Dave Hillman posted:
>     What is the effect, if any, of
>     one of the four "spokes" going from a grounded pad to the clad area
>     being broken.  I've been under the opinion that one of the four
>     "spokes" being disrupted would not cause significant reduction in the
>     electrical or thermal properties of the grounded through.  Would you
>     gentlemen please give your opinion of the effect of one spoke being
>     damaged and whether you feel a repair is needed."
>
>
>     Dave Hillman
>     Rockwell Collins
>     [log in to unmask]
Dave,
        The effect of one spoke being broken is the loss of 25% of the
copper crossectional area of the path to that via.  This would create
additional power loss in the rest of the spokes and would increase the
temperature of the copper and the board at that point.  The result is some
loss of the reliability of that particular hole and some (probably very
small) increase in the total voltage drop in that net. Whether or not to
repair the missing spoke is impossible to answer without knowing the end
use (ie, required MTBF of the board) and the built in redundancy (ie, how
many holes can fail before the whole board is a failure).  Here, where most
of work goes into far away and unrepairable locations and we do
one-of-a-kind stuff, we'd repair it.
        Howard Feldmesser
        Johns Hopkins University Applied Physics Laboratory


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