Identifying Corrosion and Liquid Damage

Section Overview

Liquid damage opens the last chapter of this volume because it is one of the most common ways a board fails and one of the most deceptive — the spill dries, the visible mess wipes away, and the real damage goes on corroding underneath, so identifying it correctly is the first step to fixing it (§4.5). This section is about reading a liquid-damaged board before touching a repair. The signs of ingress come first. A drying pool of liquid leaves a tide line — a stain or crust marking where it sat — and along with residue, spotting, and staining, these mark where liquid reached and where it pooled and did its worst. Then the corrosion itself. Corrosion leaves a corrosion product — the green, white, or blue deposit of eaten metal — and shows as dull, pitted, or missing copper where a trace, pad, or lead has been consumed (dendrite). Then power's role. A board that was powered when it got wet suffers electrolytic corrosion, where the voltage across the liquid drives metal away far faster and more selectively than a dried, unpowered spill ever would. Then the spread. Liquid wicks under components, along traces, and into connectors, so the damage reaches further than the visible mess, and tracing it is part of reading the board (§5.1). Then the severity. How bad it is depends on how far the corrosion went, whether it was powered, and what the liquid was — clean water, a sugary drink, salt water, and battery electrolyte are not equally destructive. Learn to spot the signs, recognise the corrosion, understand power's role, trace the spread, and judge the severity — and you can assess a liquid-damaged board and know what its repair will take.

Why This Matters

Identifying liquid damage correctly is what makes its repair possible — because the corrosion is often worse and more widespread than it looks, and a board judged by its visible mess alone is a board half-repaired and soon to fail again. This matters because corrosion hides and spreads: liquid wicks under components and into connectors and keeps corroding after the board looks dry, so the real extent is found by looking, not assuming, and missing it leaves live damage behind (§5.1). This matters because power changes everything: a board corroded under power has suffered electrolytic attack that eats specific nets fast, so knowing whether it was powered tells you how bad and how selective the damage may be. It matters because the liquid decides the severity: clean water that dried quickly may leave little, while salt water or battery electrolyte corrodes aggressively and keeps going, so the kind of liquid steers the whole assessment. It matters because identification drives the repair-or-retire decision: widespread corrosion into vias, under BGAs, or through connectors may be beyond hand repair, and recognising that early saves wasted effort (§4.5). And it matters because safety depends on it: a wet or corroded board can short, and a liquid-damaged battery can be a fire hazard, so identifying the state of the board is also identifying its dangers. Read the damage truly — its signs, extent, cause, and severity — and the repair that follows is aimed at the whole problem, not just the part you could see.

Required Prerequisites

• Identifying Damaged Traces — Section 5.1 taught how to find and read damaged traces by eye and meter, the same inspection skills applied here to corrosion and liquid damage.
• Repairability Assessment — Section 4.5 framed the go/no-go decision on whether a board is worth repairing, which identifying liquid damage feeds directly. A liquid-damaged board can hold charge and hold corrosive residue — read the Safety Notes before handling one.

Recommended Consumables

• Isopropyl alcohol and cotton swabs — to gently clean a spot for inspection without spreading corrosion (cleanliness testing)
• Gloves and eye protection — to handle corrosive residues and battery electrolyte safely
• Lint-free wipes — to lift residue and reveal the metal beneath
• A notebook and camera — to record the extent and pattern of the damage before cleaning
• Example liquid-damaged scrap boards to study — to learn the signs; handle safely and do not power them

Recommended Practice Hardware

• A magnifier, loupe, or microscope with a bright, raking light — to see tide lines, corrosion products, and pitted metal that flat light hides
• A multimeter with continuity and resistance ranges — to find corroded-open connections and leakage paths (§5.1)
• Fine tweezers and a probe — to lift a corrosion crust and test whether metal survives beneath it
• A UV light where available — to reveal some residues and tide lines that fluoresce
• The board's history — to learn what was spilled and whether it was powered, which steers the assessment
• A board holder — to hold the board under magnification while inspecting

Real-World Applications

Identifying liquid damage is the first move in every liquid-damage repair, across phones, laptops, appliances, vehicles, and industrial gear. A technician opening a drink-spilled laptop looks for tide lines and corrosion products to map where the liquid reached before deciding what to clean and repair. A repairer assessing a water-damaged phone checks whether it was powered when wet, because electrolytic corrosion on a live board points to fast, selective damage on powered nets. Someone facing a board with battery-electrolyte damage recognises the aggressive corrosion for what it is and handles the caustic residue with care (§4.5). A technician inspecting a corroded connector traces how far the corrosion has wicked along the pins and into the housing, beyond the green crust in view (§5.1). And a repairer judging a badly corroded board assesses whether the damage — into vias, under chips, through connectors — is within hand repair or beyond it. The failures this skill prevents: cleaning only what shows and leaving live corrosion behind, missing power-driven damage, and starting a repair on a board that was never worth it.

Common Challenges

• Judging by the visible mess alone. Corrosion wicks and hides, so the damage reaches further than it looks — inspect under magnification and meter beyond the obvious (§5.1).
• Missing that the board was powered. Electrolytic corrosion under power is fast and selective — learn the board's history and read the pattern of damage.
• Underestimating the liquid. Salt water and electrolyte corrode far worse than clean water — identify the liquid and assess accordingly.

Safety Notes

Risk Level: Medium. A liquid-damaged board can still hold charge, can short if powered wet, and can carry corrosive residue or a damaged battery — so inspecting one has real electrical, chemical, and fire hazards even though it is not hot work.

Professional Tips Before Starting

• Record before you clean. Photograph and note the pattern of tide lines and corrosion first — the map of where the liquid went guides the whole repair and is lost once you clean (§5.1).
• Learn the board's history. Find out what was spilled and whether it was powered — the liquid and the power tell you how bad and how selective the damage will be.
• Look, do not assume. Inspect under magnification and meter beyond the visible mess — corrosion hides under parts and wicks along traces further than it shows.

Reading a Liquid-Damaged Board

Recap and Frame

This volume has repaired mechanical and manufacturing damage to boards — cracked traces, lifted pads, broken vias; this chapter turns to a different enemy, one that keeps working after the event, and the frame to hold is that liquid damage is not the spill but the corrosion the spill starts (§4.5). That distinction shapes everything. A crack happens once and stays put, but corrosion is an ongoing chemical and electrochemical attack that continues after the board dries, spreads beyond where the liquid was, and is often worse under the surface than on it. So reading a liquid-damaged board is detective work, not a glance. You look for the evidence the liquid left — tide lines, residue, corrosion products — and read from it where the liquid went, how much metal it has eaten, and whether it is still going (§5.1). You weigh the two things that decide severity: whether the board was powered, which drives fast electrolytic corrosion, and what the liquid was, which sets how aggressive the attack is. And you trace the spread, because the damage hides under components and wicks along paths the eye does not follow. This section is only the identifying — the cleaning, repair, and verification come after — but it is the step everything else depends on, because you cannot clean or repair damage you have not found (§9.2). Hold the frame — liquid damage is ongoing corrosion, read from the evidence it leaves, worse where power and aggressive liquid met it — and you assess the board truly before you touch it.

The Signs of Liquid Ingress

The first task is to establish that liquid reached the board and to map where it went, which the liquid records in the marks it leaves as it dries. Read the tide lines. As a pool of liquid evaporates it leaves a tide line — a ring or crust of dried residue at the edge where it sat — and these lines map the shorelines of every pool, showing exactly where liquid reached and lingered. Spot residue and staining. Dried liquid leaves residue, spotting, and discoloration across the surfaces it wetted — a dulled, filmed, or stained area is a sign liquid was there even where no tide line formed. Find where liquid pooled. Liquid runs downhill and collects in low places — under and around large components, in board corners, in connector wells, beneath shields — so these low, sheltered spots are where the most liquid sat longest and the damage is worst. Check the ingress path. Follow the evidence back to where the liquid entered — a vent, a seam, a port — because the path of entry often runs through the worst-damaged area. Look for liquid-damage indicators. Many devices carry a small indicator that changes colour on contact with water, a quick confirmation the device was wetted, though it does not show how much or where (§4.5). Use raking light. A light held low across the surface throws tide lines, residue, and texture into relief that flat, straight-on light hides. Tide lines mapped, residue found, pools and paths located — and you know where the liquid went. Read where the liquid was, and you know where to look hardest for what it did.

