Thick Film Heater
The term “thick film” relates to the circuit or heating element that is deposited via screen printing (0.0005” thick) on the substrate. Most ink materials come in forms of liquid or paste that can be printed. Uncured ink paste consists of metallic particles suspended in a resin or binder. When cured, the binder shrinks and hardens. This actions fuse the metal particles together and creates electrical continuity.
Inks made by mixing ceramics and metals are known as Cermet inks. Cermet inks can be fired on plane or tubular substrates of steel, stainless steel, Aluminum, ceramics and glass. Typical metallic materials include silver, gold, silver palladium, gold platinum, copper, and ruthenium. Ceramic inks are also used for the dielectric layer (glass under the circuit) and for encapsulates over the circuit layers.
Feature of metal substrate thick film heaters / resistors:
- vibration and shock resistant
- thin profile, space saving
- high watt density, high operation temperature (up to 500°C)
- customized shape and heat pattern
- fast response, uniform steady state
- cost effective at high volume
Polymer Thick Film (PTF) Heater
The production of PTF heater starts by screen printing polymeric, silver-based paste onto the polyester substrate in the desired circuit pattern. The substrate is then dried in the oven to cure or “set” the element. Finally each circuit is die cut apart and installed with terminals for lead attachment.
Heater of PTC characteristic can be obtained by mixing silver-based paste with PTC carbon compositions. The PTC carbon compositions generate resistive heat up to a specific temperature. Due to their molecular nature, they are not able to surpass this threshold. The figure below illustrates the PTC characteristic of our mirror heaters.
Compared to etched foil heating elements, polymer thick films have the following limitations:
- Polymer based flexible heater are less conductive, meaning less watt density and slower heating speed
- Polymer thick film can't withstand repeated flexing
- The maximum temperature that polymer thick film can withstand is lower