Computers Overview
Commodore PET
Sinclair ZX80
Sinclair ZX81
BBC Micro
Sinclair Spectrum
Memotech MTX
    User Groups
    Video Wall
Memotech CP/M
Atari ST
DEC 3000 AXP
Raspberry Pi



University of Connecticut Paper on Counterfeit Integrated Circuits

This paper, developed by the Center for Hardware Assurance, Security and Engineering at the University of Connecticut and published in the Journal of Electronic Testing: Theory and Applications, discusses the dangers of counterfeits and some techniques to identify and avoid them. The paper appears to have been removed from the UConn website, but can be downloaded from here.


This page was inspired by the problems that Martin experienced when testing his version of the MTXPlus+ CPU Board. We had intended to use the 20MHz Z80 CPUs that we had been given by Lez Anderson, clocked at 16MHz for compatibility with the RAM and ROM chips that Lez had also donated.

However, Martin was unable to get either of the two processors that he tried to run reliably above 10 MHz, whereas he was able to significantly over-clock a 10MHz Z80 CPU obtained from Mouser Electronics to 20MHz and beyond. This made Martin wonder whether the CPUs were really 20MHz after all.

 The maximum speed of an NMOS Z80 is 8MHz for a Z80H CPU, other available NMOS CPUs are Z80B (6MHz), Z80A (4MHz) and the original Z80 (2.5MHz).  Using the CMOS Z84C00 range, DIP packaged chips with speeds ranging from 4MHz to 20MHz are available, including the 20MHz Z84C0020PEC that we had intended to use.

I did a bit of "Googling" and found a method of determining programmatically whether a Z80 was an NMOS or CMOS version. The basis of this method was described in a Usenet posting by Simon Cooke in 1996, Google Groups hosts an archive of Usenet posts, including this one.

With an NMOS Z80, an OUT (C),0 instruction outputs 0,  with a CMOS Z80, OUT (C),0 outputs FFh. Martin used this information to run tests on a number of Z80 CPUs that he had to hand, which gave the results shown :

Chip ID Label Logic



Max Speed


Out (0), 0

Test Result

NEC D70C NMOS 2.5 MHz 4 MHz &00
Zilog Z80A NMOS 4MHz 8 MHz &00
Zilog Z84C0010PEC CMOS 10 MHz > 20 MHz &FF
Zilog Z84C0020PEC CMOS 20 MHz 10 MHz &00
Zilog Z84C0020PEC CMOS 20 MHz 10 MHz &00

From the very limited testing, it can be seen that the 10MHz CMOS chip performed exceptionally and the NMOS chips all performed above their rated speed. The "20" MHz "CMOS" chips on the other hand were very disappointing, the test values indicating that they were actually NMOS chips and given the maximum operating speeds achieved, were more than likely actually Z80H components.

The Bigger Picture

I guess we are all aware of the dangers associated with buying components from China through the likes of eBay, but for the casual hobbyist, the potential cash savings mean that the risks are probably worth taking. In fact, even multi-national corporations, the US government and NASA are not immune from being affected by counterfeit components. The situation is not helped by the component manufacturers efforts to drive down costs by out-sourcing the manufacture of genuine components to China.

The two most common methods of "counterfeiting" integrated circuits are excess production and "blacktopping".

Excess Production

Even when manufacturing in low cost centres such as China, the component designers drive the unit costs as low as possible. It is apparently not uncommon for the component factories to overproduce components in excess of the original order and  market them through the grey market. Though probably not subject to the same quality control and testing as the official production run, such items are at least manufactured to the same design and specifications as the original.


This is the more common way of counterfeiting components and almost certainly what has been done with the "20" MHz CPUs that we have. In this technique, the top surface of the chip is removed and a new "black top" coating applied to obscure the original manufacturing part number and date code. A replacement ID and date code is then reapplied by either painting or laser etching the new surface.

In this way, for example, genuine Zilog Z80H NMOS chips can be remarked as CMOS components with higher speed ratings which sell at higher prices. The price differential is illustrated by the prices Martin found for different speed ratings of CMOS components on the Mouser website:

  • Z84C0006PEC = £2.84 + VAT
  • Z84C0008PEC = £2.84 + VAT 
  • Z84C0010PEC = £2.84 + VAT
  • Z84C0020PEC = £6.94 + VAT

Beating the Counterfeiters?

So, how can you protect yourself from being caught out by counterfeit chips? The standard response from the semiconductor companies is to "always buy from approved suppliers", but whilst the incidence is much less common, buying from an approved supplier is not a guarantee that you will be getting genuine components.

As illustrated above, it may be possible to test the components to determine whether or not they are genuine, but this is only likely to be an option in a very limited number of cases. The majority of the time, the only method of identifying counterfeits is visually - which is becoming more difficult as the fakes get better.

