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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 24 Feb 2010 17:14:41 -0600
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Hi folks! Inge - just a comment and a question after looking over the SEM 
images. There is a considerable amount of voiding and grain boundary 
structure definition in the BGA pad fracture surface - much more than I am 
used to seeing in a brittle fracture situation anyway. Have you completed 
a cross-section of one of these pads? A cross section would give you a 
good idea of the overall plating quality. 

Dave Hillman
Rockwell Collins
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Steve Gregory <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
02/24/2010 04:22 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Gregory <[log in to unmask]>


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Subject
Re: [TN] Hackneyed?






Hi Inge!

Well, we are getting ready to get hammered by another winter storm. Starts
tonight sometime after midnight and will last until Friday. They're
forecasting anywhere from 12-16" of snow. I'm having a hard time getting
used to the Pennsylvania winters...

Anyways, I have your pictures posted. I'll paste the links into your email
below as you are explaining the pictures. That way everyone can follow 
along
easier.

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Wednesday, February 24, 2010 2:54 PM
To: [log in to unmask]
Subject: [TN] Hackneyed?

Hi Folks,

am asking you to sacrifice  a minute on a topic that may make you sick, as 

much as it has been discussed. Have a look at the SEM images that 
(hopefully) will be beamed by our most honorable guy,  Dr Gregory.  By 
order:

1. Pic 38 BGA ball after the preying off the 560 ball BGA from the board. 
SEI mode.
http://stevezeva.homestead.com/files/XILINX_Daniel_38.jpg

2. pic 39,  same at x 5,000
http://stevezeva.homestead.com/files/XILINX_Daniel_39.jpg

3. pic 40,samet at x 10,000
http://stevezeva.homestead.com/files/XILINX_Daniel_40.jpg

4.pic, 41 same at x 20,000
These four show the face of the pulled-off balls. The package/board was 
sectioned into halv by half inch pieces with a thin blade diamond saw and 
then each BGA section was separated from the board
by means of a steel.
http://stevezeva.homestead.com/files/XILINX_Daniel_41.jpg
 
After SEM 1-4 I made EDS, which can be seen below.

5. http://stevezeva.homestead.com/files/XILINX_Backlund_Ball_2.doc
As you can see, there is nearly no Lead (!), a high w/% Nickel, a little 
Tin

and lots of Phosphorous. Clearly, the separation has been in a 

Now, continue with having a look at the board pads after the preying-off.

6. pic 44, Board pad at low magnification and SEI mode.
http://stevezeva.homestead.com/files/XILINX_Daniel_44.jpg

7.pic 46,  same at x 5,000
http://stevezeva.homestead.com/files/XILINX_Daniel_46.jpg

8.pic 48, same at x 10,000
http://stevezeva.homestead.com/files/XILINX_Daniel_48.jpg

9. pic 50, same at x 20,000
http://stevezeva.homestead.com/files/XILINX_Daniel_50.jpg

10. pic 51, same but with BS mode
http://stevezeva.homestead.com/files/XILINX_Daniel_51.jpg

11. XILINX_backlund_pad_1.doc
http://stevezeva.homestead.com/files/XILINX_Backlund_Pad_1.doc

As you can see here, there is more Lead, a high w/% Nickell, much more Tin 

and still lots of Phosphorous.

Discussion:
Obviously,  real and reliable solder joints are only in the 
circumperipheric

of the whole (best understood with pic 10).  How strong the adhesion was 
in 
the main part of the joint, we don't know.  From the function (final) 
electrical testing, we have experienced several cases with disturbed 
signals.  Many a times, we have had to remove the BGA and supersede with a 

fresh one. The test engineer told me, that by slightly add pressure to the 

BGA, he may get the signal through again.  He thinks we have an issue with 

the uvias, others think there is a problem with the BGAs, myself I'm 
committed to my theory that this has to do with the rotten interface 
between

the Tin/Lead and the ENIG pads.

Question:
Is anyone familiar with the said?  What is your opinion  about the 
demonstrated solder joints? Can yoy get cracks and electrical misfunction, 

despite that hundreds of balls are holding the BGA close to the board in a 

'iron grip' ?

Wayne? Steve? Dave? George W? Vlad?

Thanks in advance.  You'll have to wait for Steve to fix the exhibition.

/Inge
 


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