Stuffing boards with pulled QFP chips

[Jon Elson]

On 04/01/2017 11:27 PM, Chuck Guzis via cctalk wrote:
> What do you do about boards with SMT components on *both* 
> sides? I can't see how it would work with a toaster oven
Oh, part 2.  Most of my boards have parts on both sides.  If 
you have a glue dispenser, you can apply glue to your first 
side part locations after solder paste but before part 
placement, then print solder for 2nd side, place parts and 
then reflow both sides at once.  Well, I don't have a glue 
dispenser, although it is an option on my P&P machine.

So, I print the solder paste on the back side (mostly 
decoupling caps) place these parts and reflow, then print 
solder paste for the front, place the ICs, etc. and reflow 
again.  I do have one board with a 5-lead TO-220 switching 
regulator chip on the back side.  I didn't know if it would 
fall off or not, but tried it, and was amazed that I've 
NEVER had one fall off when the top side was reflowed.  The 
solder almost certainly goes liquid again, but the surface 
tension holds even this large part in place!  The small 
passives on the back will be held by surface tension for sure!

Jon