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    removing anodized coating from aluminum

    I have a bunch of SK104-STCB heatsinks and Im doing a board were the pins need to be conducting into the fet drain.

    The heatsinks are anodized and the 2 pins do not conduct. What can I soak the heatsinks into for the removal of the anodized coating without destroying the heatsinks?

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    Re: removing anodized coating from aluminum

    Which FET package are you trying to mount on SK104-STCB? There should be better ways to connect the drain terminal.

    I doubt that the solder pins are intended as electrical connection. Neither the heatsink surface, particularly with a clip mounted transistor. Even a raw aluminium surface won't give reliable contact if the transistor isn't screwed to the heatsink.

    Milling would be the most appropriate method to remove the coating, grinding should work as well.

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    Re: removing anodized coating from aluminum

    Quote Originally Posted by Zak28 View Post
    I have a bunch of SK104-STCB heatsinks and Im doing a board were the pins need to be conducting into the fet drain.

    The heatsinks are anodized and the 2 pins do not conduct. What can I soak the heatsinks into for the removal of the anodized coating without destroying the heatsinks?
    If your wanting to remove it all oven cleaner seems to work well. Just take care to remove the residue as well as you can. Maybe soaking in vinegar solution afterwards.

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    Re: removing anodized coating from aluminum

    Hi,

    If your wanting to remove it all oven cleaner seems to work well. Just take care to remove the residue as well as you can. Maybe soaking in vinegar solution afterwards.
    Afaik, alkaline solution could work, acid won´t work.

    But I agree that it will not be the best solution because aluminum tends to generate an AlOx surface within minutes on air ...

    Klaus
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    Re: removing anodized coating from aluminum

    Drain cleaners which are hydroxide based, will do it
    real quick.

    There is a gray goop you can find in the electrical
    supplies section of home improvement stores (or a
    specialty electrics distributor) that's meant to maintain
    good connections between copper and aluminum wiring
    in breaker panels. I'd suggest having this ready, and a
    mounting stud too, so you can keep the "open time" to
    a minimum.

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    Re: removing anodized coating from aluminum

    Quote Originally Posted by KlausST View Post
    Hi,


    Afaik, alkaline solution could work, acid won´t work.

    But I agree that it will not be the best solution because aluminum tends to generate an AlOx surface within minutes on air ...

    Klaus
    The oxide layer shouldn't be enough to block current flow.

    Quote Originally Posted by FvM View Post
    Which FET package are you trying to mount on SK104-STCB? There should be better ways to connect the drain terminal.

    I doubt that the solder pins are intended as electrical connection. Neither the heatsink surface, particularly with a clip mounted transistor. Even a raw aluminium surface won't give reliable contact if the transistor isn't screwed to the heatsink.

    Milling would be the most appropriate method to remove the coating, grinding should work as well.
    I have a lot of ra-t2x-38e heatsinks they are anodized also and they are absolutely shortcircuit between pins but they are just too large for the board.

    I can dremel the coating off with a nylon wheel but I want the pins to conduct and turning them with pliers makes them conduct but not enough. Soaking the heatsinks in oven cleaner will probably cause the pins to conduct without twisting them with pliers.

    Trying to mount to220 Im pretty sure other outline packages would not work well unless its sot227 or some other package with bare metal exposed as much as a to220 has.
    Last edited by Zak28; 8th January 2019 at 00:44.

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    Re: removing anodized coating from aluminum

    Fischer can probably provide the heat sinks as raw aluminium version (they make about anything on special order, even in relative small quantities).

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    Re: removing anodized coating from aluminum

    Hi,

    The oxide layer shouldn't be enough to block current flow.
    Not block. But I used blank aluminum with a 250A line...and it almost caused fire. 1mOhm causes more than 60W of heat!
    Just a thin plate to reduce space....

    Klaus
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    Re: removing anodized coating from aluminum

    I tried the dollar store 'heavy duty' oven cleaner for ~20mins and it did nothing, not even dent the anodized surface.

    However the pin resistance dropped from open circuit to ~10meg down to ~400R not sure what to do here.

    Im considering to snip off the drain pin and use a ring terminal and screw to the drain back and solder the wire onto the board.

    Maybe I should leave it in for longer with the oven cleaner since it did substantially drop the pin resistance.

    It seems the heatsink is actually painted since I obtained it off aliexpress and not a reputable vendor.

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    Re: removing anodized coating from aluminum

    To remove my anodised aluminium pieces I use NaOH - drain cleaner/caustic soda.

    Immersing the aluminium into a bucket of concentrated NaOH causes the anodised piece to bubble vigorously. The thick anodised layer dissolves away.

    BEWARE a strong solution of NaOH will damage you. It's best to use the solution outdoors, the gasses released when you dip the Aluminium into the bucket are not pleasant.
    After a while depending on the size of the piece you will be left with a very cosmetically poor looking heat-sink.

    Though it takes only a few pico seconds for the aluminium to re-oxidise its surface and create a very thin layer, eventually over time the piece will continue to oxidise and form white powder on its surface.

    Anodising creates a thicker oxide layer which seals it - after the electrical anodising process and boiling water - with or without a dye to colour the piece as desired.

    Anodising seals the aluminium surface to further oxidation, protects it and becomes non conducting.

    Have a look at these sites for practical anodising, removing an anodised layer and cleaning the aluminium.

    http://www.observationsblog.com/scie...t-battery-acid

    http://astro.neutral.org/anodise5.shtml
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    Re: removing anodized coating from aluminum

    Im considering to snip off the drain pin and use a ring terminal and screw to the drain back and solder the wire onto the board.
    Still unclear what you want to achieve. TO220 package can connect through drain pin, why do you want to connect the heatsink at all?

    It seems the heatsink is actually painted since I obtained it off aliexpress and not a reputable vendor.
    A sealing of the anodized surface isn't necessarily insufficiency, it can be a feature.

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    Re: removing anodized coating from aluminum

    Quote Originally Posted by FvM View Post
    Still unclear what you want to achieve. TO220 package can connect through drain pin, why do you want to connect the heatsink at all?


    A sealing of the anodized surface isn't necessarily insufficiency, it can be a feature.
    Because connecting the heatsink would not require me to make a ring terminal and an extra pad for wires but using the heatsink pins for conducting current is unreliable unless it was made to do so. The board is 2 layer and Im trying to avoid routing both sides with thick drain traces

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    Re: removing anodized coating from aluminum

    The oxide layer shouldn't be enough to block current flow.
    Right, but a very thin oxide layer is rectifying and there will be considerable resistance developed over time.

    Aluminium conductors are widely used in power applications but the conductors must be pressed very hard so that no oxygen access is possible.

    The problem can be severe when using dissimilar metals.

    Tightening with a nut-and bolt is a good solution but may not work if the voltages are low.

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