Localized Laser Sintering of Metal Nanoparticle Inks Printed with Aerosol Jet® Technology for Flexible Electronics

Abstract

Direct-write methods, such as the Aerosol Jet® technology, have enabled fabrication of flexible multifunctional 3-D devices by printing electronic circuits on thermoplastic and thermoset polymer materials. Conductive traces printed by additive manufacturing typically start in the form of liquid metal nanoparticle inks. To produce functional circuits, the printed metal nanoparticle ink material must be postprocessed to form conductive metal by sintering at elevated temperature. Metal nanoparticles are widely used in conductive inks because they can be sintered at relatively low temperatures compared with the melting temperature of bulk metal. This is desirable for fabricating circuits on low-cost plastic substrates. To minimize thermal damage to the plastics, while effectively sintering the metal nanoparticle inks, we describe a laser sintering process that generates a localized heataffected zone (HAZ) when scanning over a printed feature. For sintering metal nanoparticles that are reactive to oxygen, an inert or reducing gas shroud is applied around the laser spot to shield the HAZ from ambient oxygen. With the shroud gas-shielded laser, oxygen-sensitive nanoparticles, such as those made of copper and nickel, can be successfully sintered in open air. With very short heating time and small HAZ, the localized peak sintering temperature can be substantially higher than that of damage threshold for the underlying substrate, for effective metallization of nanoparticle inks. Here, we demonstrate capabilities for producing conductive tracks of silver, copper, and copper-nickel alloys on flexible films as well as fabricating functional thermocouples and strain gauge sensors, with printed metal nanoparticle inks sintered by shroud-gas-shielded laser.

Aerosol Jet Printing of Silver Lines with A High Aspect Ratio on A Heated Silicon Substrate

“…Obtaining lines with a high aspect ratio is possible only using additional approaches for processing the substrate or the deposited material. Therefore, one of the approaches is to structure the substrate using imprinting or lithography, which limits the spreading of ink on it [24], and the second approach is based on the use of multiple printing passes in combination with local laser sintering of the deposited material [25][26][27][28]. Both presented approaches significantly complicate and increase the cost of the aerosol jet printing process through the use of additional lithographic, laser and optomechanical equipment.…”

Laser-Assisted Printed Flexible Sensors: A Review

“…Renn et al [112] analyzed the experimental results from the different parameters of the laser-sintering method for fabricating a flexible sensor. They have shown that the localized heat affected zone (HAZ) should be minimized for printing the metal on a flexible substrate, unless higher temperatures can damage the underlying substrate.…”

In-Space Manufacturing at NASA Marshall Space Flight Center: A Portfolio of Fabrication and Recycling Technology Development for the International Space Station

“…The goal of the phase I project was to enhance the Optomec Aerosol Jet(R) technology for additive manufacturing of electronics through the addition of an Adaptive Laser Sintering System (ALSS) module. This enables a fully automated, end to end system for printed electronics and extends Optomec's Aeresol Jet technology to the printed electronics market 19 . ALSS can significantly reduce thermal damage to low Tg polymer substrates (such as acrylic, PET, etc.).…”