[sdiy] Re: IC parts binning

[Robin Whittle]

Hi Dave,

I am not being a troll.

I found Paul's article very interesting, particularly regarding the
importance of testing time and therefore costs.

Its one thing to design a CPU logically, another to figure out how to
make it as a billion transistors on a single piece of silicon.  Then
there is the daunting task of actually making them, for not too high
a price.  But how do you test these things, at a single temperature,
for a few seconds only, and be confident those which pass will, with
a very high probability, go out into the world and work reliably for
decades, at a range of different temperatures and voltages?

How do they test EEPROM, FLASH cells etc to be sure they don't leak?

I recall reading that Lattice GAL chips and the had the cells
programmed and then by varying the power supply voltage it was
possible to measure the threshold voltage of each cell precisely - by
the power supply voltage changing the reference voltage of the sense
amp.   Then, I recall, they would store this information and stash
the wafers, or the packaged chips perhaps, for a few weeks.  Then
they would measure the threshold voltages again and chuck out any
chip in which a voltage drifted by too much.

I guess with the mass gigabit FLASH chips they must have extra arrays
to use in place of arrays with dead cells.  But how do they test for
leakage on such a massive scale?

Different testing problems would arise with simpler, but more
finicky, analogue devices.  Digital stuff just has to race to the
correct on or off voltage range in a given time.  Analogue stuff
needs to be precise, stable, noise-free etc.

All these chips are supposed to work reasonably reliably when running
for years at temperatures way too hot to touch.


> Samppa Tolvanen wrote:
>
>> Basically the coolest post ever I've seen on SDIY.
>
> I'm trying to figure out how this is actually a troll.
>
> It looks like a compliment.
>
> But it has to be a troll.  Doesn't it?

I wonder how much caffeine have you had in the last few days.

Now I am arguably being a troll!  Or I would be if I hadn't admitted
the possibility of such.

But its the truth:  I do wonder why someone would see a
straightforward, appreciative compliment as something quite the
opposite.


  - Robin