Tony:
Since your pad width on the PQFP are 12 mil,I would recommend a stencil
thickness of 6 mils.  I would size the PQFP apertures at 10 mil wide.  This
will give you an aspect ratio of 1.67 (10 mil aperture / 6 mil stencil
thickness), and sufficient solder volume.

For good release of solder paste in the screen printing process, it is best
to strive for 2, but not less than 1.5.  When your aspect ratio reduces and
approaches 1.5 it is difficult to achieve repeatable/reliable release of
solder paste from the apertures.

Kelly

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------