of 10 mm, and then immediately water-cooled to obtain a slab; the total deformation of the hot rolling is 80% and the processing rate is 0.05s -1 The pressing amount of a single pass is 15% of the initial thickness, and the steel is returned to the furnace and kept warm for 10 minutes after each pass.

[0062] Step 2.3. After drying the slab, place it in a box-type heat treatment furnace for solution treatment. The temperature is raised from room temperature to 900°C at a rate of 10°C / min, and then water-cooled after being kept for 2 hours to obtain a plate with a supersaturated solid solution state with uniform composition.

[0063] Step 2.4. Mill the solution treated plate to remove surface oxides and heat treatment defects. The surface and side milling depth are both 1 mm.

[0064] Step 2.5. The milled plate is cold rolled to obtain a plate strip with a thickness of 1.6 mm; the total deformation of the cold rolling is 80%, the pressure of a single pass is 10%-15%, and the processing rate is 0.05s -1 .

[0065] Step 2.6: 500℃ and 450℃ combined rapid cooling cycle aging: Place the strip obtained in step 2.5 in a box-type heat treatment furnace, and heat the material to 500℃ at a rate of 10℃ / min. After keeping it warm for 120 minutes, immediately place it in liquid nitrogen and quickly cool it to -196℃ for 24 hours. Take the plate strip out of the liquid nitrogen and immediately place it in a box-type heat treatment furnace at a temperature of 450℃ and keep it warm for 120 minutes. Then immediately place it in water and quickly cool it to obtain the finished lead frame material. The hardness, tensile strength and conductivity of the Cu-Ni-Co-Si alloy strip prepared in this embodiment were tested, and the results are shown in Table 1.

[0066] Embodiment 3:

[0067] The finished lead frame copper alloy material is prepared by two rapid cooling cycles at 450°C, and the method is as follows:

[0068] Step 1: Melting of alloy.

[0069] Step 1.1. Cut the copper busbar into strips with a width of less than 30 mm and remove the surface grease by ultrasonic cleaning at room temperature. Weigh the materials according to the mass percentage of Ni 1.8%, Co 0.7%, Si 0.6%, and the balance Cu, and weigh 10 kg of copper busbar, nickel plate, high-purity cobalt particles, and high-purity silicon particles. Dry the raw materials in a drying oven at a drying temperature of 40°C and a drying time of 2 hours.

[0070] Step 1.2. Place the dried copper bar in the crucible in the medium frequency vacuum induction melting furnace. Close the furnace chamber and start evacuating the vacuum until the vacuum in the furnace chamber reaches 1×10 -2 Pa, stop vacuuming and backwash argon to 0.06MPa. Turn on the medium frequency power supply to start melting. Raise the temperature to 1150℃. After the copper bar in the crucible is completely melted, add the nickel plate, silicon particles and cobalt particles weighed in step 1.1 into the copper-silicon melt and continue to raise the temperature to 1350℃ and keep it warm for 40 minutes to obtain a Cu-Ni-Co-Si melt.

[0071] Step 1.3. When the melt is cooled to 1200°C, the melt is uniformly poured into a crucible to obtain an ingot.

[0072] Step 2: Deformation heat treatment before aging.

[0073] Step 2.1. The alloy ingot obtained in step 1.3 is placed in a box-type heat treatment furnace for homogenization treatment, and the ingot is heated to 975°C at a rate of 10°C / min. After being kept warm for 2 hours, it is water-cooled to obtain a supersaturated solid solution with uniform composition.

[0074] Step 2.2. The alloy is kept at 975°C for 30 minutes, and hot rolled to a thickness of 7 mm, and then immediately water-cooled to obtain a slab; wherein the total deformation of the hot rolling is 80%, and the processing rate is 0.01s -1 The pressing amount of a single pass is 10% of the initial thickness, and the steel is returned to the furnace and kept warm for 5 minutes after each pass.

[0075] Step 2.3. After drying the slab, place it in a box-type heat treatment furnace for solution treatment. The temperature is raised from room temperature to 975°C at a rate of 8°C / min, and then water-cooled after being kept for 2 hours to obtain a plate with a supersaturated solid solution with uniform composition.

