NASA-DOD LEAD-FREE ELECTRONICS PROJECT: MECHANICAL SHOCK TESTAuthors: Thomas A. Woodrow, Ph.D.
Company: Boeing Research and Technology
Date Published: 10/24/2010 Conference: SMTA International
Twenty one test vehicles were subjected to the shock test conditions (in four batches). The Shock Response Spectrum (SRS) input was increased during the test after every 100 shock pulses in an effort to fail as many components as possible within the time allotted for the test.
The solder joints on the components were electrically monitored using event detectors and any solder joint failures were recorded on a Labview-based data collection system. The number of shocks required to fail a given component attached with SnPb solder was then compared to the number of shocks required to fail the same component attached with lead-free solder.
A complete modal analysis was conducted on one test vehicle using a laser vibrometer system which measured velocities, accelerations, and displacements at one hundred points. The laser vibrometer data was used to determine the frequencies of the major modes of the test vehicle and the shapes of the modes. In addition, laser vibrometer data collected during the mechanical shock test was used to calculate the strains generated (using custom software).
After completion of the testing, all of the test vehicles were visually inspected and cross sections were made. Broken component leads and other unwanted failure modes were documented.
Key words: mechanical shock, lead-free solder, NASA, reliability
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