What problems will appear in the tin spraying process of PCB?
The process of hot air leveling in PCB factory is relatively simple, which mainly includes pre-treatment of hot air leveling, cleaning after hot air leveling and inspection. Although the process of hot air leveling is simple, there are still many technological conditions to be grasped if we want to leveling out excellent and qualified PCB by hot air, such as solder temperature, air temperature of air knife, pressure of air knife, dipping time, lifting speed and so on. These conditions all have set values, but when working, they must be changed according to the external conditions of PCB and the requirements of the processing order, such as: plate thickness, plate length of different one-sided, double-sided, multi-layer board. The conditions adopted are different. Only by familiarizing with various process parameters, according to different types of PCB, different requirements, patience, meticulous and reasonable adjustment of the machine, can the qualified PCB be leveled by hot air. The following common problems often occur in hot air leveling. Based on working experience, some treatment methods are put forward for reference only.
一． Hot air leveling exhaust outlet dripping residual liquid, this phenomenon is from the hot air leveling exhaust outlet downward dripping yellow liquid, this liquid is mainly the soldering flux that is normally inhaled by the exhaust outlet. Days and days accumulate in the exhaust duct, can not be discharged, then drop around the exhaust outlet, drop in anywhere, such as hot air pipeline, air knife mouth, air knife mouth maintenance cover drops most, sometimes, work will also drop on the operator's head, work clothes, after closing the exhaust, for example, the greatest amount of residual liquid drops. Hot melting, these liquids are coated on the equipment, and the equipment has been corroded greatly for a long time. Refer to the structure of lampblack remover, make a funnel-type wire mesh on the suction outlet to drain the residual liquid, which can reduce or deal with this situation. It can introduce a ditch or put waste liquid into the waste liquid trough at the lower end of the funnel mesh. After this is done, the residual liquid will flow down from the suction outlet and through the wire, which will cause a large part of the residual liquid in the circuit board factory. The liquid flows down the wire. And make a few more spares such as corroded and replaceable.
二．The gloves usually worn by hot air are usually canvas gloves. One glove is put into another glove to work. The flux is immersed in the glove at any moment, which greatly reduces the heat insulation ability of the glove. Moreover, the flux is also harmful to the opponent. The gloves immersed in flux can be used again after washing, but the effect is not good, because the canvas becomes soft, flux immersion speed is very fast and large, it is recommended to use a fine canvas glove in the immersed gloves. The key problem is that the size of the rubber gloves is appropriate, heat insulation is good, and the softness is good.
三．Flexible board and PCB reworked after milling shape how to hot-air leveling, flexible board because the board is soft, hot-air leveling is very easy to occur problems, the need for extra caution, hot-air leveling should be done before milling and flexible board margin consistent with the border, and then in the border and flexible board margin each punch several relative holes, generally in each side of the border. Three holes can be punched on each side. The flexible board with wide edge and long edge can punch several more holes to avoid the normal hot air. Because of the few holes, the PCB factory is not fixed firmly and the flexible board surface wrinkles occur. Correspond the edge holes to the edge holes of the flexible plate one by one, then tie them with fine copper wire through the holes. After binding firmly, the hot air leveling should be carried out. In general, attention should be paid to reducing the time of solder immersion, reducing the pressure of the air cutter, and milling the matching edge frame when the plate of the milling shape is reworked. Place the plate in the edge frame, and then use leveling glue. The tape is bonded, and the tape on the surface of the board is flattened by rollers, so that the hot air leveling can be carried out after treatment.
四．Reasons for the clamping between guideways in PCB factories:
Adjusting the guide rail can be handled. The distance between the guide rail and the plate is too close or too far.
Correction of hanging plate hole position can be handled. The hanging plate hole is not in the center of the edge of the PCB.
Borders can be handled. The edges and corners of PCB are irregular.
Punch the printed circuit board into the solder tank by hand and take it out. The marginal tin hanging is too thick when the PCB factory reworks.
Hot solder can be used to melt away, lead and tin blocked the lead and tin hole of the guide rail to form a clamp plate. It can be ejected with hard objects.
The article originated from Jiangmen single-sided and double-sided circuit boards. http://www.yonghongpcb.com