words of Jorge Agustín Nicolás Ruiz de Santayana y Borrás (aka
George Santayana) immediately
came to mind when I saw this Bell Telephone Laboratories advertisement in a 1955
issue of Radio & Television News magazine: "Those who cannot remember
the past are condemned to repeat it." Anyone involved in the electronics field at
the beginning of the lead-free (Pb-Free) craze in the early 2000's probably remembers
the purportedly unexpected phenomenon of
tin whiskers growing
out of lead-free solder joints and wreaking havoc with the short circuits caused
when whiskers between adjacent elements made contact. The problem appeared with
closely spaced connector pins, fine pitch integrated circuit packages, high density
surface mount circuit board layouts, etc. Military and aerospace engineers and scientists
had fits initially trying to figure out what was going on. As it turns out, the
issue was known and dealt with half a century earlier. In the rush to reduce the
presence of lead by a miniscule fraction in the electronics industry, a huge problem
was created. Keep that in mind when you see that Pb-Free
RoHS symbol now so proudly displayed by vendors.
Bell Telephone Laboratories Ad
Whiskers on tin-plated steel, enlarged 6
times. Immense yield strength of metals in whisker form was discovered by Bell scientists.
The clue of the metal whiskers
The habit of close observation at Bell Laboratories often turns "tremendous trifles"
into important scientific progress. Such a case occurred when unexplained short
circuits in wave filters seemed to be associated with a zinc-plated mounting bracket.
Close scrutiny disclosed a whiskery growth on the zinc plating. Similar whiskers
of tin were found growing on tin-plated equipment. Studies showed the whiskers to
be tiny single crystals of metal.
Suspecting that these unusual crystals might be of essentially perfect structure,
alert Laboratories scientists saw an opportunity at last to test an important metallurgical
The scientists studied the whiskers, grew larger ones, and showed that the crystals
had enormously high yield strength as predicted by the theory for perfect crystals
- a strength far greater than for the same metal in any other known form. This clue
has opened new frontiers in the study of what makes metals strong or weak, and has
excited metallurgists all over the world.
Thus, another new advance has come out of the Bell Telephone Laboratories practice
of scrutinizing everything that can play a part in better telephone service. Through
the study of thousands of specially cultivated whiskers, Bell scientists seek to
prevent treacherous growths in telephone equipment.
Bell Telephone Laboratories
Improving Telephone Service for America Provides Carers for Creative Men in Scientific
and Technical Fields
Posted August 25, 2020