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LMZ22005TZ INTERNAL SHORTS

Victor Mendez
Prodigy 50 points
Other Parts Discussed in Thread: LMZ22005

LMZ22005TZ is used 6 times in one of our designs and the same reference U part exhibits a dead short (less than 1 ohm) from the output pin 7 to GND pin 4.  This has occurred in 3 CCAs out of 60+.  While it is possible (being investigated) that we're inducing the problem during 'SAFE TO POWER ON' tests (continuity/isolation tests), I'd like to know why the datasheet was updated to the effect that one "should be limited to one reflow".  What has TI uncovered that lead them to add this new section?  In our case we have a few modules on top and a few on the bottom, thus some of these modules would be exposed to two reflow processes.  Changing the design is out of the question, so, aside from hand soldering the 2nd side, I'd like to know what's the story on the limited # of reflows to one.

Regards,

V. Mendez

GDLS

  • 0
    Expert 1995 points

    We also have 3 projects using LMZ22005TZ.

    We have the same problems with about 10% of failure which is totally unacceptable, in the first preproduction lot of 100 pieces each.

    In one case, by bending the output pin (to disconnect it from PCB), in order to measure it, the short disappeared, then the pin was soldered again to PCB and it started to work ok!!!


    This indicates an internal short.

    Is the component good? Can we trust it? Please someone from TI reply.

    We used only one reflow cycle by setting the temperature profile as suggested.

    best regards

  • 0 in reply to Massimiliano Cialdi
    TI__Expert 3840 points

    Hi - Please make sure the attached reflow temperature profile is being followed by your manufacturing process.  This will make sure you have first pass success.  This is application note SNVA214 - LMZ1 and LMZ2 Power Module Design.snaa214 Design Summary LMZ1-2.pdf

    Best Regards,

    -JP

  • 0 in reply to Juan Paulo Fung
    Expert 1995 points

    We read the app note long time ago, before manufacturing.

    Our manufacturing department used initially the suggested temperature profiles and adopted all the suggestions. After the first defective runs, temperature were decreased further, with little improvement. Today we have about 10% of faulty boards. Each board hosts two LMZ22005. In some cases input was shorted to output, damaging all the ICs on the board.

    Our conclusion is to never use your modules in the future.

    Today the bad news are delays in the manufacturing due to your LMZ and three PCBs to reiterate to implement an alternate (not TI) solution.

    Sorry, but PSU reliability is not an option.

    Regards