Turbulent Wave: 6 Setup Rules for Through-Hole

A turbulent wave is the second, rougher wave in a wave soldering machine, and it exists to push solder up into plated barrels and around tall leads. The first wave is laminar and fast, and it does most of the wetting. The turbulent one follows a few centimetres later and fills what the first wave left behind.

Setting it correctly is a matter of geometry. Wave height, contact length, conveyor speed and the condition of the nozzle decide how much solder reaches the top of the barrel, and each of them can be measured. This guide covers what to set, what to check and how the numbers interact on a mixed technology board.

What the Turbulent Wave Does That the Chip Wave Cannot

The first solder wave is designed for high speed wetting with a short contact time, which suits small surface mount pads but leaves plated barrels partly filled. The turbulent wave flows with a churning, vertical component, so solder is driven up the hole rather than only across the board.

On a board with both surface mount and through-hole parts, the two waves do different jobs and neither replaces the other. Running only the turbulent wave overheats the surface mount side, while running only the chip wave leaves barrel fill below the acceptance limit for many designs.

Wave Height and Contact Geometry

Wave height sets how deep the board sits into the solder. Too low and the solder only touches the pads, so it cannot climb the barrel; too high and solder floods the top side through the holes and reaches components that should never see it. The target is a contact depth of roughly half the board thickness, and nozzle height is the setting that produces it on the machine.

Record the height as a number at a fixed measuring point with the pump running, not as an operator judgement. Height changes with pump speed, pot level, the nozzle height setting and nozzle wear, so a weekly reading catches a drift long before the joints themselves do.

Nozzle Design, Dross and Flow Condition

The nozzle shapes the solder wave, and its condition decides whether the flow stays even across the working width of the machine. Oxidation and dross collect at the nozzle edges, narrowing the gap and making the wave higher in the middle than at the ends. The effect is a board that fills at the centre and stalls at the rails.

Skim and clean on a schedule rather than when a defect appears, and keep the pot chemistry under control alongside the nozzle condition. Dross management on the pot is covered in pot skimming, and it has a direct effect on wave stability.

Flux Application and Preheating Ahead of the Wave

Flux has to be present and active when the board meets the solder. Spray fluxers apply a thin, even coat, while foam fluxers are more forgiving on assemblies with tall parts. The solids content and the specific gravity of the flux decide how much active material reaches the joint.

Preheat then brings the board to temperature so that the flux activates and moisture leaves before the wave. Too little preheat produces spattering and poor fill; too much consumes the flux and leaves a dull joint. Measure top side board temperature before the wave, not the heater setting.

Conveyor Speed, Angle and Contact Time

Conveyor speed sets contact time with the wave, and the angle of the conveyor sets how the solder drains away. A contact time of about three to four seconds is a common starting point for a mixed assembly, and it should be confirmed by the fill result rather than assumed.

Increasing the angle improves drainage and reduces bridging, but it also shortens the contact and lets solder leave the joint earlier. Move one variable at a time, and note both values in the setup sheet so a later operator can repeat the setting without guessing.

Through-Hole Fill and Barrel Rise

Fill is the measurement that matters for through-hole joints. It is expressed as the percentage of barrel height wetted by solder, and the acceptance limit follows the IPC class the product is built to. A fillet on the top side does not prove the barrel is filled.

Check fill by cross sectioning a sample or by X-ray on boards where the barrels can be seen. Where fill is consistently short, the causes in order of likelihood are wave height, preheat, hole diameter against lead diameter, and flux activity.

Bridging, Icicling and What Causes Them

Bridging between adjacent pins is a drainage problem, not a wetting problem. The solder leaves the board with the last edge while still liquid, and a wave that is too high or an angle that is too shallow traps it between two leads. Lead length and pad spacing on the trailing edge make it worse.

Icicles form in the same way, from solder that solidifies while still hanging from the joint. Raising the conveyor angle and reducing the wave height usually clears both, and the pallet design used for pallet care has to allow the solder to drain off the board cleanly.

Solder Pot Chemistry and Contamination

Copper, gold and other metals dissolve into the pot as boards pass over it, and the alloy drifts from the specification over time. A pot that is out of spec wets differently, and the change appears as a joint cosmetic issue before it becomes a fill problem.

Sample the pot on a fixed schedule and add fresh alloy as the analysis requires, since the pot volume falls as boards carry solder away with them and the level then changes the wave height. Contamination control is the reason that solder pot contamination records belong with the wave setup sheet rather than in the maintenance office.

Setup Sheet, First Article and Daily Checks

The setup sheet should carry the wave heights for both waves, the flux type and amount, preheat temperatures, conveyor speed and angle, and the pot alloy analysis date. That set of numbers is what makes a wave soldering process repeatable between shifts and between machines.

First article should confirm fill by section on a sample, joint appearance on both sides and the absence of bridging. Daily checks cover wave height, flux level and preheat, and they take less time than a single rework operation when something is missed.

FAQ

Is the turbulent wave needed for every through-hole board? No. Boards with short barrels, generous hole clearance and few plated holes can meet fill limits with the chip wave alone. Where the acceptance class requires a high barrel fill, the turbulent wave is the practical way to reach it.

Why does barrel fill drop even when the wave looks normal? Wave height can fall as the pot level drops, and preheat can drift without any visible change. Measure the height and the top side board temperature before assuming the flux is at fault, as the checks in the wave soldering guide set out.

Can selective soldering replace the wave for mixed boards? For low volumes and unusual layouts it can, and the nozzle by nozzle approach described in selective soldering gives more control per joint. For high volume panels the solder wave remains faster, provided the setup is measured and recorded rather than inherited from the last product that ran.