Page 328 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

306 CORROSION CONTROL AND PREVENTION

4.32.6 Corrosion of Aluminum in Chlorinated Media
Both liquid and vapor phase halogenated solvents used for production of ICs and
PCs readily corrode the aluminum components. Water contamination of the solvents
increases the time-to-corrosion, on the one hand, but increases the corrosion, on the
other hand. Dilution of the stabilized solvents with alcohol solvents leads to break-
down of halogenated solvent and formation of chloride ions, which corrode aluminum
and aluminum–copper alloys.

4.32.7 Solder Corrosion
Lead–tin alloy solder’s resistance to corrosion in aqueous and gaseous environments
is a function of the alloy composition. The corrosion resistance of the alloy increases
with tin content above 2 wt%. Lead forms unstable oxides, which readily react with
chlorides, borates, and sulfates.

4.32.8 Corrosion of Magnetic and Magneto-Optic Devices

Corrosion-related failures can occur in advanced magnetic and magneto-optic storage
devices, where thin-film metal discs, thin-film inductive heads, and magneto-optic
layers are affected. Corrosion occurs in sites where the deposited carbon overcoat
is lacking because of the intentional roughening of the disc and where the magnetic
cobalt-based layer and nickel–phosphorus substrate become exposed. The potential
differences between the noble (positive) carbon and the metal substrate, a galvanic
couple may form resulting in rapid galvanic-induced dissolution of the magnetic
material.
Magneto-optic devices use very reactive alloys for the recording media. Exposure
of magneto-optic films to aqueous solutions or high humidity results in pitting, even
during storage in ambient office conditions.
Mitigation of corrosion of electronics equipment by encapsulating the components
in plastics has been done. It should be noted that polymers are permeable to moisture.
Hermetically sealed ceramic packaging is more successful; care must be taken to
prevent moisture and other contaminants from being sealed in. A common useful
approach for mitigating corrosion of circuits housed in large chassis consists of using
volatile corrosion inhibitors. This will require periodic replacement of the carrier.

4.33 HOME APPLIANCES

The three basic corrosion control methods used in corrosion control of home appli-
ances are: (i) corrosion control by sacrificial anodes; (ii) use of corrosion-resistant
materials; (iii) corrosion control by coatings and paint.

4.33.1 Corrosion Control by Sacrificial Anodes
The life of a hot water heater can be extended by checking and changing the dete-
riorating anode. The direct cost of not having to replace broken water heaters can