How to do a rapid etch of tracks in very thin aluminum foil?

[irpheus]

... I am a bit unsure of whether or not this is the subforum to post this thread - if not I'd appreciate if you let me know ...

Hello everyone ;-)

I have for some time now been trying to find a solution for rapid etching of tracks (1-6 mm width) in very thin aluminum (<3um thickness) that is fused to a thin mylar membrane. Rapid etching means that a maximum of 1 minute is allowed for the etching process (less time is better).

The tracks may either be covered mechanically with a mechanical structure so that the etchant cannot get into the area of the tracks - or they are covered with a PCB resist that is commonly used in PCB manufacturing.

The PCB resist is normally removed using an NaOH or similar substance so using NaOH to do the etching will not work as it dissolves the PCB resist ...

To do the etching I have tried kitchen salt in water as part of an electrolytic process, however, this tends to take too long (the aluminum releases from the mylar) and does not entirely remove the aluminum ... small flakes of aluminum remains which is not acceptable in this context.

I have also tried a combination of HCL & vinegar, yet again it takes too long. The temperature of this solution was ~ 20 degr. C.

So, by posting here, I hope one of you know of a rapid etching solution for etching such a thin layer of aluminum... Please note additionally that the etchant needs be very reasonably non-harmful to both the environment (when released in very low amounts), the building where the etching takes place, and, not least, to myself.

I hope there may be a way of doing this and would much appreciate your feedback.

Cheers,

Jesper M

 

[dik]

Can you use a sodium hydroxide solution?

Dik

 

[IRstuff]

NaOH may still be OK, if the relative etch time ratio is high, say, 10:1.

The semiconductor industry used to use hot phosphoric acid to etch aluminum.

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[irpheus]

Hi both - & thanks for your feedbacks ...

@dik:

In other applications NaOH may be a good solution, however, as I write in my post, NaOH also dissolves the photoresist on the aluminum foil so it won't work, unfortunately ...

@IRstuff:

Hmmmm ... It could be a solution. Do you know which temperatures was required for the etching to be quick? To this end I found this link where a combination of H3PO4 & HNO3 is used (Amir Hassanfiroozi post - second last):

https://www.researchgate.net/post/I...ng_H3PO4_HNO3_H2O_without_presence_of_CH3COOH

... but I am not sure the etching speed is fast enough. As it is I can try out various solutions but since it takes the better part of a day to prepare for just one etch trial, and I already have tried some, I admittedly would like to be pretty sure that I am on the right track from the beginning ...

Cheers,

Jesper

 

[IRstuff]

I think we were running a few minutes. According to the last posting in your link, their etch rate would result in about a 9-minute etch which seems very reasonable. Why do you need such a short etch time?

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[irpheus]

Hi again,


The issue is that with longer etch times the aluminum tends to release from the mylar. I am not (yet, I hope) quite sure why this happens but I suppose the etchant somehow creeps in under the tiny non-fused parts of the mylar/aluminum interface. This is why I assume that a rapid etch may be preferable. I have BTW done some more searches on the internet and the company microchemicals (also within the EU) appears to have some solutions for this. And they also recommend an H3PO4/HNO3 (and CH3COOH - but not mandatory) mixture. More info in this document (should someone be interested):

https://www.microchemicals.eu/technical_information/aluminium_etching.pdf

Cheers & thanks again for replying ,

Jesper

 

[Compositepro]

Just be aware that aluminum is a very reactive metal, and is protected by an oxide layer that forms by reacting with air. It is the oxide layer that delays the etching rate. Rubbing with a brush or sponge will greatly accellerate the process.

I would not call 3 microns of aluminum a foil. It is an evaporated vacuum coating. There is probably more oxide than aluminum metal in your coating.

 

[irpheus]

@compositepro: Hmmm ... thanks for your feedback. As I understand it in the H3PO4/HNO3 etchant the HNO3's main function is to eliminate the oxide layer thus allowing the H3PO4 access to the aluminum. Also, in the article I linked to in the previous post (microchemicals) an elevated temperature is part of the approach. So, I reckon these two factors may speed up the etching process significantly.

I just wonder if the H3PO4/HNO3 mixture will also etch other metals close by. I understand that HCL will do so but maybe the H3PO4/HNO3 mixture is more specific. Any of you know about this?

Have a good day ;-)

Jesper

 

[IRstuff]

Depends on the metal. If you're using resist, then it should be deposited so as to cover the other, etchable portions of the item in question.

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