Design evaluation and product reliability assessment using accelerated reliability fatigue life tests

Accelerated reliability stress tests were performed to evaluate a design concern on a printed circuit board assembly (PCBA) for a disk drive product. Preliminary design tests indicated that a motor driver 176 pin PQFP (plastic quad flat package) IC package mounted on the PCBA may have a reliability problem in the field. The function of the motor driver chip was to provide electrical contact to the motor bearing assembly housed in the HDA. An elastomeric connector mounted on the PCBA under the 176 pin PQFP IC package was used to provide the electrical connection between the IC and the motor bearing assembly. A minimum force was required to maintain the electrical contact through the imbedded wires used in the elastomeric connector sandwiched between the PQFP package and the HDA. This force was provided by a hold down screw used to push the PCBA on the HDA. The reliability concern was that pin 1 and pin 176 on the corner of the PQFP package and closest to the elastomeric connector will break due to the high bending stress experienced, the effect of which is aggravated due to the coupling of thermal stress during operation. Typically stresses are higher on the four corner pins of an IC package, and gradually reduce to zero towards the middle of the package on each side. Accelerated reliability stress tests were performed to answer the reliability concerns, and if there was indeed a reliability issue, recommend design solutions to the problem and finally predict fatigue life.