Thanks Steve for the good info. The procedures are
very similar, and hopefully Alexandre from Africa will
post some of his info too?

I don't use a thermocouple, but I first put a ceramic
block in the oven at different locations and times and
measured it's temp with my non-contact thermometer.

Surface mount production is much more gentle than rework,
the boards are treated very well. With my setup the
oven just brings the solder to melt and is turned off
a few seconds later. Since I know the max rate the oven
can heat, this ensures the total board heating never
gets over the safe amount. According to my non-contact
thermometer, the max temp of the chips and board is LESS
than normal soldering with my temp controlled weller
iron.

The solder joints are very bright and nicely wetted,
microscope inspection shows they are very high qualty
soldered. I use the 2% silver solder paste that Alexandre
suggested.
-Roman



Steve Baldwin wrote:
>
> > Are you kidding? You sure better post "everything" about
> > this, otherwise someone will try to patent it out from
> > under you.
> >
> > A toaster oven usually works by direct radiation. What
> > temperature do you suppose the surface of the pcb gets up
> > to? And is this allowable, regards the specs for the chips?
> > And how does this compare to commercial smt cookers?
>
> I use a toaster oven too. I used to use a hot air gun and the results
> were pretty good but required a lot of operator skill and attention.
> Very easy to stuff it up. Then I tried experimenting with a pop-up
> toaster on its side, working on the theory that the smaller air
> volume would be better for control. The theory was OK but
> implementing it with a mass produced product wasn't all that
> practical. Because of the volume thing, I wasn't too sure how the
> toaster oven would go.
>
> I bought a fan forced toaster oven and after a bit of experimentation,
> found that putting the boards on the mica element formers from the
> previous toaster experiments was perfect as it forms a bit of a
> barrier between the top and bottom halves of the oven. I played
> around a bit with shelf height to get good even heat coverage.
>
> My procedure is also manual at this stage but it will be simple to
> automate as soon as I get time.
> I use a single thermocouple (as I know from experiments that it is
> representative) and the temp meter I use has time on the display.
> Put the boards in the oven.
> Set temp to max, top & bottom elements and fan on.
> When temp reads about 5 degrees below preheat, turn everything
> off. (the 5 degrees compenstates for the system lag so the temp
> will reach the setpoint and hold steady for around 30 sec).
> Wait the preheat period.
> Select grill and max temp. No fan.
> When temp reaches 200 degrees, turn off.
> The board temp will peak at 210-215 and drop off.
> At about 190 (solder solid again), turn the fan on with no elements
> (mixes in the slightly cooler air from below).
> I open the door a little at 160 degrees and fully at about 100
> degrees.
>
> If I plot the temp and time it's almost exactly on the line provided
> by the solder manufacturer. The whole cycle is about 5 minutes
> from board in to board out and yield so far has been no failures in
> about 75 board/panels.

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