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
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