A Wicking Defect is the flow of solder either up the lead of the component or along traces and possibly under insulation and through via holes. It robs solder from the interconnection, and is usually caused by uneven heating between the materials being joined. This is seldom observed in convection dominant reflow and was more a trait in older IR dominant reflow and vapor-phase technologies. Solder mask can be used to control the flow of solder down a trace. A proper heating profile, particularly with a controlled preheat is a remedy to differential heating.