Tham khảo tài liệu 'volume 06 - welding, brazing and soldering part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Circuit board soldering and structural applications are described below as general examples. Circuit Board Soldering. First flux is applied to the leads and circuit board unless flux-cored soldering wire is used in which case this step is omitted. The coated area should extend beyond the immediate joint to ensure adequate wetting by the solder. Next the soldering iron is made to contact the lead never the circuit board land and the solder wire is fed so that it contacts the opposite side of the lead. Melting of the solder indicates that the lead has reached temperature. The wire followed by the iron tip is then removed from the joint area upon formation of the joint fillet. Structural Applications. The larger thermal mass of typical workpieces requires preheating in order to bring the joint area to the working temperature. Then the flux is applied to fully cover the hot surface. The joint is further heated and the filler metal is applied to the joint surfaces. Most inorganic and organic fluxes can tolerate the high temperatures required to supply heat to larger members. The rosin-base fluxes can quickly degrade as indicated by the formation of thick blackened residues on the surface. Heat and solder are removed when an adequate fillet forms at the joint opening in order to ensure complete filling of the joint gap. The hot dip coating of parts can be performed by ultrasonic activation without using a flux. Ultrasonic energy is coupled to the sample through the solder bath Fig. 22 . Optimum coupling is a function of the sample geometry power level and workpiece-horn separation. Oxide removal does not occur through simple line-of-sight erosion by the horn Ref 28 . Rather the oxide is disrupted by the ultrasonic energy that is transferred from the horn into the substrate. Therefore hidden surfaces can also be coated by the solder. Hot-dipped coatings can be applied to large workpieces or to leads on small electronic devices. In the latter case care should be taken to .
