Nickel plated polyimide--where to get?

...alternate..vacuum sputter deposit for any thickness you want; control can be as good as 1/10 wavelength of light (pick your favorite color). ...another alternate..perhaps gold film?

Not sure about the nickel, but Minco will do custom polyimide film heaters to your design:

Thanks, I asked them already--they aren't interested in supplying plain sheets.

I thought about vacuum dep, but it'll get expensive in the sort of quantity I want, and there's still the adhesion issue. If I still had my own evaporator, I'd probably do it that way--I could just wrap the PI round the inside of the bell jar!

Cheers

Phil Hobbs

I assume aluminized mylar won't work. I didn't know you could nickle plate onto plastic? Could you get a local electroplater to put nickel on aluminized mylar and solder to that?

George H.

Stupid question...

Wouldn't it be possible to make the polyimide conductive by rubbing graphite into its surface ("The Audio Amateur" had at least one article about home-made electrostatic speakers that showed how to do this with Mylar), then plate it?

Thanks.

I'm planning to use it as a really big RTD, so I need a continuous film of reasonably pure metal with reasonably uniform thickness. The films have a tendency to crack if the base layer is too thin or too flexible, which is bad. If I roll it into a cylinder with the metal side in, I'll put enough of a compressive preload on the nickel to keep it from cracking under temperature cycling. When the process is better developed, it might be useful to do the plating on the outside of a cylinder, so that there'll be a preload when it straightens out.

I'm not sure what temperature the plating is done at, but for lower temperatures there should be a compressive preload anyway, due to the differential thermal expansion.

I have a roll of copper-clad polyimide, which is beautiful stuff, in fact about 250 times too good for this job--the copper is 12 times too thick and 20 times too conductive. A 40 microinch nickel film is just the ticket.

Mylar isn't really solderable--it isn't refractive enough. Indium might work.

Cheers

Phil

I'd be worried about the film adhesion--the nickel would only stick as well as the graphite. Plating plastic involves stuff like chromic acid dips, reducing palladium salts to form Pd nucleation sites on the film, and then electroless plating.

Not your ideal home project unfortunately!

Cheers

Phil Hobbs

You might find your local electroplating shop can do electroless nickel plating from a physical reducing bath.

Just about DIYable for small quantities if you don't want a very thick layer. Might even be possible to pattern it with a suitable resist.

Nickel is one of the metals for which reducing baths work well.

Regards, Martin Brown

Could you do electro-etching to thin the copper down until it was resistive enough? You would need to get down from 12.5 micron of copper to about 0.03 micron, which would be tricky - since the copper isn't going to be a uniform 12.5 micron thick layer to start with, you'd probably end up with a network of isolated islands if you tried to do it in one hit.

Alternating electro-erosion and electro-polishing might work.

I've been in situations where even a single-atom thick layer of metal was too conductive for my purposes, but 40 microinches/ 1 micron of nickel would be a good deal more conductive than that.

-- Bill Sloman, Nijmegen

Thanks for the clarification.

This is the sort of problem you'd think would have been solved decades ago. The original SX-70 used copper-coated (plated?) polysulfone, which was then plated with nickel and chrome. The plating sticks to the plastic with a tenacity that's almost unbelievable. You actually have to break the plastic before the plating comes loose.

Oh, it's been solved, all right--Minco advertises nickel film RTDs. I tried to get them to make the films, but they either couldn't or didn't want to, and I didn't want to have to deal with making artwork--I'm going to pattern it with a Sharpie and some ferric chloride. (Ferric chloride works well on thin sputtered nickel, so I'm hoping the plated stuff doesn't have some weird passivation. I should try it out on a bolt or something before I take the plunge. Of course I can also electropolish it away in KOH solution.)

BTW the Minco rep is a good guy, who gave me a steer to somebody who may be their supplier--I just haven't heard from them yet.

Anyway, if it works, I'll try licensing it to them. ;) It should be good for at least 100x reduction in thermal forcing for the down-hole application I'm working on--sort of the thermal equivalent of a Faraday shield.

Cheers

Phil Hobbs

So, plate your nickel onto anything you want, then apply/bake the polyimide as a conformal coating, and etch away the 'anything' layer?

I'm attempting to throw money at the problem, hopefully in the direction of somebody who's done it many times before. That way I can get on with the parts I'm not sure will work!

Cheers

Phil Hobbs

Copper is not going to work--you need some reasonable thickness to get continuity. A pity.

Cheers

Phil Hobbs

Jut had a dumb idea..how about unrolling mylar or other plastic caps?

it

k,

A thermal Faraday shield sounds like some sort of distributed heating (cooling?) Can you mock something up, by soldering together bits of nickel wire? (I like phosphur bronze for heaters.)

George H.

I don't think I could find a 6-inch long one to begin with.... ;)

Cheers

Phil Hobbs

I think I can get an improvement of 40 dB or maybe even more in thermal forcing rejection, but it needs to be something technologically feasible....and anything involving wire is going to be too conductive.

Sorry to be mysterious about it--if it works I'm certainly going to patent it. A cheap and simple gizmo that makes an improvement of that magnitude will be worth actual money, I should hope. It's nice and discoverable, too, which is another plus, and the actual hardware is easy to make on standard production equipment. It's getting the blanket material to play with that's the problem.

It's no secret that the way to get speed in thermal control systems is to keep everything close together--heat conduction is what's slow.

Cheers

Phil Hobbs

Then my roll of metalized film from Sprague won't help you. It came from their Orlando plant closing, about 20 years ago.