Hi Chris,
I would second Dean Stadem's remarks.
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Feb 12, 2010 2:36 pm
Subject: Re: [TN] Die cracks
Hi Wayne, and all
Thanks for the great feedback so far.
We use the Mark-V 4" X 0.012 precision balanced diamond cutoff blades. We run
them slow, in water. We encapsulated the entire part first. But, surely there
is always some chance that we caused it during mounting/sectioning.
I guess the question is whether the crack signature tells us anything.
I had a response that suggested the crack may be following an interface between
the annealed and un-annealed bulk Si crystal? Any seconds for that?
At least it would explain the signature, maybe not which strain is to blame..
Chris
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
Sent: Friday, February 12, 2010 2:07 PM
To: [log in to unmask]
Subject: Re: [TN] Die cracks
Hi Chris!
How was the sample prep done?
I have gotten similar types of cracks by using exceptionally crude tools to
begin sectioning the part--like a bandsaw. Silicon is very brittle, so using a
coarse tool like that will set up nasty shockwaves. I didn't care since I was
interested in the solder joints, not the die.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Friday, February 12, 2010 1:48 PM
To: [log in to unmask]
Subject: Re: [TN] Die cracks
Not delamination of diebond.
Not overstress from CTE.
Not flexure stress from underfill void.
Possible flexure stress crack from ICT (but not functional test or HASS
testing)
Possible flexure stress crack from handling issues prior to underfill.
Probable flexure stress crack from too rapid cooldown during reflow, or
insufficient PWB support. The solder solidifies, but the board is still
sagging from heat, and as it continues to cool down after the solder has
solidified it straightens out and this puts enormous stress on
components. Note that the fracture is through the length of the die in
the horizontal axis. This indicates a horizontal stress movement.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Friday, February 12, 2010 10:45 AM
To: [log in to unmask]
Subject: [TN] Die cracks
Hi TN
We are in desperate need of QUICK expertise and/or opinions wrt the die
cracks that can be seen from the links below. Sorry Steve, didn't want
to circumvent you but I've got to come up with an opinion by EOD.
BGA/CSPs were encapsulated in slow cure epoxy prior to excision. We
section BGAs everyday and rarely see die cracks.
I've got to decide whether we should recommend that the CM build up a
few more for NDT (acoustics, CT..)
I know: max cool-down was probably 2.2-2.8C/ second; ICT was not strain
engineered or tested; SAC305 balls, paste; parts passed ICT, ..but
cracks don't look to reach active circuitry
Don't know: laminate, peak reflow
Can't say: pretty much anything else
Thanks!
Chris
https://robisan.sharefile.com/d-s7b37c04078d4889b
https://robisan.sharefile.com/d-sc19f7716a0645489
https://robisan.sharefile.com/d-sb215d22cbf54972b
https://robisan.sharefile.com/d-s22d269ff34d4018a
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