Air Knife for PCB Cleaning: How It Removes Water Without Contact

2026-05-22

The Problem: Water on PCBs Causes Real Defects

PCBs go through many wet steps. They go through etching. They go through stripping. They go through electroplating. They go through chemical cleaning.

Water stays on the board after these steps. Water sits on the flat surface. Water gets inside the through-holes. Water pools around the pads. Water pools around the component footprints.

How Water Damages PCBs

This water has chemicals inside. The chemicals come from the processing liquid. If the water dries on the PCB, it leaves chemical dirt. This dirt causes three big problems:

l It causes rust on copper traces.

l It causes oxidation on metal pads.

l It stops the solder from sticking well.

The Danger of Trapped Water

The problem is worse for through-holes. It is worse for blind vias. Water gets trapped deep inside the holes. This hidden water does not dry fast.

The PCB moves to the next step with water still inside. The next steps are plating, printing, or reflow ovens. This hidden water turns into steam or traps air. It causes three factory defects:

l It leaves empty holes in the plating.

l It makes the solder joints weak.

l It makes the PCB break after the customer buys it.

The Solution

Air knives solve this problem completely. The air knife blows a clean sheet of air. It removes water from the PCB surface. It blows water out of the tiny holes. It works very fast. It dries the board evenly. The air knife does all this without touching the PCB.

How an Air Knife Removes Water from PCBs

An air knife is a long, hollow chamber with a precision-machined slot along one edge. It connects to a blower. The blower pushes air into the chamber, and the air exits through the slot as a flat, high-velocity curtain.

The board travels on a conveyor through this air curtain. The airstream hits the board surface at an angle and shears the water film off. No rollers. No contact. No wipers.

Why angle matters

Most PCB air knife setups angle the blade at 15°–45° from the board surface, pointing in the direction of conveyor travel. This lets the airstream push water toward the trailing edge of the board and off the surface, rather than pushing it back across clean areas.

For double-sided boards, you need air knives above and below the conveyor. Both sides get dried in one pass.

What about through-holes?

Standard slot air knives handle surface water well. But through-holes are different — water inside a 0.3 mm or 0.5 mm hole does not come out from a laminar air curtain alone. The air velocity at the hole entrance is not high enough to push water all the way through.

This is where QXY Machinery's small hole air knife is designed for PCB work. It uses a thickened blade edge with a dual-row hole pattern: one row of straight holes and one row of angled holes. The standard hole diameter is 1 mm. This concentrates airflow into focused jets that penetrate hole openings and drive water through the board.

The blade edge thickening is intentional — it increases air pressure concentration at the outlet and strengthens the wind force. That extra force is what clears holes that a standard slot knife cannot reach.

Where Air Knives Go on a PCB Wet Processing Line

Air knives are not just placed at the final exit of the cleaning machine. On a properly designed PCB wet line, you find them at multiple points:

• After developing: Removes developer solution from the board surface before the board enters the etching tank. Reduces chemical carryover and keeps etch chemistry clean.

• After etching: Removes etchant from the board. Copper etchant left on the surface continues reacting. Even a 10-second delay causes over-etching at the edges of traces.

• After stripping: Removes stripping solution after the dry film resist is removed. Critical for preventing contamination of the next chemical bath.

• After final rinse: The most important position. This is where all chemical residues must be removed before the board moves to drying or the next process. The air knife here needs to handle both surface water and through-hole water.

• Before soldering or printing: A final blow-off to remove any particles or moisture that settled during inter-stage transport.

On a horizontal wet processing line — which is the standard for most PCB production today — the air knife integrates directly into the machine. Boards ride rollers through the machine, and the air knife mounts across the full board width at each exit point.

How to Choose the Right Air Knife for Your PCB Line

The choice depends on three things: where on the line, what chemistry the board is coming out of, and whether you have through-holes to deal with.

Position 1: After developing or after final rinse (no acid, mild chemistry)

Standard aluminum alloy air knife. Adjustable slot, 0.5–1 mm gap for most PCB boards. Mount above and below for double-sided drying. Knife length = board width + 20 mm minimum overhang each side.

Position 2: After etching or stripping (acid/alkaline chemistry)

Use stainless steel (Grade 304) or PVC. Aluminum corrodes in acid etchant environments over time. Stainless holds up better and maintains slot dimension accuracy. PVC is the lower-cost option where temperatures are not high.

Position 3: Through-hole boards (PTH, blind vias, buried vias)

Add the small hole air knife — either as the primary knife or mounted after the slot knife. The dual-row hole pattern (straight + angled, 1 mm diameter standard) drives airflow into holes that a flat slot curtain cannot reach. If your boards have 0.3 mm or smaller holes, discuss custom hole sizing with QXY.

Position 4: Before soldering or final assembly

Aluminum alloy air knife for particle removal. Low pressure setting (1–2 psi) is enough here. The goal is removing particles, not liquid. Too much pressure at this stage can move fine SMD components if they are pre-placed.

Knife length selection

Match the knife length to your conveyor width. If your board is 600 mm wide and your conveyor is 650 mm, use a 700 mm knife. Standard lengths from QXY go up to 1,000 mm stock, with custom lengths up to 6 meters for wide-format panel lines. For knives over 600 mm, dual-inlet supply is recommended to maintain even airflow across the full length.

