A copper alloy for a multi-phase collaborative lead frame and a preparation method thereof

Abstract

The present invention belongs to the technical field of materials and their preparation and processing, and specifically relates to a copper alloy for a multiphase collaborative lead frame and a preparation method thereof. By mass percentage, the alloy components include: 0.5 - 0.9% of Cr, 0.08 - 0.25% of Zr, 0.4 - 1% of Ni, 0.1 - 0.3% of Si, 0.01 - 0.05% of Co, 0.02 - 0.06% of Sn, and the balance is matrix Cu. The two short-process preparation methods of the alloy include: (1) vacuum induction melting and casting → homogenization annealing → double surface milling → hot rolling → solution treatment → cold rolling with a large deformation amount → primary aging → cold precision rolling → secondary aging; (2) continuous casting → continuous extrusion of plates → cold rolling with a large deformation amount → primary aging → cold precision rolling → secondary aging. The copper alloy for a multiphase collaborative lead frame of the present invention obtains a copper alloy with a tensile strength greater than 650 MPa and a conductivity greater than 65% IACS by optimizing the alloy element design, cooperating with the large deformation cold rolling process and the deformation-aging treatment system, meeting the use requirements of high-end semiconductor lead frames.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials and their preparation and processing, and particularly relates to a copper alloy for a multi-phase collaborative lead frame and a preparation method thereof. Background Art

[0002] With the increasingly prominent role of the electronics and information industries in the national economic industries and the construction of national defense and military industries, their strategic, fundamental, and leading characteristics have become increasingly prominent. Along with the continuous upgrading of the technology of the electronic information industry, copper alloys, as one of the important materials therein, are also continuously improving their performance. The new generation of copper alloys is required to have a tensile strength of more than 650 MPa and a conductivity of more than 65% IACS, and will be widely used in the lead frames of large-scale and ultra-large-scale integrated circuits in the future. The main function of the lead frame is to connect the semiconductor chip of the integrated circuit and the external circuit as a skeleton and a bridge, and to transfer heat and electrical signals. The new generation of copper alloys has good conductivity and strong tensile strength, and its good plastic processing performance enables it to be processed into small and precise lead frames with excellent performance. These excellent performance characteristics are one of the important reasons for the new generation of copper alloys to replace traditional copper alloys and become the trend materials. Based on the research foundation of multi-phase collaborative microalloying, by adding a variety of elements to introduce a variety of precipitation strengthening precipitated phases, the precipitated phases also provide nucleation sites to promote the precipitation of elements dissolved in the matrix, thereby improving the conductivity. The research and development of the new generation of copper alloys and the adjustment of the properties of copper alloys by adding alloying elements have increasingly attracted the attention of domestic and foreign scholars in the industry. For example:

[0003] Patent application: "A preparation method of a copper alloy semiconductor lead frame (Publication No. CN103667774A)", proposed that in the case of a Cu-Fe-P base alloy system, by adding Zn and Sn elements, a precipitation-hardening copper alloy with both excellent mechanical properties and electrical conductivity was obtained, with a tensile strength of 500-600 MPa and a conductivity of 50-70% IACS.

[0004] Patent application: "A high-strength, high-conductivity, stress-relaxation-resistant copper alloy lead frame material and its preparation method (Publication No. CN109930026A)", proposed that by adding Ni, Si, P, Fe, Sn, Co to Cu, through melting, hot rolling, cold rolling, aging, precision rolling, and final annealing, a tensile strength greater than 700 MPa and a conductivity greater than 70% IACS were obtained to achieve the matching of strength, electrical conductivity, bending, and etching performance.

[0005] Patent application: "A copper alloy for high-performance lead frames and its preparation method (Publication No. CN111549252A)" proposes adding Fe, P, Zn, Co, Zr, and Ti to a multi-element copper alloy with a low Fe content, i.e., in Cu, to obtain a copper alloy with a tensile strength of 700 - 850 MPa, an electrical conductivity of 40 - 50% IACS, an elongation of 6 - 10%, and a stress relaxation resistance of 88 - 92%, having high strength, high conductivity, and high stress relaxation resistance characteristics.

[0006] Patent application: "A copper alloy lead frame material (Publication No. CN113981267A)" proposes a copper alloy with Sn, Ni, Zn, P, and B as strengthening elements. By coordinating the control of the copper alloy composition and the preparation method, a copper alloy lead frame material with low cost, low thermal shrinkage rate, high strength, high conductivity, and excellent etching performance is obtained, with a tensile strength greater than 500 MPa and a conductivity greater than 30% IACS.

