Printed circuit boards (PCBs) are essential components in most electronic devices. Over time, PCBs can accumulate dirt, dust, and other contaminants that can negatively impact performance. Cleaning PCBs helps remove these contaminants and restore optimal functioning.

When cleaning PCBs, high purity isopropyl alcohol (IPA) is generally recommended as the solvent of choice. But what exactly is IPA and why is it well-suited for PCB cleaning? This article provides a detailed overview of using alcohol to safely and effectively clean PCBs.

Why Clean PCBs?

There are several key reasons to periodically clean PCBs:

Remove Dirt, Dust, and Debris

Dust, dirt, metal particles, and other contaminants can gradually build up on PCBs during manufacturing and use. These particulates can cause issues like:

• Short circuits – Conductive debris can lead to short circuiting between PCB traces. This disrupts current flow.
• Overheating – Contaminants can interfere with heat dissipation, leading to excessive component heating.
• Corrosion – Moisture absorption by contaminants promotes oxidation and corrosion of copper traces.
• Interference – Particles can interfere with sensitive electronic components and disrupt performance.

Regular cleaning removes these contaminants to prevent damage and maintain optimal functioning.

Remove Existing Flux Residue

Flux residues are left behind after soldering PCBs. Flux helps solder adhere to PCB components during manufacturing. However, residual flux can absorb moisture and cause corrosion over time. Cleaning removes leftover flux.

Remove Oils and Greases

Oils and greases from handling can also accumulate on PCBs during manufacturing and repair. Cleaning helps eliminate residues that may negatively impact surface insulation resistance.

Improve Thermal Conductivity

Dust and greases act as thermal insulators that inhibit effective heat dissipation from PCB components. Cleaning improves surface contact between components so heat can be conducted away more efficiently.

Prevent Signal Loss

Dirt and dust can interfere with signals, especially high frequency signals. Cleaning helps prevent attenuation or distortion of signals between PCB components.

Properties That Make IPA Ideal for PCB Cleaning

Isopropyl alcohol (2-propanol) offers a combination of properties that make it exceptionally well-suited for cleaning delicate PCB electronics.

Non-Conductive

IPA does not conduct electricity. This is critical since PCB cleaning solvents must not short circuit or otherwise interfere with PCB operation. IPA’s non-conductive nature prevents any short circuiting.

Low Surface Tension

IPA has a lower surface tension than water. This allows IPA to penetrate into tight spaces and fully displace moisture, dissolve residues, and displace contaminants on PCBs.

Rinses Residue-Free

Unlike some solvents, IPA leaves no residue after evaporation. This means no unwanted coatings or deposits are left behind on PCBs after cleaning.

Fast Drying

A volatile solvent, IPA dries quickly at room temperature without needing heat. This rapid drying limits any potential damage from moisture absorption after cleaning.

Non-Corrosive

IPA does not corrode the metals and components used in PCB fabrication. It will not damage traces, leads, or pads.

High Purity

Medical and electronics grade IPA are purified to contain almost exclusively the 2-propanol isomer. Impurities could lead to electrical shorts or corrosion, so high purity IPA is required.

Cost Effective and Readily Available

As a mass produced solvent with a wide array of uses, IPA is affordable and easy to source in the purity required for PCB cleaning.

IPA Grades for Cleaning PCBs

Isopropyl alcohol is available in different purities or grades including:

• Consumer/Technical grade – Typically 70-90% IPA mixed with water. Not recommended for electronics.
• Reagent grade – 90-99% purity suitable for some electronics applications.
• Medical grade – ACS grade IPA of 99.5% purity or greater for medical device cleaning.
• Electronics grade – Ultra high 99.9%+ purity IPA intended for PCB and semiconductor cleaning. May contain additives for enhanced performance.

For most effective PCB cleaning with minimal residue or potential for shorts, electronics-grade IPA is strongly recommended. Anything less than 90% purity risks leaving detectable residues behind. 99% reagent grade may be suitable for less demanding hobbyist cleaning.

Cleaning Methods

IPA can be applied to PCBs in several ways:

IPA Wipes

Pre-saturated wipes provide a convenient method of applying IPA for PCB cleaning. The textured surface of wipes can help displace contaminants. The wipe material must be lint-free to avoid leaving behind fibers.

Wipes should use high purity electronics grade IPA. Kimtech and Chemtronics are leading brands. Wipes with additives may be more effective at dissolving harder-to-remove fluxes.

Spray Bottles

Bottles containing pure IPA allow direct application via spraying onto PCBs. The spray should be of fine mist consistency for most effective cleaning. Spraying works well for easily accessible board areas.

