Avionics News March 2015 - 34

AVIONICS CORROSION CONTROL
Continued from page 33

"The newer avionics are micro-millivolt based, and it takes
very low amps to run them," Pearson stated. "They do wonderful things with low amperage, but they don't like any resistance
caused by even a slight bit of corrosion on their contacts.
"The older analog avionics would actually withstand a fair
amount of electrical resistance and still function pretty well. Put
even a tiny bit of corrosion resistance in the pin connectors of a
digital unit, and you can have all kinds of erroneous readings, if
it works at all."
I talked to one avionics shop manager who shared a story
about a problem his team experienced with a customer who had
a pair of new Garmin GNS 430s put in his float-equipped Cessna
182.
"We had all kinds of issues getting the nav/comm to work
right in that airplane," he said. "After the third or fourth try, we
removed the antennas and found the connectors were all corroded. We cleaned them and sprayed them with a CPC (corrosion
preventative compound), and they worked great."

CPCs: Better flying through chemistry

"The thing that is really too bad is that virtually all of these
corrosion-related problems can be prevented," Knight said.
"There are some really good products that can protect the aircraft and avionics from corrosion damage; they just aren't being
used."
Corrosion preventative compounds are a family of chemicals
that form a barrier to keep the electrolytes (moisture) from being able to interact with the exposed metals. They're relatively
inexpensive and easy to use.
So why aren't avionics technicians using CPCs? Well, the
simplest reason is that many technicians who have tried using
CPCs probably did so many years ago. Those products were
waxy, heavy and hard to deal with, and they were often much
more trouble than they were worth.
"Waxy, heavy CPCs are not intended for avionics," Pearson
said. "Those heavier materials tend to actually accumulate dirt
and debris over time and attract more moisture to the area. That's
not good."
"We introduced our SuperCORR A CPC/lubricant nine years
ago, and then we've continually altered and improved the product," Knight said. "So the product we make today is much better than it was back then. Technicians need to keep this in mind
when looking at using CPCs today. Read the labels and see
what's in them and how they work.
"There are CPCs for every part of the aircraft, so avionics
technicians have better tools today than ever. For any avionics
or electronics, you want to use an ultra-thin film coating material. Use one that has been tested for that application, and then
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avionics news

march

2015

apply it in the thinnest possible coating on the board, connector
or switch. More is not better."
Pearson's earlier point about a CPC being tested for that application is critical. If you are looking to add CPCs to your toolbox, take time to do research and ensure the product you choose
will do the job you want. Many companies have websites full
of useful information. If you're still not clear, pick up the phone
and call.
With regards to the best application method, Pearson suggested avionics technicians forego an aerosol spray can and instead
opt for the fine misting with an artist's airbrush.
"You just dial back the flow to where you can hardly see it and
mist it onto the component or connector," he explained. "After
seeing all kinds of ways, I think that is the absolutely prefect way
to apply these products to avionics.
"When spraying boards, make sure to apply the CPC to the
back side where the points come through and are soldered. Leftover flux from the process will eventually attract moisture and
form an acid that will start the corrosion process in these areas."
If you're looking to treat larger areas, perhaps behind a panel
or the insides of a nose- or aft-located avionics bay, the tool of
choice is a "fogging" wand. You attach it to a container of CPC
with an atomizing pump, and use the wand to fog the material
into the critical areas. Remember though, a little goes a long way.

Where's Waldo?

Now that you've seen the corrosion - even a tiny bit can
often lead to major headaches - you're probably wondering
what to look for when inspecting units.
Corrosion is often difficult to spot on avionics. Like we established before, it doesn't take much to alter a connection's
resistance path. It can often be found under a tiny break in a
connector or a pin's plating.
"Airplanes are not stable platforms, so their components
and connections do a lot of bouncing around and vibrating,"
Knight said. "This leads to metal-to-metal wear, which rubs
away any protective coatings or platings. This allows any ambient moisture to get in there and start the corrosion process."
And while we're on the subject of plating - gold plating, in
particular - don't be fooled into thinking that if there's gold
on it, it won't corrode.
"The corrosion levels on gold-plated pins and connectors
will certainly be reduced, but they're not immune," Pearson
said. "Gold or any plating process is not perfect. There are
going to be micro cracks or imperfections in there from manufacturing or where the gold has worn away from vibration.
Either way, any breaks in the plate coatings open the door for
moisture to intrude. Sooner or later, the less noble metal is
going to corrode."
Continued on page 36

Avionics News March 2015

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