A typical facility for solid encapsulant fabrication and test should be a
clean, controlled-access area. This will prevent unwarranted traffic
through the area and prevent contamination by untrained personnel.
Contamination can cause many failures in a high voltage power supply even
though the best materials and components are applied. The controlled
area should contain the following:
- Receiving inspection
- Necessary workstations
- Inspection station
- Segregated encapsulating equipment for epoxy and silicones
- Test facilities for:
- Corona testing
- Component testing
- Subassembly testing
- Top assembly testing
All personnel working in this area should be required to wear white cotton,
lint-free gloves. If assemblies have ESD sensitive components, they
should be handled at an ESD workstation, which meets the guidelines of
MIL-STD-1686. However, human safety and high voltage handling procedures
must take precedence over ESD procedures. The following areas are
critical and should be designed to prevent contamination of other areas.
- Abrasive Cleaning - The abrasive cleaning area should be sealed and
vented to an outside area.
- Encapsulation Rooms - Segregated encapsulating equipment is required for
epoxies and silicone rubber to eliminate cross-contamination. Vacuum
pump exhausts should be filtered and routed outside the area. The oven
used for curing the insulation systems should be treated the same as the
vacuum pumps. The encapsulation system should be a vacuum-transfer
system with pressure-curing capability.
- Cleaning Station - The cleaning station should consist of an
environmentally acceptable vapor degreaser, with spray attachment and other
cleaning aids, such as cleaning brushes, disposable lint-free tissues and a
vacuum drying oven for dry cleaning and removing unwanted moisture.