AN1923 Motorola / Freescale Semiconductor, AN1923 Datasheet - Page 6

• Manufacturer Part Number: AN1923
• Description: AN1923 Application Note Mounting Method with Mechanical Fasteners for the MRF19090 and Similar Packages
• Manufacturer: Motorola / Freescale Semiconductor

several PCBs using a scanning Infrared microscope after the
power cycling.
approximately 100 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 package up to 90 Watts of output power.
the thermal and electrical performance of the device. The
mounting method described here uses thermal grease as an
interface between the source contact of the MRF19090 device
and the customer’s heatsink. There are number of options
6
The mounting scheme design significantly influences both
Lead and solder joint temperatures were measured on
Lead temperatures were found to be
Figure 11. Typical IR Scan Image of the MRF19090 Lead and Solder Joint
This prescribed mounting
MOTOROLA SEMICONDUCTOR APPLICATION INFORMATION
available for the interface layer. It is highly recommended that
the customer carefully evaluate which interface material will
provide adequate 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. The total thermal 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. The mounting method described here is a guide; it
should not be substituted for a complete system–level
performance analysis.