Flexible circuit board FPC hot air leveling

(1) The thickness of FPC electroplating, electroplating metal deposition rate is directly related to the electric field strength, electric field strength with the shape of the line figure, electrode position and change, the general wire wire width is thinner, the terminal part of the terminal, the closer the distance from the electrode the greater the electric field strength, the thicker the coating. In the use of flexible printed boards, in the same line many wire widths are very different, which is more likely to produce uneven coating thickness, in order to prevent this, can be installed around the line shunt cathode graphics, absorb the distribution of uneven current on the electroplating graphics, to ensure the maximum thickness of all parts of the uniform coating. So you have to work on the structure of the electrode. A compromise is proposed here. The standards for the parts with high uniformity of coating thickness are strict, and the standards for other parts are relatively relaxed, such as the lead plating of molten welding, the gold plating of metal wire (welding), etc., are high, and for the general corrosion protection of lead plating, the coating thickness requirements are relatively relaxed.

(2) FPC electroplating stains, dirt just electroplating good coating status, especially the appearance of no problems, but soon after some surface stains, dirt, discoloration phenomenon, especially when the factory inspection did not find anything strange, but to be received by the user, found that there are appearance problems. This is due to insufficient drift, coating on the surface of the residual plating solution, after a period of time slowly caused by chemical reactions. Especially flexible printed board, due to soft and not very smooth, its concave easy to have a variety of solution "accumulation? In order to prevent this from happening, it is necessary not only to fully drift, but also to fully dry. Adequate drifting can be confirmed by thermal aging tests at high temperatures.

2. FPC electroless plating of flexible circuit board

Electroless plating is performed only when the conductor of the line to be electroplated is isolated and cannot be used as an electrode. The plating solution used in general electroless plating has strong chemical action, and the chemical plating process is a typical example. Chemical gilding solution is alkaline water solution with very high pH value. When using this plating process, it is easy to get the plating solution under the overlay, especially if the quality management of the overlay lamination process is lax and the bonding strength is low, it is more likely to occur.

Due to the characteristics of plating solution, plating solution is more likely to be drilled into the coating layer, so it is difficult to obtain ideal plating conditions by this process.

3. Flexible circuit board FPC hot air leveling

Hot-air plain is a technology developed for rigid printed board PCB coated with lead tin. Because of its simplicity, this technology is also applied to flexible printed board FPC. Hot air leveling is to immerse the board directly into the molten lead tin groove vertically, and the excess solder is blown away with hot air. This condition is very harsh for the flexible printed board FPC, if the flexible printed board FPC do not take any measures can not be immersed in the solder, must be the flexible printed board FPC clip to titanium steel screen in the middle, then immersed in the molten solder, of course, also prior to the surface of the flexible printed board FPC cleaning treatment and coating flux.

Because of the harsh conditions of the hot air smoothing process, it is easy to drill solder from the end of the covering layer to under the covering layer, especially when the bonding strength of the covering layer and copper foil surface is low, this phenomenon is more likely to occur frequently. Because polyimide film is easy to absorb moisture, hot air leveling process, moisture absorption will cause the covering layer foaming or even peeling due to rapid heat evaporation, so before FPC hot air leveling, must be dry treatment and moisture-proof management.