Hi Russ,

     You can't get much faster than printing epoxy dots that's for sure, but
there are some things to be careful of. You may have already thought about
this, but I'll ask anyway, do you really need to dispense epoxy? If there's
minimal through hole, and/or the through hole that is on the board is layed-
out with enough clear area around the leads on the bottomside, you might want
to think about making a wavesolder fixture so you mask the surface mount and
only expose the through hole to the wave. Then you can double side reflow the
SMT...that's always a lot easier than dealing with epoxy in my
book...eliminates one whole process step and you don't have all the headaches
you have with epoxy.

     That being said, make sure you get the right epoxy formula if you're
going to print. Most vendors will have a dispensable epoxy and a printable
epoxy. The difference is that the printable epoxy doesn't absorb moisture from
the air the way a dispensable one does. The moisture will turn to steam during
cure, and create a nice big fat void in the cured epoxy which will trap flux
during wave that can't be cleaned out...it'll kill the board in nothing flat!

     I hope all the bottomside parts are passive components, I've not had a
whole lotta luck with getting dot's tall enough to do anything else without
making a mess...it can be done mind you, but not as easily or as good as
passives.

     The type of printer I like to use is one that has a function from the ol'
screen printing days, you know, flood and print? That's where one print stroke
floods the pattern with epoxy, and then the next stroke is when the squeegee
actually does the print. Epoxy doesn't behave very much like solder paste when
you print it, and I found that if you flood the pattern first it gives the
epoxy a chance to settle into the apertures and contact the PCB surface to
make a better dot that way.

     'Bout the only other thing I can say is that it is faster than
dispensing, but you'll sure waste a lot of epoxy...

                                           -Steve Gregory-

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