Frequently Asked Questions
Electrically conductive adhesives can be either isotropic (ICA) or anisotropic (ACA). Both types use a dispersion of metallic particles in a polymeric matrix to induce conductivity. Copper, nickel, gold and silver have commonly been used. Adhesives based on either thermosetting or thermoplastic polymers are available, including epoxies, silicones, polyimides, etc.
Isotropic conductive adhesives exhibit high loading of filler (e.g. silver, typically 70-80wt%, 25-30vol%) and are conductive in all directions. Conductivity is dependent on touching-contact between the silver flakes and the substrate/component surfaces. Isotropic adhesives have generated significant interest as solder replacements in surface mount assembly, particularly with increasing legislation regarding the use of lead.
Anisotropic adhesives, often known as Z-axis adhesives, contain a lower concentration of metallic particles (typically 5-20vol%) and only conduct in one direction. Conductive joints are produced with ACAs by pressing component and substrate together until the metal particles (usually silver- or gold-coated spheres) bridge the gap. A disadvantage of ACAs is that it is difficult to determine the exact amount of pressure and heat necessary to cure the adhesive and achieve the required conductive path. The use of ACAs in flip-chip technology and liquid crystal displays (LCDs) has increased in recent years.
The advantages offered by electrically conductive adhesives include:
- reduced costs through reduction in number of processing steps
- low curing temperatures; low thermal stresses
- no lead (Pb) content
- ability to accommodate reducing assembly size and component pitch
- better fatigue resistance than solder joints
- processing characteristics (e.g. curing temperatures) and other properties (e.g. CTE) can be better matched to specific substrate and application requirements
- no fluxing requirements
- rework potential
- compatibility with a range of substrates including non-solderable materials
Disadvantages associated with use of conductive adhesives may include:
- insufficient fundamental knowledge
- lack of long-term performance data, compared with solders
- electrical performance during life, particularly joint resistance
- compliance with Mil/company specification
- time necessary to develop the process and train operators
- higher electrical and thermal resistance compared with solders
FAQ: How reliable are Electrically Conductive Adhesives (ECAs)?
FAQ: Can Electrically Conductive Adhesives (ECAs) be reworked?
Case study: Conductive adhesive for ultrasound catheter
Sticking to the path of good conduct - the future for ECAs (only available to TWI Industrial Members)