10 Jul
2016
10 Jul
'16
6:07 p.m.
On Jul 10, 2016, at 9:07 AM, Tothwolf <tothwolf at
concentric.net> wrote:
On Sun, 10 Jul 2016, Paul Birkel wrote:
While "don't mix contact surfaces" is sufficient, it isn't necessary.
What matters is the "anodic index" of the metal, or rather, the difference
between those two values for the two metals in contact. If that difference is large, you
have a problem; if it's small enough, you do not. "Small enough" depends on
the environment; aboard an oceangoing ship the number has to be smaller than in an office
setting. I remember looking into this topic for an investigation of what types of contact
platings are acceptable for lithium coin cell battery holders in IT equipment.
https://en.wikipedia.org/wiki/Galvanic_corrosion has some information.
paul
Stated Tothwolf tothwolf at concentric.net:
I'm not familiar with them used in DEC systems in that way, but the problems with
mixing tin and gold plated connectors is well documented. Even the connector manufacturers
warn against mixing different platings. "Both contact surfaces must also be the same
material or tin oxide will form on the surface of the gold plating and cause a major
headache. This was a serious problem with 486 and earlier Pentium PCs with 30 and 72 pin
SIMMs and it led to a number of lawsuits."
Almost every DEC System Unit ("backplane") that I've ever seen uses
tinned-contacts, yet the Modules all use gold-plated fingers.