Daniel,
There are several remedies to your problem. The first, and perhaps
easiest, would be to go to a .006" stencil. Since the finest pitch part on
your board is 20 mils., this shouldn't create any problems with the other
parts (solder bridges, etc.). A second alternative would be to go to a
"stepped" stencil, whereby the area under the 20 mil. pitch part would be
.006" or .007" thick, and the rest of the stencil would still be .005". A
third alternative would be to have the apertures opened up slightly,
although this could open up the possibility of bridging. It depends on how
the apertures are "cropped". If they are currently .009" (for the .020"
part), you might have them opened up to .010". In addition, you may be able
to partially cure your problem by manipulating the parameters on your
printer. Hope this helps. Good luck.
Regards,
Michael Sanders
Process Engineer
SMTC - Austin
Daniel Woon
<[log in to unmask] To: [log in to unmask]
ING.MY> cc:
Sent by: Subject: [TN] QFP 20 mils pitch printing
TechNet
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10/03/2000
07:13 AM
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Please
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Daniel Woon
Hi Technetters,
We are now starting the fine pitch printing (20 mils pitch). Previously,
the smallest pitch size is 25 mils. However, we encountered paste printing
problem.
We do not have problem with the paste deposition on the pads which parallel
to the squeegee flow direction. However, we found insufficient solder
paste on those pads which are perpendicular to the squeegee flow direction.
We are using a semi-auto screen printer with rubber squeegee (durometer
#90). Stencil thickness is 5 mils.
May I know the remedy action for such process problem?
Many thanks in advance
Best regards,
WW Woon
email: [log in to unmask]
Daniel Woon
Assistant Manager, PCBA Department
Comacraft Sdn Bhd (A Subsidiary of Dynavest Group-Asia)
2033, Jalan Bukit Minyak,
Kawasan Industri Ringan Asas Jaya,
14100 Bukit Mertajam,
Penang, Malaysia.
Tel : 60-4-5889933
Fax : 60-4-5889953
H/P : 60-19-4706083
Email : [log in to unmask]
Website: http://www.dynavest.com.sg
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