[0007] Through the above research, by adding alloy strengthening elements and conventional preparation processes, lead frame and electronic connector copper alloy materials with better performance are obtained. However, only relying on the strength and conductivity contributions provided by single-phase or dual-phase or undissolved larger-sized elemental alloy elements, and the conventional preparation process includes multiple processing steps such as melting and casting, hot rolling, surface milling, primary rolling, intermediate annealing, pickling, intermediate rolling, high-temperature online solution treatment, finish rolling, and aging annealing treatment, which brings great difficulties to the precise control of alloy microstructure and production cost control. To further improve the comprehensive performance of the new generation of copper alloys, through the new design of the total composition, using the industrial short-process preparation method to precisely control the microstructure evolution process and the behavior of precipitation phases, and introducing three or more kinds of nano-precipitation strengthening during the aging process, more in-depth research and discussion are needed to improve the volume fraction of solid solution elements in the Cu matrix to increase the conductivity. Summary of the Invention

[0008] In view of the above reasons, the purpose of the present invention is to provide a copper alloy for multi-phase synergistic lead frames and its preparation method, which can meet the high-strength and high-conductivity performance requirements of high-end semiconductor lead frame copper alloys. By reasonably configuring alloy strengthening elements, shortening the process flow, introducing large deformation cold rolling and deformation-aging treatment systems, precise control of the microstructure of high-end semiconductor lead frames, conventional low-cost, low-energy consumption, low-emission, and high-performance short-process preparation are realized.

[0009] To achieve the above purpose, the technical solution of the present invention is:

[0010] A copper alloy for a multiphase synergistic lead frame, by mass percentage, the alloy components include: Cr is 0.5 - 0.9%, Zr is 0.08 - 0.25%, Ni is 0.4 - 1%, Si is 0.1 - 0.3%, Co is 0.01 - 0.05%, Sn is 0.02 - 0.06%, and the balance is matrix Cu.

[0011] For the copper alloy for the multiphase synergistic lead frame, preferably, by mass percentage, the alloy components are as follows: Cr is 0.6 - 0.7%, Zr is 0.1 - 0.15%, Ni is 0.7 - 0.9%, Si is 0.2 - 0.3%, Co is 0.02 - 0.04%, Sn is 0.02 - 0.04%, and the balance is matrix Cu.

[0012] The preparation method of the copper alloy for the multiphase synergistic lead frame includes the following steps: (1) vacuum induction melting and casting; (2) homogenization treatment; (3) double surface milling; (4) hot rolling; (5) solution treatment; (6) cold rolling with a large deformation amount; (7) primary aging; (8) cold precision rolling; (9) secondary aging.

[0013] The preparation method of the copper alloy for the multiphase synergistic lead frame includes the following steps: (1) continuous casting; (2) continuous extrusion of plates; (3) cold rolling with a large deformation amount; (4) primary aging; (5) cold precision rolling; (6) secondary aging.

[0014] For the copper alloy for the multiphase synergistic lead frame, during cold rolling with a large deformation amount, the total cold rolling deformation amount is 85% - 99%, and the thickness after cold rolling with a large deformation amount is 1 - 0.5 mm.

[0015] For the copper alloy for the multiphase synergistic lead frame, the total cold precision rolling deformation amount is 80% - 90%, and the thickness after cold precision rolling is 0.1 - 0.2 mm.

[0016] The design concept of the present invention is:

[0017] Utilize the characteristic that strengthening phases precipitate during the aging process of the copper alloy. By adding several elements, the purpose of synergistic strengthening of multiple nano - precipitate phases in the copper alloy is achieved. At the same time, by adding elements with low solid solubility in Cu but strong affinity with other main elements, the purity of the Cu matrix can be promoted to improve the electrical conductivity. And the introduction of the large - deformation cold rolling process can further promote the precipitation of precipitate phases, increase the dislocation density of the alloy, and break large - sized precipitate phases.

[0018] In the alloy component design of the present invention, it is preferably to control the alloy element components as follows: Cr is 0.6 - 0.7%, Zr is 0.1 - 0.15%, Ni is 0.7 - 0.9%, Si is 0.2 - 0.3%, Co is 0.02 - 0.04%, Sn is 0.02 - 0.04%. Among them:

[0019] The role of Cr is as follows: It forms an fcc Cr phase at the nanoscale and forms a stable Cr3Si phase with Si, reducing the concentration of Si in the matrix to increase the conductivity and enhancing the thermal stability of the overall microstructure and properties. When Cr < 0.6 wt%, or the amount is too small to form stable Cr3Si, the attraction to Si is weakened; when Cr > 0.7 wt%, due to the high melting point of Cr, when an excessive amount of Cr is introduced, Cr cannot be dissolved into the matrix, and large-scale elemental Cr points are formed during melting and solidification, affecting the strength.

