Chris,
3 possible mechanisms for cracks propagating from the trace side are but most likely a combination of all:
1) Residual contamination of the Ni-Au surface during plating and chemical exchange due to soldermask bleed - more likely on SMOBC ENIG PCBs
2) Solder joint at the solder/soldermask interface has no filleting causing mechanical stress concentration at the IM interface where the solderball and the PCB soldermask touch
3) Solder paste "blow out" between soldermask and solderball during reflow makes reverse angle fillet to serve as a stress concentrator and drives gas into solder-pad interface
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Monday, October 11, 2010 1:36 PM
To: [log in to unmask]
Subject: Re: [TN] Mech. damage or poor wetting?
Werner, I've tried to describe it better
Fan-out clocking correlation: The fractures/poor wetting appear to start at the trace to land junction, rather than what one might expect from t-cycling fatigue, or ict strain. In the pictures I posted, I tried to show the damage clocking around with the traces.
I thought that I had heard or read somewhere that this is common, but you guys are a lot faster than a literature search.
Chris
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Monday, October 11, 2010 4:10 PM
To: [log in to unmask]; Chris Mahanna
Subject: Re: [TN] Mech. damage or poor wetting?
Hi Chris,
What do you mean by 'fanout clocking?'
I think you have a combination of 'Black Pad' and component warpage.
'What points to 'Black Pad' is the periphery location-during soldering the periphery gets a lot more heat than the interior, thus more Ni goes into solution with Sn, thus leaving a higher P-concentration at periphery pads, thus they are weaker, thus component warping causes interfacial separation on the periphery & pad cratering where the P-concentration is lower.
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Oct 11, 2010 2:40 pm
Subject: Re: [TN] Mech. damage or poor wetting?
Here are a few pictures
http://ipc-technet.groupsite.com/gallery/16011
this job is a mixed bag. Currently we suspect soldering, cratering, ICT and
t-cycling damage
Chris
From: [log in to unmask]<mailto:[log in to unmask]> [mailto:[log in to unmask]<mailto:[log in to unmask]>]
Sent: Monday, October 11, 2010 2:22 PM
To: TechNet E-Mail Forum; Chris Mahanna
Cc: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Mech. damage or poor wetting?
Hi Chris - do you have any pictures you can share?
Dave Hillman
Rockwell Collins
[log in to unmask]<mailto:[log in to unmask]>
Chris Mahanna <[log in to unmask]<mailto:[log in to unmask]>>
Sent by: TechNet <[log in to unmask]<mailto:[log in to unmask]>>
10/11/2010 11:29 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]<mailto:[log in to unmask]>>; Please respond to
Chris Mahanna <[log in to unmask]<mailto:[log in to unmask]>>
To
[log in to unmask]<mailto:[log in to unmask]>
cc
Subject
[TN] Mech. damage or poor wetting?
We have a BGA dye-n-pry job that shows board side sj damage with a strong
correlation to fan-out clocking.
We also have some microsection evidence of poor wetting.
All damage/dye is on perimeters.
Is this an indication of heat sinking and subpar wetting, or can it be
completely mechanical? Both?
Thanks
Chris
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]<mailto:[log in to unmask]>
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]> or
847-615-7100 ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]<mailto:[log in to unmask]>
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]> or
847-615-7100 ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
==============================================================================
This email and any attachments thereto may contain private, confidential, and
privileged material for the sole use of the intended recipient. Any review, copying,
or distribution of this email (or any attachments thereto) by others is strictly prohibited.
If you are not the intended recipient, please contact [log in to unmask]
immediately and permanently delete the original and any copies of this email and
any attachments thereto.
==============================================================================
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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
-----------------------------------------------------
|
