Tom:
- Parylene/Paraxylyene is a great coating and can be selectively removed by
several methods.  The IPC-7711 (Rework of Electronic Assemblies) has a
section devoted to removing the five generic types of conformal coating.
According to that document the best method is to use thermal energy
(overcuring the parylene and removing by abrasion - usually with a dental
tool or similar item).  The next best method is to use a grinding/scraping
method (again, dental tool, minor surgery scalpel, rotary brush, etc.).  The
Micro Blasting comes in last.  Micro blasting can be an efficient method to
remove coating, but to my knowledge (sales claims aside) no one has yet
perfected a way to use micro blasting without developing significant static
charges.
- In an earlier life I was the program manager for a US Navy Rework and
Repair Program for electronics equipment (mostly airborne stuff).  We thought
that micro blasting would be great, but were never able to get the static
charge build up problem whipped.  Typical values were 3,000 volts after a 60
second exposure to a micro blaster using baking soda as an abrasive medium
(other mediums resulted in higher values).  Would be glad to talk to you
off-line regarding this if you want additional information.
Regards, Jim Moffitt, Moffitt Consulting Services

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