Copper alloy wire rod strengthening method based on mechanical induction heterogeneous interface element interpenetration

Abstract

The invention provides a method for strengthening a copper alloy wire rod based on mechanical induction of interpenetration of heterogeneous interface elements, which comprises the following steps of: firstly, preparing a Cu20Ag rod blank with the diameter of 8-10mm in a vertical continuous casting manner; then, by controlling the drawing speed and the deformation amount of each pass in the continuous cold drawing deformation process of the rod blank, a layered or strip-shaped strengthened structure can be generated in the cold drawing deformation process, and nano twin crystals can be induced to be generated through interpenetration of heterogeneous interface elements for strengthening; and the high-strength copper alloy wire rod with the diameter of 20 microns is further obtained.

Description

Technical Field

[0001] The invention relates to the field of preparation and processing of copper alloy wires for large-scale integrated circuits, in particular to a copper alloy wire strengthening method based on mechanized induction of interpenetration of heterogeneous interface elements. Background Art

[0002] Copper-silver (CuAg) alloy can be used as bonding wire for integrated circuits. With the extreme miniaturization and high integration of integrated circuits, the wire diameter and strength requirements for bonding wires are getting higher and higher: tensile strength ≥1.2GPa, wire diameter ≤20μm.

[0003] There are many studies on copper-silver alloys at present. For example, the patent with publication number CN104818443A discloses a short-process and efficient production method of copper-silver alloy wire, which adopts a warm-mold continuous casting method to prepare a copper-silver alloy wire billet with a columnar crystal structure with a high degree of orientation along the length direction and a diameter of 1 to 30 mm. The warm-mold continuous casting billet drawing speed is 1 to 600 mm / min; the wire billet is rolled or roughly drawn at room temperature or at a temperature 20 to 50°C lower than the recrystallization temperature of the wire billet, and then finely drawn to a wire with a diameter of 10 to 50 μm. However, a certain degree of annealing treatment is still required in the process, and its applicability to high-silver content copper alloys is still unclear.

[0004] In order to further improve the strength of the wire, more Ag needs to be added. However, the solid solubility of Ag in Cu at room temperature is extremely limited (up to 7.8wt.%). When the Ag content is too high, it is easy to precipitate in the Cu matrix to form a nearly independent phase. The interface between Cu and Ag heterogeneous phases is relatively weak during deformation, which is prone to stress concentration and thus becomes a failure point. Under extremely fine wire diameters, the wire is more sensitive to the distribution of stress, the micro-area deformation behavior is more complex, it is more difficult to draw, and it is easier to break the wire. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a copper alloy wire strengthening method based on mechanized induced interpenetration of heterogeneous interface elements. By controlling the drawing speed and the deformation amount of each pass during the continuous cold drawing deformation of the rod blank, a layered or banded strengthening structure can be generated during the cold drawing deformation process, and the interpenetration of heterogeneous interface elements can induce the generation of nano twins for strengthening, thereby obtaining a high-strength copper alloy wire with a diameter of 20 μm.

[0006] In order to achieve the above object, the specific scheme adopted by the present invention is: A copper alloy wire strengthening method based on mechanized induction of heterogeneous interface element interpenetration mainly comprises the following steps: Step (1), preparing a Cu20Ag rod blank with a diameter of 8-10 mm by vertical continuous casting; Step (2), continuously cold drawing the rod blank, controlling the drawing speed to be 80 m / min to 600 m / min, and the cross-sectional shrinkage rate of each pass to be 5.56% to 54.43%, so that a layered or banded strengthening structure can be generated during the cold drawing deformation process, and nano twins can be induced to strengthen through the interpenetration of heterogeneous interface elements, and finally a copper alloy wire with a diameter of 20 μm is obtained.

[0007] Furthermore, in step (2), the total number of passes is 150-160 times, and the cross-sectional reduction rate of the total number of passes is 99.999375%.

[0008] Furthermore, the tensile strength of the obtained copper alloy wire reaches 1655 MPa, and the yield strength reaches 1581 MPa.

[0009] Beneficial effects:

[0010] In response to the requirements of large-scale integrated circuits for bonding wire size and strength, a copper alloy wire strengthening method that mechanized induced interpenetration of heterogeneous interface elements was developed to obtain copper alloy wires with size and strength that met the requirements.

[0011] The core of the present invention is to solve the problem that the wire is easy to break and the strength does not meet the requirements when the current enterprises prepare ultra-fine wires. A high Ag content (Cu20Ag) rod blank is prepared by vertical continuous casting, and the rod blank is continuously cold drawn without active annealing. During the process, the interpenetration degree of Cu and Ag heterogeneous interface elements is detected, and the drawing speed and pass deformation amount are adjusted based on the interpenetration degree. Finally, a copper alloy wire that meets the size and strength requirements is prepared. The tensile strength of the 20μm wire diameter wire reaches 1655MPa, and the yield strength reaches 1581MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a graph showing the results of detecting the interpenetration degree of elements at the interface of Cu and Ag heterogeneous phases in the product and intermediate product obtained in Example 1.

