Isothermal Cyclic Bend Fatigue Test Method for Lead-Free Solder Joints

[+] Author and Article Information
John H. Pang

School of Mechanical and Aerospace Engineering,  Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singaporemhlpang@ntu.edu.sg

F. X. Che

School of Mechanical and Aerospace Engineering,  Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

J. Electron. Packag 129(4), 496-503 (Aug 27, 2007) (8 pages) doi:10.1115/1.2809442 History: Received January 23, 2007; Revised August 27, 2007

Isothermal three-point and four-point cyclic bend fatigue test methods have been developed for Sn–Ag–Cu solder joints. Reported bend tests from the literature were conducted at room temperature (25°C) and there is lack of data for lead-free solder joints. In this study, very-thin quad flat no-lead (VQFN) assembly with Sn–Ag–Cu lead-free solder was tested under three-point and four-point cyclic bending loads at both room temperature (25°C) and high temperature (125°C). The correlation between three-point and four-point bend tests was developed. Two different board surface finishes of electroless Ni and immersion gold (ENIG) and organic solderability preservatives (OSP) were investigated. Bending fatigue resistance of VQFN with OSP finish is slightly better than ENIG finish case. The acceleration factor of failure at high temperature (125°C) is higher than that at room temperature (25°C). Finite element analysis modeling and simulation were performed for different test conditions to investigate the solder joint stress-strain behavior. Volume-averaged energy density was used as a fatigue damage parameter and energy-based bending fatigue models were developed for VQFN with Sn–Ag–Cu solder joint under cyclic bending load at both 25°C and 125°C.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Board size and VQFN package layout

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Figure 2

Three- and four-point bending test fixtures

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Figure 3

Strain gauge location on test board

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Figure 4

Strain measurement of different locations

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Figure 5

Failure mode and site in solder joint

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Figure 6

Weibull plot of cycle to failure from four-point bend test

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Figure 7

Quarter FEA global model for four-point bend case and submodel

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Figure 8

Global simulation results for three-point bend

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Figure 9

Solder joint mesh in submodel and energy density contour for bottom and top layers

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Figure 10

Convergence history of volume-averaged energy density for center column component

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Figure 11

Correlation between four-point and three-point bending simulation results

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Figure 12

Strain results from FEA simulation with a displacement load of 2.16mm

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Figure 13

Result comparison between four-point bend simulation at 25°C and at 125°C

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Figure 14

Bending fatigue model for VQFN with Sn–Ag–Cu solder at 25°C

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Figure 15

Bending fatigue model for VQFN with Sn–Ag–Cu solder at 125°C



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