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November 2009

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Subject:
From:
Vladimir Igoshev <[log in to unmask]>
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Date:
Fri, 20 Nov 2009 21:34:56 +0000
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Guy,

If you are talking about Pb-free solders, then yes it's possible that fracture occurs along the intermetallics/pad interface making the exposed surface unsolderable (particularly in case of ENIG).

Regards,

Vladimir

SENTEC
------Original Message------
From: Guy Ramsey
Sender: TechNet
To: [log in to unmask]
ReplyTo: TechNet E-Mail Forum
ReplyTo: Guy Ramsey
Sent: Nov 20, 2009 15:28
Subject: [TN] solder fracture solderable?

I was visiting a customer earlier this week. They were attempting to cut a
the top part off of a package  on package, BGA on top of BGA. 

They didn't want to reflow it off because they didn't want to damage the
balls on the bottom of the bottom package. 

They had made a little fixture affair with two knives adjusted to slice
between the two packages.  

They placed the PoP in the tool and pushed it through the knives, rotated 90
degrees and repeated the cycle. 

Most of the pads on top of the bottom package ended up with half a ball
remaining on the pad.

But some of the pads did not have any solder on them at all. The entire pad
was mat finish silver in color. 

None of these features would  accept solder. The number of pads without
solder varied from one or two to 30% of the pads.

 

I wondered if rather than cutting through, some of the connections has
simply fractured along the intermetallic, leaving a non-solderable surface
with this uniform appearance. 

Some of those observing conjectured that the package was bad, They
conjectured that the silver was merely solder loaded with gold and that the
nickel had never accepted solder. 

 

I asked where their SEM was and if they had EDAX equipment . . .  nope.

 

Would anyone care to guess  along?  How likely is it that prying off a BGA
would fracture the connection right along the intermetallic and leave a
completely non-solderable surface? 

 

 

 

 


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