Shunt Resistors are mainly used for current detection, and their core requirements are low resistance, high precision, low temperature drift, and the ability to withstand large currents without causing accuracy degradation or damage due to excessive temperature rise. Therefore, the primary considerations for its packaging design are current carrying capacity, heat dissipation efficiency, and low parasitic inductance. The common packaging forms mainly include the following categories:
Metal Strip/Tab Packages - Bolt Mounted
Structural features: This is the most common packaging for high-power splitters. The resistor body is usually made of low temperature coefficient alloys such as manganese copper in a flat strip or specific shape (such as U-shaped or S-shaped with increased length), with large-sized metal terminals (usually copper or copper alloy) at both ends and mounting holes.
Advantages:
Extremely high current carrying capacity: up to several hundred amperes or even thousands of amperes.
Excellent heat dissipation performance: The large metal body and terminals facilitate the conduction of heat to the copper foil of the heat sink or PCB. Usually needs to be used in conjunction with a radiator.
Low parasitic inductance: The flat structure helps reduce the loop area of the current path and minimize measurement errors in high-frequency switch applications.
Low thermal electromotive force: using alloys such as manganese copper and copper terminals to reduce thermoelectric effect errors.
Typical applications: motor drive, high-power power supply, battery management system (BMS), main current path detection in industrial control.
Common shapes: straight bar, U-shaped, S-shaped, special shapes with heat dissipation fins.
Surface Mount Device (SMD)
Structural features: Adopting standard SMD packaging form, but optimizing the internal structure, materials (metal alloy or thick film), and design for low resistance and high current.
Type segmentation:
Standard SMD (such as 0603, 0805, 1206, 2010, 2512): used for detecting small currents (usually a few amperes to 20-30 amperes). The resistance range is wide, but the temperature rise is significant under high current, and the accuracy and temperature drift may not be as good as specialized splitters.
Metal alloy power type SMD: packaged in larger sizes such as 4020, 4527, 5930, 7343, etc. The core feature is the use of metal alloy resistor cores (such as manganese copper), produced through precision photolithography technology, with extremely low temperature coefficient and high precision. It usually has a Kelvin Connection/4-terminal design, which includes independent current terminals and voltage detection terminals to eliminate the influence of lead resistance and contact resistance.
Type with heat dissipation pad: such as Power Metal Strip ®` (Vishay), WSLT/WSBS (Vishay), LRMAP (KOA) and other series. On the basis of standard SMD, a large exposed metal heat dissipation pad (Thermal Pad) is added at the bottom, which is soldered onto the large-area copper foil (copper plated) of the PCB, significantly improving the heat dissipation capability. The current capacity can reach 50A or even 100A or more (such as the SMD version packaged in TO-220).
Advantages:
Suitable for automated production: standard SMT process.
Compact size: saves space.
Kelvin Connection: Provides high-precision measurements (as low as 0.5% or even 0.1%).
Good heat dissipation (with heat dissipation pad type): close to the heat dissipation capability of through-hole devices.
Typical applications: Output current detection of switching power supplies, DC-DC converters, motor control (small and medium power), current monitoring in consumer electronics, and communication equipment.
Through Hole (THT)
Structural features: With axial or radial leads, it needs to be inserted into PCB through holes for soldering.
Type segmentation:
Axial Lead: A traditional cylindrical or rectangular lead that leads out from both ends. Limited current capacity and average heat dissipation.
Power type/bolt mounted type (TO-220, TO-247, etc.): Although this type of package looks like a transistor, it contains precision shunt resistor alloy sheets inside. Equipped with a metal backplate (with mounting holes) for fixing onto the heat sink, and lead wires (usually 4-wire Kelvin connections) for soldering. This is a miniaturized and standardized form of metal sheet packaging.
Advantages:
Stable installation (bolt type): suitable for environments with vibration.
Good heat dissipation (bolt type): The radiator can handle large currents (such as TO-220 up to 50-100A).
Kelvin connection optional: available on some models.
Typical applications: Medium power applications (such as desktop computer power supplies, industrial power modules), applications that require additional mechanical strength or heat dissipation. Axial type is used for low current detection with low requirements.
Integrated Printed Circuit Board (PCB)
Structural features: Strictly speaking, this is not an independent "package", but a function of directly designing shunt resistors on the PCB. Common methods include:
Use a precision PCB trace (usually copper) as a shunt resistor. Accurate calculation of wire length, width, thickness, and electrical resistivity/temperature coefficient of copper foil is required. Poor accuracy and temperature drift.
Open a window on the PCB and solder a dedicated Manganin Shunt Bar. This combines the convenience of PCB integration with the excellent performance of specialized alloys.
Advantages: Low cost (especially for wiring schemes), flexible design, and space saving (without additional components).
Disadvantages: The accuracy and stability are usually not as good as specialized discrete devices (especially pure wiring schemes), the design is complex, and precise calculations and compensation are required.
Typical applications: Large batch products that are extremely cost sensitive and do not require high accuracy (such as overcurrent protection threshold detection), or applications that require special shapes/positions.
Key considerations for selecting shunt resistor packaging:
Rated current: determines the required packaging size and heat dissipation capacity.
Power consumption/temperature rise: The square of the current multiplied by the resistance value is the power consumption, which must be effectively dissipated by encapsulation to control the temperature rise within the allowable range (temperature rise directly affects accuracy and lifespan).
Measurement accuracy requirements: For high-precision measurement, a metal alloy package with low temperature coefficient and Kelvin connection (SMD with heat dissipation pads or metal sheet/TO type) must be selected.
Space limitations: PCB area and height.
Heat dissipation conditions: PCB copper foil area, presence or absence of additional heat sinks, ventilation conditions.
Installation method: SMT vs THT, does it require bolt fixation.
Cost: Precision metal alloy SMD and metal sheet packaging have higher costs, while PCB integration has the lowest cost.
The packaging of shunt resistors is a key determinant of their performance. From metal sheet/strip bolt installation for high current and forced heat dissipation, to metal alloy Kelvin connection SMD suitable for high-precision, automated production, and small to medium power (especially with heat dissipation pad type), to traditional power type through-hole packaging (TO-220/247) and PCB integration solutions with the lowest cost but poor accuracy, engineers need to make the most suitable choice based on specific current size, accuracy requirements, heat dissipation conditions, space, and cost budget. Metal alloy Kelvin connected SMD packaging is widely used in modern electronic design due to its excellent performance and SMT compatibility.