[0076] Step 2.4. Mill the solution treated plate to remove surface oxides and heat treatment defects. The surface milling depth is 1 mm and the side milling depth is 2 mm.

[0077] Step 2.5. The milled plate is cold rolled to obtain a plate with a thickness of 1 mm; the total deformation of the cold rolling is 80%, the pressure of a single pass is 10%-15%, and the processing rate is 0.01s -1 .

[0078] Step 2.6. 450℃ two rapid cooling cycle aging: Place the plate and strip material obtained in step 2.5 in a box-type heat treatment furnace, and heat the material to 450℃ at a rate of 8℃ / min with the furnace. After keeping warm for 80 minutes, immediately place it in liquid nitrogen and quickly cool it to -196℃ and continue for 20 hours. Take the plate and strip material out of the liquid nitrogen and immediately place it in a box-type heat treatment furnace at a temperature of 450℃. After keeping warm for 80 minutes, immediately place it in liquid nitrogen and quickly cool it to -196℃ and continue for 20 hours. After taking the plate and strip material out of the liquid nitrogen, immediately place it in a box-type heat treatment furnace at a temperature of 450℃. After keeping warm for 80 minutes, immediately place it in water and quickly cool it to obtain the finished lead frame copper alloy material. The hardness, tensile strength and conductivity of the finished lead frame copper alloy material prepared in this embodiment were tested, and the results are shown in Table 1.

[0079] Embodiment 4:

[0080] The finished lead frame copper alloy material is prepared by two rapid cooling cycles at 450°C and 500°C, and the method is as follows:

[0081] Step 1: Melting of alloy.

[0082] Step 1.1. Cut the copper busbar into strips with a width of less than 30 mm and remove the surface grease by ultrasonic cleaning at room temperature. Weigh the materials according to the mass percentage of Ni 1.8%, Co 0.7%, Si 0.6%, and the balance Cu, and weigh 10 kg of copper busbar, nickel plate, high-purity cobalt particles, and high-purity silicon particles. Dry the raw materials in a drying oven at a drying temperature of 40°C and a drying time of 2 hours.

[0083] Step 1.2. Place the dried copper bar in the crucible in the medium frequency vacuum induction melting furnace. Close the furnace chamber and start evacuating the vacuum until the vacuum in the furnace chamber reaches 1×10 -2 Pa, stop vacuuming and backwash argon to 0.06MPa. Turn on the medium frequency power supply to start melting. Raise the temperature to 1200℃, and after the copper bar in the crucible is completely melted, add the nickel bar, silicon particles and cobalt particles weighed in step 1.1 to the copper-silicon melt and continue to raise the temperature. Continue to raise the temperature to 1400℃ and keep it warm for 30 minutes to obtain a Cu-Ni-Co-Si melt.

[0084] Step 1.3. When the melt is cooled to 1200°C, the melt is uniformly poured into a crucible to obtain an ingot.

[0085] Step 2: Deformation heat treatment before aging.

[0086] Step 2.1. The alloy ingot obtained in step 1.3 is placed in a box-type heat treatment furnace for homogenization treatment, and the ingot is heated to 925°C at a rate of 10°C / min. After being kept warm for 4 hours, it is water-cooled to obtain a supersaturated solid solution with uniform composition.

[0087] Step 2.2. The alloy is kept at 925°C for 30 minutes, and hot rolled to a thickness of 12 mm, and then immediately water-cooled to obtain a slab; wherein the total deformation of the hot rolling is 80%, and the processing rate is 0.05 s -1 The pressing amount of a single pass is 10% of the initial thickness, and the steel is returned to the furnace and kept warm for 5 minutes after each pass.

[0088] Step 2.3. After drying the slab, place it in a box-type heat treatment furnace for solution treatment. The temperature is raised from room temperature to 925°C at a rate of 5°C / min, and then water-cooled after being kept for 3 hours to obtain a plate with a uniform supersaturated solid solution.

