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Membrane Switch: Screen Printing 101

(March 2010) posted on Mon Mar 29, 2010

The membrane-switch market has experienced dramatic growth and soared to an unprecedented level.

By Mike Young

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When selecting mesh, keep in mind that certain types you don’t have in stock may be required for the electronics side of the work. The most critical screen is the one used for printing conductive paste. Generally speaking, thinner thread diameters work better because the percentage of open area is larger, thereby making it easier for the metallic particles to transfer through the mesh rather than clogging up the openings and risking rejects. Either yellow- or orange-dyed mesh works best if you work with direct films. Being photographically safe, they prevent undercutting during exposure and ensure a crisper looking edge that will eventually help to more effectively meet resistivity requirements.

Mesh suppliers make charts available that list recommended mesh tensions to use according to the type of work on press. They state either a range to use, such as 24-36 N/cm or give three levels to choose from, such as Level I at 24 N/cm, Level II at 29 N/cm, and Level III at 36 N/cm. While it is not the intention of this article to suggest a particular level of tension or go further into detail about the subject, the aim is to try to attain Level II at the very least in tensioning requirements. What is more important than the actual tension number is consistency; so, for example, if 29 N/cm were the highest obtainable tension you could repeatedly reach without ripping screens, then 29 would be the magic number to adopt as the new in-house tension level for conductive prints.

Thickness of the emulsion coating, emulsion over mesh (EOM) should be kept low, perhaps not more than 10 μm. One of the biggest misconceptions regarding emulsion thickness is that a thicker coating will do a better job of resisting premature breakdown. Wrong! Screen makers tend to apply too much emulsion instead of what’s really good for the integrity of the final printed product.


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