Build a controlled high-mix PCBA cleaning process before conformal coating using validated chemistry, DI-water rinsing, drying and cleanliness testing.
ByadminHigh-mix PCBAs should be cleaned before conformal coating through a controlled set of validated cleaning recipes—not one aggressive process applied to every assembly.
Group the PCBAs by flux chemistry, contamination, component geometry, material compatibility and cleanliness requirement. Each group can then use a defined wash, DI-water rinse, drying and verification process.
Determine the appropriate cleaning method based on the surface condition of the assembled PCB, taking into account factors such as the chemical nature of residues, component standoff height, shadowed areas, connectors, labels, coatings, and moisture-sensitive materials.
Conformal coating must bond to the PCBA surface. Flux residue, oil, fingerprints, dust, adhesive and remaining cleaning agent can interfere with wetting, curing and adhesion.
Surfaces should be free from moisture, dirt, wax, grease, flux residue and other contaminants before coating.
Contamination beneath the coating is not removed or neutralised by covering it. Depending on its chemistry and the operating environment, it may contribute to:
Some contamination is invisible. Visual inspection can identify particles and visible flux, but it cannot establish the ionic cleanliness of an assembly. Potentially harmful ionic and non-ionic contamination may not be visible, even under magnification.
High-mix production usually contains multiple PCB sizes, flux systems, soldering processes and component layouts. Creating a separate cleaning process for every part number is difficult to control, while using one recipe for everything may produce incomplete cleaning or material damage.
| Process-family factor | Why it matters |
|---|---|
| Flux or solder-paste type | Determines which cleaning chemistry can dissolve or separate the residue |
| Reflow, wave, selective or manual soldering | Changes the amount, location and thermal condition of the residue |
| PCBA dimensions and component height | Determines basket loading and spray access |
| BGA, QFN and other low-standoff packages | Restrict liquid exchange beneath components |
| Connectors, switches and open components | May trap liquid or impose washing and drying restrictions |
| Labels, adhesives, plastics and coatings | Require chemical and temperature compatibility |
| Visible residue or defined ionic limit | Determines how the cleaning result must be verified |
| Conformal-coating material | Determines required surface condition and compatibility |
| Batch quantity and product-change frequency | Determines whether offline batch or continuous inline cleaning is appropriate |
Assemblies may share one recipe only when the cleaning chemistry, process parameters and drying conditions are compatible with every product in that family.
For full-board cleaning before conformal coating, the normal process is:
Chemical Wash → DI-Water Rinse → Hot-Air Dry → Cleanliness Verification → Conformal Coating
Each stage solves a different problem.
The wash stage combines suitable cleaning chemistry with temperature, time and mechanical spray action.
The chemistry must be selected according to the actual flux or contamination. Do not specify acetone, IPA, alkaline cleaner, acid or another chemical solely from the appearance of the residue.
For example, a cleaner that removes one no-clean flux may be ineffective against another formulation. Excessive heat exposure during soldering can also harden or polymerise residue, changing the required cleaning window.
Run sample tests with the actual PCBA, flux and cleaning agent before establishing the production recipe.
DI water is the rinse medium, not the primary cleaning stage.
After chemical washing has dissolved or separated the contamination, the DI-water rinse removes:
Insufficient rinsing can leave cleaning chemistry or redistributed contamination on the PCBA. Control the rinse process through water quality, flow, temperature, coverage and replacement or discharge conditions.
A surface that looks dry may still contain water beneath components, inside connectors or between closely spaced structures.
Drying conditions must consider:
There is no universal drying temperature for every high-mix PCBA. Establish the temperature and time from the most sensitive material in each cleaning family, then verify that retained moisture has been removed.
After cleaning, handle PCBAs with clean gloves and controlled fixtures. Do not return cleaned boards to contaminated trays, worktops or packaging.
If coating cannot begin immediately, define the permitted waiting time and storage condition. HumiSeal guidance recommends controlled storage when cleaned assemblies cannot proceed directly to coating.
The DEZ-C743 offline PCBA cleaning machine is the primary DEZ recommendation for high-mix production before conformal coating.
Different PCBAs can be loaded into its two-level basket and processed using validated settings for their cleaning family. Chemical spray washing, DI-water rinsing and hot-air drying take place inside the same enclosed SUS304 chamber.
| Parameter | DEZ-C743 |
|---|---|
| Cleaning format | Offline batch spray cleaning |
| Process | Chemical wash, DI-water rinse and hot-air dry |
| Basket size | 610 × 560 × 100 mm |
| Basket configuration | Two levels |
| Maximum batch load | 10 kg |
| Maximum product height | 100 mm |
| Wash temperature | 25–75°C |
| Maximum drying temperature | 99°C |
| Wash, rinse and drying time | Each adjustable from 1–99 minutes |
| Chemical filtration | 0.45 μm |
| DI-water discharge filtration | 0.45 μm |
| Required DI-water resistivity | More than 15 MΩ·cm |
| DI-water inflow | 0.3 m³/h |
Use the DEZ-C1360 inline PCBA cleaning machine when production contains repeated PCBA families with sufficient volume for continuous processing.
The C1360 conveys assemblies through chemical spray washing, DI-water rinsing and two hot-air drying zones. It supports product widths from 50–500 mm on a 500 mm-wide mesh conveyor, with adjustable conveyor speed from 0–1000 mm/min.
The C1360 is more suitable when:
For frequent small batches and regular model changes, the offline DEZ-C743 normally provides more practical loading and recipe control.
A single-sided brush cleaner should not be the default choice when the complete PCBA will receive conformal coating.
The DEZ-C758 and DEZ-C760 are appropriate when visible flux marks or loose solder balls are concentrated on one accessible solder side. Their brushes cannot provide complete access beneath densely assembled components, and they do not include a full-board DI-water rinsing process.
The DEZ-C7310 dry ice cleaning machine can be evaluated when compatible flux residue is confined to an accessible rework area and the PCBA should not enter a water-based process.
Dry ice cleaning does not provide the dissolution and DI-water rinsing mechanism used for full-board ionic-contamination control. Use it for a validated local application, not as an automatic substitute for complete pre-coating cleaning.
A high-mix cleaning process needs both process control and product verification.
| Verification | What it checks |
|---|---|
| Visual inspection under suitable magnification | Visible flux, particles, solder balls, water marks and staining |
| ROSE testing | Bulk ionic-contamination screening under the specified extraction method |
| Ion chromatography | Identity and quantity of selected ionic species |
| SIR testing | Electrical behaviour under controlled humidity, temperature and bias |
| Coating wetting and adhesion test | Compatibility between the cleaned surface and selected coating |
| Dryness verification | Moisture retained beneath components, inside connectors or in restricted areas |
Do not create one universal ionic limit for all products. The acceptance method and limit must come from the customer requirement, product risk, coating process or applicable manufacturing standard.
Not automatically. Ultrasonic suitability depends on component construction, frequency, power, exposure time, chemistry and fixture arrangement. It should not be selected only because a board is multilayer, HDI, thick or densely assembled.
To establish a high-mix cleaning process, Contact DEZ. We can test representative assemblies, determine whether offline batch or inline cleaning fits the production mix, and develop the equipment configuration and cleaning cycle for validation.
