In November, a reader asked about the use of a chemical called Stabilant 22A for use on edge connectors on plug-in cards such as used in many types of communications equipment. I had asked you for comments about personal experience with the product. Because this column had to be written well before February, I have not yet received any comments from the field. So, I did some investigating on the Internet and elsewhere. Keep in mind that the source of this information is, for the most part, from the manufacturer and must be viewed in that light.
What is Stabilant 22A? Stabilant 22A is an initially nonconductive block polymer that becomes conductive in a thin film under the effect of an electrical field or when used in a narrow gap between metal contacts. The electrical field gradient at which conductivity occurs is set so that the material will not cause leakage between adjacent contacts in a multiple-contact environment. It can provide the connection with the reliability of a soldered joint without bonding the contacting surfaces together.
Although Stabilant 22A exhibits surfactant action, it is not sold as a contact cleaner. It exhibits good lubricating properties, but it is not sold as a contact lubricant. Its main strength is in its active properties when used in a connection, and the other properties are a bonus. To understand how the chemicals work let's take a quick look at the causes of connector failures.
LMR connector problems Generally, contaminants causing problems in connectors fall into four classes:
o plain contaminants.
o corrosive contaminants.
o contaminants that are modified by materials present in the connector itself.
o galvanic corrosive contaminants.
Apart from contamination, vibration can also lead to connector failure. Vibration may wear away a protective plating, or it may allow contamination to enter the connector.
Plain contaminants include road salts, tar and nicotine, paving material, oils, resins from trees, airborne industrial particulates and plant resins. They can also be plasticizers given off by vehicle upholstery, carpeting, undercoating or paints and plastics. These contaminants are more often found in mobile applications, and they may become concentrated when equipment modules are installed near vehicle heating vents or air-conditioning outlets. They may also be found in the home or office. Typically, contaminants form a thin film on the contact's surface where they can cause problems ranging from simple intermittence and distortion to RF demodulation. In data circuits or microprocessor-controlled equipment, even a single malfunctioning contact can crash the system.
Once inside a connector, corrosive contaminants corrode either the surface plating on the connector parts or, more seriously, corrode the underlying substrate metal. Because corrosion products occupy more space than the original metal, they can form pockets that 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 underlying material. This damage is often encountered in card-edge connectors used chemical or pulp-and-paper industrial environments.
Some metal plating can develop microscopic cracks when it and the materials on which it is plated are formed during connector manufacturing. Tin-plating, for example, undergoes a crystalline-lattice modification during temperature change. Stress alters the dimension of the material, enlarging the cracks and separating the plated surface from the substrate. As a result, potentially corrosive materials can accumulate under the plating, leading to premature failure of the connector. In some cases, storage and shipment of these types of connectors in corrugated cartons (without a sealed plastic protective bag) has caused failures because sulfates and sulfides have migrated from the cardboard.
The third class of contaminants, which includes low-saturation oils, doesn't cause problems in its original state. These contaminants can be cross-linked into polymer films because of the presence of other contaminants. For example, many plastics used in connectors are thermosetting resins that contain catalysts or curing agents that 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 used in connectors and automobiles. Where connector materials use the so-called "free-machining alloys," the presence of the sulfur that gives these alloys their machinability can cause cross-linking of oils and subsequent connector failure.
The final class, galvanic corrosive contaminants, is present where two dissimilar metals are used in contact with the connector. Dissimilar metals are not normally found in connectors supplied as mating pairs by reputable manufacturers. Instead, they are 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. Die-cast connector shells (forming the ground circuit) mated with silver-plated components are more typical.
The dissimilarity of the metals itself will generate an electrical potential between the connector components that can result in disintegration of the donor metal and/or plating of the donor metal onto the other component.
Although the subject is connectors, similar problems may be encountered with switches as well.
Other equipment applications Stabilant 22A can be used wherever electrical contacts are found, whether in connectors or in switches. With many circuits designed to use minimum power, such as CMOS frequency synthesizer modules, the power level in the individual contacts is often so low that even a small amount of contaminant film will either prevent the units from functioning, or lead to the collection of false frequency information. With the increasing sophistication of mobile equipment, it is not unusual to find this power-conservation type of design everywhere except in the final power amplifier itself. These designs conserve power or minimize heat-dissipation requirements, or both.
Portable radios are more likely to fail under heavy use and harsh conditions, often when they are needed most, such as during a storm that causes power outages. Weather and intense equipment use can often combine to knock a radio out of service - just when it is desperately needed.
When connections are less than perfect, thin-film rectification or oxide-film rectification may occur, making the system more susceptible to the electromagnetic pulses caused by lightning. Such rectification may also cause sideband spatter, or it may reduce sideband rejection and reduce signal-to-noise ratios by making the system more susceptible to RF interference from many other sources. As a result, the unit thereafter might be "jammed" when it is used near high-power sources of RF, such as AM, FM or TV broadcast transmitters.
The number of connections in most systems has also increased substantially. Although microprocessor control makes it easier to perform self-checks on some of the new equipment, it has made the same equipment much more sensitive to connector problems, whether they be card-edge connectors or those in socket-mounted ICs.
Some of the most perplexing, intermittent problems with radio equipment can be traced to poor electrical contact either with plug-in boards or other types of connections. How many times have you just removed a board and reseated it to clear a problem? The trouble, is the problem usually returns sooner or later - usually sooner. A long-lasting contact cleaner and enhancer could certainly reduce callbacks for those troublesome intermittent electrical connections.
Stabilant 22A can be purchased from Motorola under the Motorola part number 11C80367E78. This is a 15ml (about 1/2oz.) container. The product can also be found in NAPA automotive parts stores under the part number CE-1.
The manufacturer of Stabilant is D.W. Electrochemicals. The web address is www.stabilant.com.
As always, product safety Keep on hand a material safety data sheet (MSDS) for any chemical product you use or with which you might come into contact. The MSDS for Stabilant can be found on the manufacturer's Web site.
Again, the material presented here is based on information from the Web site mentioned above. Personally, I can neither support nor repudiate the claims of the manufacturer. The material is simply presented here in an effort to inform. If you have a tip about the use of other contact enhancers that may give long-lasting results, please email me or write to me if you wish to share the information with other readers.
Joseph J. Carr On a personal note, I was saddened to learn of the passing of Joseph J. Carr, a highly respected and prolific author of radio books and magazine articles. Many of his books on RF and radio communications occupy my shelves. We will miss his contributions to our chosen field. Our deepest sympathy to his family.
Until next time...stay tuned!