[time-nuts] A look inside the DS3231

Trent Piepho tpiepho at gmail.com
Thu Jul 27 15:46:20 EDT 2017

Looks like it still says "DALLAS SEMICONDUCTOR" to the left of Maxim.
Maybe Maxim only wanted to change the mask enough to find some empty
space to sign it?

On Thu, Jul 27, 2017 at 12:31 PM, Pete Stephenson <pete at heypete.com> wrote:
> Hi all,
> A few days ago I reported the results from letting a DS3231 RTC run for
> a year, and how the chip kept time well within the published specs.
> Since I had acquired several DS3231s from dubious sources (Asian vendors
> on a major auction site) as part of an RTC module that fits on the
> Raspberry Pi's header pins, I was doubtful of the authenticity of the
> chips. I decided to sacrifice one in the name of science and decapped it
> at home using alternating heat (a lighter) and cold (a glass of cold
> water) to embrittle the epoxy casing, then sanded down the back of the
> chip on fine-grain sandpaper to expose what I hoped was the back of the
> internals (so as not to damage the die itself).
> Other than inadvertently sanding through half of the crystal's housing,
> thus breaking one of the forks of the crystal, this was a success. (I
> was prepared to decap one in acid had my attempt at physically removing
> the epoxy package failed.) I slightly scratched the die itself while
> separating it from the epoxy, but the die itself is clearly visible.
> Based on a sample size of one and the markings on the die itself, it
> appears the chip is authentic. The markings on the outside of the epoxy
> package look a bit dubious and not like typical Maxim laser-markings, so
> it's possible the chip was re-labeled at some point. I'll contact Maxim
> to see if they can look up the lot information.
> I used my 2 megapixel USB microscope to take some images throughout the
> process that you might find interesting. The microscope has limited
> resolution, particularly at high magnification, so some of the photos
> may not be perfectly clear. I have access to a Zeiss petrographic
> microscope at my work and will see if I can get some better images
> tomorrow. I'll try to get high-quality images of the whole chip and
> stitch them together into a larger composite.
> Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
> add more photos from the petrographic microscope tomorrow. I focused
> mainly on the markings on the die that indicated it was, in fact, a
> Maxim chip but if there's any other region of the chip that you'd like
> images of, please let me know and I'd be happy to take some more
> pictures.
> I hope you find this as interesting as I did.
> Cheers!
> -Pete
> --
> Pete Stephenson
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