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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.

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  • Update:

    Regarding question 2

    Yes, the boards have been assembled in compliance to this standard. If the maximum applied temperature is of interest—it was 238°C. According to Table 4-2 (J-STD-020C Proposed Std Jan04.pdf), packages with a thickness of less than 1.6 mm (which is the case for the ADM7150) can withstand a peak temperature of 260°C for 60–150 seconds (see Table 5-2).

    Regarding question 3

    Yes chips were X-rayed and sufficient solder was observed

    We ordered an Eval kit for the ADM7150 to check supplies that had failed and found the following. Chips that failed require a much larger voltage drop to work than the datasheet specs.  Nominally we have a 5V input to the ADM7150 in our design and are observing anywhere from 0 V to 1.5V on devices that are not working.  On the evaluation kit the bad devices are able to regulate 3.3 V with a load of 80 mA but at a load of 680 mA it requires 6 V.  The datasheet specifies in the worst case scenario the minimum dropout required is 1 V.  What we are observing is that a drop out of > 2V is required to regulate properly on bad devices.

    This chip is currently unavailable everywhere... Was there a known bad batch?

Reply
  • Update:

    Regarding question 2

    Yes, the boards have been assembled in compliance to this standard. If the maximum applied temperature is of interest—it was 238°C. According to Table 4-2 (J-STD-020C Proposed Std Jan04.pdf), packages with a thickness of less than 1.6 mm (which is the case for the ADM7150) can withstand a peak temperature of 260°C for 60–150 seconds (see Table 5-2).

    Regarding question 3

    Yes chips were X-rayed and sufficient solder was observed

    We ordered an Eval kit for the ADM7150 to check supplies that had failed and found the following. Chips that failed require a much larger voltage drop to work than the datasheet specs.  Nominally we have a 5V input to the ADM7150 in our design and are observing anywhere from 0 V to 1.5V on devices that are not working.  On the evaluation kit the bad devices are able to regulate 3.3 V with a load of 80 mA but at a load of 680 mA it requires 6 V.  The datasheet specifies in the worst case scenario the minimum dropout required is 1 V.  What we are observing is that a drop out of > 2V is required to regulate properly on bad devices.

    This chip is currently unavailable everywhere... Was there a known bad batch?

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