Steady-State Thermal Analysis of a Transistor

1. Steady-State Thermal Analysis of a Transistor An ANSYS input file for this workshop is provided in Appendix C Basic Problem Description: • A transistor is mounted on a copper isolator which is in turn mounted on an aluminum heat sink. The transistor generates heat, and the system also receives heat radiated by other nearby components. The system is fan cooled. Design Requirements: • The steady-state temperature of the system must be less than 100°C. Transistor Copper isolator Aluminum heat sink plane of symmetry Inventory #00446 March 15, 2001 WS2-1

2. Steady-State Thermal Analysis of a Transistor Dimensions: • Assumptions • One plane of mirror symmetry. • Use SI units. (kg, m, s, W, J) • Radiation from surrounding components is modeled as an equivalent uniform heat flux. • Neglect contact resistance at component interfaces. • Homogeneous transistor material. • Uniform transistor heat generation. • No heat transfer on front and back surfaces; (i.e., no axial temp gradient). • Convection modeled with uniform film coefficient and constant bulk fluid temperature. • Depth is 0.025m • All dimensions shown are in meters. Inventory #00446 March 15, 2001 WS2-2

3. Equivalent heat flux due to radiation from other devices: q* = 1500 W/m2 Transistor Power Dissipation:20 W - high power Thermal Loads Symmetry Plane Forced convection from high speed cooling fan on fin surfaces: h = 51 W/m2 °C T = 50 °C Steady-State Thermal Analysis of a Transistor Inventory #00446 March 15, 2001 WS2-3