Thermal Data
Two-parameter model
This model provides a more precise description of the thermal
characteristics to be used for thermal calculations.
Thermally the power module can be considered as a component
and the case temperature can be used to characterize the
properties. The thermal data for a power module with the
substrate in contact with the case can be described with two
thermal resistances. One from the case to ambient air and one
from case to PB (Printed Board).
The thermal characteristics can be calculated from the following
formula:
T
PB
= (T
C
–T
A
)×(R
th C–PB
+R
th C–A
)/R
th C–A
–P
d
×R
th C–PB
+T
A
Where:
P
d
:
dissipated power, calculated as P
O
×(l/h–1)
max average case temperature
T
C
:
T
A
:
ambient air temperature at the lower side of the power
module
T
PB
:
temperature in the PB between the PKF connection pins
R
th C-PB
: thermal resistance from case to PB under the power
module
R
th C-A
: thermal resistance from case to ambient air
v:
velocity of ambient air.
R
th C-PB
is constant and R
th C-A
is dependent on the air velocity.
Free convection is equal to an air velocity of approx.
0.2 – 0.3 m/s. See figure below.
Reflow Soldering Information
The PKF series of DC/DC power modules are manufactured in
surface mount technology. Extra precautions must therefore be
taken when reflow soldering the surface mount version. Neglec-
ting the soldering information given below may result in perma-
nent damage or significant degradation of power module per-
formance.
The PKF series can be reflow soldered using IR, Natural
Convection, Forced Convection or Combined IR/Convection
Technologies. The high thermal mass of the component and its
effect on
DT
(°C) requires that particular attention be paid to
other temperature sensitive components.
IR Reflow technology may require the overall profile time to be
extended to approximately 8–10 minutes to ensure an acceptable
DT.
Higher activity flux may be more suitable to overcome the
increase in oxidation and to avoid flux burn-up.
The general profile parameters detailed in the diagram, with this
ex-tended time to reach peak temperatures, would then be
suitable.
Note!
These are maximum parameters. Depending on process
variations, an appropriate margin must be added.
Palladium plating is used on the terminal pins. A pin tem-perature
(T
p
) in excess of the solder fusing temperature (+183°C for Sn/Pb
63/37) for more than 25 seconds and a peak temperature above
195°C, is required to guarantee a reliable solder joint.
Both pin 1 and pin 9 must be monitored.
No responsibility is assumed if these recommendations are
not strictly followed.
4
EN/LZT 146 31 R1B © Ericsson Power Modules AB, March 2004
ERICSSON [ ERICSSON ]
