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Topic: Quick and efficient way of etching aluminum?  (Read 4731 times)

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Offline Jesper

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Quick and efficient way of etching aluminum?
« on: May 22, 2016, 10:17:34 AM »
Hi all,

I have a question that I hope one of you can help with ...

As it is I am looking for a way to etch tracks in an aluminum foil which has a thickness of 0.1 um (micron) very efficiently and rapidly - i.e. preferably as fast as practically possible (while being a reasonably healthy & environmentally safe process).

The reason why speed is needed is that the foil is mounted on a mylar membrane with a glue that likely does not adhere well in (etching) liquids. Thus, I need the etching process to be fast and efficient - and probably completed in about 1-2 minutes.

I've already tried with Sodium Persulphate which I use for etching PCB laminates (copper), however, it is too slow even when heated to ~ 50 degr. Celsius.

Reading around the internet HCL & H2O2 as well as ferric chloride appears to be other options but it seems that the first causes some quite toxic gases to be developed whereas the ferric chloride might not be as quick as needed.

Thus, I hope someone here may know of an efficient and quick way of etching a thin aluminum foil. I do have an etching bath (stainless steel) that can be heated so the relevant fluid may be heated up to probably around 70 degr. C., if needed.

Thanks for any help  ;)

Jesper

Offline Arkcon

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Re: Quick and efficient way of etching aluminum?
« Reply #1 on: May 22, 2016, 02:26:02 PM »
Hmmm ... interesting.  OK, so the aluminum over mylar 1s 0.1 u thick, and you have to etch it away completely, down to the mylar, without damaging the mylar. Hmmm ... tricky.  Have you considered laser ablation, or just scratching it off with some tool?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Enthalpy

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Re: Quick and efficient way of etching aluminum?
« Reply #2 on: May 22, 2016, 08:05:53 PM »
I etched 2mm of Al-Cu4-etc alloy in 2 hours with a boiling FeCl3 aqueous solution, so 0.1µm should take 1/3s except for an induction time due to the oxide layer.

Just in case your stack is a space blanket, beware a polymer layer protects the aluminium. The stack is: transparent mylar film, ultrathin aluminium, coloured varnish thinner than the mylar. Acetone on a cloth dissolves the varnish.

Traditionally, such a thin aluminium layer is evaporated on the mylar film, not glued, and it adheres decently well. 0.1µm would be impractical to handle separately.

Offline Jesper

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Re: Quick and efficient way of etching aluminum?
« Reply #3 on: May 23, 2016, 03:28:05 AM »
Hi both,

- & thanks for your replies & suggestions  ;)

@Arkcon:

Quote
Have you considered laser ablation, or just scratching it off with some tool?
... No I have not considered laser ablation and - without knowing much about this technique - my guess would be that it's not that simple to use in this case. The mylar is 0.9 um thick so it would require a very fine control of the ablation laser if the mylar is not to be damaged. Something that I do not have and (at least while this is in a trial phase) am not aware that I have access to. Please correct if you would say that an ablation laser would work anyway ...

@Enthalpy:

Quote
I etched 2mm of Al-Cu4-etc alloy in 2 hours with a boiling FeCl3 aqueous solution, so 0.1µm should take 1/3s except for an induction time due to the oxide layer.
... This is good news! Do you have a suggestion as to an optimal relative ratio of FeCl3 to water if I heat the solution to e.g. 60 degr. Celsius (I'm not sure how well the glue or the photo-resist goes with a boiling condition)?

Quote
Just in case your stack is a space blanket
... Well, thanks for mentioning this - as it is it isn't but it made me curious as to what such a varnish could be made from ... Do you know of this?

