Residue and water content come from the manufacturing route and the grade specification, not the bottle. Here is how IPA is actually made and what each grade certifies. How Isopropyl Alcohol Is Made →
There is a four-dollar bottle in millions of homes, repair shops, and cleanrooms that quietly does the same job at both ends of the technology world. It wipes the thermal paste off a gaming CPU, lifts solder flux off a freshly repaired phone board, and — purified to a level most people never see — is used in the final rinse and drying of silicon wafers. That bottle is isopropyl alcohol. This guide walks the whole electronics chain: which concentration to actually use, how to clean flux and thermal paste correctly, and what changes as you climb from the repair bench to a semiconductor fab.
Why do electronics techs reach for isopropyl alcohol?
Isopropyl alcohol is the go-to electronics solvent because it dissolves the contaminants that matter, dries quickly, and leaves nothing conductive behind. Most other household liquids fail at least one of those tests — water conducts and corrodes, oils smear, and harsh solvents attack plastics and conformal coatings.
Specifically, pure IPA:
- Dissolves rosin solder flux, light oils, skin oils, and adhesive residue — the exact gunk that builds up on boards and connectors.
- Evaporates fast and clean (boiling point 82.6 °C), so you are not left waiting or wiping.
- Leaves almost nothing behind when it dries: our sample COAs cap non-volatile residue at 0.005% for 99% Technical and 0.001% for 99.9% ACS Reagent. That matters, because a residue that bridges two traces can cause leakage current or shorts.
- Is gentle on most electronics plastics and PCBs (always spot-test painted, rubberized, or coated surfaces first).
- Is cheap and widely available in the concentrations that actually work.
CAS Number: 67-63-0 | Formula: (CH₃)₂CHOH (C₃H₈O) | Boiling point: 82.6 °C | Flash point (closed cup, our SDSs): 12 °C for 99% and 99.9%, 14–18 °C for 91%, 18–22 °C for 70%. Every strength is a highly flammable liquid. Same CAS regardless of concentration or grade.
Why not just use water, acetone, or a contact cleaner?
Because each of the obvious alternatives fails the electronics test in a different way. Water conducts, corrodes, and dries slowly. Acetone cleans aggressively but melts many plastics, dissolves silk-screen legends and some component markings, and attacks certain conformal coatings — it is the wrong default for a populated board. Aerosol “contact cleaners” vary wildly: some are IPA-based, others leave a lubricating film or use solvents that are hard on plastics. Pure isopropyl alcohol hits the sweet spot — strong enough to dissolve flux and oils, mild enough to leave most plastics and coatings alone, and clean enough to flash off with no residue. That is why it became the industry default rather than a niche product.
That combination is why one solvent quietly handles a huge range of electronics jobs. The same bottle that lifts flux also degreases connector pins and edge-card fingers, clears the residue a leaking electrolytic capacitor sprays across a board, wipes optical drive lenses and camera modules, preps surfaces for adhesive or conformal coating, and cleans the read/write heads and contacts that grime quietly degrades. It is the closest thing the electronics world has to a universal cleaner — which is exactly why it pays to understand the few places it does not belong (covered below).
What percentage of isopropyl alcohol is best for cleaning electronics?
For cleaning electronics, the highest practical concentration wins: 99% (or 99.9%) is best, 91% is acceptable for general cleaning, and 70% should be avoided. The single variable that decides this is water content — and with electronics, water is the enemy.
Every percentage point that is not alcohol is mostly water. That water (a) dries more slowly than the alcohol, so it lingers in connectors and under components, (b) can promote oxidation and corrosion on exposed metal, and (c) can pick up whatever ionic residue is already on the board. The lower the percentage, the more water you are painting onto your board.
| Strength | Water (limit) | Residue after drying (limit) | On electronics? |
|---|---|---|---|
| 70% USP | 28–32% by volume | ≤0.01% (5 mg per 50 mL) | No: far too much water to leave on a board |
| 91% USP | about 7–9% (assay 91.0–93.0% by volume) | ≤0.005% (2.5 mg per 50 mL) | OK for cases and keyboards; let it dry fully |
| 99% Technical | ≤0.2% | ≤0.005% (5 mg per 100 mL) | The default for boards, flux, thermal paste, connectors |
| 99.9% ACS Reagent | ≤0.2% | ≤0.001% | Optics, sensors, residue-critical work |
Specification limits from our published sample certificates of analysis (read 2026-11-10), not measurements of any lot. Our 70% and 91% state strength by volume; our 99% and 99.9% state it by weight.
What the spec sheets show that the labels do not: our 99.9% ACS Reagent does not allow less water than our 99% Technical. Both are capped at 0.2%. What the ACS grade buys is a residue limit five times tighter (0.001% against 0.005%) and an assay of at least 99.5% by weight. And because our 70% and 91% are made with deionized water, their problem on a board is the water itself, not minerals in it.
