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Random Failures in Latest Build

Category: Hardware
Product Number: ADM7171

We have been using the ADM7171 for couple of years now, all low volume runs <60 pcs per run, and have never had any issues.  On our most recent run we are now seeing, as far as we can tell, random failures of the ADM7150ACPZ-3.3.  We have six of these supplies per board and the failures are random within and between boards.  There is no systematic failure we have been able to identify and as mentioned we have been using this part with these components for a couple of years and have never once seen a failure.

All failures have been observed off of the assembly line.  Occasionally we have seen a failure after rework when using a part from the same batch, currently these parts are on order at all suppliers so we have not been able to purchase more.

The failure is generally been observed as an output voltage of ~1.3 V to 1.4 V instead of the fixed 3.3 V.

We have had a change in manufacturers on the most recent run switching to a vapor phase process instead of conventional reflow.  No other parts on the board have experienced failures, off of the assembly line.

The parts purchased this run were from a recommended distributer, Arrow.

Parents
  • 1.a Schematic was unchanged around all 6 supplies from the last run of boards. 

    1.b The capacitor used on the BYP pin changed from TCSOPL1A226M8R to T529P226M010AAE200.  Both caps are 22uF tantalum caps, 200 mOhm ESR, and 0805 footprint.  The only difference between the 6 on the board is 2 supplies have their enable pin controlled while the other 4 have enable tied to VIN.  Failures have been observed for both cases.

    1.c Gerbers were checked for one of the supplies, that had experienced a failure, and no difference could be seen between previous working runs and the latest board with failures.

    2. I have reviewed the Board Design section and all recommendations are implemented.  I have handed off to the manufacturer for input.

    3. Will follow up with manufacturer and update post after.

    4. See image below.  All 6 supplies are fed from a 5V DC-DC regulator.  Some are working and some are not working from the same rail.  It has been verified to be correct at 4.97V.

Reply
  • 1.a Schematic was unchanged around all 6 supplies from the last run of boards. 

    1.b The capacitor used on the BYP pin changed from TCSOPL1A226M8R to T529P226M010AAE200.  Both caps are 22uF tantalum caps, 200 mOhm ESR, and 0805 footprint.  The only difference between the 6 on the board is 2 supplies have their enable pin controlled while the other 4 have enable tied to VIN.  Failures have been observed for both cases.

    1.c Gerbers were checked for one of the supplies, that had experienced a failure, and no difference could be seen between previous working runs and the latest board with failures.

    2. I have reviewed the Board Design section and all recommendations are implemented.  I have handed off to the manufacturer for input.

    3. Will follow up with manufacturer and update post after.

    4. See image below.  All 6 supplies are fed from a 5V DC-DC regulator.  Some are working and some are not working from the same rail.  It has been verified to be correct at 4.97V.

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