Chiman!,

What is the customer's purpose of plugging vias completely with
solder mask?  I don't think it is possible.  Maybe some fab guru's
can elaborate on it.

 We tent all via holes from the bottom side to prevent solder
pluggings during wavesoldering process.  It does a wonderful
job with LPISM, even though holes are not plugged with
soldermask.   Our via size is from 0.4 - 0.6mm.  If via is bigger
than 0.7mm, it does plug the hole with solder sometimes.

Try DFPISM (dry film), it does excellent job of tenting small and
large vias with soldermask.

regards
Matthew S. Park
NII Norsat International Inc.


>>> Chi-man Chan <[log in to unmask]> September 24,
1998  2:59 am >>>
Currently we have a big problem on plugging vias with solder
resist. Our
customer requires that vias must be completely filled with solder
resist. (i.e. light cannot go through). The via size is 0.3-0.5 mm.
We
use liquid imageable solder resist. I have tried to print with 43T
then
32T open screen wet on wet on both side of the board. It does
not work.
The vias seems to be blocked with resist after screen-printing.
However,
some vias open again after track dry and developing. I have
reduced the
thinner from 5% to 2%. It does not work and causes a lot of
bubbles
among tracks. In order to completely plug these vias, we now
print these
boards with dot pattern before solder resist  printing and after hot
air
solder leveling. Some vias are very close to SMD. It is a very hard
and
time-consuming job. I think there should be an easier way to do
this
job.

Any feedback is appreciated.


Regards,

Chan Chi Man
[log in to unmask]

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