I would suggest that you will see the voiding if present at the interfaces. 

You would not see voids in the balls. If you discount the difference in
density between copper and high lead balls in x-ray and colour during
optical inspection the joints would look like this pdf.

www.ASKbobwillis.com/pdfs/posterexample.pdf 


Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
 
www.ASKbobwillis.com
New Bob Willis "Printed Board Inspection & Quality Control Workshop" 24th
March www.ASKbobwillis.com/faworkshops.pdf
 
"Troubleshooting Your Assembly Yields Workshop" 25th March
www.ASKbobwillis.com/faworkshops.pdf
 
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: 18 September 2008 16:00
To: [log in to unmask]
Subject: Re: [TN] Copper BGA balls

We don't have a choice on the ball type.
That is the way the manufacturer makes the part that we use.
We are just trying to figure out what we should be expecting to see when
we X-Ray them.  Is it normal to see voiding in them? 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: September 17, 2008 7:58 PM
To: [log in to unmask]
Subject: Re: [TN] Copper BGA balls

Hi Genny,
Why would you want to use Cu balls--they do not improve reliability,
because the ball is too rigid and you wind up with 2 very thin solder
joints. Now polymer balls covered in Cu and solder is another
matter--they improve reliability.




Werner


-----Original Message-----
From: Genny Gibbard <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, 17 Sep 2008 7:00 pm
Subject: [TN] Copper BGA balls








Anyone have experience with components using a tinned copper ball
instead of a SAC alloy solder ball?
Have you ever X-rayed one?
We are seeing voiding that does not meet the IPC-7095B spec for incoming
inspection with a transmission x-ray.  However, we don't know if this is
a concern for this type of ball, or if this spec even applies to this
type of ball.  I don't think these are meant to collapse and mix with
the solder on the board, like a normal solder alloy ball might. 

Once again, thanks in advance for sharing your knowledge.

Genny 

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