In electronic assembly production, the first process, SMD printing, plays a decisive role: it is the process in which, in the worst case, the defects only become apparent after soldering. For this reason, SPIs and other inspection solutions have been developed to detect defects early. The biggest source of errors is the process itself. By using solder pastes and SMT adhesives, stencils, or their laser-cut holes, can become clogged if material accumulates and dries out in these holes. Therefore a manual or mechanical stencil underside cleaning is necessary. The cleaning process is as much in focus as the cleaning media used. These should not attack the surface of the stencils, protect existing nano-coatings and possibly also be used when cleaning misprinted circuit boards. Especially when cleaning fine pitch stencils, all material must be reliably removed from the holes.
When cleaning stencils manually, a cloth should be used which, due to its material, is not subject to lint formation and does not leave any other residues on the stencil. The cleaner used must clean the surface reliably and thoroughly, as otherwise users often try to achieve a satisfactory cleaning performance with more force. This can lead to stencils being bent or otherwise damaged. In addition, care must be taken to ensure that manual cleaning is performed using media that are compatible with the employees in all respects.
The cleaning of the stencil underside is usually done inside the SMT printer, between printing processes or before a stencil change. The cleaning results must be consistently good. Therefore, the cleaning medium used plays a very important role. It should clean reliably and be low in consumption. Furthermore, a cleaning medium must not change the condition of the solder paste, for example the viscosity, because the medium can come into contact with the solder paste during the cleaning process. Therefore, special underside cleaners have been developed for this purpose.
This water- or solvent-based, pH-neutral cleaning medium efficiently removes residues of lead-containing, lead-free or so-called no-clean solder pastes and SMT adhesives. After the printing process, the medium optimally wets the cleaning roller or cleaning fleece as well as the stencil side, so that consistently high and qualitatively reproducible cleaning results are achieved. The mild odour composition combines good cleaning properties with low odour and optimum drying properties, thus significantly minimizing smearing of solder paste on the stencil underside. Depending on the printer model and manufacturer, the cleaning medium is either filled directly into the storage tank of the stencil printer undiluted at room temperature or sucked directly from the delivery container.
Do you have questions regarding this matter?
Your contact person: Markus Geßner
company: Emil Otto