Hi Amol,
There is one very confusing observation in your e-mail.
You are saying:
"The IMC fractures were secondary failures occurring after the pad had
failed" and I can not understand it. Once a joint is broken (either
through the laminate or joint itself), there is no more mechanical
stress applied to the joint. So, how come IMC can get broken after the
board underneath the joint had cracked???
Regards,
Vladimir
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: Thursday, June 19, 2008 10:05 AM
To: [log in to unmask]
Subject: Re: [TN] [LF] [TN] SN100 for Reflow Application
Hi Werner,
The cracks show up as opens in ICT. The board is very thin and flexible
(bows under its own wt when a populated board is picked up from one
end), so it has to be handled with kid gloves, not always possible in a
production environment.
As I mentioned in an earlier E-mail, we did a pad strength test using
pull testing on the SnPb laminate, and LF Laminate with LF process
temperatures, and SnPb laminate with SnPb temperatures. The SnPb
laminate subjected to the SnPb process exhibited only pad cratering
failures. The SnPb laminate and LF laminate subjected to Pb-Free
processing exhibited mixed-mode failures; both cratering and IMC
fracture was observed. The IMC fractures were secondary failures
occurring after the pad had failed. Fracture of resin was shallow and
does not expose the glass fibers.
The customer cannot change the board thickness, the location (the BGA is
in the lower left hand quadrant of the board) and size of the part.
after SMT, the board goes thru a stuff line, over the wave in a wave
pallet, and then de-panelized and ICT'ed. It will eventually be inserted
in a slot on a Chassis for the life of the assembly.
We have a (rather expensive) option of attaching strain gauges to the
BGA and measuring stresses during different operations, but I am
currently working on a simple fact that IF we get peel strengths, not
significantly different from our SnPb variant of the same product (which
works without any issues), then we have a solution
Amol S. Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing
941 Route 38
Owego, NY 13827
Phone: 607-687-7669 Ext. 349
Fax: 607-687-9733
Email: [log in to unmask]
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, June 18, 2008 4:36 PM
To: Kane, Amol (349); [log in to unmask]
Subject: Re: [LF] [TN] SN100 for Reflow Application
Hi Amol,
Enhance tooth profile will do nothing for you, since the separation is
not between the ED Cu foil and the resin.
You say: "The cracks appear later in the process and are typical stress
fractures (near the edges of the BGA)." What are these 'later
processes'? Something is making the components/PCB warp.
Werner Engelmaier
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, June 19, London
Interconnect Failures and Design for Reliability for PCB PTHs, June 19,
London
Solder Joint Reliability: Parts 1 through 4, July 17/18, Thal,
Switzerland
Pb-Free Soldering Processes-Survival, Quality, Reliability, August 18,
Orlando
Reliability Issues with Lead-Free Soldering Processes, September 22,
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle
Fracture, ENIG), September 22, Schaumburg
**************
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