One other thing I'd add to this discussion is that when you have a cracked ceramic capacitor, its leakage current can go up significantly after it is exposed to high humidity. That creates very-hard-to-diagnose field failures, as the failed products can either heal themselves (dry out) during shipping back to the manufacturer, or they'll heal themselves as soon as someone touches a soldering iron to them in the course of troubleshooting.

  One company I know of had a heck of a time diagnosing some field failures because of exactly that symptom, the customer swore up and down that product was not working properly, but when the product got back to the office it worked fine.

  -Camille Good
  Portland, Oregon

Werner Engelmaier <[log in to unmask]> wrote:
  Hi Ahmet,
Capacitor cracking with SAC solders is more prevelant then with SnPb solders.
The reasons are:
1) a larger delta-T from solidification to RT;
2) SAC is stiffer and stronger;
3) SAC creeps slower.
The way to solve the problem is to reduce significantly--or better yet
eliminate-- the solder fillets at the end caps. This can be accomplished by
significantly reducing the soldering pad size on the PCB.

Werner

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