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TECHNICAL PAPERS

A New Thermal-Fatigue Life Prediction Model for Wafer Level Chip Scale Package (WLCSP) Solder Joints

[+] Author and Article Information
John H. Lau, Stephen H. Pan, Chris Chang

Agilent Technologies, Inc., 350 W. Trimble Road, MS 90LJ, San Jose, CA 95131

J. Electron. Packag 124(3), 212-220 (Jul 26, 2002) (9 pages) doi:10.1115/1.1462625 History: Received August 07, 2000; Online July 26, 2002
Copyright © 2002 by ASME
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References

Figures

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A memory chip with redistribution pads
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Cross section of the WLCSP
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Cross section of the WLCSP on PCB
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Cross sections of WLCSP-PCB assembly
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Temperature profile for thermal cycling; also mismatch displacement at the corner solder joint
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Solder joint cracklength distribution
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Cross sections of the corner solder joint at different thermal cycles. (a) 800 cycles (no obvious cracks), (b) 1000 cycles with 40 μm crack (outer crack), (c) 1200 cycles with 48μm crack (outer crack), (d) 1500 cycles with 100 μm crack (puter crack), (e) 2000 cycles with cracks from two edges, and (f) 2400 cycles with crack passing through solder joint.
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Schematic of the corner solder joint at different stages of thermal cycles. (a) No obvious crack at low temperature cycles, (b) crack initiates from the outer edge first, (c) crack initiates from the inner edge later, and (d) cracks grow through the whole solder joint.
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Test results: crack length versus cycle numbers
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Curve-fitting of crack length versus cycle numbers
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Corner solder joint for modeling
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Constitutive equation of 60Sn-40Pb solder under creep deformation
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Elements around a crack tip for averaged strain energy density calculation
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Deformed shape of the corner solder joint (crack length=0.056 mm,T=−20°C)
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Deformed shape of the corner solder joint (crack length=0.084 mm,T=−20°C)
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Deformed shape of the corner solder joint (crack length=0.112 mm,T=−20°C)
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Mises stress contour at the tip of outer (left) and inner (right) cracks (crack length=0.112 mm)
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Shear creep strain history at the middle of crack tips of the corner solder joint
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Shear stress history at the middle of crack tips of the corner solder joint
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Hysteresis loops at the middle of crack tips of the corner solder joint
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Shear creep strain history near one of the crack tips of the corner solder joint
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Shear stress history near one of the crack tips of the corner solder joint
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Hysteresis loops near one of the crack tips of the corner solder joint
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Average strain energy density range of different crack length in the corner solder joint
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Curve-fitting of the average strain energy density range of different crack length in the corner solder joint
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Fatigue crack growth rate curves of the corner solder joint

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