Alumina?

Discussion in 'General Electronics Chat' started by benha, Dec 21, 2012.

  1. benha

    Thread Starter Active Member

    Jan 4, 2011
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    Hi, folks.

    I recently inherited a bunch of tools and parts from my late uncle. Include in that collection is a box full of small pieces of Alumina, most of it gold plated. By "small pieces," I mean rectangles and squares of 1" to 2" on a side.

    I'm fairly sure this is for some sort of electronics purpose, but frankly I don't know; and remarkably the Googles have been less than helpful.

    Is this stuff valuable? To what kind of person?

    Pic of what I'm talking about below...

    Thanks for any help you can provide!
    -Ben


    [​IMG]
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Alumina (aluminum oxide) PCBs are used for high temperature applications. If you scratch off the gold, you will likely find copper under it.

    google the words, gold plated alumina
    You will see a PDF from kyocera - a ceramics company (and electronics company).
     
  3. GopherT

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    Nov 23, 2012
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    Also, 150 micro-inches is only about 1/20th of the diameter of a human hair (0.0038 mm). Not enough gold to pay for the heat to melt it off of the surface.
     
  4. benha

    Thread Starter Active Member

    Jan 4, 2011
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    Thanks a bunch for the info!

    I wasn't so much thinking the gold itself was valuable, but more that anything that needed gold plating might have value for the overall "thing."

    I see nothing like this on eBay or whatever though, which makes it interesting to try to find a home for it.

    I'll probably just throw the whole lot up there and cross my fingers. I have no use for the stuff anyway...

    -Ben
     
  5. GopherT

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    Nov 23, 2012
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    It will be good for the new, high power LEDs and connectors for electric heating elements.
     
  6. GopherT

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    Nov 23, 2012
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    On second thought, LEDs will need heat sinks and alumina is not a good heat transfer medium. Keep it to heaters - possibly vacuum tube mounts back in the day.
     
  7. kubeek

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    Sep 20, 2005
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    Actually it has far better thermal conductivity than mica, so it is sometimes used for insulators under transistors.
     
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  8. ErnieM

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    Apr 24, 2011
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    I've use alumina as a substrate material for years, it's a standard for the hybrid industry. Here "hybrid" means the method of assembly. Conductors (typically gold or silver) are silk screened to the substrate and fired in. Glass insulating layers may also be added to make multilayer connections, and resistors may also be fired right onto the substrate. Chips come in real chip form, bare die epoxied down and wire bond connection made from the chip top to the substrate. All goes inside a hermetic tub with leads.

    All very custom stuff for military and aerospace uses. All very $$$ too.
     
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  9. Wendy

    Moderator

    Mar 24, 2008
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    We use it to make microelectronics, they treat it like a PCB. Etch it, glue chip and transistor die onto it (along with capacitors or resistors), and you can custom make parts that aren't quite as small as ICs, but are much cheaper (and higher performance) for small runs. They are also repairable.
     
  10. Pragathi

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    Feb 26, 2015
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    Is alumina a dielectric material, ceramic material or ceramic material???
     
  11. GopherT

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    Nov 23, 2012
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    Yes. Alumina is also known as aluminum oxide or Al2O3

    A very crystalline form is sapphire the blue is from contaminants of chromium. Very, very, pure crystals are made in factories and used for mineral watch crystals that are scratch resistant. Also, these crystals are used for the substrate of high-brightness LEDs (GaN). Corundum is a common name. Look where it is on the hardness scale.
     
  12. BR-549

    Well-Known Member

    Sep 22, 2013
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    I am not a chemist, but I don't think there is any oxygen there. The gold is the "oxide".
     
  13. GopherT

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    which post are you referring to and what gold are you talking about?
     
  14. SLK001

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    Nov 29, 2011
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    No, the substrate - the white stuff in the middle, is alumina, or Al2O3. The gold is there for bonding and for circuit traces. These parts are high frequency blank PC boards, for use in the microwave freqs.
     
  15. BR-549

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  16. SLK001

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    Nov 29, 2011
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    Go by the label. It says, "99.5% Alumina Cr/Au".

    This translates to: Substrate, 99.5% Alumina. First sputter, chromium, end plating 150 microinches gold.
    There is probably a copper plate over the chromium prior to the gold plate.
     
  17. GopherT

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    Nov 23, 2012
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    First, read the question of post #10 (and the date). Then look at the date on posts 1 - 9. You will see they are completely independent questions and eras.

    Second, Cr/Au is a plating sequence. The thickness (in micro-inches) of the gold layer is listed on the package. Plated metals are NOT alloys.

    Note, the most recent question above was about Alumina being a dielectric. In this case, Alumina is what the board is made of (in place of FR4 in most circuit boards). They were not asking about anything else.
     
  18. BR-549

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    Sep 22, 2013
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    Thank you....that helps to clear up my confusion.
     
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