Reflow Soldering Information
Thermal Data
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.
Over-temperature protection
The PKF 5000 series will automatically shut down when the internal
junction temperature of the control IC in the converter reaches typ.
150°C.
It will automatically re-start when the junction temperature cools
below typ. 140°C.
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.
Two-parameter model
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.
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 the
case to ambient air and one from case to PB (Printed Board).
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 varia-
tions, an appropriate margin must be added.
The thermal characteristics can be calculated from the following
formula:
TPB = (TC–TA)×(Rth C–PB+Rth C–A)/Rth C–A–P ×Rth C–PB+TA
d
Where:
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
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.
R
th 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.
4
EN/LZT 146 32 R1A (Replaces EN/LZT 137 27 R3) ©Ericsson Microelectronics, June 2000
ERICSSON [ ERICSSON ]
