FPC flexible circuit board surface plating knowledge

1, FPC plating

(1) FPC electroplating pretreatment flexible PCB FPC after coated layer process exposed copper conductor surface adhesive or ink pollution, also there will be generated by the high temperature process of oxidation and color change, to obtain good adhesion closely the coating must be the pollution and oxidation of the surface of a conductor layer removal, cleaning the surface of conductor. But these pollution and some copper conductors with very strong and weak cleaning agent and can not be completely removed, so most often used have a certain intensity of alkaline polishing agent and polishing brush and processing, covering the adhesive layer are epoxy resin and alkali resistant performance is poor, this will lead to decreased the adhesion strength, although not visible, but in FPC electroplating process, plating solution may from the infiltration of the edge of the cover layer, serious when can make the cover layer stripping. In the end welding occurs when the solder drill to cover the following phenomenon. Can be said before the cleaning process will have a significant impact on the basic characteristics of the flexible printed board F{C, must give full attention to the processing conditions.

(2) the FPC electroplating plating thickness, metal plating deposition velocity and electric field strength have direct relationship, electric field intensity and position with circuit patterns shape electrode, change, wire width more fine, terminals of the terminal part of the tip, the distance between the electrode and the more near electric field strength is greater, the parts of the coating more thick. And the flexible printed board related purposes in the, in the same line in many wire width difference greatly exist which are more likely to produce coating thickness is not uniform, in order to prevent the occurrence of can be around the line attached to shunt cathode graphics, absorption and distribution uneven pattern plating current, the maximum guarantee in all parts of the coating thickness uniformity. So it is necessary to work hard on the structure of the electrode. Here is proposed a compromise, rigorously for coating thickness uniformity requirements for the high part of the standard, standard for other parts of the relatively relaxed, such as welding melting terne, wires (welding) of gold plated layer standard is higher, and for general anticorrosive terne, the coating thickness requirements relatively relaxed.

(3) FPC electroplating stains, dirt just electroplated coating, especially the appearance and there is no problem, but shortly after some surface stains, dirt, discoloration and other phenomena, especially the factory inspection did not find anything unusual, but to be a user of receiving inspection, found to have the appearance of a problem. This is due to drift is not sufficient, plating on the surface of the residual plating solution, after a period of time for the chemical reaction caused by. Especially flexible printed circuit board, due to soft and not very smooth, concave tend to have a solution "accumulation, and will occur at the site of a reaction of chromotropic, in order to prevent the occurrence of such a situation not only to fully drifting, but also sufficient drying processing. Can be confirmed by the high temperature thermal aging test is fully drifting.

2, FPC chemical plating

Electroless plating can only be carried out when the conductor of the electroplating line is isolated and cannot be used as an electrode. Generally, the use of electroless plating bath has a strong chemical effect, chemical gold plating process is a typical example. Electroless gold plating solution is a very high pH value of alkaline aqueous solution. When using this kind of electroplating process, it is easy to occur under the cover of the drilling fluid, especially if the film laminating process quality management is not strict, the bonding strength is low, more prone to this problem.

Due to the characteristics of the plating solution, the chemical plating of the replacement reaction is more likely to occur under the cover layer, and it is difficult to obtain the ideal electroplating conditions.

3, FPC hot air leveling

Hot air leveling was originally for rigid printed PCB board coated with tin and developed technology, as this technique is simple, has also been used in flexible printed board FPC on. Hot air leveling is put in the tin groove plate directly dipped in the molten, excess solder to blow air. The conditions of flexible printed circuit board (FPC is very demanding of, if the flexible PCB FPC does not take any measures to solder immersion must take flexible printed board FPC folder in the middle of the screen is made of titanium steel, and then immersed in the molten solder, of course, prior to the surface of flexible printed board FPC for cleaning and coating flux. Due to the harsh conditions of hot air leveling is also easy to solder from end of the cover layer to layer beneath the cover of drill, especially covering layer and a copper foil surface bonding strength is low, more likely to occur frequently this phenomenon. Due to the polyimide film is easy to absorb moisture, the hot air leveling, tide moisture absorption will due to the rapid heating evaporation caused by covering layer blister stripping even, so before the FPC hot air leveling must dry and moisture management.


 

(Source: http://www.pcblover.com/raoxing/2012/raoxing_3566.htm)

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