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The thickness of FPC electroplating, the deposition rate of electroplating metal is directly related to the electric field strength.
The surface of copper conductor exposed in FPC after coating process may be contaminated by adhesive or ink, as well as oxidation and discoloration due to high temperature process. In order to obtain a compact coating with good adhesion, the contamination and oxide layer on the surface of the conductor must be removed to make the surface of the conductor clean.
However, some of these pollutions are firmly combined with copper conductor and cannot be completely removed with weak cleaning agent. Therefore, most of them are treated with alkaline abrasives and polishing brush with certain strength. Most of the coating adhesives are epoxy resin and have poor alkali resistance, which will lead to the decrease of bonding strength. Although it will not be obvious, in FPC electroplating process, the plating solution is possible to penetrate from the edge of the covering layer, and the overburden layer will be peeled off in serious cases.During the final welding, the solder will reach under the coating.
We know that the pre-treatment and cleaning process will have a significant impact on the basic characteristics of FPC, and the treatment conditions must be given full attention. The thickness of FPC electroplating, the deposition rate of electroplating metal is directly related to the electric field strength, and the electric field strength changes with the shape of the circuit figure and the position of the electrode. The thinner the wire width is, the sharper the terminal is at the terminal, and the closer the distance is from the electrode, the greater the electric field strength is, and the thicker the coating is.
In the application related to flexible printed circuit board, there are many cases in which the width of many wires in the same circuit is greatly different, which makes it easier to produce uneven coating thickness. In order to prevent this situation, a shunt cathode pattern can be attached around the circuit to absorb the uneven current distributed on the electroplating pattern, so as to ensure the uniform coating thickness on all parts.
Therefore, efforts must be made on the structure of the electrode. In this paper, a compromise scheme is proposed. The standards for the parts with high requirements for uniformity of coating thickness are strict, and the standards for other parts are relatively relaxed. For example, the standards for lead and tin plating for fusion welding and gold plating for metal wire lap (welding) are higher, while for general lead tin plating for anticorrosion, the coating thickness requirements are relatively relaxed.
The stain and dirt of FPC electroplating, the plating state of which has just been electroplated, especially the appearance, has no problem. However, some surface problems such as stain, dirt and discoloration appear soon, especially in the factory inspection. However, the appearance problems are found when the user carries out the receiving inspection. This is due to insufficient drifting and residual plating solution on the surface of the coating, slow chemical reaction after a period of time can cause it.
In particular, flexible printed circuit board, due to its softness and not very smooth, its concave is easy to have various solutions accumulated, and then it will react and change color in this part. In order to prevent this situation, we should not only fully cleaning, but also fully dry. The high temperature thermal aging test can be used to confirm whether the cleaning is sufficient.
