Electrically conductive adhesives (ECAs), created as an alternative to tin-lead solder for use in the construction of electronic circuits, have recently gained popularity in a number of industries for their durable and abrasion resistant properties.
The electric conductivity is provided by a component that constitutes approximately 80% of
the total mass of an electrically conductive adhesive. This conductive component is placed in an adhesive component that holds the electrically conductive adhesive together.
Electric current is made possible by the conductive component’s particles coming into contact with one another. ECAs obtain their adhesive properties by joining metals such as silver, gold, copper, nickel and graphite with an adhesive component such as varnish,
synthetic resin, or silicone.
The resin could be either thermosetting (e.g., silicone or epoxy) or thermoplastic (e.g., polyimide). As for the metal filler, silver is the most widely used metal due to its low cost and conductive oxide.
The resistivity of the adhesive depends on the type and concentration of conductive component. Unlike ECAs, many adhesives ranging from epoxy to acrylic adhesives work as electrical insulators, therefore they are not suitable for use in electronic circuits.
On the other hand, some heat-sensitive electronic components may be harmed by solder reflow temperatures, which renders them non-solderable. Soldering is a process in which two (and sometimes more) items are joined by melting and placing a filler metal into the joint, the filler metal having a lower melting point than the main metal.
Even though soldering has its advantages, such as requiring low power and providing an easy operation, it may fail to attach capacitors during temperature cycling, since solder can be worn and detached. In this regard, ECAs are an excellent alternative to soldering.
Types of Electrically Conductive Adhesives
Electrically conductive epoxies are one of the best materials to use in processes where there is a high risk of mechanical and thermal cracking. Epoxies are frequently used when joining components that are heat-sensitive and therefore not suitable for soldering.
Electrically conductive epoxies give a production line flexibility and a wider range of options for electronic assembly thanks to their variety of curing temperatures and application
techniques (jetting, dispensing, screen printing).
Epoxies that are electrically conductive are available as one or two-part adhesives. Electrically conductive epoxies in one component are typically heat cured.
Therefore, it is important to choose a cure schedule carefully in order to protect delicate electronic components Electrically conductive epoxy adhesives are frequently used by manufacturers to connect parts of automotive radar and camera systems.
Because of this, they have many uses in electronic assembly, and especially in ADAS (Advanced driver-assistance system) sensors. These adhesives support ADAS, a tool that is becoming more and more crucial in ensuring the safety of the road, due to the flexibility requirements relating to processibility and application.
Electrically conductive silicon adhesives are especially made for applications that require both excellent conductivity and high flexibility. They have tightly regulated viscosity and offer an excellent defense against exposure to moisture, vibration, and thermal cycling.
Products are easily applied with automatic dispensing equipment, have outstanding tensile strength, high elongation, and protection against corrosion. Electrically conductive silicons are frequently applied to mount small components to a range of interconnect substrates.
Just as epoxies, electrically conductive silicon adhesives are often used as a connective interconnect for ADAS cameras and radars in the automotive industry. They can also be utilized in electronic assembly in a variety of sectors, including healthcare, telecommunications, and aerospace.
Importance of Process
In addition to choosing an adhesive based on the properties of the adhesive’s raw materials, it is also quite important to consider how the adhesive is processed. For instance, caution must be exercised when dispensing a silver-filled epoxy to avoid flow or spreading over or between circuit lines, which increases the risk of electrical shorts, metal migration, or particle detachment.
Bleedout, a separation and migration of one of the epoxy’s components during cure, is another possibility. On a ceramic or gold-plated surface, the epoxy’s resin or hardener/
catalyst component may creep.
Different adhesives, their level of cure, the type of surface being used, and variations in the substrate’s cleanliness and surface conditions all affect how much bleed-out occurs. Under
certain circumstances, bleed-out contaminates wire bond pad sites and may impact the wire bonds’ initial bondability as well as their long-term integrity.
It has been discovered that cleaning in an oxygen or oxygenargon plasma is effective at getting rid of the bleed-out materials.
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?matchtyp
e=b&network=g&device=c&adposition=&keyword=%2Belectrically%20%2Bconductive%20
%2Badhesive&gclid=Cj0KCQiAsdKbBhDHARIsANJ6-jcuf97UeLKB5LPSRMd_6AMa0oYSR5S148Jhf
bmBSaWJSwRWeTpXh_saAvEMEALw_wcB
• Görseller / Images by: www.istockphoto.com / www.pixabay.com
Translation and Compilation by: Murat Soygür
