Investigations on the Thermal Conductivity of Micro-Scale Cu-Sn Intermetallic Compounds Using Femtosecond Laser Time-Domain Thermoreflectance System
ZHOU Lijun1,2, WEI Song1,2,3, GUO Jingdong1,2(), SUN Fangyuan4(), WANG Xinwei5, TANG Dawei5
1.Shenyang National Laboratory for Materials Science, 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 Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin 541004, China 4.School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China 5.School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China
Cite this article:
ZHOU Lijun, WEI Song, GUO Jingdong, SUN Fangyuan, WANG Xinwei, TANG Dawei. Investigations on the Thermal Conductivity of Micro-Scale Cu-Sn Intermetallic Compounds Using Femtosecond Laser Time-Domain Thermoreflectance System. Acta Metall Sin, 2022, 58(12): 1645-1654.
An accurate temperature analysis of electronic packaging requires an understanding of the thermal-transport parameters of the material. However, studies on the thermal conductivity of intermetallic compounds (IMCs) in micro-interconnect solder joints are scarce, particularly common IMCs forming in Cu-Sn systems, which seriously affect the precise prediction of the temperature field and thermal stress for electronic packaging structures. This work proposes a novel method to quantitatively measure the thermophysical parameters of Cu-Sn IMCs based on the dual-wavelength femtosecond laser time-domain thermoreflectance (TDTR) system. Cu-Sn diffusion couple samples were prepared using a reflow and aging process. Two layers of Cu6Sn5 and Cu3Sn IMCs formed at the interface with micron thickness, and the (001) crystal plane of Cu6Sn5 was the preferred orientation. The sensitivity of the experimental parameters to the measurement parameters affects the fitting accuracy. Therefore, before testing, the effects of the aluminum transducer thickness and pump laser modulation frequency on the phase signal sensitivity in the thermal conductivity measurements of Cu6Sn5 and Cu3Sn were analyzed to help select the specific experimental parameters. After testing, the thermal conductivities of Cu6Sn5 and Cu3Sn were 47.4 and 87.6 W/(m·K), respectively, which are slightly higher than the previous results because of the microstructure discrepancy caused by different material preparation techniques. Finally, the influence of the pump laser diameter, aluminum transducer thickness, and material specific heat on the measurement error of thermal conductivity for Cu6Sn5 and Cu3Sn was examined. The test errors of the Cu6Sn5 and Cu3Sn thermal conductivity were -6.8%~4.6% and -7.1%~4.4%, respectively. Overall, the TDTR technology can evaluate the thermal-transport characteristics of micron-scale intermetallic compounds in electronic packaging and guide the thermal design and reliability evaluations of electronic components.
Fund: National Natural Science Foundation of China(51971231);National Natural Science Foundation of China(52105327);National Natural Science Foundation of China(51720105007);National Key Scientific Instrument and Equipment Development Projects of China(2013YQ120355);Fundamental Research Funds for the Central Universities(FRF-BD-20-09A)
About author: SUN Fangyuan, associate professor, Tel: 15011316319, E-mail: sunfangyuan@ustb.edu.cn GUO Jingdong, professor, Tel: 13066761355, E-mail: jdguo@imr.ac.cn
Fig.1 Schematic of femtosecond laser time-domain thermoreflectance (TDTR) system
Fig.2 Microstructure analyses of the interface for Cu-Sn diffusion couple specimens (a) SEM image of microstructure (b) EDS element maps of square region in Fig.2a (c) XRD spectrum of Cu-Sn specimen
Fig.3 Orientation distributions of Cu6Sn5 grains (a) band contrast image (b) Euler color image (?1, Φ, ?2—Euler angles) (c) orientation color image perpendicular to RD-TD plane (RD—rolling direction, TD—transverse direction) (d) (001) pole figure (e) (100) pole figure (f) (301) pole figure
Fig.4 Orientation distributions of Cu3Sngrains (a) band contrast image (b) Euler color image (c) orientation color image perpendicular to RD-TD plane (d) (001) pole figure (e) (100) pole figure (f) (301) pole figure
Fig.5 Influences of aluminum transducer thickness (a, b) and pump laser modulation frequency (c, d) on phase signal sensitivity in thermal conductivity measurement for Cu6Sn5 (a, c) and Cu3Sn (b, d)
Fig.6 Experimental data of thermal conductivity measurement and the fitting curves of phase angle signal (a, b) and amplitude signal (c, d) for Cu6Sn5 (a, c) and Cu3Sn (b, d)
Fig.7 Influences of pump laser diameter (Dpump) (a), aluminum transducer thickness (dAl) (b), and material specific heat (cp ) (c) on thermal conductivity measurement for Cu6Sn5 and Cu3Sn
Item
Raw data
4.2% (cp )
-2.1% (cp )
1 nm (dAl)
-1 nm (dAl)
1 μm (Dpump)
-1 μm (Dpump)
Error
±0.6%
-4.0%
2.1%
1.5%
-1.8%
0.4%
-0.4%
1
47.0
45.1
48.0
47.7
46.3
47.2
46.8
2
47.7
45.8
48.7
48.4
46.9
47.8
47.5
3
47.5
45.7
48.5
48.2
46.8
47.7
47.4
Mean
47.4
45.5
48.4
48.1
46.7
47.6
47.2
Table 1 Statistics of calculated results of thermal conductivity and corresponding error of Cu6Sn5
Item
Raw data
4.1% (cp )
-1.2% (cp )
1 nm (dAl)
-1 nm (dAl)
1 μm (Dpump)
-1 μm (Dpump)
Error
±1.4%
-4.0%
1.3%
1.5%
-1.5%
0.2%
-0.2%
1
89.3
85.7
90.4
90.7
88.0
89.5
89.1
2
87.1
83.6
88.2
88.4
85.8
87.3
86.9
3
86.5
83.0
87.5
87.8
85.2
86.7
86.3
Mean
87.6
84.1
88.7
89.0
86.3
87.8
87.4
Table 2 Statistics of calculated results of thermal conductivity and corresponding error of Cu3Sn
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