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Research Papers

Stress–Strain Behavior of SAC305 at High Strain Rates

[+] Author and Article Information
Pradeep Lall

Department of Mechanical Engineering,
NSF-CAVE3 Electronics Research Center,
Auburn University,
Auburn, AL 36849
e-mail: lall@auburn.edu

Sandeep Shantaram, Jeff Suhling

Department of Mechanical Engineering,
NSF-CAVE3 Electronics Research Center,
Auburn University,
Auburn, AL 36849

David Locker

U.S. AMRDEC,
Redstone Arsenal,
Huntsville, AL 35802

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received January 1, 2014; final manuscript received September 19, 2014; published online November 14, 2014. Assoc. Editor: Yi-Shao Lai.

J. Electron. Packag 137(1), 011010 (Mar 01, 2015) (16 pages) Paper No: EP-14-1001; doi: 10.1115/1.4028641 History: Received January 01, 2014; Revised September 19, 2014; Online November 14, 2014

Electronic products are subjected to high G-levels during mechanical shock and vibration. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. The second-level interconnects may be experience high strain rates and accrue damage during repetitive exposure to mechanical shock. Industry migration to lead-free solders has resulted in proliferation of a wide variety of solder alloy compositions. One of the popular tin-silver-copper alloys is Sn3Ag0.5Cu. The high strain rate properties of lead-free solder alloys are scarce. Typical material tests systems are not well suited for measurement of high strain rates typical of mechanical shock. Previously, high strain rates techniques such as the split Hopkinson pressure bar (SHPB) can be used for strain rates of 1000 s−1. However, measurement of materials at strain rates of 1–100 s−1 which are typical of mechanical shock is difficult to address. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1–100 s−1. High-speed cameras operating at 300,000 fps have been used in conjunction with digital image correlation (DIC) for the measurement of full-field strain during the test. Constancy of crosshead velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC305 solder. Constitutive model has been fit to the material data. Samples have been tested at various time under thermal aging at 25 °C and 125 °C. The constitutive model has been embedded into an explicit finite element framework for the purpose of life-prediction of lead-free interconnects. Test assemblies has been fabricated and tested under Joint Electron Device Engineering Council (JEDEC) JESD22-B111 specified condition for mechanical shock. Model predictions have been correlated with experimental data.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Specimen preparation setup

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Fig. 2

Cooling profile implemented for specimen preparation

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Fig. 3

Specimen inside glass tube

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Fig. 5

Specimen configuration with a slip-joint

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Fig. 6

High-speed camera (CAM 2) monitoring targets during tensile testing event

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Fig. 7

Crosshead motion time-history and specimen deformation

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Fig. 8

Displacement time-history for crosshead velocity of 0.84 m/s

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Fig. 9

Displacement time-history for crosshead velocity of 2.26 m/s

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Fig. 10

Strain time-history and strain rate for crosshead velocity of 0.84 m/s

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Fig. 11

Strain time-history and strain rate for crosshead velocity of 2.26 m/s

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Fig. 12

3D-DIC measurement for a truss member

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Fig. 13

Images captured by the high-speed cameras from time t = 0 to time t > failure time of the speckle patterned test specimen subjected to high-speed uniaxial tensile test

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Fig. 14

Repeatability of the test method

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Fig. 15

Effect of thermal aging on stress–strain behavior of SAC305 at strain rate of (ɛ· = 10 s−1)

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Fig. 16

Effect of thermal aging on stress–strain behavior of SAC305 at strain rate of (ɛ· = 35 s−1)

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Fig. 17

Comparison of circular and rectangular grid formation

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Fig. 19

Peridynamics based finite element model (hybrid model)

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Fig. 20

Peridynamics truss region in FE model

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Fig. 21

Stress field prediction for high-speed uniaxial tensile test at various time steps

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Fig. 22

Time to failure and failure mode predicted by FEM based on peridynamic theory

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Fig. 23

PCB (L × B = 132 × 77 mm2 and thickness 1.5 mm) and one PBGA-324 package located at center of the test board

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Fig. 24

Test board showing unique four quadrants continuity design for PBGA324 package

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Fig. 25

Test board with targets A, B, C to measure relative displacements

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Fig. 26

Measured acceleration curve corresponding to drop height 60 in.

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Fig. 27

Speckle patterned test board indicating failure locations

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Fig. 28

Continuity time history in 0 deg drop-shock indicating the failure time for package subregions D

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Fig. 29

Continuity time history in 0 deg drop-shock indicating the failure time for various package subregions B

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Fig. 31

DIC based 2D full-field strain contour (E11) on board (within 1-ms of the drop event)

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Fig. 32

DIC based 2D full-field strain contour (E11) on board (first cycle of the drop event)

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Fig. 33

Strain (E11) along the length of the board at center location and corresponding velocity component in dropping direction

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Fig. 34

Speckle patterned test board indicating discrete locations where velocity components (V3) are being extracted using DIC technique

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Fig. 35

Velocity (V3) components along dropping directions of the board at eight discrete locations using DIC technique

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Fig. 36

Peridynamic based FE modeling concept for electronic package across the solder interconnect interface

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Fig. 37

3D view of the peridynamics based truss elements across the solder interconnect interface (elements within dotted ellipse represents peridynamic truss region)

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Fig. 38

Corner solder balls locations represented as LT, RT, RB, and LB

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Fig. 39

Damage initiation and damage progression across LB solder interconnect on board side

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