The following steps can be distinguished into the process.
(1) Predips may be used prior to etching to overcome two problems in parts.
The first reason is to improve the surface of poorly molded, highly stressed
parts. By slightly swelling the surface, a more uniform surface attack in
etching is possible, reducing non-uniform etch conditions and improving
overall adhesion. Secondly, a predip is used to facilitate etching on normally
hard to etch plastics, e.g. Xantar polycarbonate.
This is also done by attacking and swelling the surface. A different solvent
is needed for each polymer and high molded-in stresses should be avoided as
they may lead to cracking during pre-dip.
(2) Etching. If the plastic contains butadiene rubber particles, which serve
as an impact modifier, the etchant may be chromium acid, permanganate,
chromium trioxide, or sulphuric acid. The butadiene is selectively removed,
thus leaving small ball shaped holes or bonding sites for mechanical
(3) After etching, the parts are rinsed in water and then put into a
neutralizer, such as sodium bisulphite. Care must be taken that all etchants
are completely removed, with no traces left in blind holes, as this may lead
to poor metallizing if the etchant bleeds out in subsequent metallization
(4) In the next step a catalyst (or activator) is applied by submersing the
part in a palladium tin colloid bath. Palladium is deposited during the