DCT developed and validated a cleaning process for removing KOKI S3X58-M500C flux residues from PCBAs with dense component layouts, including low-standoff BGA and QFN packages. The application used Decotron® 411A in an InJet® 388 CRD 2PR Spray-In-Air cleaning system.
- Application
- Post-soldering PCBA cleaning
- Residue type
- KOKI S3X58-M500C flux residues
- Cleaning agent
- Decotron® 411A
- Cleaning system
- InJet® 388 CRD 2PR
- Critical components
- BGA, QFN and low-standoff areas
- Validated cycle
- 10 min wash · 5 min rinse · 10 min dry
- Verification
- Physical tear-off inspection
- Observed result
- Complete removal on tested boards
Executive summary
Flux residues trapped under low-standoff components can compromise the long-term reliability of electronic assemblies. In this case, DCT evaluated the removal of KOKI S3X58-M500C residues from PCBAs with challenging package geometries and hard-to-access contamination areas.
Challenge
The customer needed a repeatable cleaning process capable of removing flux residues from dense PCBAs, including residues located beneath BGA and QFN packages where mechanical access and liquid exchange are limited.
Solution
DCT selected Decotron® 411A and validated it in the InJet® 388 CRD 2PR using a controlled Spray-In-Air process with chemical cleaning, DI-water rinsing and hot-air drying.
Outcome
Under the validated 10 + 5 + 10 minute process, DCT observed complete removal of the targeted KOKI flux residues on the tested boards. The result was confirmed by physical tear-off inspection and visual assessment.
Why flux residues are critical on PCBAs
Flux residues can remain on PCBAs after soldering, especially around component terminations and under packages with limited clearance. If residues are not properly removed, they may increase the risk of electrochemical migration, leakage currents, corrosion, dendrite growth and long-term reliability failures.
Why the application was difficult
BGA, QFN and similar low-standoff packages create narrow gaps where residues are difficult to reach, dissolve, displace and rinse. A successful process therefore requires a controlled combination of chemistry, mechanical energy, temperature, rinsing quality and drying performance.
Risks of insufficient cleaning
- Electrical reliability issues caused by ionic or conductive residues.
- Electrochemical migration in humid or high-voltage operating conditions.
- Corrosion around solder joints, component terminations and exposed metal surfaces.
- Poor coating adhesion when conformal coating is applied after soldering.
- Unstable process quality when cleaning parameters are not validated for the specific assembly.
Application scope of this case study
This case study describes an application-specific cleaning process developed for the tested PCBAs and the targeted KOKI S3X58-M500C flux residues. The parameters below should be treated as a validated starting point for this application, not as a universal recipe for every assembly, flux formulation or cleanliness specification.
| Parameter | Case-study scope |
|---|---|
| Assembly type | PCBAs with dense layouts and low-standoff component areas. |
| Target contamination | KOKI S3X58-M500C solder paste flux residues. |
| Critical locations | Areas beneath and around BGA, QFN and similar package types. |
| Cleaning chemistry | Decotron® 411A water-based alkaline cleaning fluid. |
| Cleaning technology | Spray-In-Air cleaning in an InJet® 388 CRD 2PR system. |
| Verification method | Physical tear-off inspection and visual assessment of cleaned areas. |
| Result statement | Complete removal of targeted residues was observed on the tested boards under the stated process conditions. |
Selected cleaning solution
DCT combined Decotron® 411A with the InJet® 388 CRD 2PR cleaning system to create a controlled process for chemical dissolution, mechanical residue removal, DI-water rinsing and final drying.
Cleaning agent: Decotron® 411A
Decotron® 411A is a water-based alkaline cleaning fluid designed for electronic assembly cleaning applications. In this case, it was selected for its ability to remove difficult flux residues when used with appropriate temperature, spray energy, rinsing and drying conditions.
- Suitable for high-pressure Spray-In-Air cleaning processes.
- Used with a DI-water rinse after the chemical cleaning phase.
- Applied in a controlled process where temperature and exposure time are defined.
Cleaning system: InJet® 388 CRD 2PR
The InJet® 388 CRD 2PR is a single-chamber Spray-In-Air cleaning system used for precision cleaning of electronic assemblies. For this application, it provided the process control required for cleaning, rinsing and drying the tested PCBAs.
- Spray-In-Air cleaning for mechanical residue removal.
- Controlled cleaning, rinsing and drying phases.
- Suitable for process development, validation and selected production applications.
Validated cleaning process
Initial short-cycle testing was not sufficient for the target residue profile. DCT therefore optimized the process into a defined cleaning, rinsing and drying sequence. The final validated cycle for the tested PCBAs used a 10-minute chemical cleaning phase, followed by DI-water rinsing and hot-air drying.
