[Lf] Litz wire soldering

[Andre' Kesteloot]

To All from PA0SE

May I inject an item on a low-tech subject into the stream
of high-tech stuff that has been coming to us via the
reflector?

I know that soldering litz wire has been discussed
extensively lately but by chance I came across an article on
the
subject written by a professional that may interest you. It
relates to litz wire with strands covered by enamel.
Modern litz has a coating that dissolves in molten solder
and soldering  is no problem.

I found the article in the 1949 edition of ELECTRONICS
MANUAL FOR RADIO ENGINEERS  (McGraw-Hill).

I wish you and yours a happy and healthy New Year with
extreme DX!

73, Dick, PA0SE
JO22GD

                                      Soldering Litz Ends

                                       By EMERICK TOTH

The writer had occasion to design a receiver for aircraft
using coils of litzendraht wire. These coils ranged in
diameter from 12 inches, wound with litz of about 180
strands of number 38 wire, to little fellows of 1/2 inch ID
using 7/41 litz. Over 150 coils were involved, a total of
more than 300 coil ends, thousands of individual strands
that
must be properly tinned and soldered. Careful tests were
made of the following three methods:
  (1)  Cautious removal of the silk and enamel from the
coils end by abrasion against a relatively soft high-speed
rotary wirebrush.
  (2)  Heating of the coils end in an alcohol or
Bunsen-burner flame and subsequent plunging of the hot coil
end into
alcohol.
  (3)  Application of a small quantity of a paste of zinc
chloride and water to the coil end and heating with a
soldering
iron, immediately followed by tinning with rosin-core solder
while the resulting zinc chloride and enamel mixture
was still boiling. The silk insulation was burned and
stripped off by a very short exposure to a flame, and
subsequent wiping with a rag prior application of the zinc
chloride.
  Method (1) was found to damage individual strands
excessively, and did not clean all strands in sizes of litz
with
many strands, such as 70/38 and 180/38.
  Method (2) was difficult to control. Insufficient exposure
to the flame resulted in the enamel not cracking off when
the hot coil end was plunged into cold alcohol. Overheating
caused individual strands to burn off. Even when
satisfactory cleaning was obtained, the copper was left so
brittle that soldered coil end would break easily.
  Method (3) provides easy and effective tinning. The
appearance of the tinned end was neat and clean  after the
residue of zinc chloride, enamel, rosin, and solder had been
wiped off while still hot with a damp rag. The ease of
tinning even 180/38 litz suggested that inside strands were
not properly coated. Several samples were cut in
cross-section but all strands appeared to be clean of enamel
and tinned.
  Samples were placed in a salt-spray chamber and subjected
to the Navy's standard salt-spray test for two hours.
It was found that except for a light accumulation of powdery
salt the samples were in no way affected by the test
and all 300 coil ends were  processed as outlined in method
(3) above.
  Eighteen months after delivery, one equipment was examined
which had been in service in Panama for a year.  No
trace of corrosion or any other damage was found.
  Zinc chloride is very hygroscopic and should be kept in a
suitable well-stoppered glass bottle, with only as much
paste prepared at one time as is needed for a few hours use.