Attaching a really thin layer of aluminum to a really thin layer of mylar.

[cheesehead]

For a project I'm working on, I need to make many thin traces of aluminum on a very thin layer of Kapton polymide film - basically name-brand mylar. While buying 7.6-micron mylar and 5-micron aluminum foil isn't that difficult, getting the two to adhere without adding a bunch of weight is quite tricky.

Any suggestions?

 

[CycloWizard]

That's potentially very tricky. Do you need a uniform adhesive film between the two layers? How much weight is too much? And, of course, how big are the pieces that you're attaching?

Simple cyanoacrylate (common ingredient in superglues) will bond just about anything under the right conditions without adding much weight. However, if the sheets you're bonding are large enough, it won't cure properly because it will be oxygen-starved in interior regions. There are pressure-sensitive adhesives that might be perfect for your application, but they are more expensive and require more advanced processing techniques as well.

 

[Born2bwire]

Originally posted by: CycloWizard
That's potentially very tricky. Do you need a uniform adhesive film between the two layers? How much weight is too much? And, of course, how big are the pieces that you're attaching?

This. If I had to do it, I would put down epoxy and use a press or rollers to force the sheets together and the epoxy out. That should leave a very thin film of adhesive, promote adequate coverage, and remove the various air bubles and such. But it really depends upon the specifics.

 

[wwswimming]

Originally posted by: Cheesehead
For a project I'm working on, I need to make many thin traces of aluminum on a very thin layer of Kapton polymide film - basically name-brand mylar. While buying 7.6-micron mylar and 5-micron aluminum foil isn't that difficult, getting the two to adhere without adding a bunch of weight is quite tricky.

Any suggestions?

this sounds a lot like Rigid-flex circuit board, except with aluminum instead of
copper.

it is simple for people that do it as part of their business, and they have fixtures
every step of the way.

are you talking about attaching a square foot of Kapton to a square foot of
aluminum ? (what size material are you starting with).

http://en.wikipedia.org/wiki/Mylar

not quite the same as polyimide/Kapton.

 

[cheesehead]

Originally posted by: CycloWizard
That's potentially very tricky. Do you need a uniform adhesive film between the two layers? How much weight is too much? And, of course, how big are the pieces that you're attaching?

Simple cyanoacrylate (common ingredient in superglues) will bond just about anything under the right conditions without adding much weight. However, if the sheets you're bonding are large enough, it won't cure properly because it will be oxygen-starved in interior regions. There are pressure-sensitive adhesives that might be perfect for your application, but they are more expensive and require more advanced processing techniques as well.

The pieces will be up to 4" x 4", making the problem of oxygen starvation a big one. While a uniform adhesive film is not required, I don't want any traces lifting up off of the mylar after I etch it.

If anyone's wondering, I'm currently trying to replicate both the Take.T air motion transformer headphones and the old version Fostex T50 orthodynamic headphones (which are nothing like the new ones.) To do so, I need a very light diaphragm covered with many very thin conductive traces to create a magnetic field.

This is easier said than done, which is why I'm here.

 

[BladeVenom]

Would a circuit pen or defog repair kit work for making the traces?

 

[CycloWizard]

If you need to prevent trace separation, it's probably a good idea to generate a uniform film. I would recommend a pressure-sensitive epoxy. I don't have one in particular that I'd recommend since I have just about no practical experience with them, but it shouldn't be too hard to find.

 

[cheesehead]

DuPont actually sells kapton with a layer of copper - it's just that it's much, much thicker than I would have wanted.

 

[PottedMeat]

Originally posted by: Cheesehead
DuPont actually sells kapton with a layer of copper - it's just that it's much, much thicker than I would have wanted.

You could etch that, then take off the remaining photoresist, then etch it again. You'd have to get the etchant temperature right as well as the etch time.

 

[cheesehead]

Would'nt that just take off all the copper?

