|"What happens if you put the same motherboard in a case made of cardboard?" |
You'd get five minutes of spectacular gaming performance before your house burns down. :)
If it got so hot that it would ignite that cardboard then you would have some really serious problems. The computer would fail long before the cardboard got hot enough to ignite.
The fire point is 258°C, the ignition temperature 427°C
Just to give you a comparison, the solder that holds the electronics circuits together melts at around 180C. Long after most CPU has fried themselves into oblivion.