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| Date: | Thu, 20 Mar 97 13:50:55 UT |
| Content-Type: | text/plain |
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It is worth noting that the printer has an impact on the dams you can hold.
Most printers have large reflectors which diffuses the illumination . This
translates into partially cured mask around each feature which at a minimum
shrinks your process window. We recommend point source printers with
reflectors that are approximately 10" square.
If you would like more information please contact me.
Bert Ohlig
[log in to unmask]
714 930 2500
714 930 2506 Fax
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From: [log in to unmask]
Sent: Tuesday, March 18, 1997 9:12 PM
To: [log in to unmask]
Subject: Re: Solder Mask on fine pitch SMT component
Many PWB manufacturers are today using liquid, photoimageable (LPI) solder
mask dams between 25 and 20 mil pitch SMT features and many of their
customers require it. Numerous LPI manufacturers offer products which can
achieve solder mask dams down to 3.0 mils wide.
These dams can offer advantages between fine pitch SMT pads, such as:
1. Prevention of solder shorts between pads, especially when IR or convection
f usion of the solder paste is used.
2. Support for the solder paste stencil during the actual printing of the
solder paste. This ensures that an even solder paste deposit is applied to
each pad and prevents distortion (ie prolongs the working life) of the
stencil.
One key is to make sure that the height of the solder mask dam is no higher
that the SMT pad. Ideally, the best situation is solder mask dams exactly the
same height as the SMT pad (or +/- 0.2 mils)
Larry Fisher
Dexter Electronic Materials
[log in to unmask]
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