Anecdote: Tin Whiskers Inside of AF114 Transistors

NASA
Anecdote: Tin Whiskers Inside of AF114 Transistors

Anecdote: Tin Whiskers Growing on Internal Walls of Transistor Can (Vintage Radios)

This anecdote describes how collectors of vintage radios have combated the electrical shorting malfunction of certain transistors utilized in a variety of collectable radio sets.

Over the years members of the UK Vintage Radio Forum have shared tips and strategies with each other to temporarily restore operation of a family of notoriously malfunctioning transistors by methods such as

Tapping the case with a screw driver
Physically disconnecting the transistor terminal connected to case
Passing elevated current through the suspected short circuited terminals to fuse open the unknown shorting material inside the transistor package by discharging a capacitor between the terminals.
Replacing the transistor with a suitable alternative device (though sometimes difficult to locate)

The remedies usually proved temporary and sometimes destructive. Later, it was discovered by one forum participant that the root cause of failure was electrical shorting due to tin whiskers growing from the tin-coated walls inside of the transistor case. Over time, the tin whiskers would grow long enough to short from the case to one or several of the internal connections to the transistor. The discovery of tin whiskers inside made evident the reasons why the remedies such as described above would be temporary. For example, tapping the case or passing elevated current might only physically shift or melt those whiskers that were presently in a shorting position. Later, other whiskers would continue to grow until they too produced an electrical short thus repeating the cycle of faulty operation.

Read More About this Anecdote Here:

Video Describing This Tin Whisker Experience

1960s era Germanium Transistor inside of a tin-plated package	1960s era Germanium Transistor inside of a tin-plated package
Transistor with the package cut open to reveal tin whisker formation on the inner walls of the package	Transistor with the package cut open to reveal tin whisker formation on the inner walls of the package
Tin whiskers growing from inside walls of tin-plated transistor	Tin whiskers shorting from tin-plated transistor case to an internal lead
Tin whiskers shorting from tin-plated transistor case to an internal lead	Tin whiskers shorting from tin-plated transistor case to an internal lead
Tin whiskers shorting from tin-plated transistor case to an internal lead	Tin whiskers shorting from tin-plated transistor case to an internal lead

Acknowledgment to Mr. Paul Stenning who manages the UK Vintage Radio Forum and his colleagues who shared discussion of their experiences and then samples of the offending transistors with engineers at NASA Goddard to enable the analysis herein.

Responsible NASA Officials: Michael Sampson/NASA GSFC Code 306 Dr. Henning Leidecker/NASA GSFC Code 562	Additional Researchers: Jay Brusse/Perot Systems Jong Kim/Orbital Sciences Corp.	Last Updated: August 3, 2009
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