Printed, Hybrid, Structural, & 3D Electronics
ACI Alchemy Conductive Inks Enabling
Vice President of Engineering - ACI Materials
Next Generation Flexible and 3D Electronics
Percolation Conductors vs
Challenges of Percolation Conductors
Currently the conductive inks used commercially are of the traditional polymer thick film (PTF) silver type. These are "percolation" type conductors comprised of conductive fillers dispersed at high loadings in to thermoplastic polymers that have been dissolved in a solvent. After printing, drying forces the solvent out, shrinking the polymer phase, forcing the conductive fillers into near contact. The upside is good adhesion due to the amount of polymer wetting the substrate interface. The downside is the polymers and organics stabilizers on the particles create contact resistance diminishing electrical performance, and even best ones only achieve volume resistivity on the order of lead (Pb).
Wet as Printed
Polymer & “lubricants” from
flaking create contact “resistance”.
Resin at substrate interface
Next Level - Sinterable Conductors
In order to overcome the interparticle contact resistance inherent of PTF conductors, sinterable conductors were introduced over the last 20 years. Under the right conditions (higher curing temps or longer cure times, typically thinner film thickness) they can provide conductivity a step above percolation conductors; even close to bulk silver. This allows silver usage and thus cost reduction. However, it is very difficult to formulate them with enough resin to wet the substrate well, but without so much it doesn’t interfere with sintering and thus improvement to resistivity. It is also challenging to drive sintering at equivalent temperatures to which PTF conductors can be dried. Therefore, although these conductors have been commercially available for decades, and perform well in a lab, few have been used in commercial electronic devices.
Wet as Printed
Sintering yields no contact
resistance. Difficult to get
resin to substrate without
ACI's Inks of the Future
Semi-Sintering or Hybrid Conductors
ACI’s Alchemy Conductive Inks offer the ‘best of both worlds’. They contain enough resin to achieve perfect adhesion on typical substrates like PTF products, and can be cured in similar times in many cases. However, the particles sinter resulting in resistivity similar to most nanoparticle and complex based inks, but also at much higher film thickness. The Alchemy name comes from the analogy that one could directly replace their current material that performs like lead with something performing much closer to gold. This also allows lower usage of silver and thus cost reduction as nano inks typically claim.
Wet as Printed
Some sintering between
particles and high aspect flakes.
Higher resin content than pure nano
sintering materials yield superior adhesion
Alchemy Series Benefits
Lower Volume Resistivity in Less Time
Lower Sheet Resistance & Faster Cure Times
Superior Hard Crease Survivability
EMI Spray Shielding Coatings
Enables Reflow Soldering
Note: Developed in partnership with Semi, FlexTech and Army Research Laboratory - (see below)
High-Resolution Printing Without Compromise
Alchemy Inks Reduce Cost Per Device
Developed in partnership with Semi, FlexTech and Army Research Laboratory
This material is based on research sponsored by Army Research Laboratory under agreement number W911NF-19-2-0345. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Army Research Laboratory ( ARL) or the U.S. Government.
Alchemy Series In Use
Flexible Hybrid Electronics
High Current Density Busbars
“From automotive to industrial equipment, transparent heaters made from CHASM’s CNT Hybrid material are generating significant excitement with product innovators across many industries and ranging in size from a few square inches to many square feet,” said Ken Klapproth, Chief Marketing Officer, CHASM Advanced Materials, Inc. “Having a range of compatible materials at our disposal such as ACI’s Alchemy conductive inks gives us the versatility we need to produce the best flexible printed electronics customers will never see.”—Images courtesy of CHASM
Enabling Unique Form Factors
Sintering Pastes for Die Attach & More
RD0090x Sintering Pastes
Differentiation & Value Add
The Unbundling Challenge
Pre-cavitation mixing samples show large bundles of chords of SWCNT. Chords widths rang in the 50-200nm (nominal diameter of individual SWCNT ~2.5nm, so 20-80 tubes wide). Due to the immense surface area of the SWCNT and the Van der Waal attractions, the SWCNT have a propensity to bind together strongly. This makes it very challenging to unbundle the chords, without causing significant damage to the SWCNT aspect ratio. The SEM has a limited capability to assess the nano structure of the chords, which can be revealed using other imaging techniques that ACI Materials currently does not have. It is also uncertain that dried films would be able to remain un-aggregated as the solvent vaporizes. It is likely that much of the CNT content would stick back to each other, due to the ultra-high surface area.
Red bars indicate 10µm scale, showing that some bundles are greater than 10µm in diameter and greater than 30µm in length.
The 7k X magnification shows the nature of how the bundles are made up of chords.
The 70k X magnification shows the scale of the chords. The yellow ticks are ~50nm in width.
Cavitation - The Unbundling Solution
Through controlling the cavitation processing parameters, we are able to effectively unbundle CNTs while keeping their aspect ratio intact. We can control the amount of unbundling that occurs so that the outcome is a balance of targeted Volume Resistivity and Sheet Resistance, as well as desired rheological properties.
Viscosity & Volume Resistance
Through ACI Material's precise control of cavitation processing parameters, it is able to effectively unbundle CNTs while keeping their aspect ratio intact. The process can control the amount of unbundling and dispersing that occurs, so that the outcome is an optimal balance of volume resistivity and desired rheological properties.
The graph demonstrates how processing control allows for ACI to choose which conditions give the best electrical performance at an appropriate viscosity for the given application. These volume resistivity values are evaluated from dried, stencil printed films of pure SWCNTs at various processing conditions.