Specifications
for Electropolishing
Specifications for electropolishing vary with the end use of the parts. A knowledge
of the end-user's requirements is of great importance in designing an electropolishing
line and the process control system. MCP process control methods are designed
for a broad spectrum of quality assurance applications ranging from simple deburring
to the most demanding SEMI, FDA, or ISO requirements.
The simplest requirements for electropolishing are for a "clean, bright, cosmetically
attractive" finish. Results are judged primarily by appearance. Other common
specifications require a specified level of deburring without regard to cosmetic
appearance. Inspection techniques vary from simple snagging tests on woven or
knitted cloth to microscopic examination to evaluate the level of deburring.
These applications may be satisfied with a relatively simple approach to the
electropolishing equipment and process.
Processes for passivation are defined by the American Society for Testing Materials (ASTM). ASTM A380 covers various methods of chemical passivation, detailing the sequence of operations and the test methods to be followed. In recent years ASTM A967 and ASTM B912 have expanded the scope of ASTM A380 to include electropolishing as a means of passivation. ASTM specifications may be obtained by downloading from the Society web site at www.astm.org. The Federal specification QQ-P-35C, formerly used as a guide for passivation of stainless steels, has been superceded by the ASTM documents.
The use of electropolishing to improve surface finishes for pharmaceutical,
semiconductor, and cleanroom applications becomes increasingly more sophisticated.
Many end-user specifications now include photographic images produced by scanning
electron microscope (SEM) at magnifications between 1,000X and 10,000X. Surface
profiles in the range of 2-5 Ra are frequently specified, and research efforts
continue to strive for methods to achieve even finer finishes. Electron spectroscopy
techniques are used to define the thickness and composition of the surface oxide layer, the ratio of chromium to iron, or the occurence of specific contaminants. Ultra-clean gas systems may require
limitations in the parts per billion range for outgassing from the polished
surface. Detailed specifications can be downloaded from the semiconductor trade association web site, www.semi.org.
