I am a student attempting to manufacture thin film heaters by depositing
>platinum on a ceramic base. My heaters keep burning open when I apply
>even low voltages.
Measure the current. Are they failing by over-current, because the
overall resistance is too high ? Or are they failing by localised
over-heating, which is probably caused by a small region of high
resistance. Identifying this might give you a hint as to their failure
And never test with a constant voltage source that isn't current
is your serpentine pattern comprised of sharp 90 degree turns or are
you using an "S"-type of pattern with smooth transitions. Sharp
"corners" in film heater patterns can cause a failure site.
You indicated that you depositing onto a ceramic base. I presume your
standard 96% Al2O3 substrates. If so, you will want to check the
orientation of the areal surfaces. One surface is "smoother" then the
You might also want to consider a higher grade substrate. Possibly 99%
Al2O3 which are used in Thick Film RF circuitry. These are more
expensive, but have a much smoother surface finish.
Additionally, where the trace reduces in width from several
millimeters to a fraction of a millimeter the "squares" of the
conductor trace in this region increase with a resultant increase in
"local resistance". Take your probes (use 4 point to compensate for
the low resistivity of Pt) and measure the ohms at the beginning and
end of the wide regions and at the beginning and end of the narrow
regions. I expect there are major differences.
One means of preventing overheating in this region would be to
increase the thickness of the trace in the narrow zone thus decreasing