Chemical cleaning
The PCBAs were cleaned with Decotron® 411A at 50 °C for 10 minutes to dissolve and remove KOKI S3X58-M500C flux residues from accessible and low-standoff areas.
DI-water rinsing
The assemblies were rinsed with DI water at 25 °C for 5 minutes to remove dissolved residues and remaining cleaning-fluid residues from the PCBA surface.
Hot-air drying
The cleaned and rinsed PCBAs were dried with hot air at 80 °C for 10 minutes to remove remaining moisture from the assembly after rinsing.
| Process phase | Medium or method | Temperature | Time | Purpose |
|---|---|---|---|---|
| Chemical cleaning | Decotron® 411A | 50 °C | 10 minutes | Dissolve and remove KOKI S3X58-M500C flux residues from accessible and low-standoff areas. |
| Rinsing | DI water | 25 °C | 5 minutes | Remove dissolved residues and cleaning-fluid residues from the PCBA surface. |
| Drying | Hot-air drying | 80 °C | 10 minutes | Remove remaining moisture from the assembly after rinsing. |
The 10 + 5 + 10 minute cycle is the validated process for the tested application. Other board designs, component geometries, residue loads, soldering profiles or cleanliness criteria may require process adjustment.
Validation and evidence layer
The result was verified by physical tear-off inspection and visual assessment of the cleaned areas. This approach enabled DCT to inspect locations that are difficult to evaluate from the outside, especially areas beneath and around low-standoff components where flux entrapment is most likely.
What was verified
DCT verified whether the targeted KOKI S3X58-M500C flux residues were removed from the tested PCBAs after the defined cleaning, rinsing and drying cycle.
How it was verified
The cleaned boards were evaluated using physical tear-off inspection and visual assessment of the relevant cleaned areas.
What the result means
Under the stated process conditions, DCT observed complete removal of the targeted flux residues on the tested boards.
What it does not automatically prove
The result does not automatically define a universal process for every PCBA, every flux system or every customer-specific cleanliness requirement.
Results
The optimized process removed the targeted KOKI S3X58-M500C flux residues from the tested PCBAs, including difficult low-standoff areas. The combination of Decotron® 411A, controlled cleaning temperature, DI-water rinsing and hot-air drying produced a clean result under the validated cycle.
Final outcome
Complete removal of the targeted flux residues was observed on the tested boards after the validated 10-minute cleaning, 5-minute rinsing and 10-minute drying process.
Process relevance
The result demonstrates that a properly selected cleaning agent and Spray-In-Air process can remove difficult flux residues from complex PCBA geometries when the process is validated for the specific assembly.
Production relevance
The validated process can serve as a basis for customer-specific process qualification, production scale-up and further cleanliness testing according to internal or industry-specific acceptance criteria.
When this cleaning approach is relevant
This approach is relevant for electronics manufacturers that need to remove flux residues from high-density assemblies, especially where low-standoff packages make standard cleaning more difficult.
This method is relevant when
- Flux residues remain beneath or around BGA, QFN or similar packages.
- The assembly requires higher reliability than an uncleaned process can support.
- Cleaning must be validated with controlled time, temperature, rinsing and drying parameters.
- The manufacturer needs a documented cleaning process before moving into production.
- Conformal coating, high humidity or sensitive operating conditions increase the risk of residue-related failures.
Additional testing may be required when
- The assembly uses a different solder paste, flux formulation or soldering profile.
- The board has larger thermal mass, more complex component shielding or narrower cleaning gaps.
- The customer must meet a defined ionic cleanliness, ROSE, SIR or internal reliability specification.
- The process must be transferred from laboratory validation to high-volume production.
- The production line requires stronger separation between wash, rinse and dry process stages.
Equipment selection and production scale-up
The InJet® 388 CRD 2PR was used for this validated case. For production environments with higher throughput, stricter process separation or lower cross-contamination requirements, DCT can evaluate two-chamber and three-chamber InJet configurations.
| Requirement | Recommended direction | Reason |
|---|---|---|
| Process development and application testing | InJet® 388 CRD 2PR | Suitable for validating cleaning, rinsing and drying parameters on representative assemblies. |
| Higher production demand | Two-chamber InJet configuration | Allows stronger process separation and can support improved throughput depending on the application. |
| Lowest practical cross-contamination risk | Three-chamber InJet configuration | Supports stronger separation of process stages where cleaning, rinsing and drying must be managed with maximum control. |
Final equipment selection should always be based on the assembly design, production volume, residue type, cleanliness requirements, basket loading, process time and required separation between process stages.
Scope boundaries and technical limitations
A cleaning result is only meaningful when the application scope is clear. The result in this case study applies to the tested PCBAs, the targeted KOKI S3X58-M500C residues and the stated process conditions.
- The process should not be copied to a different assembly without validation.
- Different solder pastes, flux systems or soldering profiles may require different parameters.
