I just sat and looked at your images and the documents.
Why are you seeing so much Gold on your pads?
That would not seem to be good.
Regards
Rex
Rex Waygood
Technical Manager
Hansatech EMS provides value manufacturing through engineering and
quality
Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset
BH17 0RY
+44 (0)1202 338200
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: 24 February 2010 19:54
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.
2. pic 39, same at x 5,000
3. pic 40,samet at x 10,000
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.
After SEM 1-4 I made EDS, which can be seen below.
5. 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
Sn/Ni/P-layer.
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.
7.pic 46, same at x 5,000
8.pic 48, same at x 10,000
9. pic 50, same at x 20,000
10. pic 51, same but with BS mode
11. 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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