ACI Alchemy Conductive Inks—Enabling Flexible & 3D Electronics
Printable conductors for low-temperature flexible substrates generally fall into two classes: polymer thick film (PTF) percolation-based or sinterable conductors (nanoparticle, reactive complex-based, etc). Both have inferior conductivity to copper foils in PCB's due to the inclusion of polymers, organics, and porosity in their microstructure. PTF inks advantageosly have superior adhesion, but inferior conductivity compared to sintered films. Some existing sinterable inks can achieve resistivity closer to copper foil, but usually only under ideal curing conditions. Unfortunately ideal often means temperatures exceeding the limits of low-cost substrates, residence times not possible in installed R2R or conveyor dryer systems, requiring calendering, or at limited dry film thickness. Further, their adhesion is almost always inferior to PTF materials.
Ultimately these factors yield higher trace resistance, limited current/power carrying capability, and worse signal or antennae performance compared to even the thinnest copper foils. In order to additively manufacture more advanced electronic devices or standard electronics for ubiquitous applications, there is a need to be able to print conductors thick, with low resistivity, thus low sheet resistance. The potential applications range from automotive to medical devices to aerospace. All require improved material performance, narrower traces to enable higher density interconnects, or the ability to apply them to 3D shapes to reduce size and weight.
ACI Materials recently released its Alchemy Conductive Inks which overcome many traditional limitations of existing printed conductors. These hybrid or semi-sinterable conductors offer the ease of use and processing of PTF inks and coatings, but with the superior electrical performance of sintered inks. These formulations cure at rates amenable to traditional dryers, unlike many existing nanoinks. Their ability to sinter at greater film thickness than nano and metal complex inks allows for not only low resistivity but low sheet resistance films able to carry more current or power without overheating. Even when cured at lower temperatures (80-100 C) the films often show superior electrical performance and film cohesion than PTF inks.
The ability to formulate Alchemy Conductorive Inks incorporating a range of polymers/resins allows for adhesion to a wide range of substrates (including ITO) similar to PTF inks, and unlike most nano and metalorganic inks. They have the ability to be printed as significantly thinner films with equivalent sheet resistance to PTF conductors. This allows for superior flex ductility and hard crease-resistance similar to that seen with thinner copper foils. One may think all these benefits come with a high price, but the low volume resistivity (high conductivity) of these materials and their ability to print thinner films enable lower cost in use than PTF silvers.
The small particle size of the formulations allows screen printing, 2D/3D microdispensing or extrusion direct write printing, and jetting and spraying of finer interconnects. Under proper curing conditions Alchemy inks wet nicely by BiSn(Ag) low-temperature solder pastes, so on some substrates reflow solder-based attach may be possible. These materials can enable additive manufacture or more complex flexible hybrid electronics than previously possible.
