Regarding annular ring: 

The main reason for annular ring in the original printe board specs was to
provide a space for the solder to filet between the teminal or eyelet and the
land.  All of the current IPC specs., IPC-RB-276 and IPC-6012 allow breakouts
in the Class 2 (90 degree) and Class 1 (180 degree).  Many tests have been
run to determine if breakout was a real or cosmetic defect.  Several that I
am aware of showed that an annular ring circumscribing the hole had no effect
long term life or reliability.  However, until the past few years when more
circuitry in less space became a necessity, some of us die-hards said that we
like the totally circumscribng annular ring.  No one seems to know if
tangency, 1 mil, 2 mils or 5 mils if better, one test that I heard about said
that there was no significant difference.  The majority of circuit board
product unless it is Military spec. has a 90 degree breakout acceptable.     

There is a test program that was done by ITRI on "landless holes" and the
data is presently or soon to be available.  We hope to be reviewing this data
with possibility of incorporating it in IPC-6012 at the Rigid Board
Performance Task Group meeting in San Jose.  Meeting is Sun Mar 9th. 

Phil Hinton     

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