Date of Award

Summer 2005

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)


Electrical Engineering

First Advisor

Fournelle, Raymond

Second Advisor

Nigro, Nicholas

Third Advisor

Heinrich, Stephen


A new test method for analyzing the isothermal low cycle fatigue experienced in a solder joint on a circuit board has been developed. This new test method simulates the strains that a solder joint experiences during temperature cycling by mechanically cycling test boards with rectangular copper "components" soldered to them. The mismatch in the elastic moduli of the rectangular copper "component" and the fiberglass circuit board generate strains in the solder joints, when mechanically cycled, similar to the strains generated during thermal cycles and caused by the mismatch of the thermal expansion coefficients of boards and components. This test involves direct measurements of strains in the surface of rectangular copper specimen soldered to the board, which can be converted into average shear stresses and strains in the solder joints, and, by running isothermal tests, the effects of temperature and strain on the solder joints can be uncoupled. The results of this test for a Sn-Ag-Cu (SAC) solder alloy show that increased load amplitudes during mechanical cycling lead to shorter lifetimes of solder joints and that the solder joints cyclically soften prior to failure. They also show that plastic strain gradually shifts to the joint initially exhibiting the softening.



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