Dear all,
        I would like to introduce myself, I am the process Engineer working for
the Electronics assembly company in Thailand.
        I have the problem on one product which has the SMD and COB(Chip On
Board). I found the dot solder splash on the bonding lead (use for COB)
which effect to COB operation.
        The cause are
        1. the stencil wiping at screen printing is not effective. The past method
was manual wiping with the sheet of lint free, I solved by use the lint
free paper in a roll form, wipe one direction only and roll up the paper
every wiping. The solder splash from this operation
reduce 95%
        2. Too long reflow time but I can not adjust because with the PCB design I
use it require the long reflow time, if not the solder quality will be
effected. I have evaluated the preheat in the range of solder paste's
vendor recommendation but did not better.
        Currently, we attach the Kapton tape on the COB area before go to SMD
process. I can eliminate the solder splash on the bonding lead but the
problem is the high cost of Kapton tape.
        Moreover, I have evaluated the water soluble solder mask #110 of Alpha
metal to instead the Kapton tape, I applied by using the silk screen
technic, it worked it could protect the solder splash as good as the Kapton
tape but the problem is short stencil life it dry within 4 hour that I have
often cleaned stencil(15 minute/Time) then it is not suit for mass
production.
        Does anyone can help me to solve this problem.
        1. Is there the other type of water soluble solder mask which has the
longer stencil life?
        2. Is there the other method able to support my current solder mask?
        3. Is there the other mat'l to instead the Kapton tape?
        4. Is there the other way to eliminate the solder splash otherwise the
tape applying?

        The return information will be aprreciation.

With best regards,
Noppadol S.

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