Thermal Resistance Basics

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Thermal Resistance Basics

• Randy Lasater
• NSWC Dahlgren
• Lasaterrj_at_nswc.navy.mil
• 540-653-7725

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Power FET Channel-to-Package Thermal Resistance
(RTH)
Channel Temperature
FET Chip
RD is Channel-to-Package RTH
Conductive Adhesive
Package
Package Temperature
Package-to-Heatsink Interface
Heatsink
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Thermal Circuit
RD is the channel-to-package thermal resistance
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Thermal Impedance (RTH)
is the channel-to-package thermal resistance
(K/W)
TCH is the channel temperature (K or deg C) TP is
the package or module temperature (K or deg C) PD
is the power dissipated by the device, PD VDS x
IDS PIN - POUT (W)
is the die attach (adhesive) thermal resistance
(K/W)
is the adhesive thermal conductivity (W/mmK)
t is the adhesive thickness (mm) L is the chip
length (mm) W is the chip width (mm)
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Thermal Impedance (RTH) contd
PD /mm2 5-6W/mm2 the power dissipated by
the die gt
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Material Thermal Conductivities