What Is a Conductive Paste?
A conductive paste is a mixture of metal particles (filler), organic materials (various resins), surfactants, and polymers (binders).
A conductive paste is applied to the part to be made conductive and heat-treated to make it conductive at the same time as it is bonded. Other methods of adding conductivity include soldering and bonding with conductive tape, but the elements expected of conductive paste include lead-free, low temperature, heat resistance, and low weight.
In recent years, in particular, there has been a remarkable innovation in low-temperature technology, and its application in the semiconductor field is flourishing. In contrast to the melting temperature of solder, which is approximately 360°F (425°F for lead-free solder), materials with a processing temperature of less than 212°F are now in practical use for conductive paste. Another feature of conductive paste is that it is more flexible than solder adhesion.
Because of its advantage of being easily used at low temperatures, conductive paste is widely used in scientific experiments as well as in applied settings. For example, in scanning tunneling microscopes (STM) and other applications where there is a need for conductivity between the specimen base and the specimen, a conductive paste can be applied to the specimen without applying excessive heat to it.
Uses of Conductive Pastes
Conductive pastes are mainly used as a conductive adhesive for electronic devices used in smartphones and PCs. It is also often used in scientific experiments.
As electronic devices continue to become smaller and lighter, lower temperatures for conductive adhesion have become an essential issue for the semiconductor industry. In addition to the fact that conductive pastes are lead-free, this background is another reason why low-temperature bonding with conductive pastes is gaining prominence.
Conductive pastes are also used for in-vehicle modules such as drive recorders, where the excellent heat resistance of conductive pastes is expected to prevent deterioration of product quality even when the vehicle is hot during the day.
Principle of Conductive Pastes
Conductive pastes are made by dispersing metal nanoparticles with high conductivity in organic material and hardening the resin to give conductivity between joined objects. Ag (silver), which has high thermal conductivity, is the most commonly used metal particle mixed in conductive pastes.
Conductive pastes with silver particles are called silver pastes. Other metals include Ni (nickel), Au (gold), Cu (copper), and C (carbon).
On the other hand, there is a wide variety of organic materials and polymers that can be mixed into conductive pastes, depending on the application and the manufacturer. For example, epoxy resins, phenolic resins, acrylic resins, urethane resins, and silicone resins are used.
Although metallic nanoparticles and organic materials are mixed to prevent agglomeration, the stability, heat resistance, and other properties of conductive pastes vary depending on the combination of organic materials and polymers to be mixed.
How to Select Conductive Paste
Conductive pastes cannot be used in places where it is heated to high temperatures because of their low processing temperature. However, some products have high-temperature resistance and low degas, so it is important to select the type of conductive pastes that best suits the application.
Another feature of conductive pastes is that if it is not heat-treated, it is coated with an organic material and is not conductive. Some types can be used simply by drying without heat treatment, which hardens the resin. Note that workability, long-term storage stability, curing conditions, adhesive strength, and resistance to moisture and heat vary depending on the type of binder used.
It is recommended to use conductive pastes with a binder that is appropriate for the place to be made conductive. Since some require refrigeration for storage and some may harden and become unusable if stored for a long period, it is necessary to check the instruction manual for the conductive pastes being used.