- Higher residue load, tighter component spacing or larger thermal mass may require longer cleaning, different spray settings or adjusted drying.
- Customer-specific reliability requirements may require additional testing such as ionic contamination testing, ROSE testing, SIR testing, coating adhesion testing or environmental reliability testing.
- The result should be treated as an application-specific validation, not as a universal guarantee for all PCBAs.
Recommended next step for similar PCBAs
For similar assemblies, DCT recommends starting with an application test using representative boards, the actual solder paste or flux system, and the cleanliness criteria required by the customer. The cleaning cycle can then be adjusted based on board geometry, residue load, component standoff, process throughput and the required validation method.
Share application data
Provide the assembly specification, solder paste or flux type, target cleanliness requirement and expected production volume.
Identify critical areas
Define the components and locations where residues are most difficult to remove, especially low-standoff areas.
Run application testing
Test the cleaning process with Decotron® 411A and an appropriate InJet® system using representative boards.
Verify the result
Confirm the result using the required inspection or cleanliness method, such as visual inspection, tear-off evaluation, ionic cleanliness, ROSE, SIR or a customer-specific method.
Scale into production
Transfer the validated process into the appropriate production equipment configuration based on throughput, process separation and cleanliness requirements.
FAQ: Flux residue removal from PCBAs
Key technical questions about this application, the validated process and the limits of using the same parameters on other assemblies.
What was the main cleaning challenge in this case study?
The main challenge was removing KOKI S3X58-M500C flux residues from PCBAs with dense layouts and low-standoff components. These geometries make it difficult for the cleaning fluid, spray energy and rinse water to reach and remove residues from critical areas.
Which cleaning fluid was used?
DCT used Decotron® 411A, a water-based alkaline cleaning fluid suitable for Spray-In-Air cleaning processes in electronics manufacturing.
Which cleaning system was used?
The process was validated in the InJet® 388 CRD 2PR cleaning system. This system provided controlled Spray-In-Air cleaning, DI-water rinsing and hot-air drying for the tested PCBAs.
What process parameters removed the residues?
The validated process for the tested PCBAs consisted of 10 minutes of chemical cleaning at 50 °C, 5 minutes of DI-water rinsing at 25 °C and 10 minutes of hot-air drying at 80 °C.
Was a shorter cleaning cycle sufficient?
Short-cycle testing was not sufficient for the targeted residue profile. The final validated process required a longer chemical cleaning phase followed by controlled rinsing and drying.
How was the cleaning result verified?
The result was verified using physical tear-off inspection and visual assessment of the relevant cleaned areas. This made it possible to evaluate locations that are difficult to inspect from the outside, including areas beneath low-standoff components.
Does this process apply to all PCBAs?
No. The process applies to the tested boards, the targeted KOKI S3X58-M500C residues and the stated process conditions. Other assemblies, flux systems, component geometries or cleanliness specifications should be validated separately.
Why is DI-water rinsing required after the cleaning phase?
DI-water rinsing removes dissolved residues and remaining cleaning-fluid residues from the assembly surface. Rinsing quality is critical because an effective cleaning step must be followed by controlled residue removal and drying.
When is a single-chamber machine enough?
A single-chamber system can be suitable for application testing, process validation and selected production requirements. The final decision depends on throughput, residue load, cleanliness requirements, required process separation and cross-contamination risk.
When should a two- or three-chamber system be considered?
A two- or three-chamber system should be considered when the production process requires higher throughput, stronger separation between cleaning and rinsing stages, or lower cross-contamination risk. DCT can evaluate the appropriate configuration based on the application.
Can Decotron® 411A be used for other flux residues?
Decotron® 411A can be evaluated for other flux residues, but performance depends on the flux formulation, soldering profile, residue load, component geometry and required cleanliness level. DCT recommends testing representative assemblies before production use.
What information does DCT need to evaluate a similar cleaning process?
DCT typically needs the assembly type, solder paste or flux type, component layout, critical residue locations, production volume, cleanliness requirements and any required validation method such as visual inspection, ionic cleanliness, ROSE, SIR or customer-specific reliability testing.
Related DCT solutions
Decotron® 411A
Water-based alkaline cleaning fluid used in this case study for removing KOKI S3X58-M500C flux residues from PCBAs.
InJet® 388 CRD 2PR
Spray-In-Air cleaning system used for the validated cleaning, rinsing and drying process in this application.
PCBA cleaning process development
Application testing and cleaning-process optimization for electronics manufacturers with defined reliability and cleanliness requirements.
Need to validate flux residue removal on your PCBAs?
Send DCT your assembly specification, solder paste or flux type, contamination challenge and cleanliness requirement. DCT can help evaluate the cleaning chemistry, process parameters and equipment configuration required for reliable PCBA cleaning.