Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Actually the idea of the Foreman grill might be promising but for another
reason: Temperature profile control.



First, add some temperature controller to the grill and a thermocouple for
readout and often that is part of the controller. And fix the legs so the
board will be horizontal.



Leave the bottom ribs, if possible, just machine the tips so they form a
solid support and not twisting or rocking the board but I like the airspace
below the board. The sharper the tips and the less contact, the better. I
would machine off the top ribs to make space for the components.



Placing an SMT board directly on a flat hotplate will likely create a severe
thermal shock to the board and the components. That is why a real system
has controlled preheat and cool of sections.



So keep the grill closed, let it come up to operating temperature, open it
wide and place the PCB on the ribs and wait XX seconds (that is our first
part of the pre-heat) and then close the grill. The entrapped air is
approximately at room temperature but it will very quickly heat up to the
grill temperature. That air plus the infrared radiation will gradually
bring up the board temperature to the soldering point and it will be
repeatable and gradual without the direct hotplate contact. After xx
seconds, open the grill but leave the board to cool off a little on the
grill with some air circulation. After the solder has solidified and a
little further cooling, maybe a fan added on the side, the board can be
removed.



This process can be well-controlled since the temperature can be controlled
and the time per step can be timed with a watch.

Happy grilling,

Bertho

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From: Brian Sent: Thursday, April 03, 2008 13:44
I am new to this group, and never thought about making my own PCB's.
I have usually ordered them, but I see the benefit and am curious
about this.

Now on this thread...It would seem to me that you could modify a
George Foreman grill to use flat plates instead of the ribbed ones
and limit the heat and whammo a simple small double sided hotplate.

Am I completely wrong on this? If not, I might look into it as I
have a couple laying around. And even so, they are only like 20
bucks for the small one.

Brian





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