The following detailed procedures are required:
Insulating Material Test Procedures
Insulating material specifications and test procedures are required to test
the received material for conformance to rigid specifications, including
expiration date. Contaminated material which is received and not tested at
this point in the manufacturing cycle may cause a subsequent failure.
Abrasive Cleaning Procedures
The abrasive cleaning procedures specify the type of equipment and abrasive
material. The abrasive material should remove any gloss or contamination that
is on the components. The engineering drawing should specify which components
require abrasive cleaning.
Vacuum encapsulation procedures should be detailed as to mixing ratio, time
under vacuum, vacuum level, pot life, cure time, temperature and pressure, if
Some insulation systems create gas bubbles during curing, and curing under
pressure will drive the gases back into the solution, thus allowing them to
cure as a solid. The use of a ratio dispensing system is a preferred method of
dispensing compounds. This system eliminates operator error and prevents
contamination of materials. Power mixing is preferred to hand mixing, and,
when properly used, it produces a superior mixture. Records of mixed batches
and control samples should be preserved.
Cleaning procedures are the most critical procedures in the high-voltage
assembly area. The first operation to be performed on all components is
abrasive cleaning, if required. The second is chemical cleaning before
starting assembly operations. As the assemblies are fabricated, it may be
impossible to clean some of the components. White gloves should be worn at all
times to ensure that the assemblies are not contaminated with fingerprints.
The use of special cleaning agents required to remove solder fluxes should be
followed by cleaning with fluorocarbons. All cleaning agents should be
monitored to ensure that they are not contaminated. Finished assemblies should
be stored in containers after final cleaning, if they are not going to be
encapsulated immediately. If extended storage is required, the container
should be filled with dry nitrogen.