HOW TO CLEAN PRINTED CIRCUIT BOARDS

 

Introduction to PCB Cleaning

Printed Circuit Boards (PCBs) form the backbone of almost every electronic device we use today. From smartphones and computers to industrial equipment and medical devices, PCBs are essential components that require proper maintenance to ensure optimal performance and longevity. One of the most critical aspects of PCB maintenance is cleaning, which removes contaminants that can lead to short circuits, corrosion, and ultimately, device failure.

The importance of proper PCB cleaning cannot be overstated. Contamination on PCBs can come from various sources including flux residues from the soldering process, dust, moisture, oils from fingerprints, and environmental pollutants. These contaminants can cause a range of problems:

• Decreased insulation resistance between conductors
• Formation of dendritic growth and electrochemical migration
• Corrosion of metal components
• Poor adhesion during conformal coating or potting
• Interference with thermal dissipation
• Aesthetically unpleasing appearance that may concern customers

This comprehensive guide will walk you through everything you need to know about PCB cleaning, from understanding different types of contaminants to selecting the appropriate cleaning methods and implementing effective cleaning protocols for various applications.

Understanding PCB Contamination

Types of Contaminants

Before diving into cleaning methods, it's essential to understand the different types of contaminants that can affect PCBs:

1. Flux Residues

Flux is used during the soldering process to remove oxides from metal surfaces and facilitate proper solder joints. However, after soldering, flux residues often remain on the PCB. These residues can be:

• Rosin-based flux residues: Traditional fluxes containing natural rosin acids
• Water-soluble flux residues: Typically containing organic acids and activators
• No-clean flux residues: Designed to leave minimal, supposedly benign residues
• Synthetic flux residues: Modern alternatives to rosin fluxes

Even "no-clean" flux residues can be problematic in high-reliability applications, as they may become conductive when exposed to moisture or high humidity.

2. Particulate Matter

Tiny particles can accumulate on PCBs during manufacturing, handling, and operation:

• Dust and fibers: From the environment or clothing
• Metal shavings: From drilling, cutting, or mechanical assembly processes
• Solder balls: Tiny spheres of solder that can break free during the soldering process
• Component debris: Small fragments from components or packaging materials

3. Ionic Contaminants

Ionic contaminants are particularly dangerous because they can cause electrochemical migration when moisture is present:

• Halides: Including chlorides and bromides, often from flux activators
• Sodium and potassium salts: From fingerprints or process water
• Acid residues: From etching or cleaning processes
• Metal ions: Copper, tin, lead, or other metals from the manufacturing process

4. Organic Contaminants

Various organic substances can contaminate PCBs:

• Fingerprint oils: Natural oils from human skin
• Lubricants: From assembly equipment or components
• Adhesive residues: From tapes, labels, or component attachment
• Release agents: Used in molding processes

5. Environmental Pollutants

PCBs operating in harsh environments may be exposed to:

• Sulfur compounds: Can cause silver and copper sulfidation
• Nitrogen oxides: Can combine with moisture to form acids
• Salt spray: In marine or coastal environments
• Industrial chemicals: In factory or processing plant environments

Impact of Contamination on PCB Performance

The presence of contaminants can lead to several failure mechanisms:

Electrochemical Migration (ECM)

When ionic contaminants are present along with moisture, metal ions can migrate from one conductor to another under an electrical bias, eventually forming conductive dendrites that cause short circuits. This process accelerates with:

• Higher humidity
• Higher voltage differentials
• Smaller conductor spacing
• Greater concentration of ionic contaminants

Surface Insulation Resistance (SIR) Reduction

Contaminants can reduce the insulation resistance between conductors, leading to increased leakage currents and potential malfunction, especially in high-impedance circuits.

Parasitic Leakage Currents

Similar to SIR reduction, contaminants can create unwanted current paths that may interfere with sensitive analog circuits or increase power consumption.

Corrosion

Many contaminants, especially when combined with moisture, can initiate corrosion of metal parts including:

• Copper traces
• Component leads
• Connector contacts
• Bond pads

Thermal Issues

Contaminant layers can act as thermal insulators, preventing proper heat dissipation from components, which may lead to overheating and reduced reliability.

