Thick film circuit performance is controlled by the combination of substrate, conductor paste, resistor paste, dielectric paste, firing atmosphere, and package environment. Material selection should be made as a matched system.
Substrates
Alumina is widely used because it balances electrical insulation, mechanical strength, thermal stability, and cost. Aluminum nitride is selected when thermal conductivity is more important. Stainless steel, aluminum, and PI are used for specific heater and flexible resistor applications.
Conductor paste
Conductor systems may include silver, palladium-silver, platinum-silver, gold, copper, or other formulations. The selection depends on solderability, wire bonding, migration resistance, firing atmosphere, cost, and compatibility with resistor and dielectric layers.
Resistor paste
Thick film resistor pastes are selected by sheet resistance, TCR, stability, noise, power density, and trimming behavior. The final resistance depends on paste chemistry, printed geometry, fired thickness, firing profile, and post-fire trimming.
Dielectric paste
Dielectric materials provide insulation, crossover layers, protection, or capacitive structures. Key concerns include dielectric strength, pinhole control, adhesion, thermal expansion match, and compatibility with underlying conductors.
Glass frit and adhesion
Many fired thick film systems use glass frit or ceramic bonding phases. These help bind functional particles to each other and to the substrate. Adhesion can fail when substrate surface, firing profile, paste compatibility, or thermal expansion mismatch is poorly controlled.
Material compatibility
Changing one material can affect the whole circuit. For example, a conductor change may affect resistor terminations, soldering, wire bonding, silver migration risk, and dielectric crossover reliability. This is why custom thick film design should review material stack, process, and application environment together.