Definition

PCB
Printed Circuit Board
A board that is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or traces etched from copper sheets laminated onto a non-conductive substrate.
Component
A logical unit that includes integrated circuit chip and packing. The interfaces to the PCB and cold plate(optional) is included in the model
Component Substrate
A logical unit that represent a combined unit of the die of integrated circuit chip and substrate
Component Encapsulant
The molding that is used to cover the die and the rest of the substrate to provide protection to the die from the environment.
Board Interface
Account for leads and thermal pad or air gap between the component and PCB
PCB with Vias
The part of PCB underneat the component that includes through-hole vias. The effect of vias are reflected in the modified value of K in z direction only. The modified and orignal K value are smeared using weighted area rule and the effective Kz value is used for the area underneath of each component.
Cold plate
A solid plate made of highly conductive material that is connected to the component with the purpose of providing additional heat flow path.
Conduction bar
A solid block of highly conductive material that conects the cold plate to PCB.
Boundary Region
A region of model in which a specified conditions are enfored on all the grid point.
h
Convective coefficient Average convection heat transfer coefficient over the area A, W/m^2 K
Thermal resistance
The temperature difference across a structure when a unit of heat energy flows through it in unit time.
k
Thermal conductivity The property of a material that indicates its ability to conduct heat. A reciprocal of thermal resistance.
Natural convection
A mechanism, or type of heat transport in which the motion of the fluid is caused solely by differences in density resulting from temperature gradients and is not aided by a pump or a fan.
Forced convection
A mechanism, or type of heat transport in which fluid motion is generated by an external source (like a pump, fan, suction device, etc)
Steady State
A state of a system, in which the recently observed behavior of the system will continue into the future.
Transient
A state of a system, in which a process variable has been changed and they system has not reached steady state.
2-D board
Representation of board using 2 dimensional shell model
3-D board
Representation of board using 3 dimensional solid model
Thermal Analysis
A type of analysis where the change of temperature in the system is simulated, subject to the given set of boundary conditions
Stress Analysis
A type of analysis where the change of stress in the system is simulated, subject to the given set of boundary conditions
Ambient temperature
Ambient temperature. Ambient temperature is subtracted from estimated surface temperature in order to determine temperature gradient
Estimated surface temperature
Estimated, average surface temperature. Ambient temperature is subtracted from estimated surface temperature in order to determine temperature gradient
Air flow direction
Direction of incoming airflow
Air mass flow
Total amount of air mass moving through a unit surface per unit time
CFM
Cubic feet per minute
Heat input
Heat dissipation in the component
Nusselt equation
Dimensionless heat transfer coefficient. For forced convection, different equations are used for different boundary conditions :
NuH1
Average Nusselt number for uniform heat flux in flow direction and uniform wall temperature ay any cross section
NuH2
Average Nusselt number for uniform heat flux both axially and circumferentially
NuT
Average Nusselt number for uniform wall temperature
Re
Reynolds Number
A dimensionless parameter that quantitatively relates the viscous and inertial forces and whose value determines the transition from laminar to turbulent flow
? ? U? x ? ? = U? x ? ?
Gr
Grashoff Number
Ratio of buoyant to viscous forces
? g ? (Ts-T?) L3? ?2
Pr
Prandtl Number
Ratio of molecular momentum diffusivity to thermal diffusivity
? Cp ? ? k = ? ? ?
Ra
Raylengh Number
Product of Grashof and Prandtl numbers
? Gr*Pr