SMT Stencil Cleaning – A Decision that Could Affect Production

SMT stencil cleaning has traditionally been thought of as a‘maintenance’ procedure with little or no impact on production. Today, CFC and VOC cleaning processes are being replaced because of environmental concerns, and fine‐pitch and ultra fine‐pitch assemblies are commonplace. These changes in cleaning processes and product specifications have shed new light on the importance of properly cleaning SMT screens and stencils in order to prevent damage to the stencil and potential production‐related problems.This paper takes an unbiased look at the different stencil cleaning processes available through the eyes of an SMT stencil manufacturer. The paper outlines the advantages and disadvantages of using ‘jet spray’ washersvs ‘ultrasonic’ washers, aqueous and semi‐aqueous vssolvent cleaning agents, and the effects of hot wash solutions and hot drying air vsambient wash solutions and drying techniques.Specific criteria evaluated include: cleaning effectiveness of the process;potential adverse effects of the process on the integrity of the stencil; production down‐time and other potential production‐related problems; potential health hazards to users; environmental impact of the process, and waste stream management.Magnified photography is used to demonstrate the relative effectiveness of various cleaning technologies. Third party references of other industry experts, along with the author's own experiences, are cited to support the information provided.