Silver Solution Ink Makes Faster Flexible Circuits

judgecorp writes "Silver-based compounds dissolved in ammonia could make finer and more flexible circuits, according to researchers at the University of Illinois. Existing inkjet based circuit printing systems use particles which are less predictable. The silver-based ink remains dissolved until the ammonia evaporates, and can be delivered through 100nm nozzles. In all senses, it's a better solution."

Comments

Corrosion?

[Kenja]

There's a reason copper or gold is used in circuit boards despite silver being a far better conductor, how does this new solution avoid corrosion?

Re:Corrosion?

[Sponge Bath]

This suggests corrosion is not a problem. Highlights: "It is quite resistant to corrosion and does not oxidize easily, although it readily forms a surface tarnish of silver sulfide." and "Silver plating is widely used on contacts and other conductive parts in electrical apparatus such as switchgear and motor control centers because of the superior conductivity and longevity."

Re:Corrosion?

[introcept]

It doesn't need to, it should be fine under a layer solder mask/conformal coat/lacquer with plated contacts if necessary.
In a flexible circuit you'd be sandwiching it between two layer of polymer anyway

Re:Corrosion?

[LordLimecat]

Copper corrodes far worse than silver does.

Re:Corrosion?

[wierd_w]

Assuming this is metalic silver being deposited (this process seems eerily similar to traditional silver mirroring processes with ammonia, dextrose, and silver nitrate) then it can be rapidly plated with gold using a solution bath. (Gold dissolved in nitric and hydrochloric acid mixture)

An interesting idea would be to print the two solutions (dextrose + ammonia) + (silver nitrate) with a dual head printer, then print dissolved gold after it has had time to deposit.

This would chemically replace/plate (depending on thickness) the silver traces with gold ones. A simple distilled water wash afterwards would clean up the piece.

Makes me wonder if I could repurpose a color print cartridge for this process. I strongly suspect that the nitrate and aqua regia solutions would be very very bad for the printheads though. (Dextrose + ammonia solution would probably just clog and nothing more.)

Re:Corrosion?

[Anonymous Coward]

There's a reason copper or gold is used in circuit boards despite silver being a far better conductor.

Silver isn't a better electrical conductor than copper, it's a better thermal conductor.

Silver is tremendously better at conducting heat than aluminum, and slightly better than copper and gold. In the past, I've melted blobs of silver solder over flat aluminum heatsinks, mostly to absorb temperature spikes (to steady temperatures).

How does this new solution avoid corrosion?

It isn't really necessary to avoid the corrosion of silver in most cases (in breathable air). Unlike copper oxide (a semiconductor/insulator), or aluminum oxide (insulator), silver oxide remains a decent electrical conductor. Conducting electricity despite oxidation is why it's great for electrical connectors, because all bare metal corrodes in the presence of oxygen (except gold; most of them form protective oxide layers on the surface like stainless steel, but most oxides have high electrical resistance).

Regardless of the metal being used, you can protect the circuit traces against abrasion, shorts and corrosion with a protective coating. Tinning the traces would be an obvious choice, if the heat from soldering doesn't melt or burn the PCB material. Smearing silicone sealant across it might work, but any general purpose PCB coatings will just flake off something flexible.

Corrosion isn't always oxidation, though. Another poster mentioned silver sulfide, which is different (aka silver tarnish). Oxides and sulfides of metals have different physical properties, silver oxide conducts but other reactions may or may not. Keep in mind you'd only get silver sulfide from hydrogen sulfide (air pollution or other biological sources). So, unless you're eating off the circuit board, or expose it to smog, oxidation is the primary type of corrosion.

Every fucking month

[atari2600a]

We get a Silver Ink story, as if it hadn't been invented years ago available at any Frys electronics ready to mend any severed circuit.

Re:Every fucking month

[tobt4josh]

The fact that this new ink reaches the bulk conductivity of pure silver upon annealing is nothing short of amazing. My company has been working on some printed electronics application, and most of the conductive inks (including silver based) have conductivities that are too low to conduct any useful amount of current.

Re:dpi?

[SmlFreshwaterBuffalo]

I'm sure it also has to do with the resolution of the nozzle positioning system as well as the spread of the droplets once they hit the surface. To get true 10 million dpi, I think you would need to be able to create 2 dots 100 nm apart without them shorting together.

Of course, it sounds like the resolution is still much better than existing technology, just not 10 million dpi.

Link to the research group doing this:

[Hartree]

http://colloids.matse.illinois.edu/

Jennifer Lewis' research group here at the University of Illinois did this work.

They've got a link on that page to a youtube video that shows how to make and use this conducting ink, but it goes through Boing Boing and is down at the moment due to the SOPA protest.

Here's a direct link: http://www.youtube.com/watch?v=dfNByi-rrO4

Seriously cool work.

Not this sense

[Prime Mover]

> In all senses, it's a better solution
Ammonia? Not in my sense of smell.

Tell me when they have a silver/Mendocino Oatmeal Stout solution.