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I deigning a PCB for an open-source RadioSonde with 403Mhz transmissions using Si4063 ic. Now, these radiosondes are supposed to be inexpensive since there is quite tough competition in the market over the pricing. One of the major costs is due to 4 layer PCBs being currently used in the design. Since the distance between copper layers, is quite low in 4 layer PCB, the trace width is quite low (I have observed this rule of thumb that the trace width for 50 ohms is generally twice the distance between copper layers...). Now when I am calculating trace width for 2 layers 50-ohm matching, it is coming around 3mm which is quite larger than the pin size in the footprint itself. I wonder if this would cause a mismatch at the junction.

I haven't tried calculation for differential pair matching, though the problem is that this particular IC doesn't even have the differential output... it has single port 50-ohm match output. Help me with directions on how to make this PCB design economical mostly in a 2 layer PCB.

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    \$\begingroup\$ Can you make the PCB thinner? \$\endgroup\$ Oct 15, 2021 at 5:06
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    \$\begingroup\$ The wavelength at 403 MHz is, you know, 740 mm. So the mismatch at the output of the IC to 3mm trace is probably not going to cause too large of a problem. But it would be much better to make the board thin as others have suggested, because 3mm traces really are excessively large for many practical reasons. \$\endgroup\$
    – user57037
    Oct 15, 2021 at 5:50
  • \$\begingroup\$ Redesigning the board to not use controlled impedance traces at all might be an option give that your wavelength is almost a meter. \$\endgroup\$ Oct 15, 2021 at 6:18

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Instead of using a standard 1.6mm PCB (1/16"), use a 0.6mm board and then your trace width (per the rule-of-thumb that you want to use) will be 1.2mm. The Chinese prototype board houses like JLCPCB offer 0.6mm boards at essentially the same price as standard pcb and, the shipping will be lower than standard PCB because they are thinner and lighter. Good luck.

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  • \$\begingroup\$ I used 0.6mm two layer boards for 50 Ohm traces. However it was tricky to reflow it with LGA parts because the board bent easily and not all pins touched down properly \$\endgroup\$
    – tobalt
    Oct 15, 2021 at 6:02

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