Surface Mount Technology
Understanding SMT for RF
SMT is the dominant assembly technology for RF circuits. The shorter connections and smaller packages reduce parasitic inductance and capacitance, extending the usable frequency range of passive components and improving circuit performance.
SMT Package Sizes
| Package | Size (mm) | Typical Use |
|---|---|---|
| 01005 | 0.4 x 0.2 | mmWave passives |
| 0201 | 0.6 x 0.3 | RF passives, DC-40 GHz |
| 0402 | 1.0 x 0.5 | Standard RF, DC-20 GHz |
| 0603 | 1.6 x 0.8 | General RF, DC-6 GHz |
| QFN | 3-7 mm | MMIC, amplifier ICs |
Frequently Asked Questions
What is SMT?
SMT mounts components directly on the PCB surface instead of through holes. Smaller packages, automated assembly, and reduced parasitics enable higher frequency operation. The standard for all modern RF circuit manufacturing.
Why is SMT better for RF than through-hole?
Through-hole leads add 1-3 nH of inductance per pin. At 1 GHz, 1 nH = 6.3 ohms reactance. SMT pads have < 0.1 nH parasitic. This allows SMT components to work at much higher frequencies with less parasitic effects.
What is the smallest practical SMT package for RF?
0201 (0.6x0.3 mm) is standard for production RF circuits to 40 GHz. 01005 (0.4x0.2 mm) is used in the most demanding mmWave applications but requires specialized placement equipment. 0402 is the most common for general RF.