Materials library
Flood damage to electronics is mostly chemistry that happens after the water arrives. This library explains the materials that slow that chemistry and the failure mechanisms it causes. Each entry starts in plain language; open "Engineering detail" for more depth.
Why salt water is worse than fresh water
Clean water alone is a poor conductor and corrodes metal slowly. Flood water is never clean, and seawater is especially aggressive for three reasons.
- It conducts electricity far better. Seawater is roughly a hundred times more conductive than typical river water. Corrosion is an electrical process, so a better conductor means faster corrosion.
- Chloride ions attack protective films. Metals such as stainless steel, aluminum, and tin rely on a thin oxide skin to protect them. Chloride ions break through that skin at weak spots and start pits that keep growing.
- Salt residue keeps working after the water leaves. Dried salt pulls moisture out of the air (it is hygroscopic), so a salt-crusted board stays slightly damp and keeps corroding for days or weeks unless it is rinsed.
Brackish water, the mix of river and seawater found in Newark Bay and the lower Hackensack and Passaic rivers, falls between the two but behaves much more like seawater than fresh water for electronics.
Engineering detail
Seawater has a salinity of about 35 parts per thousand, with chloride around 19,000 mg/L, and a conductivity near 50 mS/cm. Fresh surface water typically ranges from tens to a few hundred µS/cm. Chloride is a small, highly mobile anion that adsorbs at defects in passive films and stabilizes local acidic conditions, which is why it drives pitting and crevice corrosion in passivating alloys. On circuit assemblies, chloride also forms soluble metal complexes (with copper, tin, and silver) that make electrochemical migration much faster.
Contamination residue
As flood water evaporates, everything dissolved or suspended in it is left behind: salts, silt, sewage, fuel, and cleaning chemicals. This film is often invisible. It conducts electricity when it absorbs moisture from the air, and it feeds every failure mechanism described below. That is why rinsing with deionized or distilled water is the most important salvage step, and why tap water is a poor rinse: it leaves its own minerals behind.
Engineering detail
Ionic residue lowers surface insulation resistance (SIR) as soon as relative humidity rises above the deliquescence point of the salts present. For sodium chloride that is about 75% RH. Mixed contaminants can deliquesce at lower humidity. Cleanliness can be verified with resistivity of solvent extract (ROSE) testing for a bulk figure, or with ion chromatography to identify specific ions such as chloride, bromide, and sulfate.
Conformal coatings
A conformal coating is a thin protective film sprayed, brushed, dipped, or vapor-deposited over a finished circuit board. It keeps moisture and contaminants off the conductors. IPC-CC-830 is the main standard for qualifying these coatings, and it uses two-letter type codes: AR, SR, UR, ER, and XY.
No coating makes a board waterproof
Coatings slow corrosion and buy time. In prolonged immersion, water still reaches the board at connectors (which must be left uncoated), board edges, pinholes, and thin spots. Elevation is the protection that actually works; coatings are the backup.
Acrylic (AR)
The easiest to apply and repair.
Acrylic dries quickly and protects well against humidity and condensation. Its big advantage is that solvents dissolve it, so technicians can remove it to repair a board and then recoat the spot. The flip side is that solvents, fuel, and some cleaning chemicals attack it, and it is not a strong barrier against salt-water immersion.
Best for: indoor equipment in humid rooms, and boards that may need repair.
Engineering detail
Usually solvent-borne acrylic resins applied by spray or selective coating. Thickness commonly cited in IPC-A-610 guidance is 30 to 130 µm (about 1.2 to 5 mil). Good dielectric properties and fluorescent tracers make coverage inspection easy under UV. Continuous service is typically limited to about 125 °C. Moisture vapor transmission is moderate, so acrylic is a humidity barrier rather than an immersion barrier.
Silicone (SR)
The best for temperature extremes and outdoor use.
Silicone stays flexible from deep cold to high heat and copes well with condensation, which makes it common in outdoor and automotive electronics. It is applied thicker than most coatings. It is soft, so it scuffs easily, and it is difficult to remove for repairs. Silicone residue also makes it hard for other coatings or adhesives to stick later.
Best for: outdoor cameras, sensors, and anything that sees big temperature swings.
Engineering detail
Thickness commonly cited in IPC-A-610 guidance is 50 to 210 µm (about 2 to 8 mil). Service range often runs from about -55 °C to 200 °C. Silicones are hydrophobic but have relatively high gas and moisture vapor permeability. They tend to resist liquid water well while letting vapor through, so performance under long-term condensation depends heavily on board cleanliness beneath the coating. Rework requires mechanical removal or specialist strippers.
