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Research Papers

Joint Level Test Methods for Solder Pad Cratering Investigations

[+] Author and Article Information
Brian D. Roggeman

 Universal Instruments Corp., Conklin, NY 13748Roggeman@uic.com

Venkatesh Raghavan, Peter Borgesen

Systems Science and Industrial Engineering,  Binghamton University, Binghamton, NY 13902

J. Electron. Packag 133(3), 031007 (Sep 14, 2011) (8 pages) doi:10.1115/1.4004182 History: Received February 22, 2010; Revised March 14, 2011; Published September 14, 2011; Online September 14, 2011

The introduction of less compliant lead free solders together with weaker and more brittle laminate materials has led to major concerns with respect to the resistance of the latter to pad cratering. For purposes of laminate selection as well as for the quantification of acceptable handling and use conditions, there is a general interest in the testing for cratering at the joint level, rather than by testing entire assemblies. Joint level testing is cheaper, faster, and offers more quantitative results. Joint level testing also allows the elimination of confounding factors such as PCB and component stiffness. Developing test procedures and testing, it is important to distinguish between wear out under repeated loads and the failure due to a single overstress. Correlations between these two damage scenarios are largely fortuitous. Focusing on strength testing we have compared alternative methods and identified the most relevant approach. Occasions may arise where shear testing is the most appropriate, but most pad cratering scenarios are best represented by so-called Hot Bump Pull at an angle of about 30° to the pad normal. Replacing the solder balls by paste deposits or pulling in a direction normal to the pad may lead to a different ranking of materials and otherwise obscure systematic trends. We also recommend taking loading rate and temperature effects into account.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Bending of printed circuit board assembly causes stresses on pads

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Figure 2

PCB pad is not in simple tension as a result of PCB flexure

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Figure 3

Finite element model shows that pin pull at 30° better represents board flexure stresses than pin pull at 0°

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Figure 4

Pin alignment to pad with either a paste deposit (left) or solder ball (right)

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Figure 5

Illustration of cold ball pull

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Figure 6

Illustration of solder ball shear test for pad cratering

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Figure 7

Shear strength for a range of test speeds on a filled phenolic resin (material B)

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Figure 8

Shear strength for a range of test speeds on an unfilled multifunctional resin (material A). Note that two solder failures were observed at 0.1 mm/s

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Figure 9

Pad strength dependence on pull angle of a filled phenolic resin (material B)

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Figure 10

Failure mode seen in pull (top) and shear (bottom) of a filled phenolic resin (material B). Glass bundles are only exposed when pads are sheared

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Figure 11

Pad strength dependence on pull angle of three different resin systems

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Figure 12

Comparison of vertical pull methods on a filled phenolic resin (material B)

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Figure 13

Comparison of vertical pull methods on four resin systems

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Figure 14

Pad strength dependence on pull speed. Filled phenolic (left) and unfilled multifunctional (right)

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Figure 15

Pad strength dependence in pull with different types of solder balls attached to the pad

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Figure 16

Failure mode seen in pull (top) and shear (bottom) of an unfilled multifunctional resin (material A). Glass bundles are observed in both cases

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Figure 17

Strength comparison of five resin systems in pull (left) and shear (right). The strength ranking changes based on the testing method

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Figure 18

Shear testing is conducted at some height above the sample and thus can induce significant moment at the pad in addition to the shear force

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Figure 19

Pad strength dependence on test temperature for two resins (resin G tested with two glass styles)

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Figure 20

Pad strength dependence on test temperature addition for four resins systems. The reduction in strength is not constant and depends on the material

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