Very High Lead Count SMT Backplane Connector Rework Process: Recognizing the Challenges

Abstract

The ever growing demand for improved bandwidth, signal speeds, and performance in enterprise servers continues to drive increased circuit density and complex board designs. Single ended mode signaling is one design approach to address these challenges. A tightly integrated design team must carefully control the interfaces and trade-off complexity of chip and package designs to maintain power budgets at target performances. This single ended design approach has necessitated the use of very large (5040 contacts) surface mount connectors. These connectors are assembled to thick, densely wired, high copper content printed circuit boards which press the limits of conventional assembly and rework processes and tooling. Classical automated hot gas rework techniques, even with the best controls and practices in place, may not be capable of providing consistent, reliable connector rework. Extensive tooling modifications may also prove to be inadequate. Given these complex issues, in conjunction with shortening product development cycles, it is critical to define and investigate multiple rework approaches concurrently, so the probability of finding a manufacturable solution is greatly increased. This paper will discuss 1) the thermo-mechanical challenges encountered when trying to perform rework of this high lead count connector, 2) the tooling and process modifications attempted with respect to classical hot gas rework, and 3) the implemented solution which was full connector rework using a local vapor phase process. The local vapor phase process offers many advantages as the industry prepares for the transition to lead free when the RoHS server exemption expires. These advantages will also be discussed.