If you only keep one bottle on the bench for electronics, make it 99%. If you already have 91%, it is fine for wiping down a keyboard or a case — just give it longer to dry and keep it off anything water-sensitive.
Is 70% isopropyl alcohol safe for electronics?
No — 70% isopropyl alcohol is not the right choice for electronics, even though it is the most common bottle on the shelf. The roughly 30% water it contains is exactly what you do not want near a circuit board.
70% is roughly 30% water by design. That is fine on a hard exterior surface you can wipe dry, and wrong for a motherboard. On electronics the water means:
- Slow drying: the water outlasts the alcohol and stays in connectors and under components.
- Corrosion and oxidation risk on exposed copper, contacts, and battery terminals.
- Liquid on a live circuit: never apply any strength to a powered device.
The rule: 99% for anything that carries current, 91% for cases and keyboards, and keep 70% USP off the board. If a job involves traces, contacts, or anything that carries current, reach for 99%.
How do you remove solder flux with isopropyl alcohol?
To remove solder flux, brush 99% isopropyl alcohol onto the joints, scrub gently, lift the dissolved residue with a lint-free wipe, and let it flash off — repeating until the board looks clean and matte. Rosin-based fluxes (R, RMA, and most rosin-core solder) dissolve readily in IPA, which is why it is the standard post-soldering cleaner.
A clean, repeatable method:
- Power off and disconnect the board (and remove the battery where possible).
- Flood the flux with 99% IPA using an acid/flux brush, ESD-safe brush, or a saturated foam swab.
- Agitate gently to break up the sticky rosin — work it, do not just dab.
- Wick the dissolved residue away with a lint-free wipe or cloth so you remove it, rather than spreading a thin film.
- Repeat until no amber tackiness remains, then let it dry fully before powering on.
Rosin, no-clean, and water-soluble flux — which ones need IPA?
Not all flux behaves the same. Rosin (R, RMA) flux is the classic case: it is sticky, mildly active, and dissolves cleanly in isopropyl alcohol — IPA is its natural solvent. No-clean flux is formulated to leave a residue that is safe to leave behind if it was fully heat-activated; the trouble is hand-soldering and rework often under-heat it, leaving tacky, partially-active residue that is best removed — and IPA handles it. Water-soluble (organic-acid) flux is the exception: it is aggressively corrosive and must be removed, but it is designed to wash off with water (often warm DI water), not alcohol. Know which flux you used before you reach for a solvent.
Why bother: Left-behind active flux residue can absorb moisture and drive electrochemical migration (dendrite growth) between traces — slow, hidden failures that show up weeks later as intermittent faults or leakage. Cleanliness is measured by surface insulation resistance (SIR) and ionic-contamination testing, and the expectations live in standards like IPC J-STD-001 and IPC-A-610. For anything that has to last, clean it.
Can you clean a PCB, motherboard, or circuit board with isopropyl alcohol?
Yes — 99% isopropyl alcohol is the standard way to clean a PCB, motherboard, or any circuit board, as long as the board is powered off and you let it dry completely before reconnecting power. It safely lifts dust, flux, fingerprints, and spilled-liquid residue from the board and its connectors.
Cleaning thermal paste off a CPU or GPU
99% IPA is also the right tool for re-pasting. Old thermal paste wipes off the CPU or GPU heat-spreader and the cooler’s cold plate with a little 99% on a lint-free cloth or coffee filter; let it flash off, and the surface is ready for fresh paste. 70% leaves moisture you do not want trapped under a heatsink.
Heavier cleaning
For badly contaminated boards, repair shops use IPA in an immersion or ultrasonic bath, then dry thoroughly. This is also where buying IPA by the gallon, drum, or tote instead of tiny spray bottles starts to matter — bench-scale habits become a real line item at shop volume.
From the repair bench to the fab: how far does one molecule go?
The isopropyl alcohol on a hobbyist’s bench and the isopropyl alcohol in a multi-billion-dollar semiconductor fab are the exact same molecule — what changes is purity. As you climb the electronics chain, the contaminant you care about gets smaller and smaller, until you are counting individual particles and metal ions per billion.
- Repair bench & field service: 99% Technical Grade. Removes flux, paste, and grime. “No visible residue” is clean enough.
- Precision assembly, optics, sensors, R&D: 99.9% ACS Reagent Grade. Residue after evaporation capped at 0.001% on our sample COA, for when a fingerprint of contamination matters.
- Semiconductor production fabs: certified SEMI / electronic grade, a tier above ACS. The governing standard is SEMI C41, which sets the requirements and test methods for each grade of 2-propanol used in semiconductor manufacturing. It is used for the final wafer rinse and Marangoni drying.
