What are the differences between SOT-323 and SOD-323 packaging

What are the differences between SOT-323 and SOD-323 packaging
introduction
In the field of electronic components, the packaging form directly affects the performance, reliability, and applicable scenarios of the device. SOT-323 (Small Outline Transitor-323) and SOD-323 (Small Outline Diode-323), as two common surface mount packages, have similar names but significant differences in design goals, physical characteristics, and application scenarios. This article will compare the core differences between packaging standards, physical structure, electrical performance, and application fields from four dimensions.
1、 Encapsulation standards and naming logic
1.1 JEDEC Standard Definition
SOT-323 and SOD-323 both follow the standardized specifications developed by JEDEC (Joint Electron Device Engineering Committee), but belong to different types of packaging:
SOT-323: classified as a transistor package, mainly used for semiconductor devices such as transistors and MOSFETs.
SOD-323: Classified as a diode package, specifically designed for diodes, ESD protection devices, and other applications.
1.2 Naming Logic
SOT (Small Outline Transistor): emphasizes the "transistor" attribute, with subsequent numbers indicating the number of pins or variants (such as SOT-23 with 3 pins and SOT-323 as an improved version).
SOD (Small Outline Diode): emphasizes the "diode" attribute, and the numerical part also represents the pin configuration or size level.
2、 Comparison of Physical Structures
2.1 Pin configuration and size
Characteristics SOT-323 SOD-323
Pin count 3 pins (standard type) 2 pins (standard type)
Size (mm) approximately 2.1 × 1.25 × 0.9, approximately 1.6 × 0.8 × 0.6
Pin spacing 0.65mm 0.5mm (more compact)
Typical devices include transistor, double transistor (6-pin) diode, ESD protection device
2.2 Structural Features
SOT-323：
Adopting a single row pin layout, it is suitable for transistors that require three control terminals (such as base, collector, and emitter).
The metal shell design improves heat dissipation efficiency and is suitable for medium power scenarios (such as Johnson&Johnson's BAS40W-AU Schottky diode with a rated current of 0.2A).
SOD-323：
Minimalist dual pin design, occupying less PCB area, suitable for high-frequency or high-density circuits (such as NXP's varactor diode, used for tuners, etc.) VCO）。
The plastic packaging material complies with UL 94V-0 fire protection standards (such as Dongwo Electronics' SD36C ESD device) and is suitable for industrial grade environments.
3、 Differences in electrical performance
3.1 Comparison of Typical Parameters
Parameter SOT-323 (taking BAS40W-AU as an example) SOD-323 (taking SD36C as an example)
Working voltage 40V 36V
Maximum current 0.2A 5A (peak pulse current)
Reverse leakage current 1 μ A (typical value) 1 μ A (typical value)
Response time nanosecond level (Schottky diode)<1ns (ESD protection)
Special function quick switching, low forward voltage drop, high-power ESD protection, tuning ratio 8.9
3.2 Application scenario adaptation
SOT-323：
Low power amplifier and switch: such as the small signal transistor in the RF module of a mobile phone.
Power management: MOSFETs are used for lithium battery protection circuits.
Automated production: Compliant with JEDEC automatic SMT standards and compatible with SMT processes.
SOD-323：
Electrostatic Discharge (ESD): protects sensitive components such as USB interfaces and display screens (such as the SOD-323 ESD device from Lei Mao Electronics, which can withstand ± 18kV air discharge).
High frequency tuning: Variable capacitance diodes are used in 5G base station RF modules (such as NXP products, with a tuning ratio of 8.9).
Power stabilization: Zener diodes achieve precise voltage reference.
4、 Design selection suggestions
4.1 Core principles of selection
Considerations for SOT-323 Applicable Scenarios SOD-323 Applicable Scenarios
Pin requirements require 3 control terminals (such as transistors) and only positive and negative poles (such as diodes)
Medium density circuits with limited space (such as consumer electronics motherboards) and ultra-high density designs (such as inside mobile phones)
Low power demand (<1W), low power but requiring high transient protection (such as ESD)
Frequency characteristics: Audio to RF frequency band (<5GHz), microwave frequency band (such as 5G communication)
4.2 Typical Cases
SOT-323 case:
Bluetooth earphones: using SOT-323 packaged MOSFET to control power switch, achieving low-power standby.
Automotive ECU: The transistor is used to control the window motor and needs to withstand a temperature range of -40 ℃ to 125 ℃.
SOD-323 case:
Smartphone: SOD-323 ESD device protects Type-C interface to prevent static electricity from damaging the main control chip.
Base station RF module: Variable capacitance diode achieves frequency tuning to ensure signal stability.
5、 Summary
The difference between SOT-323 and SOD-323 packaging is essentially due to the different types of target devices:
SOT-323: Designed for active devices such as transistors and MOSFETs, emphasizing medium power control and heat dissipation capabilities.
SOD-323: Optimize passive devices such as diodes and ESD protection devices, focusing on high-frequency response and space efficiency.
When designing, it is necessary to consider specific circuit requirements, weigh the number of pins, power capacity, frequency characteristics, and cost factors, and choose the most suitable packaging form. With the trend of miniaturization of electronic devices, the proportion of SOD-323 in mobile terminals continues to increase, while SOT-323 will still occupy an important position in the field of power control.