We had a bumper crop of HID Prox ( 125Khz ) ID cards which failed this year, many had a very visible "melt" spot around where the RFID chip should be. Excuse the first few from the mobile phone
of extracting the dies.
I then used a mini core saw to cut out the RFID chip area from several of the cards based on the location of the dimple, then dissolved away the PVC card material in solvent:
After some cleaning, this produced a "rich deposit" of RFID chips and fragments.
To give you a sense of size, the die is about 1 x 1.5 mm. The leads looks ridiculous.
And now to the microscope... This is a hasty stitch ( not great ) of 3 shots.
About half of the chips are broken at the same spot, near the pads. When the chip is broken under the pad, it is held together, like this one:
You can see the crack extends across the whole die as seen in this crop.
The chip itself is a standard issue Atmel part used for ... RFID.
The best working theory is that people are exposing the cards to wireless charging stations. The field coil goes to a rectifier that produces power for the chip. When there is an excess of power, it shunts it through a diode, so I suspect the analog section under the pads over heats and the chip cracks.
