it all depends.  some of the newer x-ray machine comes with 2D to 3D
calculation... here is the guru's paper... you can ask him directly ;-)
http://www.ipc.org/committee/comments/5-22a_c_Hillman-BGA-void-paper.pdf
             jk
> 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
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>> Via Kennedy Ingresso 2, 20871 Vimercate (MB) - Italy
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>>
>>
>>
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>
>
> --
> Ed Hare
> gmail - [log in to unmask]
> gvoice - 360-453-7550
>
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