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

Nano-reinforced adhesives for applications in high-performance electronics use often ultrasonic dispersion for nanoparticle distribution.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 Dispersion for

  • Electrically conductive adhesives (ECA)
  • – Isotropically conductive adhesives (ICA)
  • – Anisotropic conductive adhesives (ACA)
  • Non-conductive / electrically insulating adhesives

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Ultrasonic dispersion is a highly efficient technology for detangling and deagglomerating nanoparticles. Therefore, ultrasonicators from Hielscher Ultrasonics are widely used in industry to produce larger-scale nanodispersions and nano-structured suspensions.

Industrial installation of ultrasonic dispersers (2x UIP1000hdT) for processing nanoparticles and nanotubes in continuous in-line mode.

The video shows the ultrasonic mixing and dispersing of Graphite in 250mL of Epoxy Resin (Toolcraft L), using an ultrasonic homogenizer (UP400St, Hielscher Ultrasonics). Hielscher Ultrasonics makes equipment to disperse graphite, graphene, carbon-nanotubes, nanowires or fillers in the lab or in high volume production processes. Typical applications are the dispersing nano materials and micro materials during the functionalization process or for dispersing into resins or polymers.

Mix Epoxy Resin with Graphite Filler using Ultrasonic Homogenizer UP400St (400 Watts)

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.

Ultrasonic dispersing results in a very narrow particle size distribution.

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.

Ultrasonic dispersion is highly efficient in dispersing and deagglomerating nanoparticles.

PLGA nanoparticles. (A): Size distribution of particles prepared at polymer concentration/ sonication power of 2%/ 32W, 5%/ 32W, and 2%/ 25W%; residence time = 14 s. (B),(C): SEM pictures of particles prepared from 2 and 5% polymer solutions, respectively. Residence time = 14s; sonication power = 32W. Bars represent 1 micron.
(Study and pictures: © Freitas et al., 2006)

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Ultrasonicator UP200St (200W) dispersing carbon black in water using 1%wt Tween80 as surfactant.

Ultrasonic Dispersion of Carbon Black using the ultrasonicator UP200St

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.

Ultrasonic graphene exfoliation in water

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)

Ultrasonic benchtop setup for the preparation of nanocomposites, e.g., for high-performance adhesives.

UIP1000hdT – Ultrasonic benchtop setup for the preparation of nanocomposites, e.g., for high-performance adhesives.

In this video we show you a 2 kilowatt ultrasonic system for inline operation in a purgeable cabinet. Hielscher supplies ultrasonic equipment to almost all industries, such as the chemical industry, pharmaceutical, cosmetics, petrochemical processes as well as for solvent based extraction processes. This purgeable stainless steel cabinet is designed for operation in hazardous areas. For this purpose, the sealed cabinet can be purged by the customer with nitrogen or fresh air to prevent flammable gases or vapors from entering the cabinet.

2x 1000 Watts Ultrasonicators in Purgeable Cabinet for Installation in Hazardous Areas

Advantages of Ultrasonic Nano-Dispersing and Milling

  • efficacious nano-processing: efficient & time-saving
  • adaptable to specific product formulations
  • uniform processing
  • precisely controllable process conditions
  • reproducible results
  • cost-efficiency
  • safe operation
  • simple installation, low maintenance
  • linear scale-up to any volume
  • environmental-friendly
Ultrasonic high-shear mixing and dispersion is used to incorporate nano-fillers into polymer matrices, e.g. for high-performance adhesive production

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:

Batch Volume Flow Rate Recommended Devices
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Ultrasonic high-shear homogenizers are used in lab, bench-top, pilot and industrial processing.

Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers for mixing applications, dispersion, emulsification and extraction on lab, pilot and industrial scale.



Literature / References


High performance ultrasonics! Hielscher's product range covers the full spectrum from the compact lab ultrasonicator over bench-top units to full-industrial ultrasonic systems.

Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers from lab to industrial size.