Recognising Corrosion and Its Products

Where liquid sat, corrosion follows, so the next task is to recognise corrosion itself and the products it leaves — the direct evidence of metal being eaten. Know the corrosion products. Corrosion leaves a corrosion product — a deposit of the compounds formed as metal is consumed — most often the green and blue of copper corrosion, the white or grey of tin, aluminium, and solder, and rust-brown on steel, crusty or powdery on the surface. Read the deposit as a marker. A corrosion product marks exactly where metal is being attacked, so a green crust on a trace, a white bloom on a pad, or a furred lead points straight at the damage beneath it (dendrite). Look at the metal itself. Beneath or beside the deposit, corroded metal is dull, dark, pitted, thinned, or gone — a bright trace has survived, a dull or green-crusted one is under attack, and a missing stretch has been eaten through. Test whether metal survives. Gently lift a crust and check whether sound metal remains beneath or whether the trace, pad, or lead has been consumed, because a corrosion product can bridge a gap where the metal underneath is already open. Watch for corrosion-formed shorts and opens. Corrosion both eats metal to make opens and deposits conductive or semi-conductive products and dendrites that bridge to make shorts and leakage, so a corroded board can fail both ways at once (conductive anodic filament). Distinguish flux residue from corrosion. Not every deposit is corrosion — old flux residue can look similar — so read the colour, texture, and location, and whether metal beneath is sound, to tell them apart (cleanliness testing). Products recognised, the metal read, survival tested — and you know what the corrosion has done. See the corrosion for what it is, and you can judge how much metal is left to work with.

How Power Makes It Worse

Whether the board was powered when it got wet is one of the two great determinants of how bad the damage is, because electricity turns a passive spill into an active, accelerated attack. Understand electrolytic corrosion. When liquid bridges two points at different voltages, the liquid becomes an electrolyte and current flows through it, driving electrolytic corrosion — an electrochemical process that strips metal from one point and deposits or corrodes at another far faster than chemical corrosion alone. See why power accelerates it. A dried, unpowered spill corrodes slowly by ordinary chemistry, but under power the voltage forces the reaction, so a board wetted while running can lose metal in minutes where an unpowered one would take days. Read its selective pattern. Electrolytic corrosion follows the voltage, so it attacks hardest between nets at different potentials and along powered rails, leaving a selective pattern — heavy damage on some nets, little on others — that points to which were live. Recognise the higher-voltage danger. The greater the voltage across the liquid, the faster and more aggressive the attack, so higher-voltage rails and larger potential differences drive the worst electrolytic damage. Connect it to the battery. A device left with its battery connected is "powered" even when off, so standby rails can corrode electrolytically long after a spill, which is why isolating the battery early matters (§4.5). Use it to gauge severity. Knowing the board was powered tells you to expect fast, selective, and possibly deep damage on live nets, and to look hardest there. Electrolytic corrosion understood, its speed and pattern read, its link to the battery seen — and power's role in the damage is clear. Know whether it was live, and you know how fast and how far the corrosion likely ran.

Tracing How Far the Damage Has Gone

Corrosion reaches beyond what shows, so a true assessment traces the full extent of the damage — including where it hides — rather than stopping at the visible crust. Follow the wicking. Liquid wicks by capillary action under components, along the gaps beside traces, into via barrels, and between board layers, carrying corrosion far past the visible pool, so trace the likely wicked paths, not just the stained ones (§5.1). Look under and around components. The worst corrosion often hides beneath components where liquid pooled and could not dry — under ICs, connectors, and shields — so inspect and, where you can, lift or look under parts in the damaged area. Probe the hidden connections. Meter across connections in and around the damage for opens and for leakage between nets, because corrosion can eat a trace open or bridge two nets under a component where you cannot see it (§5.1). Check connectors and their pins. Connectors wick liquid along their pins into the housing and corrode internally, so a connector in a wetted area is suspect even if its visible pins look clean. Map the full extent. Build a picture of everywhere the liquid reached and everywhere corrosion is working — visible and inferred — so the cleaning and repair to come address the whole affected area, not a fraction (§9.2). Look for secondary damage. Corrosion that has opened a rail or bridged nets may already have caused secondary failures elsewhere, which a full trace begins to reveal (§4.5). Wicking followed, hidden areas inspected, connections probed, the full extent mapped — and you know how far the damage truly reaches. Trace it all the way, and no live corrosion is left behind to fail the repair.

