Electrically Conductive Adhesives

Electrically Conductive Adhesives Electrically conductive adhesives (ECA), developed as an alternative to tin-lead soldering for use in the manufacture of electronic circuits, have recently gained popularity in many sectors due to their durability and wear-resistant properties. In electrically conductive adhesives, electrical conductivity is provided by a component that comprises approximately 80% of the total mass of the adhesive. This conductive component is embedded within an adhesive binder that holds the electrically conductive adhesive together. Electric current becomes possible through contact between particles of the conductive component. Electrically conductive adhesives obtain their adhesive properties by combining metals such as silver, gold, copper, nickel and graphite with an adhesive binder such as lacquer, synthetic resin or silicone. The resin can be of the heat-curing type (for example, silicone or epoxy) or thermoplastic (for example polyimide). Silver is the most widely used metal as a filler material due to its low cost and the conductive oxide it contains. The electrical resistance of the adhesive depends on the type and concentration of the conductive component. Unlike electrically conductive adhesives, many adhesives from epoxy to acrylic serve as electrical insulators and are therefore not suitable for use in electronic circuits. On the other hand, some heat-sensitive electronic components may be damaged by reflow soldering temperatures, making them unsuitable for soldering. Soldering is a process in which two (or more) elements are joined by melting and placing a filler metal with a melting point lower than the base metal at the connection point. Although this process has advantages such as low power requirements and ease of operation, solder can wear away, which may result in failure to bond capacitors during thermal cycling. In this context, electrically conductive adhesives are an excellent alternative to soldering.

Types of Electrically Conductive Adhesives

Electrically conductive epoxies are among the best materials that can be used in processes where the risk of mechanical and thermal cracking is high. They are frequently used in bonding components that are heat-sensitive and therefore unsuitable for soldering. Electrically conductive epoxies offer flexibility to the production line and more options for electronic assembly due to their various curing temperatures and application techniques (pressure application, dispensing, screen printing). Epoxies with this property are available as one or two-part adhesives. Single-component electrically conductive epoxies are typically heat-cured. For this reason, careful selection of a curing program is important to protect sensitive electronic components. Electrically conductive epoxy adhesives are frequently used by manufacturers to bond parts of automotive radar and camera systems. For this reason, these types of epoxies have many applications in electronic assembly and especially in ADAS (Advanced Driver Assistance Systems) sensors. These adhesives support ADAS, a tool that is becoming increasingly important in ensuring road safety due to processability and flexibility requirements related to application. Electrically conductive silicone adhesives are manufactured especially for applications requiring both excellent conductivity and high flexibility. They have tightly controlled viscosity and provide excellent protection against exposure to moisture, vibration and thermal cycling. Products are easily applied with automatic dispensing equipment and have superior tensile strength, high elongation and corrosion protection. Electrically conductive silicones are frequently applied to mount small components on a series of intermediate interconnect substrates. Like epoxies, electrically conductive silicone adhesives are typically used as bonding interconnects in ADAS cameras and radars in the automotive industry. They can also be used in electronic assembly in various sectors including healthcare, telecommunications and aerospace.

Process Importance

In addition to selecting an adhesive appropriate to the properties of the adhesive's raw materials, it is also very important to consider how the adhesive is processed. For example, when dispensing a silver-filled epoxy, care must be taken to prevent flow and spread over or between circuit lines, which increases the risk of electrical short circuits, metal migration or particle separation. Bleeding, in which one of the epoxy components separates and displaces during curing, is another possibility. The resin or hardener/catalyst component of the epoxy may flow over a ceramic or gold-plated surface. Different adhesives, curing levels, the type of surface used and variations in substrate cleanliness and surface conditions all affect how much bleeding will occur. In some cases, bleeding contaminates wire bond pad areas and can affect the initial bonds and long-term integrity of the wires. It has been demonstrated that cleaning in an oxygen or oxygen-argon plasma is effective in eliminating outflowing materials. Translation and Compilation: Murat Soygür

Sources

• https://www.henkel-adhesives.com/us/en/products/industrial-adhesives/electrically-conductiveadhesives.html • https://www.sciencedirect.com/topics/engineering/electrically-conductive-adhesive • https://www.masterbond.com/properties/electrically-conductive-adhesive-systems matchtype=b&network=g&device=c&adposition=&keyword=%2Belectrically%20%2Bconductive%20%2Badhesive&gclid=Cj0KCQiAsdKbBhDHARIsANJ6jcuf97UeLKB5LPSRMd_6AMa0oYSR5S148JhfbmBSaWJSwRWeTpXh_saAvEMEALw_wcB • Images: www.istockphoto.com / www.pixabay.com