Abstract
ABSTRACT A method for non-destructively tracking the integrity of flip chip solder joints through life is investigated in this paper. An industry standard double-sided PCB was designed and manufactured with 14 flip chips to assess the failure patterns of each flip chip and each solder joint in lifetime vibration tests. Two configurations of PCB finish were tested, Electro Nickel Immersion Gold (ENIG) and Hot Air Surface Levelled lead (Pb HASL) using automotive industry manufacturing processes and quality standards. A random vibration test over a frequency range 10 Hz to 1000 Hz was specified by automotive engineers to replicate vibrations typically found on road vehicles. This vibration profile was applied to test circuit board assemblies (CBA) for 4-minute intervals until failure of all chips. At each interval test boards were extensively scanned by an acoustic micro-imaging (AMI) microscope to non-destructively measure parameters of solder joints. This enabled tracking of mechanical joint connection through-life. Methods were developed to process the large number of acoustic images of each solder joint and form metrics to evaluate solder joint integrity. Results from AMI show that the solder joints exhibit three distinct zones as they age: crack initiation, crack propagation and then failure.
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