lectrically conductive adhesives are usually thermally curing epoxy resin-based adhesives or UV-curing acrylate-based
adhesives augmented withmetallic fillers, such as silver. Grade, shape, grain size and grain distribution of the filling material are critical influencers to optimising adhesive conductivity. However, a significant contributor to electrical conductivity is the adhesive curing process – improper curing can cause a deterioration of performance and integrity of the bonded parts. Such adhesives are often used as a more
effective alternative to conventional soldering. They are particularly suitable for making electrical contacts on temperature-sensitive substrates, as their curing temperature lies clearly below soldering temperature. In addition, the adhesives aremuchmore flexible than solder and are therefore better able to withstand vibrations; and they are lead- and solvent-free. There are two types of electrically conductive
adhesives: isotropic and anisotropic. Isotropic conductive adhesives (ICA) are electrically conductive in all directions. They are used in applications such as chip contacting and bonding of electrically conductive SMDs. Anisotropic conductive adhesives (ACA) contain
special conductive particles in the µm range, which conduct electricity only in one direction. These are used, for example, in many sensitive structures on circuit boards, such as LCD connections or contacting flexible PCBs, or for bonding antenna structures on RFIDs.
The Elecolit range of silver filled, single- component and two component conductive adhesives, which can be simply applied with dispensers, jets, brushes or screen-printed, are
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available from Eurobond Adhesives. Both the single component and two component adhesives can cure either at room temperature or the process can be accelerated by thermally curing. Hardener systems in many of the one part epoxy based adhesives develop ‘cure’ within minutes and these can be used to connect heat sensitive components to printed circuit boards, wave guide plumbing, hybrid circuit assembly, connecting ground wires to components, making conductive tracks or pathways and bonding discrete devices and hybrid circuits. Other applications include bonding
conductive paths in heated car windscreens and mirrors, RFID applications, bonding batteries to foil/film, bonding flexible film LCD’s to hard FR4 boards, circuit track repairs, populating PCB’s the list is almost endless. Today, the range of conductive adhesives and
conductive adhesive tapes and their applications is vast and varied. Conductive adhesives are tailored to suit almost any application. So, when selecting the right adhesive for your
specific project it is important to consider the following points and discuss them in depth with your chosen specialist adhesive supplier: •What type of dispensingmethod will you employ, ie. syringe, stamp, screen print or jet?
•What type of filler do you need, ie. Silver, Copper or Graphite?
•What viscosity of the adhesive, perhaps a paste or a liquid adhesive?
•Whether it should be an Isotropic or Anisotropic adhesive?
• Which pot life best suits your particular application?
• Is there a specific cure time and cure method you need to employ?
• What volume resistivity does your application require?
• Does the application require a specific bond line thickness and or specific geometry? Other points to consider are shelf life and
storage. The conductive filler in one or two part materials can potentially separate out from the base resin and sediment onto the bottom of the container, necessitating the need to mix/stir the material to evenly resuspend the conductive particles before use. Storing the adhesive in a refrigerator at around 5˚C will slow the process and help prolong its shelf-life. Some conductive adhesives, however, need
to be shipped and stored in deep freeze. The catalyst curingmechanismis held in suspended animation until thematerial is thawed and ready to use. Of course, this type ofmaterial can have considerable and costly waste if the complete container is not used as it cannot be re-frozen.
Eurobond’s electrically conductive adhesive tapes have been developed for a range of applications in the electronics industry; and are suitable for bonding,masking, shielding and surface protection. In fact the company’s products have excellent properties for the high specification demands of the electronics industry in the 21st-century. High grade acrylic, silicone and electrically conductive adhesives are used in conjunction with the best available films and metal foils to give outstanding results for high- performance consumer electronics, avionics, industrial electronics and telecoms. Applications for these include: electrical
installation; EMI/RFI shielding; anti-static applications. PCBmasking; bonding to high temperature surfaces; conductive connection and fixing. Typically, electrically conductive adhesive tape will have a shelf life of approximately two years and are not particularly affected by adverse temperatures during storage.
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