The reason for annular ring orginated in pre-MIL-P-55110 Signal Corps spec.
that reuqired it in order to get a good solder fillet around the teminals
that were staked into every hole to mount resistors, capacitors and tube
sockets.

Annular ring breakout is of no consequence in many test that have been run in
the world.  In one study that I am aware of the boards were 10 layer with 1
oz. copper; the board thicknesses were .060, 090 and .125; breakouts were
none, 90 degrees and 180 degrees; hole sizes were .018 and .036; testiing was
1000cycles (-40 to 125) and  3 solder dips at 266 deg C. The evaluations were
by electrical test and microsection.  Results were that there was no
significant difference between any of the three breakout types.

The breakouts in this case were all oriented by offsetting drill rather than
random as might be experience in a printed board.  The test, also did not
test if the breakout occurred at the trace-to-hole intersection.  I
understand that one of the groups is doing this test 
presentl.

Phil Hinton 
Hinton PWB Engineering 
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