Urethane (UR)
The tough all-rounder for harsh sites.
Urethane coatings are hard and resist moisture, salt fog, and chemicals such as fuels. That makes them a strong choice for coastal and industrial sites. They are harder to remove than acrylic, so repairs take more effort.
Best for: equipment near salt air or chemical exposure.
Engineering detail
One- or two-part polyurethane systems. Thickness commonly cited in IPC-A-610 guidance is 30 to 130 µm. Low moisture vapor permeability and good abrasion and solvent resistance. Removal usually needs dedicated chemical strippers or burn-through with a soldering iron, which can release irritating fumes, so rework should be done with ventilation.
Epoxy (ER)
Very hard, but nearly impossible to repair.
Epoxy forms a hard, chemical-resistant shell. Once cured, it is extremely difficult to remove without damaging the board, and it can put stress on delicate components as it shrinks and as temperatures change. It suits potted sensors and small sealed modules better than computer boards.
Best for: small, single-purpose modules that will never be repaired.
Engineering detail
Usually two-part systems. Thickness commonly cited for coating use is 30 to 130 µm; much thicker when used as potting. The high modulus and cure shrinkage can crack glass-bodied diodes or solder joints on fine-pitch parts during thermal cycling unless a buffer coat is used. Excellent moisture and chemical resistance.
Parylene (XY)
The strongest barrier, at the highest cost.
Parylene is deposited as a vapor inside a vacuum chamber, so it forms an extremely thin, even film that reaches under components and has essentially no pinholes. It is the best barrier against moisture and salt of the common coatings, and the only one that reliably survives short immersion. It costs more, requires a specialist shop, needs connectors masked off before coating, and is very hard to remove for repairs.
Best for: high-value or critical boards at sites with real immersion risk.
Engineering detail
Deposited by chemical vapor deposition (the Gorham process) from a dimer that is vaporized, pyrolyzed to a monomer, and polymerized on the room-temperature substrate. Common variants are Parylene C (the usual choice for moisture barrier), N, and fluorinated grades for higher temperature. Thickness commonly cited in IPC-A-610 guidance is 10 to 50 µm (about 0.4 to 2 mil). Adhesion depends on surface preparation, often a silane adhesion promoter. Because it is a batch vacuum process, masking quality largely determines where ingress paths remain.
PCB surface finishes
A bare circuit board's copper pads would oxidize before parts could be soldered on, so manufacturers cover them with a surface finish. The finish also determines how well any pad left uncovered after assembly resists corrosion. You can only choose it for custom boards, but it is a fair question to ask vendors of industrial and outdoor equipment.
ENIG (electroless nickel, immersion gold)
Flat, reliable, and widely used.
A layer of nickel covered by a very thin layer of gold. It is flat enough for the tiny parts on modern boards and resists tarnish well. Its weakness is that the gold is so thin it has microscopic pores. In salt or sulfur-laden air, the nickel underneath corrodes through those pores. A related finish, ENEPIG, adds a palladium layer between the nickel and gold that reduces this problem.
Engineering detail
Typical nickel is 3 to 6 µm with immersion gold around 0.05 to 0.1 µm. Because immersion gold is a displacement reaction, porosity is inherent. Pore corrosion of the nickel is driven galvanically, with the noble gold acting as a large cathode against small exposed nickel anodes, which is especially aggressive in chloride and sulfur environments. A known manufacturing defect, "black pad," is hyper-corrosion of the nickel during gold deposition that leads to brittle solder joints. ENEPIG's palladium layer limits nickel exposure and is also wire-bondable.
Immersion silver
Good and cheap indoors; poor near salt or sulfur.
A thin silver layer that solders well and costs less than ENIG. Silver tarnishes when exposed to sulfur compounds and chlorides in the air, and it can suffer creep corrosion, where corrosion products spread across the board surface until they bridge neighboring pads.
Engineering detail
Typical thickness is about 0.05 to 0.3 µm. Creep corrosion, the migration of copper and silver sulfide corrosion products across solder mask, has been widely reported on immersion silver boards in high-sulfur environments, which are severity classes G2 and above under ISA-71.04. Silver is also the metal most prone to electrochemical migration under bias and humidity.
OSP (organic solderability preservative)
The cheapest finish, with little protection after assembly.
