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Pulse Anodic Dissolution of Macroscopically Non-uniform Surface with Artificial Insulation


Author: Olga Redcozubova
Degree:doctor of chemistry
Speciality: 02.00.05 - Electrochemistry
Year:2004
Scientific adviser: Alexandru Dicusar
doctor habilitat, professor, Institute of Applied Physics of the
Institution:
Scientific council:

Status

The thesis was presented on the 7 October, 2004
Approved by NCAA on the 23 December, 2004

Abstract

Adobe PDF document – 0.63 Mb / in romanian
Adobe PDF document – 0.65 Mb / in russian

Keywords

electrochemical micromachining in presence of photoresist masks, micro- and macrodistribution of local dissolution rates, high-rate dissolution inside a cavity, pulse anodic-cathodic machining, etch localization (Etch Factor)

Summary

The etching rate, and also the behavior of micro- and macrodistribution of local dis-solution rates during electrochemical micromachining in presence of photoresist masks have been investigated by example of anodic dissolution of different metals and alloys (copper, mild steel, Invar alloy (Fe – 36 % Ni)) in activating (NaCl) and passivating (NaNO3) electrolytes under various geometrical, hydrodynamic condition (RDE, sprayer (jet) flow, “recessed” RDE) and at various insulation thickness.

It is shown that the conditions providing the maxim localization of microdissolution (dissolution inside a cavity) at the greatest possible uniformity of macrodistribution under conditions of use of a direct current are high-rate dissolution with rates close to limiting anodic current density, high rates of ionic mass transfer at a sprayer flow and their uniform distribution on all machining surface.

We demonstrate that pulse anodic-cathodic machining of a surface is a method of dissolution localization control, when surface concentration of anodic dissolution products in the area of undercutting exceeds surface concentration of the products formed during dissolution in a normal direction (conditions of prevalence of the tertiary current distribu-tion). Under these conditions we postulate the preferential electrodeposition in the area of undercutting during cathodic component of the pulse.

It is shown that anodic-cathodic micromachining (etching) results in significant in-creasing of the Etch Factor, especially so at small dimensionless etch depths (Н) and rela-tively small resist thickness (L ≤ 1).

Optimum modes of pulse anodic-cathodic machining have been determined with ra-tio of anodic charge to cathodic charge pulses Qa/Qc ∼ 2 – 3; the average pulse anodic cur-rent density close to limiting anodic current density (i⊂l); and equal duration of anodic and cathodic pulses at ∼ 0,1 s.

We demonstrate that additional increase in etch localization can be obtained under combined process involving anodic-cathodic pulse and direct current electrochemical etching. It was possible to achieve values of Etch Factor ∼ 6 at etching rate ∼ 100 µm/min. De-pending on hydrodynamic conditions and machining surface geometry the ratio of the passed electric charge of anodic-cathodic pulses and direct current was γ ∼ 0,3 – 0,5. Faster etching rates and better localization (Etch Factor) compared to values obtainable by chemi-cal etching were observed.