PCB Cleaning Assessment

Before cleaning a PCB, it's essential to determine if cleaning is necessary and what level of cleanliness is required.

When Cleaning is Necessary

High-Reliability Applications

PCBs used in these applications typically require thorough cleaning:

• Medical devices: Implantable devices, life-support equipment
• Aerospace and military equipment: Satellite systems, guidance systems
• Automotive safety systems: ABS, airbag controllers
• Industrial control systems: Critical process controllers

Long-Life Products

Products expected to operate for many years should have clean PCBs to prevent long-term degradation:

• Infrastructure equipment: Telecommunication systems, traffic control
• Industrial machinery: Factory automation systems
• Building systems: Fire alarm systems, security systems

Harsh Environment Operation

PCBs exposed to challenging conditions need thorough cleaning:

• High humidity environments
• Marine or coastal locations
• Dusty industrial settings
• Temperature cycling applications

Subsequent Assembly Processes

Cleaning is often necessary when the PCB will undergo additional manufacturing steps:

• Conformal coating application
• Potting or encapsulation
• Wire bonding
• Additional soldering operations

When Cleaning May Be Optional

Some applications may not require thorough cleaning:

• Consumer electronics with short expected lifespans
• Non-critical applications in controlled environments
• Products using genuine no-clean processes throughout
• Designs with wide conductor spacing in dry environments

Cleanliness Assessment Methods

Various methods exist to assess PCB cleanliness before and after cleaning:

Visual Inspection

The simplest method involves examining the PCB under proper lighting:

• Naked eye inspection: Can detect obvious contamination
• Magnification: 5-10x magnification can reveal flux residues and particulates
• UV light inspection: Some contaminants fluoresce under UV light

Contact Angle Measurement

This method assesses the surface tension by measuring how water droplets bead on the surface:

• Low contact angle: Indicates hydrophilic surface, possibly with ionic contaminants
• High contact angle: Indicates hydrophobic surface, possibly with organic contaminants

Solvent Extract Conductivity Testing

This involves:

1. Washing the PCB with a solvent mixture
2. Measuring the ionic content of the resulting solution
3. Calculating contamination levels based on board surface area

Ion Chromatography (IC)

More sophisticated than conductivity testing, IC can identify specific ionic species present on the PCB.

Surface Insulation Resistance (SIR) Testing

SIR testing measures the resistance between adjacent conductors under elevated temperature and humidity conditions, which can reveal the presence of potentially harmful contaminants.

Pre-Cleaning Considerations

Before beginning the cleaning process, several factors must be considered to ensure effective cleaning without damaging the PCB or components.

Component Compatibility

Not all electronic components can withstand all cleaning methods. Consider:

Temperature Sensitivity

• Plastic components: May deform at elevated temperatures
• Batteries: May be damaged by heat
• LCD displays: May be permanently damaged by excessive heat
• Temperature-sensitive ICs: Some components have strict maximum temperature limits

Chemical Compatibility

Components that may be damaged by certain cleaning chemicals include:

• Unsealed electrolytic capacitors: Can absorb cleaning fluids
• Unsealed switches: May have lubricants washed away
• Potentiometers: Internal lubricants may be affected
• Certain plastics: May be attacked by aggressive solvents
• Rubber seals: May swell or deteriorate with solvent exposure

Mechanical Sensitivity

Some components may be damaged by mechanical cleaning methods:

• BGA packages: May be damaged by aggressive brushing
• Wire bonds: Extremely fragile
• MEMS devices: Contain delicate mechanical structures
• Connectors with delicate contacts

PCB Material Compatibility

The PCB substrate itself must be compatible with the cleaning method:

• FR-4: Generally resistant to most cleaning methods
• Flexible circuits: May absorb solvents or be damaged by aggressive mechanical cleaning
• High-frequency substrates: Some specialized substrates may be affected by certain solvents
• Paper-phenolic boards: May absorb water and warp

Conformal Coating Considerations

If the PCB has a conformal coating, consider:

• Coating type: Acrylic, urethane, silicone, epoxy, or parylene
• Solvent resistance: Some coatings dissolve in certain solvents
• Mechanical resistance: Some coatings are easily scratched

