A significant proportion of the total market for microelectronics has been captured by thick film circuitry. In particular they have found use in computers, automobile and medical electronics; and in military and consumer durables applications. These circuits are being developed intensively as a second generation printed circuit board, to which discrete active devices are bonded to produce a hybrid circuit; and recently they have been used as an interconnection pattern for silicon devices in medium scale integration.
Thick film circuits are made by successive screen printing, drying and firing operations. The first step is to screen and fire a pattern of conductive dispersion onto a ceramic substrate. Resistors and dielectric layers are then added by succesively screening and firing patterns in registration with the first, using the appropriate dispersion to obtain the desired electrical properties. The resultant circuit is hard, adherent and abrasion resistant, capable of dissipating up to 50 W/sq. in. resistor area, and can operate in unfavorable ambient conditions withour the need for encapsulation.
The number of screen printable dispersions available to this technology has multiplied; they can, however, be classified into three categories, namely those for conductive, resistive, and dielectric applications.
Resistor dispersions are classified according to the resistive pigment employed; the properties of the different dispersions are discussed. Conductive inks are discussed according to the noble metal used and the composition of the glassy binder. Dielectric dispersions are discussed according to the end use of the dielectric layer, i.e. as a cross-over insulation and as a capacitor dielectric.
