Au + Ag → Bling (?)
Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Friday, January 16, 2009 2:44 PM
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
Augh! You can never have too much Au, unless it's more flash than
substance.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner engelmaier
Sent: Friday, January 16, 2009 12:35 PM
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
Hi richard,
where do these PCBs come from? Not everything called ENIG is in fact
immersion Au--thus, you can have too m uch Au.
Werner
Future workshops:
Pb-Free Soldering Processes: Survival, Quality, Reliability-PROBLEMS &
SOLUTIONS, March 3, IPC/JEDEC Santa Clara, CA
Solder Joint Reliability: Part 1-Solder Joint Reliability Fundamentals,
March 29, IPC EXPO/APEX Las Vegas
Pb-Free Soldering Processes: Survival, Quality, Reliability: PROBLEMS &
SOLUTIONS, March 30, IPC EXPO/APEX Las Vegas
-----Original Message-----
From: Thayer, Wayne <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, 16 Jan 2009 11:02 am
Subject: Re: [TN] Possible cause on open
My vote says this is not ENIG--it is ENEG!
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Friday, January 16, 2009 10:48 AM
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
I expanded the images and I am sending them back to Steve for
re-posting. I can
see a lot of flower-petal patterns, a lot of rod and cone structures
just above
the IMC. It appears as if there are very heavy gold intermetallics along
the top
of the IMC, and the gold nucleated back towards the IMC from the solder
ball.
The IMC layer is very thin.
The solder between the edge of the soldermask and the edge of the pad
causes the
pad edge to look like they curled at the edges, but I think you can see
that it
is just the crack curling downwards inside of the sol
der. Full reflow obviously
took place because the solder melted down the sides of the pads and
filled the
space between the soldermask and the curled edges of the pad. In the
image taken
near the center of the pad, it is obvious the crack propogated through
the
solder in some areas.
The crack along the entire length of the pad and down the sides
indicates severe
stresses due to either the vibration forces or the CTE from the
temperature
cycling, or both. The crack probably formed due to the brittle nature of
the
IMF, what with having the worst possible combination of ENIG, lead-free
solder,
and lateral stresses. There are some voids with flux debris above the
whole
thing that tend to confuse the issues going on.
Steve, I am sending my expanded image to you for posting separately.
Thanks.
Richard
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Igoshev, Vladimir
Sent: Thursday, January 15, 2009 8:42 PM
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
Thank you for sending me the image. Honestly, I don't quite understand
what I
see. The finish doesn't look like ENIG and the cavity above something
that DOES
NOT look like a typical intermetallic shouldn't be there, not to mention
a
"hair-like" something (crack?????) above the cavity.
It looks like a proper joint had never been formed. Can you ask the lab
to
slightly etch the section?
Regards,
Vladimir
________________________________
From: Tan Geok Ang
To: Igoshev, Vladimir; TechNet@IP
C.ORG
Sent: Thu Jan 15 20:09:33 2009
Subject: RE: [TN] Possible cause on open
About 1.05um
________________________________
From: Igoshev, Vladimir [mailto:[log in to unmask]]
Sent: Friday, 16 January 2009 9:01 AM
To: Tan Geok Ang; [log in to unmask]
Subject: Re: [TN] Possible cause on open
The info I'm asking about is at the bottom of the images you sent to
Steve. You
should be able to read from the originals what it says (how many
microns)
Regards,
Vladimir
----- Original Message -----
From: Tan Geok Ang <[log in to unmask]>
To: TechNet E-Mail Forum <[log in to unmask]>; Igoshev, Vladimir
Sent: Thu Jan 15 19:53:13 2009
Subject: RE: [TN] Possible cause on open
The service lab has not come out much information at this time. Will
input you
once I have the information. Thank you.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Igoshev, Vladimir
Sent: Thursday, 15 January 2009 10:50 PM
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
It looks like there could be something fishy in the intermetallic layer.
GA, can you tell me please what is the reading on the micron bars?
Regards,
Vladimir
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, January 15, 2009 8:05 AM
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
Mornin' Everbody!
Well, here in Tulsa, we're just like a lot of other people in the
country this
morning, trying to stay warm. Right now we're sitting at -10 C. with
a wind
chill of -15 C. It's supposed to be colder tomorrow...
GA, I have your pictures posted now. They're at:
http://stevezeva.homestead.com/files/Fracture1.jpg
http://stevezeva.homestead.com/files/Fracture2.jpg
Hopefully someone can give you some ideas...
Steve
________________________________
From: Tan Geok Ang [mailto:[log in to unmask]]
Sent: Wednesday, January 14, 2009 7:27 PM
To: [log in to unmask]; Steve Gregory
Subject: Possible cause on open
Hi Steve,
Please help to download these pictures TechNet, thanks.
Hi All experts,
Testing (combine test of 16G at 85 oC) was performed on
evaluation
boards with under-filled BGAs. Open issue (cracks) was detected only at
some
corners of the BGA (35x35mm with 1156 balls) after the test. Lead-free
process
and PCB with ENIG surface finish. Peak temperature is 248 oC with a 65
sec above
217 oC.
FYI, the service lab has not come out a report.
What are the possible causes? (CET mismatches, Lead-free
alloy
related, material, processes)
Thank you in advance.
Regards
GA Tan
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