Query about annular rings

[mayd85]

Hi,

IPC-2221 standard talks about annular rings for plated through holes. It mentions three types, viz.

1) External Supported
2) External Unsupported
3) Internal Supported

I understand that Internal/External means it is on internal/external layer. But what is the difference between supported and unsupported annular rings?

 

[FvM]

The terminology is a bit cryptic. IPC-2221A clarifies explicitely that "unsupported holes" means non-plated holes.