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Mechanical failure of 0603 SMT diodes.

Former Member

Hi all,

We use Farnell  part number 815-0192 (TS4148RZ 0603 SMT diode) on one of our products.

We have made around 10000 of this product in last couple of years all with the same part.

Recently we have started getting failures of the product around 3 to 6 months old.

 

Upon investigation we have found that the diode has suffered mechanical failure, the 2 pads on the bottom of the diode have come away from the main body of the diode.

The diode pads are still soldered to the PCB.

You are probably going to suggest that they have been physically damaged, but, this PCB is potted in Electolube UR5528 resin (Farnell part 108788) inside an aluminium tube so it can't have been damaged.

When the potting has been carefully removed the diodes are sitting there in the potting detached from there pads.

 

The product is used at ambient temperatures.

The current through the diode is only 13ma so they aren't overheating, it's just a reverse protection diode in series with the power input.

 

Can anybody suggest any reason for these failures ?, it has us puzzled.

 

They seem to be made from a tiny PCB with i presume the silicon chip for the diode on the top half.

Could the diode PCB material be reacting with the UR5528 potting compound ?

 

I can try and take some pictures through a microscope if it would help.

 

Many thanks.

 

Jim Hearne

  • 0

    My immediate thought was batches of PCBs with printing issues. If the way in which the boards were made changed any, combined with the other processes may induce separation.

    So, do check the potting compound. You might also want to check with devices made some time ago to see if the separation happened there too, but delayed.

     

    Another option is a change in the run of diodes. I had a batch of logic ICs once that would not perform like previous runs. It happens all the time.

     

    Cabe

    http://twitter.com/Cabe_e14

  • 0 in reply to Catwell

    Hi Jim,

     

    It might have to do with diferent thermal expansion coefficients of PCB material and diode package material.

    Pay attention to PCB material you are using, maybe it has excessive thermal expansion which might cause similar problems not only with diodes but with other 0603 devices as well. If ambient temperature changes over wide range, you may have to reconsider the PCB material.

    An simple (but not sure) solution might be just rotating diode placeholder by 45 or 90 degrees compared to current position,

    taking advantage of possibly different expansion in X/Y axes (depending on PCB material/structure).

     

    Jordan