To achieve a thermal equilibrium, the board has to be cooled. A good cooling environment (e.g. when strong fans are present) will lead to a low temperature and suppressed cooling (e.g. in an enclosure) to a high temperature (at same power).

Ambient temperature:

The air temperature in vicinity of top and bottom side.

Fixed Heat exchange:

One way to simulate cooling is to perform a hydrodynamic flow field calculation, which is by far too time consuming and not appropriate for our purpose. PCB-I uses an approach known from mechanical engineering. The quantity, which can parameterize the heat flux to the ambient, is called heat transfer coefficient h (W/(m²K)). The larger h, the more effective heat can flow to the ambient. h is not a material property! PCBI-Physics uses a total value h, which is the sum of convective and radiative contribution.

Heat exchange calculator:

A standard value for h is between 10 to 12 W/m2K. But h depends on power, the board size, the board orientation and the ambient air temperature. The calculator gives a good estimate working in most situations.

• Freestanding: Board in the lab like you would place it in front of an infrared camera. No enclosure.
• Plastic encl.: Board inside a plastic box or a painted metallic box without direct contact between PCB and walls. Polymers have good infrared absorption and emission properties.
• Select:  .

• Read the value: 

• Replace the default value 12.0 by the new value. Ambient temperature is air temperature outside the enclosure: 

• metallic encl.: Board inside a non-painted (shiny, polished) metallic box without direct contact between PCB and walls. Polished metals have poor infrared absorption and emission properties.
• analogous actions.

Dynamic Heat Exchange:

The (total) Heat Exchange is assumed as a sum of a convective and radiative part. This option is available only in transient or pseudo-transient mode, for top and for bootm side. 

First, you have to specify the radiation emissivity. Radiation is always calculated at all surface points depending on their temperature and the housing options. Radiation emissivity describes how a material or a body surface exchanges infrared radiation with its surroundings. The maximum emissivity value is 1.

The most commonly used are listed here: 

• Paints and FR4:               0,95
• Ceramic:                          0,21
• Aluminium polished:       0,04

For the convectional part, there are the following three options:

• Free convection: The convective part is estimated at each simulation point in time using the mean board temperature, the board orientation and housing options.
• Air speed: Convection is estimated for a given positive air speed across the board (x-axis and y-axis).
• Fixed convection: The convective heat transfer coefficient can be entered as a parameter.

Operating Parameter:

Defining the initial operating temperature, you can choose between a uniform distribution of temperature or the temperature map. Furthermore, you have to determine the general conditions of the board, e.g. if there is a housing (plastic or metal) or not. The orientation is important for the simulation as it affects the convection of the board.