[njovin]

I've read the same, but for me, a newly-formatted microSD will overheat as soon as it's plugged into the MBP. The OS may be reading/writing something to cause that, but it's automated as part of the mounting process from what I've seen.

[giantrobot]

You can try 'sudo mdutil -i off /Volumes/microSDCardName' which will disable Spotlight indexing on it. While a Spotlight index of an empty disk shouldn't cause overheating...there's bugs somewhere in the chain. To say nothing of quality issues on the cards themselves. I often use an app called Disk Arbitrator[0] to mount disks read-only or block automounts when I'm dealing with SD cards because of overheating issues.

[0] https://github.com/aburgh/Disk-Arbitrator