Talking to the Experts: Electrically Conductive Adhesives

Electronic devices are fundamental to the way that modern society lives. They're everywhere, from the computers we use at work, to the mobile phones we have become so reliant on. However, electronic devices have not always been so accessible and common place. Once, huge machines operated by experts in climate controlled laboratories, electronic devices and in particular computers are now becoming unfeasibly powerful (for their size) and extremely versatile in their application. Modern electronics are facing increasing pressure to be smaller, more efficient and more powerful while complying with stricter environmental and industrial manufacturing and operational legislation.

The design and implementation of electronic circuitry is critical to its performance but the assembly and packaging of components can be just as important. To meet the challenges of modern electronics design, engineers are finding new ways to assemble and package systems. Shorter leads and interconnects on circuitry, present an increased risk of heat damage during traditional manufacturing techniques. To combat these issues Master Bond has designed a range of environmentally friendly adhesives to achieve high bond strength without compromising electrical conductivity. AZoM spoke to the guys at Master Bond to find out more...

How do electrically conductive adhesives work?

Electrically conductive adhesives typically consist of an epoxy resin or silicone filled with randomly distributed metallic or conductive carbon particles. Once the adhesive is fully cured it provides an electrically conductive pathway between the bonding substrates via particle-to-particle contacts within the adhesive. It is possible to control the performance and conductivity of an adhesive by changing the ratio of conductive 'filler' particles to resin. A higher proportion of filler particles will result in higher conductivity but may weaken the bond strength as this will displace some of the adhesive material.

Microscopic Image of silver filler particles in an epoxy compound

Microscopic Image of silver filler particles in an epoxy compound

What are the fundamental factors used to specify and manage the 'filler' material used in the manufacture of electrically conductive adhesives?

One great thing about electrically conductive adhesives is that they can be designed and customized to suit a diverse range of applications. Apart from the obvious necessity for the filler material to be highly conductive, one of the main factors determining the material used is its stability during the manufacturing of the adhesive.

For example, the conductivity of the adhesive may be dramatically reduced if the conductive particles contain any contaminants such as, metal oxides or by-products from manufacturing. Metal oxides may form when the material is exposed to moisture or air and it is therefore very important to specify a filler material that offers chemical stability, ease of manufacture and is cost competitive. Non-reactive metals such as gold or platinum offer great conductivity but the raw material costs are often too expensive to use economically. Therefore, silver, silver-coated nickel, nickel or graphite are predominantly used. The choice of filler material largely depends on the conductivity and budgetary requirements of the specific application.

As engineers face the increasing pressure to fit greater computing power into smaller spaces, manufacturers are looking for more environmentally friendly ways to improve efficiency, boost performance and maximise quality. What do electrically conductive adhesives offer over the more traditional solder methods?

Although the tin/lead soldering technique has been widely used for making electrical connections and packaging for electronic components, it is being replaced by lead-free alternatives for various reasons. The first and foremost issue with lead solders is toxicity. Due to the toxicity and the environmental impact issues, the electronic industry is replacing lead soldering at a fast pace. To overcome these drawbacks of lead soldering, Master Bond offers various one and two component, RoHS compliant, electrically conductive systems for use in the electronic industry.

Electrically conductive adhesives can be engineered to combine bond strength, conductivity and other service-critical properties. Elongation, shock absorption, moisture resistance, chemical resistance and thermal cycling are all properties that Master Bond electrically conductive adhesives can be optimized for. Formulations can also be designed to withstand ultra-high temperatures, to bond specific substrates or to meet certain industry standards. For example, NASA low outgassing specifications etc.

The ability to fix temperature sensitive components with less risk of thermal damage is one benefit of Master Bond electrically conductive adhesives. At what temperatures do Master Bond adhesives cure? And how does this compare to traditional solder and lead-solder methods?

Many electrically conductive adhesives also offer thermal conductivity, therefore serving multiple purposes in circuit assembly, both bonding the component to the board and providing electrical conductivity while also cooling the component. Master Bond offers a range of curing options; snap cures, elevated temperature rapid curing for fast assembly and prolonged cures at room temperatures. Adhesive curing temperatures are substantially lower than the minimum temperature required for lead-free solder processing (450°F) and significantly below the 361°F minimum temperature for lead-bearing solder. Typical temperatures for rapid cure adhesives are between 250°F and 350°F.

Electrically conductive adhesives are employed in numerous industries. What options do Master Bond electrically conductive compounds offer?

Master Bond electrically conductive adhesives are designed to meet performance requirements in a wide range of applications. To accommodate a variety of manufacturing situations, adhesives can be formulated to offer different cure rates, electrical and thermal conductivity, viscosity, peel and shear strength, moisture resistance, chemical resistance etc. Special Master Bond adhesives are formulated to be low outgassing and USP Class VI biocompatible. Additionally these environmentally friendly compounds are solvent free and RoHS compliant.

What are the typical applications for Master Bond electrically conductive adhesives?

Electrically conductive adhesives are used across a diverse range of applications including but not limited to:

  • Electrical modules
  • PCBs
  • High frequency shields
  • Wave guides
  • EMI/RFI shielding
  • Entertainment systems
  • Specialty heat sinks
  • Interconnection repair
  • Digital signal processors
  • Solar cell manufacturing
  • Electrical ground plane interface
  • RFID tagging
  • Printed wiring board applications
  • LED packaging
  • Wireless headsets
  • Wafer lamination
  • Membrane switches
  • Antenna assemblies
  • Stack bonding
  • Copper/polymide (PI) circuits
  • Integrated circuitry
  • Flip chip packaging
  • Thermistors
  • Microprocessors
  • Stress control devices
  • Wire tacking
  • SMD attachment
  • Hermetic lid-seal processes
  • Communication systems
  • Electronic test equipment
  • Hybrid microelectronic packaging

As electronic circuits become more complex how do Master Bond electrically conductive adhesives help ease the burden on the engineering and design of modern electronics?

It is possible for engineers to specify a whole range of the mechanical properties of the adhesive. Offering such a diverse range of adhesives with unique and customizable properties gives engineers the confidence to meet the increasing challenges associated with the assembly and packaging of complex electronic circuitry.

Physical, functional, environmental, budgetary and regulatory requirements can all be addressed.

For more information about Masterbond Electrically Conductive Adhesives, please contact Masterbond.

This information has been sourced, reviewed and adapted from materials provided by Master Bond Inc.

For more information on this source, please visit Master Bond Inc.

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