1.FPC plating
Copper conductor surface pretreatment FPC FPC plating after exposing the coated layer process may have adhesive or ink pollution, also will be generated due to high temperature oxidation and color change process, in order to obtain good adhesion force to close the conductor surface pollution and oxide removal, cleaning surface of conductor. But some of these pollution conductors and copper binding is very strong, with a weak cleaning agent can not completely removed, so most often used to have a certain strength of the alkaline abrasive and polishing brush is used for processing, coating adhesive are epoxy resin and alkali resistance is poor, which will cause the bond strength decreased, although not obvious visible, but in the FPC plating process, the plating solution will be from the covering the edge of infiltration, serious will overburden stripping. In the final welding, there is a phenomenon that the solder is under the cover. It can be said that the pretreatment of the cleaning process will have a significant impact on the basic characteristics of FPC.
FPC the thickness of plating electroplating, metal plating deposition rate has a direct relationship with the electric field strength, and the change of position and relation of electric field intensity in line with the shape of electrodes, wires, the general linewidth is fine, terminal parts of the electrode tip, and the closer the electric field strength is greater, the parts of the the coating was more thick. With the use of flexible printed board, on the same line in many wire width vary greatly the presence of which is more prone to the thickness of the coating is not uniform, in order to prevent the occurrence of such a situation, in line with shunt around cathode absorption current in the electroplating graphics graphics, uneven distribution, maximum guarantee all parts of the uniform coating thickness. Therefore, it is necessary to work on the structure of the electrode. Proposed a compromise here, for the standard uniform coating thickness requirements of parts for other parts of the standard strictly, relatively relaxed, such as melting welding plating tin lead wires (welding), the gold layer standards must be high, but for general corrosion with terne plating thickness, the requirements are relatively relaxed.
FPC coating electroplating stains, dirt plating just good, especially the appearance and not what problem, but soon after some surface stains, dirt, discoloration and other phenomena, especially the factory inspection did not find what is strange, but when the user receives a check, found that the appearance of problems. This is due to the drift is not enough, the surface of the coating on the residual plating solution, after a period of time to carry out chemical reactions caused by. Especially for flexible printed boards, as soft and very smooth, easy to accumulate the various solutions "recess? And then in this part of the reaction and color change, in order to prevent the occurrence of this situation not only to the full drift, but also to carry out a full drying treatment. High temperature thermal aging test can confirm whether the drift is sufficient.
2.FPC electroless plating
When the circuit conductor to be implemented is isolated and can not be used as an electrode, it can only be electroless plating. General chemical plating using the plating solution has a strong chemical effect, chemical plating process is a typical example. Chemical gold plating solution is a very high pH alkaline aqueous solution. It is very easy to use the electroplating process, especially in the case of the poor quality management and the low adhesion strength of the coating film laminating process.
Due to the characteristics of the plating solution, the electroless plating of the replacement reaction is more likely to occur under the cover of the plating solution.
3.FPC HAL
HAL was originally for rigid printed board PCB coated tin and developed technology, because the technology is simple, has also been applied to the FPC. Hot air leveling is put in the tin groove plate directly dipped in the molten, excess solder to blow air. This condition is very harsh for FPC, if you do not take any measures of FPC cannot solder immersion, must put the FPC into the center made of titanium steel wire mesh, and then immersed in the molten solder, of course, should also be on the FPC surface cleaning and coating flux.
Because the hot air leveling harsh conditions is also prone to solder from the end cover into the layer beneath the cover of the phenomenon, especially the covering layer and the copper foil surface bonding strength is low, more susceptible to frequent occurrence of this phenomenon. Because the polyimide film is easy to absorb moisture, the hot air leveling, moisture absorption and moisture evaporation caused by sharp coating blistering or even peeling, so before FPC HASL, must be dried and moisture management.
