Wave Height and Nozzle Control in Wave Soldering
Wave height sets how deeply the board touches the molten solder, and the contact depth that results decides whether holes fill and whether bridges form. It is a mechanical setting with a chemical consequence, and the nozzle that produces the wave is the part most often neglected until a fill problem appears.
What Wave Height Controls
The wave is a standing flow of molten solder above the nozzle, and its height determines how far the board is pushed into the solder as it passes. Too little contact and the solder does not reach the top of a plated hole; too much and solder floods the topside, bridging adjacent pins and contaminating surfaces that should stay clear.
Because the setting is mechanical, it interacts with the board itself: thickness, warpage, pallet flatness and conveyor angle all change the effective contact depth for the same wave height. That is why the correct setting is established with the product’s own pallet and a measurement plate rather than copied from a previous job.
Contact Depth and Hole Fill
Contact depth is the fraction of the board thickness immersed in the wave, and a common working target is around half to two thirds of the thickness, roughly 0.5 to 1.0 mm on a typical board. Contact time at the wave is usually two to four seconds, set by conveyor speed and the width of the contact zone.
Hole fill improves with depth and time up to a point, then plateaus and eventually degrades as the extra heat and turbulence push solder onto the topside. A joint that fills to 75 percent of the barrel height satisfies most acceptance criteria; chasing the last quarter by increasing depth is how bridging problems begin.
Nozzle Geometry and Flow
The nozzle slot width and the pump setting determine the flow rate and the shape of the wave. A narrow slot with high flow produces a turbulent wave that reaches into holes well but entrains oxide and can splash; a wide slot with lower flow gives a smoother wave that is gentler on the assembly and better at wetting the pads on top.
Chip wave and main wave are separate in most machines, and they are set for different purposes. The chip wave is turbulent and fast, aimed at small surface-mount joints, while the main wave is smooth and slower. Setting both to the same flow defeats the design of the machine. Where a machine has only one wave, the compromise is a slightly wider slot with a lower flow, which gives acceptable fill on most assemblies without the splash of a narrow, fast wave.
Setting the Wave for a Mixed Board
A board carrying both through-hole and surface-mount parts needs a setting that fills the holes without disturbing the glued parts. Adhesive-cured components can be lifted by a wave that is too high or too turbulent, and the failure appears as a part that is dislodged on one side of the board rather than as a fill defect.
Where the board has regions of very different density, the pallet and the board support matter as much as the wave height. Shadowing behind a tall feature reduces contact in a way that no increase in wave height can fix, and adding height only floods the parts that are already well contacted. The same effect appears where a large connector sits near the wave entry, because the solder is cooler and slower at the leading edge than in the middle of the contact zone.
Dross and Oxide on the Wave
A wave carries oxide into the joint area continuously, and the oxide appears both as dross on the pot surface and as a film on the wave crest. A crest that looks dull rather than bright is carrying oxide into the contact zone, which reduces wetting and adds inclusions to the joint.
Skimming, nitrogen blanketing and a correctly set flow all reduce the oxide load. The flow setting itself matters: a wave that is too turbulent folds air into the solder and generates more oxide than it carries away, so lowering the flow can improve both the oxide level and the joint quality.
Chip Wave, SMD Adhesive and Shadowing
Surface-mount parts on the underside are held by adhesive during wave soldering, and the adhesive has to be cured before the board reaches the wave. An undercured adhesive softens in the wave and allows the part to shift, while an overcured one becomes brittle and can crack during thermal expansion.
The chip wave should contact the adhesive-bonded parts directly, with the wave height set so that solder reaches the joints without lifting the body. Where a part sits close to a through-hole feature, the wave direction determines whether it is shadowed, and reorienting the part on the panel is sometimes the only effective fix.
Measuring and Recording the Wave
Wave height is measured with a plate that passes over the nozzle and a depth gauge or glass plate that shows the crest. The measurement should be taken at the start of each shift and after any change of pallet, nozzle or product, and the value recorded rather than noted as acceptable.
Contact depth is confirmed by measuring the solder level on a test board or by the telltale line that appears on the pallet finger. Both measurements together define the setup, and neither alone is sufficient, because a wave height that is correct with one pallet is wrong with another of a different thickness.
Maintenance and Nozzle Wear
Nozzle slots erode with use, and an eroded slot widens, lowering the crest velocity for the same pump setting. The change is gradual, so the wave height reading stays constant while the filling behaviour deteriorates an operator cannot explain. Measuring the slot width at each scheduled maintenance catches the wear before it shows up in the joints.
Dross that is allowed to build on the nozzle edge distorts the wave shape and creates dead zones in the flow. Cleaning the nozzle on the same schedule as the pot skimming keeps the crest even, and the difference between a cleaned and a fouled nozzle is visible in the fill rate on a marginal board. Keep the pump impeller in the maintenance plan as well, since a worn impeller reduces flow for the same setting and produces the symptoms of a low wave.
Troubleshooting Fill and Bridging Together
Incomplete fill and bridging often appear on the same board, which tells you the setting is wrong in both directions at once. High wave height fills the holes but floods the topside; low height leaves the holes short but avoids bridging. The correct setting is the one that fills the barrels without leaving excess solder, and it is found by measuring fill on a sectioned sample at two or three heights.
Where fill is poor across the whole board at any height, look at flux application and preheat before the wave. Where it is poor only behind a feature, look at shadowing and pallet design. The joint criteria give the target, and the wave settings are the means of reaching it.
FAQ
What contact depth should a wave solder process use? Roughly half to two thirds of the board thickness, about 0.5 to 1.0 mm, with a contact time of two to four seconds set by conveyor speed.
Why does the wave height setting change with a different pallet? Pallet thickness and flatness change how far the board sits into the wave. The setting is a property of the pallet and board combination rather than of the machine alone.
How does nozzle wear affect hole fill? An eroded slot widens and lowers crest velocity for the same pump setting, so filling deteriorates while the wave height reading stays unchanged. Measure slot width during maintenance.
