Wherever electrical components are in use, regulations and safety standards are vital to protect consumer safety. In the world of thermal management, UL certification is a critical standard to meet.
Electrical and electronic components are ubiquitous in automotive and transportation applications. Conventional internal combustion engine (ICE) vehicles contain ignition coils, engine control modules, transmission control modules, sensors, power supplies, transformers, and various other electronics. Electric vehicles (EVs) contain batteries, on-board chargers, inverters and converters, and electric motors, all of which operate at high power densities (power per unit volume or weight). At high power density, generation of heat and the resulting high temperature of the component can become a limiting factor in device operation. Thermal management materials provide a means to reducing the component temperatures, thereby improving the performance and extending the lifetime of the device.
For example, EV batteries operate at high power density during charge and discharge cycles, so many battery manufacturers use thermal interface materials (TIMs) between the battery pack and the cooling plate to maximize heat transfer away from the batteries. LORD CoolTherm® liquid-dispensed gap fillers and adhesives are excellent TIMs because they displace air and fill in the gaps between the battery cell or module and the heat sink, providing maximum heat transfer upon curing to a solid.
EV on-board chargers also operate at high power density during fast charging, and the rate of charging is limited by temperature. LORD CoolTherm® potting materials are low-viscosity liquid polymer systems that are poured over the electronics components to displace the air inside the electronic assembly and then cure to a thermally conductive solid that connects the hot electronic components to the heat sink. These materials are used to dissipate heat from the inductors and transformers in on-board chargers to allow for rapid battery recharging.
While LORD CoolTherm® gap fillers, adhesives, and potting materials improve the performance of high power density components, they must also meet important lifetime and safety standards required for any consumer electrical device. All thermal management materials are therefore tested and certified under the relevant UL standards for electrical performance, heat and flame resistance, and temperature rating.
UL certification is a symbol of trust. UL labs have developed comprehensive tests to determine the mechanical, physical and electrical characteristics of polymeric materials, ensuring that they are safe to use in electrical equipment. Several applicable UL standards govern the flammability requirements and other specific material behaviors of thermal management materials. After testing, a Performance Level Category (PLC) is assigned to the tested material.
UL 94: Tests for Flammability of Plastic Materials for Parts in Devices and Appliances
Tests for UL 94 involve applying a flame underneath a material sample. The material is observed to see if ignition occurs; if so, the time to ignition is measured in seconds. These results determine the UL rating. Lord thermal management materials meet the highest rating V0 for vertical burning test.
UL 746A: Polymeric Materials – Short Term Property Evaluations
Among the short term properties listed in UL 746A, hot wire ignition (HWI), high-ampere arc ignition (HAI) and comparative tracking index (CTI) are often requested by LORD customers. HWI involves wrapping resistance wire around a material sample to dissipate applied electrical energy. If the specimen ignites, the time to ignition is measured in seconds. Categories range from 0 to 5 with 0 being the best performance at 120 seconds or longer. HAI measures the material’s resistance to ignition when exposed to arcing, with arcing episodes being applied during testing according to a standardized procedure. Again, 0 is the best performance rating, with 120 or more arc exposures without ignition being required to achieve the high rating. CTI measures electrical breakdown, or tracking, of the material. Testing involves applying a large voltage to the material’s surface and assessing the amount of charcoal produced. A material enduring 600 volts or more will achieve the highest rating of 0.
UL 746B: Polymeric Materials – Long Term Property Evaluations
A key property governed by UL 746B is relative thermal index (RTI). Because UL 746B assesses long term reliability, the material to be certified together with a benchmark material are subjected to aging at a few elevated temperatures. Then the mechanical and electrical properties are tested periodically during aging. The actual RTI rating will be assigned based on testing results. A default RTI rating (measured in unit temperature) can be assigned without testing based on general benchmarks achieved through multi-year testing on materials with the same chemistry.
Conforming to UL standards is an important qualification for LORD thermal management materials. The certification not only ensures optimal safety, but long-term performance.