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Research Papers

Relationship Between the Intermetallic Compounds Growth and the Microcracking Behavior of Lead-Free Solder Joints

[+] Author and Article Information
Tong An

Laboratory of Advanced Electronic Packaging
Technology and Reliability,
College of Mechanical Engineering and
Applied Electronics Technology,
Beijing University of Technology,
Beijing 100124, China
e-mail: antong@bjut.edu.cn

Fei Qin

Laboratory of Advanced Electronic Packaging
Technology and Reliability,
College of Mechanical Engineering and
Applied Electronics Technology,
Beijing University of Technology,
Beijing 100124, China

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 30, 2015; final manuscript received December 19, 2015; published online March 10, 2016. Assoc. Editor: Yi-Shao Lai.

J. Electron. Packag 138(1), 011002 (Mar 10, 2016) (10 pages) Paper No: EP-15-1079; doi: 10.1115/1.4032349 History: Received August 30, 2015; Revised December 19, 2015

This paper investigates the formation and the growth of the intermetallic compound (IMC) layer at the interface between the Sn3.0Ag0.5Cu Pb-free solder and the Cu substrate during isothermal aging at 150 °C. We measure the thickness of the IMC layer and the roughness of the solder/IMC interface, and these two factors are assumed to control the tensile behavior of the solder joints. First, it utilizes the tensile tests of the aged solder joints for analyzing the effect of the IMC growth on the tensile behavior of the solder joints. Then, the microcracking behavior of the IMC layer is investigated by finite element method (FEM). In addition, qualitative numerical simulations are applied to study the effect of the IMC layer thickness and the solder/IMC interfacial roughness on the overall response and the failure mode of solder joints. The experimental results indicate that when the aging time increases, both the thickness and the roughness of the IMC layer have a strong influence on the strength and the failure mode of solder joints. The numerical simulation results suggest that the overall strength of solder joints is reduced when the IMC layer is thick and the solder/IMC interface is rough, and the dominant failure mode migrates to the microcracks within the IMC layer when the IMC layer is thick and the solder/IMC interface is flat.

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Figures

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Fig. 1

Geometry of the tensile test sample of the solder joint (unit: mm)

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Fig. 2

Definition of the parameters to characterize the IMC morphology

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Fig. 3

SEM images of the Sn3.0Ag0.5Cu/Cu interface aged at 150 °C for (a) 0 hr, (b) 72 hrs, (c) 288 hrs, and (d) 500 hrs

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Fig. 4

Tensile stress–strain curves of the aged Sn3.0Ag0.5Cu/Cu solder joints tested at the strain rates of 2 × 10−2 s−1

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Fig. 5

Relationship between the tensile strength of the solder joints and the morphology parameters of the IMC layer aged for different time

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Fig. 6

The solder/Cu6Sn5 grain/Cu pad structure of model I

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Fig. 7

Effect of the IMC base thickness db on the reaction force–displacement response

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Fig. 8

Effect of the solder/IMC interfacial Rrms on the reaction force–displacement response

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Fig. 9

Effect of the solder/IMC interfacial λave on the reaction force–displacement response

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Fig. 10

Relationship between the ultimate overall load and the morphology parameters of the IMC layer

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Fig. 11

SEM images of the fractured surfaces of the solder joints aged at 150 °C for (a) 0 hr, (b) 72 hrs, (c) 288 hrs, and (d) 500 hrs

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Fig. 12

Three failure modes of solder joints

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Fig. 13

Microcracking pattern of model I: db = 4 μm, λave = 12 μm, and Rrms = 8 μm

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Fig. 14

Microcracking pattern of model III: db = 9 μm, λave = 12 μm, and Rrms = 8 μm

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Fig. 15

Microcracking pattern of model IV: db = 7.5 μm, λave = 12 μm, and Rrms = 2 μm

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Fig. 16

Microcracking pattern of model II: db = 7.5 μm, λave = 12 μm, and Rrms = 8 μm

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Fig. 17

Microcracking pattern of model VI: db = 7.5 μm, λave = 24 μm, and Rrms = 8 μm

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Fig. 18

Microcracking pattern of model VII: db = 7.5 μm, λave = 36 μm, and Rrms = 8 μm

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