This paper presents observations on some electronic components where n
on linear thermal effects play a dominant role. Our interpretation has
been assisted by the use of novel numerical modelling techniques whic
h can either solve for a single field variable, or can be used in coup
led form to investigate systems where different field variables may in
teract. Non linear thermal effects appear to be responsible for premat
ure failure in metal film resistors when operated under pulsed conditi
ons. This is thought to be due to the effects of competing thermal pat
hs which involve the metal and non-metal parts of the device. There is
also a discussion on some relatively novel ideas concerning the opera
tion of the electric fuse.