Tan Geok,
these photos will lead to no answers. If you have a serious issue, you have many more samples to prepare, right?
If you are not used to the art of cross sectioning, you may have someone around to assist you.
The cross section should be polished in steps from grain 600 to 4,000, then diamond polished down to one micron. After the polishing, do a few seconds of copper etching, followed by a very short lead/tin etching. These steps will give you a better definition. The etching must take just some fractions of a micrometer, or rather nanometers, not more.
After the etching you need take colour photos as well as black/white ones for comparison. You should then see clear distinctions between Copper, Nickel, Tin, Lead, and also various intermetals. There are so many failure modes in this game, so the better your preparation is, the better the chance to get help from TechNet.
Your photos should look like e.g. row 7, middle, on Steve's homestead page1, have a look at the photos marked #1 and #2. That is the kind of pictures we need.
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: fredag 16 januari 2009 19:26
To: [log in to unmask]
Subject: Re: [TN] Possible cause on open
Hi Richard!
Finally got your *.doc file posted. It's at:
http://stevezeva.homestead.com/files/expanded_images.doc
It's warmed up a little today. Supposed to get in the mid 50's F.
tomorrow. We have the craziest weather here! Near zero one day, then three days later it's in the 50's!
Steve
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Friday, January 16, 2009 9:48 AM
To: TechNet E-Mail Forum; Igoshev, Vladimir
Cc: Steve Gregory
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 solder. 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; [log in to unmask]
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
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
