Why Thermal Simulation?
The initial work flow is to start with the development of products. When you have the first time problems with your product, you need to find the root of the trouble. This is normally done by measurements in the laboratory. But when you design the next product or create the redesign, you better apply design rules to avoid these errors. An efficient work flow contains both, measurements and simulations to predict reliable product quality.
The famous quote of Tony Kordyban
"Nobody trusts a computer simulation except the guy who did it, and everybody trusts experimental data except the guy who did it.
Why not combine the two and get results everybody can mistrust a little."
Monitoring temperatures is often necessary when doing tests on electronic circuits or prototypes. In many cases the failure of semiconductors, transformers and other components occur due to thermal overload. Observing the temperature of critical components during a test can prevent this. Temperature measurements are challenging due to accessibility, size and material of components. It is often unknown how measurement errors occur, unreliable temperature measurements are very common without noticing. Errors of a few tenths degrees Celsius are no exception.
Sources of temperature measurement errors
- Thermocouple wires need to be brought into a housing
- Difficult to have a good thermal contact to components
- Access to components on dense PCBs
- Impossible to measure temperatures inside semiconductors (junction temperature)
- Difficult to measure under components
- Difficult to measure small SMD parts (0201, 01005)
Measurement with Thermocouple
Thermocouple thermometers exist in various designs. The thermocouple sensor (hot-junction) consists of two wires of different metals that are welded. This probe cable needs to be placed inside the housing. Standard Thermocouples are only suitable for measurements of liquids and gases. But there are special sensors with ring terminals available that are better suitable for surfaces. The accuracy of measurements with thermocouples depends on a good thermal contact with the (hard flat) surface of electrical components.
Measurement with IR-Thermometer or Camera
Any object warmer than 0 K (-273 °C) transmitting electromagnetic waves, especially in the infra-red spectrum. This infra-red radiation can be measured with an IR-thermometer. The advantage of IR-thermometers is that they don't need a physical contact with the measured surface. It is possible to measure temperatures on moving objects or on parts with hazardous voltages. Specific emission coefficients must be set to get correct values that correspond with the measured surface. By painting the surface with special paint (well-defined emission coefficient) measurement errors will be greatly reduced.
Limitations of IR-Cameras:
- Cameras with a resolution greater than 320x240 pixel are expensive
- Pictures need to be calibrated to emission coefficient for all materials
- Reflexions on metal surfaces can influence the results
- Results have a tolerance of ±2% and more
- Only measurements of surface temperatures are possible