I’ve had a career in military electronics. Commercial grade chips are generally specified to 70ºC, which does not mean they will instantly die if that temperature is exceeded, just that they have not been tested and are not guaranteed to operate within their specifications at that ambient temperature. The temperature is extended to 85ºC for Industrial, and 125ºC for Military spec.
The troublesome bit is not so much the ambient temperature as the measures taken to mitigate the temperature of the chip itself, inside the packaging. There is “thermal resistance”, which limits the rate at which heat generated can be dissipated. Thermal resistance can be reduced by fitting the chip with a heat sink, for example. The figure for thermal resistance tells you how much higher than ambient the temperature of the silicon is per watt that it has to dissipate.
Just for the sake of argument, let’s suppose the stepper drivers (when working hard) are dissipating 1W, and their thermal resistance when mounted on a PCB with no active cooling is 20ºC/W (I don’t know whether these figures are representative). That results in the silicon temperature being 20ºC higher than ambient, but in this case “ambient” means the temperature inside the enclosure, not the room temperature. As you can see, in this example, add 20ºC to the 105ºC inside the enclosure and you get a 125ºC operating temperature for the silicon.
Figures in Texas Instruments datasheets I used to work to de-rated expected life for silicon chips from nominal at 105ºC to 0.2 x nominal at 125ºC, so yes this is a concern. Perhaps motor drivers are made using an exotic process such as silicon carbide to withstand high temperatures, but I doubt we could afford them if they were.
To my mind, it is key that the power control electronics and anything else that gets hot (eg the processor, and the power supply) are not exposed to elevated enclosure temperatures. Unfortunately there’s nothing that can be done to protect the electronics in the tool heads.
Additional to concerns about lifetime of electronics, I would also worry about the ratings of mechanical components such as drive belts, and the stepper motors themselves. Steppers get hot, and in a high-temperature environment they will get hotter still – potentially to the melting point of the plastics they are mounted on.
Time will tell. If my fears are real, we’ll get a flood of posts about temperature stress once the top cover is widely delivered and people have started using it to print ABS, PC, whatever. My recommendation is not to be the guinea pig.
