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SMS_Tabs_IBM_Report_Dec2007



From: Robert Garner
Date: December 18, 2007 9:25:57 PM PST
To: 1401 Restoration Team <1401_team@computerhistory.org>
Cc: pdp-1-team@googlegroups.com
Subject: IBM report on 1401 SMS card tab metallurgy and corrosion

Attachment: SMS_Tabs_IBM_Report_Dec2007.pdf, 1.5 MByte

This past summer we were debating and learning about the efficacy of using a corrosion inhibitor/lubricant on the 1401's SMS edge connector gold-plated tabs.

At that time I sent two sample SMS cards to IBM Systems and Technology, Poughkeepsie, PJ Singh's Materials & Process Engineering group in order to:

  1. reveal the metallurgy of the SMS card tabs, ?(I couldn't find any pub or anyone's memory that stated the metal stackup/thickness), and
  2. seek a recommendation as to which, if any, corrosion-inhibitor/lubricants we might employ to best preserve the SMS connectors for the future.
PJ Singh's study analyzed the IBM and clone "TRANSCO" SMS edge tabs with cross-sectional and SEM/EDX (Energy Dispersive X-ray fluorescence (XRF)). The final report presentation (1.5 MB) is now on our web site: http://www.ed-thelen.org/1401Project/SMS_Tabs_IBM_Report_Dec2007.pdf

The analysis, based on "energy dispersive X-Ray fluorescense" (EDX), determined the SMS edge connector stackup to be 100 micro-inches (2.54 microns) of Gold over 750 micro-inches of Nickel over Copper. Scanning electron microscopy (SEM) determined that there was no exposed Nickel nor any signs of Gold porosity nor significant surface wear.

PJ Singh's conclusion is that there's NO need for a corrosion inhibitor/lubricant. His recommendation is to clean SMS tabs with isopropyl alcohol as necessary.

My thanks go to PJ Singh and his team for donating their time and resources to do this timely study for us!

- Robert

* There are other possibilities, as metallic connectors were a new research field in the late 50's and 1960's. ?For example, there is an IBM Poughkeepsie 1966 paper that argued for 95.5% Gold / 0.5% Cobalt alloy directly over Copper (no Nickel).

** Our Gold's 2.54-micron thickness is substantially thicker than today's connector gold overcoats, 3/4 ?to 1 micron. ?Or even thinner, 0.38 micron or 15 microinches, for 10-year-lifetime, office-grade equipment starting in early 1980's, ?when standard practice had already dropped Gold thickness to 1.27 microns, or 50 microinches. They don't make 'em like they used to! ?;-)

p.s. Some more PJ Singh feedback in the report:


> In the bygone days, ATT and others thought that connectors needed 
> many microns of gold plating with nickel underplate. Today 3/4 
> micro-meter of gold with nickel underplate does a good job. 
> I am not in favor of contact lubricants for gold platings. One 
> micrometer gold plating with nickel underplate, with high contact 
> force and no vibration needs no lubricant. Lubricant complicates 
> connector reliability because one cannot predict the long-term 
> chemical behavior of lubricants. 
> But maybe we are barking up the wrong tree: ?Computers in data 
> centers are exposed to 40-50%RH clean air at less than 20 degrees C.
> Generally, metallic corrosion is not a concern below 50% RH. 
- Robert

IBM Almaden Research Center, San Jose, CA
Office: ?408-927-1739
Mobile: 408-679-0976
robgarn@us.ibm.com


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