Why does purity scale so dramatically? Because the defect you are fighting shrinks. On a repair board, “clean” means no visible flux and no conductive bridge you can measure. On a silicon wafer with features a few nanometers wide, a single dried-on water spot or a stray sub-micron particle can kill a die worth thousands of dollars — so the final isopropyl-alcohol rinse has to be cleaner than the surface it touches. That is the whole reason fabs use Marangoni drying, where a controlled IPA vapor pulls water off the wafer edge-first so it leaves zero droplets behind. Same molecule, same job (get the surface clean and dry with no residue), but the tolerance went from “looks clean” to “measured in parts per billion.”
That last step is its own story — see our deep dive on isopropyl alcohol in semiconductor wafer cleaning & drying and the broader chemistry in solvents in PCB manufacturing.
Honest grade note: our highest-purity IPA is 99.9% ACS Reagent Grade — excellent for R&D, pilot lines, optics, MEMS, and lab work. Production fabs require certified SEMI/electronic-grade IPA, which is a separate certification tier; we do not claim SEMI purity we do not certify. Tell us the application and we will tell you honestly whether ACS is the right fit.
Technical vs ACS vs SEMI: which isopropyl alcohol grade do you actually need?
For most electronics work you need 99% Technical Grade; step up to 99.9% ACS Reagent Grade only when residue or trace contamination is genuinely critical. Grade is a promise about what else is in the bottle, not just how much alcohol.
| Grade | What our spec sheet limits | Use it for |
|---|---|---|
| USP (70% / 91%) | Strength by volume (70%: 68.0–72.0%; 91%: 91.0–93.0%); the rest is deionized water | General surface and case cleaning, not boards |
| 99% Technical | Assay ≥99.0% by weight, water ≤0.2%, non-volatile matter ≤5 mg/100 mL | Flux, thermal paste, PCBs, connectors, shop work |
| 99.9% ACS Reagent | Assay ≥99.5% by weight, water ≤0.2%, residue after evaporation ≤0.001% | Optics, sensors, MEMS, R&D, residue-critical cleaning |
| SEMI / Electronic | Set by SEMI C41 (we do not sell this grade) | Wafer fabs (we supply up to ACS; see note above) |
What should you never clean with isopropyl alcohol?
Isopropyl alcohol is safe on most electronics, but a few surfaces and habits will cost you a screen, a speaker, or a board. Keep IPA away from these:
- Screen oleophobic coatings. The anti-fingerprint layer on phone and tablet glass is thin and IPA can wear it away over repeated use. Clean glass with a barely-damp microfiber, not a soaked alcohol wipe — save the 99% for the board inside, not the display.
- Speaker and microphone membranes. The thin diaphragms in micro-speakers can be deformed or have their coatings attacked by solvent. Do not flood them.
- Some rubbers, silk-screen legends, and soft-touch coatings. Certain rubberized cases and printed labels can soften, smear, or whiten. Spot-test an inconspicuous corner first.
- Powered or energized boards. Liquid on a live circuit can bridge contacts, and the vapor is highly flammable. Always power down, unplug, and remove the battery before cleaning.
Two technique mistakes that ruin good cleaning: using paper towels (they shed lint that traps under components — use lint-free wipes or swabs), and not letting the board dry fully before power-on. Even fast-drying 99% needs a moment in tight connectors. When in doubt, give it a minute.
Is isopropyl alcohol safe to handle, and how should you store it?
Isopropyl alcohol is safe to use with basic precautions, but it is highly flammable and the main hazard is fire, not toxicity. Our SDSs give closed-cup flash points of 12 °C for 99% and 99.9%, 14–18 °C for 91% and 18–22 °C for 70%, so the vapor can ignite at room temperature at every strength, so handling is about controlling ignition sources and ventilation.
- Keep it away from flame, sparks, and hot soldering irons. Do not clean a board near an active iron or hot-air station; let tools cool or move the cleaning step away.
- Work in a ventilated area and avoid breathing concentrated vapor; the higher the concentration, the faster it evaporates into the air.
- Wear chemical-resistant gloves and safety goggles, as section 8 of the SDS directs. Ground and bond containers when you transfer larger volumes.
- Mind ESD. Use ESD-safe brushes and a grounded mat when cleaning sensitive boards.
- Store tightly closed, upright, away from heat and ignition, in its original or a compatible solvent-rated container. Always keep the SDS on hand.
How do you buy isopropyl alcohol for electronics without overpaying?
Buy the concentration the job needs and the pack size your volume justifies — and stop paying retail prices for water. A drugstore 70% bottle is roughly one-third water; for electronics you want 99%, where nearly every dollar is solvent that actually cleans.
- Match the grade to the work — 91% for general cleaning, 99% for boards and flux, 99.9% ACS for precision. Do not over-buy purity you will never use, or under-spec a step that matters.