QXY Machinery PCB Air Knife Products:Specifications

QXY Machinery (Shenzhen Qixingyuan) produces several air knife types used in PCB cleaning lines. Here are the key specifications for the models most relevant to circuit board processing:all Hole Air Knife (PCB-Specific)

Primary application: PCB horizontal wet processing lines — through-hole drying

Hole configuration: Dual-row: 1 row straight holes + 1 row angled holes (standard); custom patterns available

Standard hole diameter: 1 mm (customizable to customer requirement)

Variants: With wings / without wings (customer choice)

Blade edge design: Thickened edge for increased outlet air pressure and stronger wind force

Available materials: Aluminum alloy (standard); stainless steel on request

Length: Customized to conveyor width; contact QXY for sizing

Air inlet: Side inlet; quantity and diameter matched to board width and required flow

Notes: Slot width calibrated at factory; contact QXY if field adjustment neededAlloy Air Knife (Standard Slot — Surface Drying)

Primary application: Surface water removal on PCB boards and panels; general wet line blow-off

Slot width: Adjustable; standard range 0.5–2 mm (set at factory per order)

Slot accuracy: Air speed uniformity ±5% across full knife length

Air inlet diameter: 50 mm standard (multiple sizes available)

Inlet quantity: 1 or 2 per knife depending on knife length

Available lengths: 150 mm / 300 mm / 450 mm / 600 mm / 800 mm / 1000 mm; custom lengths up to 6 m

Material: Aluminum alloy, hard-anodized surface

Wind resistance: Low — internal dual-deflector plate design for uniform exit velocity

Operating pressure: Compatible with blower systems; 2–6 psi typical working pressure

Temperature rating: Up to 82°C (180°F) with standard plastic shim

Notes: Blade width adjustable; mold-production process for cost efficiency

Primary application: PCB wet lines using acid etchants, alkaline strippers, or aggressive chemistries

Material grade: 304 stainless steel (standard); 316 available on request

Slot width: Adjustable to customer specification

Resistance: Corrosion-resistant to most PCB process chemicals; suitable for chemical splash zones

Surface finish: Smooth interior and exterior; no crevice geometry

Available lengths: Custom to conveyor width; QXY advises on sizing

Notes: Recommended for etching exit, stripping exit, and any position with direct chemical exposure

PVC Air Knife (Acid / Alkali Chemical Drying)

Primary application: PCB lines with concentrated acid or alkali chemistry — where aluminum would corrode

Material: Polyvinyl chloride (PVC)

Slot width: Adjustable; simple field-adjustment design

Chemical resistance: Suitable for acid and alkaline liquid-adjacent environments

Notes: Lower cost than stainless for chemical-resistant applications; not recommended for high-temperature positions

About QXY Machinery

QXY Machinery (Shenzhen Qixingyuan Machinery Equipment Co., Ltd.) has been producing air knives since 2011. The company is based in Shenzhen — the center of PCB and electronics manufacturing in China — and has supplied air knife systems to PCB production lines, LCD cleaning machines, electronic component lines, and other precision manufacturing applications for over 10 years.

QXY holds patents on adjustable air knife designs and produces over 15 standard air knife types, including the small hole air knife developed specifically for PCB through-hole drying. Products are manufactured using mold production processes, which keeps tolerances tight and costs competitive versus custom-machined alternatives. All knives are calibrated at the factory before delivery.

Materials available: aluminum alloy, stainless steel (304/316), PVC, titanium alloy. Custom lengths, hole patterns, inlet configurations, and slot widths are all available. QXY's technical team can calculate blower requirements based on knife length and application — just share your board width, line speed, and process chemistry.

→ Contact QXY Machinery to get an air knife specification for your PCB cleaning line.

Common Problems and How to Fix Them

Problem: Water remains in through-holes after air knife

Cause: Using a standard slot air knife — laminar curtain cannot penetrate small holes

Fix: Switch to or add a small hole air knife. The focused jets from the dual-row hole pattern enter the hole opening and push water through. Increase blower pressure slightly if holes are below 0.5 mm.

Problem: Uneven drying — dry on one side, wet on the other

Cause: Single-sided air knife setup, or slot gap uneven across knife length

Fix: Install air knives above and below the conveyor for double-sided boards. Check slot gap uniformity — if one end of the slot is wider than the other, exit velocity will be inconsistent. Re-set slot gap to factory spec or contact QXY.

Problem: Water streaks (dry stripes and wet stripes on board surface)

Cause: Blower pressure too low, or knife mounted too far from board

Fix: Reduce knife-to-board distance to 20–50 mm. Check blower output pressure. Verify slot gap is set correctly — too wide a gap reduces exit velocity. Aim for 2–4 psi working pressure at the knife inlet for typical PCB surface drying.

Problem: Boards showing oxidation spots after drying

Cause: Chemical residue left on board before drying — incomplete rinse, or air knife not removing all liquid

Fix: Check the final rinse stage first. Air knives remove liquid, not dissolved chemistry — if chemical concentration in rinse water is too high, the residue left behind after drying will oxidize. Once rinse quality is confirmed, optimize air knife angle and pressure.

Problem: Air knife corroding after a few months near etch station

Cause: Using aluminum air knife in acid etchant vapor zone

Fix: Replace with stainless steel (Grade 304) or PVC air knife. Aluminum alloy degrades in acid environments. Corrosion inside the slot changes the gap dimension and ruins airflow uniformity.