Biomedical Engineering Reference
In-Depth Information
The basic theory of electrodeposition is to allow electric current
conduction to move ions through the interior of the transmission.
Upon contact with the electrode and solution, a reaction occurs
between the electrode and the moving charge. At the anode,
dissolution of the metal surface produces oxygen and oxidation
(anodic oxidation), while on the cathode side; precipitation of
metal produces a hydrogen reduction reaction (cathodic reduction).
Basically, electroplating uses the appropriate potential energy from
the electrical low of current to produce electrochemical cathode
precipitation and attract it to the material. Metal ions come from the
electroplating solution or from the consumable anode; the electricity
restores them and deposits them at the cathode. Electroplating is an
electrochemical reaction, and Faraday's law of induction regulates
the amount of plating. Electroplate the previously discussed photo-
resistant processed side of a stainless steel substrate with nickel
requires three steps: pre-treatment, plating, and post-treatment:
(a) Pre-treatment: With 20 ASD (A/dm
2
) in a 10% sulfuric
acid solution at room temperature activates anodes using a
stainless steel plate that has been processed with lithography.
The purpose of this procedure is for etching to increase the
plating area at the bottom of the plate and to activate the
oxidized layer materials.
(b) Plating: This requires a nickel-plating solution composed of
the basic ingredients of a sulfuric acid bath (e.g., Ni
2
SO
4
), an
ingredient to activate the soluble auxiliary anode and higher
conductivity (e.g., Ni
2
Cl
2
, NH
4
Cl), and an ingredient to prevent
changes in buffer pH (e.g., boric acid). For low-cost plating,
a low-stress sulfamate bath with high scalability, better
sealing, and high concentration formulations has replaced
most sulfuric acid baths. Coating structures and performance
improvements, such as improved gloss and smoothness, are
mainly achieved by using organic additives. Generally, nickel
additives can be classiied as brightener and wetting agents,
structure modiiers, lattening agents, and carriers. A brightener
enhances the relective properties of metal coatings. For good
performance, the roughness of metal relective coatings must
be considerably below the wavelength of incidental light.
Therefore, adding a brightener is essential to reducing the
size of sedimentary particles, and making the coating brighter.
After a brightener is added to nickel plating, the cathode
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