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SMD Resistor
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SMD resistor is a passive electrical component that implements electrical resistance. An SMD is any electronic component that is made to use with Surface Mount Technology (SMT). SMT was developed to meet the ongoing demand for printed circuit board (PCB) manufacturers to use smaller components that are faster, more efficient, and cheaper. SMDs are smaller than through-hole resistors and instead of having wire leads that go through PCB, they have terminations that are soldered to pads on the surface of the board. This eliminates the need for holes in the board and allows both sides of the board to be used more fully.
SMD resistors are available in two types: flat and cylindrical (MELF).
Flat resistors are rectangular with metallized ends. The case type is determined by the dimensions and the maximum power depends on this size. Two systems are used to code the case and its dimensions. The code, dimensions and power are given in Table 1 in the imperial system and in the metric system in Table 2.
Table 1. Imperial code system
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Resistor case code
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Length (in)
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Width (in)
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Power (W)
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01005
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0.016
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0.008
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0.031
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0201
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0.02
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0.01
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0.05
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0402
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0.04
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0.02
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0.062
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0603
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0.06
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0.03
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0.1
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0805
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0.08
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0.05
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0.125
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1206
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0.125
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0.06
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0.25
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1210
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0.125
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0.10
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0.5
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1812
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0.18
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0.125
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0.75
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2010
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0.20
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0.10
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0.75
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2512
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0.25
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0.125
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1
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Table 2. Metric code system
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Resistor case code
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Length (mm)
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Width (mm)
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Power (W)
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0402
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0.4
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0.2
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0.031
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0603
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0.6
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0.3
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0.05
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1005
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1.0
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0.5
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0.062
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1608
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1.6
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0.8
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0.1
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2012
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2.0
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1.25
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0.125
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3216
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3.2
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1.6
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0.25
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3225
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3.2
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2.5
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0.5
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4532
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4.5
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3.2
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0.75
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5025
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5.0
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2.5
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0.75
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6332
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6.3
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3.2
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1
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Cylindrical resistors with metallized ends - MELF (Metal Electrode Leadless Face).
The code, dimensions and power are given in Table 3.
Table 3. MELF resistors codes
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Name
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Code
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Length (mm)
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Diameter (mm)
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Power (W)
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MicroMELF (MMU)
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0102
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2.2
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1.1
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0.2 – 0.3
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MiniMELF (MMA)
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0204
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3.6
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1.4
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0.25 – 0.4
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MELF (MMB)
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0207
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5.8
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2.2
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0.4 – 1.0
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Learn more about EIA-96 SMD resistor code.
To determine the value of a SMD resistor by the markings found on the device please use our online SMD Resistor Code Calculator.
Frequently Asked Questions
What is the difference between thick film and thin film SMD resistors?
The difference lies in the fabrication methodology and electrical performance stability:
- Thick Film Resistors: Manufactured by screen-printing a conductive paste onto a ceramic substrate. They are cost-effective and have high power handling capabilities, but exhibit lower precision (typically ±1% to ±5%) and higher thermal noise.
- Thin Film Resistors: Created via vacuum sputtering a microscopic uniform layer of resistive metal onto the substrate. They offer extreme precision (down to ±0.01%), excellent thermal stability, and exceptionally low noise profiles, making them mandatory for instrumentation amplifiers, medical hardware, and RF circuits.
How do SMD resistor case sizes (like 0805 or 0603) relate to their power dissipation ratings?
The structural dimensions of an SMD resistor package directly dictate its surface area and its ability to radiate thermal energy into the PCB plane. Case sizes use standard imperial naming codes representing length and width measurements: an 0805 package measures approximately 0.08 × 0.05 inches.
- An 0603 package is typically rated for 0.1 W (1/10 W).
- An 0805 package handles up to 0.125 W (1/8 W).
- A larger 1206 package safely dissipates 0.25 W (1/4 W).
Exceeding these continuous wattage limitations causes localized thermal expansion, shifts the internal resistance value, and can crack the solder joints.
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