Using a well estrablished water soluble solder paste, but having problems with tack time. Data sheet recommend a couple of hours but we are seeing problems after about 15 minutes with 0402/0603 componenets bouncing off. The printer environment is controlled and monitored and the ambient temperature and humidity are also controlled . The PCB is an entek finished product with adequate support pins during placement. 15 minute process window is just not acceptable, Any ideas ?
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.