If the connectors are designed so that there is a low contact to contact pressure, and if the connector is being operated in a high temperature, high humidity environment the mating of a gold-plated contact to a solder-alloy plated contact is no recommended under any circumstance; either with or without Stabilant 22/22A/22E. This combination, under conditions of high humidity, temperature, and high frequency operation seems to speed up the formation of a hard black deposit consisting of mixed oxides of tin and lead. This coating is a poor conductor at best and will cause contact problems.
The exception occurs where the connector is designed to maintain sufficient pressure at the point of contact so as to exclude the entry of oxygen. This condition is typically met on good-quality IC sockets. Providing the contact pressure is in the range of 500 to 800 lb./in 2 this will usually exclude oxygen from the junction and stop the problem under most circumstances; nevertheless the use of Stabilant 22/22A/22E will enhance the contact's reliability over a longer period of time.
A better solution is of course the use of gold-plated to gold-plated contacts, or eve solder-alloy-plated to solder-alloy-plated contacts, either of which may be made more reliable by Stabilant 22/22A/22E.
Yes, many of the first enhancement boards made to fit the Maclntosh TM (Apple TM) computer used a "connector clip" which snapped down over the 68000 microprocessor chip on the main board. The initial design had gold-plated contacts which exerted only a low pressure over a fairly large area of the corresponding solder-alloy plated IC contact. The design of the "clip" together with the shielding effect of the board to which it was attached ensured that a high-temperature environment was created in the vicinity of the contacts. As the plastic housing for the "clip" was molded of polycarbonate plastic, which will absorb small amounts of moisture when cool, releasing it when heated up, It was not unusual to find that the enhancement board became erratic after two to three weeks of operation. Examination of the hard black film that formed at the junction of the two metals revealed that it was substantiate composed of oxides of tin and lead.
Redesign of the "clip" has significantly reduced the problem, nevertheless a number of companies servicing this equipment have still found it prudent to apply Stabilant to the contacts, and they report that this has taken care of the marginal cases.
Where the older graphic accelerator boards have still been encountered, the application of Stabilant 22 alone increased the mean time between failure from the two week period to about seven weeks; but this order of magnitude of MTBF is not acceptable in the application, and additional contact cleaning was necessary.
On the basis of solving similar problems with other types of connectors, our recommendation was that the gold-plate be changed to solder-alloy-plate, and that the contact pressure be increased either by the use of a thicker contact stock or the use of a small dome protrusion on the contact.
We have found that a solder-alloy to solder alloy contact under these circumstances, treated with Stabilant 22, will have a MTBF well in excess of several years.
Yes there are, but the bulk of them are hardly the type of materials that could be used where a good contact had to be maintained.
It is not good engineering practice to employ a design using contacts where the surfaces are materials lying at grossly different potentials on the galvanic scale. It is an open invitation to "Galvanic corrosion". (An example of this would be a low contact pressure gold to aluminum contact.) Even if the corrosion products are conductive they often exhibit semi-conductor or rectifying properties and will often demodulate any RF signals present on the lines as well as cause rise-time problems that can 'crash" the computer or peripheral using the connector. Contact pressures should be high enough to reduce the entry of oxygen into the contact pairs. While the use of Stabilants will reduce the problem by negating most of the thin film rectification problems, it is still better practice to employ connectors where the contacts are of identical materials or are close in their galvanic potential.
Revision 3
Stabilants are a product of Dayton Wright research & development and are made in Canada
NATO Supply Code 38948
15 mL of S22A has NATO Part # 5999-21-900-6937
The Stabilants are patented in Canada - 1987; US Patent number 4696832. World-wide patents pending. Because the patents cover contacts treated with the material, a Point-of-sale License is granted with each sale of the material.
Stabilant, Stabilant 22, and product type variations thereof are Trade Marks of D.W. Electrochemicals Ltd.
© Copyright 1987, '88. '89, '90 - D.W. Electrochemicals Ltd. This note may be reproduced or copied, provided its content is not altered. The term "contact enhancer", © 1983 Wright Electroacoustics.
NOTICE: This Application Note is based on customer-supplied information, and D.W. Electrochemicals is publishing it for information purposes only. In the event of a conflict between the instructions supplied by the manufacturer of the equipment on which the Stabilant material was used, and the service procedure employed by our customer, we recommend that the manufacturer be contacted to make sure that warranties will not be voided by the procedures.
While to our knowledge the information is accurate, prospective users of the material should determine the suitability of the Stabilant materials for their application by running their own tests. Neither D.W. Electrochemicals Ltd., their distributors, or their dealers assume any responsibility or liability for damages to equipment and/or any consequent damages, howsoever caused, based on the use of this information.
Stabilant, Stabilant 22, and product type variations thereof are Trade Marks of D.W Electrochemicals Ltd.
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