SMD Adhesive Cleaning

摘要

There are several established processes for cleaning solder paste from stencils and misprinted PCBs. However, as screening SMD adhesives is gaining popularity, an effective method for cleaning the adhesives from stencils and misprinted PCBs continues to be an enigma for SMT assemblers. Can the same equipment and chemistry used for cleaning solder paste be used for removing adhesives? If so, are there any modifications required? Precautions? Or, is a completely new process warranted? What equipment and chemistry is necessary? In either case, what resulting waste streams can be expected. Manual cleaning is inconsistent, time consuming, hazardous and will likely lead to stencil damage. Therefore, automated methodologies will be critiqued based on the associated chemistries, equipment and related waste streams. A limiting factor for most assemblers in establishing a good cleaning process is usually the capital investment. As a result, when searching for a new cleaning process, many users make the mistake of evaluating equipment first. This paper emphasizes the importance of the cleaning chemistry over that of the cleaning machine. Upon establishing the proper cleaning chemistry, the capital equipment becomes secondary as to the best way to apply the chemistry. Equipment using spray-in-air, spray-under-immersion and ultrasonic technology will be discussed.