WATCH THAT FLUX!
Dave Heller, K3TX, Copyright 1997: X-Mitter Vol. 34 No. 2.
(Refer to Building High Performance Small Loop Antennas post by Bill
Jones, KD7S; QRP-L 12/17/96, kd7s@psnw.com.)
The criticism that follows follows does not apply to the theory or
general construction details by KD7S; my reading shows no significant
flaw in the text. This caveat applies to a single suggestion in the
construction of a loop: the method of soldering copper tubing or rigid
piping.
KD7S correctly emphasizes the necessity of excellent soldering of
adjacent copper components. It is essential that mating surfaces be very
well cleaned - even polished - to permit the soldering process to have
the maximum possible fully wetted (tinned) interface. Otherwise the
mandatory minimization of circuit resistance cannot be achieved. If the
copper is bright and clean the solder will flow evenly and form a low
loss joint. Correct. A high quality paste flux in conjunction with a
hand-held propane torch will make the job easy. Correct - but please
note the underlined paste flux. This will often mean the use of
commercial plumbing fluxes such as No-Korode or Lako (or worse if
such exists.) The aforementioned brands are commonly known as acid
fluxes. Their well-known recipe is a mix of zinc chloride plus ammonium
chloride dissolved in water and emulsified in axle grease. The mix does
a commendable job of solder-fluxing on reasonably clean copper, tin plate
and some steels, and does very little harm on normal plumbing work.
Electrical work is a different story. The gook is hydroscopic, meaning
it attracts water. It is extremely difficult to remove with normal
cleaning methods. And when it is wetted with water (remember, it s
hydroscopic) one of the byproducts is HCL -hydrochloric acid. The
resultant is, in electrical work, corrosive as hell, and conductive just
where it s not wanted. This the absolute rule: Never, but never may it
be used in or near electrical work, much less delicate electronics.
Furthermore, remembering it s extremely difficult to remove, tools used
around these pastes fluxes must never again be used around electronics
unless they are properly cleaned, meaning much more than soap and water.
How, then, should KD7S article be modified to make it acceptable? I
recommend the mating copper tubing and fittings be polished as suggested
and then tinned with out usual rosin-cored solder, or with a separate
suitable electronic flux such as is used for circuit boards. Once tinned
the usual electronic (solid or rosin-cored) solder will work fine. Not
as easy as using a potent paste, but the job will last, and the chance of
contaminating other electronics greatly reduced. In summary,
non-electronic paste fluxes must NEVER be used near electrical or
electronic components or assemblies.
Note: This does not apply to the solder pastes used for circuit board
assembly, especially with surface mount techniques. They re of course,
entirely safe and acceptable in our radios. X-M
Dave Heller, K3TX
k3tx@juno.com
PENN WIRELESS ASSOCIATION
Public Service Through Communication
http://www.pennwireless.org
[
QRP-L Archive |
]
[
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
2000
]