Evaluation of reliability of ?BGA solder joints through twisting and bending 1
The paper describes a study on the solder joint mechanical reliability evaluation of two grid array packages: a micro land grid array (?LGA) and a micro ball grid array (?BGA) for mobile phones. The ?GA packages considered in this paper are at early development stages and significant changes are expected in the future. The study was carried out to evaluate whether solder joints can stand mechanical stresses induced on PCBs during normal use. Stresses induced in normal use can include: thermal changes and stresses during indoor and outdoor use, in keypad pressing, carrying phones in (tight) jeans pockets, in accidentally dropping phones, etc. The above was studied by subjecting PCBs to two types of mechanical stresses. These were cyclic twisting and bending PCBs with ?BGAs to failure, while continuously monitoring the electrical continuity. Cyclic twisting and bending tests were carried at two levels. Time to failure test data was analyzed using the Weibull model. Results indicate that it is most unlikely to anticipate ?BGA solder joint failures in normal use. Solder joint failures were analysed by micro sectioning and X-raying. Failure analysis revealed as expected that solder joint failure occurs primarily due to fatigue. It is recommended to continue tests with more representative, updated packages and to carry out comparative tests with current technology PCBs.
?bga solder joints mechanical reliability weibull modeling bending and twisting of pcbs