M24256-DFCS6TP/K serial EEPROM unreliable

[davide.b]

Hello everyone,

I have been working at a design for a product that features the M24256-DFCS6TP/K I2C EEPROM by ST in the WLCSP packaging. A batch of PCBA were ordered from a company. When I started programming the boards, I noticed that the EEPROM did not work correctly on some boards. That is to say, while on some boards the code I wrote works well and I am able to read from and write to the EEPROM, on some other boards the write operation fails while the read operation is fine and on some other boards I can neither read or write.
After some investigation, I was able to exclude PCB manufacturing issues and bad soldering issues.
Has anyone had the same problem with this kind of package? Do you know what could be the cause of such an unreliable performance across multiple boards? Maybe some particular heat curve in the reflow process is necessary? Maybe some special layout requirements?
The space on the PCB is quite tight, but maybe I could fit the UTDFN package instead. Would you think that is going to be more reliable?