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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 11 May 2015 16:31:47 -0400
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it is all depend upon what kind of stress - temp cycle most likely you
have experience shear load, vib and impact are different, pending on
direction (6 faces, x-edge, y corner, etc.).  strain rate also place the
role.  voiding can not be a uniform acceptable criteria... it is all
depend upon how much design margin allow.  (we can see the cow go home...)
    jk
> 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:
>>     +39.039.8908.5051 <tel:%2B39.039.8908.5051> - Mobile: +39.335
>>     6833616 <tel:%2B39.335%206833616>
>>     E-Mail:[log in to unmask]
>>
>>
>>
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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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