The NASA wonks are correct in their citation of construction practices.
However, as hams we like to know "why" as well as "thou shalt not": In
this case the bad thing being avoided is called "cold-working". The
solder used to solder parts is an alloy of two of more metals, which
arrange themselves in a lattice of greatest strength immediately before
solidification of the joint. Any deformation of that joint after
solidification (including that caused by thermal expansion and
contraction) is called cold-working, and embrittles the joint to some
degree, setting it up for future failure in a way which is nearly
undetectable by our feeble eyes.
This is why you shouldn't use toenail clippers, etc. to get at the last
nub of an exposed lead -- by doing so you are cold-working the joint.
Clip it instead at the top of the meniscus formed by the solder on the lead.
FWIW, SMD parts are designed to thermally expand at roughly the same
rate as PCB material in order to minimize this phenomenon, or else they
are constructed so as to relieve thermal stress.
Darwin, Keith wrote:
Above the board or above the top of the solder joint?
Why leave wire protruding?
- Keith KD1E -
--
Marshall Jose, WA3VPZ
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