Connector corrosion

Connector corrosion is well known and understood as a familiar problem that contributes significantly to electrical wiring failures. Connector corrosion also plays a 

A problem discovered by an air force corrosion engineer was the corrosion of tin-plated electrical connector pins mated with gold-plated sockets. Fretting corrosion between these very small contacts appears to have been implicated in as many as six F-16 fighter aircraft crashes when their main fuel shutoff valves closed uncommanded (17). 

Dendrite growth can be very rapid. Failures because of dendrite growth have been known to occur in less than 30 min or can occur in several months or longer. The rate of growth of a dendrite depends on the applied voltage, the extent and quantity of contamination, and surface moisture. The amoimt of contamination required for silver dendrites can be extremely snoall. 

A failure may be defined as an unsatisfactory condition or a deviation from the original state or condition that is undesirable or unsatisfactory to a particular user or a context. The determination that a condition is unsatisfactory, however, depends on the failure consequences in a given operating context (18). 

The exact dividing line of demarcation between satisfactory and unsatisfactory conditions will depend not only on the function of the item in question, but also on the nature of the equipment in which it is installed and the operating context in which the equipment is used. Thus the determination will vary from one operating organization to another. Within a particular organization, however, it is essential that the boundaries between satisfactory and unsatisfactory conditions be defined for each item in clear and unambiguous terms. 

---

Lead—tin (1.8—2.5 wt %) is used both as a cable sheathing ahoy (BS 801 ahoy A and DIN 17640) and as a battery connector ahoy ia sealed lead—calcium—tin batteries (15). Tia is generahy added to lead—arsenic cable ahoys ia smah amounts. The arsenic ahoys have excehent creep resistance and mechanical properties, but are unstable and lose arsenic readily by oxidation. The addition of smah amounts of tin (0.10—0.20 wt %) eliminates arsenic loss. Lead ahoys having 0.4 wt % tin and 0.15 % cadmium, which are used for cable sheathing, do not age harden, show excehent corrosion and creep resistance, and are very ductile. 

Copper and nickel can be alloyed with zinc to form nickel silvers. Nickel silvers are ductile, easily formed and machined, have good corrosion resistance, can be worked to provide a range of mechanical properties, and have an attractive white color. These alloys are used for ornamental purposes, as sHverplated and uncoated tableware and flatware in the electrical iadustry as contacts, connections, and springs and as many formed and machined parts (see Electrical connectors). 

Table 16 illustrates the property enhancements and tradeoffs seen when tin is added to a copper—zinc brass base composition. The most commonly used alloys for electrical connectors are the Cu—10 Zn—Sn brasses, such as C411, C422, and C425. These lower level zinc—tin alloys offer good corrosion resistance along with the good formabiHty, conductivity, and strength levels of brass. 

The contact ends of printed circuit boards are copper. Alloys of nickel and iron are used as substrates in hermetic connectors in which glass (qv) is the dielectric material. Terminals are fabricated from brass or copper from nickel, for high temperature appHcations from aluminum, when aluminum conductors are used and from steel when high strength is required. Because steel has poor corrosion resistance, it is always plated using a protective metal, such as tin (see Tin and tin alloys). Other substrates can be unplated when high contact normal forces, usually more than 5 N, are available to mechanically dismpt insulating oxide films on the surfaces and thereby assure metaUic contact (see Corrosion and corrosion control). 

Porosity ranks next to thickness in importance, especially when the finishes must serve in polluted and/or humid environments which promote tarnish and corrosion. Pores, openings in the surface that extend to the underplate or substrate, can be intrinsic in the coating (14), or can be produced by mechanical wear or by forming operations involved in manufacturing. In some environments the substrate can tarnish or corrode at pore sites and can produce localized areas of insulating films which cause contact resistance to increase. Porosity is less important for connectors that operate indoors at moderate to low relative humidities and in the absence of corrosive pollutants (15). 

Fretting corrosion (36,37) can lead to high contact resistance of base metal contacts, such as tin plate in electronic connectors. Small cycHcal displacements of the connector halves occur because of external vibration or differential thermal expansion and contraction of the mating contacts. The wear debris that is formed remains in the contact zone. The accumulation of oxide debris in the contact region leads to increased contact resistance. Solutions to this problem are stmctures that do not permit movement of contact surfaces with respect to one another, the use of gold as a contact finish, and the appHcation of thick coatings of contact lubricants and greases, which reduce the rate of wear and restrict access of air to the contact surfaces. 

For lower pressure systems of approximately 150 psig at 400°F or 225 psig at 100°F, and w here sanitary precautions (food products or chemicals used in food products) or some corrosion resistance is necessary, tubing is used. It is joined together by butt welds (Figure 2-8) or special compression or hub-type end connectors. This style of piping is not too common in the... 

Cathodic protection applications in fresh water include use of ferrite-coated niobium , and the more usual platinum-coated niobium . Platinised niobium anodes have been used in seawater, underground and in deep wells " and niobium connectors have been used for joining current leads Excellent service has been reported in open-seawater, where anodic potentials of up to 120V are not deleterious, but crevice corrosion can occur at 20 to 40V due to local surface damage, impurities such as copper and iron, and under deposits or in mud ... 

Palladium Advantages have been claimed for new baths (e.g. using chelated complexes ). Antler summarised the use of palladium as coatings, inlays and weldments in electronic connectors . Crosby noted that palladium deposits are of two kinds (1) soft but continuous or (2) hard but porous or cracked. To resist wear and substrate corrosion on contacts, he proposed the application of type 1 (from a bath with tetranitropalladium(ii) anion) over type 2 (from solution containing tetramminepalladium(ii) cation) . 

Nickel-based alloys-Determination of resis-ance to intergranular corrosion Corrosion tests in artificial amospheres at very low concentrations of polluting gas(es) Test /. .-sulphur dioxide test for contacts and connectors... 

Materials in the whole system must be appropriate, that means reactor and piping for ozone gas as well as for ozonated water must be chosen carefully. For example, the material of the reactor and sampling system, especially the seals, has also to be chosen to avoid not only corrosion from ozone, but adsorption of the compound(s) being studied. It is advisable to let the liquid phase contact only glass and stainless steel. In stirred reactors for example, the stirrer seals (unless the stirrer is a magnetic bar) and all connectors for piping are best placed at the top of the reactor, so that the liquid does not come in contact with them. 

---