In printed circuit board (PCB) manufacturing, conductive pastes used for via filling serve critical functions such as electrical interconnection, heat dissipation, and electromagnetic shielding. Here are some of the most common types of conductive pastes and their key features.
Silver Paste
Composition: Silver particles (nano or micron-sized), along with an organic vehicle (resins, solvents).
Characteristics:
Excellent conductivity (low resistivity, typically <10⁻⁴ Ω·cm).
Good oxidation resistance, though prolonged exposure may lead to sulfuration (tarnishing).
High cost, making it suitable for high-reliability applications (e.g., high-frequency circuits, RF modules).
Applications: High-Density Interconnect (HDI) boards, flexible printed circuits (FPC), and sensors.
Copper Paste
Composition: Copper powder, an anti-oxidation coating (e.g., silver plating), and an organic vehicle.
Characteristics:
Conductivity is comparable to silver paste, but at a lower cost.
Prone to oxidation, requiring surface treatment or curing in an inert atmosphere.
Requires low-temperature sintering to prevent copper oxidation.
Applications: Consumer electronics, LED substrates, and low-cost PCBs.
Carbon Paste
Composition: Carbon black/graphite mixed with a resin-based binder.
Characteristics:
Lower conductivity (higher resistivity, approximately 10⁻² to 10⁰ Ω·cm).
Good corrosion resistance, low cost, and excellent mechanical flexibility.
Applications: Anti-static coatings, low-power circuits, and touchscreens.
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