AN644

10

Rev. 0.3

1.6. Thermal Performance for Two-Layer Module Applications

When designing a small, two-layer based on the Si477x, the module size must be no less than 3 x 5 cm to achieve

best thermal performance, as a larger board area dissipates heat more readily. Place all LDOs on the base board if

possible, to eliminate heat sources on the module. Lowering VA from 5.0 V to 4.8 V decreases board temperature

without RF performance degradation.

Connect the IC ground paddle to the bottom layer PCB ground using vias to dissipate heat. Place large vias on the

ground paddle connected to the bottom layer ground as shown in Figure 9. Do not use vias with diameter greater

than 20 mils, as this may impact RF performance. Standard 1 mil via plating lowers thermal resistance and helps

decrease temperature.

Figure 9. Si477x Ground Paddle Via Placement

ground fill to lower thermal resistance.

For two-layer module designs, 2 oz Cu weight (70 µm) is required to maximize thermal performance. FR4-370HR

PCB material is recommended for best thermal and RF performance due to its thermal conductivity.