[UPDATE]
The repair is still good after several days however I have read a lot of literature regarding NXP LDMOS RF devices and the techniques used to heatsink these RF FETS.
I appears that the mounting of the output FET is very technical and completed in highly controlled reflow conditions using special jigs and equipment that the home repair does not have access to (even advanced hobbyist)?
I think the issue with my radio was that the soldered (paste or pre-form) had heated up and pumped out. The whole back of the transistor was a mess. It is not practical to reflow the solder as the temperatures required are difficult to administer.
I have obtained an IC Graphite cooling pad from Innovation Cooling, a graphite pad also recommended by NXP in their literature)?
Bolt Down Mounting Method for High Power RF Transistors and RFICs in Over-Molded Plastic Packages
This PDF paper discusses test they carried?out using several paste and solder methods to maximise heat and conductivity to the heatsink and they concluded that TGON 805 graphite was the best mixture of cost and ease/performance.
Although my output FET is working OK, it is likely stressed a lot from the excess eat and mechanical movement and so I will be replacing it with a new genuine AFT5M31N from mouser that has now arrived, along with the IC Graphite material as a heat pad.
I will update the thread when completed.
Thanks, Scot
M0RWV