And then I have an additional question that I would hope one/both of you have a suggestion for ... As it is I glue the 0.1 um alu-membrane to the 0.9 um mylar - and it actually works quite well - but the glue I use is water based which probably is why the etching needs be quick. In case it exists it would be feasible to try with a non-water based glue/adhesive process (efficient layer less than 0.1 um) also to reduce any influence from varying humidity. Might one of you know of such a glue/adhesion process (for various reasons it cannot be evaporation) - that is also reasonably healthy/environmentally safe?

Thanks again for any assistance in this  ;)

Jesper

Offline Enthalpy

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Re: Quick and efficient way of etching aluminum?
« Reply #4 on: May 23, 2016, 12:08:13 PM »
Optimum concentration of FeCl3: I don't quite remember, but it was close to the usual concentration to etch copper for printed circuit boards. For such small amounts of aluminium, you can try directly in an etch bath used commonly for printed circuits, it won't deteriorate the bath. Your aluminium is probably very pure and will resist etching better than my Al-Cu4, but for 100nm it won't last long.

My solution boiled only because etching was so fast with aluminium. At the beginning it had the outside air temperature. And since the aluminium was a long tube and the FeCl3 was inside, in 50kg amount, this experiment was the dirtiest I made. ;D

0.9µm, that's damn thin! I feel 12.7µm Mylar already weak enough. Hey, as soon as you can manufacture and handle 1km2 foils (preferibly of Kapton or any PI), I want them for solar sails! I have already a pleasant concept for lightweight booms there
http://www.scienceforums.net/topic/78265-solar-sails-bits-and-pieces/#entry857978
but presently 12.7µm or 6.3µm (the thinnest laminated by the chemical industry) is the minimum.

I propose in message #1 there a method to thin an existing polymer foil. In case this is possible and fits your needs, you could:
  • Evaporate the aluminium on a thicker polymer film. Good adhesion. Or better, buy the aluminised mylar film.
  • Etch the well adhering metal as you need.
  • Thin the polymer film as needed.
The thinning machine would resemble an aluminium evaporation machine that passes the film from one big roll to and other and processes it in vacuum in between. In fact, I suggest to modify such an existing machine. Instead of evaporating aluminium there, it would etch the polymer film, for instance by plasma and possibly in several passes, controlling the remaining thickness for instance optically in a feedback loop.

I ignore the nature of the varnish on space blankets.

Laser ablation works for very thin materials. The trick is to use very short pulses (like fs from Ti:sapphire) so the heat has no time to diffuse to the depth, and then it evaporate the nearest surface without damage deeper. My concern is that Mylar may absorb more light than aluminium.

When I worked with semiconductors (during the paleomonolithic era) we had made stencils of milled metal to deposit aluminium through them by evaporation. This spared us etching the aluminium and sufficed for mm-sized patterns. Adherence was good thanks to evaporation. Stencils of silicon could be eched much finer; put them in contact with your film to limit blurring.

Offline Jesper

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Re: Quick and efficient way of etching aluminum?
« Reply #5 on: May 24, 2016, 02:12:46 AM »
Hi Enthalpy,

Thanks again for replying & suggesting  :)

I'll try with FeCl3 in the concentrations used for etching copper - I reckon I can find such information on the internet.

Quote
My solution boiled only because etching was so fast with aluminium.
Well, yes, sounds as an "intensive" experiment you were making ... thinking mine will be less so ...  8)

I also just briefly looked at your solar sail idea - interesting that light's pressure may be enough to drive "anything" although the area of the sail is not exactly small. I reckon that in practice, i.e. in space, the sail may also be damaged by many of the particles/objects floating around there ... ? (Please note though that this is not a field of knowledge that I'm much familiar with ...)

Hmmm ... In what I'm doing economy is also important and though I can see the idea in what you otherwise describe/suggest I don't know of any companies in the vicinity that has such equipment - or can do this. And at least for a start I prefer to keep things simple (with the least of machinery) so as to try out whether the principles I am testing actually works. But I'll keep your suggestions in mind should things turn out differently than I hoped for ...

Cheers & thanks again  ;)

Jesper

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