Knowledge of FPC surface plating

FPC means PCB made of flexible material. It meets the need of high density, high reliability, miniaturization and lightweight development of electronic products, and also meets the strict economic requirements and the need of market and technology competition.

1. FPC electroplating

(1) 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 these pollution 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 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.

During the final soldering, the solder drillers appear under the overburden.

It can be said that the pretreatment cleaning process will have a significant impact on the basic characteristics of flexible printing plate.

(2) The thickness of the FPC electroplating, plating metal deposition rate is directly related to the intensity of electric field 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 thicker.

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 not uniform, in order to prevent the issue 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 stain and dirt have just been electroplated on the coating state, especially there is no problem with the appearance. However, some surface stains, dirt, discoloration and other phenomena appear soon after. In particular, no abnormal appearance is found in the factory inspection.

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

In particular, flexible printing plate, due to soft and not very smooth, its concave is easy to have various solutions accumulated?

In order to prevent the occurrence of this situation, not only sufficient drift, but also sufficient dry treatment should be carried out.

The high temperature thermal aging test can confirm whether the drift is sufficient.

2. FPC electroless plating

When the conductor of a line to be electroplated is isolated and cannot be used as an electrode, only chemical plating can be carried out.

Generally, the plating solution used for electroless plating has strong chemical effect.

The chemical plating solution is an alkaline solution with a very high PH.

This kind of electroplating process can easily occur under the coating layer, especially if the lamination process quality management is not strict and the bonding strength is low.

The chemical plating of replacement reaction is more likely to occur under the covering layer due to the characteristics of the plating solution.

3. FPC hot air leveling for flexible circuit board

Hot air plain is a technology developed to coat lead and tin on rigid PCB.

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

This condition is too rigid for FPC, if the FPC do not take any measures cannot be immersed in the solder, must take 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 hot air leveling process, the phenomenon of solder drilling from the end of the overburden to below the overburden is also easy to occur, especially when the overburden and copper foil surface adhesion strength is low, which is more likely to occur frequently.

As polyimide film is easy to absorb moisture, the moisture absorbed by hot air leveling process will cause the overburden to bubble or even peel due to rapid evaporation. Therefore, dry treatment and moisture-proof management must be carried out before FPC hot air leveling.