Rootcause of Vf failures in LED

Discussion in 'General Electronics Chat' started by rickysanchez, Jul 5, 2011.

  1. rickysanchez

    Thread Starter New Member

    Jul 5, 2011
    We encounterred many Vf failures in the LED production line.
    Is it possible that Vf failures is related to die/wafer?
  2. Wendy


    Mar 24, 2008
    Welcome to AAC!

    You should know more about this than I, but Vf is an extremely variable number. It is indeed possible that the manufacterer has varied the reciepe somehow. What color, what is the average Vf, and what is the range?

    Also, how are you bonding to them? Wirebonding is a subject I know something about.
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    This is a bit like saying "Is it possible that car fuel consumption problems could be related to the engine?" Of course, as Bill Marsden points out there are other possibilities, but in the absence of other information we can't rule out issues with the dies.
  4. SgtWookie


    Jul 17, 2007
    Well, what all could it be?

    Bad/high resistance metal used for the LED leads (I have plenty of LEDs that have leads made of steel).
    Poor/improper bonding of the leads to the die
    Defective die.

    The Vf of LEDs can vary widely anyway, even in the same batch. I've seen differences exceeding 10% on LEDs that came from the same reel of tape.
  5. rickysanchez

    Thread Starter New Member

    Jul 5, 2011
    Well, the Vf specs <1.8V in 100 mA.
    we use aluminum wirebonding, but the Vf failures came from the same wafer batch that's why I think it is related to die/wafer.
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    The LEDs should have been tested and disposed at source, if they are proper LEDs from a reputable source. They should have very good Vf and no failures.

    If you buy bulk LEDs from ebay you should be aware that many are rejects that have all failed testing or are a reject batch where the failures are > than the official allowed rate so the whole batch was dumped. And since good LEDs are cheap I hope you got the reject LEDs VERY cheap... ;)