HIGH COMPLEXITY LEAD-FREE WAVE AND REWORK: THE EFFECTS OF MATERIAL, PROCESS AND BOARD DESIGN ON BARREL FILL

The current “lead in solder” exemption for server and network infrastructure products in the European Union’s RoHS legislation is currently scheduled to expire in 2014. Numerous studies have identified the interactions between wave solder process parameters and the various materials and chemistries currently in use. However, it is critical to confirm the capability of manufacturing large, high complex products in a lead-free environment, and to characterize the capability of existing equipment and material technologies. It is important to understand the factors which maximize hole-fill and more importantly identify gaps which may currently exist in order to allow time to address these challenges prior to the legislative deadline. This paper focuses on the outcome of a development program which was designed to address the ability to maximize pin-through-hole solder joint quality and reliability performance for use in high complexity server/storage class hardware assemblies. Factors including alloy type, flux selection, surface finishes, atmosphere and wave nozzle configurations are studied. This program utilized both an internally designed test vehicle (TV), in addition to a product vehicle (PV). Actual product design points and connector technologies were integrated into the test vehicle design, in order to represent real-life design features throughout the experiment. In addition, various design features such as, pin-to-hole ratio, ground layer connections and thermal relief designs were incorporated into the test vehicle design, to understand the impact of board design on final barrel fill results and provide a data set to support any design for manufacturing (DFM) change recommendations.