Environmental and Safety Considerations

Cleaning processes should consider:

• Waste disposal regulations: For used cleaning fluids
• Workplace exposure limits: For solvent vapors
• Fire and explosion hazards: With flammable solvents
• Environmental impact: VOC emissions, ozone depletion potential

Pre-Cleaning Preparation Steps

Before cleaning, take these preparatory steps:

1. Documentation review: Check manufacturer guidelines for components
2. Test cleaning: On a sample board if possible
3. Component protection: Mask sensitive components if necessary
4. Connector protection: Cover or seal connectors if needed
5. Parts removal: Remove batteries or other sensitive parts if possible
6. ESD protection: Set up proper ESD controls for the cleaning area

PCB Cleaning Methods and Technologies

Various cleaning technologies are used for PCBs, each with its own advantages and limitations.

Manual Cleaning Methods

Brush Cleaning

This involves using brushes with cleaning solvents:

• Soft brushes: For general cleaning of robust boards
• ESD-safe brushes: To prevent static damage
• Specialized shapes: For cleaning under and around components

Best practices:

• Use natural or ESD-safe synthetic bristles
• Apply minimal pressure to avoid component damage
• Brush in line with components rather than across them
• Use fresh solvent regularly

Wipe Cleaning

Using lint-free wipes with appropriate solvents:

• Microfiber cloths: For general wiping
• Lint-free wipes: To avoid leaving fibers
• Pre-moistened wipes: With controlled solvent content

Best practices:

• Use minimal pressure
• Change wipes frequently
• Wipe in one direction rather than circular motions
• Start from the cleanest area and move toward dirtier areas

Cotton Swab Application

For precision cleaning of small areas:

• Wooden sticks: Traditional but may shed splinters
• Plastic sticks: Less likely to shed particles
• Foam-tipped swabs: For sensitive surfaces

Best practices:

• Use high-quality, lint-free swabs
• Apply minimal pressure
• Rotate the swab while using to present a clean surface
• Dispose of used swabs immediately to prevent cross-contamination

Automated Cleaning Systems

Ultrasonic Cleaning

Uses high-frequency sound waves to create microscopic bubbles that implode against surfaces, dislodging contaminants:

• Frequency ranges: Typically 25-40 kHz for PCBs
• Power levels: Must be controlled to prevent component damage
• Temperature control: Usually 40-60°C for optimal cleaning

Advantages:

• Excellent for removing stubborn flux residues
• Can clean under low-standoff components
• Very effective for through-hole assemblies

Limitations:

• May damage sensitive components like MEMS devices
• Not suitable for water-sensitive components unless using non-aqueous solutions
• Requires thorough rinsing and drying

Spray-in-Air Systems

These systems spray cleaning solution onto PCBs:

• Pressure ranges: Typically 0.5-3 bar
• Spray patterns: Various nozzle configurations
• Multiple stages: Often combined with rinsing and drying stages

Advantages:

• Good for high-volume production
• Effective for removing most flux residues
• Relatively quick process

Limitations:

• May not clean effectively under very low-standoff components
• Shadow effects can leave uncleaned areas
• Higher initial investment cost

Immersion Cleaning

Involves submerging PCBs in cleaning solutions, often with agitation:

• Static immersion: Simple soaking in solvent
• Agitated immersion: With mechanical movement or bubbling
• Multi-stage immersion: Moving through different solutions

Advantages:

• Good penetration under components
• Gentle on delicate assemblies
• Effective for hard-to-reach areas

Limitations:

• May require longer cleaning times
• Can be difficult to remove particulates without agitation
• Cleaning fluid becomes contaminated over time

Vapor Phase Cleaning

Uses the condensation of hot solvent vapor to clean PCBs:

• Boiling solvents: Create pure solvent vapor
• Cooling PCBs: Cause vapor to condense on surfaces
• Condensed solvent: Dissolves contaminants and drains back to boil sump

Advantages:

• Uses fresh, distilled solvent for each cleaning cycle
• Very effective for removing flux residues
• Minimal mechanical stress on components

Limitations:

