PCB News - Some common problems in PCBA tin spraying

Some common problems in PCBA tin spraying
PCB hot air leveling is also called PCBA tin spraying. Its working principle is to use hot air to remove excess solder from the surface and holes of the printed circuit board, and the remaining solder is evenly coated on the pads, non-solder lines and surface packaging points.

The process of PCB hot air leveling is relatively simple, mainly: placing the board (sticking with gold-plated plug protective tape) - PCB hot air leveling pretreatment - PCB hot air leveling - PCB hot air leveling and cleaning - inspection. Although the process of PCB hot air leveling is simple, if you want PCB hot air leveling to produce a good and qualified printed circuit board, there are still many process conditions that need to be mastered, such as: solder temperature, air knife air temperature, air knife pressure, dip soldering Time, speed and so on. These conditions have set values, but they must be changed according to the external conditions of the printed circuit board and the requirements of the processing order when working, such as: single-sided, double-sided, and multi-layer boards with different board thicknesses and lengths. The conditions they use are different. Only by familiarizing and mastering various process parameters, according to different types of printed circuit boards, different requirements, patience, meticulous, and reasonable adjustment of the machine, can the PCB hot air level out qualified printed circuits. plate. The following common problems often appear in PCB hot air leveling. Some solutions are proposed based on work experience for reference only.

one. PCB hot air leveling air outlet drips residual liquid. This phenomenon is that yellow liquid drips down from the PCB hot air leveling air outlet. This liquid is mainly the flux sucked in by the air outlet during leveling. It accumulates in the exhaust pipe for a long time and cannot be discharged. It drips around the exhaust port. The drips occur everywhere. Like hot air pipes, the air knife edge, the protective cover on the air knife edge drips the most. Sometimes, it will also be at work. It drips on the operator's head, work clothes, and the most residual liquid, such as hot melt, drips after the exhaust is closed after get off work. These liquids cover the equipment and cause great damage to the equipment over time. Refer to the structure of the range hood, and make a funnel-shaped wire mesh on the air outlet to drain the residual liquid, which can reduce or solve this situation. You can introduce the trench or put it into the waste liquid tank at the bottom of the funnel. When the liquid flows downward from the suction port, when it flows through the iron wire, a large part of the residual liquid will flow down the iron wire. And make a few more spares if it is damaged, it can be replaced.

two. For PCBA hot air leveling, canvas gloves are usually used for PCBA hot air leveling. Put one pair of gloves into another pair of gloves and wear them on your hands for work. After a while, the flux is immersed in the gloves. At this time, The heat insulation capacity of the glove is greatly reduced, and the flux immersed in the hand will also cause a certain amount of damage to the opponent. This kind of gloves immersed in flux can be used again after washing, but the effect is not good. Because the canvas becomes soft, the flux is soaked very fast and the amount is large. It is recommended to add a fine canvas glove inside the dipping glove. The key question is: the size of the rubber gloves should be appropriate, the heat insulation should be good, and the softness should be good.

three. How to flatten flexible boards and printed circuit boards that have been milled and reworked with hot air? Because the flexible boards are soft, they are prone to problems when the PCB is leveled with hot air. You need to be extra cautious. PCBA should be milled and flexed before hot air leveling. The edge of the flexible board matches the frame, and then punch a few opposite holes at the edge of the frame and the flexible board. Generally, three holes on each side of the frame are enough. There are more flexible boards with wide and long sides. Punch a few holes to prevent wrinkles on the flexible board surface due to few holes and weak fixation when the PCB is leveled by hot air. Align the frame holes with the edge holes of the flexible board, and then use thin copper wires to pass through the holes for binding. After the binding is firm, the PCB should be leveled with hot air. When leveling, attention should be paid to shorten the solder immersion time and reduce the pressure of the air knife. When reworking a small, milled board, you must also mill the matching frame, put the board into the frame, and then glue it with a flattening tape, flatten the tape on the board with a pressure roller, so that it can be processed after processing PCB hot air leveling.
Four. The reason why the board is stuck between the guide rails:

1. If the distance between the guide rail and the board is too close or too far, it can be solved by adjusting the guide rail.
2. The mounting hole is not in the center of the edge of the printed circuit board, it can be solved by correcting the position of the mounting hole.
3. The edges and corners of the printed circuit board are irregular, which can be solved by adding a frame.
4. When the printed circuit board is reworked, the edge hanging tin is too thick. Insert the printed circuit board into the solder tank by hand and then take it out.
5. The tin-out hole of the guide rail is blocked by lead and tin too much, which causes the PCB board, which can be melted by hot solder, and can be ejected with a hard object.
6. After PCB hot air leveling, the printed circuit board is stuck between the nails and the top of the guide rail, causing deformation. Replace the suspension arm shock absorber in time.