i am not talking about the (2-1) theory. Dave, you under estimated
me ;-). micro voids as a second phase embedded in 96% Pb high melt
fine C4 do have advantage. think about CTE mismatch....
By the way, anyone want send your selfie to space? here is your
chance. you guys go ahead and send your selfie. I am too ugly...
don't want to scare the alien.
jk:-)
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On May 12, 2015, at 10:03 AM, David Hillman wrote:
> Hi team! I have been just sitting in the background watching the
> conversation but Joyce got me to finally hit the keyboard. There is a
> ginormous amount of information on BGA voids in the public domain.
> Some of
> it is very good and some is, well, less good. Rockwell Collins and
> several
> other OEMs (Lockheed, HP, Blackberry, etc.) looked at voiding (both
> tin/lead and lead-free) for the JSTD-001 specification committee as
> part of
> an activity to change the BGA voiding requirement. It was an effort
> that
> took 4 years and several co-ops to finish but the outcome was the
> following:
>
> 1) BGA voiding is driven by the reflow profile and the specific
> solderpaste
> formulation you are using. If you try to intentionally make voids
> for an
> investigation, it takes extreme efforts. Voids are a result of poor
> reflow
> soldering process so if you are getting voids (more that 1%-5% is
> typical
> depending on the paste you are using) then you need to track down
> the root
> cause.
>
> 2) There are still two "void theories" that are still running
> around the
> industry: (1) voids are beneficial to solder joints because the
> "blunt"
> crack growth and/or provide compliancy to the solder joint; (2)
> voids are
> detrimental to solder joints because the accelerate cracking by
> shortening
> the crack path length necessary for failure. Two really seemingly
> logical
> ideas that have very very very little published, data supported
> rationale.
> IMHO I don't think either idea has significant merit and I have looked
> really hard for the supporting data.
>
> 3) It would be really cool if simple Force per Area calculations would
> provide the industry the answer but when you look at the published
> data,
> that idea falls apart very fast. The primary reason is that the
> overall
> problem is complex as the forces involved (shear, bending, etc.),
> the BGA
> construction, the PCB construction, and the nonlinear solder alloy
> characteristics over temperature play a role on the solder joint
> integrity.
> There are BGA solder joints that are nearly "hollow" that haven't
> cracked
> after 2000 thermal cycles from -55C to +125C.
>
> 4) The JSTD-001 specification has the BGA void requirement criteria
> and the
> IPC-7095 standard contains an enormous amount of information on
> void/process control and Xray assessment methodologies. Don't
> confuse the
> two documents as they both fulfill important and significant needs
> that are
> not the same - lots of folks do and it creates industry confusion.
>
> 5) It would be awesome if everyone had an Xray system that would
> provide 3D
> imaging but that isn't a realistic approach for the industry or the
> specifications. The industry data does support that if your voiding
> stacks
> up at the shear interface at either the component pad/solder joint
> or board
> pad/solder joint then you will lose solder joint integrity quickly.
> But -
> given that BGA voiding should be/is nontypical then the use of
> transmission
> Xray assessment should be adequate. Again, the IPC-7095 standard
> contains
> significant information on how to address void control/assessment.
>
> BGA voiding is one of those topics that really gets discussions going!
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
> On Mon, May 11, 2015 at 5:33 PM, Yuan-chia Joyce Koo
> <[log in to unmask]>
> wrote:
>
>> 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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