The hot air leveling is also called tin-spraying. Its working principle is to use hot air to remove the excess solder on the surface of the printed board and the holes. The remaining solder evenly covers the pads and the unresisted solder lines and surface package points.
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The process of hot air leveling is relatively simple, mainly: placing the board (pushing gold-plated plug protection tape) → pre-treatment of hot air leveling → hot air leveling → cleaning after hot air leveling → inspection. Although the process of hot air leveling is simple, there are still many process conditions to be mastered if the hot air is flattened out of a good qualified printed board, such as: solder temperature, air knife air temperature, air knife pressure, dip soldering time, lifting. Speed ​​and more. These conditions have set values, but they must be changed according to the external conditions of the printed board and the requirements of the processing sheet, such as: single thickness, double side, multi-layer board with different thickness. The conditions they use are different. Only when they are familiar with various process parameters, according to different types of printed boards, different requirements, patience, meticulous and reasonable adjustment of the machine, the hot air can be used to level out the qualified printed boards. The following common problems often occur in hot air leveling. Some solutions are proposed based on work experience for reference only.
one. The hot air leveling drains the residual liquid. This phenomenon is to drip the yellow liquid downward from the air outlet of the hot air leveling. This liquid is mainly the flux that is sucked in by the air outlet when leveling. It has been accumulated in the exhaust pipe for a long time, and it can not be discharged. It will drip around the exhaust port and fall where it is. Like the hot air pipe, the wind knife edge, the protective cover on the wind knife edge drops most, sometimes, at work. Dropped on the operator's head, on the overalls, the most residual liquid dripping after the ventilation is turned off after work, such as hot melt, these liquids are applied to the equipment, and the corrosion of the equipment is great for a long time. Refer to the structure of the exhaust hood, make a funnel-type wire mesh drainage residual liquid on the air outlet, which can reduce or solve this situation. It can be introduced into the trench at the lower end of the funnel net or put into the waste tank. When the liquid flows downward from the air outlet, a large part of the residual liquid flows down the wire when flowing through the wire. And do more spares such as corrosion can be replaced.
two. When the hot air is leveled, the gloves are usually made of canvas gloves when the hot air is leveled. Put a pair of gloves into the other gloves and put them on the hands to work. After a long time, the flux is immersed in the gloves. The heat insulation capacity is greatly reduced, and the flux is immersed in the hands and the opponent also has some damage. This kind of glove immersed in the flux can be used again after washing, but the effect is not good. Since the canvas is soft, the flux immersion speed is very fast and the amount is large. It is recommended to add a thin canvas glove inside the dip glove. The key issue is that the rubber gloves are the right size, the insulation is good, and the softness is good.
three. The flexible board and the finished printed circuit board have a hot air leveling. The flexible board is easy to cause problems when the hot air is leveled due to the softness of the board. It needs to be extra cautious. Before the hot air leveling, it should be milled to the edge of the flexible board. Match the border, then make several opposite holes at the edge of the frame and the flexible board. Generally, three holes can be made on each side of the frame. The side width can be increased by several holes. .
four. Reasons for the card between the rails:
1. If the distance between the guide rail and the board is too close or too far, the adjustment rail can be solved.
2. The hanging plate hole is not at the center of the edge of the printed board, and correcting the position of the hanging plate hole can be solved.
3. The corners of the printed board are irregular, and the border can be solved.
4. When the printed board is reworked, the edge of the tin is too thick, and the printed board is inserted into the solder bath by hand and then taken out.
5. The tin-out hole of the guide rail is blocked by lead-tin and the card is too much, which can be melted by hot solder and can be ejected by a hard object.
6. After the hot air is leveled, the printed board is hung with the rails and the top is stuck in the middle to cause deformation, and the arm shock absorber is replaced in time. 
