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I am trying to design a PCB in KiCAD using the antenna described in Texas Instruments' Application Note 043. The note reads (p4):

It is also recommended to use the same thickness and type of PCB material as used in the reference design. Information about the PCB can be found in a separate readme file included in the reference design.

The README file says:

PCB DESCRIPTION: 1-2 LAYER PCB 0.25 MM NOMINAL 2-3 LAYER PCB 0.50 MM NOMINAL 3-4 LAYER PCB 0.25 MM NOMINAL THICKNESS FR4 WITH 35um Cu PER LAYER Dimensions in mil (0.001 inch) DOUBLE SIDE SOLDER MASK, DOUBLE SIDE SILKSCREEN 8 MIL MIN TRACE WIDTH AND 6 MIL MIN ISOLATION Dielectric constant for FR4 is 4.5

If I understand correctly, the first and last dielectric layers have 0.25 mm nominal thickness, while the middle one has 0.5 mm. With the 4 copper layers of 0.035 mm and the 2 layers of solder mask (0.01 mm each) that sums up to 1.16 mm total thickness, which is not standard. The closest standard thickness is 1.2 mm. Where are the 0.04 mm that are missing? Am I forgetting something?

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    \$\begingroup\$ Is there a requirement that the resulting thickness be something other than 1.16 mm? I don't think there are "standard" thicknesses so much as common ones. Where your application note is for a 2.4 GHz antenna, it is quite possible the PCB designer selected the thickness to facilitate controlled-impedance traces of a specific geometry. \$\endgroup\$ Commented Apr 21 at 21:21
  • \$\begingroup\$ @JYelton You're right, it could be completely custom. But so many manufacturers have common thicknesses of 1.6, 1.2, 1mm and making in these generally comes without added cost. It surprises me that TI would choose a thickness so close to a typical value but not that value. Not you ? \$\endgroup\$ Commented Apr 22 at 8:21
  • \$\begingroup\$ PCB manufacturers will have a variety of core and prepreg material, and can often customize the stackup to suit your needs. They often will have some basic or common arrangements for customers who don't need or care about certain details, and that's fine. When you need a specific copper thickness for power, or dielectric thickness for impedance control, or overall thickness for some physical constraint, etc., the extra options then start to make sense. \$\endgroup\$ Commented Apr 22 at 20:30

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