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Subject:
From:
Yuan-chia Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Yuan-chia Joyce Koo <[log in to unmask]>
Date:
Mon, 11 May 2015 18:33:46 -0400
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text/plain
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text/plain (173 lines)
minor voiding actually are good for solder joints (a old old story -  
provide it is uniform and small and not that many and round).  not  
sure if there is any digital record... early 90 and late 80 stuff.   
Am I dated myself? OMG...
       jk
On May 11, 2015, at 6:23 PM, Wayne Thayer wrote:

> 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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