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February 2004

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Subject:
From:
"Blair K. Hogg" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 10 Feb 2004 08:53:29 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (100 lines)
The iron should be grounded to the same point as the mat, but I don't think you need to go through a 1 MegOhm resistor. The 1M resistance is primarily for operator safety in the event that they would be working on a live circuit (i.e. during test) and happen to touch an energized part of the circuit, the 1M resistance protects them from harm. Unless you are performing soldering on live equipment (not recommended - I tried it once and the results weren't pretty) the iron should not have to have a resistance to ground. 
 
For EOS situations you need to determine what kind of components you are soldering, what their sensitivities are, and what the source of the EOS is. a 2V EOS doesn't sound like much, but a 2V high current (low impedance) source can easily destroy a bipolar P-N junction but probably wont hurt the gate of a CMOS device. If the 2V drops to 0V with ~1Kohm of resistance applied to ground it *might* not hurt, but I wouldn't take the chance. On the other hand, if it is a 200V potential, which drops to 2V when the load of a multimeter is applied, it might hurt a sensitive device even though the strength of the source is low. 
 
My recommendation is to find the source of this voltage and eliminate it. 
Blair

>>> [log in to unmask] 02/10/04 08:27AM >>>
Dear Ramsey

Our electrical ground and the ESD ground point are deferent , I mean that is
two deferent pits.

I checked and that are not open.Now I grounded our irons with same ESD mat
through a 1M resistor and disconnect the electric ground from the iron, then
I measure that the potential is coming around .5 to 2V in deferent irons. Is
that the safe at the EOS point of view actually we have a major failure in
laser sensor IC.

The iron we using Weller WTCP 50

Best regards and thanks for previous info.

Pankaj

> -----Original Message-----
> From: Guy Ramsey [SMTP:[log in to unmask]] 
> Sent: Tuesday, February 10, 2004 6:28 PM
> To:   'TechNet E-Mail Forum.'; 'Karnwal, Pankaj'
> Subject:      RE: [TN] iron tip potential
>
> They should be the same, as Blair said. Sounds like the soldering iron
> and mat are not connected to the same "ground". This is not an ESD
> issue, rather an EOS issue and yes it could be very damaging. When the
> electrical system ground is open I have measured potentials between 40
> and 90 volts. That is where I would look first. What is the resistance
> to ground through the iron? Do you have a GFI on the solder iron? Check
> for a faulty ground at the outlet. Then check the AC box. How old is the
> building?
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Karnwal, Pankaj
> > Sent: Tuesday, February 10, 2004 4:26 AM
> > To: [log in to unmask] 
> > Subject: [TN] iron tip potential
> >
> >
> > Dear all, hello
> >
> > My question about the potential deference between the
> > soldering iron tip and the ESD grounded mat. I observed that
> > it is about 20 to 30 volts, is it safe for ESD sensitive
> > device? and is it mandatory to keep the iron tip on same
> > potential with ESD grounded mat.
> >
> >
> >
> > Pankaj Karnwal
> > Jr. Engineer QA
> >
> > Barco Electronics System  (P) Ltd.
> >
> www.barco.com 
> mailto:[log in to unmask] 
>

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