TECHNET Archives

May 2015

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Wayne Thayer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wayne Thayer <[log in to unmask]>
Date:
Mon, 11 May 2015 22:23:07 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (133 lines)
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]
>>
>>
>>
>>
______________________________________________________________________
>>     This email has been scanned by the Symantec Email Security.cloud
>>     service.
>>     For more information please contact helpdesk at x2960 or
>>     [log in to unmask] <mailto:[log in to unmask]>
>>     
>> _____________________________________________________________________
>> _
>>
>>
>>
>>
>> --
>> 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]
>
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or 
> [log in to unmask] 
> ______________________________________________________________________
>


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________

ATOM RSS1 RSS2