The exposed pad on CY15B104Q-LHXI should not be soldered. Soldering the exposed pad will expose the F-RAM die to excessive heat, which may result in bit failures and margin loss. Hence it should be left floating without connecting to any pad on the PCB.
It does appear that you have not soldered the exposed pad but observing failures at 60 degrees C. Is it correct ?
Can you describe the failure in detail ?
a. Out of 8, how many devices fail at 60C ? Is the failure repeatable and at the same address ?
b. Does the write/read work at room temp for all 8 devices ?
c. Is there any other components on board which can cause failure at 60C ? If the failure is seen at specific address and repeatable, I would recommend capturing write/read waveforms at the F-RAM device.
Did you get a chance to go through my reply? For timely support, I would suggest to create a technical support case.
For doing that, please create an account in www.cypress.com. On the top right, under login details, there is link to MyCases and you can open a technical support case.