One shop I work with asks for soldermasks to be at least 5 mills wide. If you have two adjacent pads with solder mask between the pads that soldermask should be at least 5 mills wide. So I suspect for PCBexpress that they need the soldermask to be at least 8mills wide. The issues has to do with alignment tolerences. Soldermask put on with a stencil has worse tolerences the soldermask applied with a photo imagable process.
Steve Meier Dave N6NZ wrote: > Here is the rule in question from PCBexpress web site: > > Solder mask swell is at least .008 larger than copper surfaces to keep > mask off pads. > > Am I interpreting that correctly? That I need .008 all around the > copper pad? Or is a mask .008 wider than the pad sufficient? > > -dave > > Dave N6NZ wrote: >> Thought I just saw a thread on this topic, but I deleted the whole >> works and can't find it in the archives. >> >> I'm trying to reconcile a data sheet for a TSSOP-20, 0.65mm lead >> pitch package with PCBexpress's design rules. The problem: 26mil >> l.p. and 10mil pad width leaves 16mil btw pads. The rule: "8mil >> between mask and copper" leaves exactly 0 mils of mask between pins. >> >> So.... can I bend something here and get a reasonable board? >> Something like: go to an 8mil pad width so that I get 2mil of mask in >> between. Pad is too skinny, but I guessing should reflow well... >> those of you with more experience than me at SMT need to clue me up. >> Will 2mil of mask be too skinny to work well? Other option: live with >> no mask between pins and hope I don't bridge. >> >> Thoughts? >> >> -dave >> >> >> _______________________________________________ >> geda-user mailing list >> geda-user@moria.seul.org >> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user >> >> > > > _______________________________________________ > geda-user mailing list > geda-user@moria.seul.org > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user