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PCB HASL common problems and solutions
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PCB HASL common problems and solutions
Hot air leveling solder coating process is the most common method in PCB surface technology. Its working principle is that the printed circuit board is immersed in the molten tin solder, and then through two air knives (high-pressure hot air), the surplus solder on the board surface and in the metallization hole is blown off with hot compressed air to obtain a smooth, bright and uniform solder coating layer. Although the process of hot air leveling is simple, there are many process conditions to master if you want to produce qualified PCB by hot air leveling, such as solder temperature, air knife air temperature, air knife pressure, immersion welding time, lifting speed, etc.Get more news about Pcb Board Roller Leveller,you can vist our website!
All of these conditions have set values, but they have to be changed according to the external conditions of printed circuit boards and the requirements of processing sheets, such as single-sided, double-sided and multi-layer boards with different board thickness and length. The conditions adopted by them are different. Only by mastering various process parameters and adjusting the machine patiently, carefully and reasonably according to different types and requirements of PCB, can qualified PCB be produced by hot air leveling.
1) Yellow liquid may drips down from the air outlet of hot air leveling. This liquid is mainly the flux absorbed by the air outlet during leveling. If it is accumulated in the exhaust pipe for a long time and cannot be discharged, it drips along the air outlet, and drops everywhere. For example, the hot air pipe, the blade edge and the protective cover of the air knife drop the most. Sometimes, it drips on the head of the operator and on the work clothes. After the ventilation is turned off in the next shift, the residual liquid drops most, such as hot melting. These liquids are covered on the equipment, and the time is up After a long time, the corrosion of the equipment is very large. Referring to the structure of the range hood, a funnel-shaped wire mesh can be made on the air outlet to drain the residual liquid, which can be reduced or solved by introducing a trench at the lower end of the funnel net or putting it into a waste liquid tank. After that, when the residual liquid flows downward from the air outlet, a large part of the residual liquid will flow down along the iron wire when it flows through the iron wire.2) The gloves for hot air leveling usually use canvas gloves. One pair of gloves is put into another pair of gloves to wear on the hand for work. If the time is a little longer, the flux will be immersed in the gloves. At this time, the heat insulation capacity of the gloves will be greatly reduced. Moreover, if the welding flux is immersed in the hands, the opponent will also be hurt. After washing, the gloves immersed in flux can still be reused, but the effect is not good. Because the canvas becomes soft while the flux immersion speed is very fast and the amount is large. It is suggested to add a thin canvas glove into the plastic dipping glove. The key point is that the size of the rubber glove should be appropriate, the heat insulation is good, and the softness should be good.
3) How to hot air level the flexible board and the printed board with the shape reworked after milling. Because the flexible board is soft, it is easy to have problems in hot air leveling, so we need to be very careful. Before hot air leveling, we should mill the frame that is consistent with the edge of the flexible board, and then drill several relative holes at the edge of the frame and the flexible board. Generally, three holes can be drilled on each side of the frame. The folding phenomenon of flexible plate surface is caused by less holes and unstable fixation. The frame hole and the edge hole of the flexible board should be matched one by one, and then the thin copper wire should be used to tie through the hole. After the binding is firm, the hot air leveling should be carried out. During leveling, attention should be paid to shorten the time of solder dipping and the pressure of air knife. When the plate with milling shape is reworked, the corresponding frame should be milled, and the board should be placed in the frame, and then bonded with leveling tape, and the tape on the board surface should be flattened with a pressure roller Hot air leveling can be carried out after sample treatment.4) 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. The hanging board hole is not in the center of the edge of the printed circuit board. Correcting the position of the hanging board hole can solve the problem. The edges and corners of printed circuit board are irregular, which can be solved by adding frame. When the PCB is reworked, the tin hanging on the edge is too thick. Insert the PCB into the solder groove by hand and then take it out. The tin hole of guide rail is blocked too much by lead and tin, which can be melted by hot solder and pushed out by hard object. After hot air leveling, the PCB is stuck in the middle between the hanging nail and the top of the guide rail, resulting in deformation, so the hanging arm shock absorb-er should be replaced in time.