An inexpensive solution to a reasonably expensive, albeit necessary, electronic soldering accessory.
This is my first Instructable! Please give advice, constructive criticism, AND PRAISE! (I can't believe I forgot to list the last one. Jeez!!! :)
[EDIT: As one commenter suggested, (and I failed to realize) your mat should have a conductive top layer and a non-conductive bottom layer, NOT the three layer /resistive-conductive-resistive/ version I have made here. I haven't yet found a proper substitute for the aluminum (it is not durable enough to use as a top layer). I will edit this -Ible to reflect the correct 'two-layer' assembly once I have the proper material for an acceptable price! (Free.... Obviously...) Thanks for reading on!]
Step 1: Explanations
All Anti Static mats, aka ESD mats, have one purpose - to dissipate the static charge that can, and usually does, build up on the human body during a typical day in a controlled manner. This condition can cause a short in your components from a rapid discharge of electrostatic energy. Really creative name for the mat, huh?
To be more accurate, an Anti Static mat drastically slows the rate of static energy discharge or maintain at zero, the difference in the common electrical potential of the operator relative to the many components he, or she, may come in contact with. This eliminates the possibility of discharging the static into a sensitive electronic component possibly causing it irreparably damage.
The mats are typically constructed of an electrically resistive rubber or plastic derived material combined with a conductive layer that leads to a ground plane such as a three pronged outlet (here in the US) or a grounding rod in the ground outside of your hobby shop. See the two images above for an example.
Some mats implement a direct connection with the operator through a wrist strap or floor mat. The bench top mat that I am constructing will use a wrist strap to provide a complete circuit from the skin, through the mat, and into the chosen grounding plane. As I understand things, this setup can provide a more stable and consistent rate of discharge over a day's work period.
ESD mats will usually have at the least a 1 mega ohm resistor inline with the circuit somewhere to slow the rate of ElectroStatic Discharge and prevent shock from the grounding plane reaching the operator.
Step 2: Our Ultimate Goal
Our ultimate goal is simply a mat that provides a resistive surface that will still provide a complete line to the grounded prong in my bench power outlet. Hopefully we will produce something that will accomplish this without allowing voltage to reach the operator from the outlet and still discharge the static buildup. Having about ten feet of yoga mat on hand and a roll of foil made the layout and construction easy. Just fold and cut, match and cut, assemble various components, and glue like crazy! See? Easy...
Above is a quickly assembled prototype of what we are after. I omitted the glue on half of this replica to be able to clearly show the different parts, construction order, and finished product.
Step 3: Tools!!!
1. Hobby knife
2. Wire strippers/Cutters
4. Straight Edge or Metal Ruler
6. 7/16 long socket (for my build at least)
7. 3/16 drill bit or punch
8. Awl or hole punch
9. Soldering Iron
10. Heat gun or lighter
12. heat shrink tubing
Note: The socket and drill bit are for the snap insert. I snap tool would be MUCH better.
Step 4: Materials
1. One electrically resistive layer. (The old yoga mat)
2. One electrically conductive layer. (The aluminum foil)
3. ALOT of glue or other adhesive. When it is dry, it should adhere the parts well and still be very flexible. ( I grabbed something out of an old work cabinet I found from previous tenants I guess. It wasn't nearly enough.)
4. One length of wire approximately a foot longer than the distance from the location you will be using your mat to your chosen outlet. Choose the smallest wire that is bigger that 22 gauge but not larger than 10 gauge and is multi stranded. Remember that the smaller diameter of wire will provide the largest gain in resistance. It may also provide feedback in the form of heat. But I HIGHLY doubt it. (Actually doing the math on this one might help you pinpoint the exact wire gauge if you are worried. I guessed.)
5. One anti-static wrist strap (you can purchase one of these online or opt for the cheaper, disposable versions at your local hardware box store. Just make sure it has a one (1) mega-ohm resistor)
6. One clothing snap and mate assembly OR a steel nut and screw/bolt. (make sure that whatever you choose has conductive properties)
7. One male end of old extension cord
Step 5: Prep
Cut your resistive material into two equal parts and matching shape.
cut your conductive material to match your resistive material. Be sure to cut a small piece of the foil about 2" x 4" (See the second picture). This will be used for reinforcement at the snap location. Just set it aside for now.
Overlap is okay in either material. We're going to trim everything to size later. Just be sure to save as much material of each layer as possible so that your ESD mat can be as large as possible. Or layer your foil for bigger mats. (the primary picture as an example)
Remove the plastic sheath from a short length of your grounding wire, say about 1" (inch) and spread out the strands into a fan. (See the third picture)
Thoroughly clean the resistive material on both sides of both parts.
Bond your male plug to your grounding wire with a crimp fastener or solder. Be sure to remove any part of the positive and negative wires that are or could be exposed to you, the air, or metal. If your chosen plug can be disassembled. Be certain to take advantage of this and remove any wire connected to the +/- prongs only connecting the wire from your ESD mat to the ground/neutral prong.
Locate the placement of your snap or bolt. Make a hole in the top resistive layer and conductive layer. Include the small piece of foil we cut earlier. Fold the small piece of foil over and under your conductive layer where you are making your hole. DO NOT MAKE A HOLE IN YOUR BOTTOM RESISTIVE LAYER.
Step 6: Construction
With proper preparation. This becomes the easy part.
For parts reference:
Identifier / Name
A / Bottom resistive layer
B1 / Conductive layer
B2 / reinforcement layer of conductive material
C / Upper resistive layer
D / Grounding wire prong assembly
E1 / Male Snap assembly base
E2 / Male Snap assembly top
This reference chart may be overkill but it also represents the construction order. Let me know!
Lay part C on your clean work surface upside down. The side to be glued should be facing up.
Flood the surface of part C with the adhesive. Using a paint brush or squeegee spread the adhesive to the edges evening it out as you spread it. Be sure to follow the instructions on the bottle for proper adhesion.
With part B2 still correctly located on part B1, carefully lay your conductive layer on part C. Check that your pre-made holes line up and allow the adhesive to dry enough to handle.
Once the adhesive has had time to cure, place the fan side of your ground wire on or in your pre-made hole. Place part E1 in the hole and use it to hold the grounding wire in place. Flip the partial assembly over and place part E2 over the stud of part E1.
Take a moment and make an Ohm check from your conductive layer to the ground prong in your plug. If you get a positive reading: install the snap making sure there is a strong connection between the wire and your snap assembly.
If not: time to trouble shoot... booooo.
Lay part A on your clean work surface with the side to be glued facing up.
Flood part A with adhesive, repeating the actions of Step 2.
Carefully place your assembled upper layers onto part A and press out the air bubbles. Make an Ohm check to be certain the circuit is intact.
If all is well, place weight onto the assembly, evenly applying pressure across the entire part. Allow the glue to cure completely.
Use your straight edge to measure and cut the assembly to the sized mat you want.
Attach your wrist strap. Make another Ohm check from the ground prong to your strap. Assuming everything checks out. Record the R measurement and place somewhere for safe keeping. We want to be able to accurately test the performance of our mats over time for safety.
Place the mat on your work station and plug in your ground cord. THAT'S IT! YOUR DONE!
Step 7: Conclusion
Well, like I just said, we're ALL DONE! Do one more Ohm check to make sure you are getting the kind of resistance you were looking for. Obviously the more resistance the better.
I hope this is helpful. Again, please leave a comment! Tips, tricks, how your's went, anything you need to know from me, and any advice on how to write a better instructable!
-Maker T Elam