Board Strain Analysis to Investigate Chassis Design Effects

Abstract

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.

Board Design Influence on BGA Mechanical Reliability

“…Chan et al [3] also studied the impact due to package design features including ball pitch, board thickness, and package size on mechanical performance. Limited literature studies on board and enabling thermal solution mechanical design [4,5] utilized flexural deformation and strains to approximate the complex solder joint dynamic behavior on a motherboard. Further studies by Shah and Mello [6] highlighted the limitations behind these approaches and an alternative proposal was made to quantify BGA solder joint failure limit through the use of solder ball force states with special emphasis towards defining a heat sink mass limit on the motherboard.…”