Surface mount device (SMD)

Surface-mounting devices (SMD) are developed on the basis of the original Dual Inline Package (DIP) devices. They are an important indicator for the development of through-hole technology (THT) to SMT and are also important for the development of SMT. driving force. Surface-mounting devices mainly include semiconductor discrete devices and integrated circuit ICs.

1, Semiconductor discrete device

Typical package types for semiconductor discrete devices are small outline packaged SOD and small outline packaged transistors SOT

(1) Small outline package diode. Small outline packaged diodes (SODs) are available in both cylindrical and rectangular packages.

The cylindrical diodes are available in LL34, LL41, and DL41. The cylindrical diodes are packaged in a glass package. The diode chip is packaged in a glass tube with electrodes. The glass tube has a metal cap positive and negative electrodes at both ends, and the side with the black channel is usually the negative electrode. The package size is 0805., 126, 2309 and so on.

The chip-type light-emitting diode is a newly developed product in recent years. It is characterized by small size, high light intensity, low power, high reliability, long life, and is mainly used for LCD backlight, automotive instrument lighting and surface mount structured electronic products, etc.

(2) Small outline package transistors. The package form of small outline package transistor (SOT) mainly includes SOT-23. SOT-89 SOT-143, SOT-252 and so on.

1. SOT-23, SOT-23 is the most commonly used triode package form, with three wing-shaped pins, namely collector, emitter and base, which are arranged on both sides of the long side of the component, of which the emitter and the base is on the same side, the lead material is No. 42 alloy, the strength is good, but the weldability is poor. The SOT-23 operates at 150-300 mW and is commonly found in small power transistors, FETs, and compound transistors with resistor networks.

2. SOT-89.SOT-89 has three thin short pins distributed on one side of the transistor and the other side is a metal heat sink connected to the base to increase heat dissipation. SOT-89 is suitable for higher power applications and consumes 300mw to 2w. This type of package is commonly used in silicon power surface mount transistors.

3 SOT-143, SOT-143 has 4 wing-shaped short pins, which are led out from both sides. The one with a larger width in the pin is the collector. Its thermal performance is basically the same as that of SOT-23. This type of package is commonly used in dual-gate FETs and high-frequency transistors.

4. SOT-252, SOT-252 power consumption between 2-50w, is a high power transistor. The pin distribution is similar to that of SOTs. Three pins are pulled out from one side. The middle one pin is short and has a short flat shape. It is a collector and is connected to a larger pin at the other end. This pin is a heat-dissipating copper sheet.

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