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> Interesting - in my experiments, devices that are supposed to heat things
> tend to be rated into kW...
See how long you can hold on to a 60 W light bulb for after you switch it
on...
Now imagine all that power concentrated into a tiny area inside a plastic
case.
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>> Interesting - in my experiments, devices that are supposed to heat
>> things tend to be rated into kW...
>
> See how long you can hold on to a 60 W light bulb for after you switch
> it on...
>
> Now imagine all that power concentrated into a tiny area inside a
> plastic case.
Mmm, crispy...
So, how come the entire board isn't melted? Just one little chip?
Presumably all that current had to get *in* to the board somehow...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> So, how come the entire board isn't melted? Just one little chip?
> Presumably all that current had to get *in* to the board somehow...
Of course, but presumably the PCB tracks have low enough resistance not to
instantly melt the PCB when a couple of amps goes through them. The same
can't be said for the tiny tiny wires inside an IC. Remember, heating is
due to power not current.
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On Tue, 20 May 2008 11:46:48 +0200, "scott" <sco### [at] scott com> wrote:
>Remember, heating is
>due to power not current.
>
P = I^2 * R :)
--
Regards
Stephen
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scott wrote:
> Remember, heating is due to power not current.
That's interesting - this is the first I've heard of this. I thought
*all* electric effects are due to current?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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>> Remember, heating is due to power not current.
>
> That's interesting - this is the first I've heard of this.
It's simple physics, any electrical energy lost inside a component must be
converted to some other form of energy, usually the majority of which is
heat. The electrical energy lost inside a component does not depend solely
on current, but on power.
Example 1: 10 amps going through a thick cable of resistance .001 ohms.
Power dissipated = 1 W. Heating effect: very small
Example 2: 10 amps going through a heating element of resistance 10 ohms.
Power dissipated = 1000 W. Heating effect: a warm room.
You can compare those examples to the tracks on your PCB and the IC.
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Invisible wrote:
> Picture the scene:
>
> I get called to a PC that won't boot any more. I remove one of the PCI
> cards, and suddenly the PC works perfectly. Hmm.
>
> On closer inspection, one of the ICs on the PCI card looks... Well let's
> put it this way. The writing appears to be scortched. The surface of the
> IC is apparently damp with an oily liquid. There's a bulge in the
> surface of the IC, together with a few small cracks.
>
> Here's a question for you: Why would an IC suddenly do this?
>
> [And more importantly, how in the name of God does a device which only
> has access to a few milliwatts manage to get warm enough to physically
> melt??]
IC chips are almost always connected to the power supply (usually 5V)
and ground. If there is a shorted component in the IC, then the power
that briefly flows through the IC will be better measurable in watts,
and not milliwatts.
Regards,
John
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Here's an additional item of data: This particular IC has been switched
on 24/7 for approximately 8 years or so. [Except for the occasional shut
down now and then.]
for a new PCI board, eh? o_O
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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stbenge wrote:
> I guess these are the reasons I unplug my computer from both wall and
> phone line during a thunderstorm...
>
> Sam
Thet is a good idea!
I had bought two surge protectors one for my phone one for my PC.
With out me knowing the telephone line lost it's ground and the phone
surge protector acted as a ground. Luckily I only lost the modem when
the power surge came.
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Invisible wrote:
> Here's a question for you: Why would an IC suddenly do this?
In addition to what everyone else said, there's the effect of "thermal
runaway". Every semiconductor has a tiny leakage current, caused by
quantum effects, which is why devices use current even when not
switching. There's more leakage when the device gets hotter, because
there's more heat jiggling things around, basically. The more leakage,
the more current, the more heat, the more leakage .... >POP<
--
Darren New / San Diego, CA, USA (PST)
"That's pretty. Where's that?"
"It's the Age of Channelwood."
"We should go there on vacation some time."
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