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[on:]

This might seem a stupid question and i believe it is but:
I would like to know why do electronics burn/get fried? Is it because of over current, because that over current causes an extreme increase in temperature at a specific spot which actually melts the material of the electronic component or for any other reasons? (eg voltage related)

Two cases:
Case 1:
Lets say i have a fuse rated for 1A. I pass 5 A through while keeping it cool with liquid nitrogen. Will the fuse burn?

Case 2:
Lets say i configure pin 5 of the arduino as output and set it low(ground it) with digital write, so that it sinks current. If i pass 1A (@5volts)(It is supposed to withstand 40mA of current) for as little time as it takes to go from 1 line of code to the next
{
digitalWrite(5,LOW)
digitalWrite(5,HIGH)
}
will the chip or pin burn?

Thank you in advance people

[Reply #1 on:]

This might seem a stupid question and i believe it is but:
I would like to know why do electronics burn/get fried? Is it because of over current, because that over current causes an extreme increase in temperature at a specific spot which actually melts the material of the electronic component

Yes.

[Reply #2 on:]

> Case 1: Lets say i have a fuse rated for 1A. I pass 5 A through while keeping it cool with liquid nitrogen. Will the fuse burn?

Hard to say.  It depends on how well insulated the fuse is.  Even under liquid nitrogen it may heat up fast enough to melt.  I'd guess about 50% chance it would melt and 50% chance the liquid nitrogen would boil fast enough to keep it cooled below the melting point.

> Case 2: Lets say i configure pin 5 of the arduino as output and set it low(ground it) with digital write, so that it sinks current. If i pass 1A (@5volts)...

You may not be able to pass 1A at 5V.  The current will depend on the output transistor.  At 20mA the voltage on the output pin is 0.47 Volts so the output resistance is about 23.5 Ohms.  At 5V and 23.5 Ohms the current sink will be about 212 mA.

I'd guess that in the few microseconds that high current is passing through the output transistor it may not get hot enough to melt anything.

[Reply #3 on:]

There are several ways electronics are damaged - including over-voltage, over-temperature and over-current.

Over-voltage can cause dielectric breakdown and sudden catastrophic discharge - for instance the gate
oxide layer in a FET.  In semiconductors a reverse-biased pn-junction can breakdown (often this then
causes high currents and over-temperature).

Over-temperature can melt, deform or change the material properties of something.  For silicon semiconductors anything
over 175C will diffuse the donor and acceptor impurities and destroy the electronic structure (but 165C will also do this, only slower). 
125C or 150C is the usual max sustained temperature specified (way way below the melting point of silicon, note).  Different
semiconductors have different temperature sensitivities (LEDs for instance).

Temperature-cycling can cause mechanical fatigue and then failure, even if the temperatures aren't too high in
themselves - better packaging technology (ceramic for instance) helps with this.

For over-current (without over-temperature) there are a few situations where damage can happen - in the aluminium metalisation of a chip for instance high-current densities can cause atoms to physically migrate, gradually etching away the structure.

Concerning the second example - brief over current will mean a smaller temperature rise, which may be enough to prevent
thermal damage, but as mentioned above there are other failure mechanisms too.

[Reply #4 on:]

You may be at the stage I was at for YEARS... thinking that current WILL somehow "force itself" into a component.

Current is what happens AFTER you have set up the voltage and resistance of a given situation.

(That sounds so simple. Sadly, it isn't. Voltage isn't always what you would think it "should" be, and wen you get to the point of burning things, resistance "goes funny" too... but you might find....

http://www.arunet.co.uk/tkboyd/ele1bb.htm

... useful, anyway.

[Reply #5 on:]

I wouldn't try the fuse and liquid nitrogen because there are always different results with different fuses; the material is different, and therefore the insulation would change. Insulation is a large factor in this case.