Wet PCB cleaning rarely creates static charge. It creates current paths — metal, water and electronics meeting inside one enclosure. Static control in a wet zone therefore becomes a grounding and insulation question you can measure, rather than a materials question you settle at the purchasing desk. The seven checks below are ordered, each closes one question, and each ends with a signature.
The reference machine is the CHUANGQI CQ-C9610 Inline PCBA Water Cleaning Machine, and the structural facts come from its published specification sheet: a corrosion-resistant imported PP body, a stainless steel SUS316 mesh belt, DI water resistivity above 15 MΩ, DI water entering the machine at 1.0 m³/h, and a workpiece envelope that tops out at 580 × 450 × 80 mm. Every unit also runs an ionic cleanliness check with a test board before it ships. Those are specification facts. This article draws no compliance verdict from them, because the outcome depends on your floor bonding, your ducting and your people.
Key takeaways
- Wet cleaning adds current paths more often than it adds static charge.
- Six metal-to-water interfaces exist on CQ-C9610 and each needs a bond check.
- DI water above 15 MΩ is a water-quality spec, not an ESD proof.
- Two of the seven checks need an electrician, not a line operator.
- No numeric limit is quoted here; a programme standard names no machine.
Seven leakage checks that decide whether a wet line is ESD-capable
Scope first, because this sheet is not a standard. The seven checks come from the machine structure published on the CHUANGQI product page, set alongside the factory sequence applied to every unit: water-tightness checks, spray-pressure calibration, a dry-zone uniformity pass, a 72-hour nonstop run, and the ionic cleanliness test board. No resistance figure, decay time or ion-balance voltage appears in this article. ANSI/ESD S20.20-2021 (the ESD Association’s standard for developing an ESD control programme, per EOS/ESD Association, esda.org) governs how a facility organises its programme; it does not certify a washer, and this article quotes its name and stated purpose only.
Read the seven as a sequence. Each one closes a single question: is there a conductor here that is not bonded, an insulator here that will hold charge, or a measurement nobody has taken?
1. Cabinet-to-earth bond
The cabinet is built from corrosion-resistant imported PP — an insulator, and deliberately so, since that is what survives years of detergent. The frame, the pump housing and every metal bracket bolted to it must therefore be bonded and checked one by one. Measure protective earth continuity from the plant earth bar to each metal part at installation, and again after any service that moves a panel.
2. The wet-zone metal that touches product
The SUS316 mesh belt is stainless steel, and it carries the board through wash, rinse and dry. Stainless conducts, and it stays in contact with board edges and, on a dense assembly, with exposed copper. Confirm the conveyor frame is bonded rather than floating, and confirm the bond survives belt tension adjustment — the usual failure is a strap bolted to a bracket that somebody later repositions.
3. Nozzle and pipework continuity
Spray headers and DI pipework form a second conductive network in the same cabinet. Where a plastic fitting interrupts a run, each metallic segment needs its own route to earth. Mark the pipe runs on the P&ID, note which segments are isolated, and treat those as the ones requiring a strap.
4. DI water and detergent lines
Resistivity above 15 MΩ describes how poorly the rinse water conducts; it is a water-quality specification and never a static-control number, so the two should not be used interchangeably on a datasheet. Poorly conducting water also means charge on wetted surfaces drains slowly through the liquid. Record the rinse-stage reading at commissioning and treat drift as a process deviation to investigate.
5. Air knives and blow-off nozzles
Dry-off air is where a wet process most resembles a dry one. High-velocity air across a dry board can transfer charge, and a non-conductive blow-off nozzle can hold it. Establish whether the air knives are bonded to the frame and whether an ionising bar is fitted, offered or absent. On the CHUANGQI CQ-C753 Automatic PCB Substrate Cleaning Machine, an ioniser with built-in static elimination is listed as an option on the specification sheet; on a spray washer the air knife is normally specified as bonded metal, and that belongs in writing rather than in an assumption.
6. Load and unload interfaces
Boards arrive from the SMT line and leave towards test, so two earthing systems meet at two points. Measure across the gap between the upstream conveyor frame and the washer frame before bolting them together, then record which side was bonded to which.
7. Fixtures, masks and carriers
Every carrier, pallet and masking jig that enters the wet zone adds an insulator. List each carrier type by material, confirm which are dissipative on the supplier’s declaration, and file the declaration reference. A supplier statement is a document; a colour is not.
Where the current path actually sits in a wash–rinse–dry line
The table maps each check onto the part of the machine it belongs to, the measurement it requires, and the role that signs it off. The last column carries more weight than it appears to: a check that never reaches a signature is a check nobody repeats after the next service visit.
| Check | Where it sits on CQ-C9610 | What you measure | Signed by |
|---|---|---|---|
| 1 Cabinet bond | PP body, frame, pump housing | Earth continuity to plant bar | Electrician |
| 2 Mesh belt | SUS316 belt and conveyor frame | Bond after tension adjustment | Electrician |
| 3 Pipework | Spray headers and DI lines | Segment-by-segment bond map | Maintenance |
| 4 DI water | Rinse stage, 10–16 L/min draw | Resistivity log above 15 MΩ | Process engineer |
| 5 Air knives | Dry stage blow-off | Bond status, ioniser fitted or not | Process engineer |
| 6 Interfaces | Load and unload conveyors | Which side bonded, recorded | Line owner |
| 7 Carriers | Fixtures entering the wet zone | Supplier declaration on file | Quality |
Data source: the CQ-C9610 specification sheet as published by CHUANGQI on its own site, October 2026. The checks and sign-off roles are a process recommendation rather than a standard requirement.
