If the criterion was the evaluation of the ratio load/area, one should 
sum only the void areas that lie on a same plane (perpendicular to the 
load),

For example, if the direction of the load is vertical, the areas of 
voids placed on higher or lower planes shouldn't be summed, because the 
solder joint area which bears the load in each plane depends on the 
voids intersected by that plane, not on the voids placed higher or lower 
in the solder joints.

Since the sum is extended to the entire volume of the solder joint, the 
criterion would seem another one.

Enrico

Il 08/05/2015 15.55, Ed Hare ha scritto:
> 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 <http://www.semlab.com>
>
> On Fri, May 8, 2015 at 5:15 AM, Enrico Galbiati 
> <[log in to unmask] <mailto:[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
>     Via Kennedy Ingresso 2, 20871 Vimercate (MB) - Italy
>     Desk: +39.039.8908.4547 <tel:%2B39.039.8908.4547> - Fax:
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>
>
>
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> -- 
> Ed Hare
> gmail - [log in to unmask] <mailto:[log in to unmask]>
> gvoice - 360-453-7550

-- 
Enrico Galbiati
Consulenza Affidabilità e Normative
Via Kennedy Ingresso 2, 20871 Vimercate (MB) - Italy
Desk: +39.039.8908.4547 - Fax: +39.039.8908.5051 - Mobile: +39.335 6833616
E-Mail:[log in to unmask]



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