Homebrew PCBs

On the Reprap forums we have been discussing various ways to make/use
heated beds to prevent warping of plastic parts as they are extruded.An
inexpensive way to make a very flat, controllable hot plate would be to
take a plate of aluminum about ¼" or 6 mm thick a little bigger than
the biggest board you want to tin. Attach either power resistors or
nichrome wire to the underside, along with a thermocouple or thermistor,
and use a power MOSFET to turn on and off 12volt power. You can either
use an op-amp circuit to cycle power on and off at an adjustable set
point, or a microcontroller chip to read the temp and drive the MOSFET
either on/off (bang-bang mode) or with PWM to get a very stable
temperature. This would double as an SMD mounting hot plate.



Parts list:

12"x12"x1/4" aluminum plate   mcmaster.com
<http://www.mcmaster.com/#aluminum-bars/=82rjl9>
$19

99' of 24 gauge nichrome wire mcmaster.com
<http://www.mcmaster.com/#nickel-chromium-%28nichrome%29-wire/=82st34>
$11

½" Kapton heat resistant tape   mcmaster.com
<http://www.mcmaster.com/#polyimide-%28kapton%29-tape/=82rm4p>
$5

(4) ceramic stand offs   1"x ¾" tapped for 1/4"-20
mcmaster.com <http://www.mcmaster.com/#ceramic-standoffs/=82sts6>       
$17

60V 30A isolated MOSFET   Digikey
<http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=IRLIZ4\
4GPBF-ND>
$3

ATTiny24 microcontroller   Digikey
<http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ATTINY\
24-20PU-ND>
$3

50K -60-300C thermistor   Digikey
<http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=480-31\
40-ND>
$1

Total
$59



I have not yet made such a hot plate, but it should be fairly straight
forward for people who make their own PC boards! J



Mike



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