The first image of the can unfurled looks like the seal of the can allowed
moisture to enter and cause rusting of the interior/inside surface of the
can.

If not moisture infiltration, then I would suspect that the metal (or
plating/coating material) was incompatible with other materials inside the
can.

Another possibility could be that the metal used for the can was specified
to be extremely reliable, but the metal alloy/finish was flawed or otherwise
contaminated before assembly of the diode.

The design construction technique is flawed IMO if the can isn't more secure
than just a pressed-together fit.
It might be interesting to see if the military/areospace version of these
devices were fabricated by the same method.

Rust is conductive, and I would suspect that the diode failure was going to
happen eventually.

So much for long term reliability of heavy duty semiconductors.

--
Cheers,
WB
..............


"N_Cook" wrote in message
...
Some pics of all this, 1mm graph paper background

The sides of the cap unfurled, A-A is the distinct cutoff line of the
rusted
part, the roughness at the ends is my butchery, also clean originally
http://home.graffiti.net/diverse:gra...t/1N5812_a.jpg

The green glass filled seal around the anode pin
http://home.graffiti.net/diverse:gra...t/1N5812_b.jpg

Its unaffected partner, as far as not being ohmic anyway
http://home.graffiti.net/diverse:gra...t/1N5812_c.jpg

View of the gold metalisation over the base metal stub, Os are below some
of
the largest areas of erosion. I don't know where the missing gold went to
,
no flakes or obvious dust lying around in the diode when first broken
into.
The weld for the anode pin is off-centre as can be seen in the pic, is
that
relevant ?
http://home.graffiti.net/diverse:gra...t/1N5812_d.jpg

Edgewise view of the die , showing gold metalisation up to the die but
much
is eroded away , eg base metal showing between C-C and the most obvious
accretion bridging the edge of the die marked with the Vs
http://home.graffiti.net/diverse:gra...t/1N5812_e.jpg

looking down on the large gold metalised areas with Bs showing the most
obvious bits of base metal, the bright line is the die edge
http://home.graffiti.net/diverse:gra...t/1N5812_f.jpg
the wavy gold edge ,near it, is probably metalisation over some underlying
pad so presumably at manufacture rather than a later formation

These diodes were stored anode upwards in kit , untouched for 13 years, so
something made the dust aggregate and migrate vertically , against gravity

it is now reading 13 ohms


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/