Date   : Thu, 28 Oct 2010 02:24:24 +0100
From   : list-a_cloud9.bbc-micro@... (Theo Markettos)
Subject: Reversing the Tube ULA (destructively)

In article <AANLkTinf=3La8nf+0yhOe6XEBp-nZuh=7j-ExpcK7R3B@...>
you wrote:
> That's great!  I see that acetone for the plastic and violinist's rosin for
> epoxy is supposed to work
> (http://s3cu14r.wordpress.com/2010/07/15/boiling-chips-in-tree-sap/)  - has
> anyone tried it?

I hadn't heard of this, but there's a number of chips I've been wanting to
depackage so I may give it a go sometime.  Rosin is also used in soldering
flux, so possibly a pot of plumber's flux might be another source.

A cautionary note.  I assume these ULAs have a single metal layer which
constitutes the user-defined connections.  Do you have access to any data on
the 'blank' layout that lives underneath?  There will be some NMOS dopant
(and PMOS too if it's a CMOS device), some polysilicon gates, and then the
metal layer(s) on top.  Polysilicon is typically used as wiring, so the
metal mask doesn't tell you enough information to reconstruct the chip
unless you know the areas of dopant and the polysilicon.

There are imaging and etching techiques to strip off the layers one by one,
but they require a lot of trial and error... and there aren't plenty of
samples to test on.

(Though my experience is on chips about 20 years younger than these, so I
might be wrong in my understanding of old chip fabrication technologies)

Theo