There are two types of conductive silver paste:
①Polymer silver conductive paste (dried or cured to form a film with organic polymer as the bonding phase);
② Sintered silver conductive paste (sintering film formation, sintering temperature> 500 ℃, glass frit or oxide as bonding phase). Silver powder is classified according to its particle size, with an average particle size of <0.1 μm (100 nm) as nano-silver powder; 0.1 μm <Dav (average particle size) 10.0 μm is coarse silver powder. The three types of silver conductor pastes require different types of silver powders or combinations as conductive fillers, and even different formulations in each category require different silver powders as conductive functional materials. The purpose is to use a minimum of the determined formula or film-forming process. The silver powder achieves the maximum utilization of silver’s electrical conductivity and thermal conductivity, which is related to the optimization of the film performance and cost.
There are many ways to prepare powders. As far as silver is concerned, physical methods (plasma, atomization) and chemical methods (silver nitrate thermal decomposition method, liquid phase reduction) can be used at one time. Because silver is a precious metal, it is easy to be reduced and returned to the elemental state. Therefore, the liquid phase reduction method is the most important method for preparing silver powder. That is, the silver salt (silver nitrate, etc.) is dissolved in water, and a chemical reducing agent (such as hydrazine hydrate, etc.) is added to deposit a silver powder, which is washed and dried to obtain a silver reducing powder, with an average particle size between 0.1-10.0 μm. The choice of agents, control of reaction conditions, and use of surfactants can prepare silver fine powders with different physical and chemical characteristics (particle morphology, degree of dispersion, average particle size and particle size distribution, specific surface area, bulk density, tap density, Grain size, crystallinity, etc.), the reduced powder is machined (ball milling, etc.) to obtain polished silver powder and silver flake.
According to the use of silver powder in silver conductor paste. The silver powder for the electronics industry is now divided into seven categories:
① High-sintering active silver powder for high-temperature sintering silver conductive paste
② High-dispersion silver powder for high-temperature sintered silver conductive paste
③ Highly conductive reduced silver powder
Electronic industry silver powder
④ bright silver powder
⑤Flake silver powder
⑥ Nano silver powder
Coarse silver powder
①②③ are collectively referred to as silver fine powder (or reducing powder), ⑥ The application of silver powder in silver conductor paste is in the process of being explored, and ⑦ coarse silver powder is mainly used for silver and other electrical aspects.
The largest types of silver paste currently used include:
① Low temperature silver paste for PET-based film switches and flexible circuit boards
② Slurry for ceramic capacitors
③Silver paste for varistor and thermistor
④Silver paste for piezoelectric ceramics
⑤Silver electrode paste for carbon film potentiometer
Low-temperature and normal-temperature-curing conductive silver adhesives are mainly used: low curing temperature, extremely high bonding strength, stable electrical properties, and suitable for screen printing. It is suitable for conductive and thermally conductive bonding at room temperature curing welding occasions, such as quartz crystals, infrared pyroelectric detectors, piezoelectric ceramics, potentiometers, flash tubes, shielding, and circuit repair. It can also be used for conductive bonding in the radio instrument industry. ; Can also be used instead of solder paste to achieve conductive bonding.