--- In
Homebrew_PCBs@yahoogroups.com, "Jim Lewis" <jim.lewis@...> wrote:
>
> I have a problem with SMT chips jumping off the board during reflow. I preheat for 2.5 minutes 1/4" above the hot plate and then reflow 1.5 minutes directly on the hot plate at 375F with a cover. Paste is from Stencils Unlimited. Any solutions?
>
Sounds like popcorning. It could be moisture in the chips or in the solderpaste.
If the moisture is in the chips, you could try warming them at around 150F for 30 minutes to an hour to drive out any moisture. You could also have moisture in the solder paste itself. I am not sure how how you would deal with that. Maybe a longer preheat at a lower temperature may help there as well.