MMRF1320 LDMOS Idq drop

[indumathis]

Hi
Regarding MMRF1320N .... The transistor was tested for CW 100W (Idle current Idq 800mA) in lab setup a few years back (4 years). The amplifier was stored in lab environment (never turned on). When turned on recently, the Idq has dropped to 500mA. On susbsequent testing, the power has also dropped to CW 50W and further Idq dropped to 100mA.
We tried removing the transistor, cleaning and mounting it back with heat sink compound on same baseplate with teflon clamp. When power test is done, Idq initially gets back to 800mA for a few seconds and then decreases to 100mA. Even a newer device on the baseplate shows decrease in Idq. A RF power test gets back idq momentarily but then Idq drops.
Just looking to see If anyone could suggest possible ways to get back device to working mode. 

Note: The impedance of input and output network were measured and verfied to be same as that years back.

[ErikaC · Accepted solution]

Hello,

If the devices were removed from their original packaging and not properly baked before reflow or mounting, moisture absorption could lead to delamination or internal damage, especially during thermal cycling. We recommend baking the devices according to JEDEC standards before use to eliminate moisture.