A circuit board response was used to characterize five chassis that were manufactured by five different suppliers to two form factors: slim and mid-tower designs. The board responses were compared to that in a reference test chassis. All the chassis were shocked to the same input. The board response was characterized by strain gauges mounted on the PCB around critical BGA components. The board strains measurements were able to detect the manufacturing variability of the chassis fabricated and was used to identify the second level interconnection (SLI) risk for BGA placement at the measured location. This paper presents an empirically driven methodology comparing supply line chassis variation and their direct affect on BGA SLI reliability and the need to revise the procurement specification to ensure repeatable and predictable BGA or any critical SLI performance.
This paper presents two simple and unique tests to extract shock-level loading limits for eutectic and lead free solders. A wide range of loading rates, from quasi-static to high speed, was applied to a through-hole-mounted anchor assembly test coupon. The high speed shock tests were conducted on a drop shock table where the impacting velocities were derived through table input adjustments. The quasi-static tests were done using controlled hydraulic linear actuator with a load cell. As would be assumed, the dynamic load to cause solder joint failure was found to increase with higher loading rate. However, at such a high loading rate range, the impact velocity did not change the load to failure. This study leads to an interesting hypothesis that at high loading rates, the solder joint strain rate may not see a significant change as observed at low rates.
ATCA is a new form factor for communication equipment applications. Finite element model (FEM) was created to predict the dynamic response of an ATCA design during a table drop shock. The model was built with 2nd order brick elements for minimizing the meshing sensitivity. Modal method was used and followed by dynamic transient analysis with superposition approach and validated by comparing the modal test data for matching the natural frequencies and the modal shapes. The model was further validated by comparing the board displacement with direct displacement measurement using a high speed camera. As a result the localized board strain predictions matched the measured board strain at each networking processor unit. The validated model was used to predict the risk areas for solder joints, which later proved to be accurate during board design verification tests. This paper presents the modeling and model validation processes, as well as the ATCA mechanical design evaluations.
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