Tried to shop the image, not easy, not many bites to manipulate. However, 
seems NOT to be polishing debris.  Such stuff use always to spread 
uniformally all over the sample's cross section, which is not the case here. 
Instead I think the voids are filled with unmolten solder particles  (seem 
to be nicely rounded).  That's why I asked for Silver adds.  Recommend a 
EDAX on the particles in the voids.  You may avoid voiding the contract by 
contraction of the voids?

Inge

--------------------------------------------------
From: "Victor Hernandez" <[log in to unmask]>
Sent: den 11 June 2010 18:24
To: <[log in to unmask]>
Subject: Re: [TN] Weird formation of voids

> Was this BGA reworked?
>
> Victor,
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of stephen gregory
> Sent: Friday, June 11, 2010 10:21 AM
> To: [log in to unmask]
> Subject: Re: [TN] Weird formation of voids
>
> Hi Bev!
>
> Got your picture today, and have it posted now:
>
> http://stevezeva.homestead.com/Bevs_Ball.jpg
>
> Almost looks like little pieces of dross. I wonder if something is going 
> on with the solder paste? Or leaded reflow profile with a lead-free BGA?
>
> Steve
>
> --- On Wed, 6/9/10, Bev Christian <[log in to unmask]> wrote:
>
>
> From: Bev Christian <[log in to unmask]>
> Subject: [TN] Weird formation of voids
> To: [log in to unmask]
> Date: Wednesday, June 9, 2010, 9:51 AM
>
>
> TechNetters,
> I am sending a picture to Steve to post.  I have labs in three locations. 
> One of them has seen weird voids in cross-sections of BGAs while the other 
> two locations have not.  For the lab that has seen them, the 
> cross-sections were prepared by different people on different days for 
> different products, using the same equipment. The voids are not in all 
> balls cross-sectioned but may be only in one of two of the balls in a row 
> of multiple solder joints examined.
>
> Have you seen anything like this?  Do you know the root cause?
>
> Vlad,
> You know what is going on, so please don't respond.
>
> Bev
>
>
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