1. Composition

Conductive carrier

As you can see, conductive carrier has excellent conductivity and good chemical stability. It is not easily reduced or lost in conductivity due to the presence of active gases in the environment. The source of raw materials is rich. at the same time, in order to achieve the purpose of low resistance, the shape and particle size of conductive carrier should meet specific requirements.

Adhesive

Adhesion between the adhesive and the base material is crucial. Pay attention to the flexibility of adhesive resin. The weather resistance of the adhesive, especially high temperature and high humidity are what we take care of.

Solvent

The boiling point is the most direct parameter that reflects solvent volatilization. In silkscreen printing, solvent with a boiling point of 180 to 220°C ensures non-drying screens. And the film thickness remains basically consistent. Toxic solvents directly harm the health of workers.

Choosing non-toxic solvents is the first thing when preparing silver paste. The solubility of the solvent to the resin must be appropriate. If the solubility is too good, the viscosity will be low. It's hard for silkscreen printing.

Auxiliary

Most conductive carriers use micron powder, and additives help them disperse evenly, and prevent re-agglomeration. So we choose suitable dispersant or additive. There are often bubbles during the pulping. If bubbles cannot be effectively removed, they will cause burrs or even breakage during silkscreen printing.

The mutual performance of these four parts is directly reflected in the overall performance of silver paste. Therefore, the selection of all raw materials is not isolated. At the same time, formula is not ideal, and there is room for improvement.

The particle size and distribution of the conductive carrier will vary depending on the resin. Different packing densities directly lead to different resistance values. Solvents vary in their solubility to resins. The difference in wetting degree of the conductive carrier surface also directly affects the resistance value. The raw materials of each component interact with each other, thus determining the complexity of silver paste.

2. Conductivity

When the content of glass powder doesn't change, the resistivity decreases within a certain range as the silver powder gradually increases. When the content of silver powder is too large, the resistivity increases instead.

What's the reason? The silver powder is too much, and the glass powder remains unchanged, that is, the solid content of the paste is too much, and the organic carrier content is not enough. The viscosity of silver paste is too high, and the leveling properties are poor. It is difficult to form continuous and dense silver film during silkscreen printing. So the resistivity is too high.

When the silver powder remains unchanged, the resistivity gradually increases within a certain range as the glass powder gradually increases. The conductive property becomes worse. During the sintering process, as the temperature rises, the glass powder melts. And due to capillary action, it infiltrates and wraps the silver particles. The silver powder dissolves in the molten glass phase in the form of silver ions.

When the glass powder in silver paste is not enough, the silver powder cannot be spread on the substrate due to the lack of liquid phase. And the silver particles tend to grow in the vertical direction, resulting in poor contact between the silver particles.

When the glass powder increases to a certain value, the glass powder can effectively wet the silver powder, allowing the silver powder to fully spread on the substrate. The silver particles grow in the horizontal direction, and the silver particles are in closer contact, effectively forming a conductive network.

When the glass powder continues to increase, excess glass powder will accumulate on the surface. The conductive properties will decrease, and the resistivity will increase.

When glass powder is too much, the content of organic carrier will be low. The content of organic carrier directly affects the viscosity of silver paste. The lower the content of organic carrier, the higher the viscosity. During the silkscreen printing, The leveling property of the paste is very poor, which is not conducive to the uniform distribution. And the silver powder and glass powder are easy to agglomerate.