Microscope images of a DS3231

[cdev]

I saw this post linked to on the time-nuts site and thought it would be interesting.

http://imgur.com/a/0zudj

These nice pictures (see imgur link) of the DS3231 die were made by Pete S.

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>>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


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I also have two of these very cheap - very possibly recycled - Dallas RTCs that I bought on ebay.

One seemed to have some issues but the other one is working okay so far.

[floobydust]

There are very nice pictures of the IC's internals. Thanks for posting the pics link and Pete S thanks for the IC teardown.

It helps explain the datasheet "Run no PCB traces underneath the IC", for keeping noise from the crystal leads. Most designs miss that.

It's a great RTC, but expensive in North America ~$11 and I can almost buy an entire LED digital clock for that many dollars, that comes with DS3231 from eBay.

[cdev]

Another good deal on timekeeping is the navspark mini. I recently picked up a package deal on them and I am putting them in my computing hardware. They seem to be more accurate than my capacity to measure them, also they are very sensitive. Sensitive enough to work indoors with no issues, no loss of 3d fix, ever. The navspark has an internal RTC with battery backup and I am wondering if it would be possible to move my working DS3231 to some other hardware that needs it and use the navspark with battery backup as the RPI's primary RTC.

Tragically, PC hardware seems to lose all the accuracy of any add-on RTC that has better granularity than one second, as far as I can tell.