Hi, 

I have a question regarding what we can expect with "old" soldermask
technology. This is our quandry.  We would like to pour solid copper close
to pads and traces on our PCB designs.  However we have started doing this
and we are anything but happy with the results.  This leads me to the
following list of questions.  First a little background.  The pcb's are all
single sided FR-4 1 ounce starting copper.  The soldermasking technology
used in Lonco or Enthone and is screened on.  With that said....

1.  What is the minimum acceptable comfortable tolerance for registration of 
    screenable masks?  Is it still +/- 0.010.  I don't want to know a tolerance 
    that will cause a premium, just what board houses are comfortable with.

2.  What is the minimum accpetable comfortable tolerance for swells on pads?
    Is it still 0.010 per side for a total of 0.020.  Again, as above, what
    are board houses comfortable with?

3.  If I was to use a zero swell on the pads and allow "some" soldermask on pads
    why or why not is this such a bad practice if the solder joint is good?
    I may end up doing this to our designs to help with short problems we are
    experiencing where the lead is longer than the pad, the mask is 
    misregistered but still withing tolerance and causes the lead to short to
    a nearby track.

4.  Does LPI cause a board you pay $1.50 for to go to $15.00 or is this just
    a board house trying to scare us because they can't or won't do LPI?

You must understand that the designs are shrinking by a factor of 2 every
year, the component count is not going down (usually around 250 components
minimum), and I have hit the point where I can't afford to keep traces 0.020
to 0.030 away from nearby pads.  That is why I am asking these questions.
BTW, Double sided boards are out of the question, I do need to keep this job.

Thanks for any input you guys can offer!


Mark Ross
Product Design Engineer
Stanley Electronics
A subsidiary of Stanley Door Systems, a division of the Stanley Works, Doing
business as Stanley Home Automation.

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