After an "image transfert and development" step, now you will have to:
-Create a copper layer on the developped areas of the dry film, to create tracks of the outerlayer of PCB.
-Thereafter create a selective tinning on tracks to protect Copper from the aggressiveness of etching.
- Copper plating
This operation is devided into 3 steps:
*Surface preparation: degreasing (ELECTROPOSIT PC CLEANER) and micro-etching to increase the surafce roughness and improve adhesion.
*Activation: is done in the solvent of the copper plating bath (sulfuric acid).
*Electrolytic Copper:
To perform this plating, two kind of current are possible:
Pulse current (PPR) or Direct Current (DC).
Pulse current can be used in horizontal (COPPER GLEAM PPR-H) or in vertical mode (CuPulse). However, it is less used and requires insoluble anodes.
Direct current is more usual on French PCB manufacturing lines. CTS proposes:
-COPPER GLEAM PC
-COPPER GLEAM 125
-COPPER GLEAM CLX
-COPPER GLEAM HT 55
Via filling process allows to Copper plate small size holes and blind holes, but requires as well insoluble anodes and the use of copper oxide.
N.B.: The additive promotes high current densities. the higher the current density, the higher the additive consumption.
Approximately one hour is necessary to plate 30 µm.
- Selective tinning
Selective tinning can be realised with tin (Sn) or with an alloy of tin and Lead (Sn/Pb).
Tin:
A thin layer (4-6µm) of Tin is filed because it will be stripped afterward.
-in MSA (MetaneSulfonic Acid) middle: SOLDERON PCT
-in sulfuric middle: RONASTAN EC
-in sulfuric acid middle - Bright Tin: TIN GLEAM CD
Tin / Lead (60/40):
A layer of about 10µm of this aloy is filed.
-IN MSA middle: SOLDERON PC
Close from the eutectic point of the Tin / Lead alloy.