Avoid using spray bottles that might have contained other solvents to prevent chemical cross-contamination. Bottles specifically sold for electronic cleaning applications are ideal.

Immersion Baths

For more aggressive full board cleaning, PCBs can be fully immersed in an IPA bath. Ultrasonic agitation can supplement soaking to provide impulsive energy to fully dissolve surface contaminants. Cleanliness of the bath is paramount.

Immersion typically makes use of re-circulating solvent feed systems. Fresh make-up IPA is periodically added while dissolved contaminants are filtered out.

Brushing

For stubborn, caked-on contaminants, agitation by manual brushing may be necessary. Soft bristle brushes with either natural or nylon bristles are recommended. Brushing should be done minimally and with light force to avoid damaging PCB components or traces.

Vacuum Extraction

Vacuum extraction or suction systems can be useful for removing IPA and dissolved contaminants from intricate or confined PCB assemblies after immersion or spraying. Vacuum systems with anti-static attachments are ideal for eliminating any electrostatic charges that could damage static-sensitive components.

Vapor Phase

In vapor phase cleaning, components are exposed to IPA vapors condensing from cooled vapor. This creates a continuous “rinse” of pure IPA that leaves no residues. Effective for cleaning confined spaces. Requires vapor phase equipment.

Cleaning Procedure Basics

Here are some general guidelines to follow when cleaning PCBs with isopropyl alcohol:

• Wear nitrile gloves to prevent skin oils from being deposited onto the PCB surface. Ground yourself as needed to prevent electrostatic discharge.
• Select the appropriate IPA grade and cleaning method for the specifics of your board and types of contaminants.
• Only use each wipe or cotton swab on one area of the board to avoid spreading contaminants.
• Apply IPA liberally to dissolve surface contaminants but avoid oversaturating the board as excess IPA may not evaporate fully.
• Let IPA-wetted surfaces dry fully before reactivation. Drying usually takes 1-2 minutes.
• For immersion cleaning, use wash-rinse-dry cycles with fresh IPA for the rinse stage. Multiple rinses may be necessary.
• Dry boards using vacuum extraction, compressed air, or gentle heat below 60°C. Avoid high heat levels that could damage PCB components.
• Visually inspect boards after cleaning to identify any remaining contaminant residues requiring spot cleaning.

Thorough cleaning followed by proper drying helps restore PCBs to like-new condition while avoiding damage from moisture or electrostatic discharge.

Cleaning Products to Avoid

While isopropyl alcohol is ideal for safely and effectively cleaning electronics, some solvents must be avoided:

• Acetone – Too aggressive. Can dissolve components and damage plastic parts. Highly flammable.
• Methanol – High water solubility promotes electrical shorts. Toxic.
• Ethanol – High water solubility increases corrosion potential during drying stage.
• Toluene, xylene – Slow evaporation makes complete drying difficult. Health hazards.
• Methylene chloride – Aggressive on plastics with lengthy dry times. Toxic.
• Water – Promotes corrosion, electrical shorts. Conductive residue may remain after drying.
• Abrasives – Never use abrasive cleaners or scouring pads. Risks scratching PCB surface.

While marketed as electronics cleaners, some commercial products contain hazardous solvents like those above or have inadequate purity levels. Verify composition if not using pure electronics grade IPA.

Cleaning Considerations by PCB Class

The specifics of the PCB cleaning process may vary somewhat depending on the class or fabrication details of the board:

Class 1 PCBs

Consumer electronics with minimal component density and larger features require less stringent cleaning. Reagent grade IPA is often sufficient for superficial dust and flux removal.

Class 2 PCBs

More involved cleaning is recommended for these intermediate density PCBs. Tighter tolerances and smaller components necessitate medical or electronics grade IPA with immersion, wiping, or spraying application.

Class 3 PCBs

Very high density boards with extremely fine features and tight thermal budgets found in aerospace, military, and telecommunications applications demand the highest purity IPA grades, more extensive cleaning methods, and extra care in drying these static-sensitive components.

High Frequency PCBs

Microwave and RF PCBs require ultra-clean surfaces to prevent signal loss at interfaces between closely spaced components. Multiple rinse stages are advised.

Coated PCBs

Conformal coatings protect PCBs but also necessitate removing coating residues when cleaning boards. This may require more aggressive techniques combined with clean IPA rinses.

Flexible PCBs

The thinner flexible substrate is more prone to swelling or permeation issues during cleaning. Shorter duration immersion cycle are advised for flexible PCBs.

