Reagent

Suitable for

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  Foam fluxing

  Foam fluxing is a technology used in electronics assembly to apply flux to the PCB board in the wave soldering process. The flux is needed to deoxydise the surfaces to be soldered. The technology has mainly been replaced by spray fluxing but does offer some advantages. It provides good and equal flux wetting of the PCB and through holes and it is a simple and cheap unit with no moving parts. The disadvantages are that the applied flux volume cannot be varied and is always maximal. Furthermore it is an open system with evaporation of the flux solvent and potential absorption of water from the air (typical for alcohol based fluxes) that requires monitoring of the solid content or density of the flux and adjusting with flux thinner. Also pollution from the boards that pass through the flux can affect the foaming ability and properties of the flux. A foam stone with very fine holes (~10-20µm) is mounted in a nozzle which is submerged in flux. Pressurised air is pushed through the foam stone to create a foam that will move up the nozzle. The PCB board is transported through the foam that exits the nozzle. The foam will fall back into the flux tank. The flux tank and nozzle are usually made out of stainless steel but can also be made out of a solvent resistent plastic like HDPE. Some important parameters are: The pressurised air needs to be free from water and oil, an oil and water separator are required. The length of the foam stone is preferrably as big as the nozzle to get an equal foam formation across the nozzle. It is advisable that the top of the foam stone is kept submerged at least 3 cm underneath the flux surface. To keep the flux level in the tank stable, some systems will use an overflow system where the flux will be pumped around and in some cases is filtered. Avoid that foam stone will make contact with the air as flux residues can dry and block the holes. If that happens, the foam stone needs to be cleaned in a solvent or be replaced. The flux nozzle opening is preferrably 8-10mm. Adjust the air pressure until a smooth foam formation is achieved. The contact of the foam with the PCB can be checked with a glass plate. With this glass plate also the setting of the air knife can be checked. The air knife is a tube with drilled holes that are preferrably 1 mm in diameter and 5mm apart from eachother. This will create an even air curtain with pressurised air. The air knife is mounted behind the foam fluxer under an angle so that the air curtain will blow off excessive flux from the PCB that will fall back into the flux tank. On the glass plate no dry stripes may be formed. If this is the case the air pressure on the air knife needs to be reduced. No flux drops may fall off the glass plate after that it has passed the air knife. If this is the case the air pressure on the air knife needs to be increased. Most water based fluxes are not suitable for foaming. PacIFic 2010F is a water based flux specifically designed for foaming.