Surface Mount Reflow Profile Impacts on Reliability

This paper describes the potential impacts of surface mount (SMT) reflow processes on the expected reliability of a Circuit Card Assembly (CCA) and a way to help control those concerns. The impacts can be present as either immediately detectable or latent defects on the CCA. Some defects are easily detected visually while others may take stress screening to fully manifest. Controlling the reflow process will significantly reduce the probability of defects and some can be eliminated completely. A CCA may have only one component to thousands of components. As the component count rises, so does the risk of defects. Other risk factors include the pitch of the connection points, density of the components, Printed Circuit Board (PCB) material and design, and component termination location to name a few. The control method proposed in this paper attempts to find the optimal reflow oven recipe (the temperatures of the oven zones combined with the conveyer speed). This requires “tuning” to achieve a reflow profile (characterization of a fully populated CCA through the oven recipe) that remains within the acceptable window of temperatures and durations for the solder paste and all components. The proposal focuses heavily on Bottom Terminated Components (BTC), especially Ball Grid Array (BGA) components, but does not overlook the solder paste and other component requirements.