Challenges regarding photo forming are the process for the plate separation and plating layer thickness management. Oxide, chromate, sulfide film are used for the separation layer. [Table.1] shows some examples of the process configurations.

[Table.1] Separation film forming processes

Electroplating is usually used for its speed of deposition. A variety of plating solutions can be used, but copper and nickel are mostly used. In rare instances gold and silver are used.
Electroplating is typically performed with a system such as the one shown in [Fig.1]. Continuous filtering of the solution is a special point to note in order not to allow precipitation of foreign objects within the solution and from anode slime. A fine meshed bag is also used on the anode to prevent slime from intruding. Organic impurities that degrade the plating glossiness and physical properties are removed by activated charcoal treatment.

In order to ensure unified plating layer thickness, the plating bath solution is stirred, as well as the substrate is rotated and rocked. This is to adjust the distance from the anode and to account for the effects of agitating the solution. [Fig.2] shows how the plating layer grows and reaches the desired thickness by continued plating.

Good products are obtained when the plating layer thickness is within the resist's thickness. But when the plating becomes thicker than the resist layer, the plating spills over the pattern and the accuracy is degraded. The excess plating spilled over is called Side Spreading.