I'm trying to source some parts for a kit and the most expensive part I have by far is the DS1307+ RTC chip. They run about $4 in single buys and $1.96 in larger quantity.

But then there's this: http://www.aliexpress.com/item/100-PCS-lot-DS1307-DIP-8-1307-64-x-8-Serial-I2C-Real-Time-Clock-Free/552264214.html

They are selling the same (supposedly) chip for $0.12!

What I worry here is that these are just counterfeits and will have a high failure rate.

The numbers below DS1307 on the chip in the picture is a little different than the chips I bought from Mouser, but I'm not sure what they mean. Anyone know?

Is there anyway to tell if these are legit?

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    \$\begingroup\$ -1: Way to specific to a particular place and time, and unlikely to be of any help to someone coming along a year from now with a similar questions. More general questions about identifying counterfeit parts would be fine with me, though. \$\endgroup\$
    – DarenW
    Sep 1, 2013 at 3:57
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    \$\begingroup\$ Simple answer: They could be, but also, Digikey or any US vendor's volume pricing in many ICs is often 10 times or more the price in China for various reasons. \$\endgroup\$ Sep 1, 2013 at 4:01
  • \$\begingroup\$ too localized (we used to have this as a pre-set option) \$\endgroup\$ Sep 1, 2013 at 6:17
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    \$\begingroup\$ @NickAlexeev while answers specific to OP's ic would be too localized, a general answer to why any given IC could be counterfeit outside of recognized chains of distribution would not be. \$\endgroup\$
    – Passerby
    Sep 1, 2013 at 7:45
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    \$\begingroup\$ @travis more like "possible ways an ic can be counterfeited" because the only real way of telling if a part is counterfeited is decapping it and using thousand dollar electron microscopes to look at its various wafer layers. \$\endgroup\$
    – Passerby
    Sep 1, 2013 at 8:16

2 Answers 2


For the question of the different numbers between the chips they are probably the date codes / lot number that many manufacturers use to track when and where a part was made. When customers report failures that can be useful to isolate manufacturing problems down to particular factories or batches.

I couldn't find documentation for the DS1307 in particular but here's an example for another Maxim DS series part:

Clarification of DS1804 Ordering Information and Package Marking

For that part the final two lines are:



  • yy = Last 2 digits of year of assembly
  • ww = Work week of assembly
  • rr = Die revision code
  • ### = Last 3 digits of lot number
  • xx = Up to 2 alpha characters of lot number suffix

If you are going outside of legitimate or recognized or trusted sources, then yes, they could definitely be counterfeit. Maxim-Dallas has a list of valid distributors here: http://www.maximintegrated.com/sales/offices/distributor/franchise.mvp#

Mainly Digikey, Mouser and Avnet in the US. Outside of these chains, buyer beware.

You could be buying one of multiple parts. Best case scenario, Parts Pin and Code compatible. Then you have parts that are from Ghost Shifts, where legitimate manufacturer plants/equipment is used off the clock to produce extra parts. You could have parts where legitimate runs are deemed defective (say 10% of a run's samples are bad, they scrap the entire run) but instead of trashed someone steals them for resale. You could have unauthorized parts designed to meet the specs but under quality. Or the worst case, you have duds that are relabled or worse, parts with no electronics inside (I.E. Just Epoxy and Leads, no wafer).

The only way to tell if the parts are good is testing EVERY SINGLE ONE AND PRAY. You could order samples (free or paid) or a small quantity (say 10~20) but you might end up with good parts (or parts that will take extended testing to break) intended to trick the buyer (you) into ordering a larger quantity, which will end up being lemons.

Basically, Cavet Emptor.

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    \$\begingroup\$ I frequently wonder how - if real - the countless sellers in HK and similar get the ICs they claim to have. This applies especially to proprietary/single-product ICs - like many I've bought (& never seem to get around to hooking up). Finally, someone provides some rationale! "Ghost Shifts" & trash-digging are intriguing. +1. My idea before was that maybe when mfgs wind down a product, they firesell spares to any stockpiler who'll take them... but given how many would rather incinerate stuff than leak IP, I've always thought that unconvincing. Anyway, indeed, practically, only testing can tell. \$\endgroup\$ May 21, 2016 at 15:45

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