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Date: | Wed, 6 Oct 2010 20:37:22 -0500 |
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I think you should be careful of the statement that
"A larger pad dia puts the pad-to-trace connection further away from the pivot
point and thus the interface area would be subjected to greater deflection."
Using that logic, a direct-connect to a plane would be worst-case, because
the whole plane will deflect! (grin) ...but it won't. The copper is more ductile
than that, so I wouldn't think of pad rotation like a rigid see-saw (where the
longer the see-saw the higher the damage). In fact, I would think the larger
pad and connecting trace would tend to keep the copper "tacked down" to the
material. The more important factor is probably going to be the angle of
deflection at the knee, right?
Jack
.
On Tue, 5 Oct 2010 15:02:13 -0400, Glidden, Kevin
<[log in to unmask]> wrote:
>I've been reading about PTH reliability, mainly through Paul Reid's articles and
old TN posts from Werner....
>
>If you have a PTH with a surface trace attached to the top side pad, would
there be more stress (and thus propensity for cracking / separation between
the pad and joining trace) at the pad / trace interface area with a smaller or
larger pad size?
>
>The "pad rotation" pivots about the knee. A larger pad dia puts the pad-to-
trace connection further away from the pivot point and thus the interface area
would be subjected to greater deflection. Alternately, a smaller pad area (I
believe 6012 requires .002" min) would have less connecting surface area ???
>
>Or is the pad to trace interconnection not a primary failure mode when
compared to barrel or corner cracks?
>
>Thanks!
>
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