The problem with the copper-covered kapton is that it's quite thick - 12.5 microns of kapton, 12.5 microns of copper, and a bit of adhesive in between. Also, copper is quite heavy.

I'm shooting for about half the thickness (5 micron aluminum + 7.5 microns of kapton) and a third the weight.

 

[herm0016]

we print screen print (very much like doing a t-shirt) circuit traces with a silver ink on layers of kapton for flexible circuit construction. I believe this will be the best bet. you can make the traces very accurately.

 

[cheesehead]

Originally posted by: herm0016
we print screen print (very much like doing a t-shirt) circuit traces with a silver ink on layers of kapton for flexible circuit construction. I believe this will be the best bet. you can make the traces very accurately.

Interesting.

Any chance you do small batches?

 

[silverpig]

Lithography + evaporation would do that easily. You can easily get photoresists that will do that thickness, and evaporating 5 um of Al, while quite a bit, won't take longer than an hour.

 

[ScottMac]

Check out 3M "Super 77" spray adhesive and similar products.

Good adhesion, a very thin coat is possible (it's an aerosol spray adhesive frequently used for wet/dry mounting art).

If your school has an electron-microscopy lab, they would also have a vacuum evaporator or film deposit system. You can dial it down to the micron.

Good Luck

 

[herm0016]

well, we do it in a research lab. see if your local print shop will do it? of course they would not have experence on such small things, or the correct ink. you should be able to find some company to do it.
I also think vapor deposition would be the absolute best bet though.

 

[silverpig]

Originally posted by: ScottMac
Check out 3M "Super 77" spray adhesive and similar products.

Good adhesion, a very thin coat is possible (it's an aerosol spray adhesive frequently used for wet/dry mounting art).

If your school has an electron-microscopy lab, they would also have a vacuum evaporator or film deposit system. You can dial it down to the micron.

Good Luck

You can get evaporation down to the nanometer quite easily...

 

[firewolfsm]

For oxygen starvation you can just start from the center out.

Am I missing something, that seems obvious.

 

[Howard]

Mmmm... if you were going after small pieces I would've recommending taking apart a coax cable with a foil shield and etching the aluminum off.

 

[dkozloski]

Party balloons.
Potato chip sacks.

 

[CycloWizard]

Originally posted by: firewolfsm
For oxygen starvation you can just start from the center out.

Am I missing something, that seems obvious.

If you're bonding two rigid flat plates together, then it's not that easy. You'd have to find a way to pump the superglue in to the center, but the point where it's being delivered must change with time. Not only that, but it needs to be distributed circumferentially about the center at all times.

 

[cheesehead]

Originally posted by: herm0016
well, we do it in a research lab. see if your local print shop will do it? of course they would not have experence on such small things, or the correct ink. you should be able to find some company to do it.
I also think vapor deposition would be the absolute best bet though.

Hmm. This does seem to be the best option by far.

Here's hoping I can bribe a grad student into doing it for me.

I hear a 20" pepperoni pie will go a long way....

 

[CycloWizard]

Originally posted by: Cheesehead
Hmm. This does seem to be the best option by far.

Here's hoping I can bribe a grad student into doing it for me.

I hear a 20" pepperoni pie will go a long way....

Yes, free food is trading well against the American dollar these days, at least in grad school. Pizza==Benjamin.

 

[DisgruntledVirus]

While I don't know the difficulty behind it, what about a bath approach? Aluminum in liquid (not molten) state, that you can pull the mylar through and when it comes out the liquid the AL is dissolved in evaporates away leaving a thin sheet of AL on the mylar.

If that isn't really possible, than the printing method would be my second choice.

 

[DrPizza]

Someone mentioned it above. Power was knocked out during the Bills game last Sunday due to them... but mylar balloons have a thin coating of aluminum on them (aluminum, as reported by the news agencies). How do they do it so efficiently?

 

[Comdrpopnfresh]

how thin do these traces need to be? couldn't you just get aluminized mylar and find a way to isolate the traces, or remove what you don't need?