Beta Systemcore eMMC Failure Analysis

Discovery

Two FRC teams reported that their beta Systemcore units would not boot properly. One of the teams (9408) probed the CM5 and found it was failing to boot due to a stuck eMMC. Upon receiving the two broken units, we confirmed the eMMC failures were identical. There was no damage to the mainboard or other CM5 elements, as USB booting enabled full functionality.

Reproduction

eMMC failure could not be reproduced during full ESD re-characterization. 9408 tested two modified Systemcores to help us narrow-down the root cause.

eMMC failure was reproduced after the identification of witness marks on all stuck eMMCs. During assembly, the orientation of the Systemcore mainboard influences the amount of pressure applied to a critical region of the board during CM5 insertion. If the board is over-flexed, one of the USB-A port mechanical retention pins pierces the eMMC which leads to immediate or eventual failure.

Resolution

A jig prevents board flex during final assembly, and USB-A mechanical retention pins are clipped to increase clearance between the pins and the eMMC. Before reproduction, USB-boot capability was added which allows Systemcore to operate without an eMMC. Standard design clearance checks have been updated.

Action for Users

As this failure may appear on pre-production units, alpha/beta testers should prepare a flash drive with the latest USB image using the latest hardware manager release in case a beta unit fails to boot.