[Coco] 6809 wafer on eBay

Arthur Flexser flexser at fiu.edu
Thu Aug 22 15:35:59 EDT 2013


Thanks for enlightening me about the "boule", Mark.  I'd never have guessed
the cause of the roundness of the wafer was that it was cut out of a giant
sausage-shaped silicon crystal!

Art


On Thu, Aug 22, 2013 at 2:38 AM, Mark J. Blair <nf6x at nf6x.net> wrote:

>
> On Aug 21, 2013, at 23:10 , Arthur Flexser <flexser at fiu.edu> wrote:
> > As one who is not at all knowledgeable about the manufacture of CPU
> chips,
> > could somebody please enlighten me as to what exactly this 4"/100 wafer
> > thing is?  It's 4 inches in diameter and contains the makings of 100
> > 6809s?
>
> Correct.
>
> >   Is each of the little squares something that gets mounted in the
> > center of the actual 6809 chip in such a way as to make contact with its
> 40
> > pins?
>
> That is exactly correct.
>
> >  Why would the shape be a disc with many of the squares cut off in
> > the middle, rather than rectangular?
>
> That disc-shaped wafer is a thin slice of a long, round, billet of silicon
> which is called a "boule":
>
>   http://en.wikipedia.org/wiki/Boule_(crystal)
>
> The wafer is very pure elemental silicon, and it's a single, uniform
> crystal with very few defects in its crystal lattice. That's important to
> how semiconductors ("electronic stuff") works. In order to make that
> gigantic, pure crystal, they start with a pool of molten silicon, and dip a
> small bit of solid silicon (called a "seed") into the pool. The molten
> silicon begins to crystallize around that seed, and they then slowly draw
> the seed out of the pool, with the crystal growing out of the pool as they
> lift the seed up. Eventually, they end up with a great big sausage-shaped
> boule of pure silicon, which can then be sliced up into wafers. So, that's
> why the wafers end up round.
>
> A whole bunch of very complicated processing steps are then done to form
> many copies of the desired device (in this case, an MC6809) on each wafer.
> It's very expensive to make each wafer, but that cost is divided up among
> all of the devices on the wafer, which is why it's even economically
> possible to make things like computer chips.
>
> Next, those individual devices are split up by sawing the wafer into
> little rectangular bits. Each one is called a "die", and the plural form is
> "dice". That's because the wafer is diced up much like an onion slice.
>
> Now that they've cut that wafer up into hundreds of dice, each one of them
> gets mounted in a package with pins on the sides (or these days, more often
> balls on the bottom). The contacts on the die need to get connected to the
> pins of the package, and on an MC6809 that would be done with a process
> called wire bonding:
>
>   http://en.wikipedia.org/wiki/Wire_bond
>
> That was very simplified, but I hope it helps make some sense.
>
>
>



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