Agreed.

 


 

 

-----Original Message-----
From: David D. Hillman <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Apr 20, 2010 12:06 pm
Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls


Hi Werner - we are both on the same page (I should have typed out a more 
detailed response). As you detailed, the actual metallurgical reactions of 
shrinkage are the same, the focus should be on what is staying molten 
last. We have observed on some BGA solderballs that were part of the 
circuit connection to ground planes some slightly different shrinkage void 
differences due to the solidification reactions. Interesting from a 
technical viewpoint but didn't make a difference from a solder joint 
integrity perspective.

Dave



Werner Engelmaier <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
04/20/2010 10:55 AM
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Re: [TN] SAC Shrinkage Voids in BGA Balls






 Hi Dave,
A shrinkage void in an ingot occurs where it solidifies last---in its 
center.
The same is true for SJs, except that they do not necessarily cool from 
the outside in. but a connected to various heatsinks and reservoirs---the 
component is typically a heat sink [coolest] and the PCB is a reservoir 
[hottest], with various heat transfer conditions on the surface due to 
forced air/N2.
Overall, SJs tend to solidify first at their surface; hence, most 
shrinkage voids are to be found there.
Werner 

 


 

 

-----Original Message-----
From: David D. Hillman <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Apr 20, 2010 10:13 am
Subject: Re: [TN] SAC Shrinkage Voids in BGA Balls


Hi Bev - in theory, a shrinkage void in a solderball is the same physics 
as a shrinkage void in a aluminum or steel casting so no, the shrinkage 
void  would not have to necessarily always reach a surface. However, after 

looking at several hundred SAC BGA/CSP cross-sections, I have nearly 
always (99.999%)  found a path of a shrinkage void to the solderball 
surface. Because we have a very limited and very small molten solder 
"volume", I think you will find a surface connection.  And I guess I'll 
bite - why the question?

Dave Hillman
Rockwell Collins
[log in to unmask]




Bev Christian <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
04/20/2010 08:16 AM
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[TN] SAC Shrinkage Voids in BGA Balls






TechNetters,
Do all SAC shrinkage voids in BGA balls reach/start at the surface of
the ball?  I realize I may be stumped by a 2D cross-section of a 3D
phenomenon, but I thought I would ask this august body.
Bev
RIM

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