Agree with what other people have said, particularly Dave, this is not the
right way to do FA if you just have one sample. Anyway with PoP you can
still use x-ray for all balls, ERSA Scope or similar for the first two rows
if you take some time.

In a similar way when I want to measure the shear force of balls I grind
through the top of the package or up through the board as you would do a
microsection but without the mounting epoxy. Its how I have short fingers.
You use the same thing when looking at Underfill around balls, exposing head
in pillow to look at the joint interfaces.

Have a great weekend one and all

Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
www.SolderingStandards.com 
New Package on Package Workshops 24th November AXIOM
www.ASKbobwillis.com/PoPWorkshops.pdf 

New Package on Package Assembly & Inspection Workshops 21th January ITRI
www.ASKbobwillis.com/PoPWorkshops.pdf
Printed Board Inspection & Quality Control Workshop 9th June at ITRI
www.ASKbobwillis.com/FAWorkshops.pdf 
Practical Failure Analysis Workshop 10th June at ITRI
www.ASKbobwillis.com/FAWorkshops.pdf 
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: 20 November 2009 20:28
To: [log in to unmask]
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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