Re: gEDA-user: bending design rules for TSSOP20 -- need advice

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxx
>> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
>>
>>
>
>
> _______________________________________________
> geda-user mailing list
> geda-user@xxxxxxxxxxxxxx
> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
>



_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user