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February 2010

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Wed, 3 Feb 2010 17:27:31 -0500
Content-Type:
text/plain
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text/plain (184 lines)
Hi Chris,

Boy, I'm learning new stuff everyday! I have your pics posted, they are
here:

http://stevezeva.homestead.com/files/05-4_-_0_CRATERING.jpg

http://stevezeva.homestead.com/files/05-4_-_2_CRATERING.jpg

http://stevezeva.homestead.com/files/28391_E4-C2_CRATERING.jpg

http://stevezeva.homestead.com/files/28530_Corner_ball_crater.jpg

http://stevezeva.homestead.com/files/CRATERING_WL.jpg

THANKS!

Steve


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Wednesday, February 03, 2010 4:13 PM
To: [log in to unmask]
Subject: Re: [TN] track lifting

Pearl, et al

Be very glad that you got the buckle!  Looks like an extreme case of (very
common) land cratering (see Werner's posts on how to avoid).  The much more
typical case is that the mask stakes down the trace and you have a latent
defect.  It becomes patent when thermal cycling fractures the foil at the
edge of the soldermask.  At room temperature the crater re-seats itself and
is very hard to see even in a microsection under polarization.  In
microsection, you'll be looking for the sj crack, but of course there won't
be one, because the stress was relieved by the crater.  Worse yet, the trace
probably isn't in the section because of the fan-out.  It is a horrible
latent defect.  I'll try to find some good pics for Steve, or IPC or...

Chris

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Wednesday, February 03, 2010 11:47 AM
To: [log in to unmask]
Subject: Re: [TN] track lifting

Possible, but looking at the two interconnects on the left - as I pointed
out the trace ends where they meet the pads appear to be broken at the
interface without any sign of buckle or lift on those traces.

I will be very ineterested to see the FA results on that whatever the cause
- what we as engineers find "interesting" the rest of the company normally
views as an unmitigated disaster...8-) .....and of course - I will buy you
lunch Richard any time....8-)

Best regards,

John 


John Burke
(408) 515 4992


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, February 03, 2010 6:33 AM
To: [log in to unmask]
Subject: Re: [TN] track lifting

Like Steve, my first thoughts were that the BGA in the picture was
apparently impacted, or somehow lifted and then put back down and reflowed. 
However if that had happened, it could not have happened without many other
traces on each side of the lifted ones also being lifted and damaged, but
they are not.
Therefore I agree with Werner, that this is a case of damage due to severe
CTE mismatch. I have never seen this before. 
Burke, I'll take you up on that bet. I doubt that there will be any
delamination issues. This appears to be a case where the PWB expanded and
shrunk back in the X and Y axis during reflow or temperature cycling, but I
doubt that it saw any significant Z-axis expansion.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, February 03, 2010 8:13 AM
To: [log in to unmask]
Subject: Re: [TN] track lifting

 

 Hi Brian,
I would appreciate pictures, possibly also to Steve, that I could use in my
reliability column-this is a failure  mode fairly new and unknown to most
people.
If you could, I also would appreciate the base material, the peak reflow
temperature, the cooling rate after reflow, the Cu trace thickness and
whether it was covered with solder, and what solder. I now, its asking a
lot, but only with all the pertinent info can we make sense of this.
Werner


 

 

-----Original Message-----
From: Brian Chandler <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Feb 3, 2010 7:28 am
Subject: Re: [TN] track lifting


We just conducted a study on acceptable strain levels for lead free
products. 
Our BGA test coupons showed this exact result from excess strain.

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