Hi Chris,
That may still be 'Black Pad'—remember the PCB is much hotter than the BGA and the solder joints are reflowed by conductive heating through the PCB. It stands to reason, that the traces are even hotter than just the resin surface ;thus, causing more Ni going into Sn-solution right there.
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: Werner Engelmaier <[log in to unmask]>; [log in to unmask] <[log in to unmask]>
Sent: Mon, Oct 11, 2010 4:36 pm
Subject: RE: [TN] Mech. damage or poor wetting?
Werner, I’ve tried to describe it better
Fan-out clocking correlation: The fractures/poor wetting appearto start at the trace to land junction, rather than what one might expect from t-cyclingfatigue, or ict strain. In the pictures I posted, I tried to show the damageclocking 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 componentwarpage.
'What points to 'Black Pad' is the periphery location—during soldering theperiphery gets a lot more heat than the interior, thus more Ni goes intosolution with Sn, thus leaving a higher P-concentration at periphery pads, thusthey are weaker, thus component warping causes interfacial separation on theperiphery & 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]]
Sent: Monday, October 11, 2010 2:22 PM
To: TechNet E-Mail Forum; Chris Mahanna
Cc: [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]
Chris Mahanna <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
10/11/2010 11:29 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Chris Mahanna <[log in to unmask]>
To
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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
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