Connector problems encountered in mobile and ham radio

While we will be talking about connectors, the problems outlined are also encountered with switches, of which many types can also be treated with Stabilant 22.

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Generally, contaminants causing problems in connectors can be broken down into four classes; plain contamination, corrosive contamination, contamination which itself is modified by materials present as part of the connector or by contaminants that cause galvanic corrosion.

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Apart from contamination, vibration of connectors can also lead to failure. This could be caused by wearing away of a protective plating, or even an action that would promote the entry of contamination into the connector itself.

Plain contamination can come from many sources as diverse as road salts, tar from smoke, paving material oils, resins from trees, industrial-origin airborne materials, to resins and plasticizers given off by upholstery, carpeting, undercoating or paints and plastics.

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While these contaminants are more often found in mobile applications and may actually be concentrated through location of equipment modules near heater, vent, or air-conditioning outlets they may also be found in the home or office environment.

Typically, the contaminant materials will form a thin film on the contact's surface where they will cause problems ranging from intermittent faults and distortion to RF demodulation. In data circuits or microprocessor-controlled equipment even a single malfunctioning contact can crash the system.

Corrosive contaminants are, as their name implies, chemicals that once in place within a connector, can cause corrosion the surface plating on the connector parts. In more serious cases, corrosion can affect the underlying substrate metal. Because corrosion products occupy more space than the original; metal, they can form pockets which can force clean contacting surfaces away from each other causing the connector to fail. Some contaminants can even penetrate the thin gold plating that is commonly used, destroying the underlying material. This is often encountered in card-edge connectors in the chemical or pulp-and-paper industries.

Some metal plating can micro-crack when they and the materials on which they are plated are formed during manufacture of the connector. A good example of this would be tin plating, which during temperature changes, undergoes a crystalline lattice modification which actually alters the dimension of the material, leading to enlargement of the cracks and, as a parallel problem, spalling of the plated surface from the substrate. In this situation, potential corrosive materials can accumulate under the plating, leading to premature failure of the connector. We have encountered cases where storage and shipment of these types of connectors in corrugated cartons (without a sealed plastic protective bag) can cause failures due to the migration of sulfur compounds present in the cardboard itself!

We need not dwell on the effects of the salts used to melt ice on the highways, or salt contamination in ocean-side areas, but people forget that various salts such as calcium chloride, are also used to hold moisture in gravel roads and road foundations.

The third class of contaminants are those, such as low saturation oils, which while they themselves don't cause problems in their original state, can be cross-linked into polymer films because of the presence of other contaminants. For example, many plastics used in connectors are thermo-setting resins and contain catalysts or curing agents which can act on unsaturated oils or partially saturated oils to make them cross link into gummy varnish-like films. The same sort of thing can be caused by some of the rubber materials encountered in connectors or even in automobiles. Where connector materials use the so-called free- machining alloys, the presence of the sulphur which gives these alloys their machinability can cause cross-linking of oils and subsequent connector failure.

The final class is that of galvanic corrosion. This occurs where two dissimilar metals are used in contact in the connector. Not normally found in connectors supplied as mating pairs by reputable manufactures, they are most often found where the male and female connector parts are obtained from different sources. One of the worst matches of this type would be the use of a good gold-plated connector mated to an aluminum bodied connector. More typical are die cast connector shells (forming the ground circuit) which are mated with silver plated components.

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The dissimilar electrochemical potentials of the metals themselves will generate a small voltage between the connector components which can result of disintegration of the donor metal and or plating of the donor metal onto the other component.