Thick film low resistance resistors (usually in the range of milliohms to a few ohms) are widely used in fields such as current detection, power supply, and motor control due to their relatively low cost and good power processing capabilities. Its packaging forms are diverse, mainly depending on power requirements, application scenarios, and installation methods. The following are some of the main packaging forms, logically and clearly introduced:
Standard Surface Mount Packaging (SMD/SMT):
Description: This is the most mainstream form of packaging. Using thick film technology to directly print resistor paste and conductors on ceramic substrates (such as alumina), forming resistors and terminal electrodes.
Common sizes: from small packages such as 0201, 0402, 0603, 0805, to power type packages such as 1206, 1210, 2010, 2512, etc.
Low resistance implementation:
Small size and low resistance: In small packages such as 0402 and 0603, thick film technology can also achieve milliohm level resistors (such as 5m Ω, 10m Ω, 20m Ω) by optimizing the paste and design (such as short width resistors), which is commonly used for precision current detection with limited space.
Power type low resistance: Thick film technology can produce resistors with lower resistance values (as low as 1m Ω or even lower) and the ability to withstand higher power (such as 1W, 2W, 3W) on sizes 1206, 2512, and larger. This usually requires designing wider and thicker resistor paths and good heat dissipation structures (such as bottom metal heat dissipation layers).
Features: Small size, suitable for automated mounting, high cost-effectiveness, wide selection range.
Application: Current detection, current limiting, etc. in motherboards, power modules, DC-DC converters, battery management systems (BMS).
Power SMD package (enhanced heat dissipation SMD):
Description: Specially optimized based on standard surface mount packaging to handle higher power, especially suitable for low resistance (high heat generation).
Characteristics:
Metallized bottom electrode: There are large metal pads at the bottom (usually tin plated or solderable coated) that are easy to solder onto the copper foil of the PCB, using the PCB as a heat sink.
Top heat sink: Some models come with weldable metal heat sinks on the top to further assist in heat dissipation.
Size: Usually larger or thicker than standard power patches, such as 3820, 5920, etc.
Low resistance implementation: By increasing the effective heat dissipation area and optimizing the resistor design, it can withstand several watts to tens of watts of power in the range of a few milliohms to a few tenths of ohms.
Application: Current detection for high current switching power supplies (SMPS), shunt resistors in motor drivers and inverters.
Metal Electrode Face Down (MELF):
Description: A cylindrical lead-free surface mount resistor with metal cap electrodes at both ends. Thick film resistor layer printed on ceramic substrate.
Common models: MicroMELF (MMU-0102), MiniMELF (MMA-0204), MELF (MMB-0207).
Low resistance implementation: The MELF structure provides a good heat dissipation path (through metal caps and solder joints), and the resistor path design is relatively flexible. Thick film technology can provide milliohm level low resistance options in MiniMELF and MELF sizes, and has good power tolerance and stability.
Features: Good stability, strong anti pulse ability, no sensitivity (suitable for high frequency), good heat dissipation.
Applications: Automotive electronics, industrial control, current detection circuits that require high reliability and pulse resistance.
Substrate Mount/Power Resin Modules:
Description: Thick film low resistance resistors are directly fabricated on larger insulating and thermally conductive substrates (such as alumina ceramics, aluminum nitride ceramics, or copper-clad ceramic substrates - DBC) to form independent power resistor modules.
Characteristics:
Extremely strong heat dissipation: The large-area substrate directly conducts heat and can withstand power of tens to hundreds of watts.
Low inductance design: Easy to design into a structure with low parasitic inductance.
Integration: Multiple resistors can be integrated on a single substrate or combined with other components such as capacitors and MOSFETs.
Connection method: Lead out through welded terminals, screw terminals, or metal strips.
Low resistance implementation: This is an ideal way to achieve extremely low resistance (<1m Ω) and high power (>10W). Accurate measurement can be achieved by designing a wide and thick conductor path, connecting multiple resistor units in parallel, or using Kelvin connections (4 terminals).
Applications: Main current detection and pre charge/discharge resistors in high-power frequency converters, electric vehicle chargers, high current power supplies, welding machines, and servo drives.
Kelvin Connection Package (4 Terminals/Kelvin Sense):
Description: This is not an independent physical packaging form, but a key connection design method that can be applied to various packaging (especially power patch, MELF, substrate installation), specifically designed for precise measurement of voltage drop (i.e. current) on low resistance resistors.
Structure: The resistor has two pairs of terminals:
Force/Power Terminals: Larger, used to pass the measured current.
Voltage terminals (Sense/Kelvin Terminals): They are relatively fine and are led out from specific positions inside the resistor, specifically used for measuring voltage drop. This design eliminates the influence of lead and contact resistance on the current path.
The core of low resistance implementation: for milliohms or even lower resistance, the influence of lead and contact resistance cannot be ignored. A 4-terminal design is a necessary means to ensure measurement accuracy. Thick film technology can accurately design and manufacture resistor structures with separated terminals.
Physical form: It can be a specially designed SMD (such as some 2512 sizes with 4 pads), a plug-in package with 4 pins, or 4 connection points on a substrate module.
Application: For all occasions that require high-precision current measurement, such as precision power supplies, battery current monitoring in BMS, and laboratory instruments.
Leaded/Terminals package with pins/terminals:
Description: Traditional lead packaging, although not as mainstream as SMT, is still used in high-power applications that require strong mechanical connections, are easy to manually solder or repair, or require air convection for heat dissipation.
Type:
Axial lead: The resistor is in the middle, and the lead extends from both ends. Suitable for lower power requirements.
Radial lead/bolt installation: The resistor is fixed on a metal bracket or heat sink and connected through welding, screw terminals, or thick leads. Suitable for higher power.
Metal strip/strip terminals: Thick film low resistance resistors with high power may use metal strips or copper strips as terminals, which are convenient to connect to high current busbars with screws.
Low resistance implementation: Thick film resistor paste is printed on a ceramic substrate, which is then mounted in a housing/bracket with leads or terminals. The power capability depends on the heat dissipation design.
Application: Maintenance and replacement of industrial equipment, power electronics, and old power sources.
Summarize key logic:
Core objective: To achieve low resistance and effectively handle the resulting high current and high heat generation.
Core factors for packaging selection:
Power level: The higher the power, the larger the required heat dissipation area and the larger the packaging (from small SMD to large substrate/module).
Accuracy requirement: High precision measurement must use a 4-terminal (Kelvin) connection design.
Space limitation: Choose small SMD (such as 0402 low impedance) or MELF for compact space.
Heat dissipation conditions: Whether there is a heat sink and the heat dissipation ability of PCB copper foil determines whether to choose standard SMD, bottom metal SMD, or independent substrate/module.
Installation method: Automated SMT/MELF vs manual welding/screw connection (lead/terminal/module).
Cost: Standard SMD is usually the most cost-effective, while complex packages (4-terminal, high-power modules) have higher costs.
The advantages of thick film technology are reflected in its process flexibility, which enables it to adapt to various packaging requirements from ultra small SMD to large substrates. Through the optimization of materials (slurry formula, substrate) and design (resistor shape, terminal structure, heat dissipation path), it can economically and effectively achieve low resistance resistors of different specifications.
Therefore, when selecting thick film low resistance resistors, it is necessary to make the most suitable choice among the above packaging forms based on specific power, resistance accuracy, space, heat dissipation, and installation requirements.