Selective Solder Nozzle Geometry and Thermal Preheat Window Boundaries
Optimal selective soldering requires balancing nozzle orifice dimensions with precise top-side preheat windows to achieve Class 3 vertical barrel fill.
Non-Wettable Nozzle
Dispensary Hardware
Soldering tool fabricated from stainless steel or specialized alloys resists the adhesion of molten metal to its external surfaces. The non-wettable nozzle allows the solder to form a stable bubble or wave that does not cling to the side of the tip during movement. This physical property is necessary for maintaining a consistent wave height.
Mechanical Action
Molten alloy flows through the center of the aperture and cascades down the sides without wetting the outer skin of the tool. Because the non-wettable nozzle does not bond with the solder, it requires less frequent cleaning and specialized maintenance compared to wettable alternatives. The lack of adhesion prevents the solder from being pulled away from the PCB as the nozzle moves to the next location.
It relies on the velocity of the pump and the precision of the aperture design to stabilize the fluid dynamic.
Process Suitability
Selective soldering applications involving large clearance areas often utilize this type of hardware because of its durability. These nozzles are less prone to erosion from aggressive lead-free alloys over long production runs. A potential drawback is the lower precision in solder drainage which might lead to small icicles or flags if the exit velocity is not tuned.
Most high-volume machines use these for their long service life.