Defective processors

[mbeffa]

Sequent Microsystems designs and sells Automation Systems using Raspberry Pi. All our products use STM processors. We use about 10,000 processors per year in different configurations. Generally we do not have any quality problems, but occasionally we run into a defective lot. On a recent run of 30 prototypes using STM32G431CBT6, 50% were defective. We replaced the processors and all boards worked as expected. We buy all out processors from a Chinese distributor.

We saved the defective processors and I would like to know if you would have any interest in inspecting them to find out why they entered the distribution chain, and to advise us how to avoid this problem in the future.

Mihai Beffa

CEO

Sequent Microsystems

[Andrew Neil]

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@mbeffa wrote:

 We buy all out processors from a Chinese distributor.

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So have you contacted that distributor for support?

Are they an Authorised distributor?

Sounds like you should be talking direct to ST rather than posting on this public forum?

Raise a direct support ticket: https://ols.st.com/s/

ST Sales offices, Official distributors, etc: https://www.st.com/content/st_com/en/contact-us.html

[mƎALLEm]

Hello @mbeffa and welcome to the ST community,

We don't handle such requests here in the community. As stated by @Andrew Neil , you need to raise an online support ticket over this link https://ols.st.com/s/

or contact your local distributor or your local FAE.

[STOne-32]

Dear @mbeffa ,

On top of previous comments from @Andrew Neil  and @mƎALLEm , Thank you for posting such comment as other members may face similar experience which is for sure not convenient:

"On a recent run of 30 prototypes using STM32G431CBT6, 50% were defective. We replaced the processors and all boards worked as expected"   -> 50% of defective Parts is not a quality issue but another kind of damage such as reworked parts having abnormal stress. is that possible to know what kind of issues they have at board level :

• Excessive current  
• Continuous reset
• Not booting and executing startup before jumping to main  

If possible, to provide the package top picture and also provide all of this information to our https://ols.st.com/s/

Thanks again 

STOne-32

[mbeffa]

This is not a rework issue. The defective boards are factory assembled,
just like all out boards.
Virtually all defective processors behave the same.
We program the processor through the JTAG interface, then we talk to the
processor through the I2C interface. A defective processor programs
normally through the JTAG, but the I2C port is dead.
If we replace the processor with a stock bought from Digikey, the processor
always works.
On the lot of 50% defective, we used I2C port1 (pins PB9, PB15), STM32G431

[Andrew Neil]

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@mbeffa wrote:
If we replace the processor with a stock bought from Digikey, the processor
always works.

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So the problem definitely seems to be with your Chinese "distributor".

Edit: or perhaps not - see below.

Again, have you contacted that distributor for support?

Are they an Authorised distributor?

Are you sure they are shipping you new, genuine product?

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@mbeffa wrote:
 the I2C port is dead.

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How do you determine that?

Do the pins work as plain GPIO?

Have you done any testing on the removed, "faulty" chips?

[STOne-32]

Dear @mbeffa  Thank you for the follow-up, further questions please:

• if possible, to elaborate on the I2C port is dead - communication? these Pins are working normally as GPIO, simple toggling PB9 and PB15 ?
• Picture of the top marking for the devices from that lot vs the others lots.

Thank you

STOne-32

[mbeffa]

What I can tell you at this point is that the I2C port is not operational.
When we replace the processor, the port works.
In order to determine if the pins can be used as GPIO, we have to write a
special piece of code to do it. If you think this might help we can do it.

Here are two pictures, bad_prog and good_proc.

[image: good_procs.jpg]
[image: bad_procs.jpg]

[mbeffa]

My hope was you STM might be interested to find out why defective
processors enter the distribution chain. If I contact the distributor, most
likely they will offer to replace the bad processors. We'll save maybe
$100, but the problem might show up again on the next lot.

I do not know if they are shipping new products, but I do not believe there
are STM knock-offs, so probably the products are genuine. Maybe they failed
some tests on the production line, but then should not enter the
distribution, authorized or not.

The distributor is probably the largest in China.

[STOne-32]

Thanks for the follow-up.  is that possible to attach the images again.  based on the trace code we can check our main distribution.