>
>Evan Jones, a fellow Technetter asked me:-
>
>>Your question has raised another one I have. We have some products with
>>carbon
>>ink for button contact. We also use no-clean, but have tended to use water
>>soluble for these products to eliminate residues on the carbon ink surface.
>>Do
>>you mask the carbon ink before fluxing or does the no-clean residue pose no
>>problems for button contact?
>
>We do not see any residue on the carbon ink surface. The carbon goes into the
>wave and the
>flux burns off, there are sometimes residues around the cooler edge of the
>printed circuit panel and on
>the top side. The carbon ink is screened onto copper as we buy solder mask
>over bare copper (SMOC)
>boards, we ask for 0.001 inch thickness. I am currently trying to specify
>more of the ink's parameters
>such as ohms per square, and the surface finish.
>Does the IPC have a specification for carbon used as a Contact for rubber
>membrain switches?
>
>Alan Shaw
>

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