A very thin organic film that stops the copper oxidizing until soldering. It burns off during soldering, so any pad, via, or test point not covered by solder ends up as nearly bare copper. It is fine in dry indoor equipment but a poor choice where flooding or condensation is likely, unless the whole board is conformal-coated.
Engineering detail
Azole-based films (benzimidazole derivatives), typically 0.2 to 0.5 µm. The finish degrades with each thermal excursion, so double-sided reflow can leave second-side pads partly unprotected. Exposed copper on test points and unfilled vias is the usual corrosion initiation site in humid service.
HASL (hot air solder leveling)
Thick and tough, but bumpy.
The board is dipped in molten solder, and hot air knives blow off the excess. The thick solder layer protects the copper very well, which makes HASL robust in harsh environments. The surface is uneven, so it does not work for the fine-pitch parts on modern computer boards, but it is excellent for power supplies, sensors, and simpler controllers. Lead-free versions are now standard.
Engineering detail
Lead-free HASL usually uses a tin-copper-nickel alloy. Thickness varies widely across a panel, from about 1 µm to more than 25 µm, which causes coplanarity problems for fine-pitch QFPs and small BGAs. The intermetallic layer formed during HASL is stable, and the thick tin-rich coating gives good shelf life and corrosion resistance. Immersion tin is a related flat alternative but is prone to tin whiskers and has a shorter shelf life.
Connector plating
Connectors are the weak point of every protected assembly: they cannot be coated, they open and close, and water collects in them. What their contacts are plated with determines how they fare.
- Gold over nickel is the standard for signal and data contacts. Gold does not corrode, and the nickel underneath stops copper from migrating up through it. Thickness matters. For harsh environments, a commonly specified minimum is 30 µin (0.76 µm) of gold over 50 µin (1.27 µm) of nickel. Thin "flash" gold is porous, and corrosion starts at the pores in salt.
- Tin is inexpensive and common on power connectors. It suffers fretting corrosion: tiny movements from vibration or thermal cycling wear through the surface, and oxide builds up until resistance climbs. Tin needs high contact force, a contact lubricant, and ideally a sealed housing.
- Silver conducts best and is used for high-current contacts, but it tarnishes in sulfur and is the metal most prone to electrochemical migration.
Never mix platings. A gold contact mated to a tin contact forms a galvanic pair, and fretting makes it worse. Match the plating on both halves of every connection.
For outdoor and coastal equipment, use connectors with an IP67 rating (such as M12 circular connectors or sealed RJ45), cap unused ports, and add drip loops so water runs off before it reaches the connector.
Engineering detail
Hard gold (cobalt- or nickel-hardened) is used for durability across many mating cycles. Porosity falls steeply as gold thickness increases, which is why harsh-environment specifications ask for 30 to 50 µin. The nickel underplate also acts as a diffusion barrier and, when the gold is breached, as a less active substrate than copper. Mixed-flowing-gas tests (such as those defined by EIA-364-65) are used to qualify connector platings for corrosive environments.
Enclosure materials
The box around the electronics is the first line of defense against splashes, rain, and salt air. In a full flood, most ventilated enclosures fill with water. The material choice decides whether the box itself survives and keeps protecting what is inside afterward.
316 versus 304 stainless steel
The molybdenum makes the difference near salt water.
Both are "18-8" type stainless steels, but 316 adds roughly 2 to 3% molybdenum, which greatly improves its resistance to pitting from chlorides. Near salt water or after a salt flood, 304 develops rust spots ("tea staining") and pits, sometimes within months, while 316 holds up far better. Use 316 fasteners with 316 enclosures, and rinse with fresh water after any salt exposure.
Engineering detail
Pitting resistance is often compared with the pitting resistance equivalent number, PREN = %Cr + 3.3 × %Mo + 16 × %N. Typical values are about 19 for 304 and about 24 for 316. "L" grades (304L, 316L) have low carbon, which prevents sensitization (chromium carbide formation) in weld zones. Even 316 can suffer crevice corrosion under gaskets and deposits in stagnant seawater, so design to drain and avoid tight crevices.
Anodized aluminum
Light, good at shedding heat, but careful with fasteners.
Aluminum forms its own protective oxide, and anodizing thickens that layer. Marine-grade alloys such as 5052 and 6061 with sealed anodizing resist salt air well. The danger is galvanic corrosion: in salt water, aluminum touching stainless steel corrodes rapidly at the contact point. Isolate the two with nylon washers or sleeves.
