Thông lượng sóng

It also reduces the concern about flux that has not been completely heated inadvertently transferring to the top side of the circuit board. Fluxes that have high solids content, as well as higher amounts of halogen, tend to be more heat-stable and solder better with a variety of board types, sizes, and thicknesses. Fluxes with lower solids contents and no rosin tend to be easier to electronically probe-test and have less visually apparent residue. Halogen content is not necessarily an indicator of final circuit board reliability since halogen types vary and rosin in the flux will enhance an assembly’s surface insulation resistance.

In addition to limiting the amount of volatile organic compounds (VOC) into the atmosphere, sometimes associated with global warming, VOC-free fluxes are also non-flammable. The disadvantage of VOC-free/water-based fluxes is that they require more pre-heat to drive off the water than similar alcohol-based fluxes. In addition, assemblers must be careful to ensure that the top side of the circuit board is dry, otherwise it could lead to reliability issues in the form of electromigration.

The advantage of water wash fluxes is that they can be formulated to be very active so that they can solder virtually any assembly without a concern for reliability, since the residue will be removed after the soldering process. The disadvantage of water wash fluxes is that assemblers must have an additional piece of equipment, the water wash system, to remove the flux residue, and must deal with the effluent. Neutral pH fluxes can generally be left on the circuit board for extended periods of time before washing, while the “low” pH fluxes generally solder somewhat better.

To this day, some contracts still exist that require fluxes that conform to the old Mil-Spec Mil-F-14256 or QQ-S-571 as a type R, RMA, or RA, even though these specifications have officially been folded into the J-Standard. Rosin-based fluxes were popular because not only is rosin a natural weak flux when molten, but it is also a good dielectric material when solid. Small amounts of residue left on the assembly generally will not harm the assembly unless it operates at high temperature and humidity.