[0020] The role of Zr is as follows: It forms a Ni2SiZr phase with Ni and Si elements to increase the conductivity. When Zr < 0.1 wt%, there is not enough Zr element to form a concentration gradient to attract Ni and Si to react; when Zr > 0.15 wt%, the excessive Zr will attract excessive Ni and Si elements, resulting in insufficient quantity of nanoscale Ni2Si and unable to play the role of precipitation strengthening, thus reducing the strength of the copper alloy.

[0021] The role of Ni is as follows: It is a key element for multiple elements to form nanoscale alloy phases. When Ni < 0.7 wt%, there is not enough nano-strengthening phase for the alloy; when Ni > 0.9 wt%, due to the infinite solid solubility of Ni and Cu, the excessive Ni will be dissolved in the Cu matrix. When the precipitation driving force is insufficient, it cannot precipitate sufficiently, thus affecting the lattice and shear modulus mismatch of the Cu matrix and the conductivity of the Cu alloy.

[0022] The role of Si is as follows: It forms stable precipitation phases of different scales with Ni, Zr, Cr, and Co, and is one of the most important elements for strengthening copper alloys. When Si < 0.2 wt%, there are not enough elements to form a large number of precipitation strengthening phases; when Si > 0.3 wt%, it cannot precipitate sufficiently from the matrix, thus affecting the strength and conductivity.

[0023] The role of Co is as follows: It has the same role as Ni but a higher strengthening effect than Ni. It is one of the key elements for realizing short-process preparation when forming (Ni, Co)2Si with Ni and Si elements to promote the further precipitation of Ni and Si. When Co < 0.02 wt%, the nano-strengthening phase cannot be formed sufficiently; when Co > 0.04 wt%, the solid solution of the element in Cu intensifies, affecting the conductivity.

[0024] The role of Sn is as follows: It increases the strength of the alloy and increases the conductivity due to its low solid solubility with Cu. When Sn < 0.02 wt%, the alloy is solution strengthened and affects the conductivity; when Sn > 0.04 wt%, it forms a face-centered cubic (Cu, Ni)3Sn compound for precipitation strengthening, but it will cause a large number of insoluble Sn points, affecting the microstructure and properties of the alloy.

[0025] The advantages and beneficial effects of the present invention are as follows:

[0026] The present invention can meet the requirements of high strength and high conductivity of copper alloys for high-end semiconductor lead frames. Due to the introduction of large deformation cold rolling, the sizes of the precipitated phases are uniform, and most of them are dispersed in the Cu matrix. The smaller precipitated phases preferentially precipitate within the grains, and the volume fraction of the precipitated phases distributed at the grain boundaries is small. A variety of stable and metastable nanoscale precipitated phases enable the tensile strength of the alloy to be stably greater than 650 MPa and the conductivity to be greater than 65% IACS. Brief Description of the Drawings

[0027] Figure 1 It is a flow chart of the preparation method of the first multi-phase cooperative copper alloy for lead frames.

[0028] Figure 2 It is a flow chart of the preparation method of the second multi-phase cooperative copper alloy for lead frames. Detailed Embodiments

[0029] In the specific implementation process, the multi-phase cooperative copper alloy for lead frames of the present invention can be prepared by two short process preparation methods. The specific processes are as follows: (1) Vacuum induction melting and casting → Homogenization treatment → Double milling → Hot rolling → Solution treatment → Cold rolling with large deformation → First aging → Cold precision rolling → Second aging; (2) Continuous casting → Continuous extrusion of plates → Cold rolling with large deformation → First aging → Cold precision rolling → Second aging.

[0030] Hereinafter, the embodiments of the present invention will be further described in detail with reference to the accompanying drawings.

[0031] Example 1:

[0032] In this example, a multi-phase cooperative copper alloy (wt%) for lead frames that meets the requirements of high strength and high conductivity of copper alloys for high-end semiconductor lead frames is designed and developed: Cr is 0.62%, Zr is 0.13%, Ni is 0.75%, Si is 0.24%, Co is 0.036%, Sn is 0.028%, and the balance is matrix Cu.

[0033] As Figure 1 shown, the preparation method of the above multi-phase cooperative copper alloy for lead frames is specifically described as follows:

[0034] (1) Vacuum induction melting and casting: Weigh electrolytic Cu with a purity above 99.96 wt%, electrolytic Ni with a purity above 99.96 wt%, polycrystalline Si with a purity above 99.99 wt%, Cr with a purity above 99.96 wt%, Co with a purity above 99.96 wt%, and Sn with a purity above 99.96 wt% in proportion. After charging and evacuating the vacuum, start heating up for melting. After all the above materials are melted, adjust the temperature to 1200 ± 10 °C, refine for 20 min. After refining, fill the furnace with argon and input pure Zr wrapped with copper foil or Cu-Zr master alloy through the secondary feeding bin. When the liquid surface is calm and no bubbles escape, that is, when it is completely melted, stir evenly. During casting, cast while charging electricity, and control the temperature at 1150 ± 10 °C.

