I have read Colibri iMX8X datasheet par 8.4 Thermal Specification (link) and KB Thermal Management mechanical considerations and T20 reports here but I have still some doubt about this point: from your experience which kind of heatsink, if any, is needed or recommended for the iMX8X in the conditions like the following?
low-mid CPU load for simple UI, some Ethernet communication
WiFi may be connected but with low communication
outdoor usage 0-45°C environment
internal case with other electronics, air circulation
Using figures from thermal specification section from Colibri iMX8X datasheet, I have made some estimations of working conditions but I am not sure about the meaning of the RθJA parameter in the datasheet. Who has written the datasheet, considered it as to be placed “in parallel” to the thermal resistance of an external heat sink, placed on top of the chip case?
Thermal Resistance Junction-to-Ambient, i.MX 8X only. (RθJA) 15.2°C/W from datasheet
Thermal Resistance Junction-to-Top of i.MX 8X chip case. (RθJCtop) 0.7°C/W from datasheet
Junction temperature SoC max 125°C from datasheet
Thermal Resistance of an heat sink like the one used for Colibri T20 tests (RθHA) 26.9°C/W from Digikey
In that case, a parallel thermal resistance could be around RθJA ~ RθJA//RθHA = 9.7°C/W and a full CPU+GPU load of the iMX8X of 7 W (like this) could get junction temperature limit at ambient temperature of 125°C - 9.7°C/W x 7 W = 57.1°C.
