[sdiy] destroying flash memory cell on a PIC

Richie Burnett rburnett at richieburnett.co.uk
Wed Mar 17 19:50:17 CET 2021


Thanks Eric.  That's a very interesting insight into what happens at the die 
level !

You know sometimes you see things in your career that just don't make sense 
at the time.  And the manufacturer just quickly snaffled away the removed 
defective chips with little explanation other than guidance on what we could 
do differently ("work-arounds.")  Today that particular mystery just got a 
bit clearer!  Thank you :-)

-Richie,


-----Original Message----- 
From: Eric Brombaugh
Sent: Wednesday, March 17, 2021 6:19 PM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] destroying flash memory cell on a PIC

On 3/17/21 9:26 AM, Richie Burnett wrote:
> But since SRAM is really just a bunch of D-type flip-flops I can't see why 
> this should cause it to eventually fail.

In most digital processes a high-density SRAM bit is not just a D
flip-flop - typically it's cross-coupled arrangement of 4-6 MOS
transistors in a stable loop where writing requires essentially forcing
a new state on the loop by overriding the existing state. I could
imagine that if the drive strengths of various transistors were not
proportioned correctly that high currents could be consumed during the
write operation, resulting in local heating that could build up during
multiple writes in quick succession, leading to eventual damage. It's
definitely *not* a forgivable mistake, but I can understand how it might
happen.

Eric
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