Hello Rick,

Personally, I would window the groups as suggested. I always do this with
such fine pitch devices with no problems.
In the past, I have left the small sliver of mask between the pads, and
under the microscope you can see where some have broken and detached,
causing a problem with them fouling the solder pads.
If your board shop can register the solder mask to a much tighter
clearance, and guarantee that the mask will not break away between the
pads, that may be an option, but in my opinion, probably not worth the hassle.

regards,

Phil.

At 16:31 31/08/00 -0700, you wrote:
>Hi,
>
>We have a customer who has a board with 20 mil pitch QFP's on it.  The
>actual pad size is 11.8 mils wide and there is a 2 mil gap in the soldermask
>around the pads leaving 4.2 mils of solder mask between the pads.  The board
>house that is building these says they can't maintain the soldermask between
>the pads and is asking for a window around all leads in the group or a
>tightening of the soldermask openings around the pads.  Before I go to our
>customer with this, I'd like to get some feedback on whether or not this is
>unreasonable?  Are these dimensions acheivable or should I ask our customer
>for a deviation?
>
>Thanks in advance,
>
>
>Rick Thompson
>Ventura Electronics Assembly
>2665A Park Center Dr.
>Simi Valley, CA 93065
>
>+1 (805) 584-9858 voice
>+1 (805) 584-1529 fax
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Phil Dutton C.I.D.
Senior CAD Technician
IPC Certified Interconnect Designer

Tenix Defence Systems Pty Ltd
Systems Division - Adelaide
Second Avenue, Technology Park,
Mawson Lakes.  SOUTH AUSTRALIA  5095

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