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RESEARCH PAPERS

Test Method Development to Quantify the In Situ Elastic and Plastic Behavior of 62%Sn–36%Pb–2%Ag Solder Ball Arrays in Commercial Area Array Packages at 40°C, 23 °C, and 125 °C

[+] Author and Article Information
Ahmad Abu Obaid, Antonio Paesano

Center for Composite Materials, University of Delaware, Newark, DE 19716

Jay G. Sloan, Mark A. Lamontia

 DuPont Engineering Technology, Beech Street Engineering Center, Wilmington, DE 19803-0840

Subhotosh Khan

 DuPont Thermount® Business Team, Richmond, VA 23234

John W. Gillespie1

Center for Composite Materials, Department of Materials Science and Engineering, and Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716gillespie@ccm.udel.edu

Hereafter referred to as an AAP/PWB.

1

To whom correspondence should be addressed.

J. Electron. Packag 127(4), 483-495 (Mar 21, 2005) (13 pages) doi:10.1115/1.2070048 History: Received June 08, 2004; Revised March 21, 2005

The objective of this study is to describe and evaluate test methods developed to experimentally characterize the in situ mechanical behavior of solder ball arrays connecting printed wiring boards to area array packages under tensile, compressive, and shear loading at 40, 23, and 125 °C. The solder ball arrays tested were composed of 62%Sn–36%Pb–2%Ag solder alloy. Finite element modeling was performed. The results indicated that the test fixture should be geometrically equivalent to the projected shape of the ball grid array to achieve uniform loading. Tension, compression, and shear tests were conducted. For tensile loading the interfaces and the solder balls are loaded in series resulting in a large apparent strain (13%). Various interfacial failure modes are observed. Under compression and shear loading the effect of the interfaces are negligible and therefore a significant deformation and a remarkable yielding behavior of solder ball arrays can be observed. Furthermore, the specimens tested under shear loading showed different failure modes such as cohesive or adhesive failure modes depending on the test temperature. From the overall results, it has been determined that shear loading is the most representative test to measure the actual mechanical behavior of solder in ball grid arrays.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Modified 8×8 model with steel block matching the solder ball array size

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Figure 6

Von Mises stresses in 8×8 solder ball array with steel block matching array size

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Figure 7

Shear loaded 3×3 solder ball array model with specifications: ABAQUS FEA code, 20-noded element mesh, symmetry boundary conditions on xz plane, the solder balls are constrained in the z direction on top and bottom of steel block, and move top block in the x direction

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Figure 1

(a) Three-dimensional schematic of AAP/PWB specimen, showing the solder ball arrays, chip, and PWB and (b) schematic of center cross section of AAP/PWB specimen, showing the central area free of solder balls

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Figure 2

Finite element model of 3×3 solder ball array loaded in tension with specifications: ABAQUS FEA code, 20-noded element mesh, symmetry boundary conditions on yz and xz planes, and the solder balls are constrained in the z direction at solder ball midplane

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Figure 3

Von Mises stresses in 3×3 tensile model

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Figure 4

Von Mises stresses in 8×8 tensile model

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Figure 11

Mechanical test fixture for shear test. Compressive load applied vertically.

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Figure 12

Corrected load-displacement curves for AAP/PWB specimens loaded under tension at 23 °C

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Figure 13

Stress-strain curves for AAP/PWB specimens loaded under tension at 23 °C

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Figure 8

Von Mises stresses in 3×3 solder ball array under shear loading

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Figure 9

(a) Mechanical test fixtures for tension and compressive loading, and (b) mechanical test fixture with AAP/PWB specimen bonded to the fixtures. Tensile and compressive loads applied vertically.

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Figure 10

Mechanical test fixtures for shear test. The fixture is machined out of stainless steel and made of two identical parts. Specimen is simply positioned on the shear fixture.

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Figure 14

Cross section of solder ball printed in PWB

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Figure 15

Pictures of the solder ball fracture surface (a) and location where the solder ball did fracture on PWB-surface (b)

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Figure 16

Images of the AAP/PWB specimen under tension at 23 °C: (a) at start of test; (b) at failure, showing a significant delamination failure in the chip and separation of solder balls from the layers of the chip

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Figure 17

Load-displacement curves for AAP/PWB specimens tested under compression at 23 °C

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Figure 18

Images of a specimen at the start (a) and end (b) of compressive testing at 23 °C, showing a significant increase in the solder ball diameter

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Figure 19

Chip and PWB surfaces of AAP/PWB specimens after shear testing at −40°C. The solder ball arrays exhibit cohesive and adhesive failure modes.

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Figure 20

Chip and PWB surfaces of AAP/PWB specimens after shear testing at 23 °C. The solder ball arrays exhibit cohesive and adhesive failure modes.

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Figure 21

Chip and PWB surfaces of AAP/PWB specimens after shear testing at 125 °C. All solder ball arrays are being fractured cohesively.

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Figure 22

Load-displacement curves for AAP/PWB specimens tested under shear at 23 °C

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Figure 23

Shear stress-strain curves for AAP/PWB specimens tested under shear at 23 °C

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