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<\/p>\nElectrically conductive adhesive products are primarily used for electronics applications where components must be held in place, and electrical current can be passed between them.<\/p>\n
Depending on the gap between components, most general adhesives (such as anaerobics, cyanoacrylates, epoxies, and acrylic-based adhesives) act as an electrical insulator. In addition, some offer improved thermal conductivity to help with thermal management of electronic components and heat sinks, directing heat away from sensitive components. Because in many cases (particularly when using an anaerobic or cyanoacrylate adhesive) there is no glue line control and effectively parts are touching (with adhesives filling in microscopic crevices), some electrical charge can still be transferred as there is enough metal to metal contact still occurring.<\/p>\n
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Certain temperature-sensitive electronic components cannot be soldered because the intense heat of liquid solder and the soldering iron can cause damage to the component. This type of application calls for an electrically conductive adhesive that can be used instead of solder. PCBs with components attached to both sides can also benefit from using an electrically conductive adhesive as the assembly process is easier without the risk of components dropping off the underside when parts are soldered on the top. Furthermore, when using electrically conductive adhesive for an entire electrical assembly, it negates the requirement to undergo a solder re-flow process.<\/p>\n
Applications for electrically conductive adhesives aren\u2019t just limited to bonding components onto PCBs or die attach; they can be very useful for other electronic applications where substrates are temperature sensitive \u2013 such as for touch-panels, LCD displays, coating and bonding RFID chips, and mounting LEDs. Solar cells also use adhesives instead of solder as there is less warpage and damage to the sensitive wafers that make up solar cells.<\/p>\n
There are some vital points to consider when selecting an electrically conductive adhesive:<\/p>\n
Electrically conductive adhesive can be based on several different chemistries:<\/p>\n
As with many things in life, there are certain trade-offs. In the case of electrically conductive adhesive they are:<\/p>\n
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Conductive fillers:<\/p>\n
| \n Material<\/b><\/p>\n<\/td>\n | \n Conductivity (1\/(\u2126m))<\/b><\/p>\n<\/td>\n | \n Cost<\/b><\/p>\n<\/td>\n | \n Comment<\/b><\/p>\n<\/td>\n<\/tr>\n Ag (Silver)<\/p>\n<\/td>\n 6.29 x 107<\/sup><\/p>\n<\/td>\n Very high<\/p>\n<\/td>\n Best material but very expensive.<\/p>\n<\/td>\n<\/tr>\n Cu (Copper)<\/p>\n<\/td>\n 5.95 x 107<\/sup><\/p>\n<\/td>\n High<\/p>\n<\/td>\n Beware of impurities and material strength.<\/p>\n<\/td>\n<\/tr>\n Al (Aluminium)<\/p>\n<\/td>\n 3.77 x 107<\/sup><\/p>\n<\/td>\n Medium<\/p>\n<\/td>\n Limited conductivity.<\/p>\n<\/td>\n<\/tr>\n Fe (Iron)<\/p>\n<\/td>\n 1.03 x 107<\/sup><\/p>\n<\/td>\n Low<\/p>\n<\/td>\n Adhesive becomes very thick, heavy, and difficult to dispense. Very What are conductivity, resistivity, and dielectric strength? And what do the measurements mean? Looking at technical datasheets comparing products can be very confusing. The industry uses so many different units of measurement, and it is very difficult to compare competitor products when nobody is using the same test methods or UOM. For this reason, it is always a good idea to test the adhesives to check suitability rather than condemn an adhesive based on comparing technical datasheets.<\/p>\n This pertains to electrically insulating adhesive i.e. the electricity must not be conducted. Many potting and encapsulation applications require an epoxy glue with high dielectric strength.<\/p>\n This is the maximum voltage the adhesive can withstand before it is destroyed. Another term for dielectric strength is \u201cbreakdown voltage.\u201d<\/p>\n The standard industry test is ASTM D-149. Adhesive thickness and the test temperature affect the results. So, it is important to compare like-for-like!<\/p>\n In the US, dielectric strength is often specified as volts per mil (a thousandth of an inch). Whereas elsewhere, it is mainly V\/cm (or mm or m)<\/p>\n To convert:<\/p>\n As a comparison, typical dielectric strengths of different adhesive types are:<\/p>\n Anaerobic<\/p>\n<\/td>\n 11 kV\/mm<\/p>\n<\/td>\n<\/tr>\n Cyanoacrylate<\/p>\n<\/td>\n 25 kV\/mm<\/p>\n<\/td>\n<\/tr>\n Structural Acrylic<\/p>\n<\/td>\n 30-50 kV\/mm<\/p>\n<\/td>\n<\/tr>\n Heat Cure Epoxy<\/p>\n<\/td>\n Between 17 and 45 kV\/mm<\/p>\n<\/td>\n<\/tr>\n 2-Part Epoxy<\/p>\n<\/td>\n 15 to 25 kV\/mm<\/p>\n<\/td>\n<\/tr>\n UV Curable Adhesive<\/p>\n<\/td>\n 12-30 kV\/mm<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n This is the ability of the adhesive to store a charge (electric flux). The temperature and glass transition temperature (Tg) of the adhesive affect its ability to store charge. Insulating properties change above and below the Tg. So, the higher the Tg, the better the retention of dielectric properties at elevated temperatures. Typical values for insulating epoxy glues are around 4 to 6 at around 1 mHz.<\/p>\n This measures the electrical conductivity or electrical resistance of materials, taking into account sample dimensions (hence the \u201cvolume\u201d part). Test standards associated with this are the old MIL STD-883, ASTM D2739, and ASTM D257-99, a test method for measuring DC resistance or conductance of insulating materials. Units of measurement associated with Volume resistivity are typically Ohm\u2219cm. Accordingly, the lower the figure, the more electrically conductive the adhesive is.<\/p>\n Isotropic conductive adhesives are electrically conductive in all directions and are therefore ideal for die attach, chip bonding, attaching SMDs, etc. Anisotropic conductive adhesives only conduct electricity in one direction. Sensitive electronic components such as LEDs, LCDs, and RFIDs use anisotropic conductive adhesives.<\/p>\n For further help and advice, product recommendations, and information about Permabond\u2019s adhesives for electronic components, please feel free to contact<\/a> Permabond, and we will arrange for our chemists to assist you further.<\/p>\n |