- Scale the pack size — quarts for the bench, gallons and 5-gallon pails for a shop, drums and 275-gallon totes for a production line. Cost-per-clean drops fast with volume.
- Get the paperwork: the safety data sheet for each product, and a lot-specific Certificate of Analysis (COA) on request at no charge, so your purity and safety records hold up.
Isopropyl alcohol for electronics: key numbers & sources
The atomic facts behind everything above, with primary sources for verification:
| Property / fact | Value | Source |
|---|---|---|
| CAS Number | 67-63-0 | PubChem CID 3776 |
| Water and residue limits by grade | See the table above | Our sample COAs (docs.alliancechemical.com/coa) |
| Molecular formula | C₃H₈O / (CH₃)₂CHOH | PubChem |
| Boiling point | 82.6 °C (180.7 °F) | PubChem |
| Flash point (highly flammable) | 53 °F (about 12 °C) for pure IPA; our SDSs: 12 °C (99%, 99.9%) to 18–22 °C (70%) | NIOSH Pocket Guide; our product SDSs |
| OSHA PEL (8-hr TWA) | 400 ppm | OSHA |
| Assembly cleanliness standards | IPC J-STD-001, IPC-A-610 | IPC |
How we researched this
Our own documents: the published sample certificates of analysis for our 70%, 91%, 99% and 99.9% isopropyl alcohol (specification limits and reference values, not lot certificates; a lot-specific COA is available on request at no charge) and the safety data sheets for the same four products (hazard class and flash point, not cleaning performance).
Public references: PubChem, the NIOSH Pocket Guide, OSHA, IPC (J-STD-001, IPC-A-610) and SEMI C41. Where the drying-time or cleanliness claims you see elsewhere had no test record behind them, we left them out.
Where our product stops: our highest IPA purity is 99.9% ACS Reagent Grade. Production semiconductor fabs require certified SEMI/electronic-grade IPA, a separate tier we do not supply.
Last reviewed November 10, 2026. General information, not engineering advice for a specific assembly: follow the device maker's cleaning instructions.
Related: The Chemistry of Photonics Manufacturing — the wet-chemistry backbone of optical-device and silicon-photonics fabrication.
Related: How to Remove Sticker Residue: The Solvent That Works, and the Surfaces It Ruins — removing label residue near electronics: which solvent, and which surfaces to keep it off.
Frequently asked questions
What percentage of isopropyl alcohol is best for cleaning electronics?
99%. Our 99% Technical and 99.9% ACS isopropyl alcohol allow no more than 0.2% water, so almost nothing but alcohol goes onto the board. 91% (about 7 to 9% water) is fine for cases and keyboards if you let it dry fully. Keep 70% (28 to 32% water) off circuit boards.
Can I use 91% isopropyl alcohol to clean electronics?
Yes, for general jobs like keyboards, cases and connectors, as long as the device is off and everything dries fully before power-on. It carries about 7 to 9% water, so for boards, flux and thermal paste 99% is the better choice.
Is 70% isopropyl alcohol safe for electronics?
Not on circuit boards. Our 70% is 28 to 32% water by volume. That water dries more slowly than the alcohol, stays in connectors and under components, and can promote corrosion on exposed metal. Use 99% for anything that carries current.
Why is higher concentration isopropyl alcohol better for electronics?
Less water. Water dries more slowly than the alcohol, lingers in tight spaces and can promote corrosion on copper and contacts. Our 99% and 99.9% grades allow at most 0.2% water and cap residue after drying at 0.005% and 0.001%.
How do you remove solder flux with isopropyl alcohol?
Brush 99% isopropyl alcohol onto the flux, agitate to dissolve the rosin, then wick the residue away with a lint-free wipe and let it dry. Repeat until no amber tackiness remains. Rosin-based fluxes dissolve readily in IPA; water-soluble fluxes are made to be washed off with water instead.
Can you clean a motherboard or PCB with isopropyl alcohol?
Yes. With the board powered off and the battery removed where possible, 99% isopropyl alcohol removes dust, flux, fingerprints and spill residue from a PCB or motherboard. Let it dry completely, including inside connectors, before reconnecting power.
What isopropyl alcohol should I use to clean thermal paste?
Use 99% isopropyl alcohol on a lint-free cloth or coffee filter to remove old thermal paste from a CPU or GPU heat-spreader and the cooler cold plate. Avoid 70%, which leaves moisture that can be trapped under the heatsink.
What grade of isopropyl alcohol do semiconductor fabs use?
Production fabs use certified SEMI / electronic-grade isopropyl alcohol, specified under the SEMI C41 standard, for the final wafer rinse and Marangoni drying. That is a tier above ACS Reagent Grade. Our highest grade is 99.9% ACS Reagent, suited to R&D, optics, MEMS and lab work.
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About the author
Andre Taki
This article is for informational purposes only.
