Weller workstation grounding issues

[bonelli]

Hello,

I have burned too much RF devices using my Weller workstation, unsoldering and soldering L&C for matching purposes.

My working area is not officially approved to be EPA but all good things are used (dissipative floor, ESD chairs, desks, ESD gown...).

Some years ago I've burned several RF active devices. Nothing was plugged in the jack connector of the weller workstation, meaning the tips was connected to earth.

I then decided to use this jack connector to connect the tip to the ground with a 1Mohm resistor using standard ESD wiring cables. Things were going well. Certainly because I've stopped to work on RF projects.

Today, I'm back to RF and I've burned 2 LNAs.

I took some measurements using a DMM between the tip and the earth:
- With the jack : Vac=4V, Iac=15µA (yes, V, not mV, this is not a typo)
- Without the jack : Vac=0.1V, Iac=5~15mA (yes, mA, this is not a typo)

I both cases, I believe these voltages/currents are sufficient to burn a sensitive RF chip.

How do you manage that ? I'm going to take a croco clip to directly connect the tip to my PCB ground (not earth).

Thanks

[floobydust]

Your odd high current (low voltage) reading 5~15mA seems to mean the soldering station PE ground (tip) is not the same as wherever your DMM was grounded. So I would suspect a bad ground or they are using neutral as the PE ground in an old building with old outlet wiring.

I once had similar problems with expensive parts getting zapped and spent a lot of time figuring it out. I find it's two things:

Keep the soldering iron tip hard-grounded, after verifying the outlet PE ground is done right and proper.
Never use a 1MEGΩ resistor to ground a soldering iron (tip). This is because almost always there is a lot of capacitance between mains and the soldering iron tip, so it will be at a high potential voltage due to capacitive-coupling.
The power transformer pri-sec winding capacitance and (if SMPS) Y-cap are to blame.
Although one (German model) Weller station has a well made (split-bobbin) power transformer with very low pri-sec capacitance and it's double-insulated to keep it safe and it uses no PE ground at all, it's got a 2-prong power cord. But this is rare.


The bench's ESD mat - again, using a 1MEGΩ resistor to ground this does not work as expected. I found the mat would get several VAC on it and traced it down to mains power cords lying on the mat. It's capacitive coupling (around 70pF) from the mains cord to the ESD mat that will impose AC. If you have no power cords touching the mat, it's OK.

The 1MEGΩ resistor I only use for my ESD wrist-strap. Also, I added a GFCI to my workbench power so if I short a live circuit board to the ESD mat, it trips and no shock hazard as well.

To troubleshoot things, I added two high-efficiency LEDs in series with the bench ESD mat ground. Try it, you can see any uA leakage currents or ESD hits. If you have super-bright green LED's you would be surprised at what it shows.
The actual AC voltage is higher than you measure because a DMM has 10-20MEGΩ input impedance which loads it down.

[Hamelec]

Please let us know which Model of Weller workstation you are talking..

[bonelli]

Please let us know which Model of Weller workstation you are talking..

WX2
https://www.weller-tools.com/professional/USA/us/Professional/Product+lines/WX+Line/WX2

[floobydust]

The WX2 user manual is full of cartoons and not clear about PE grounding. I can't make sense of this, looks like a two-prong plug yet 3-pin IEC entry, and something something don't ground... 
Doc's show a toroidal power transformer and website says "equipotential bonding = on" so I have no idea how Weller has done it.