The difference between electroless and immersion is in the chemistry and what
drives the reduction of palladium in solution to pure metal.   Electroless
solutions contain reducing chemicals that cause the palladium to go from an
oxidized state to elemental (zero).   If you keep adding ionic palladium and
more reducing agent, the reaction will keep on going, and going, etc.

Immersion reactions dissolve some of the metal being plated to drive the
reduction reaction of the palladium in solution.   That is, once the
deposited elemental palladium covers the underlying metal, the reaction
stops.

Immersion reactions only work based on the electromotive series of elements.
 Think of it as a reverse battery.   Electroless reactions do not depend
strictly on the electromotive  series of elements - a strong reducing
chemical system can drive anything - even gold.

Denny Fritz
MacDermid - Waterbury

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