Chip resistor (SMD)
A chip resistor is the default surface-mount resistor — a thick- or thin-film resistive element printed on an alumina substrate with metal end terminations. It's the part that shows up by the thousand on every modern PCB.
Thick-film parts laser-trim a ruthenium-oxide paste fired onto alumina to hit the target value to ±1 %. Thin-film parts sputter a nichrome layer and trim it for ±0.1 % tolerance and lower noise. End caps of nickel-barrier and tin solder make the part compatible with reflow profiles.
In plain terms
Imagine a wide pipe with one narrow section. Water still flows, but the narrow part forces a pressure drop. A resistor is that narrow section for electric charge.
Why designers use it
- Pull-up/pull-down resistors on every digital line.
- Series termination on transmission lines to damp ringing.
- Voltage divider feedback in regulators and ADC front-ends.
- Current-sense, gate ballast, snubber, and dozens of other roles.
Best for
- Digital pull-ups
- Series termination
- Feedback dividers
- RC filters
Key specifications
- Range: 0.001 Ω – 100 MΩ
- Tolerance: ±0.1 % – ±5 %
- Power: 1/32 W (01005) – 1 W (2512)
- Tempco: ±25 – ±200 ppm/°C
- Voltage rating: 15 V – 200 V
When not to use it
- When the dissipation exceeds the case rating — a 0402 burns out at 1/16 W; jump to 0805/1206 for power.
- When ultra-tight tempco is required — generic ±200 ppm/°C parts walk the operating point with temperature; pick thin-film.
- Pulse loads above the part's pulse rating — a 0603 takes far less peak energy than a 1206.
Common mistakes
- Specifying a 0402 1 % everywhere and never noticing the case has a max voltage of 50 V — split your voltage divider into series parts.
- Believing the marked code (e.g. 103) is the value in ohms — it's exponent notation, so 103 means 10 kΩ.
- Hand-soldering 0201s without flux paste — the joint rolls into a tombstone.
Where you will find it
- A USB-to-UART adapter uses 33 Ω chip resistors in series on every data line: the resistors damp the signal's rising edge enough to prevent reflections at the impedance mismatch where the trace meets the connector, eliminating the ringing that causes bit errors.
- A keyboard matrix controller uses 10 kΩ chip resistors as pull-ups on every column line: without them the microcontroller's input would float to an undefined voltage between key presses, randomly triggering key events.
- A camera flash LED uses a precise 100 mΩ chip resistor as the current-sense element: the voltage drop across it tells the driver IC how much current is flowing and limits it to the LED's maximum rating, preventing the rapid thermal runaway that destroys LEDs.
A short history
A chip resistor is a compact resistor package for dense electronic assemblies. One example is ROHM's thick-film MCR series, which uses a metal-glaze resistive element. Resistance, tolerance, temperature coefficient and rated power remain separate selection criteria; the small package does not give every chip resistor the same electrical behaviour.
Good to know
- A 0402 chip resistor weighs about 0.6 mg; SMT lines place them at 200,000+ per hour per head.
- Thick-film (the cheap default) prints a ruthenium-oxide paste; thin-film sputters a nichrome layer for tighter tolerance and lower noise.
- 0805 1206 numbers come from imperial dimensions (0.08"×0.05", 0.12"×0.06") even though they're spec'd in mm by JEDEC.