The reliability of a semiconductor is determined by the junction temperature, which in
turn is dependent on several factors including device layout and mounting, package
thermal resistance, PCB layout, heat sink interface, and ambient operating temperature.
This application note describes PCB layout guidelines for the best thermal
performance and reports on junction temperature measurements of the TRF1123 and
the TRF1223. Finally, the failure rate of the TRF1123 and the TRF1223 are calculated
using measured junction temperatures and known reliability data for the MESFET
process.
The TRF1123 and TRF1223 are GaAs Monolithic Integrated Circuit MMICs packaged
in a low-cost, 5 mm x 5 mm, 32-lead leadless plastic chip carrier (LPCC) package. The
package has an 8 mil thick copper base (paddle) that extends through the bottom of
the package. The package is designed to solder reflow the paddle to a ground pad on
the PCB so that a low thermal resistance and excellent RF performance is achieved.
The die is attached to the copper paddle using high thermal conductivity silver epoxy:
Ablestik Ablebond 84-1 LMIS. The epoxy thickness is kept to a minimum. For the
junction temperature test, the die are mounted in packages which have the tops
removed so that the surface of the die is visible for infrared temperature measurement.