If you are considering the missing mass (and I agree on it), the volume
of the voids is more appropriate.
Also the evaluation of the volume of the voids can be done easily with
the X-rays: you just sum the void diameters raised to power 3 (instead
of power 2 as in case of the evaluation of the area) and divide the
result by the solder joint diameter raised to power 3 too.
So the evaluation of the volume is not more complicated than the
evaluation of the area.
Enrico
Il 12/05/2015 0.23, Wayne Thayer ha scritto:
> Practically, XRAYS are used to measure voiding since that is
> non-destructive. The XRAYS used are uni-directional, so they basically have
> no clue as to vertical position of a void: They only allow you to estimate
> areas where there is less mass for the XRAYS to interact with. Hence we use
> area. (And this seems adequate also!) Since the XRAYS are good detectors of
> missing material, what is called "area" is really something about missing
> mass. In fact, if the actual void is 2 microns tall and occupies 95% of the
> area on a joint, the XRAYS just plain don't see it at all.
>
> Wayne Thayer
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
> Sent: Monday, May 11, 2015 4:32 PM
> To: [log in to unmask]
> Subject: Re: [TN] Voiding evaluation
>
> 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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>>
>>
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--
Enrico Galbiati
Consulenza Affidabilità e Normative
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