Bonding tasks in the manufacture of electronic components consistently present development and construction engineers with extraordinary challenges. The components are becoming ever smaller, more powerful and more complex. When components need to be joined in such applications, double-sided adhesive tapes are frequently used in the form of die-cuts.
Electrically-conductive adhesive tapes are of particular importance as they provide multifunctional properties and can add value to the design and function of the overall component and its manufacturing process.
The parameter of interest when dealing with electrically-conductive tapes is the resistance. As the conductivity decreases with increasing resistance, engineers are in need of materials with a low resistance, such as gold or silver (specific electrical resistance of 2.44x10-8 and 1.59x10-8, respectively). However, to manufacture cost-sensitively, often a compromise has to be found.
Since adhesive systems mostly consist of monomers and polymers, these are in principle regarded as electrical insulators, and have a resistance of about 1012 and higher. By lamination of additional conductive films, or by adding fillers to the base formulation of the adhesive, the specific resistance of the adhesive tape can be decreased, and conductivity significantly increased. When films are employed – for example thin precious metal or aluminium foils – the conductivity is established over a whole area of the tape and in all directions (X, Y and Z). That is called isotropic conductivity. The property of isotropic conductivity is used to, for example, ground large areas of metallic components.
When a relatively small percentage of particles are used compared to the adhesive formulation by volume, the adhesive system’s conductivity is only established in the Z-direction, making it anisotropically conductive. The specific resistance of anisotropic tapes significantly depends on type, size, shape and volume of the filler materials used. Use cases include establishing electronic circuits and solder-free processes.
Products such as the DuploColl EC (EC = electrically conductive) adhesive tape range from Lohmann (01908 690837) are gaining importance when both bonding and electrical properties are required. With these materials, well-established designs or component geometries can be improved. For example, the field of printed electronics today still uses rigid clamp or screw connections, which reduce the mechanical flexibility in the application and increase the volume of the overall geometry. In this case, an anisotropic adhesive tape solution offers similar properties in electrical conductivity as well as reducing the size of the construction.
Especially for applications that involve bonding on small areas, such as a ground point in a sensor/actuator (pictured), an electrically-conductive adhesive tape can remove the need for an additional wire.
The particular advantage of adhesive tapes such as the DuploColl EC range is easy handling. With light pressure, these products cling very easily to the surface of the substrates, significantly reducing the contact resistance between them and conducting the electrical signal from one point to the other, without requiring a further curing process, as liquid adhesives do. Another major advantage of pressure-sensitive tapes, when compared to liquid adhesives, are their long-term flexibility. In contrast, most liquid adhesives form a rigid solid when cured.
BOX: The new wave of electric vehicles
One of the biggest drivers of electronic goods are drivers of electric cars. According to the EV Sales Blog, nearly 3,125,000 plug-in electric cars were sold in 2020. That is an increase of 41% compared to the previous year, and amounts to a 4% market share (made up of 2.8 % battery electric vehicles and 1.2 % plug-in hybrids). It’s a huge increase in market share compared to 2019’s 2.5%, and also the first time unit sales exceeded three million.
