AN1908 Freescale Semiconductor / Motorola, AN1908 Datasheet - Page 6

• Manufacturer Part Number: AN1908
• Description: Solder Mounting Method for the MRF19090S and Similar Packages
• Manufacturer: Freescale Semiconductor / Motorola

several PCBs using a scanning infrared microscope after the
power cycling.
approximately 90 C at 135 Watts of power dissipation and a
90 C sink temperature. Figure 11 displays an image taken
from the infrared microscope. Following the power life testing,
solder joints were visually inspected and found to have no
cracks after 2000 cycles.
methodology will adequately account for the thermal and
mechanical requirements of mounting a power transistor in a
metal/ceramic up to 90 Watts of output power.
the thermal and electrical performance of the device. The
mounting method described here uses the solder as an
interface between the source contact of the MRF19090S
AN1908
Lead and solder joint temperatures were measured on
The mounting scheme design significantly influences both
6
Lead temperatures were found to be
Figure 11. Typical IR Scan Image of the MRF19090S Lead and Solder Joint
This prescribed mounting
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MOTOROLA SEMICONDUCTOR APPLICATION INFORMATION
device and the customer’s heat sink. It is highly recommended
that the customer carefully evaluate thermal and electrical
performance for their power amplifier assembly. The selection
of the interface material will depend on the customer’s sink
temperature, as well as the amount of power being dissipated
by the transistor in the application.
resistance between the junction and the sink should be such
that the temperature rise between the junction and the sink at
maximum power and maximum sink temperature condition
will still keep the junction temperature below the maximum
value based on the expected lifetime. Similarly, the interface
layer should also be evaluated to provide proper electrical
contact with the source contact.
described here is a guide; it should not be substituted for a
complete system–level performance analysis.
The mounting method
The total thermal