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LM311: Component failure on board

Paul Ostheimer
Prodigy 10 points
Part Number: LM311


We had a detector come back from our customer and it had no counts.  We disassembled the unit and performed a failure analysis and determined the U3 comparator was bad on the SP-609 PAD board. 

 

Here is a summary of the analysis:

  1. There were no counts coming out of the comparator, no AC signal passing through.
  2. The +5V DC output was present.
  3. The chip appeared intact and undamaged when it was on the PCB, but removal damaged it and broke into 2 pieces.  Possible cause is the housing was cracked when it was installed.

 

Here are our questions:

  1. Can the manufacturer analyze the chip and tell us what the failure mode is? 
    1. Did the transistor fail?
    2. Was the chip housing possibly cracked when it was assembled to the PCB and degraded more over time and caused this failure?
  2. Have you seen this issue previously?  Is there concern of a bad lot/lots of parts with this problem?

 

Attached is the electrical schematic and photos of the failed unit.  The comparator is component U3.

 

  • 0
    TI__Prodigy 225 points

    Hi Paul,

    Thank you for your post. It looks like your circuit setup in a way that should not damage the device.

    One concern that I have is that input common mode range of the LM311 may be exceeded.

    The recommended operating conditions for the input pins are: VCC- + (0.5V) to VCC+ - (1.5V)

    Also, what is the value of Vd on pin 3 on the comparator?

    Additionally, if something was being shorted to the BAL/STRB pin with sufficient current conduction, the output would remain high. This is unlikely, but it is a possibility.

    - Izak Walker

  • 0 in reply to Izak Walker
    TI__Mastermind 26460 points

    Paul

    Sorry to hear about this failure.  From your schematic, I don't see anything obvious that could have damaged the device.  Since the device is damaged and it appears to be an isolated failure (please correct me if I am wrong), this does not sound like a case where we would perform failure analysis.  The LM311 is an industry standard device that has been in production for multiple decades and does not have any known quality issues.  Were you able to replace the device and have the system become functional?  This is where I suggest we start the analysis.

    Chuck

  • 0 in reply to Chuck Sins
    TI__Mastermind 26460 points

    Closing this post since it is being handled offline.

    Chuck