What Is an SMD / Chip Resistor?
An SMD (chip) resistor is a small rectangular resistor soldered directly to the surface of a circuit board. Having no leads, it suits automated assembly and is the standard in modern electronics.
How Is the Value Read?
Instead of color bands it carries a numeric code: "472" = 47 × 10² = 4,700 Ω (4.7 kΩ). "R" is the decimal separator (e.g. "4R7" = 4.7 Ω). For detail see the color codes article.
Size Codes
| Code | Size (inch) | Typical power |
|---|---|---|
| 0402 | 0.04×0.02 | 1/16 W |
| 0603 | 0.06×0.03 | 1/10 W |
| 0805 | 0.08×0.05 | 1/8 W |
| 1206 | 0.12×0.06 | 1/4 W |
Advantages
Very small, cheap, suited to automated placement and better than a leaded resistor at high frequency (low parasitic inductance).
Limitations
It carries low power and, being small, is hard to solder by hand; it needs a fine tip and practice.
Mounting and Soldering
SMD resistors are usually placed automatically with a reflow oven: solder paste is applied, the component is placed and it's soldered in the oven. When working by hand, a fine-tip iron, tweezers and a magnifier make it easier; plenty of flux helps the solder flow cleanly.
Common Mistakes
- Exceeding the power rating: small packages carry few watts; they can overheat and burn.
- Misreading the code: "472" is not 472 Ω but 4.7 kΩ.
- Mechanical stress: board flexing can crack a chip resistor.
Frequently Asked Questions
What is a 0 Ω SMD resistor for?+
What determines an SMD resistor's power?+
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