• Limited to certain solvent types
• Not as effective for particulate removal
• Higher energy consumption

Specialized Cleaning Methods

Plasma Cleaning

Uses ionized gas to remove organic contaminants:

• Gas types: Oxygen, argon, nitrogen, hydrogen mixtures
• Vacuum chambers: Typically operate at reduced pressure
• RF energy: Creates the plasma state

Advantages:

• Extremely effective for removing organic residues
• No liquid waste
• Can reach molecular-level cleanliness

Limitations:

• Expensive equipment
• Batch process with limited throughput
• May not remove all types of contaminants

CO₂ Snow Cleaning

Uses compressed carbon dioxide expanded through a nozzle to form snow particles:

• Mechanical action: Snow particles dislodge particulates
• Thermal shock: Causes contaminants to fracture
• Solvent action: CO₂ can dissolve some organic contaminants

Advantages:

• No residue (CO₂ sublimates to gas)
• Environmentally friendly
• Effective for particle removal

Limitations:

• Less effective for ionic contaminants
• May cause thermal shock to sensitive components
• Requires specialized equipment

Supercritical CO₂ Cleaning

Uses CO₂ in its supercritical state (beyond critical temperature and pressure):

• Solvent properties: Combines properties of liquid and gas
• Additives: Often includes co-solvents for enhanced cleaning
• Pressure vessels: Operates in high-pressure chambers

Advantages:

• Excellent penetration into tight spaces
• No surface tension issues
• Environmentally friendly

Limitations:

• Very expensive equipment
• Limited throughput
• Relatively new technology

Cleaning Agents and Solvents

The choice of cleaning agent significantly affects cleaning efficacy, environmental impact, and safety.

Water-Based Cleaning Solutions

Deionized (DI) Water

Pure water with ions removed:

• Resistivity: Typically >1 MΩ·cm
• pH: Usually near neutral (6.5-7.5)
• Applications: Rinsing after chemical cleaning, cleaning water-soluble flux

Advantages:

• Environmentally friendly
• Non-toxic
• Inexpensive
• Non-flammable

Limitations:

• Not effective alone for non-water-soluble contaminants
• Requires thorough drying to prevent corrosion
• May cause issues with water-sensitive components

Aqueous Detergent Solutions

Water with added detergents and other additives:

• Saponifiers: Convert oils to water-soluble soaps
• Surfactants: Reduce surface tension for better wetting
• Buffers: Maintain optimal pH
• Corrosion inhibitors: Prevent metal corrosion

Advantages:

• Effective for many contaminants
• Relatively low toxicity
• Lower cost than many solvents
• Non-flammable

Limitations:

• Require thorough rinsing
• May leave residues if rinsing is inadequate
• Waste treatment may be required

Solvent-Based Cleaning Agents

Alcohols

Common alcohols used in PCB cleaning:

• Isopropyl alcohol (IPA): Most common, good solvent for many flux residues
• Ethanol: Less aggressive than IPA, often used in mixtures
• Denatured alcohol: Ethanol with additives to prevent consumption

Properties:

• Moderate solvency for many organics
• Relatively low toxicity
• Fast evaporation
• Flammable

Typical applications:

• Manual cleaning of small areas
• Removal of light flux residues
• Final cleaning after more aggressive cleaning

Engineered Solvents

Modern replacements for older, environmentally problematic solvents:

• Hydrofluoroethers (HFEs): Low global warming potential alternatives
• Hydrofluorocarbons (HFCs): Similar to HFEs but with different properties
• Modified alcohols: Enhanced alcohol formulations

Properties:

• Tailored solvency for specific contaminants
• Generally low toxicity
• Many have low global warming potential
• Some are non-flammable

Typical applications:

• Vapor phase cleaning
• Precision cleaning
• High-reliability applications

Hydrocarbon Solvents

Petroleum-derived solvents:

• Aliphatic hydrocarbons: Like hexane and heptane
• Terpenes: Plant-derived hydrocarbons like d-limonene
• Mixed hydrocarbon blends: Formulated for specific applications

Properties:

• Good solvency for oils and greases
• Moderate to high flammability
• Relatively slow evaporation
• Varying levels of toxicity

