Nano-Conductive Adhesives for High-Performance Electronics

Ultrasonic dispersers are used as reliable mixing and milling technique in the production of high-performance adhesives for high-performance electronics and nano-electronics. In production of high-performance electronics, adhesives such as nano-conductive adhesives are in high demand. Such high-performance adhesives are used e.g. as alternative interconnects and can replace tin/lead solder.

High-Performance Adhesives for High-Performance Electronics

For the production of high-performance electronics, adhesives with high metal adhesiveness and heat conductivity for heat decoupling and insulation are required. Nano-particles such as silver, nickel, graphene, graphene oxide and carbon nanotubes (CNTs) are frequently incorporated into epoxy resins and polymers to obtain the desired functional properties such as electrical conductivity or insulation, heat conductivity, tensile strength, Young’s modulus and flexibility. High-performance adhesives developed for high-performance electronic use metal fillers (such as silver, gold, nickel, or copper nanoparticles) to provide electrical conductivity. In order to unlock extraordinary properties of these materials, their size must be reduced to nano-scale. As size reduction and dispersion of nanoparticles is a challenging task, a powerful milling and dispersing technology is key for successful adhesive formulations.

Ultrasonic dispersing offers various advantages when compared to traditional mixing and milling techniques. Due to its reliability and effectiveness, sonication has been established in nanomaterial processing and can be found in any industry where nano-particles are synthesized and/or incorporated into liquids. Ultrasonication is therefore the ideal technique for the production of nano-conductive adhesives that contain nano-fillers such as nanoparticles, nanowires, or carbon nanotubes and graphene monolayers (nanosheets).
ECAs: A prominent example is the formulation of electrically conductive adhesives (ECAs), which are composites made of a polymeric matrix and electrically conductive fillers. In order to formulate a the high-performance adhesive for electronic applications, a polymeric resin (e.g., epoxy, silicone, polyimide) must provide physical and mechanical functionalities such as adhesion, mechanical strength, impact strength, whilst the metal filler (e.g., nano-silver, nano-gold, nano-nickel, or nano-copper) creates superior electrical conductivity. For adhesives with insulating properties, mineral-based fillers are incorporated into the adhesive composite.

Before and after sonication: The green curve shows the particle size before sonication, the red curve is the particle size distribution of ultrasonically dispersed silica.

Ultrasonic Dispersion of Nanomaterials into Viscous Adhesives

Ultrasonic homogenizers are very efficacious when particle agglomerates, aggregates and even primary particles must be reliably reduced in size. The advantage of ultrasonic mixers is their capability to mill particles down to smaller and more uniform particles sizes, whether micron- or nano-particles are targeted as process result. Whilst other technologies such as blade or rotor-stator mixers, high-pressure homogenizers, bead mills etc. show drawbacks such as incapability of producing uniformly small nanoparticles, contamination by milling media, clogged nozzles and high energy consumption, ultrasonic dispersers use the working principle of acoustic cavitation. Ultrasound-generated cavitation has been demonstrated as highly efficacious, energy-efficient and capable to disperse even highly-viscous materials such as nanoparticle-loaded pastes.

How Does Ultrasonic Dispersing Work?

Cavitational shear forces and liquid streams accelerate particles so that they collide with each other. This is known as interparticle collision. The particles themselves act as milling medium, which avoids contamination by grinding beads and the subsequent separation process, which is necessary when conventional bead mills are used. Since the particle shatter by interparticle collision at very high speeds of up to 280m/sec, extraordinarily high forces apply to the particles, which therefore break into minute fractions. Friction and erosion give those particle fragments a polished surface and uniformly shaped form. The combination of shear forces and interparticle collision give ultrasonic homogenization and dispersion the advantageous edge delivering highly homogeneous colloidal suspensions and dispersions!
Another benefit of high-shear forces generated by ultrasonics is the effect of shear-thinning. For instance, ultrasonically prepared epoxy resins filled with oxidized CNTs shows shear-thinning behaviour. As shear-thinning lowers the viscosity of the fluid temporarily, the processing of viscous composites is facilitated.

A high-speed sequence (from a to f) of frames illustrating sono-mechanical exfoliation of a graphite flake in water using the UP200S, a 200W ultrasonicator with 3-mm sonotrode. Arrows show the place of splitting (exfoliation) with cavitation bubbles penetrating the split.
(Study and pictures:© Tyurnina et al. 2020)

Comparison of different nanofillers dispersed in hardener (ultrasonication—US): (a) 0.5 wt% carbon nanofiber (CNF); (b) 0.5 wt% CNToxi; (c) 0.5 wt% carbon nanotube (CNT); (d) 0.5 wt% CNT semi-dispersed.
(Study and picture: © Zanghellini et al., 2021)

High-Power Ultrasonicators for Formulating High-Performance Adhesives

Hielscher Ultrasonics is specialist when it comes to high-performance ultrasonic equipment for liquid and slurry processing. Ultrasonic dispersers allow to process highly-viscous materials such as highly-filled resins and ensure the uniform distribution of nanomaterials within composites.
The precise control over ultrasonic process parameters such as amplitude, energy input, temperature, pressure and time allow for tailoring adhesives in the nanometer range.
Wether your formulation requires the dispersion of organic or inorganic nano-fillers such as nanotubes, cellulose nano-crystals (CNCs), nanofibers, or nano-metals, Hielscher Ultrasonics has the ideal ultrasonic setup for your adhesive formulation.
Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes and are capable to deagglomerate and disperse nanomaterials even at very high viscosities. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation.
Hielscher ultrasonicators are recognized for their quality, reliability and robustness. Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators: