Effects of Al Interlayer and Ni(V) Transition Layer on the Welding Residual Stress of Co/Al/Cu Sandwich Target Assembly
JIANG Lin1,2, ZHANG Liang1,3, LIU Zhiquan1,2,4()
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 3 School of Mechatronic Engineering, Jiangsu Normal University, Xuzhou 221116, China 4 Shenzhen Institute of Advanced Electronic Materials, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
Cite this article:
JIANG Lin, ZHANG Liang, LIU Zhiquan. Effects of Al Interlayer and Ni(V) Transition Layer on the Welding Residual Stress of Co/Al/Cu Sandwich Target Assembly. Acta Metall Sin, 2020, 56(10): 1433-1440.
Sputtering has been widely used to prepare thin film due to its good cohesion with substrate, high purity, compactness, repeatability and large area manufacture. Target is a key consumable material during production of thin film by sputtering. Generally, targets are mostly rare and high purity metal, so the cost of target is very high. In order to reduce the cost of target, to improve its stiffness, and to enhance the electrical and thermal conductivity, target is usually connected with backplane to form the target assembly. The main connection method is diffusion welding, which is used in the industrial production. However, the target and the backplane are usually two different materials with different physical properties such as coefficient of thermal expansion (CTE) and thermal conductivity. During the welding or soldering process of target, the mismatch of physical properties will lead to residual stress in target, which has a direct influence on the thickness and microstructure uniformity of the films. Hence, it is very meaningful to investigate the residual stress in target and to study its influencing factor. Based on the Co/Al/Cu sandwich structure of backplane diffusion welding, the effects of Al interlayer and Ni(V) layer on welding residual stress were studied by finite element method. It was found that the application of the Al interlayer not only can make diffusion welding process easier and lower the diffusion welding temperature, but also can reduce the maximum residual stress from 142 MPa to 126 MPa. Furthermore, the location of the maximum residual stress also changes from the outer edge of the interface between target and backplane to the position near the symmetrical axis of target and Co/Al interface. Furthermore, there is an optimal thickness for Al interlayer (7 mm). Although the existence of Ni(V) layer can inhibit the generation of brittle intermetallic compounds at the interface of Co/Al and Cu/Al, it also increases the residual stress. Moreover, we find that the increase of residual stress with Ni(V) layer at only Co/Al interface, is smaller than that of adding Ni(V) layer at both Co/Al and Cu/Al interfaces.
Table 1 Material models, sizes and element types of target assembly
Material
Thermal conductivity
W·m-1·K-1
Elastic modulus
GPa
Density
kg·m-3
c
J·kg-1·K-1
α
10-6 K-1
ν
Co target
89.5
211.0
8850
473
13.9
0.32
Cu backplane
369.0
128.0
8889
390
16.5
0.34
Al interlayer
238.0
70.6
2700
900
23.8
0.33
Ni(V) layer
76.5
199.0
8910
574
14.9
0.33
Table 2 Physical properties of target assembly
Fig.1 Geometric model of diffusion welded target assembly
Fig.2 Finite element model of diffusion welded target assembly
Fig.3 Sample of diffusion welded target assembly with stress test points before (a) and after (b) cutting (The dimension of target assembly is shown in Table 1)
Fig.4 Effects of Al interlayer on the residual stress in the target assembly (Arrows indicate the positions of maximum residual stress) Color online (a) with Al interlayer (b) without Al interlayer
Fig.5 Effects of Al interlayer thickness on the maximum residual stress in target assembly
Case
Thickness of Al
interlayer / mm
Thickness of Ni(V) layer at
Co/Al interface / mm
Thickness of Ni(V) layer at
Cu/Al interface / mm
Maximum residual
stress / MPa
I
4
0
0
124.7
II
4
0.3
0
128.7
III
4
0.3
0.3
136.9
Table 3 Effects of Ni(V) layer on maximum residual stress of target assembly
Fig.6 Effects of Ni(V) layer on the residual stress of target assembly Color online (a) just Al interlayer (b) Ni(V) (0.3 mm) at Co/Al interface (c) Ni(V) (0.3 mm) at Co/Al and Cu/Al interface
Fig.7 Distributions of residual stress in target assembly Color online (a) X component of residual stress (b) Y component of residual stress(c) Z component of residual stress (d) von Mises equivalent residual stress
Fig.8 Experimental and simulated radial residual stresses on the surface of target assembly
Fig.9 Experimental and simulated circumferential residual stresses on the surface of target assembly
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