PCB design (was MITS Altair...

[Ric Werme]

I'm not sure who said what:

>>But some of the Inspirons have multi-layer motherboards.  On these boards,
>> there are runs *inside* the fiberglass, completely covered and
>> inaccessible to a soldering iron.

>  Ohhh, that's a good point.  I didn't think of that.  Pretty much all
>motherboards are multi-layer boards.  Four or six layers are common.
>Still, the fact that people have managed to perform repairs
>successfully proves that, for at least some boards, it is possible.

>>And, yes, some designers had the dim-witted idea to run *power*
>>through these internal runs.

That's not dimwitted.  Power and ground planes provide signal integrity
and crosstalk isolation.  Frankly, I'm amazed at the clock rates people
put on a circuit boards these days and actually manage to get them running
reliably.

>>  I challenge you to find me a mass market motherboard made in the
>>past ten years which doesn't do this.  They're designed to pack tons
>>of technology into a small space, which is not easy.    Surface mount
>>solder joints have spelled the doom of the electronics hobbyist, but
>>they enable a huge increase in density.

And is another major reason why control & data signals are on the surface.
Also, if you need to do some rework, those are the signals you need to get to.
Almost any dimwit can get power and ground to an IC right, though I remember
one case where they forgot the ground.  As long as one gate wanted to
put out a low signal things worked okay.

    -Ric