Tom Lee wrote on 2/20/2021 9:25 PM:<snip>
....You could make them in dirtyrooms (take a look at early die photos of ICs -- you can see all sorts of crud; apparently, the industry then relied on cigarette ash as a dopant)....
Allegedly true story (secondhand): an engineer who worked at National Radio during the 1950s
told me about a piece of equipment which relied on sliding contacts. The contacts resided in a box
that when sealed, prevented maintenance and lubrication. The contacts developed intermittent
problems, but applying various lubricants didn't solve the problem.
By accident, an assembler dropped some cigarette ashes into one of the boxes.
Rather than taking the time to remove the ashes, the assembler sealed the
box which astonished the design engineer by passing its life test without
"What did you do differently?" asked the designer. The assembler confessed to
contaminating the box with ashes which apparently were acting as a mild abrasive
and scrubbing the contacts. "Keep it up," said the engineer, and henceforth every
box contained a sprinkling of cigarette ashes.
Until the government inspector arrived and happened to witness the
assembler taking a drag on his cigarette and then tapping the ashes into the box.
The inspector raised hell as only a government inspector can, and
after some intense negotiations allowed the process to continue--
provided that the
assembly instructions were edited to add a specification for "cleaning agent, Camel
cigarette ash, one-half inch."