Functional adhesive ∣ conductive adhesive, what secrets do you not know

Conductive adhesive is a kind of adhesive with certain conductivity after curing or drying. It can physically connect a variety of conductor materials together. At the same time, the dispensing needle cylinder can form an electrical path between the connected materials.

Working principle of conductive adhesive

The principle of conductive adhesive is to add conductive particles to the base material in the adhesive.

Classification of conductive adhesive

● according to the different types of conductive particles in conductive adhesive, conductive adhesive can be divided into silver conductive adhesive, gold conductive adhesive, copper conductive adhesive and carbon conductive adhesive. Silver conductive adhesive is the most widely used.

● according to the matrix resin of conductive adhesive: it can be divided into epoxy resin type, phenolic resin type, dispensing syringe silicone type, acrylic type, etc.

● from the perspective of application, conductive adhesive can be divided into general conductive adhesive and special conductive adhesive. General conductive adhesives only have certain requirements for the conductivity and bonding strength of conductive adhesives. Special conductive adhesives have some special requirements in addition to certain requirements for conductivity and bonding strength. Such as high temperature resistance, ultra-low temperature resistance, instant curing, anisotropy and transparency.

Three factors determining conductivity

Performance comparison of common conductive adhesives

Application of conductive adhesive

1. Substitute solder: make up for the defects of too high solder temperature and poor flexibility

2. Microelectronic connection: light emitting diode (LED), semiconductor packaging (IC), crystal resonator, etc. dispensing syringe is used for product packaging or component connection

3. Shield connection or conductive seal

Basic requirements for conductive adhesive in electronic industry

1. Good preservation and long service time at room temperature

2. Good adhesion and conductivity to gold-plated materials and silver-plated materials

3. Good flexibility, strong drop resistance and earthquake resistance

4. Good cold and heat shock resistance and strong reflow resistance

5. the dispensing needle is thinner, the conductive adhesive particles are thinner and the bonding strength is higher

6. It is not only suitable for dispensing the syringe, but also suitable for spraying

Precautions for use of conductive adhesive

1. Before storage and use, the cover can be opened only when the temperature is returned to room temperature, otherwise the entry of water vapor will affect the bonding force and resistance.

2. Mixing and mixing: generally, centrifugal mixing shall be within 60 seconds and defoaming mixing shall be within 30 seconds, and the heating during mixing shall not exceed 40 ℃

(Note: mixing process: rotation + revolution, the silver powder is evenly stirred; defoaming process: only rotation, and the silver powder is easy to sink if the time is too long)

3. Service time of conductive adhesive: after mixing, pour it into the dispensing bucket until it is used up. The dispensing process has been precipitated because of the large proportion of silver powder.

4. During the use of solvent-based conductive adhesive, the blast must be blown, and the solvent must be fully volatilized before bonding, otherwise the conductivity will be affected.

Key points of quality control of conductive adhesive

1. Accurate control of adhesive parameters (such as viscosity and rheological properties, resistivity, adhesive force, smoothness of dispensing equipment and process, tracking of curing process)

, state of cured product, etc.)

2. The compatibility of glue is good, and the dispensing syringe is not easy to layer; the dispensing needle the reasonable ratio of flake silver powder and other forms of silver powder; the reasonable ratio of silver powder to resin

3. When selecting adhesive, fully consider the surface process of bonding object (such as gold plating or silver plating)