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pcb121055 10th October 2012 01:48 AM

avoiding static
 
Hi guys.
As a noob to building an amplifier, I read Space2000's warning about mosfets carefully. Not because of the particular mosfet he was describing but because it dawned on me that I do not know what is sensitive to handling nor how to improve my chances of success in assembling my F5T kits.
The soldering iron, esd strap, conductive mat were all touched on but briefly. I do not want to trash parts during assembly. So... my question is: What would be an ideal setup for safe electronic work with regards to esd, etc?
Thanks in advance!

flg 10th October 2012 11:16 AM

45% relative humidity will get you 95% of what you need! :D

JamesBrennan4 10th October 2012 01:28 PM

You are biggest source of static. Touch the largest conductive item with your fingers before you touch the MOSFET.

Worst case, you are wearing rubber shoes, walk across the carpet and then immediately touch the MOSFET.

overtheairbroadcast 10th October 2012 02:26 PM

Here was me about a year ago collecting every piece of conductive foam, anti-static bag, and the like small bits of foam leftover from opamps, new computer parts (don't throw out the bag!), and I have this mishmash of stuff. I also have a telephone cord like thing that I picked up at an electronics and gadget show in China with an alligator clip to clip to your sleeve.

Then I met and I learned from a pretty knowledgeable gentleman that so long as you keep sensitive components in aluminum foil, it works pretty good. He stores them, handles them wrapped, and lays them out on a small sheet of aluminum foil.

I asked the reasoning behind this and it was to keep the difference in potential between the separate pins equal (or at "zero"). This is what conductive foam does as the aluminum foil is in contact with all the pins and surfaces of the transistor. He hasn't lost one yet in all his years. When he works on them, they are laid out on the aluminum foil he stored them in (touch the foil to get to the component). It also keeps it thin and less bulky than conductive foam and you can make the sheet as large or small or shaped to your needs. When you handle the foil, you have equalized the charge between you and the foil and no zapping of individual components.


Keep your feet on the floor and have some humidity in the air like flg says and I think you you will have 99.9% of what you need.

Makes sense I suppose.

PS -- I have since got rid of all the small, beat up, well used, pieces of conductive foam and krinkled antistatic bags I had. I now have more room for components (ugh!).

dazed2 10th October 2012 04:52 PM

wearing a tinfoil hat on your head works too.

overtheairbroadcast 10th October 2012 05:24 PM

Quote:

Originally Posted by dazed2 (Post 3196627)
wearing a tinfoil hat on your head works too.

Yeah, but the tinfoil hat has to be the handmade woven hat that has been braided in the Alpine mountains on a half moon night though. That is the best time to create Faraday cages.

But, it really does work... the storing of components in aluminum foil -- not the tinfoil hat (do they actually still make tinfoil for consumer use?).

What you are creating with the aluminum foil and components/chips/transistors inside of it is a Faraday Cage when you think about it...

http://en.wikipedia.org/wiki/Faraday_cage

pcb121055 11th October 2012 02:15 AM

Wow! Awesome responses. Thanks everyone. I had been in the habit of touching the cases of the computers I am destroying for the same reason of coming to the same potential so what you guys have said makes perfect sense. Never thought about the aluminum foil approach. Pretty creative. I have a few inexpensive irons but nothing exotic and was looking to pick up a soldering station for this project. Given Space2000's adventures, I want to ask if there is a particular grade of soldering iron? PS I already have the tinfoil hat :)

overtheairbroadcast 11th October 2012 03:02 AM

I have heard people on few forums rave about Metcal soldering stations, but never have seen one for sale in any of the electronics stores in Toronto (the biggest city I am close to). Most of the local stores here in Ontario and Upstate New York (I have been known to cross border shop) usually carry Weller or cheaply made ones that don't last.

I am using a plain old light blue Weller 25 Watt soldering iron (with replaceable heater in case it breaks down), a fine pencil tip, an old springy iron holder I picked up somewhere, a sink sponge, a brass Curly Kate pot scrubber, and a mat. The Weller serves my purposes, rapidly heats up, and tips and parts are easy to find. Some 63/37 solder makes it easier yet (for me at least).

h_a 11th October 2012 07:24 AM

I've build a fair number of amps and never had problems with static discharge. In fact I cannot remember any transistor failure during assembling. I also don't use any fancy sort of soldering station, just a cheap adjustable Weller.

IMHO it's the shorts that kill the amps :flame:

sofaspud 11th October 2012 07:32 AM

The gate of a MOSFET is extremely thin. Perhaps only a few molecules thick, and measured in angstroms. High voltage (like static electricity) will literally blow a hole through the gate oxide (you can probably find microscope pics of this on the web). Static electricity on a dry winter day can approach 30kV. The gate is no match for that!
All the ESD equipment simply helps to keep everything at the same potential. The "telephone cord like thing" should have a conductive wrist strap on one end, and the alligator clip connects to a ground point. NOT to your sleeve (and if you really want to get in-depth, don't wear synthetic fabrics while working with FETs). The cord should be made with a high-value resistor inline for safety purposes (else it wouldn't be pretty if you touched a live wire).
The main thing you want to avoid is touching the FET leads. Leave the parts in their conductive storage until ready to solder. Then touch some grounded metal on your workbench (a PC case is good) before handling the transistor. You can touch the tip of the soldering iron to the same metal ground point.


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