Wednesday, March 2, 2011

Studying the CD4001

Somewhat arbitrarily I decided a CD4001 would be a good chip to really study to get a better feel for how a chip was put together. While I can recognize bits and pieces of larger chips, I still lack the fundamental understanding of how to recognize raw transistor arrangements. Although such basic logic chips have heavy optimizations which can be somewhat undesirable as a study tool, I'm hoping their simplicity makes up for it.

The original chip I was going to look at was a Fairchild CD4011:

I decapsulated it and found it had nice coloring:

Hopefully "POS" doesn't refer to their confidence in their design. This was only intended to be a preliminary quick photo before cleaning, but my metal tweezers slipped and sent it flying to who knows where. I now have plastic tweezers which tend to chip the dies less and less susceptible to slipping. Anyway, take a look at what I think is a National Semiconductor 4001 (was in a tank of 4001's):

In a similar area:

Maybe its just the "natural" arrangement for this sort of configuration? I'll figure out more as I etch out the transistors. Its interesting though that ones a CD4001 and the other is a CD4011.

Another item is interest is that older Texas Instruments datasheets had top metal included. Compare a datasheet with one of my snaps:

...and the (rough) stitch:

One interesting thing with the TI parts is that you can identify pin 1 with a bullet shaped pad. Other vendors have similar things and it seems the shapes tend to be unique per vendor. For example, it seems Motorola may use an octagon like pattern (all taken from what appear to be different revisions of the same 4001):

The first two are nearly identical. The last one has a full octagon where as the first two had a square corner.

I have some etching chemicals coming that will hopefully come by this weekend and I can use to expose some transistors. I have a roll of 100 Phillips 4011's (about $6 from Jameco):

which I'll practice on and then expose other chips that I have more limited capacities after I have some results. Since these chips are so simple, I can actually make guess as to what a lot of things do, but I would like the transistors as well to complete the picture. If successfull, I'd like to write up a tutorial that takes someone through decoding the chip.

On a random note, I get a lot of my chips by scrapping old electronics. I heat gun the board (wearing my 3M industrial respirator so as to not get too many fumes) and collect chips into a tray. Usually there are only a few I really care about, such as the main CPU or some FPGAs. There are lots of leftover small chips. Its not cost effective for me to use them in anything I design for a number of reasons. So, what to do with them? How about throw them in a beaker and decap in mass:

The larger chip is an i960 that I savagely ripped out of a computer that was being junked. As such, it got cracked in two spots. Setting up for mass photography:

They are on a microscope slide with sticky tape. I estimate I spent only about 1 min on each chip. Granted, this has limited usefulness, but it does show a number of interesting designs and I was never going to use the chips otherwise. For the curious, I uploaded a bunch of them to