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THS3491: Damage to part after being installed on PCB

Jordan Smith
Prodigy 205 points
Part Number: THS3491

Hi

We use the THS3491 in our production and have seen one instance out of several hundred where a THS3491 is fitted to a PCB, tested and working perfectly, then we package and ship the device somewhere else. 

Our product uses 20 THS3491s, and in one instance we have had all 20 of the THS3491s working before shipping, then after the PCBA is shipped we see a single THS3491 fail. The failure in this case was an apparent short:

  • With the THS3491 fitted on the board, the resistance from VCC and VEE to ground was ~50 Ohms
  • With the problematic THS3491 removed from the PCBA, we see ~1 Ohm resistance between VCC and VEE, compared to ~Megaohms on a good part

I am looking for any suggestions of what type of fault could cause a working THS3491 to stop working in such a way. We tried to reflow the solder on the problematic THS3491, which made no difference. The solder pattern also looked fine after removing the part, with no obvious solder bridges.

Thanks

Jordan 

  • 0
    Guru 140200 points

    Hi Jordan,

    I hope you have seen the "supply voltage turnon turnoff maximum dV/dt" in the absolute maximum ratings?

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 17661 points

    Hello Jordan,

    Could you provide board & schematic information for the device?  It would also help to know the voltage levels the devices were tested with and operated on.  Kai's point is also important: shift in input impedance could be a breakdown of ESD diodes and result in a much lower input impedance.  This path to ground could explain the behavior.

    I will also ask my team; I appreciate any additional information you can share Jordan.  It does appear the soldering and mounting to PCB were not the main cause, if a contributor at all.  I need more information to make further assessment.  

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 205 points

    Hi Kai and Alec

    Kai - yes we have confirmed we have dv/dt ramping of the power rails several orders of magnitude lower than the maximum in the datasheet (about 10^-4 V/us, compared to the maximum of 1V/us in the datasheet).

    Alec - I can private message you with our schematic snippets. Yes any other ideas your team could have would be appreciated. 

    Thanks,

    Jordan

  • 0 in reply to Jordan Smith
    TI__Genius 17661 points

    Hello Jordan,

    Alrighty, I will look out for them.  You can also email me if preferred; I will message you my contact information.  

    Best,

    Alec

  • +1 in reply to Alec Saebeler
    TI__Genius 17661 points

    Hello forum,

    This is a quick update: the consideration for the likely cause is electrostatic discharge, known as ESD.  Even with proper protocols and shipping controls, it is possible for ESD damage to occur as controls and methods are never perfect.

    Please review your own ESD processes and enforce adherence to them in order to mitigate potential issues.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Guru 140200 points

    Hi Jordan,

    I aggree with Alec. ESD could be the cause of damage. I heavily recommend to ship the assembled printed circuit boards in metallized ESD protection bags. Not the pink and transparent ones through which you can easily zapp ESD, but the metallized ones with 50nJ energy shielding.

    Wrapping the printed circuit board in aluminium foil is also a good solution. This can give a perfect Faraday cage.

    Kai