On Sat, 20 Sep 2003 10:25:12 +0200, Markus Zingg <m.zingg@...> wrote:
>> I hope this link takes -- it's a pic of the toaster oven PCB in progress
>> -- as you can see one of the 2k resistors slid a little bit when I
>> removed the board "hot" from the oven.
>> http://www.diyaudio.com/forums/showthread.php?
>> s=&threadid=13023&perpage=15&highlight=toaster&pagenumber=2
>
> Thanks for the link - looks good :) Do you also have a picture of the
> oven itself? I'm asking cause the oven you use is likely not to be
> available where I live (europe) but a similar one might would do.
>
> Then, is there a time saving in doing it this way? I could imagine
> that placing the parts onto solder paste and especially moving the pcb
> into the oven might be terribly critical - no? So far I hand soldered
> all my boards but I agree that it takes quite a while so I'm of course
> interested in potential improvements.
>
> Markus
>
I once used a smd toaster in school.
It was a small unit for pcb size maybe 150 x 200 maximum (yes these are
metric mm).
The trick is not to put the pcb out by hand.
it had a tiny "carrigae" which slided it out at the side.
the procedure was the following:
put the pcb on the carriage.
slide it the middle position (already inside the oven).
keep it there until the timer was counted down and the beeper sounds.
then carry it further into the oven, beneath the glass observing window.
again wait for the beeper to sound when count down is at zero and then
slide it all the way
out to "outside" position.
so the middle stage was some sort of "preheating process".
i don't remember the times, please don't ask. it was in the seconds range
at both stations.
i also don't remember the temperature. it has a digital display for the
soldering stage.
i think it was between 300 and 400 but not sure about this.
i think the "preheat" stage was not seperately heated, it was "waste" heat
from the actual soldering stage.
the carriage was of a very thin fabric like material, black.
i think this is vital to allow heat to penetrate fast through it from the
bottom.
the fabric was clamped on the side.
maybe if you want to build one, this may help you.
i would buy a cheap oven, there aer plenty around.
they normally have quarz heating "lamps", most cases on top and one bottom.
maybe it would be better to put four such lamps in
also a heat regulation needs to be implemented, no problem electronically.
i don't remember how the "slits" through which the carriage with the pcb
went were sealed.
maybe they were open all time but maybe there was a door mechanism.
i guess making flaps is no problem, with levers pivoting them up/down when
the carriage passes through.
if you want to build one, the most important may be the following:
time in preheat stage at which temperature.
time in reflow stage at which temperatuer.
to have an idea with what to start.
i think the preheat is important, it brings pcb and parts up to a
temperature which won't destroy them.
when all is hot it is put in soldering temperature. the result is that it
needs less time at soldering temp. thus not "burning" the components on the
outside.
(like baking in the kitchen - too hot: fast but burnt outside and uncooked
inside).
st
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