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FEATURE


FASTENINGS & ADHESIVES Considering eleCtriCally


ConduCtive adhesives and tapes Eurobond Adhesives guides us through the benefits and


applications of electrically conductive adhesives and conductive


adhesive tapes, and examines what you need to consider in order to specify the right solution for your project


F


ound throughout the manufacturing sector, electrically conductive adhesives and conductive adhesive tapes are


contributing to the micro design of everyday consumer electronic devices such as iPads, mobile phones, touch screens, TV’s, medical devices, flexible PCB’s, wearable conductive clothing, RFID tagging, RFI shielding and more. The adhesives tend to be thermally curing


epoxy resin-based solutions, solvent based air drying adhesives/coatings or UV-curing acrylate- based adhesives augmented with metallic fillers such as silver. Grade, shape, grain size and grain distribution of the filling material are critical influencers to optimising adhesive conductivity. However, the adhesive curing process is a significant contributor to electrical conductivity, and improper curing can cause a deterioration in performance and integrity of the bonded parts.


electrically conductive adhesives


Electrically conductive adhesives are often used as a more effective alternative to conventional soldering. As well as being lead-free, these are particularly suitable for making electrical contacts on temperature-sensitive substrates, as their curing temperature lies clearly below soldering temperature. The adhesives are also much more flexible than solder and are therefore better able to withstand vibrations. There are two types of electrically conductive


adhesives: isotropic and anisotropic. Isotropic conductive adhesives (ICA) are electrically conductive in all directions and 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 adhesives are used in many sensitive structures on circuit boards, such as LCD connections or contacting flexible circuits to rigid PCBs, or for bonding antenna structures on RFIDs. The Ecolit range of silver filled, single-


component and two component conductive adhesives from Eurobond Adhesives can easily be applied with dispensers, jets, brushes or screen-printed. Both types can cure either at room temperature or can be accelerated by thermally curing. Innovative 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 etc. In fact the list is almost endless.


considerations


Today, the range of conductive adhesives and electrically conductive adhesive tapes and their applications is vast and varied, with the products tailored to suit almost any application. So when selecting the right solution for your project, it is important to consider the following points and discuss them in depth with your chosen specialist adhesive supplier: • The type of dispensing method you will employ, such as syringe, stamp, screen print, or jet manually applied tape.


• The type of conductive filler you need – Silver, Copper, Aluminium or Graphite.


• The 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? If so, then a bespoke die cut shape made from conductive adhesive tape may be best.


2 DESIGN SOLUTIONS SEPTEMBER 2022 0


Electrically conductive adhesives and conductive adhesive tapes are contributing to the design of products such as flexible PCB’s


Other important considerations 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 re-suspend 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. However, some conductive adhesives need to


be shipped and stored in deep freeze, with the catalyst curing mechanism held in suspended animation until the material is thawed and ready to use. This type of material can have considerable and costly waste if the complete container is not used as it cannot be re-frozen.


rfi shielding


When it comes to both mobile communication devices and electrical goods, it is crucial to have good RFI shielding of components and/or products to prevent electromagnetic interferences. To help, Eurobond offers electrically conductive adhesive coated foils and conductive transfer adhesive tapes suitable for bonding, masking, shielding, surface protection, and electric vehicle battery cell electrolyte sealing tape. Electrically conductive adhesive tape will


typically have a shelf life of approximately two years and is not particularly affected by adverse temperatures during storage. Conductive tapes – which can be supplied in a roll format, of varying widths, lengths and thicknesses – 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, automotive, industrial electronics and telecoms.


Eurobond Adhesives www.eurobond-adhesives.co.uk


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