I hate the "B" word because it describes an optical appea
David,
I hate the "B" word because it describes an optical appearance rather
than a failure mechanism. I've heard the "B" word as well as terms like
"weak Nickel" and "Black Line Nickel" used many times to describe ENIG
failures. The reason I don't like these terms is because they are
adjectives to describe what one thinks they see and don't describe the
failure mechanism that causes the brittle interface failures. We use
ENIG on an old telecommunications legacy product because it wouldn't be
profitable to do any engineering evaluations to qualify another surface
finish. However, since the root cause of the ENIG solder joint failure
mechanism has never been understood or resolved to the point where one
can turn it on or off, we avoid the use of ENIG surface finish on all
new products. Even though the suppliers of ENIG chemistry have done a
great job of monitoring their chemistry and educating board shops on the
proper controls to reduce the occurrences of brittle solder joint
failures they haven't been able to eliminate these type of failure.
Ingemar is one of the few people I know of on TN that not only has a
great understanding of solder joints but appreciates the process control
details one needs to follow in PCB fabrication as well as PCBA to avoid
un-reliable solder joints. His current problem (i.e., not being able to
understand the failure mechanism or predict when it is going to happen)
is the major reason we avoid the use of ENIG surface finish.
Let's just say Ingemar does a cross section and confirms that there is
"mud flat" nickel grain boundary attack, what does he do on Monday?
Your advice about having a beer because it is Friday and not worrying
about this until Monday only will help this weekend but come Monday what
does he do. I assume that he's already using a "good" board shop and a
"Good" ENIG chemistry. I know what we did and it worked for us but as
an engineer I'd really like to what the ENIG failure mechanism is and
how to avoid it.
Regards,
George
George M. Wenger
Andrew Corporation Wireless Network Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Friday, May 04, 2007 4:45 PM
To: [log in to unmask]
Subject: Re: [TN] Metalurgists, need assistance
Hi folks and thank you Steve for being "TechNet Picture Central"! Sorry
but just to warn everyone but I am going to use the "B" word shortly.
Inge
- take a close look at picture 4. As Werner pointed out the gold is
non-wetting the nickel in number of locations. What really jumped out
at
me is that "mud flat" appearance on some of the nickel surface regions -
a
"mud flat" appearance is a classic indication of black pad! I recommend
you complete a cross-section to confirm that you have nickel grain
boundary attack.
But since it is Friday, go have a beer and worry about this on Monday!
Dave Hillman
Rockwell Collins
[log in to unmask]
Steve Gregory <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/04/2007 01:45 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Gregory <[log in to unmask]>
To
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cc
Subject
Re: [TN] Metalurgists, need assistance
Hi Inge!
Got your pictures posted. Took me a bit, I was swapping our wave
solderpot from 63/37 to HMP. Done now. I'm getting quicker, I can do it
in 20-minutes now. Took me about 45-minutes when I first did it...
Anyways, here's the links:
http://stevezeva.homestead.com/files/Pic1.jpg
http://stevezeva.homestead.com/files/Pic2.jpg
http://stevezeva.homestead.com/files/Pic3.jpg
http://stevezeva.homestead.com/files/Pic4.jpg
http://stevezeva.homestead.com/files/Pic5.jpg
http://stevezeva.homestead.com/files/Pic6.jpg
-Steve-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Friday, May 04, 2007 12:22 PM
To: [log in to unmask]
Subject: [TN] Metalurgists, need assistance
Have an issue with (randomly) lifted FPGA leads.
Pic 1: good joint after pull test
Pic 2: ditto but high magnification
Pic 3: "rotten" joint after pull test
Pic 4: ditto but high magnification
Pic 5: "rotten" cross section
Pic 6: ditto but high magnification
60Sn on ENIG, obviously a brittle region. Suspect Kirkendall voids, but
the pockets with zillions of Tin spheres (0.1 to 2 um in size) points at
insufficient peak temperature to make 100% melt and good solidifying. If
these little balls were Lead, I could understand, but they are Tin!
Never seen like. Any "quickhead" out there, need fast advice.
Note: Pic 2, you can see the underlying board pad nickel as dark areas.
An experienced analyst will hopefully recognize. No Phosphorous peaks!
My Friday headache.
Inge
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