Microstructures Evolution and Properties of Sn-Ag-Cu Solder Joints
Lei SUN1,Minghe CHEN1(),Liang ZHANG2,Fan YANG2
1 College of Mechanical & Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China 1 College of Mechanical & Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Cite this article:
Lei SUN,Minghe CHEN,Liang ZHANG,Fan YANG. Microstructures Evolution and Properties of Sn-Ag-Cu Solder Joints. Acta Metall Sin, 2017, 53(5): 615-621.
SnAgCu solder alloys, such as Sn3.0Ag0.5Cu, Sn3.8Ag0.7Cu and Sn3.9Ag0.6Cu, are widely used for consumer electronics due to their good wettability, high mechanical properties and excellent thermal fatigue reliability. However, the high Ag content in SnAgCu solder can bring about a relatively high cost and poor drop impact reliability because of the formations of thicker brittle Ag3Sn compound during soldering. Therefore, the development of low Ag content SnAgCu solders to satisfy the requirements of electronic production has become a hot topic in this field. In this work, the effects of Sn0.3Ag0.7Cu, Sn1.0Ag0.5Cu and Sn3.0Ag0.5Cu solder on the melting character, wettability, mechanical properties and microstructures, phase composition were investigated by DSC, micro-joint strength tester, SEM, EDS and XRD. Under -55~125 ℃ cyclic conditions, the interfacial layer change of Sn-Ag-Cu solder joints was measured by TL-1000 high and low temperature test chamber. The results showed that, with the Ag content increased, the melting point was not changed, the wetting angle significantly decreased. And the wettability of three solders was improved under N2 atmosphere. Moreover, the mechanical properties of three solder joints were enhanced with the increase of Ag content. The matrix structure of Sn0.3Ag0.7Cu and Sn1.0Ag0.5Cu solder joint have a small amount of Ag3Sn and large Cu6Sn5 particles, and the distribution of particles were disordered. However, the matrix structure of Sn3.0Ag0.5Cu solder joint was obviously uniform. This is the reason that the mechanical properties of Sn0.3Ag0.7Cu and Sn1.0Ag0.5Cu solder joints were lower than that of Sn3.0Ag0.5Cu. In addition, the solder joints were subjected to a thermal cycling reliability test, it was found that the thickness of intermetallic compounds (IMCs) increased, and the morphology of IMCs was gradually changed from scallop-like to planar-like.
Fund: Supported by National Natural Science Foundation of China (No.51475220), Six Talent Peaks project in Jiangsu Province (No.XCL022), Qing Lan project, State Key Laboratory of Advanced Brazing Filler Metals & Technology (No.SKLABFMT201503) and China Postdoctoral Science Foundation Funded Project (No.2016M591464)
Fig.2 Schematics of pull force of quad flat package (QFP) (a) and shear test of chip resistor (b) of Sn-Ag-Cu solder joint
Fig.3 Loading specification of temperature cycle
Solder
TS
TL
Melting range
Under- cooling
Sn0.3Ag0.7Cu
213.0
228.1
15.1
22.6
Sn1.0Ag0.5Cu
213.7
227.7
14.0
17.8
Sn3.0Ag0.5Cu
213.4
219.7
6.3
8.3
Table 1 Melting temperatures of Sn-Ag-Cu solder(℃)
Fig.4 Wetting angles of Sn-Ag-Cu solders during different atmospheres
Fig.5 Mechanical properties of Sn-Ag-Cu solder joints
Fig.6 Fracture SEM images of Sn0.3Ag0.7Cu (a), Sn1.0Ag0.5Cu (b) and Sn3.0Ag0.5Cu (c)
Fig.7 SEM image (a), EDS elemental distribution map (b) and XRD spectrum (c) of Sn3.0Ag0.5Cu solder joint
Fig.8 SEM images of matrix structures of Sn0.3Ag0.7Cu (a), Sn1.0Ag0.5Cu (b) and Sn3.0Ag0.5Cu (c) solder joints
Fig.9 SEM images of interface layers of Sn0.3Ag0.7Cu (a), Sn1.0Ag0.5Cu (b) and Sn3.0Ag0.5Cu (c) solder joints
Fig.10 SEM images of interface layers of Sn0.3Ag0.7Cu (a), Sn1.0Ag0.5Cu (b) and Sn3.0Ag0.5Cu (c) solder joints after 500 cyc
Fig.11 IMC layer thickness of Sn- Ag- Cu solder joints during different ageing times
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