ESD Protection for RF Amplifiers

[adnan012]

hi,

I have worst experience with Ldmos SD57060. Many devices has be damaged (gate is damaged and short circuited with source) during design and test procedure. Last time i was using frequency generator with 880MHz @14dBm as an input source and the amplifier's output was connected with spectrum analyzer. My procedure and observations are

Dc power supply is 28v switching power supply.
Dc supply remains always on. there is a switch between power supply and power amplifier.
Biasing is same as given in SD57060.(resistive network)
First i set Biasing voltage to 2 volts then i sold drain inductor to DC rail. After that Vbias are raised to get 100mA Idq.
There is a 42v voltage suppression diode at DC power rail.
All capacitors are RF capacitors.
My soldering station has ESD protection.
I always remove soldering iron cord from ac supply during amplifier soldering. also removes all wires connected to amplifier (power supply).
Signal generator and spectrum analyzer ac cords have two pins (no pin for earth).
However only power cables are disconnected during matching network capacitors soldering and de-soldering.
I have observed that there is 60-70 volt ac signal of 50Hz when i touch oscilloscope probe with my hand (ground wire is left unconnected) in my lab.

Another thing which i have observed that whenever i sold smd LEDs with that Soldering station it glows with very dim light when i place soldering iron tip to anode pin. (first led ground pin is soled ). is it esd or somethnig else?

Many times, i have noticed that when i switched on amplifier with ( signal generator rf power off) the gate damaged instantly without any flow of Drain current and some times i have observed 3 amps of drain current before damaging. However there is one amplifier board which does not show any problem even at 60watts output power at 880MHz.

I have also used Pd20015 (which have internal esd protection) without any problem.

Is there any one who can point out issue.

 

[chuckey]

I would nominate some convenient point as earth, such as the CRO case. Use a DVM and check EVERYTHING back to this point to see if you have unconnected earths and fix them.
Frank

 

[tony_lth]

Some expert told me to replace the LDMOS with a big resistor for tune the current, if OK, then replace back to LDMOS.

 

[hosein_rabiee_g]

I've had the same problem. After earthing every thing(solder Iron, measurement Instruments, Signal generator, myself body, ...) the problem is solved.

 

[adnan012]

Thanks for reply.

In my lab there is an issue with the earth and neutral points. Once i attached earth wire to soldering iron and soldered the device. It was destroyed . i measured voltage with DVM. There was 300 volts on solder tip with respect to ground, Dc power supply etc

 

[hosein_rabiee_g]

IF you attach the earth wire to solder iron, and the solder iron has 300V voltage to GND, then your lab earth is disconnected from GND.