Thank you Werner…..I did a X-section of the BGA after reflow to determine if warpage or thermal shock during SMT was causing the joints to fracture. The BGA joints are without any defect after reflow. The cracks appear later in the process and are typical stress fractures (near the edges of the BGA). We were using a Phenolic cured filled laminate for the LF build, while use a DICY cured unfilled laminate for the SnPb build. The peel strength study we did showed significant difference in peel strengths (with DICY being higher) between the two laminates.



We are conducting further tests with a unfilled LF capable laminate to see its effect on pad strength. SMD pads and a enhanced tooth profile Cu has also been suggested to bolster pad strength.



Just wanted to do a sanity check to see if I am overlooking anything, and also look at potential alloy change if that will help………..your thoughts?



Thanks,

Amol



From: [log in to unmask] [mailto:[log in to unmask]]

Sent: Tuesday, June 17, 2008 4:33 PM

To: Kane, Amol (349); [log in to unmask]

Subject: Re: [TN] SN100 for Reflow Application



Hi Amol,

High Sn solders do have lower creep rates, higher strengths, and higher modulii of ductility relative to SnPb—this clearly contributes to the problems you observe. what you can do is slow down the cooling rates from reflow to no more than 1.5C/sec to avoid the thermal shock causing pad cratering and to some extent brittle interfacial failures.

The PCb material may also contribute—some of the LF-soldering capable PCB base materials are  more brittle.



Werner Engelmaier

Future workshops:

Reliability Issues with Lead-Free Soldering Processes, June 17, London

Interconnect Failures and Design for Reliability for PCB PTHs, June 17, 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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