Matching the IPA grade and cleaning technique to the specific contamination concern and board construction best balances effectiveness against risks.

DIY Cleaning Considerations

While professional PCB cleaning services are ideal for mission-critical electronics, hobbyists can clean their PCBs at home using pure IPA. Here are some DIY cleaning tips:

• Carefully remove any conformal coatings using a plastic scraper prior to cleaning. Avoid metallic tools.
• Use nitrile or latex gloves to prevent skin oil transfer. Disposable gloves are fine.
• Kimtech wipes and cotton swabs are readily available and lint-free. Cut swabs in half for better access to confined spaces.
• Reagent grade 99% IPA from a chemical supply retailer is reasonably affordable for home use.
• Avoid liquid spills. Use an eyedropper for applying small amounts of IPA.
• Allow a full 24 hours for IPA residues to evaporate at room temperature after cleaning.
• Visually inspect for complete dryness and any remaining contaminants. Use bright lighting.
• Proper handling, work surface grounding, and ESD precautions are essential when cleaning sensitive or high-speed PCBs at home.

With some care, hobbyists can successfully clean most PCBs at home using readily available IPA grades and tools. For homebrew cleaning of rare, expensive or mission critical electronics, consider outsourcing cleaning to reduce risks.

Health and Safety Considerations

Isopropyl alcohol is classified as a volatile organic compound (VOC) and flammable liquid. Proper safety precautions are important when handling and using IPA for cleaning:

Ventilation

Use IPA cleaning solvents only in well-ventilated areas to prevent vapor buildup. Avoid breathing fumes.

Eye and Skin Contact

Avoid contact with skin or eyes. IPA can cause dryness and irritation with repeated exposure. Use protective nitrile gloves and safety glasses.

Ingestion

Do not ingest IPA. It is toxic when swallowed. Use care when handling IPA near food or drinks.

Fire Hazard

IPA is flammable, with flash point of 53°F. Avoid open flames and excessive heat when cleaning with IPA.

Static Charge Accumulation

IPA is not electrically conductive but its volatility can produce static charges during use that may damage electronics. Use proper grounding procedures.

Waste Disposal

Collect used IPA cleaning solvents for proper waste disposal to avoid environmental contamination. Isopropyl alcohol is readily biodegradable.

With sound handling practices, IPA can be used safely and effectively for cleaning electronics. Always check product SDS for detailed safety information.

FAQs About Using Alcohol to Clean PCBs

Q: Does IPA remove all types of flux?

IPA is highly effective at dissolving and removing most common rosin, water-soluble, and no-clean flux residues from PCB assemblies. For highly stubborn baked-on no-clean fluxes, saponifiers added to IPA can help boost cleaning action.

Q: How often should I clean PCBs?

For consumer electronics, occasional cleaning to remove dust buildup may be sufficient. In industrial settings, scheduled maintenance cleaning every 1-2 years is typical. PCBs in demanding environments like mining may need cleaning every 3-6 months.

Q: Can I use a toothbrush to scrub PCBs?

No, you should never scrub PCBs as this can damage delicate components. At most, use very soft bristle brushes with gentle action to dislodge particles if wiping alone is ineffective. Acid brushes work well.

Q: Is water or soap okay for removing grime from PCBs?

Water should be avoided for PCB cleaning since any residues left after drying can create electrical shorts and corrosion. Soaps also leave unwanted residues. Use only pure solvents like high-purity IPA.

Q: How do I dry PCBs quickly after alcohol cleaning?

You can speed PCB drying by using compressed air, vacuum suction, gentle heating, or desiccant chambers after the final rinse stage. Avoid excessive heat to prevent component damage. Ensure boards are fully dry before reactivating system.

Conclusion

Cleaning accumulated dust, grease, flux, and other contaminants from printed circuit boards is essential for preventing performance issues and ensuring long-term reliability of electronics. Among available solvent choices, isopropyl alcohol offers an optimal balance of being able to effectively dissolve and displace a wide array of PCB contaminants while avoiding any conductive or corrosive residues after evaporation.

With proper handling, even high purity grades of IPA pose minimal health and fire hazards. For optimal results, the IPA grade, cleaning method, rinsing approach and drying technique should be matched to the specifics of the PCBs and degree of contamination. Reasonable care enables even hobbyists to safely and successfully clean most PCBs at home using pure IPA. For rare or mission-critical electronics, professional cleaning services are recommended to limit risks of damage. With appropriate procedures, isopropyl alcohol provides a versatile, efficient and cost-effective solution for keeping PCBs in clean, reliable operating condition.