A mechanical fatigue assessment methodology to study solder joint reliability

This paper presents a unified mechanical fatigue assessment methodology that characterizes and predicts the fatigue life performance of electronic components. It involves establishing the relationship between a solder ball damage metric and the fatigue cycles-to-failure. With the proposal of board strain as a metric, single BGA component test boards are used to produce a fatigue characterization curve - the E-N curve. The methodology was initially established using high cycle fatigue but later extended to the lower cycle fatigue region to give a complete picture of the characteristics. The methodology has been validated by predicting fatigue failure of a system board under random vibration using the rainflow-counting algorithm and Palmgren-Miner's damage accumulation. Discussion on board design implications and features to improve fatigue performance are presented. Furthermore, a case study with the methodology used to assess the mechanical integrity risk of two mobile devices is shared. The sensitivity of the methodology towards various board and package attributes is also demonstrated.