Don,
I have experienced the same thing as Russ. The fixed head systems do give the best uniformity (due to no overlap). Both Nordson and Sono-Tek offer fixed head machines that work excellent. I think the Sono-Tek system that Russ is refereeing to must be the 9500 model from Sono-Tek (this has 2 airstreams and is a bit complex for setup). My newer 2000F system has a single air stream and is simple to use. The Nordson I once used and the Sono-Tek machine I have now, both give excellent top side fillets (even with OSP coated PCB�s) and are very reliable as they don�t have any moving parts.
The disadvantage to both of the fixed head machines is that they do see lighter coverage on the outside edges if you spray over 13� width. My experience has been anything under 13� has equal uniformity on the center and the outside edges. As Russ also mentions the other disadvantage to the Nordson is the need to change spray nozzles when changing PCB width � the Sono-Tek system does not require any changes.
Good luck with your search.
Manish
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