PCB electrical measurement technology analysis
Hot Air Solder Leveling, also known as spray tinning, works by using hot air to remove excess solder from the surface of the printed board and holes. The remaining solder evenly covers the pads and the non-resistive solder lines and surface package points.
Hot air leveling process is relatively simple, mainly: put plate (sticky gold plug protection tape) → hot air leveling before treatment → hot air leveling → hot air leveling after cleaning → inspection. Although the process of hot air leveling is simple, there are many process conditions that need to be mastered if the hot air is to be leveled out for a good qualified printed board.
For example: solder temperature, air knife temperature, air knife pressure, dip solder time, lift Speed ,and so on. These conditions have set values, but they also have to be changed according to the external conditions of the printed board and the requirements of the processing orders, such as: single-sided, double-sided, and multilayer boards with different board thicknesses and board lengths. The conditions adopted by them are different. Only by familiarizing themselves with various kinds of process parameters, according to the different types of PCBs, different requirements, patience, meticulous, and reasonable adjustment of the machine, can the hot air be leveled out of qualified printed boards. In the hot air leveling, there are often the following common problems. Based on work experience, some solutions are provided for reference only one.
The hot air is used to level the exhaust outlet residue.
This phenomenon is caused by the downward flow of yellow liquid from the hot air leveling suction outlet. This liquid is mainly the flux that is sucked into the suction outlet during leveling. As time goes by, it accumulates in the ventilation ducts and cannot be discharged. Then it drips around the suction opening and falls everywhere. Like the hot air duct, the wind knife edge, the protective cover on the air blade drips up, and sometimes it will also work. Drop on the operator’s head, coveralls, in the off-duty closed after the drip drip most of the residual liquid, such as hot melt, these liquids covered on the equipment, a long time on the equipment of the great corrosion. Reference can be made to the structure of the exhaust hood, and a funnel-type wire mesh draining residue is made on the exhaust outlet to reduce or solve this problem. The trench can be introduced into the trench at the bottom of the funnel or placed in the waste tank. During the flow of the liquid from the air outlet downwards, a large part of the residual liquid flows down the wire as it flows through the wire. And do a few more spares such as corrosion can be replaced.
II. The gloves worn when the hot air is leveled are usually made of canvas gloves when the hot air leveling is in progress.
Putting a pair of gloves into another pair of gloves is put on the hands to work. A little longer time the flux is immersed in the gloves. Then the gloves are used. Insulation is greatly reduced, and the flux is immersed in the hand and the opponent has some damage. This kind of glove impregnated with flux can be reused once, but the effect is not good. Since the canvas becomes soft and the flux is immersed at a very high speed and volume, it is recommended to use a fine canvas glove inside the dip gloves. The key problem is: The rubber gloves should be of the right size, better insulation, and good softness.
three. How to wind the flexible boards and printed boards that have been reworked after milling.
The flexible boards, due to the softness of the boards, are prone to problems during hot air leveling and require special care. The edges of the flexible boards should be milled before the hot air leveling. Match the frame, and then in the border and the flexible board at the edge of each playing a few relative holes, generally on each side of the border to play three holes, the width of the side of the flexible board can play a few more holes .
IV. The reason for the card board between the rails:
1. The distance between the guide rail and the board is too close or too far away, and the adjustment guide rail can be solved.
2. The hanging plate hole is not in the center of the edge of the PCB. Correcting the position of the hanging plate hole can be solved.
3. The corners of the PCB are irregular, and the border can be solved.
4. When the PCB is reworked, the edge is too thick and the PCB is manually inserted into the solder bath and removed.
5. The tin holes in the guide rail are blocked by lead and tin, causing the card board to be melted with hot solder and can be ejected with a hard object.
6. After the hot air is leveled, the printed board is hung by nails and rails; the top card is deformed in the middle and the hanger damper is replaced in time.