Sal, Interesting problem, I have found that W.S. pastes tend to have a shorter tack time in real life than what is advertised. Usually the manufacturers specify tack time as after placement let the board sit and then turn it upside down and see if parts fall off or something like that. I have a couple of ideas that you may want to look at.
1. Do you have any fans blowing in the area? This causes paste to dry out very quickly.
2. Is it possible that placement is slightly off?
3. Placement pressure to high?
4. Have you noticed it related to a specific lot?
5. Expired paste?
All I can think of
Russ
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