how far off?  center ground plane too much paste (parts swimming flow  
up)? or completely jump off the location?  (or it is at bottom  side  
for second reflow and fall off?)
jk
On Aug 2, 2019, at 2:31 PM, Guy Ramsey wrote:

> We are experiencing a bout of QFNs that jump off the pads, even off  
> the
> assembly during reflow.
> The parts are handled in accordance with J-STD-033.
> The boards are complex multilayer sequential lamination with  
> thousands of
> vias, blind, buried, and through hole. All exposed vias are filled and
> plated,with ENIG finish.
> We bake the boards 10 hrs at 105C.
> Solder paste is FCT WS159 . . . I know, I know.  The Peregrine  
> parts don't
> solder well unless the flux is crazy active.
> Any ideas on why about 2-5 percent of the parts jump off the pads or
> assembly completely?
> Can this be just a solderability problem?