Engineering detail
In the seawater galvanic series, aluminum alloys are far more active than passive stainless steel, and the potential difference is large enough to drive significant attack when a small aluminum area meets a large stainless area. Sealing the anodic layer (hot water, nickel acetate, or dichromate seals) closes its pores and substantially improves chloride resistance. Chlorides cause pitting of aluminum wherever the anodized layer is scratched.
Polycarbonate
Cannot rust, but traps heat.
Polycarbonate enclosures do not corrode at all and resist impacts well, so they are common for outdoor junction boxes and camera housings. Choose UV-stabilized grades outdoors, or the plastic yellows and becomes brittle. Plastic does not conduct heat away like metal, so polycarbonate suits low-power devices, not servers.
Engineering detail
Polycarbonate absorbs a small amount of water and can stress-crack when exposed to some solvents and cleaners, including certain alcohols and amine-containing products, so check chemical compatibility before cleaning flood-exposed enclosures. Glass-reinforced polyester (fiberglass) is an alternative with better chemical resistance and stiffness for larger cabinets.
Powder-coated steel
The standard rack material, and the most vulnerable to salt.
Most server racks and network cabinets are cold-rolled steel with a powder coat. That works well indoors, but wherever the coating is scratched or chipped, salt water quickly starts rust that spreads underneath the paint. After a salt flood, expect to replace a rack's sheet-metal parts; after a fresh-water flood, clean, dry, and touch up scratches.
IP and NEMA ratings
Ingress protection (IP) ratings, defined in IEC 60529, tell you how well an enclosure keeps out dust (first digit) and water (second digit). In North America you will also see NEMA enclosure types, defined in NEMA 250, which include corrosion resistance and other factors that IP ratings do not cover.
| Rating | What it means for water |
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| IP65 | Dust-tight; protected against water jets. |
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| IP66 | Dust-tight; protected against powerful water jets. |
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| IP67 | Dust-tight; survives temporary immersion (tested at up to 1 m for 30 minutes). |
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| IP68 | Dust-tight; survives continuous immersion under conditions the manufacturer states, which must be stricter than IP67. |
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| NEMA 4X | Watertight against hose-directed water, plus corrosion resistant. |
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| NEMA 6P | Protected against prolonged submersion at a limited depth. |
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Two cautions. IP tests use fresh water, so a high IP rating says nothing about salt corrosion. And servers, PCs, and switches need airflow, so they cannot be sealed. For that equipment, elevation is the realistic defense.
Galvanic corrosion
When two different metals touch while wet, they form a small battery. The more "active" metal (the anode) corrodes and protects the more "noble" one (the cathode). Electronics are full of dissimilar-metal pairs: gold and nickel, tin solder and copper, aluminum heat sinks and steel screws. In fresh water this happens slowly. In salt water, which conducts far better, it can eat through thin platings and fine traces within days.
Area matters: a small anode connected to a large cathode, such as tiny nickel spots exposed through pores in a large gold surface, corrodes fastest.
Engineering detail
The driving force is the difference in corrosion potentials in the given electrolyte (the galvanic series in seawater is the usual reference). The rate is limited by electrolyte resistance and cathodic reaction kinetics. That is why conductivity, dissolved oxygen, and the cathode-to-anode area ratio dominate. Breaking the electrolyte path with coatings or sealing, or electrically isolating dissimilar metals, is more effective than material choice alone.
Electrochemical migration and dendrites
This is the reason powered equipment fares so much worse in a flood. When there is voltage between two nearby conductors and a film of water bridges them, metal dissolves at the positive conductor, travels through the water, and redeposits at the negative one as fern-like metal filaments called dendrites. When a dendrite reaches across the gap, it causes a short circuit. In salt water this can happen in minutes.
Equipment that was switched off during the flood avoids this, until someone powers it up with residue still on the board. Dried salt absorbs moisture from the air, and dendrites can then grow within hours. Always clean boards before applying power.
Engineering detail
Electrochemical migration (ECM) requires four things: a conductive path (an adsorbed or condensed water film), ionic contamination, an electric field, and a migratable metal. Susceptibility is roughly silver > copper > lead > tin, with tin often protected by its oxide except in the presence of chlorides. Halides increase metal solubility and dramatically shorten time to failure. Fine-pitch, high-voltage-gradient areas such as under QFNs and between closely spaced pads are most vulnerable. Surface insulation resistance testing under temperature, humidity, and bias is the standard way to assess ECM risk for an assembly and its cleanliness.