Typical applications:

• Removal of heavy oils and greases
• Cleaning before conformal coating
• Batch immersion cleaning

Cleaning Agent Selection Table

Contaminant Type
Water-Based Cleaners
Alcohols
Engineered Solvents
Hydrocarbons
Rosin Flux
Limited effectiveness
Moderately effective
Highly effective
Effective
Water-Soluble Flux
Highly effective
Moderately effective
Limited effectiveness
Limited effectiveness
No-Clean Flux
Limited effectiveness
Moderately effective
Effective
Effective
Fingerprint Oils
Effective with detergents
Effective
Highly effective
Highly effective
Dust/Particulates
Effective with agitation
Moderately effective
Moderately effective
Moderately effective
Ionic Contaminants
Highly effective
Limited effectiveness
Limited effectiveness
Ineffective
Adhesive Residues
Limited effectiveness
Limited effectiveness
Effective for some
Highly effective

Environmental and Safety Considerations for Cleaning Agents

Environmental Impact Factors

Cleaning Agent Type
Ozone Depletion Potential
Global Warming Potential
VOC Content
Biodegradability
Deionized Water
None
None
None
Complete
Aqueous Detergents
None
Low
Low-Medium
Medium-High
Isopropyl Alcohol
None
Low
High
Medium
Engineered Solvents (HFE)
None
Low-Medium
Low
Low
Engineered Solvents (HFC)
None
Medium-High
Low
Low
Hydrocarbon Solvents
None
Low
High
Low-Medium

Safety Considerations

Cleaning Agent Type
Flammability
Inhalation Hazard
Skin Contact Hazard
Recommended PPE
Deionized Water
None
None
None
General lab protection
Aqueous Detergents
None
Low
Mild irritant
Gloves, eye protection
Isopropyl Alcohol
High
Moderate
Drying/irritant
Gloves, eye protection, ventilation
Engineered Solvents (HFE)
Low-None
Low
Low
Gloves, eye protection
Engineered Solvents (HFC)
Low-None
Low
Low
Gloves, eye protection
Hydrocarbon Solvents
High
Moderate-High
Irritant/defatting
Gloves, eye protection, ventilation

PCB Cleaning Procedures

General Cleaning Process Flow

A typical PCB cleaning process follows these steps:

1. Pre-cleaning assessment
   • Identify contaminants
   • Determine component compatibility
   • Select appropriate cleaning method and agents
2. Preparation
   • Protect sensitive components if necessary
   • Remove any detachable parts that shouldn't be cleaned
   • Prepare cleaning equipment and solutions
3. Gross contamination removal
   • Remove large particulates or excess flux
   • May use mechanical methods like brushing or compressed air
4. Main cleaning process
   • Apply selected cleaning method (immersion, spray, ultrasonic, etc.)
   • Use appropriate cleaning agent
   • Control time, temperature, and agitation parameters
5. Rinsing
   • Remove cleaning agent and dissolved contaminants
   • May require multiple rinse stages
   • Final rinse often with high-purity water or volatile solvent
6. Drying
   • Remove all moisture or residual solvents
   • May use air drying, oven drying, or vacuum drying
7. Post-cleaning inspection
   • Visual inspection
   • Possible analytical testing
   • Documentation of results
8. Packaging
   • Place in appropriate clean packaging
   • Add desiccant if necessary
   • Label with cleaning information if required

Specific Procedures for Different Contaminants

Flux Residue Cleaning

1. For rosin-based flux:
   • Pre-clean with isopropyl alcohol to remove bulk residue
   • Main cleaning with engineered solvent or hydrocarbon cleaner
   • Rinse with fresh solvent
   • Air dry or forced air dry
2. For water-soluble flux:
   • Pre-clean with warm deionized water
   • Main cleaning with aqueous cleaning solution at 55-65°C
   • Multiple rinses with deionized water
   • Thorough drying in oven or with forced air
3. For no-clean flux (when cleaning is required):
   • Pre-clean with isopropyl alcohol
   • Main cleaning with specialized no-clean flux remover
   • Rinse with fresh solvent
   • Air dry or forced air dry