[0013] Figure 2 The microstructure diagram of the product and intermediate product obtained in Example 1. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0015] Example 1

[0016] The copper alloy wire strengthening method of mechanically inducing interpenetration of heterogeneous interface elements in this embodiment comprises the following specific steps: (1) Electrolytic Cu plates and Ag ingots were selected to melt and prepare Cu20Ag alloy by vertical continuous casting to prepare 8 mm diameter Cu20Ag rod blanks; (2) performing continuous cold drawing deformation on the 8 mm rod blank, performing 10-20 drawing passes, the drawing speed is 80-120 m / min, the deformation amount of each pass is 35.7-54.4%, and obtaining an intermediate wire A with a diameter of 5.34 mm; (3) the intermediate wire A is continuously cold drawn for 20 to 40 times at a drawing speed of 100 to 200 m / min and a deformation amount of 25.4 to 30.3% per time, to obtain an intermediate wire B with a diameter of 2.95 mm; (4) The intermediate wire B is continuously subjected to cold drawing deformation for 40-60 times at a drawing speed of 300-500 m / min and a deformation amount of 10.3-15.6% in each time, to obtain an intermediate wire C with a diameter of 1 mm. (5) The intermediate wire B is continuously subjected to cold drawing deformation for 40-80 times at a drawing speed of 400-600 m / min and a deformation amount of 5.6-8.2% in each time, to obtain a final product with a diameter of 20 μm.

[0017] The results of the interpenetration test of Cu and Ag heterogeneous phase interface elements in the product obtained in Example 1 are analyzed. Please refer to Figure 1 , Figure 1(a) shows the Cu and Ag heterogeneous interfaces of the intermediate wire sample A; Figures 1(b) and 1(c) show the Cu and Ag heterogeneous interfaces in the final product; Figure 1(d) shows the interpenetration degree of the elements in the heterogeneous interface of the intermediate wire sample A; Figure 1(e) shows the interpenetration degree of the elements in the Cu and Ag heterogeneous interface in the final product. Figure 1 As shown, when the wire sample has a larger diameter (5.34 mm), the Cu and Ag elements do not interpenetrate, and no twin structure appears in the microstructure; however, when the wire sample is continuously cold drawn to a thinner wire diameter (20 μm), the Cu and Ag elements interpenetrate significantly.

[0018] For further analysis of the microstructure of the product obtained in Example 1, please refer to Figure 2 ,in, Figure 2(a) is the organization diagram of the Cu20Ag rod blank, 2(b) is the microstructure diagram of the intermediate wire B, 2(c) is the microstructure diagram of the intermediate wire c, and 2(d) is the microstructure diagram of the final product. As the deformation continues to increase, dislocations, microbands and other structures gradually appear in the rod blank. Furthermore, a twin structure appears when the wire diameter is 1 mm, and as the deformation further increases, the twin structure gradually becomes nano-sized. In theory, copper deforms by slip while silver deforms mainly by twinning mechanism. It is difficult to form deformation twins or nano twins in pure copper, and the strengthening mechanism should also be mainly based on the strengthening of dislocations and their derived microstructures. However, the excessively high cumulative deformation and the excessively fast deformation rate cause the mechanized interpenetration of Cu and Ag near the phase interface. This mechanized interpenetration, on the basis of the layered or banded strengthening organization produced by the deformation of the wire, further induces a large number of nano twins in the wire, introduces twin strengthening, and improves the material strength.

[0019] The tensile strength and yield strength of the product and the intermediate product obtained in Example 1 were tested, and the results are shown in Table 1.

[0020] Table 1 Tensile strength and yield strength of the products and intermediates obtained in Example 1 Tensile strength / MPa Yield strength / MPa 8mm diameter Cu20Ag rod blank - 266.96 Intermediate wire A - 451.2 Intermediate wire B 642 603.48 Intermediate wire C 854 802.76 Final Product 1655 1581

[0021] Combination Figure 1-2 As shown in Table 1, when Cu and Ag elements interpenetrate significantly, a strengthened structure can be produced in the wire and a large number of nanotwins can be induced, thereby improving the strength of the material. Finally, when the wire diameter is 20 μm, the tensile strength reaches 1655 MPa and the yield strength reaches 1581 MPa.

[0022] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made according to the essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A copper alloy wire strengthening method based on mechanized induction of heterogeneous interface element interpenetration, characterized in that: The main steps are as follows: Step (1), preparing a Cu20Ag rod blank with a diameter of 8-10 mm by vertical continuous casting; In step (2), the rod blank is continuously cold drawn, the drawing speed is controlled to be 80 m / min-600 m / min, and the cross-sectional shrinkage rate of each pass is 5.56%-54.43%, so that a layered or banded strengthening structure can be generated during the cold drawing deformation process, and a large number of nano twins can be induced to strengthen through the interpenetration of heterogeneous interface elements, and finally a copper alloy wire with a diameter of 20 μm is obtained.

2. The copper alloy wire strengthening method based on mechanized induction of heterogeneous interface element interpenetration according to claim 1 is characterized in that: In step (2), the total number of passes is 150-160, and the cross-sectional reduction rate of the total number of passes is 99.999375%.

3. The copper alloy wire strengthening method based on mechanized induction of heterogeneous interface element interpenetration according to claim 1 is characterized in that: The tensile strength of the obtained copper alloy wire reaches 1655MPa, and the yield strength reaches 1581MPa.

Images