[0089] Step 2.4. Mill the solution treated plate to remove surface oxides and heat treatment defects. The surface and side milling depth are both 1 mm.

[0090] Step 2.5. The milled plate is cold rolled to obtain a plate strip with a thickness of 1 mm; the total deformation of the cold rolling is 90%, the pressure of a single pass is 10%-15%, and the processing rate is 0.05s-1 .

[0091] Step 2.6. Two rapid cooling cycles at 500°C and 450°C: Place the plate and strip obtained in step 2.5 in a box-type heat treatment furnace, and heat the material to 500°C at a rate of 5°C / min with the furnace. After keeping warm for 80 minutes, immediately place it in liquid nitrogen and quickly cool it to -196°C and continue for 20 hours. After taking the plate and strip out of the liquid nitrogen, immediately place it in a box-type heat treatment furnace at a temperature of 450°C. After keeping warm for 80 minutes, immediately place it in liquid nitrogen and quickly cool it to -196°C and continue for 24 hours. After taking the plate and strip out of the liquid nitrogen, immediately place it in a box-type heat treatment furnace at a temperature of 450°C. After keeping warm for 80 minutes, immediately place it in water and quickly cool it to obtain the finished lead frame copper alloy material. The hardness, tensile strength and conductivity of the finished lead frame copper alloy material prepared in this embodiment were tested, and the results are shown in Table 1.

[0092] The scanning electron microscope photograph of the precipitated phase of the alloy aged by two rapid cooling cycles at 500°C + 450°C in Example 4 is as follows: Figure 1 As shown in the figure, when there is no cycle, there is only one size of precipitation phase. After one cycle, there are two sizes of precipitation phases, as shown by mark point 1 and mark point 2, where mark point 1 is the primary precipitation phase formed by the first aging, and mark point 2 is the secondary precipitation phase formed by the second aging. After two cycles, a tertiary precipitation phase is formed, as shown by mark point 3.

[0093] The transmission electron microscope photos of the alloys of Example 3 and Example 4 are as follows: Figure 2 As shown in the figure, it can be seen that the samples treated with different cyclic processes have the same characteristics: 1. The precipitated phase precipitates in large quantities at the dislocation aggregation sites; 2. The precipitated phase is multi-scale; 3. The interior of the alloy is a fibrous deformation structure, and the precipitated phase hinders the release of dislocations to form substructures such as dislocation entanglement and dislocation wall.

[0094] The properties of the alloys prepared in Examples 1 to 4 of the present invention are shown in Table 1:

[0095] Table 1 Alloy properties of Example 1 to Example 4

[0096] .

[0097] As can be seen from Table 1, the properties of the alloy strips treated at different temperatures and cycles are significantly different. Aging at a higher temperature can obtain good electrical conductivity (Example 2, Example 4). Multiple cycles can obtain good mechanical properties (Example 3, Example 4).

