Printed circuit boards (PCB) need routine cleaning during manufacturing, rework and maintenance to remove contaminants like flux residues, dust, grease and other particles. Choosing the right circuit board cleaner is important to effectively remove contamination without damaging the board. This article discusses different types of PCB cleaners, how to select the appropriate one, cleaning methods and best practices.
Need for Cleaning Circuit Boards
Following are some key reasons for cleaning PCBs:
- Remove corrosive flux residues after soldering – These can degrade performance over time if not cleaned properly. No-clean flux also leaves minor residues.
- Eliminate dust, dirt and particulates – These can lead to short circuits or affect heat dissipation.
- Remove grease, oil and silicones – They can coat test pads or socket contacts hindering detection.
- Take off adhesive residues – From stickers or labels which may insulate traces.
- Get rid of oxidized copper and tarnishing – Can negatively impact soldering if not removed.
- Correct field failures by cleaning – Contamination is a common cause of field failures.
- Prepare boards for conformal coating – Coating adhesion relies on a pristine PCB surface.
- Allow inspection of boards – Cleaning facilitates easier visual inspection.
Proper cleaning is thus vital both during assembly and for maintenance of operational PCBs. Using the right cleaner avoids issues like corrosion while removing residues.
Properties of a Good PCB Cleaner
An effective PCB cleaner exhibits following desirable properties:
- Cleaning ability – Should thoroughly remove fluxes, pastes, greases, particles.
- Material compatibility – Should not damage board substrate, components, coatings.
- Residue-free cleaning – Should not leave any cleaner residues after rinsing.
- Quick drying – Fast evaporation allows quicker processing.
- Non-flammability – Important for safety given organic solvents.
- Minimal odor – Reduces environmental impact.
- Reusability – Allows multiple cleaning cycles improving economy.
- Accessibility – Easily available from supply sources.
- Low cost – Important considering regular use during production.
Types of Circuit Board Cleaners
Some common options for PCB cleaners include:
Aqueous Cleaners
- Water-based cleaners with detergents, pH modifiers.
- Non-flammable, biodegradable, usable at room temperature.
- May leave water residues requiring extra drying.
- Poor at removing some organic residues.
Semi-Aqueous Cleaners
- Contain mild solvents in water for added cleaning ability.
- Evaporate faster than aqueous cleaners.
- Less flammable than solvents. May still require rinsing.
Solvent Cleaners
- Strong organic solvents like acetone, isopropyl alcohol (IPA), methanol etc.
- Very effective at removing organic flux, greases, oils.
- Fast evaporation at room temperature. Highly flammable.
- Some chlorinated solvents like 1,1,1-Trichloroethane available but being phased out.
Terpene Cleaners
- Derived from pine, orange oils. Non-hazardous, non-flammable.
- Biodegradable but slower to evaporate than solvents.
- Weaker cleaning ability than solvents. Mostly used with frequent cleaning.
Engineered Cleaners
- Uses surfactants for cleaning combined with corrosion inhibitors.
- Provides both cleaning and temporary corrosion protection.
- Used as benchtop spray or inline cleaners.
Selecting the Right Circuit Board Cleaner
Selection criteria for PCB cleaners depends on application:
During Manufacturing
- Strongest cleaning ability preferred to remove all residues and maximize first-pass yield.
- Quick evaporation allows faster processing. Flammability addressed by safe storage.
- Low cost important as used routinely in every batch.
- Residue testing essential to avoid any cleaner vestiges.
Field Maintenance/Rework
- Strong cleaners used but with emphasis on safety. Accessibility in aerosol cans useful.
- Non-flammable, non-hazardous cleaners may be mandated.
- Cleaners with corrosion inhibitors help protect cleaned boards.
- Evaporation time and residues lesser concerns with one-off usage.
Cleaning Methods for Circuit Boards
Some ways PCB cleaners are applied:
Manual Cleaning
- Cleaner applied manually using brushes, swabs, wipes.
- Used for prototype, on-demand cleaning.
- Labor intensive but good for limited, selective cleaning.
Ultrasonic Bath
- PCBs immersed in cleaning solution tank which is ultrasonically agitated.
- Provides consistent, thorough cleaning. Particularly good for odd board shapes.
- Allows high volume batch cleaning.
Spray In Air
- Cleaner sprayed using nozzles onto PCB held in a fixture.
- Automated using a conveyorised system with multiple spray/rinse stations.
- Facilitates selective cleaning of areas. Fast.
Vapour Phase Cleaning
- PCB exposed to cleaning solvent vapours which condense selectively on cooler residues dissolving them.
- Very effective at removing even microscopic surface contaminants.
- No residues left from drying. Expensive equipment.
Dishwasher type Batch Cleaners
- PCBs loaded in a cabinet with spray nozzles.
- Automated cleaning cycles with various solutions and rinses.
- Moderate throughput suitable for small batches.
