AST selective soldering: Selective wave soldering refers to the perforated surface mount components on the circuit board welding. Selective wave soldering joints have required local machine via selective spraying solder flux and then, if necessary, can also be preheated to the circuit board. Such solder benefits are: First, no special tools or templates. Secondly, the process parameters for each of a solder joint can be respectively set according to the requirements of the welding device, so that the quality of solder on the board piece has been greatly improved. As most of the through-hole soldering technology, selective soldering form by 3 process: As with most of the through-hole soldering process, the choice of welding processes equally divided into three parts, spray flux, preheat, solder Fluxing, preheating and soldering Fluxing Spray - flux coated Jet flux spraying nozzle, moving under the PCB as programmed path, spray flux to selected area under PCB movement path can be set, X / Y stage movement, carried out for the programming point of flux spray coating Fluxing Moving path, speed, flux flow, air pressure are settable. spray path, speed, flux flow, air pressure can be set. With a point on the PCB board, to provide different amounts according to the needs of the welding flux. Preheating Preheat Two ways for preheating as wave solder, IR or hot air convection. Two ways to warm up, infrared or hot air. According PCB heat capacity, set different preheat temperature and time for PCB. According endothermic PCB board size to element endothermic size, set the preheating temperature and preheat time. An increase flux Ji activity, two increased pad wetting properties Soldering Soldering Solder pot under the work of X / Y / X moving table, melting soldering come from standard or customized nozzle, moving under the PCB as programmed path, soldering to required components at PCB. movement path can be set, X / Y / Z stage movement, for the programming of the welding point. moving path, moving speed, soldering temperaure, N2 temperature, wave height are settable. moving path, speed, solder temperature, nitrogen temperature, wave height can be set. PCB board with a welding speed can be set to different joints to get different requirements. For example, large endothermic pads, welding speed can be set slower, smaller solder pads can go faster. Selective soldering advantages and disadvantages: Advantage Advantages: Each weld welding parameters can be "tailored" and we do not have to "will." Engineers have enough space for each solder process adjustment of welding parameters (amount of flux spraying, welding time, peak height, etc.) adjusted to the optimum, thereby reducing the defect rate, we might even do a through hole yuan selective soldering defect welding device needed only for the selective soldering point flux spraying, the cleanliness of the board thus greatly improved, while ionic contamination is greatly reduced. The flux NA + CL- positive sodium ions and negative chloride ions remaining on the circuit board, if, over time will be combined with the water molecules in the air and thus form a salt etching circuit boards and solder joints, solder eventually causing an open circuit. No cleaning process for the back-end products, a significant reduction in selective soldering flux residues. Lead-free wave soldering peak temperature is generally about 260 ℃. In welding, the temperature of the circuit board through a piece from room temperature to 260 ℃, then cooled to room temperature, the process, the change process of the two temperature increase and decrease of the thermal shock will bring the circuit board of different materials Because of different thermal expansion coefficients of the object formed by shear stress, when the shear stress to a certain extent it will make the BGA form a layered and micro cracks. Such defects are difficult to detect (even if by means of X-ray machines and AOI), and the solder joints on the physical connection is still turned on (can not be detected by the test function), but when the product in actual use, the joints subject to vibration and other external factors When the influence, it is easy to form an open circuit. Selective soldering point only for a specific welding, either at the spot welding and drag soldering piece circuit board will not cause thermal shock, and therefore do not form a significant shear stress on the BGA and other surface mount devices, which Avoid all kinds of defects caused by thermal shock. Summarized in the end whether to adopt a selective soldering technology? Decided to do this, you may need to consider a comprehensive following: 1. Soldering through-hole components on the high quality requirements. 2 for the conventional treatment is not an ideal means of welding elements with large plate, a large endothermic board, the heat-absorbing member, the high component board, the characteristic difference. 3 kinds of trouble more than the existing PCB board, into a larger fixture. How much quantity or weld points 4 perforated circuit board surface mount components, PCB board to complete the CYCLE TIME production capacity can meet the requirements. 5 If there is no cleaning process, the surface cleanliness of the PCB board after the completion of welding . 6.PCB board components such as whether or not sticky flux potential, open adjustable resistance, not heated components.