Failure investigation on copper-plated blind vias in PCB

Failures like open circuit are always encountered in PCBs (printed circuit boards) due to defects in the blind vias. In this paper, systematic analysis such as macro and micro observation was carried out on cracking blind vias in PCB used for mobile phones. The predominant cracking mechanism of sulfur segregation in form of CuxS, which was generated by the excessive use of brightener additive, was proposed for the first time. Meanwhile, grain coarsening in copper deposition led by inappropriate current density was the other main cause for ductility decreasing in the plating layer. Complementarily, microcrack propagation was explained based on the finite element method (FEM) results of stress distribution after thermal cycling. Finally, suggestions and countermeasures were addressed, which were of importance for reference to the structural integrity and electrical reliability of blind vias in PCB during process and service.