MELF metal electrode face diodes and resistors used for?

Discussion in 'General Electronics Chat' started by harrison2015, Apr 29, 2015.

  1. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    What are MELF metal electrode face diodes and resistors used for? I see MELF diodes used in SMD/SMT circuit boards mostly in the power supply but why use MELF diodes and resistors.
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    to solder to. surface mount parts have no leads, just metal faces to flow solder to boards.
     
  3. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    From the datasheets of MELF diodes and resistors, is there any thing different about them than normal resistors and diodes?

    Anything special about MELF components
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    The ones I encountered that were described as MELF, were in a range of Thorn Consumer CTVs.

    The parts on the board were actually regular round bodied components with very short stub leads pressed into "mushrooms" at the ends - its hard to put into words, but think of the head of a chisel that's been used a lot. These parts are placed and soldered just like regular SMD parts, but originally came off the same production line as regular leaded components.

    AFAIK: MELF is a distinctly separate sub-family of SMD parts than the most common type you usually see.
     
  5. Brainbox

    Member

    Nov 15, 2010
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    Melf resistors are more stable and more resistant to mechanical stress.
    Often You can find them in high reliable industrial stuff.
     
  6. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    I hate MELF. They roll off the pads when you try to solder them by hand.

    And the glass MELF diodes slip out of the tweezers.
     
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  7. ian field

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    Oct 27, 2012
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    Doncha just love the way they pop out of the tweezers and disappear across the room at 90+ MPH.
     
  8. joeyd999

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    Jun 6, 2011
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    No. I. Don't.

    In fact, I believe the MELF package was developed by Satan himself -- just to give you an idea what Hell will be like.
     
  9. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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  10. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    But I always see the MELF diodes and MELF resistors in the power supply sections of of SMT/SMD circuit boards. The MELF must have a higher wattage rating?
     
  11. dl324

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    Mar 30, 2015
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    Probably not. MELF diodes look a lot like their leaded counterpart, most heat for a D02 diode is radiated from the leads, since MELF has no leads they radiate heat from the endcaps. Read earlier in this thread and elsewhere that they're higher reliability than typical SMT parts.
     
  12. harrison2015

    Thread Starter Member

    Apr 22, 2015
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    Why do they have a higher reliability than SMT parts? I don't get it
     
  13. snav

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    Aug 1, 2011
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    Looking for items recently I found these, so they are fairly versatile.
     
  14. SamEricson

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    Apr 25, 2015
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    MELF components are more stable with temperature, that is why they are used in smd smt power supply circuit boards. 5pp is really good for temperature in power supplies.
     
  15. Brainbox

    Member

    Nov 15, 2010
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    For the diodes: Glass is more stable and the springformed lead absorbs thermal stress.
    For resistors: the metal caps are not a part of the resistor body itself and can relief stress from expansion when the body heats up.
     
  16. ian field

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    Oct 27, 2012
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    I'd go along with the glass bit.

    Of the old germanium devices, more glass encapsulated types have survived to this day than metal ones. Although some metal types have suffered internal shorts from tin whiskers - which probably isn't what's meant by "stability".

    In those days, the epoxy encapsulations available then weren't good enough for germanium.
     
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