Signal and thermal simulation is software that calculates how electrical signals, power and heat will behave in a chip's package and on its circuit board, before anything is built. A package is the small sealed case around a chip, with metal contacts that are soldered to the board. The software finds problems that simple rule checks cannot find, such as a signal that is distorted between two chips, or a part that will overheat.
Three things are simulated.
The first is signal integrity: whether a fast signal arrives in good shape. A memory signal may switch billions of times a second. At that speed, a copper track on a board behaves like a small radio antenna. Signals reflect at bends and leak into nearby tracks. The software models the tracks, the chip's package and the connectors, and shows what the signal will look like when it arrives.
The second is power integrity: whether every chip still receives a steady voltage when its demand for current jumps suddenly.
The third is thermal behaviour: how hot each part gets, and where its heat goes, through the board, the case and the air.
Consider an engineering team in Coimbatore designing the controller board for a 5-horsepower solar water pump for farms. Coimbatore makes many of India's pumps. The board holds six power semiconductors, transistors that switch the motor's current on and off thousands of times a second. It also holds a microcontroller that controls them. The board was laid out in PCB design software, and now the team simulates it. The thermal model assumes 45°C inside a closed metal box on a summer afternoon. It shows that two of the power transistors would reach 135°C, close to their limit of 150°C. The team adds more copper under those two transistors to spread the heat, and fixes them to a larger heat sink, a finned aluminium block. In the next run, the hottest transistor stays at 108°C. A signal check also shows that the track that measures the motor's current picks up noise from the motor's own power tracks beside it. So the team moves it further away.
Without simulation, the team would build a sample board, test it in a hot room and find these problems. Then it would redesign, build again and test again. Each round takes weeks. Simulation does not remove the final test, but it cuts the number of rounds.
The same kind of software checks chip packages for chip companies, between chip design in electronic design automation (EDA) software and the board. It is a specialised member of the wider family of simulation software (CAE), which checks whether mechanical parts bend, break or overheat. Engineering students often first try such simulations in a virtual lab.