[0035] (2) Homogenization treatment: Keep the ingot at 960 ± 10 °C for 4 h and then cool it to room temperature in the furnace.

[0036] (3) Double milling: Remove the defects on the surface of the sheet after hot forging, and the milling depth is 0.2 mm.

[0037] (4) Hot rolling: The starting rolling temperature is 930 °C, the final rolling temperature is 750 °C, the total hot rolling deformation is 80%, and the thickness after hot rolling is 10 mm.

[0038] (5) Solution treatment: The solution temperature is 900 °C, the solution time is 1 h, and then water-cool to room temperature.

[0039] (6) Cold rolling with large deformation: The total cold rolling deformation is 95%, and the thickness after cold rolling with large deformation is 0.5 mm.

[0040] (7) First aging: The aging temperature is 460 °C, the aging time is 2 h, and then air-cool to room temperature.

[0041] (8) Cold finish rolling: The total cold finish rolling deformation is 80%, and the thickness after cold finish rolling is 0.1 mm.

[0042] (9) Second aging: The aging temperature is 410 °C, the aging time is 2 h, and then air-cool to room temperature.

[0043] In this embodiment, after the second aging, the tensile strength of the alloy reaches 713 MPa, and the conductivity reaches 69% IACS.

[0044] Example 2:

[0045] In this embodiment, a copper alloy for multi-phase collaborative lead frame (wt%) that meets the high-strength and high-conductivity performance requirements of large-scale, ultra-large-scale lead frames and high-end electronic component connectors under conventional and special environments is designed and developed: Cr is 0.67%, Zr is 0.12%, Ni is 0.86%, Si is 0.29%, Co is 0.025%, Sn is 0.038%, and the balance is matrix Cu.

[0046] As Figure 2 shown, the preparation method of the above-mentioned multiphase collaborative lead frame copper alloy is specifically described as follows:

[0047] (1) Continuous casting.

[0048] (2) Continuous extrusion of sheet.

[0049] (3) Cold rolling with a large deformation amount: The total cold rolling deformation amount is 95%, and the thickness after cold rolling with a large deformation amount is 0.5 mm.

[0050] (4) First aging: The aging temperature is 460 °C, the aging time is 2 h, and it is air-cooled to room temperature.

[0051] (5) Cold finish rolling: The total cold finish rolling deformation amount is 80%, and the thickness after cold finish rolling is 0.1 mm.

[0052] (6) Second aging: The aging temperature is 410 °C, the aging time is 2 h, and it is air-cooled to room temperature.

[0053] In this embodiment, after the second aging, the tensile strength of the alloy reaches 685 MPa, and the conductivity reaches 72% IACS.

[0054] The results of the embodiment show that the copper alloy for the multiphase collaborative lead frame of the present invention has the characteristics of high strength and high conductivity. Using the above two processes, the industrial preparation of a copper alloy with a tensile strength greater than 650 MPa and a conductivity greater than 65% IACS is realized, meeting the use requirements of high-end semiconductor lead frame copper alloys.

[0055] The above-described embodiments are only preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope disclosed by the present invention all fall within the protection scope of the present invention.

Claims

1. A copper alloy for a multiphase collaborative lead frame, characterized in that, By mass percentage, the alloy components are as follows: Cr is 0.6 - 0.7%, Zr is 0.1 - 0.15%, Ni is 0.7 - 0.9%, Si is 0.2 - 0.3%, Co is 0.02 - 0.04%, Sn is 0.02 - 0.04%, and the balance is matrix Cu.

2. The preparation method of the copper alloy for the multiphase synergistic lead frame according to claim 1, wherein, It includes the following steps: (1) vacuum induction melting and casting; (2) homogenization treatment; (3) double milling; (4) hot rolling; (5) solution treatment; (6) cold rolling with a large deformation amount; (7) primary aging; (8) cold finish rolling; (9) secondary aging.

3. The preparation method of the copper alloy for the multiphase collaborative lead frame according to claim 1, wherein, It includes the following steps: (1) continuous casting; (2) continuous extrusion of sheet; (3) cold rolling with a large deformation amount; (4) primary aging; (5) cold finish rolling; (6) secondary aging.

4. The preparation method of the copper alloy for the multiphase synergistic lead frame according to claim 2 or 3, characterized in that, During cold rolling with a large deformation amount, the total cold rolling deformation amount is 85% - 99%, and the thickness after cold rolling with a large deformation amount is 1 - 0.5 mm.

5. The preparation method of the copper alloy for the multiphase synergistic lead frame according to claim 2 or 3, characterized in that, The total cold finish rolling deformation amount is 80% - 90%, and the thickness after cold finish rolling is 0.1 - 0.2 mm.

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