The term PTF (Polymer Thick Film) refers to the technology through which some polymeric materials are applied on the printed circuit board, usually by screen printing, to create circuit elements that can perform different functions.
It comes from the technology of PTF hybrid circuits but differs from this, in order to allow the application on the substrates of the conventional printed circuit boards, for the fact that the pastes are designed to polymerize at temperatures much lower than those necessary for the sintering on hybrid ceramic.
The inks that are used can be either conductive, resistive or dielectric and allow the creation of fixed or sliding contact elements, interconnection (crossovers), shielding against electromagnetic interference, insulating layers, fixed or variable resistors, etc…
They are usually products with particles dispersed in a matrix capable of polymerizing; according to the nature of the particles may have pastes based on silver, copper, graphite (carbon), etc…
The pastes based on silver allow to realize more layers on the same face of printed circuit boards, by means of screen printed areas which connect more points of the circuit copper layer overlapping the same; the electrical insulation is ensured by one or more layers of dielectric applied also through screen printing. A typical example is the technique of Silver Jumpers (also called Silver Cross Overs). The same technique, suitably modified, allows to obtain also through holes (Silver Trough Holes).
The electrical resistivity of this kind of product is in the range of 20-30 mΩ/□.
Similar to silver-based pastes but with copper particles as conductive element, it offers the possibility to realize, in addition to through holes, also layers dedicated to the shielding of the printed circuit against electromagnetic interference, both in reception and emission.
The resistivity of the pastes based on copper is similar to the silver based ones, around 20-30 mΩ/□.
The graphite (carbon) based inks can be divided essentially into two groups: conductive products, with values of electrical resistivity from 10 to 30 Ω/□, and resistive products, available in a wide range of resistivity values, from 100 Ω/□ to even different Ω/□. The first can be used for contacts, jumpers, shieldings, etc., while the resistive products allow to realize real electronic components at solid state, printed directly on the printed circuit boiard and coplanar to the same.
In the field of PTF technology and using resistive carbon pastes, a typical application which SILGA can offer are screen printed resistors.
Selecting appropriately the product it is possible to obtain resistors with different ohmic values and during the project step, in collaboration with the customer, it is possible to define the best lay-out configuration of the resistive network.
Finally, for particular applications, we can obtaine very tight tolerances on the ohmic value of the component through laser trimming technology.