Claims

1. A method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase, characterized in that: The following steps are involved: Step 1: Melting of alloy: Step 1.1 Ingredients: Copper bars, nickel plates, cobalt particles, and silicon particles are used as raw materials and mixed according to mass percentage, and after cutting and ultrasonic cleaning, they are dried; Step 1.2 smelting: placing the raw materials in a smelting furnace for smelting to obtain a uniform Cu-Ni-Co-Si melt; Step 1.3: pouring: pouring the uniform melt obtained in step 1.2, controlling the furnace temperature, and then air-cooling to room temperature to obtain an alloy ingot; Step 2: Deformation and heat treatment of the alloy: Step 2.1 homogenization annealing: the alloy ingot is subjected to homogenization annealing treatment and then heat preservation treatment, and then cooled to room temperature to obtain an annealed alloy; wherein the annealed alloy is a supersaturated solid solution with uniform microstructure; Step 2.2 hot rolling: After the annealed alloy is kept at 900°C to 975°C, hot rolling is performed, and after each rolling, the alloy needs to be returned to the furnace for keeping warm, and then cooled to obtain a hot-rolled slab; Step 2.3 solid solution: placing the hot-rolled slab in a heat treatment furnace for heat preservation, and then cooling it to obtain a recrystallized structure in a supersaturated solid solution state; Step 2.4: Milling: Perform surface milling on the alloy after solution treatment to remove surface oxides and heat treatment defects; Step 2.5 cold rolling: cold rolling the milled alloy to obtain a cold rolled sheet; Step 2.6 Aging: The cold-rolled sheet is subjected to a heating-insulating-cooling-standing treatment cycle, and then water-cooled to room temperature after high-temperature insulation treatment to obtain a copper alloy sheet strip for a lead frame with excellent comprehensive performance; when the cold-rolled sheet is subjected to a heating-insulating-cooling-standing treatment cycle, the initial heating rate is 5°C / min to 10°C / min; The heating-keeping-cooling-standing process is specifically as follows: heating to 450° C. to 500° C., keeping the temperature in the heat treatment furnace for 60 min to 120 min, rapidly cooling with a low-temperature liquid refrigerant, and then standing for 20 h to 24 h; the number of cycles is 1 to 2 times; The low-temperature liquid refrigerant is liquid nitrogen at -196°C; the thickness of the copper alloy plate and strip is 0.5mm-2mm; In the copper alloy for lead frame, the alloy composition is Ni: 1.8%-3.0%, Co: 0.7%-1.5%, Si: 0.6%-0.72%, and the balance is Cu, wherein the three elements Ni, Co, and Si satisfy: (a) 2.0≤Ni / Co≤3.0; (b) 4.1≤(Ni+Co) / Si≤6.3; The copper alloy sheet and strip have the characteristics of work hardening, with a fibrous deformation structure inside and accompanied by dislocation proliferation; the copper alloy sheet and strip have the characteristics of aging precipitation strengthened alloy, with hard (Ni, Co)2Si nano-reinforcement phases of different sizes inside.

2. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 1.1, the purity of the copper busbar is ≥ 99.5%, and the purity of the nickel plate, silicon particles and cobalt particles is ≥ 99.9%; The ultrasonic cleaning is to perform ultrasonic cleaning in water at room temperature until there is no grease on the surface of the raw material; the drying temperature is 40° C. to 70° C., and the drying time is 1 h to 2 h.

3. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 1.2, the melting furnace is a vacuum induction melting furnace or a non-vacuum induction melting furnace; The smelting process is as follows: the copper bar is smelted at 1150°C to 1200°C, and after the copper bar is completely melted, the nickel plate, silicon particles and cobalt particles are added, and the temperature is continued to be raised to 1350°C to 1400°C, and after the alloy is completely melted, it is fully stirred and kept warm for 20min to 40min; or the copper bar, nickel plate, cobalt particles and silicon particles are placed in a crucible in a smelting furnace and smelted until the alloy is completely melted.

4. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 1.3, the furnace temperature is 1150°C to 1200°C.

5. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 2.1, during the homogenization annealing treatment, the temperature is raised to 900°C-975°C at a rate of 5°C / min-10°C / min, and the holding time is 2h-4h; the cooling method is water cooling.

6. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 2.2, the holding time of the annealed alloy is 30 min to 60 min; During hot rolling, the deformation is 60% to 90%, the deformation of each pass is 10% to 15% of the initial thickness, and the processing rate is 0.01s -1 ~0.1s -1 After each rolling, it needs to be returned to the furnace for insulation for 5min-10min; the cooling method is water cooling.

7. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 2.3, the heat preservation process is: heating the hot-rolled slab to 900°C-975°C at a rate of 5°C / min-10°C / min, and then keeping it warm for 1h-4h; the cooling method is water cooling.

8. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 2.4, when milling the surface, the single-sided milling thickness is 0.5mm to 1mm, and the single-sided milling thickness is 1mm to 2mm.

9. The method for preparing a copper alloy for a lead frame having a multi-scale precipitation phase according to claim 1, characterized in that: In step 2.5, during the cold rolling deformation process, the cold rolling deformation amount is 80%-90%, the deformation amount per pass is 10%-15%, and the processing rate is 0.01s -1 ~0.1s -1 .

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