Introduction To Flexible Circuit Board Surface Electroplating Knowledge

FPC electroplating of flexible circuit board

(1) flexible PCB FPC FPC electroplating before processing after cladding coating exposed surface of the copper conductor may have adhesive or ink pollution, also there will be generated due to the high temperature process of oxidation, discoloration, to obtain good tight adhesion coating must remove pollution and oxide layer on the surface of the conductor, the conductor surface clean.

But some of this pollution is combined with copper conductor is very strong, with weak detergent cannot completely remove, so that most often used with a certain intensity of alkaline abrasives and brush and used for processing, most layer adhesives is a kind of epoxy resin and alkali resistant performance is poor, so as to cause a decline in bonding strength, though not visible, but in FPC electroplating process, plating solution is likely from the edge of the cover, serious when overburden stripping.

It appears that the solderer is under the covering layer during the final weld.

It can be said that the pretreatment cleaning process will have a significant impact on the basic characteristics of flexible printed board FPC, and sufficient attention must be paid to the treatment conditions.

(2) the thickness of the FPC electroplating, plating metal deposition rate is directly related to the intensity of electric field and electric field intensity and with the shape of the line graph, the position relationship between electrodes, the general wire line width of the thinner, terminal parts of the terminal is pointed, the greater the closer the distance of the electric field intensity and electrode, the parts of the coating is thick.

In with the flexible PCB related use, in the same line width difference many conductors in great conditions exist it’s easier to produce coating thickness is not uniform, in order to prevent the happening of this kind of situation, can be in line attached diversion around the cathode graphics, absorb graphics on uneven current distribution in electroplating, coating thickness on the maximum guarantee all parts evenly.

So you have to work on the structure of the electrode.

Proposed a compromise here, for the part of the high standard strict coating thickness uniformity, for the other parts of the standard relatively relaxed, for example, the fusion welding lead, tin plating, metal wire by (welding) of gold plated layer standard is higher, and for general corrosion of lead, tin plating, the plating thickness required relatively relaxed.

(3) FPC electroplating stains, dirt, just good plating state, especially the appearance of no problem, but soon after some surface stains, dirt, discoloration and other phenomena, especially when the factory inspection did not find any unusual, but when the user to receive inspection, found the appearance of problems.

This is due to insufficient drift, there is residual plating solution on the surface of the coating, after a period of slow chemical reaction caused by.

Especially the flexible printed board, due to soft and not very smooth, the concave is easy to have a variety of solutions, and then the reaction will occur in the site and color, in order to prevent the occurrence of this situation not only to be fully drifting, but also to be fully dry treatment.

Sufficient drift can be confirmed by thermal aging tests at high temperatures.

Flexible circuit board FPC electroless plating

Electroless plating can only be carried out when the line conductors to be electroplated are isolated and cannot be used as electrodes.

General electroless plating baths have a strong chemical action, such as chemical plating process is a typical example.

A chemical gold-plating solution is a very alkaline aqueous solution with a very high pH.

When using this electroplating process, it is easy to drill under the coating layer, especially if the coating film laminating process quality management is not strict, the bonding strength is low, more likely to occur this problem.

Due to the characteristics of the plating solution, electroless plating of displacement reaction is more likely to happen, so it is difficult to get the ideal electroplating conditions by this process.

Flexible circuit board FPC hot air leveling

The hot air leveling technology is developed for the coating of lead and tin on rigid printed board (PCB), but it is also applied to flexible printed board (FPC) because of its simplicity.

Hot air leveling is the direct vertical immersion of the plate in the molten lead tin tank, the excess solder with hot air away.

This condition is too rigid for flexible PCB FPC, if the flexible PCB FPC do not take any measures cannot be immersed in the solder, must take flexible PCB FPC sandwiched between titanium and steel wire mesh, again into the molten solder, in advance, of course, also want to clean the surface of the flexible PCB FPC processing and coating flux.

Due to the harsh conditions of hot air leveling process, the phenomenon of solder drilling from the end of the covering layer to below the covering layer is easy to occur, 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, when adopting hot air leveling process, moisture absorption will cause blipping or even peeling of the covering layer due to rapid evaporation. Therefore, before FPC hot air leveling, drying treatment and moisture-proof management must be carried out.