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I’m currently having an issue with a SIM card that can’t be read by an LTE chip. It was deployed in a product outdoors where the temperature dropped to around -20C and the connection suddenly dropped and never reconnected (despite firmware attempting to do so). When troubleshooting at room temperature, the connection was only successful after removing and replacing the SIM card, which points to SIM card holder pins not making contact with the SIM card. A visual observation under a microscope showed no obvious signs of oxidation on the SIM card.

The system was power cycled prior to replacing the SIM card and the problem still existed therefore I ruled out the SIM card state as a possible cause of failure.

Is this a documented phenomenon? The temperature specs for the SIM card and holder are below -20C, but it seems plausible that the cold temperature caused the metal SIM card holder pins to contract enough to lose contact with the SIM card and oxidize, somehow never allowing the electrical connection to be reestablished. Any insight is much appreciated.

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  • \$\begingroup\$ If the card is fine you may need to check for corrosion on the pins as well, but if reinsertion solves the problem it may be so small as to not be particularly visible. Other factors like humidity and thermals of the device may be relevant if corrosion is a factor. \$\endgroup\$
    – K H
    Mar 10, 2021 at 6:30
  • \$\begingroup\$ Are you using lead free solder? It can get brittle at low temperatures, so the removal/replacement may have restored the connection if it was compromised in the first instance. \$\endgroup\$
    – awjlogan
    Mar 10, 2021 at 10:05
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    \$\begingroup\$ @awjlogan I believe the solder used was leaded. In either case, I did try pushing down on the car holder which probably would have restored the connection just as well as reseating the card \$\endgroup\$
    – jholdaw2
    Mar 10, 2021 at 10:20
  • \$\begingroup\$ Do you check transmission with an oscilloscope ? \$\endgroup\$
    – Sirac
    Mar 10, 2021 at 13:53
  • \$\begingroup\$ Yes, during the failure state, the LTE chip attempted to supply a low voltage to the SIM card power pin, then a high voltage, then it removed power (I am assuming because there was no response from the SIM card). I also probed the data line and there was no activity \$\endgroup\$
    – jholdaw2
    Mar 10, 2021 at 20:15

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Well, I doubt the SIM itself is rated for -20°C unless it's really well made. It could also be a case that the sim being a low power device simply didn't ``compute'' correctly at such a low temperature, or gave insufficient signal level or shape.

If the card holder were effectively rated for -20°C its finger would have been designed to keep the contact in these condition, probably. Can you contact the manufacturer?

By design the sim holder contacts are self-cleaning since they 'brush' during mating, typically they are gold plated copper berillium. Also oxidation at such a low temperature is quite difficult, for how much it was subjected?

Check the ratings, they often don't specify for how much time it can survive

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  • \$\begingroup\$ The spec sheet for the molex card holder listed on the BOM says “Operating Temperature” minimum -30C. This implies to me it should be able to operate indefinitely down to that temperature. The PCB was assembled by a low cost fabrication house in Hangzhou that may have decided to source a lower quality card holder to increase their profit on the order. Under a microscope the letters “mcd” (if I am remembering correctly) are visible on the card holder. As far as the SIM card itself, it appears not to be the problem since it works fine when reseated. \$\endgroup\$
    – jholdaw2
    Mar 10, 2021 at 10:15

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