56
AT84AD001B
2153C–BDC–04/04
Thermal Characteristics
Simplified Thermal
Model for LQFP 144
20 x 20 x 1.4 mm
The following model has been extracted from the ANSYS FEM simulations.
Assumptions: no air, no convection and no board.
Figure 62. Simplified Thermal Model for LQFP Package
Note: The above are typical values with an assumption of uniform power dissipation over 2.5 x 2.5 mm
2
of the top surface of the die.
Thermal Resistance from
Junction to Bottom of Leads
Assumptions: no air, no convection and no board.
The thermal resistance from the junction to the bottom of the leads is 15.2° C/W typical.
Thermal Resistance from
Junction to Top of Case
Assumptions: no air, no convection and no board.
The thermal resistance from the junction to the top of the case is 8.3° C/W typical.
Thermal Resistance from
Junction to Bottom of Case
Assumptions: no air, no convection and no board.
The thermal resistance from the junction to the bottom of the case is 6.4° C/W typical.
Thermal Resistance from
Junction to Bottom of Air Gap
The thermal resistance from the junction to the bottom of the air gap (bottom of pack-
age) is 17.9° C/W typical.
355 µm silicon die
25 mm
λ
= 0.95W/cm/˚C
40 µm Epoxy/Ag glue
λ
= 0.02 W/cm/˚C
Copper paddle
λ
= 2.5W/cm/˚C
Aluminium paddle
λ
= 0.75W/cm/˚C
Copper alloy leadframe
Package top
5.5˚C/watt
0.1˚C/watt
11.4˚C/watt
Package
bottom
4.3˚C/watt
1.5˚C/watt
λ
= 0.007W/cm/˚C
Silicon Junction
0.6˚C/watt
8.3˚C/watt
1.4˚C/watt
0.1˚C/watt
6.1˚C/watt
1.5˚C/watt
Leads tip
Assumptions:
Die 5.0 x 5.0 = 25 mm
40 µm thick Epoxy/Ag glue
2
Top of user board
Package bottom
connected to:
(user dependent)
Resin bottom
λ = 0.007W/cm/
˚C
2
Aluminium paddle Resin
Resin
λ
= 0.007W/cm/˚C
λ
= 25W/cm/˚C
100 µm air gap λ = 0.00027W/cm/
˚C
100 µm thermal grease gap diamater 12 mm
λ = 0.01W/cm/
˚C
