RF Electronics Chapter 11: Circuit Manufacture Page 376
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
The screens used for the printing can be made from stainless steel, with a typical fibre
diameter between 30 and 100 m, a 50 to 224 m mesh aperture and 65 to 220 m mesh
thickness with an aperture of 39 to 47%. Stainless steel screens are used for large
production runs.
Screens can also be made from polyester. Polyester screens have a shorter life but are
cheaper, and are thus used for smaller production runs. The screens have a typical fibre
diameter between 35 and 110 m, a 43 to 185 m mesh aperture and 60 to 160 m mesh
thickness with an aperture of 30 to 40%.
Pastes (Inks)
Conductivity: The conductivity of the pastes is given in terms of milliohm/square. The
resistance of a printed conductor of 10 mm x 10 mm, is the same as the resistance of a
conductor of 100 mm x 100 mm, as long as the thickness is the same.
Thick film inks [29, 30] contain precious metals, glass, and/or ceramic powders dispersed
in an organic medium. Specialized compositions create conductors, resistors, and
dielectrics for a variety of applications and operating environments. Table 11.2 shows the
typical conductivity of various conductive inks. Copper inks are difficult to use since they
require an oxygen free atmosphere in the ovens, to prevent oxidisation. The palladium
inks are used for solder pads.
Table 11.2. Comparison of sheet resistance of conductive pastes.
Conductor Material Sheet resistance (mΩ/square)
Copper 1.5
Silver platinum 2.0
Gold 3.0
Silver palladium 30
Gold palladium 30
Figure 11.9. Thick film RF circuit on Alumina. (GEC Avionics, designer Kikkert).
RF Electronics: Design and Simulation
376 www.cadence.com/go/awr
