3.2.3 Additional Tips

Important: Ensure that your PCB manufacturer can produce the specific stack-up.

If the PCB manufacturer does not have the required materials in stock and has to order them specifically, overall production costs may be increased.

Additionally, the manufacturer may recommend a different layer stack-up that can be produced at a lower cost with the materials in stock.

In such cases, a layout can be easily adapted to the recommended stack-up by changing the width of the traces so the required impedances are preserved. With the help of an impedance calculator tool, ensure that the recommendations given in this document are respected (e.g. check that enlarging the traces satisfies the impedance while not infringing the minimal spacing).

Using an impedance calculator eases the design of proper transmission lines. The following example shows the Altium Designer impedance calculator.

After defining the PCB stack-up, you can either use the software to compute the ideal trace width that will yield a specific impedance, or input the trace width so that the tool calculates the resulting impedance.

Figure 3-6. Impedance Calculation

The ATSAMA5D2C-XULT was designed on a six-layer PCB so that the final thickness of the board should be 1.6 mm. Designs which require a different board thickness can be obtained only by modifying the central dielectric height. This does not impact the previously calculated trace impedances.