Some examples of counterfeits - can you spot the genuine ones?

From the Maxim Integrated website


Tutorial 5458 : Counterfeit ICs


Also available as a PDF

Counterfeit parts are a big headache.

Author: Joe Garrison

From the Kozio blog

Showing that counterfeiting is nothing new, the Intel Pentium

And if you thought that it was just an issue for us hobbyists buying off eBay, you might like to look at this article about how Boeing's P-8 Poseidon (a military version of the 737-800) has been affected - using parts supplied by BAE Systems.

Some tips for Identifying Fakes

By the time that you receive the components it will likely be too late, but you may find this information useful. Some examples of possible indicators that the chips are not what they appear are shown below, for much more information on the subject, including detection of counterfeit integrated circuits, see the references at the bottom of the page.

The Good, the Bad and the Ugly

By way of example of a genuine part, this is an older generation Zilog Z80 DART.

Note the clear cut edges of the circular mould marks on the top and bottom. The photo does not do it justice, but the manufacturing location, in this case, the Philippines, can be easily read in one of the bottom mould marks.

And now, with the benefit of hindsight, some of the counterfeit Z84C0020PECs that we have seen - you probably need to click on the image to open it full size to see the detail
Here, the mould marks are visible - just, but they have very little depth, removal of the original chip markings has reduced the thickness of the top layer of plastic so the marks are now barely visible.

However, the bottom of the chip looks as good as the genuine part, but this is to be expected if the counterfeiter had used a genuine Zilog NMOS CPU to fake the CMOS part.

In this one, the mould marks are totally absent on the top side.

On the bottom of the same chip, even though the mould marks are present, there is no embossed text to denote the country of manufacture.

In this one, the mould marks are present but are not clean and have been contaminated by the remarking process. Mould marks on genuine chips will always have clearly defined edges.
This photo was downloaded from cpu to show the logo of a  (hopefully) genuine Zilog CPU

I don't know if this is a good indicator, but the logo on this Z84/20 looks subtly different to the one from CPU World. The font used for "ZILOG" appears to be slightly heavier and the tails of the "Z" logo appear to be more angular than the slightly rounded ones from CPU World.

All of the suspect components we have, have the Zilog name printed in upper case, genuine components use a lower case "i", i.e., "ZiLOG" as opposed to "ZILOG"

Even though all of the components had the same date code (0512), the bottom mould marks showed a number of different countries of manufacture, including Philippines, Malaysia and Indonesia, as well as some showing no information at all. This is not a good omen, according to American Electronic Resources Inc,:-

"We have done investigations with the component manufacturers and all of them we have spoken to say that a part with the same lot code as another cannot be manufactured in different countries"

And finally, having had a quick look on ebay, here is a familiar looking chip, it even has the same date code - seller's logo removed so as not to cause offence - or more importantly, get me into trouble for making potentially false accusations.

So, would you buy one of these now?

This component has an index mark at pin 1 which is not present in our examples or in any other photos of the chip that I have seen on the web, apart from on ebay, or on any of the Z80 CPUs that Martin and I have..

These are just a few examples of some of the things that you might look for, other give-aways include the resistance of the markings to solvents. There is a lot of information available on the web that can give you additional tips for spotting fake components. For example, Google "counterfeit integrated circuits" or "blacktopping integrated circuits". Alternatively, follow the links to the references at the bottom of the page.

More examples of counterfeits

An example of the use of solvent to expose the substandard markings on a fake chip.

No prizes for guessing the fake in this photo.

Photo from SMT Corporation

An example of a genuine part alongside a counterfeit.


Examples of genuine and fake MAX7219 display controllers


Some "Must See" Photos . . .

This is a comparison of genuine and cloned FTDI USB serial port chips, for really great die photos of what's inside the two, see the Zeptobars site detailed discussion here.



References :

Simon Cooke, Usenet 1996, post about the "Z80 OUT (C), 0" instruction

University of Connecticut Paper on Counterfeit Integrated Circuits

Identifying counterfeit components Emphasis Tech Tip

Counterfeit Electronic Component Detection,

Counterfeit Integrated Circuits: Detection, Avoidance, and the Challenges Ahead

Methods Used In The Detection Of Counterfeit Electronic Components, Harold Hewett, Electro-Comp Services, Inc

Component markings - solvent Resistance, US MIL-STD-883G METHOD 2015.13 18

Awareness of Marking Permanency and Black Top Testing in Today’s Electronic Component Industry, New Jersey Micro Electronics Testing Inc

Facing the Counterfeit IC Issue,

The Hidden Dangers of Chop-Shop Electronics,

Counterfeit Examples Electronic Components, Components Technology Institute - A very interesting slide pack with good example photos



mailto: Webmaster

 Terms & Conditions