Identifying the Reliability Affecting Parameters of SBB Flip Chip Interconnections for Automotive Applications

Higher reliability and miniaturization for automotive sensor applications are more and more demanded. These sensors are exposed to harsh environments like extreme temperatures, fast temperature change and humidity. Flip chip interconnections using the stud bump bonding (SBB) technology provide a solution to fulfil these demands and requirements. For SBB interconnections, the failure modes during reliability testing are shifted from bump fatigue to crack initiation and propagation in the fillet, the die as well as cracks within the underfill. The present work focuses on chip side fillet cracking. The crack initiation and propagation and therefore the reliability of a flip chip interconnection depends strongly on the geometry of the components, the used assembly technology and the materials. Therefore, different chip sizes were used. Moreover, the SBB technology using underfill as well as non conductive adhesive (NCA) were utilized. In order to identify the influence of board technology, different materials properties for the board were studied. In the FE analysis, a fracture mechanics approach was used to quantify the impact of these parameters. The locations of crack initiation in the underfill fillet were determined by conventional stress analysis. A bulk crack in the upper part of the fillet was modeled and the impact of the described parameters on the stress intensity factor was obtained. Once crack propagation occurred, the bulk cracks turns into a delamination of the vertical chip edge and the underfill. Therefore, interfacial fracture mechanics approach was utilized. The energy release rate and the bimaterial phase angle were used to characterize interfacial cracking. The virtual crack closure technique (VCCT) was used to obtain stress intensity factors for the bulk material as well as the energy release rate and phase angle for the delamination