Moisture absorption, delamination, and conductive anodic filaments
Circuit boards are made of glass fabric bonded with epoxy resin (FR-4), and chip packages are molded plastic. Both slowly absorb water. After hours to days underwater, moisture inside the board:
- lowers the insulation between conductors, causing leakage currents and erratic behavior;
- can make layers separate (delamination), visible as blisters or white spots called measling;
- under voltage, can grow copper filaments along the glass fibers inside the board. This is conductive anodic filament (CAF) growth. It is invisible from outside and can cause shorts weeks or months later.
Engineering detail
Moisture diffuses into epoxy laminates and can wick along the glass-resin interface, especially where drilling has damaged it. CAF forms when copper ions generated at an anode (a plated via, for example) migrate along that interface toward a cathode under bias, depositing a conductive copper-containing filament. Risk rises with closer via spacing, higher voltage, higher humidity, and resin systems with poorer glass adhesion. Recovery from absorbed moisture requires extended low-temperature drying; surface drying alone does not remove it.
Popcorning and bake-out
Moisture trapped inside a plastic chip package turns to steam when it is heated quickly to soldering temperatures. The pressure can crack the package or tear it away from the chip inside, sometimes with an audible pop, hence the name. This matters after a flood if anyone solders, reworks, or quickly heats the boards. It does not happen at normal operating temperatures.
The fix is to dry the parts slowly first. The electronics industry already does this for new components that have absorbed humidity, following J-STD-033 (handling) together with J-STD-020 (sensitivity classification).
Engineering detail
J-STD-020 classifies non-hermetic surface-mount devices into moisture sensitivity levels (MSL 1 to 6), each with a "floor life" before the part must be resealed or baked. J-STD-033 gives bake options at 125 °C, 90 °C (≤5% RH), and 40 °C (≤5% RH), with times that depend on package thickness and exposure. Bake temperatures above 125 °C are not allowed without consulting the supplier. Because baking grows intermetallics and oxidizes leads, cumulative bake time between 90 °C and 125 °C is limited (the standard cites 96 hours unless the supplier says otherwise). For assembled boards, the default bake is 125 °C, but boards with temperature-sensitive parts such as electrolytic capacitors, batteries, and some connectors and displays need lower temperatures for longer. A flood-saturated board should be treated as worst-case exposure.
Standards referenced
These industry standards define the terms and test methods used on this site. Standards are revised from time to time, so check with the publisher for the current revision before relying on specific numbers.
| Standard | What it covers | Why it matters for floods |
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| IPC-CC-830 | Qualification and performance of electrical insulating compounds (conformal coatings) for printed wiring assemblies. | Defines the coating types (AR, SR, UR, ER, XY) and the tests a coating must pass, including humidity and insulation resistance. |
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| IPC-A-610 | Acceptability of electronic assemblies: visual workmanship criteria for soldering, components, cleanliness, and coatings. | A practical reference when inspecting a cleaned board for corrosion, residue, and coating damage. |
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| J-STD-020 | Moisture/reflow sensitivity classification for non-hermetic surface-mount devices (IPC/JEDEC). | Defines moisture sensitivity levels, which tell you how vulnerable chip packages are to popcorning. |
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| J-STD-033 | Handling, packing, shipping, and use of moisture/reflow-sensitive surface-mount devices (IPC/JEDEC). | Gives bake-out temperatures, times, and limits to follow before soldering flood-soaked boards. |
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| ISA-71.04 | Environmental conditions for process measurement and control systems: airborne contaminants. Classifies air as G1 (mild), G2 (moderate), G3 (harsh), or GX (severe), based on how fast copper and silver test coupons corrode over 30 days. | After a salt flood, lingering humidity and salt can make a room's air corrosive. Coupon testing tells you whether the room is fit for electronics again. Data center guidance generally targets G1. |
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| IEC 60529 | Degrees of protection provided by enclosures (IP code). | Defines IP ratings such as IP67 and IP68. |
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| NEMA 250 | Enclosures for electrical equipment (NEMA types). | Defines NEMA 4X (corrosion resistant, watertight) and 6P (prolonged submersion). |
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Engineering detail: ISA-71.04 severity levels
The 2013 revision requires both copper and silver reactivity, with the higher of the two setting the class. For copper, the commonly cited thresholds are below 300 Å per 30 days for G1, below 1,000 Å for G2, below 2,000 Å for G3, and 2,000 Å or more for GX. For G1, silver must also stay below 200 Å per 30 days. Copper reactivity is sensitive to humidity and can vary seasonally; silver reactivity is much less so.