Why do electronic devices and circuit boards corrode, and how is it prevented?

In one line

Electronic devices corrode because tiny metal tracks, solder joints and connectors are exposed to moisture, ionic contamination and polluting gases while carrying voltage, and even very small metal loss can cause failure.

Explained simply

A phone or laptop has metal lines thinner than a hair and very close together. A little humidity plus salt from a fingerprint, flux residue or sweat forms an electrolyte film. With voltage between neighbouring tracks, you have a tiny electrochemical cell. A pipe can lose a millimetre of steel and still work; a chip contact cannot lose even a micrometre.

How it works

1. Sources: humidity and condensation; ionic contaminants (Cl⁻ from flux residues and fingerprints); atmospheric gases (SO₂, H₂S, NO₂, Cl₂); dust that absorbs moisture.
2. Galvanic corrosion: different metals in contact (Au, Ni, Cu, Sn, Ag, solder alloys) set up galvanic cells in the presence of moisture; the more active metal corrodes.
3. Electrolytic metal migration / dendrite growth: under applied bias, metal (especially Ag, also Cu and Sn) dissolves at the positive conductor, migrates through the moisture film and deposits at the negative conductor as tree-like dendrites, eventually short-circuiting the tracks.
4. Tarnishing: Ag and Cu react with sulphur gases forming Ag₂S or Cu₂S films that increase contact resistance.
5. Pitting and creep corrosion through pores in thin gold plating on connectors; fretting corrosion at contacts that vibrate slightly, producing insulating oxide debris.

Effects: increased contact resistance, open circuits (broken tracks or bond wires), short circuits (dendrites), signal noise and complete device failure.

Key formula

No formula. Typical anodic reaction on copper tracks: \( \mathrm{Cu \rightarrow Cu^{2+} + 2e^-} \); tarnishing: \( \mathrm{4Ag + 2H_2S + O_2 \rightarrow 2Ag_2S + 2H_2O} \).

Quick example

A phone dropped in water may work for a while and then fail days later: residual moisture and ions slowly corrode connector pins and grow dendrites between closely spaced pads. Prevention methods used in industry:

• Conformal coatings (acrylic, silicone, polyurethane, parylene) on PCBs.
• Hermetic sealing or encapsulation of chips and sensors.
• Gold plating over a nickel barrier layer on contacts; avoiding incompatible metal pairs.
• Thorough cleaning of flux residues; controlled humidity and temperature in storage and use.
• Vapour-phase corrosion inhibitors (VCI) and desiccants in packaging.

Common mistakes

• Assuming gold contacts never corrode; pores in thin gold expose the underlying metal.
• Ignoring the role of applied voltage, which drives metal migration.
• Writing only general corrosion points without device-specific causes.

How MU asks it

A newer topic: "Write a note on corrosion in electronic devices" (3–5 marks). For full marks: why electronics are sensitive, 3–4 causes/mechanisms (galvanic, metal migration/dendrites, tarnishing, fretting), effects, and 3–4 prevention methods.