Mechanical bend fatigue reliability of lead-free PBGA assemblies

In recent years, proposed legislative action and the product differentiation opportunities presented by environmentally friendly products have combined to significantly increase the development of lead-free solder materials. A few lead-reduced products are already in production and several lead-free products will be released in the next two years. Among the various lead-free solders, the SnAgCu family of solders has emerged as one of the leading candidates for high volume implementation. This paper examines the mechanical fatigue reliability of SnAgCu PBGAs on FR4 boards. While a fairly extensive reliability database is available for BGAs built with tin-lead solders, similar data is not available for BGAs assembled with lead-free solder. Mechanical bend fatigue reliability is a critical indicator for phone and BGA survival during repeated keypress, and to some extent, during drop. The lead-free reliability data is compared to that from control samples built with tin-lead solders, both in low-cycle and high-cycle fatigue. Failure analysis was conducted to identify failure modes.