Particulate Contamination Cleaning

1. For dust and loose particles:
   • Start with compressed air (clean, dry, oil-free)
   • Followed by brush cleaning with appropriate solvent
   • Rinse if necessary
   • Air dry
2. For adherent particles:
   • Ultrasonic cleaning in appropriate solution
   • Spray rinse to remove dislodged particles
   • Final rinse with clean solvent or deionized water
   • Thorough drying

Ionic Contamination Cleaning

1. For water-soluble ionic contaminants:
   • Multiple cleaning cycles with deionized water
   • Possibly add weak acid or base depending on contaminant
   • Multiple rinses with high-purity deionized water
   • Thorough drying
2. For ionic residues in organic matrices:
   • First remove organic material with appropriate solvent
   • Follow with aqueous cleaning for ionic residues
   • Multiple rinses with deionized water
   • Thorough drying

Oil and Grease Cleaning

1. For light oils:
   • Isopropyl alcohol cleaning
   • Possible ultrasonic enhancement
   • Rinse with fresh solvent
   • Air dry
2. For heavy oils and greases:
   • Pre-clean with hydrocarbon solvent
   • Main cleaning with stronger degreaser or detergent solution
   • Multiple rinses
   • Thorough drying

Specialized PCB Cleaning Procedures

High-Density PCB Cleaning

For PCBs with fine-pitch components or BGA packages:

1. Preparation:
   • Ensure cleaning agent can penetrate under low-standoff components
   • Consider using engineered solvents with low surface tension
2. Process:
   • Prefer spray-under-immersion or ultrasonic cleaning
   • Use higher temperatures within safe limits to reduce surface tension
   • Extend cleaning time to allow penetration
   • Consider vacuum-assisted processes
3. Rinsing and Drying:
   • Multiple rinse cycles
   • Extended drying time or vacuum drying
   • Consider baking at low temperature

Post-Rework Cleaning

After component rework or replacement:

1. Localized Cleaning:
   • Use precision tools to apply solvent only to affected area
   • Protect surrounding areas if necessary
2. Residue Removal:
   • Focus on removing new flux residues
   • Check for any debris from the rework process
3. Testing:
   • Perform spot testing for cleanliness
   • Visual inspection under magnification

Cleaning Before Conformal Coating

Essential for coating adhesion:

1. Thorough Degreasing:
   • Remove all oils and fingerprints
   • Use solvents compatible with the coating material
2. Surface Preparation:
   • Consider plasma cleaning for optimal adhesion
   • Ensure complete removal of all flux residues
3. Final Cleaning:
   • Use high-purity solvents for final wipe
   • Minimize time between cleaning and coating

Drying Methods

Air Drying

Natural evaporation of cleaning agents:

• Ambient air drying: Simple but slow
• Forced air drying: Using filtered air
• Heated air drying: Using warm air streams

Best for:

• Simple assemblies
• Non-water-based cleaning
• Small production volumes

Oven Drying

Using controlled heat to accelerate evaporation:

• Convection ovens: Circulating heated air
• Vacuum ovens: Heat with reduced pressure
• Infrared ovens: Using IR radiation

Parameters:

• Temperature: Typically 60-85°C
• Time: Usually 30-60 minutes
• Air circulation

Best for:

• After aqueous cleaning
• High-volume production
• Thorough drying requirements

Centrifugal Drying

Using centrifugal force to remove liquid:

• Rotation speeds: Typically 300-800 RPM
• Heated options: Often combined with warm air
• Vertical or horizontal axis systems

Best for:

• High-volume production
• After aqueous cleaning
• PCBs with complex geometries

Vacuum Drying

Using reduced pressure to lower evaporation point:

• Pressure levels: Typically 1-10 Torr
• Heated options: Often combined with gentle heat
• Gas backfill: Sometimes uses nitrogen backfill

Best for:

• High-reliability applications
• PCBs with tight spaces
• Water-based cleaning processes

Quality Control and Validation

Cleanliness Testing Methods

Visual Inspection Methods

Basic but essential quality control steps:

• Direct visual inspection: Under good lighting
• Magnified inspection: Using microscopes or magnifiers
• UV inspection: Using ultraviolet light to detect residues

