Stuffing boards with pulled QFP chips

[Paul Koning]

> On Apr 2, 2017, at 12:51 AM, Jon Elson via cctalk <cctalk at classiccmp.org> wrote:
> 
> 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.
> OK, this is going to be long.
> 
> I do small-scale production of mostly motion control boards, but also some nuclear instrumentation.  Mostly 0603 to 0805 passives and SOIC up to 0.5mm pitch QFP chips.  I use a lot of FPGAs in 144 pin packages.
> ...
> 
> One of the tricks I found out very fast was the thermocouple doesn't absorb IR the way a board does, the first board I did came out warped like a potato chip and nearly black.  It occurred the me to poke the thermocouple junction into a through-hole in the board, and then it all worked.  I still have some slight problems with some areas of the oven running a bit cooler or hotter, so I have to tweak the peak temp setting sometimes to get all the boards soldered.

I have a nice article about toaster oven SMD work.  It's in German, via the PCB Pool website if I remember right.  It mentions that problem.  The solution picked in that article was to use a spare board (same or similar layout) as the thermocouple holder.  But attaching to the actual board sounds good. 

	paul