Thermal Data
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. Neglecting the soldering
information given below may result in permanent damage or signifi-
cant degradation of power module performance.
Two-parameter model
This model provides a more precise description of the thermal charac-
teristics 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 case
to ambient air and one from case to PB (Printed circuit Board).
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 com-
ponents.
The thermal characteristics temperature can be calculated from the
following formula:
IR Reflow technology may require the overall profile time to be ex-
tended 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.
TPB = (TC–TA)×(Rth C–PB+Rth C–A)/Rth C–A–P ×Rth C–PB+TA
d
Where:
The general profile parameters detailed in the diagram, with this ex-
tended time to reach peak temperatures, would then be suitable.
Pd:
TC:
TA:
dissipated power, calculated as PO ×(l/h–1)
max average case temperature
ambient air temperature at the lower side of the power
module
Note! These are maximum parameters. Depending on process varia-
tions, an appropriate margin must be added.
TPB
:
temperature in the PB between the PKF connection pins
Rth C-PB: thermal resistance from case to PB under the power
module
Rth C-A
v:
:
thermal resistance from case to ambient air
velocity of ambient air
Rth C-PB is constant and Rth 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.
Palladium plating is used on the terminal pins. A pin temperature
(Tp) 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.
EN/LZT 146 33 R1A (Replaces EN/LZT 137 09 R7) © Ericsson Microelectronics AB, June 2000
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