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What are the four main components of SMT resistors

2018-12-04 16:14

The substrate material is generally 96% aluminum oxide ceramic. In addition to good electrical insulation, the substrate should also have excellent thermal conductivity at high temperatures. Characteristics such as electrical performance and mechanical strength. In addition, it is required that the substrate is flat and the marking is accurate. Standard to fully ensure resistance. The electrode paste is printed in place.

Resistance film:

Printed onto a ceramic substrate using a resistance paste with a certain electrical resistivity, and then sintered. Resistance paste is generally made of ruthenium dioxide.

resist film:

Covering the resistance film with protective film is mainly to protect the resistance body. On the one hand, it plays a mechanical protection role, and on the other hand, it makes the surface of the resistor body insulating, avoiding faults caused by contact between the resistor and adjacent conductors. During the process of electroplating the intermediate electrode, it can also prevent the electrolyte from eroding the resistance film and causing a decrease in resistance performance. Protective film is generally made of low melting point glass paste, which is printed and sintered.

Electrodes:

To ensure the good solderability and reliability of resistors, a three-layer electrode structure is generally adopted: inner. Medium. Outer electrode. The inner electrode is the internal electrode that connects the resistor, and its electrode material should be selected with low contact resistance with the resistor film, strong bonding force with the ceramic substrate, and good chemical resistance, making it easy to carry out electroplating operations. It is generally printed and sintered with silver palladium alloy. The intermediate electrode is a nickel plating layer, also known as a barrier layer. Its function is to improve the heat resistance of resistors during welding and buffer the thermal shock during welding. It can also prevent the migration of silver ions to the resistance film layer, avoiding the phenomenon of internal electrode corrosion (internal electrode being melted by solder), and the outer electrode tin lead layer, also known as the solderable layer. Its function is to make the electrode have good solderability and extend the shelf life of the electrode. It is generally electroplated with tin lead alloy.

Rectangular chip resistors are divided into thin film resistors and thick film resistors based on their resistance materials. The precision of thin film resistors is high, and the resistance temperature coefficient is small. Good stability, but with a narrow resistance range, suitable for precision and high-frequency fields. Thick film resistors are widely used in circuits.

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