Using thick-film materials in EV heating applications

Sponsored by Heraeus Electronics

Thick film technology is well established in the automotive industry for high reliability circuitry, challenging sensor applications, and robust passive component needs. With the evolution of electric vehicle (EV) and battery management systems (BMS), the needs for thick film materials are expanding once again. Electronic content per vehicle is doubling and tripling in comparison to current internal combustion engine (ICE) vehicles, and this will expand depending on the level of driving autonomy.

One key difference comparing EV to ICE is the waste heat generation. ICE vehicles have utilized this waste heat for several purposes including in-cabin heating. However, EVs must utilize active heating systems, as the waste heat generated from the battery systems is not sufficient to fulfill the needs for cabin comfort. Additionally, battery management systems are required to provide critical temperature control for startup, operation, and charging of the battery pack. This is particularly needed for EV use in colder climates.

Thick film is extremely well suited for this application because of the heating precision and repeatability, space constraints, design flexibility, and power handling capabilities of the technology. A heater is very simply a circuit with controlled resistance to output a desired temperature at a given power input. Depending on the choice of materials, thick film heaters can be self-limiting, or they can be designed with high or low temperature coefficient of resistance depending on the control systems desired. And thick film heaters can be built on numerous substrate types compatible to operating temperatures from below zero to upwards of 700°C with nearly unlimited power requirements.

Most commonly thick film heaters are built on stainless steel, but there are also material systems available on polymer substrates, glass, oxide and nitride-based ceramics, and aluminum. There are long-running, commercialized uses for each of these types.

Heaters built on stainless steel substrates have been a popular choice for many applications over the past years because of their high reliability, extended lifetimes, temperature cycling, and power handling capabilities. These characteristics make them a great choice for automotive applications, and this is evident from their current use in the EV space for BMS and cabin comfort. Positive thermal coefficient (PTC) block heaters are the incumbent technology for heating applications in vehicles, however thick film heaters can handle high power density even in the smallest space available, much higher then what you could realize with conventional PTC blocks (stacked in an aluminum gasket). Thick film heaters can also run at much higher temperature than PTCs, as PTCs lose their self-controlling effect when operating at high temperatures or even degrade.

Heraeus provides a full system of insulator, conductor, resistor, and protective layers including the recently released breakthrough, SD1020, which specifically addresses the current CTE mismatch between the existing thick films and stainless steel substrates, thus resulting in improved, powered long-term reliability. SD1020 is a single paste applicable on 300 and 400 stainless steel types.

The EV industry is making significant progress in market penetration especially with the recovery of the automotive sector as we come out of the grips of a global pandemic. In the meantime, suppliers are continuing to push boundaries of cost, efficiency, and battery range to further this success. The next logical step for heater technology in this direction is a substrate with lighter weight and improved thermal conductivity over stainless steel. For this case, we land on aluminum.

Heaters built on aluminum bring new challenges that require innovative solutions. Stainless steel compared to aluminum heaters are not created equal. First, the processing temperature of thick film on stainless steel and aluminum are significantly different (850°C v. 550-575°C respectively) which leads to system constraints that must be taken into consideration. This leads to design rules for each system that are quite a bit different to deliver similar heater properties between the two substrate types. The use of DC (as opposed to AC) is becoming clearly established which also requires a clear understanding of thick film heater technology. Voltages continue to increase which as well requires high design competency.

Heraeus is your go-to partner for these solutions with expertise in materials technology and significant prototyping resources to commercialize your designs quickly. With a track record over 50 years in the thick film industry, Heraeus continually demonstrates the quality and innovation customers seek for their critical projects.

Applications:

Automotive: electrical vehicle battery thermal management, cabin and comfort heating, heaters for sensors in autos, incl. advanced driver assistance
Industrial: food service, white goods, thermal print heads, e-cigarettes
Semiconductor: wafer processing
Aerospace: instrumentation, sensors
Medical: analytical equipment, temperature optimization for sensors

Advantages of Thick Film