Electronics Assembly Knowledge, Vision & Wisdom
Pad Crater Initiation in Shock Using Acoustic Emission Detection
Pad Crater Initiation in Shock Using Acoustic Emission Detection
Dye stain and cross section failure analysis techniques were used to identify pad crater damage and showed good agreement with the acoustic events.
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Authored By:
W. Carter Ralph
Southern Research Institute
Birmingham, AL, USA

Gregory N. Morscher
The University of Akron
Akron, OH, USA

Elizabeth Elias Benedetto
Hewlett-Packard
Houston, TX, USA

Keith Newman and Aileen Allen
Hewlett-Packard
Palo Alto, CA, USA

Julie Silk
Keysight Technologies
Santa Rosa, CA, USA

Summary
Acoustic emission detection was used to identify damage events on electronic assemblies during mechanical shock testing. Two board designs manufactured from several laminate types were instrumented with acoustic transducers and dropped multiple times at acceleration levels between 100 and 250g. Acoustic events that indicated a failure within the footprint of the ball grid array were identified and located using triangulation.

Dye stain and cross section failure analysis techniques were used to identify pad crater damage and showed good agreement with the acoustic events. The results indicate that acoustic emission detection can be used to identify and locate pad cratering during shock within approximately 5 mm, and has the potential to significantly improve the speed and precision of mechanical shock testing.

Conclusions
These results demonstrate that acoustic emissions from interconnect fractures can be detected in mechanical shock. The failures that were recorded corresponded to pad craters, which is a common failure mode. The locations of the pad crater events can be located within approximately 5 mm. This initial study demonstrated that AE can detect small mounts of pad cratering during mechanical shock, often at the early crack-initiation phase.

Physical failure analysis using cross-sectioning produced no observed false positives or negatives. Dye-stain could not confirm all failures detected with AE, likely due to lack of crack penetration to the surface. Further refinement in test equipment, pre-amplification settings and filtering are needed to ensure complete event capture, and reduction in the number of observed false-failures.

Acoustic emission is a promising method for detecting damage in mechanical shock. It has the potential to detect damage relatively quickly, cheaply, and accurately. Further use and development by the electronics industry is warranted.

Initially Published in the SMTA Proceedings

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