🧼 PCB Assembly Cleaning Process – Overview

PCB cleaning is the process of removing flux residues, dust, contaminants, and debris after soldering to ensure long-term electrical reliability, cosmetic quality, and product lifespan. This is critical for assemblies used in:

• High-reliability sectors (Aerospace, Medical, Automotive)

• Conformal coating preparation

• IPC Class 2 or 3 boards

Cleaning methods vary based on flux type (no-clean, water-soluble, rosin-based) and product requirement.

🔟 10 Detailed Steps in the PCB Assembly Cleaning Process

1. Determine the Cleaning Requirement

Description:
Based on product specification:

• Check if cleaning is required (based on flux type)

• Verify IPC class requirements

• Consult customer-specific standards or end-use environment
  No-clean flux may not require cleaning unless for conformal coating or high-reliability applications.

2. Select Cleaning Method

Description:
Choose appropriate cleaning method:

• Manual Cleaning (IPA + brush for small batches)

• Aqueous Cleaning (for water-soluble fluxes)

• Semi-Aqueous Cleaning (with solvents + water rinse)

• Vapor Degreasing (using solvents in a closed system)

• Ultrasonic Cleaning (delicate boards, tight spaces)

3. Set Up the Cleaning Equipment

Description:
Prepare equipment such as:

• Batch cleaning machine or inline washer

• Solvent sprayer or ultrasonic tank

• Rinse water supply and air knives or drying chambers
  Ensure correct temperature, flow rate, and detergent dosage.

4. Initial Pre-Rinse (if applicable)

Description:
In some processes, a pre-rinse removes loose contaminants or cools boards before detergent wash. Especially useful before ultrasonic cleaning.

5. Apply Cleaning Solution

Description:
Introduce cleaning agent based on selected method:

• Spray-in-air or immersion system

• Solvent like IPA, DI water with detergent, or engineered cleaners

• Ensure thorough coverage around components and under BGAs/QFNs

6. Mechanical Agitation or Ultrasonic Action

Description:
Use mechanical or ultrasonic agitation to:

• Remove residues under low standoff components

• Dislodge flux from vias and pads
  Ultrasonic waves (typically 40–60 kHz) increase cleaning effectiveness without damaging components.

7. Rinse with Deionized (DI) Water

Description:
Rinse boards with filtered DI water to remove dissolved contaminants and cleaning residues. Important to prevent:

• Ionic residue buildup

• Water spots

• Staining or corrosion

8. Drying Process

Description:
Dry the cleaned PCBs using:

• Air knives

• Convection ovens

• Vacuum drying chambers
  Ensure full moisture removal before further handling or coating.

9. Cleanliness Inspection and Ionic Testing

Description:
Perform post-cleaning inspection:

• Visual under UV light (some fluxes fluoresce)

• Ionic contamination test (ROSE test or Ion Chromatography)

• Check for white residues, water marks, and conformal coat readiness

10. Documentation and Final Release

Description:
Record cleaning batch ID, time, temperature, and result. Boards are released for:

• Final inspection

• Conformal coating

• Assembly/test phase

❓ 10 “How To” Questions for PCB Assembly Cleaning Process

1. How to Decide Whether Cleaning Is Required After Soldering?

Description:

• Review flux type (no-clean, water-soluble, rosin)

• Assess product class (IPC-A-610 Class II/III)

• Check for post-coating, medical or automotive application

• Consider cosmetic vs. electrical reliability impact

2. How to Choose the Right Cleaning Method for PCB Assembly?

Description:

• For water-soluble flux: aqueous cleaning

• For no-clean flux: solvent or semi-aqueous if cleaning is needed

• For tight spaces: ultrasonic cleaning

• For low volumes: manual cleaning with IPA

3. How to Clean Under BGAs or Low-Standoff Components?

Description:

• Use ultrasonic cleaning or spray-in-air with angled nozzles

• Allow enough dwell time in wash/rinse cycles

• Use low surface tension solvents to penetrate gaps

• Validate using X-ray or underfill compatibility

4. How to Ensure PCB Is Fully Dry After Cleaning?

Description:

• Use convection drying oven at 60–80°C

• Ensure air flow reaches all board sides

• Inspect with moisture detection (visual or sensors)

• Prevent water spotting by timely drying

5. How to Perform Ionic Cleanliness Testing?

Description:

• Use ROSE (Resistivity of Solvent Extract) test

• Pass limit usually ≤ 1.56 µg NaCl equivalent/cm² (IPC standard)

• Ion chromatography for trace-level analysis

• Log results per serial/batch number

6. How to Remove White Residue or Water Marks?

Description:

• Rewash with IPA + deionized water rinse

• Check drying process for effectiveness

• Avoid over-concentration of detergent or excessive drying delay

7. How to Set Parameters for Automatic Cleaning Machine?

Description:

• Set wash temp: ~60–70°C

• Wash duration: 5–10 minutes

• DI water rinse: until resistivity >10 MΩ-cm

• Drying: minimum 10–15 minutes or until no moisture detected

8. How to Prevent Damage During Ultrasonic Cleaning?

Description:

• Use safe frequency range (40–68 kHz)

• Avoid overexposure – 1–3 minutes usually sufficient

• Use soft baskets or holders to protect components

• Validate process on sample boards

9. How to Clean Manually Without Risking ESD or Damage?

Description:

• Wear ESD-safe gloves and work on grounded mats

• Use IPA and soft ESD-safe brushes

• Avoid scrubbing sensitive parts like connectors or RF circuits

• Rinse and blow-dry using ionized air

10. How to Ensure Repeatability and Traceability of Cleaning?

Description:

• Record cleaning cycle ID, date/time, operator, method

• Log ionic test results and visual inspection remarks

• Use barcode-based MES system for real-time tracking

• Maintain SOPs and training logs for cleaning personnel