[Elecraft] K3 ESD

[Ron D'Eau Claire]

Mark, the only really ESD-sensitive parts are those with high impedance
(resistance) gates. Bipolar transistors, resistors, capacitors and other
electrical parts are very hard to damage via ESD, although it is possible if
one gets a good charge built up on one's self then manages to make a nice
fat spark to jump to the part ;-). 

In today's highly-energy efficient electronics high impedance field-effect
"gates" are common. They need as little as a fraction of a volt at almost no
current to function. These gates are formed by a conductor terminating in an
insulator. The static charge on the conductor forms an electrostatic field
that influences current flowing in another part of the semiconductor nearby.
To be most sensitive, the insulator is usually only a few *atoms* thick and
so is limited to a maximum of only a few volts across it before it punctures
and shorts, destroying the device. 

Just squirming on a seat can instantly produce a charge of hundreds or even
thousands of volts on your body. You are unaware of it, even when touching a
ground, because the charge is too little current to feel when you touch a
ground. But there's plenty of voltage to puncture the insulation in the
sensitive gates. 

Worse, like any insulator, you can damage one without completely destroying
it. In that case the performance characteristics of the part are changed in
an unpredictable way which can badly affect the performance of the circuit
and, eventually, lead to premature failure. Such problems are extremely hard
to troubleshoot in the lab and even worse in a field environment. 

It is not just individual I.C.s or transistors that need careful handling.
When a circuit board is removed, disconnecting it from the rest of the
radio, the points were the circuit is broken at the connector may leave
sensitive gates open and just as susceptible to static damage as the
individual part. 

What you did wearing a strap was fine. It also works to touch a bare metal
ground just before handling any board or part and then touching the board or
rig it is being installed in to be sure you are all at the same potential.
The danger there is that forgetting just once can result in a damaged part. 

I have a ground right at the edge of my work table (somewhat like Vic's
excellent idea with the grounded metal rule on the edge of his table) that I
have learned to touch before touching anything inside the rig or any loose
boards or components. It's a good habit to learn. I'm so practiced that I
notice that even when I'm wearing my wrist strap I automatically touch that
ground every time I reach for something. Redundancy is good, Hi! 

I keep the ESD safe bags that boards and parts are supplied in and put any
components or boards that I have out of the circuit in them until I'm ready
to reinstall them in the rig. I also have plenty of plastic containers for
obviously non-sensitive parts, especially hardware. When disassembling a rig
like the K3, I use a separate container for each sub-assembly's hardware.
That avoids a lot of checking and measuring to ensure I have the right
screws, standoffs, etc., when reassembling the radio. 

I would not recommend anti-static spray on plastic containers. It wears off.
How fast? I don't know. If I really felt it was important to have open
containers for sensitive parts, I'd use a metal muffin tin or something
similar and connect it to the common ground used by my wrist strap and
static-dissipating mat. 

73, 

Ron AC7AC




-----Original Message-----

I used a static strap and mat when building my K1 & K2.  I left the
sensitive
componants, the ones in esd foam in the bag until needed.  I did, however,
sort the other parts into plastic bins with compartments such as are used
for screw assortments.  Is this not recomended?  If not, what should be
used?  Would this be okay if the bins were sprayed with my wife's anti-cling
stuff?
Mark, VE7YMM
--