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Original question:

LMZ31710: After SMT failure issue

LMZ31710: Failure after SMT

CY WU
Prodigy 110 points
Part Number: LMZ31710

Hi 

We have 10~20% failure rate after SMT.

Could you help to review schematic as attached? (DCBATOUT:4V, VCC_INIT:1V)

Besides, do you have recommend stencil pattern for this part?

If we bought this chip on the market (not from agent) , could we send it back to you for further failure analysis after cross verification?

BR,

CY

  • 0
    TI__Guru 50120 points

    Hi CY,

    I believe we had a previous correspondent as this question and I've provided my review of the schematic and PCB layout. Please let me know if it is okay to share both reviews on this public forum. In short the schematic looks okay and the layout can have some improvements for better robustness of design.

    Can you describe the failure in more detail? What are you observing? Is the part working for a while or does it fail at time zero? Please provide wave-forms of VIN/VOUT/INH and PH. This way it can help with the application troubleshooting process.

    I've linked the customer returns process. Please have a look and let me know if you have any further questions.

    Regards,
    Jimmy

  • 0 in reply to Jimmy Hua
    Prodigy 110 points

    Hi Jimmy

    Our phenomenon is it failed at zero after SMT

    We switch a new chip on original board, and works.

    Then we put the one failed to another board, and it still failed.

    So I am wondering is it SMT issue or just the material issue.

    What I want to do next is 

    1. modify stencil for SMT, check if it has any help.

    2. Measure resistance value for all pins of defected one, see any difference to good one.

    Do you have related data or info could share?

    BR,

    CY

  • 0 in reply to CY WU
    TI__Guru 50120 points

    Hi CY,

    The stencil design is in the land pattern data section of the datasheet on page 39.

    As for measurement of the pin, you can do some simple continuity checks to see if there are any shorts in VIN/GND, VOUT/GND, etc. 

    How many failures have you observed? It sounds like the part is damaged if the failure mode is still present when you move the part over to another board.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Prodigy 110 points

    Hi Jimmy

    Thanks for stencil design connection.

    Since we bought chip on the market, not from agent, therefore, we don't know how good the chip quality was. 

    Failure rate is around 10%, since we haven't mass production yet, so the rate might be higher or lower after.

    Is this part easily damaged by EOS/ESD? From your experience or previous return record?

    I'll review all possible items includes stencil / flow temp / source and see if failure rate drops

    includes stencil / flow temp / source and see if failure rate drops on next build.

    BR,

    CY

  • 0 in reply to CY WU
    TI__Guru 50120 points

    Hi CY,

    There have been no indication that this part is easily susceptible to EOS/ESD damage. The CQE(customer quality engineer) for this part has informed me that there have been some returns of this part as a result of customers not being compliant to the "MSL-3 Moisture Sensitivity Level-3 processes". One thing I would recommend is baking the part to remove the moisture before the SMT assembly. Other than that, there were no indications that this part has any quality issue.

    Regards,

    Jimmy