Two figures in that table are machine specifications and nothing else. The rinse draw of 10–16 L/min and the resistivity threshold above 15 MΩ both come from the published sheet, and what you read at the gauge depends on board width, detergent concentration, how many rinse stages the machine was ordered with, and the water temperature at the header. Change any one of the four and the reading moves.
What to write into the acceptance record
A static check that lives only in a commissioning email will not survive the first customer audit. Build the record from documents the machine already produces, and let the static section sit beside them rather than replace them.
- A bond map drawing — every metal part in the wet zone with its strap location, signed at commissioning.
- A resistivity log — the rinse-stage reading at acceptance plus the interval at which you will re-read it.
- A carrier register — each carrier type, its material, and the reference of the supplier declaration behind it.
- A service trigger — the sentence listing which checks repeat after a panel is opened, a belt re-tensioned, or a header replaced.
Where a customer specification asks for a cleaning record per lot, the ionic cleanliness test board result is the document they reach for first; the static sheet is what shows the wash step introduced no new failure mode. The factory acceptance test defines the measurement set, and this sheet adds the static-control section to it.
Where this method stops working
The seven checks are written for a conveyor-fed spray washer with a stainless belt and a PP cabinet. They are not suitable for an immersion or ultrasonic batch tank, where product sits in a conductive bath with no defined belt path, and they do not transfer to a dry-ice cell, where the static question follows CO₂ flow and nozzle proximity instead of water. That case has its own acceptance logic, set out in the dry-ice static acceptance protocol.
They also stop short of a programme audit. A facility that must demonstrate a full ESD control programme works from the ESD Association’s standard directly; this sheet produces only the machine-level evidence such a programme consumes. Where a customer demands a resistance figure for a carrier or a mat, the number has to come from that supplier’s test report, because a machine builder cannot certify a part it does not make.
One further boundary: none of the seven predicts field reliability. They confirm the current paths are known and bonded. Whether a bonded washer returns clean, dry boards is answered by the cleanliness test and the dry-zone record.
Specify the leakage paths, not the materials
A purchase specification that asks for “ESD-safe materials” tells the buyer very little, since most of the interesting parts of a wet line are metal inside an insulating cabinet. One that lists the seven paths, names who signs each, and requires the bond map at commissioning gives the supplier something to answer and the auditor something to read.
Send the board outline, the carrier types and the customer specification you are measured against. The engineering team will mark which of the seven checks change for that configuration, and quote within 24 hours. The CQ-C9610 Inline PCBA Water Cleaning Machine page carries the specification sheet these checks are anchored to.
Standards appear by name only in this article. No resistance value, decay time or ion-balance limit is quoted; the ANSI/ESD S20.20 reference covers the standard’s name and stated purpose as published by the EOS/ESD Association (esda.org), not its technical requirements, and any figure found elsewhere should be checked against the current standard text before it is used.
Frequently asked questions
Do I need ESD-safe brushes if I run a wet cleaning machine?
Only where a brush actually touches the board. In a conveyor-fed spray washer nobody brushes anything: the spray bars, the rinse stage and the air knives do the work, and the static question moves to the metal parts of the machine. Brushes matter in manual touch-up and in offline bench cleaning, and there the brush handle, the bench mat and the operator wrist strap form one path that has to be bonded. Buying dissipative brushes for an automated line solves a problem that line does not have.
Can I use an ionizer on a wash–rinse–dry line?
An ioniser belongs where the board is already dry, which on this class of machine means the blow-off stage, not the wet zone. Ionising air that is about to hit a soaked board does very little, because the water film carries charge away far more effectively than ions can neutralise it. Ask the supplier whether an ionising bar can be fitted to the dry stage, and confirm the air knives themselves are bonded metal before adding one.
Is an ESD audit required for a PCBA washer purchase?
Not as a purchase condition, and no machine builder can grant one. A control programme is audited at facility level by the customer or by an assessor working to the programme standard, and the washer only appears as one item inside it. What you can reasonably require from the supplier is documentation: the bond points, the earthing terminals, the cabinet material, and the factory test sequence. Those give the auditor something to read instead of a claim to believe.
How often do I re-check leakage paths after installation?
Set the interval from the events that disturb them rather than from the calendar. A panel opened for service, a belt re-tensioned, a header replaced or a conveyor re-levelled each break a bond that was previously measured, so each one triggers a re-check of the affected point. Between events, re-read the rinse-stage resistivity at whatever interval your process control already uses, and treat a step change as a deviation to investigate rather than as drift to accept.