Sorry, sent the previous e-mail "earlier" :-)
The reason I said "almost" is that black pad usually affect a whole pad and it seems not to be the case in the Inge's case :-)
Hi Dave,
I'm almost completely with you and that was another reason I asked Inge whether he happened to have a X-section of a bad lead.
:-)
Vlad
-----Original Message-----
From: [log in to unmask]
To: TechNet E-Mail Forum; Vladimir Igoshev
CC: [log in to unmask]
Sent: Fri May 04 17:55:51 2007
Subject: Re: [TN] Metallurgists, need assistance
Hi Vlad! If I am interpreting Inge's photo number 4 correctly [realize I didn't get to see it on the SEM in person : - ) ], I see the nickel surfaces which have no wetting of solder. Gold dissolves into solder at 100 uinches per second (Bader data) there should be no gold on those surfaces. In brittle interface fracture, I expect to see very few regions of nonwetting - the failure is due to the poor properties of the Sn/Ni intermetallic (e.g I get good wetting, its just not a strong interface). In cases of black pad, I expect to see very few regions of good wetting, the nickel surface has been corrupted such that I don't form the Sn/Ni intermetallic (e.g I get terrible wetting and never form a good interface). Thus my comments for picture 4.
Dave
Vladimir Igoshev <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/04/2007 04:12 PM
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Re: [TN] Metalurgists, need assistance
Hi Dave,
I'm lost:-) how come you know there was no Au in the areas where we see Ni?
Brittlle Failed ENIG joints wqill have a similar "muddy" appearance
Regards,
Vladimir
-----Original Message-----
From: TechNet
To: [log in to unmask]
Sent: Fri May 04 16:45:09 2007
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
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Steve Gregory <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/04/2007 01:45 PM
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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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