Water-based vs Solvent Circuit Board Cleaners
Water-based cleaners are safer and non-flammable but slower at removing organics while solvents evaporate faster but are hazardous. Hybrid semi-aqueous offer a compromise. Typical comparison:
| Parameter | Water-based | Semi-aqueous | Solvent-based |
|---|---|---|---|
| Cleaning Ability | Medium | Medium-High | Very High |
| Drying Time | High | Medium | Very Low |
| Flammability | None | Low | High |
| Performance on Organics | Medium | Medium-High | Excellent |
| Performance on Ionics | Excellent | Medium | Low |
| Environmental Impact | Non-hazardous | Marginally hazardous | Hazardous |
| Health/Safety | Safe | Use with caution | Risk of burns, inhalation |
| Residues after Cleaning | High chance of water residues | Low chance | None usually |
| Typical Usage | Light cleaning | General purpose | Strong contamination |
Key Considerations for Choosing Circuit Board Cleaner
- Type and extent of contamination to be removed
- Allowable flammability based on usage environment
- Evaporation rate and potential for residue formation
- Effect on board materials like plastics, coatings
- Whether ulrasonic cleaning is to be used
- Environmental regulations for effluents and disposal
- Health hazards to operators during use
- Cost, availability, reusability factors
Careful selection of the right cleaner and cleaning process ensures thorough contaminant removal without any detrimental effects on the boards or personnel.
Best Practices for Cleaning Circuit Boards
Some good practices when cleaning PCB assemblies:
- Test cleaner compatibility on a non-critical area first.
- Follow manufacturer recommended dilutions and usage guidelines.
- Apply cleaner using brushes, swabs for selective cleaning.
- Use higher temperatures to improve cleaner action but within limits.
- Rinse boards thoroughly with clean water or solvent post-cleaning.
- Dry boards immediately after rinsing using compressed air flow.
- Allow sufficient cleaning time for immersed or sprayed boards.
- Use cleaning fixtures to access difficult areas like connectors.
- Wear nitrile gloves to prevent skin contact and contamination.
- Ensure the cleaner is not expired and container is sealed properly after use.
Properly implementing the material and equipment manufacturers’ instructions helps maximize cleaning efficacy while minimizing any detrimental effects.
Troubleshooting Cleaning Issues
Some common PCB cleaning problems and remedies:
| Issue | Possible Causes | Corrective Actions |
|---|---|---|
| Incomplete cleaning | Too dilute cleaner concentration | Increase cleaner strength |
| Insufficient cleaning time | Use longer immersion time | |
| Low cleaning temperature | Increase solution temperature | |
| Excessive contamination | Do multiple-stage cleaning | |
| Cleaner leaving residues | Low rinsing | Rinse more thoroughly with water/solvent |
| Cleaner has surfactants | Select cleaner without surfactants | |
| Evaporation issues | Blow dry boards instead of air drying | |
| Corrosion observed after cleaning | No corrosion inhibitors in cleaner | Use cleaners containing inhibitors |
| Water residues left after rinsing | Dry immediately after rinsing | |
| Discoloration of boards | Chemical attack by cleaner | Reduce concentration and exposure time |
| Overexposure to cleaner | Optimize cleaner application parameters |
Careful inspection of the cleaned boards reveals most cleaning issues for troubleshooting based on board appearance and testing.
Conclusion
PCB cleaning is a critical process needing careful selection of the right chemistry and method. Aqueous, semi-aqueous and solvent-based cleaners each have specific strengths and weaknesses. Usage environment, board materials, residue tolerance, cost and environmental factors guide the cleaner choice. Following manufacturer recommendations and industry best practices for parameters like concentration, temperature and rinsing while testing on non-critical boards ensures effective contaminant removal without board or personnel hazards. Cleaning validation using ionic residue testing confirms the cleaning process is working adequately. With the growing complexity of boards requiring high first-pass yields, proper cleaning is becoming even more indispensable for quality and reliability.
FAQs
Q1. Can isopropyl alcohol (IPA) be used to clean circuit boards?
Yes, isopropyl alcohol is an excellent general purpose cleaner for PCBs due to its strong solvency power, rapid evaporation and low cost. Care must be taken regarding its flammability.
Q2. What is the ideal PCB cleaning temperature?
For water-based cleaners, 45-55°C is typically used. Some engineered cleaners work well at room temperature. Solvent cleaners are also usually used cold.
Q3. When should ultrasonic cleaning be used for PCBs?
Ultrasonic cleaning effectively removes particulate contamination and cleans blind vias and odd-shaped boards. It should be used as needed based on inspection.
Q4. What is a quick test to verify post-cleaning board cleanliness?
Using reverse osmosis/deionized water and measuring resistivity provides a good quick cleanliness verification method. High resistivity indicates the board is clean.
Q5. How can one improve the drying rate after aqueous cleaning?
Use of higher water temperatures, spray/air impingement rinses and immediate forced hot air drying after rinsing improves drying rate and prevents water residues.
