Page 207 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

ELECTRONICS 185

5. Fretting Corrosion of Separable Connectors with Tin Finishes. Fretting corro-
sion in electronic components occurs as the continuous formation and flaking
of tin oxide from a mated surface on tin-containing contacts. As more tin is
oxidized and utilized, it leaves no choice but to replace the component with a
new part.
6. Galvanic corrosion can occur when two dissimilar metals, such as aluminum
and gold, are coupled, as is commonly done for packaged (plastic-wrapped)
ICs. The polymers used for packaging are porous and the gaskets around her-
metic covers such as ceramic or metal sometimes leak; therefore, in humid
environments, moisture can permeate to the IC bond pad, leading to conducive
conditions for galvanic corrosion. Electronic devices dissipate a considerable
amount of heat during operation, which leads to reduced relative humidity.
During power-down or storage periods, the relative humidity rises leading to
the likelihood of corrosion (43).
7. Processing-Related Corrosion of ICs. ICs are exposed to aggressive corro-
sive media used in reactive ion etching (RIE) or wet etching for patterning
of aluminum lines, which can lead to corrosive residue. RIE of aluminum
metallizations utilizes a combination of aggressive chlorine-containing gases.
If removed untreated from the etcher, patterned structures are covered with
aluminum chloride residue, which hydrolyzes to give hydrochloric acid in the
presence of moisture (43).
8. Micropitting on Aluminum on ICs during Processing. Aluminum metalliza-
tions, alloyed with copper, can form intermetallic compounds such as Al Cu
2
along the grain boundaries, which act as cathodic sites relative to aluminum
adjacent to grain boundaries. This leads to dissolution of aluminum matrix in
the form of micropitting during the rinsing step after chemical etching.
9. Corrosion of Aluminum by Halogenated Solvents. Both liquid and
vapor-phase halogenated solvents used for the production of ICs and
PCs corrode aluminum-containing components. Water contamination of the
solvent increases the time to corrosion on the one hand and increases the cor-
rosion rate on the other hand. Dilution of the stabilized solvents with alcohol
results in the breakdown of halogenated solvents and the decomposition
product, chloride ion corrodes aluminum, and aluminum–copper alloys.
10. Solder Corrosion. The corrosion resistance of lead–tin solder in aqueous
environments is a function of the alloy composition. The corrosion resistance
of lead-tin increases when the tin content of the solder increases above
2 wt%. Lead forms unstable oxides, which react with chlorides, borates, and
sulfates (43).
11. 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 intentional roughening of the disc and where
the magnetic cobalt-based layer and nickel–phosphorus substrate become