Design evaluation and product reliability assessment usingaccelerated reliability fatigue life tests

摘要

Accelerated reliability stress tests were performed to evaluate adesign concern on a printed circuit board assembly (PCBA) for a diskdrive product. Preliminary design tests indicated that a motor driver176 pin PQFP (plastic quad flat package) IC package mounted on the PCBAmay have a reliability problem in the field. The function of the motordriver chip was to provide electrical contact to the motor bearingassembly housed in the HDA. An elastomeric connector mounted on the PCBAunder the 176 pin PQFP IC package was used to provide the electricalconnection between the IC and the motor bearing assembly. A minimumforce was required to maintain the electrical contact through theimbedded wires used in the elastomeric connector sandwiched between thePQFP package and the HDA. This force was provided by a hold down screwused to push the PCBA on the HDA. The reliability concern was that pin 1and pin 176 on the corner of the PQFP package and closest to theelastomeric connector will break due to the high bending stressexperienced, the effect of which is aggravated due to the coupling ofthermal stress during operation. Typically stresses are higher on thefour corner pins of an IC package, and gradually reduce to zero towardsthe middle of the package on each side. Accelerated reliability stresstests were performed to answer the reliability concerns, and if therewas indeed a reliability issue, recommend design solutions to theproblem and finally predict fatigue life