I would suggest that the area criterion is appropriate since stress =
load/area.  It is not a missing mas issue in my opinion, it is a reduction
in load bearing area that is of concern.

Ed Hare
VP SEM Lab, Inc.
www.semlab.com

On Fri, May 8, 2015 at 5:15 AM, Enrico Galbiati <[log in to unmask]
> wrote:

> I would like to ask anyone if there are any reliability data regarding the
> evaluation of voiding in a solder ball (BGA).
>
> In both the standards IPC-7095C and IPC-A-610F, the voiding in the solder
> balls is evaluated measuring the area of the voids. However, the weakening
> of balls caused by voiding should depend on the amount of the missing
> material caused by the presence of voids. If this is true, the amount of
> the missing material should be measured by the total *volume* of voids, not
> by the area. Consequently, the limit should be set on the volume, instead
> of the area.
>
> For example, with the present rule based on the percentage of area of the
> voids, a solder ball of 0,85 mm diameter, with a single void of 0,45 mm
> diameter, is acceptable, since the percentage of voiding is 28%, thus less
> than the maximum limit of 30% (ref. IPC-A-610F). In this case, the missing
> volume of the material is 15%.
>
> Considering another example, if a solder ball has 6 voids of a 0,20 mm
> diameter each, giving 33% of the area of voiding, would be rejected.
> However, in this last case the percentage of the missing volume is only 8%,
> i.e. less than the previous case (about 53% of the previous case!).
>
> So, the ball of the second case is rejected, even if it stronger that the
> one of the first case. On the contrary, it is the solder ball of the first
> case that should be rejected.
>
> Enrico
>
> --
> Enrico Galbiati
> Consulenza Affidabilità e Normative
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>
>
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-- 
Ed Hare
gmail - [log in to unmask]
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