8 September 2017
In this column, Kristen answers questions about all aspects of electronics, including computer
hardware, software, circuits, electronic theory, troubleshooting, and anything else of interest to
the hobbyist. Feel free to participate with your questions, comments, or suggestions. Send all
questions and comments to: Q&A@nutsvolts.com.
; WITH KRISTEN A. McINTYRE
Printed Circuit Board Etchants — Some
QI have been thinking about getting into photo etching my own PCBs, but I’m concerned about the chemicals involved — especially ferric chloride which seems to be the common
etchant. Once I have etched the board, how do I safely
dispose of the used etchant? I don’t want to pour it down a
drain or put a bottle of it in the trash for the landfill.
Polk City, FL
AFerric chloride (FeCl3) is indeed an unpleasant chemical that has been used to etch printed circuit boards. It also has a rather unpleasant smell! I used FeCl3 for years to etch copper, but
there are a few alternatives now that are perhaps a bit safer
for the environment. However, getting rid of the copper is
a persistent problem.
A quick aside is that FeCl3 operates by exchanging
the iron (Fe) bound to the chlorine for copper. FeCl3 and
copper undergo a two-step redox reaction, creating copper
chloride (CuCl2) and FeCl2. The iron that is exchanged
remains as FeCl2.
The disposal problem isn’t with the ferric chloride itself,
which is mostly benign. The remaining copper chloride is
more of an issue. Those two are not easily separated — at
least not at home — so you have to treat the entire solution
as hazardous waste, taking it to a hazardous waste facility.
Most municipalities have such a waste facility available.
As for alternatives, many people have had some
success with acids combined with hydrogen peroxide.
In some cases, vinegar has been used, though it’s slow
as vinegar is a rather weak acid. I found an interesting
process in an Instructable tutorial that uses fairly strong
hydrochloric acid ( 10 molar) to start the process. Handling
such an acid requires great care because it will dissolve
many common materials. The hydrochloric acid is mixed
with hydrogen peroxide.
The interesting thing here is that dissolving copper
in this solution produces cupric chloride,
which also dissolves copper. When the
solution becomes saturated with copper,
it can be regenerated, making it reusable
with a little treatment. To regenerate the
solution, more acid is added along with
oxygen by swirling or bubbling air through
I suppose that eventually the solution will become
too saturated to regenerate, but it will probably take some
time. At that point, the remaining solution will have to be
taken to a hazardous waste disposal site.
A final word of caution here. All of these chemicals
can be hazardous to humans, pets, household items,
and the environment in various ways — particularly the
concentrated hydrochloric acid. Treat them with respect
Remember also that chemical reactions can release
heat and energy. Make sure that the mix of ingredients is
correct and that nothing is contaminated. Contaminants
can cause an unexpected reaction to take place.
Check out the Instructable for the regenerable etchant
Communicating on a Light Beam
QI’d like to build a light wave communication link. Long distance is easy enough at low speeds, but reaching a useful data rate requires quiet, sensitive, and fast detectors, as well as fast bright
emitters. Are there devices or techniques within the range
of a hobbyist that make sense?
AI’ve experimented with this a bit myself. With modern semiconductor lasers, you have a nice collimated and monochromatic light source that can be quickly modulated. Using a near-infrared laser, most of the visible spectrum can be ignored,
and filters specific to the wavelength of the laser can be
employed. You don’t mention what kind of data rates
you’re looking for, but a few infrared lasers that I looked
at appear to have switching times on the order of 20 ns.
Some devices are quite powerful, so as long as the spot
doesn’t diverge too much, there should be enough energy
density to be able to detect the signal. Almost anything you
can find out there will work.
• Printed Circuit Board Etchants
• Communicating on a Light Beam
Q & A