Many thanks to everybody who helped.
We also had good electric test pass results by reflowing open solder joints.
Now, the next question is: how do you know that the connection has been 
repaired to last?
My last experience was dye penetration test and cross sectioning BGA's with 
perfect solder joints, but, as Richard mentioned, they remained warped after 
reflow.
They failed in the field and the tests showed that the solder balls lifted 
from the circuit in two ways:
Either from the nickel on the circuit pad or together with the pad causing 
cracks in the base material and intermittents in the pad conductor to the 
through hole.
The external balls were by 0.04mm shorter than the balls in the middle.
This is total loss.
Altera has an article :
http://altera.com/literature/cp/altera-panpac-2005.pdf
No need to send you pictures. Mine are EXACTLY the same, but we got the 
circuit from the field.
Needless to say that in this case I would have preferred very much to see 
opens on the component side....
But there were NONE.

Gaby

----- Original Message ----- 
From: "Dehoyos, Ramon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 28, 2005 5:26 PM
Subject: Re: [TN] SV: [TN] BGA failure and assembly repair


>        Gaby:
>        What kind of board material is it being used to make those 
> returned, failed boards. Some materials do not take much rework. It is 
> hard to just assemble parts on them without some kind of board damage. 
> Besides a good board manufacturer, the proper board material needs to be 
> used. I hate to ask, is it LF solder being used?
>        Ramon
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
> Sent: Friday, October 28, 2005 10:12 AM
> To: [log in to unmask]
> Subject: [TN] SV: [TN] BGA failure and assembly repair
>
> Gaby, think you need a real good repair equipment to begin with. We 
> started with simple ones, but realized that handling and repairing up to 
> SBGA 2,500 need precision and repeatability and no human errors. We have 
> two machines, like the below. There are lots of such machines on the 
> market.
>
> http://www.ape.com/sniper_wide.html
>
> http://www.ape.com/images/Brochure%20Sniper%20III%20Low%20Res.pdf
>
> http://www.focalspot.com/rd500.html
>
> We repair and replace CSP and BGA daily, just works fine. To replace a BGA 
> with these machines takes just a few minutes. We never do just reflow on 
> suspect boards, but go directly to replacement. Too risky relying on 
> reflow only.
>
> Inge
>
>
>
> -----Ursprungligt meddelande-----
> Från: Gabriela Bogdan [mailto:[log in to unmask]]
> Skickat: den 28 oktober 2005 12:05
> Till: Ingemar Hernefjord; 'TechNet E-Mail Forum'
> Ämne: Re: [TN] BGA failure and assembly repair
>
> Thanks, Inge, I will try to do it.
> I was thinking also about the design of the boards, like stress factors 
> after soldering.I can not eliminate those- we are just assembling a wide
>
> variety of boards and we don't always know what happes after assembly.
> I was thinking also about the residual stresses in the BGA-like 
> warping.Each failure has its own footprint, which I recognize. The 
> question is, what others are doing usually when they have to repair a BGA 
> site- what is their experience in reliability and cost?
> IPC speaks only about replacing.Is there someone who is doing additional
>
> reflow on the old component as a repair method? Is it considered reliable?
> Gaby
> ----- Original Message -----
> From: "Ingemar Hernefjord" <[log in to unmask]>
> To: "'TechNet E-Mail Forum'" <[log in to unmask]>; "'Gabriela Bogdan'"
> <[log in to unmask]>
> Sent: Friday, October 28, 2005 12:41 PM
> Subject: SV: [TN] BGA failure and assembly repair
>
>
>> Gaby,
>> If the BGAs are OK, and your is process OK, then I can't see better
>> solution than search for a better board supplier.
>>
>> You'd better send some pics on the cross sections. You told us nothing
>> about the failure freqency per position, per board, batch dependency,
>> and variations by time. To change supplier is of course a question of
>> what the failures cost you.
>>
>> Inge
>>
>> -----Ursprungligt meddelande-----
>> Från: TechNet [mailto:[log in to unmask]] För Gabriela Bogdan
>> Skickat: den 28 oktober 2005 09:37
>> Till: [log in to unmask]
>> Ämne: [TN] BGA failure and assembly repair
>>
>> Dear Technetters!
>>
>> We sometimes receive failed boards from the field with failures on
> BGA's
>> for  repair.
>> Supposing there is no problem with the BGA as a component, supposing
>> that the X-ray test (feinfocus tiger) does not reveal any problems in
>> the solder joints (with exception to cracks which are very hard to
>> detect), what procedure would you suggest?
>> We are concerned with the following:
>> Reliability
>> Cost: the assemblies are still our responsability
>> We are considering:
>> Scrap
>> Repair by reflow and electrical test
>> Repair by installing a new component and electrical test- this
> includes
>> the possibility of visual inspection of the area under the failed
>> component and finding more out about the failure mechanism)
>> Lately we have performed several destructive tests in order to  see
> the
>> nature of the failures which could not be repaired by reflow, and
> found:
>> through hole cracks or corrosion in plugged holes
>> pad lifting and conductor cracks
>> solder joint cracks
>> All these were not detected by X-ray.
>> Could you suggest the best procedure?
>>
>> Gaby
>>
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> 847-615-7100
>> ext.2815
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>>
>>
>
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