Assessing Severity and What the Liquid Tells You

With the damage found and traced, the last step is to judge how severe it is and what it will take to repair — a judgement that turns on the extent of the corrosion and the nature of the liquid. Weigh the extent. A little corrosion on a few accessible traces and pads is a straightforward repair; widespread corrosion into vias, under BGAs, through connectors, or across many nets may be beyond practical hand repair (§4.5). Read what the liquid was. Clean water that dried fast may leave little; a sugary or dirty drink leaves conductive, corrosive residue; salt water corrodes aggressively and keeps drawing moisture; and battery or other electrolyte is caustic and among the most destructive — so the liquid sets how bad and how ongoing the attack is. Factor in the power and the time. A board powered when wet, or one left wet and corroding for a long time before it reached you, is worse than one dried and dead quickly — extent, liquid, power, and time together set the severity. Judge repair versus retire. Weigh the severity against the board's value and your skill and tools, exactly as for any repairability decision — some liquid-damaged boards are worth saving, some are not (§4.5). Anticipate the repair. From the assessment, foresee what the repair will need — cleaning to stop the corrosion, trace and pad repair where metal is eaten, component and connector work, and diagnosis of secondary failures (§9.2). Set expectations honestly. Liquid damage repairs can be uncertain, because hidden corrosion may surface later, so judge and communicate the realistic odds. Extent weighed, liquid read, severity judged, and the repair anticipated — and you have assessed the board fully. Judge the whole severity, and you know whether and how to bring the board back.

Common Mistakes

• Cleaning before mapping the damage. Cleaning erases the tide lines and pattern that show where the liquid went — record the damage first (§5.1).
• Trusting the visible surface. Corrosion hides under parts and wicks along traces — inspect and meter beyond what shows.
• Ignoring whether it was powered. Electrolytic corrosion on a live board is fast and selective — learn the history and read the pattern.
• Underrating salt or electrolyte. These corrode far worse than clean water and keep going — identify the liquid and assess accordingly.
• Powering a wet board to test it. A wet, corroded board shorts and damages itself further under power — never power it until clean and dry (§4.5).

Troubleshooting Guidance

Identification problems come down to missing damage, misreading its cause, or misjudging its severity. If a board failed but looks clean: look harder under magnification and under components — corrosion hides, and tide lines may be faint (§5.1). If a deposit is unclear: read its colour, texture, and location, and check the metal beneath, to tell corrosion from flux residue (cleanliness testing). If damage is heavy on some nets and light on others: the board was likely powered, and electrolytic corrosion followed the live rails — look hardest there. If a connection reads open with no visible break: corrosion has eaten a trace under a part or in a via — trace and meter the hidden path (§5.1). If two nets show leakage: corrosion products or dendrites are bridging them — find where the deposit crosses (conductive anodic filament). If the corrosion seems to keep spreading: salt or electrolyte residue is still active and drawing moisture — it must be cleaned to stop it (§9.2). If you cannot tell how far it went: assume it went further than it shows, and trace and meter until you find sound metal all around. The throughline: map the liquid, recognise the corrosion, read power's role, trace the full extent, and judge the severity honestly.

Verification & Testing Methods

Confirm you have read the liquid damage fully before moving to cleaning:

• [ ] I mapped where liquid went from the tide line marks, residue, and the low places it pooled, and recorded it (§5.1).
• [ ] I recognised the corrosion product deposits and read the metal beneath for what has been eaten or bridged (cleanliness testing).
• [ ] I established whether the board was powered and read the pattern for electrolytic corrosion on live nets.
• [ ] I traced the damage beyond the visible — under components, along wicked paths, into vias and connectors — and metered for hidden opens and leakage (§5.1).
• [ ] I assessed the severity from the extent, the liquid, the power, and the time, and judged repair versus retire (§4.5).