Advantages:

• Quick and non-destructive
• No specialized equipment for basic inspection
• Can detect many gross contamination issues

Limitations:

• Subjective
• Cannot detect non-visible ionic contamination
• May miss contamination under components

Surface Insulation Resistance (SIR) Testing

Measures electrical resistance between adjacent conductors:

• Test patterns: Special test boards or production PCBs
• Conditions: Typically 40°C/90% RH for 168 hours
• Measurements: Resistance values under bias voltage

Standards:

• IPC-TM-650 2.6.3.7
• IPC J-STD-001
• IPC-9201

Interpretation:

• Resistance should remain above 100 MΩ
• Declining resistance indicates harmful contamination

Ionic Contamination Testing

Measures extractable ionic material:

• Methods: Resistivity of Solution (ROSE), static extraction
• Equipment: Automated systems available
• Measurement: Reported in μg NaCl equivalent/in²

Standards:

• IPC-TM-650 2.3.25
• MIL-P-28809
• IPC J-STD-001

Typical limits:

• Military: 1.56 μg NaCl equivalent/in²
• Industrial: 3-5 μg NaCl equivalent/in²
• Consumer: 6-10 μg NaCl equivalent/in²

Ion Chromatography (IC)

Analyzes specific ionic species:

• Sample preparation: Extract board in solution
• Analysis: Separates and quantifies specific ions
• Results: Concentration of each ionic species

Advantages:

• Identifies specific problematic ions
• More detailed than bulk ionic testing
• Can correlate results with failure mechanisms

Limitations:

• Expensive equipment required
• Slower process
• Destructive or semi-destructive sampling

Contact Angle Measurement

Assesses surface energy by measuring water droplet shape:

• Equipment: Goniometer or specialized systems
• Measurement: Angle between droplet and surface
• Interpretation: Lower angles indicate higher surface energy

Applications:

• Verifying cleanliness before conformal coating
• Detecting organic residues
• Assessing cleaning process effectiveness

Cleanliness Standards and Specifications

Industry Standards

Standard
Description
Typical Applications
IPC-CH-65B
Guide to Cleaning of Printed Boards and Assemblies
General guidance for all industries
IPC J-STD-001
Requirements for Soldered Electrical and Electronic Assemblies
General electronics manufacturing
IPC-CC-830
Qualification and Performance of Electrical Insulating Compound for Printed Board Assemblies
Conformal coating applications
MIL-STD-2000
Standard Requirements for Soldered Electrical and Electronic Assemblies
Military and defense electronics
ASTM F22
Standard Test Method for Hydrophobic Surface Films by the Water-Break Test
General surface cleanliness
IEC 61189-5
Test methods for electrical materials, printed boards and other interconnection structures and assemblies
International standard for electronics

Cleanliness Levels

Different industries require different cleanliness levels:

Industry
Typical Ionic Cleanliness Requirement
Common Test Method
Key Concerns
Consumer Electronics
6-10 μg NaCl eq/in²
Visual inspection, spot ROSE testing
Manufacturing cost, throughput
Industrial Electronics
3-5 μg NaCl eq/in²
ROSE testing, SIR sampling
Reliability in varied environments
Automotive
2-4 μg NaCl eq/in²
ROSE testing, SIR, IC
Temperature cycling, vibration resistance
Medical Devices
1.5-3 μg NaCl eq/in²
IC, SIR, visual inspection
Biocompatibility, long-term reliability
Military/Aerospace
<1.56 μg NaCl eq/in²
Full test suite including IC
Extreme environments, mission-critical reliability
Space Applications
<1 μg NaCl eq/in²
Full test suite plus outgassing tests
Vacuum compatibility, radiation resistance

Documentation and Traceability

Cleaning Process Documentation

Essential elements of cleaning process records:

• Process parameters: Time, temperature, concentrations
• Equipment used: Model numbers, settings
• Cleaning agents: Exact formulations, lot numbers
• Responsible personnel: Training records
• Date and time: Process chronology
• Batch information: Lot numbers, quantities

Test Results Documentation

Records of cleanliness verification:

• Test methods used: Standards