Research Papers

Ripening Growth Kinetics of Cu6Sn5 Grains in Sn-3.0Ag-0.5Cu-xTiO2/Cu Solder Joints During the Reflow Process

[+] Author and Article Information
Y. Tang

College of Automation,
Zhongkai University of Agriculture
and Engineering,
Guangzhou 510225, China
e-mail: tangyu_mycauc@163.com

S. M. Luo, C. J. Hou

College of Automation,
Zhongkai University of Agriculture
and Engineering,
Guangzhou 510225, China

G. Y. Li

School of Electronic and Information
South China University of Technology,
Guangzhou 510641, China

Z. Yang

College of Engineering,
South China Agricultural University,
Guangzhou 510642, China

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 18, 2017; final manuscript received December 26, 2017; published online March 2, 2018. Assoc. Editor: Ankur Jain.

J. Electron. Packag 140(1), 011003 (Mar 02, 2018) (11 pages) Paper No: EP-17-1089; doi: 10.1115/1.4038861 History: Received September 18, 2017; Revised December 26, 2017

The ripening growth kinetics of interfacial Cu6Sn5 grains between Cu substrates and Sn-3.0Ag-0.5Cu-xTiO2 (x = 0, 0.02, 0.05, 0.1, 0.3, and 0.6 wt %) (SAC305-xTiO2) solders were investigated. The results show that the Cu6Sn5 grain morphology is affected by the solder composition and the reflow time. The Cu6Sn5 grain size decreases upon addition of TiO2 and shows a significant decrease when the TiO2 nanoparticle fraction is increased to 0.1 wt %. At higher TiO2 nanoparticle fractions, the Cu6Sn5 grain size increases slightly. The growth of the Cu6Sn5 grains is mainly supplied by the flux of the interfacial reaction and the flux of ripening; the ripening flux plays a dominant role because it is approximately one order of magnitude greater than the interfacial reaction flux. The ripening growth of the Cu6Sn5 grains in the TiO2-containing solder joints is reduced more effectively than that of the Cu6Sn5 grains in the TiO2-free joint. For the SAC305/Cu and SAC305-0.6TiO2/Cu solder joints, the particle size distribution (PSD) of the Cu6Sn5 grains is well fit with the Marqusee and Ross (MR) model when the normalized size value of r/<r> is less than 1, and it is consistent with the flux-driven ripening (FDR) model when the value of r/<r> is greater than 1. On the other hand, for the SAC305-0.1TiO2/Cu solder joint, the Cu6Sn5 grains with a nearly hemispheric scallop shape and the PSD of the Cu6Sn5 grains show good agreement with the FDR model.

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Fig. 1

Field emission gun scanning electron microscope image of the TiO2 nanoparticles

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Fig. 2

Typical reflow temperature profile

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Fig. 3

Image processing for the size measurement of interfacial IMC grains: (a) original SEM image and (b) contour of the interfacial IMC grains

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Fig. 4

Scanning electron microscope micrographs of the top view of the Cu6Sn5 IMC layer of SAC305-xTiO2 solder joints reflowed for 12 s: (a) x = 0, (b) x = 0.02, (c) x = 0.05, (d) x = 0.1, (e) x = 0.3, and (f) x = 0.6 wt %

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Fig. 5

EMPA analysis results for the scallop-like Cu6Sn5 grains in Fig. 4(a)

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Fig. 6

Morphological evolution of Cu6Sn5 grains in the SAC305-xTiO2 solder joints reflowed for 600 s ((a)–(c)) and 3600 s ((d)–(f))

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Fig. 7

Average Cu6Sn5 grain size distributions for different nano-TiO2 proportions reflowed for (a) t = 12 s and (b) t = 3600 s

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Fig. 8

EMPA analysis results for the white spots in Fig. 6(a)

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Fig. 9

Cu6Sn5 average grain size versus TiO2 nanoparticles proportion for different reflow times in the SAC305-xTiO2 solder joints

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Fig. 10

Ln-Ln data plot of the average radius of Cu6Sn5 grain versus reflow time in the reflow process for SAC305-xTiO2 solder joints: (a) x = 0 (SAC305), (b) x = 0.02 (SAC305-0.02TiO2), (c) x = 0.05 (SAC305-0.05TiO2), (d) x = 0.1 (SAC305-0.1TiO2), (e) x = 0.3 (SAC305-0.3TiO2), and (f) x = 0.6 (SAC305-0.6TiO2) wt %

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Fig. 11

Schematic of Cu6Sn5 grain growth

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Fig. 12

(a) Consumed thickness of the Cu substrate versus reflow time and (b) consumption rate of the Cu substrate versus reflow time

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Fig. 13

Number of Cu6Sn5 grains per unit at the SAC305-xTiO2/Cu interface versus reflow time

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Fig. 14

Two kinds of Cu flux among Cu6Sn5 grains versus reflow time for the SAC305-xTiO2 solder joints

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Fig. 15

Schematic of the force balance of interfacial tension between two Cu6Sn5 neighboring grains and molten solders

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Fig. 16

Normalized size distribution of the Cu6Sn5 grains formed at the SAC305-xTiO2/Cu interface: ((a)–(c)) reflowed for 12 s and ((d)–(f)) reflowed for 3600 s: (a) SAC305, (b) SAC305-0.1TiO2, (c) SAC305-0.6TiO2, (d) SAC305, (e) SAC305-0.1TiO2, and (f) SAC305-0.6TiO2

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Fig. 17

Calculated relationships between the channel width and the diffusivity of Cu through the channels and for joints with different TiO2 nanoparticle proportions




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