Then try the practice exercises below — inspection and assessment on scrap liquid-damaged boards; scenarios differ from the quiz.

Practice Exercises

1. Map the ingress (5 minutes, hands-on). On a scrap liquid-damaged board, find and mark the tide lines, residue, and low places where liquid pooled, and sketch where the liquid went (§5.1).
2. Recognise the corrosion (5 minutes, hands-on). Identify the corrosion products by colour and location, and read the metal beneath a deposit to judge whether the trace or pad has survived.
3. Read power's role (5 minutes, reasoning). For boards with different damage patterns, judge which were likely powered when wet from where the corrosion is heaviest and most selective.
4. Assess the severity (6 minutes, reasoning). For several scenarios differing in liquid, power, and extent, assess how severe the damage is and whether the board is worth repairing (§4.5).

These core steps — spotting the signs of ingress, recognising corrosion and its products, understanding power's role, tracing the spread, and assessing severity — are tested in the Chapter Quiz at the end of this chapter, where a score of 80% is required to continue.

Key Takeaways

• Liquid damage is not the spill but the corrosion it starts, which keeps working, spreads, and is often worse under the surface — so it is read from the evidence it leaves, not judged by the visible mess (§4.5).
• Map where liquid went from the tide line marks, residue, and the low places it pooled, and record it before cleaning erases the pattern (§5.1).
• Recognise the corrosion product deposits — green, white, blue — and read the metal beneath for what has been eaten or bridged.
• A board powered when wet suffers electrolytic corrosion, which eats metal fast and selectively along live nets, so whether it was powered is a key to the severity.
• Trace the damage beyond the visible and judge severity from the extent, the liquid, the power, and the time — clean water is not salt water is not electrolyte (§4.5).

Skills Learned

• You can now recognise the signs of liquid ingress on a board.
• You can now identify corrosion and its products, and the metal it has eaten.
• You can now explain how power drives electrolytic corrosion and why it spreads.
• You can now trace how far liquid and corrosion damage has gone, including where it hides.
• You can now assess the severity of liquid damage and what the type of liquid means.

Glossary Additions

• tide line — the ring, crust, or stain of dried residue left at the edge of a pool of liquid where it sat and evaporated on a board, marking the shoreline the liquid reached. Tide lines map where liquid pooled and lingered, and so point to where corrosion is likely worst; several concentric tide lines can record a pool shrinking as it dried. Reading and recording the tide lines before cleaning is a key step in identifying how far liquid spread across a board, since cleaning removes them.
• corrosion product — the deposit of compounds formed as metal corrodes, left on and around the corroding metal as visible evidence of the attack: typically green or blue on copper, white or grey on tin, solder, and aluminium, and rust-brown on steel, often crusty or powdery. A corrosion product marks exactly where metal is being eaten, and some products are conductive or semi-conductive and can bridge nets to cause shorts and leakage even as the corrosion eats other metal open. Corrosion products must be distinguished from ordinary flux residue, which can look similar but does not indicate eaten metal.
• electrolytic corrosion — corrosion driven by an electric current flowing through a liquid that bridges points at different voltages, turning the liquid into an electrolyte and stripping metal far faster and more selectively than ordinary chemical corrosion. Electrolytic corrosion is why a board that is powered when it gets wet suffers much worse damage than an unpowered one: the voltage forces the electrochemical reaction, attacking hardest between nets at different potentials and along powered rails, and can eat a trace open in minutes. Because a connected battery keeps standby rails live, isolating the battery early is important to arrest electrolytic corrosion after a spill.

Suggested Next Sections

Must read next:

• Cleaning a Liquid-Damaged Board — Section 9.2 takes the next step after identifying the damage: cleaning the board to remove the residue and arrest the corrosion at its source, before any trace, pad, or component repair.

Recommended:

• Identifying Damaged Traces — the inspection-and-meter skills for finding damaged copper, applied here to corrosion.
• Repairability Assessment — the go/no-go decision that a liquid-damage assessment feeds.