Plating process (5)

Last time, we learned about the purpose and principles of chemical plating, as well as the detailed process up to cleaner/conditioner.

 

In this session, we will continue with the next step in the detailed process, which is soft-etching.

 

Detailed Chemical Plating Process:

cleaner/conditioner - soft etching - pre dip - catalyst - reducer - electroless copper

 

Soft Etching:

 

Removes oxide layers on the copper surface, forms a conductive layer, and enhances adhesion.

Removes the conditioning agent on the copper surface.

Imparts a positive charge (+).

There are SPS type and peroxide (H2SO4 / H2 O2) type.

Peroxide (H2SO4/H2 O2) Type Chemical Mechanism:

Cu + H2O2 + 2H+ -> 2H2O + Cu2+

 

Etch rate and plating thickness are calculated based on the difference between the initial and final weights of the specimen.

Etch rate = (Initial weight of specimen - Final weight of specimen) * Constant

Plating thickness = (Final weight of specimen - Initial weight of specimen) * Constant

(The constant is determined by the specific gravity of copper and the size of the specimen.)

Pre-Dip:

 

Prevents water inflow into the catalyst solution (for colloid-type catalysts, maintain colloid at pH below 1)

 

Protects the catalyst solution

 

Enhances surface wet ability, removes oxide layers

 

Imparts a negative charge (-) to maximize Pd adsorption on hole walls

 

There are Acid type and Alkali type.

 

Acid Type:

 

Good coverage

Relatively longer immersion cycle

Potential for impurity generation

 

Alkali Type:

No impurity or bubble generation

Requires management of catalyst concentration