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April 2010

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Werner Engelmaier <[log in to unmask]>
Date:
Tue, 20 Apr 2010 11:55:49 -0400
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 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
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Bev Christian <[log in to unmask]>


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Subject
[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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