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Name for dice on a wafer that are intentionally different than the others

jms_embedded

Active member
I've noticed on some photographs of wafers that some of the dice are different. For example:

https://pixels.com/featured/odomete...its-adam-hart-davisscience-photo-library.html -- 5 different dice near top/middle/bottom

https://www.computerhistory.org/revolution/digital-logic/12/288/1639 -- 5 dice are different, forming a cross (one in center, one near top/left/bottom/right)

https://compote.slate.com/images/df4dfbfe-9846-4c86-a168-aeed9608704e.jpeg -- 1 die in each 6x4 grid

What are these called and what are they for? (process quality control?)
 

Daniel Payne

Moderator
Good eye, the handful of different die are there for testing purposes to make precise measurements about that wafer. On the test die they can more easily and efficiently measure IV curves, junction leakages, ESD breakdown voltages, P vs N channel conductance, resistivity of interconnect, etc.
 

jms_embedded

Active member
and they're called "test die"? If so, that's unfortunate as it's nearly impossible to search for that term and distinguish between "test" as a verb which pops up a bunch of unrelated results...

https://en.wikipedia.org/wiki/Wafer_testing talks about test structures in the scribe lines between dice; why would they have a dedicated test die? I can't seem to find any references about this.

ST's intro to semiconductor technology calls them "centering targets": https://www.st.com/resource/en/appl...ctor-technology-stmicroelectronics.pdf#page=7
 

Paul2

Active member
I've noticed on some photographs of wafers that some of the dice are different. For example:

https://pixels.com/featured/odomete...its-adam-hart-davisscience-photo-library.html -- 5 different dice near top/middle/bottom

https://www.computerhistory.org/revolution/digital-logic/12/288/1639 -- 5 dice are different, forming a cross (one in center, one near top/left/bottom/right)

https://compote.slate.com/images/df4dfbfe-9846-4c86-a168-aeed9608704e.jpeg -- 1 die in each 6x4 grid

What are these called and what are they for? (process quality control?)

Devices for process control
 

Daniel Payne

Moderator
They're also called Process Control Monitors (PCM).
 

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