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Design News, February 2013

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clean bill of health Epoxy Adhesive Withstands Sterilization Medical in the form of light (UV or lasers) or heat to form electrically conductive structural bonds. These systems are capable of bond strengths of 200 psi to 300 psi as compared to 25 psi to 50 psi for traditional PSAs. In addition, these systems also enable the use of thinner bond lines, which is a limiting factor with traditional PSA systems as they require a larger surface area to deliver the same bond strength. High-Performance Conductive Formulations Two Component System EP46HT-2Med • USP Class VI certified • High bond strength • Tg > 220ºC Hackensack, NJ 07601 USA +1.201.343.8983 main@masterbond.com www.masterbond.com In all the above cases, whether the polymer backbone is silicone, rubber, or acrylic, conductive particles create pathways within the adhesive matrix to make contact from one surface to another. As discussed previously, the conductive fillers can be comprised of a number of conductive metals in the form of solid particle formats; coated onto polymers, glass particles, or carbon; or a combination of all these options. Adhesive Research's (AR's) electrically conductive technology utilizes a homogenous carbon-based formulation in conjunction with metal particles to deliver exceptionally stable bonds to electrical contact points even under extreme stress. The electrical contacts are particularly reliable because the carbon within the polymer forms chains, which move with the adhesive as it expands or contracts against bonded substrates during temperature changes. This flexibility results in uninterrupted electrical contact for reliable electrical interconnections. Figure 2 (online at designnews.com) shows the superior conductivity and reliability for a 400 x 200 micron trace when the adhesive is formulated with carbon and metal particles as opposed to a silvercoated glass particle. The conductive adhesive can be used either as a transfer adhesive to bond two layers together, or in conjunction with other conductive materials. For example, a nickel-coated polymer fabric or a thin copper foil can be used with a conductive adhesive to form a Faraday cage for an EMI shielding application. In situations where more uniform conductivity in the x-y-z direction is required, a thin carbon fiber mesh can be employed as a core with conductive adhesive on either side to form a conductive adhesive sheet with uniform conductivity. AR's electrically conductive adhesive platform technology can be customized to meet the specific needs of the end application. Conductivity is reliably achieved in the z-axis from a few millohms to a few ohms. This enables the adhesive to be used in a wide range of applications including static discharge, grounding, shielding, and flexible interconnects where soldering was previously the only reliable option available. The adhesive thickness can be adjusted from 25 microns to 100 microns. In situations where minimal cross-talk is necessary, the formulations can be tailored to provide isolation down to 300 microns x 300 microns. As the trend toward more compact, higher functioning devices continues to evolve, electrically conductive adhesives are proving to be key components in the manufacturing process, combining bonding performance with the added benefit of conductivity. Among the conductive adhesives' most desirable characteristics is the ability to be modified for various applications depending upon the desired performance characteristics. Electrically conductive PSAs can be tailored for an application's specific needs, including the polymer backbone, the type of conductive filler used, and the careful selection of an appropriate foil or mesh substrate, if needed. As illustrated in Figures 1 and 2 (online at designnews.com), through the appropriate choice of polymer and conductive fillers, it is possible to achieve traces as small as 400 microns x 200 microns with good isolation between the traces. The use of conductive carriers with an electrically conductive PSA can assist where x-y-z conductivity is required e.g. in EMI shielding and grounding applications. The ease-of-use, custom adhesive formulation, and versatile product construction of the PSA format offers electronic device manufacturers an expanded realm of functional bonding capabilities to enhance electronic product designs' manufacturing processes. Deepak Hariharan is the electronics business manager for Adhesives Research Inc., Brian Harkins is a research scientist for the company, and Benjamin Wagner serves as a senior product development chemist. For more information, go to www.adhesivesresearch.com. M4 m e d i c a l / a s up p le me nt to de s ign ne ws f e b ru a ry 2013 [www.designnews .com]

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