There are various packaging forms for switch diodes, mainly serving different application scenarios (such as power, frequency, space limitations, heat dissipation requirements, cost) and manufacturing processes (such as through-hole insertion, surface mount). The following are some common and important types of switch diode packaging, classified by main categories:
1、 Through Hole Technology (THT)
This type of packaging has pins that need to be inserted into drilled holes on a printed circuit board (PCB) and soldered. Usually large in size, but with high mechanical strength and good heat dissipation, suitable for manual welding, high current or high reliability applications.
DO series (Dior Outline):
DO35: Slender glass package with axial leads at both ends. A very classic small signal switch diode package (such as 1N4148), commonly used in low-frequency, low current applications. The advantages are low cost and small parasitic capacitance.
DO41: A larger and stronger plastic or glass package than DO35, with axial leads at both ends. Commonly used for medium power rectification and switching applications (such as the 1N4007 series rectifier tube can also be used for low-frequency switching). The heat dissipation capacity and current carrying capacity are better than DO35.
DO15, DO27: Larger axial plastic packaging for higher power diodes. Less common in switch applications and more commonly used for rectification.
Axial Glass Package: In addition to DO35, there are other sizes of glass axial packages with similar principles but different sizes and power capabilities.
Cylindrical plastic seal (such as MELF Metal Electrode Leadless Face):
Although it is a cylinder without leads, it is traditionally classified as a package that requires special installation (patch or plug). Both ends are metal electrodes. Common ones include MiniMELF (SOD80) and MELF (SOD87). It combines the low parasitic parameters of glass tubes with the size advantages of SMD, but requires high welding process requirements. Commonly used in switch applications that require good high-frequency performance (low capacitance, low inductance).
2、 Surface Mount Device (SMD)
This type of packaging is directly mounted on the surface solder pads of the PCB and soldered through reflow soldering. Small size, light weight, and high degree of automation are the mainstream choices for modern electronic devices. There are extremely diverse types.
Small signal packaging (low power consumption/high speed):
SOD series (Small Outline Dior):
SOD323: A very small package (~1.7mm x 1.25mm) with three pins (often marked with a cathode or empty pin in the middle) and two effective electrodes. Extremely commonly used in space limited small signal, high-speed switch applications (such as digital circuits, RF switches). Parasitic capacitance and inductance are very small.
SOD523: Smaller than SOD323 (~1.2mm x 0.8mm), with two pins. Used in situations where extreme miniaturization is required.
SOD123: Slightly larger (~2.65mm x 1.6mm), with two pins and a wing shape. Very popular, cost-effective in small signal switches and small to medium current applications, easy to manually weld.
SOD80 (MiniMELF): Cylindrical surface mount package, as previously described. Good performance, but not as popular as SOD323/123.
SOD882 (DFN10062): Ultra small flat no lead package (~1.0mm x 0.6mm), bottom solder pads.
SOT series (Small Outline Transistor): Although mainly used for transistors, it is also widely used for packaging diodes (single or paired/common anode/common cathode).
SOT23: Small three pin package (~2.9mm x 1.3mm). Commonly used for packaging single diodes (with two pins) or dual diodes (such as freewheeling/clamp diode pairs in switching power supplies). Strong universality.
SOT323: Reduced version of SOT23 (~2.0mm x 1.25mm).
SOT363 (SC70): A six pin package that can accommodate multiple diode arrays, used in compact designs that require multiple independent diodes or configurations (such as bridge).
SOT223: Three or four pins, larger than SOT23, with a larger heat sink pin (usually Tab). Used for medium power switching diodes (such as Schottky diodes) to provide better heat dissipation capabilities.
Power type packaging (medium high power/switching power supply):
SMA / SMB / SMC:
SMA (DO214AC): Flat plastic package with L-shaped wing shaped pins at both ends. Commonly used in small and medium power switching power supplies (such as Schottky diodes).
SMB (DO214AA): Sizes between SMA and SMC.
SMC (DO214AB): The largest among the three, with the strongest heat dissipation capability, used for higher power switch applications.
DFN/PowerDI (such as DFN20203, PowerDI 5): Flat no lead package with large exposed solder pads (heat sinks) at the bottom directly soldered onto the PCB copper foil. Excellent heat dissipation performance, it is the preferred choice for high-performance, high-density power switch applications such as synchronous rectification. Compact in size but capable of handling large currents.
TO252 (DPAK): A larger surface mount power package with metal heat sinks (Tab) soldered to PCB copper foil. Used for high-power switching diodes (such as high current Schottky or fast recovery diodes).
TO263 (D2PAK): Larger than TO252, with stronger heat dissipation capability.
Key considerations for selection
Power/current: Power consumption and current size are key factors in choosing packaging size and heat dissipation capability.
Switching speed/frequency: High frequency applications (such as RF switches, high-speed digital circuits) require low parasitic capacitance (Cj) and low package inductance. SOD323, SOD523, MiniMELF, small-sized SOT, etc. are preferred.
Space limitations: Micro SMD packages (SOD523, SOD323, DFN) are preferred for portable, high-density devices.
Heat dissipation requirements: High power applications require packaging with good heat dissipation paths (SMC, DFN/PowerDI, TO252, TO263).
Manufacturing process: Large scale production mainly using SMD (reflow soldering); THT may be used for repairs, prototypes, or special scenarios.
Cost: Typically, standard and high-volume packaging (such as SOD123, SOT23, SMA) has lower costs.
Voltage: High reverse voltage requires sufficient creepage distance and insulation capability inside the package.
Summary Table
|Main Category | Package Name | Features | Typical Application Scenarios|
|Through hole installation | DO35 | Small signal, glass tube, axial, low-cost, low parasitic capacitance | Low frequency small signal switch|
|DO41 | Medium Power, Axial Plastic/Glass | Medium Current Switch/Low Frequency Rectification|
|MiniMELF (SOD80) | Cylindrical SMD/THT, good performance | Small signal switch with performance requirements|
|Surface mount | SOD323 | Ultra small, three pin, commonly used for small signal high-speed switches | Digital circuits, RF switches, space limited applications|
|SOD523 | Smaller than SOD323 | Extremely miniaturized application|
|SOD123 | Small, wing shaped pins, high cost-effectiveness, very popular | Universal small signal/medium to small current switch|
|SOT23 | Universal three pin package, can accommodate single or double tube | Universal switch, logic circuit|
|SOT223 | With heat dissipation pins, medium power | Medium power switching power supply|
|SMA (DO214AC) | Flat plastic package, L-shaped foot, commonly used power type | Switching power supply (Schottky, etc.)|
|| SMB (DO214AA) | Size between SMA/SMC | Medium power switch|
|| SMC (DO214AB) | SMA/SMB/SMC Maximum | Higher Power Switch|
|DFN/PowerDI | No leads, large bottom heat dissipation pads, excellent heat dissipation | Preferred for high-performance, high-density power switches (such as synchronous rectification)|
|TO252 (DPAK) | With metal heat sink (Tab), high power | High current switch|
|TO263 (D2PAK) | Larger than TO252 | Ultra high power switch|
When selecting a switch diode package, it is necessary to conduct a comprehensive evaluation based on information such as power consumption, thermal resistance (R θ ja), junction temperature, installation method, and recommended pad design in the datasheet of the specific device.