lead free printed circuit board assembly
At present, lead-free wave solder flux coating method there are two kinds: foam and spray. Foaming method is the blower by means of a dip in the flux liquid, emitting a low-pressure clean air foam surface and along the chimney-type nozzle to blow through the nozzle, so that the welding surface to merge with foam, coated with a layer of uniform flux. The advantage is: compatibility and connection of the welding process, the foam required accuracy is not high, mixed pcb assembly substrate. Then the drawback is the evaporation loss is quite large, because the solution boiling point, long warm-up time, and not all the flux has good foaming properties. The other is coated with non-uniform, residue on the printed circuit board, can not control the flux coating amount would need to monitor changes in the flux and frequent replacement of the flux, the flux is consumed in large quantities, the foam method for the high solids content 5% of the flux, the effect is better. However, for lead-free solder no-clean flux residue flux, the solid content is generally less than 5%, the majority of no-clean flux solids content of 2%, low solids content flux foam does not fully not suitable for foam application. This will require another flux coating, ie, spray method.
The spray method is a popular method of no-clean soldering process. It allows precise control of the flux deposition. Flux spray system can be designed as single-channel system, non-recycling by the single-channel system in a closed container supply flux. To do this, you do not need to monitor the solids content of the flux.
Flux spray system is the use of the spray device, flux atomized spray to the PCB, after preheating wave soldering. The spray coating process with a uniform coating, with less, without any titration or the proportion of monitoring without regular emissions to the old flux, flux deposition of the control panel closed system, eliminating the help flux stain problems, recognized by many users. No-clean flux spray coating has become the future direction of development. The parameters affecting the flux is the amount of four: the substrate transfer speed, air pressure, nozzle swing speed and flux concentration. Through the control of these parameters will enable the jet's thickness was controlled at between 1-10 microns. The approach has the advantage of flux spray can be used for most of the liquid flux, and the coating thickness can be controlled, warm-up time is short.
For lead-free wave soldering, lead-free solder wettability of the solder SNPB worse, for others to ensure good welding quality, the choice of flux and coating requirements. The general lead-free wave solder no-clean flux, this flux is generally lower activity residue activity to a large extent dependent on the procedure, which requires the wave soldering equipment requirements of uniform flux spray higher coated requirements. The general lead-free wave solder no-clean flux, this flux is generally lower activity residue activity to a large extent dependent on the procedure, which requires the wave soldering equipment requirements of uniform flux spray higher coated requirements. The general lead-free wave solder no-clean flux, this flux is generally lower activity residue activity to a large extent dependent on the procedure, which requires the wave soldering equipment requirements of uniform flux spray requirements on the coating of flux spray evenly coated, and the amount of the coating flux requirements moderate. When the flux coating excessive, it will make too much residue in the PCB solder affect the appearance, and this residue on the PCB has a certain corrosive, may be caused in the course of the destruction of the circuit. In addition, too much flux in the preheating process may be dripping in the heat pipe caused fire, the impact of heat tube life. The flux coating or coating uneven, it may cause the weld, Weld or even welding.