MGC Silver (electrically) conductive epoxy

[LLCoolBeans]

Anyone have any experience with this stuff?

Just picked some up at the local electronic supply. I could have really used something like this on a couple of mods.

Any reason why it isn't used more often in the flashlight modding world? Seems to me like this would be an invaluable tool for modding.

 

[mudman cj]

Re: MGC Silver conductive epoxy

It's actually used quite often by modders, myself included. You should have no trouble finding references to Arctic Silver or Arctic Alumina epoxies in particular.

Keep in mind that Seoul emitters have slugs that are not isolated from the leads, and for those you need to use the ceramic epoxy (Arctic Alumina) instead of Arctic Silver because the silver conducts electricity in addition to heat.

 

[likeguymontag]

Re: MGC Silver conductive epoxy

Thermal epoxy is significantly less thermally conductive than regular old thermal compound. If you can figure out a way to use regular thermal compound, you're probably better off. A real metal-to-metal connection like a reflow soldered bit is significantly better still.

Oh well. Thermal epoxy has its uses, and its easy. Just make sure you use a thin layer.

 

[LLCoolBeans]

Re: MGC Silver conductive epoxy

No, No, No. I'm fully aware of and have used AA and AS both the adhesives and the compound. I am also well aware that thermal compound is more thermally conductive than the epoxy.

This stuff is electrically conductive as apposed to AA for example which is electrically insulative. I guess I should have been more clear.

 

[likeguymontag]

Re: MGC Silver conductive epoxy

No, No, No. I'm fully aware of and have used AA and AS both the adhesives and the compound. I am also well aware that thermal compound is more thermally conductive than the epoxy.

This stuff is electrically conductive as apposed to AA for example which is electrically insulative. I guess I should have been more clear.

Fascinating. I wonder what its electrical conductivity is though, and how easy it is to work with. Super viscous?

 

[LLCoolBeans]

Re: MGC Silver conductive epoxy

Fascinating. I wonder what its electrical conductivity is though, and how easy it is to work with. Super viscous?

It looked interesting, so I grabbed some at the store today. I haven't had a chance to play with it yet.

It says the following on the package:
Volume resistivity @ 25degrees C (77degrees F)
MIL-STD-883E 0.38 ohm-cm

 

[likeguymontag]

Re: MGC Silver conductive epoxy

It looked interesting, so I grabbed some at the store today. I haven't had a chance to play with it yet.

You're familiar with the electrically conductive paint sold at automotive parts stores, right? Brown, small vial with a brush. It's used to repair broken traces on rear window defoggers.

 

[LLCoolBeans]

Re: MGC Silver conductive epoxy

You're familiar with the electrically conductive paint sold at automotive parts stores, right? Brown, small vial with a brush. It's used to repair broken traces on rear window defoggers.

I've heard mention of it poking around CPF, but I am not familiar with it.

The packaging also has this to say:

Forms High Strength Conductive Bonds
Use in place of traditional solder. Perfect for joining heat sensitive components. Good for repairing defective traces and creating jumpers. Excellent for high frequency EMI/RFI shielding applications.

 

[precisionworks]

what its electrical conductivity is

The value 0.38 ohm-cm is the volume resistivity measurement of MGC Silver.

For comparison, look at a really good conductor like German Silver, which value of 33 X 10 ^6 ohm-cm. If you had a block of German Silver one cm on each side, it would measure 33 micro ohms (.000033 ohms). The same sized block of MGC Silver, at 0.38 ohm-cm, has 11,515 times the resistance of German Silver.

electrically conductive paint sold at automotive parts stores

The most common product uses powdered nickel, with a resistance of 5 to 6 ohms-cm. The best uses powdered German Silver, and measures 0.1 ohms-cm.

 

[likeguymontag]

The most common product uses powdered nickel, with a resistance of 5 to 6 ohms-cm. The best uses powdered German Silver, and measures 0.1 ohms-cm.

Crazy. I was trying to find values for that stuff just the other day and didn't have any success. I wanted to make a custom very-low-resistance resistor, which would have been easier for me than ordering a part.

a really good conductor like German Silver, which value of 33 X 10 ^6 ohm-cm.

33 X 10 ^-6 ohm-cm, right?

 

[mudman cj]

Sorry, my mistake for not looking it up and making assumptions about it.

I actually have used electrically conductive epoxy for mods that is sold for use in mounting samples for SEM analysis. I found it to be a poor substitute for solder in cases where there is a mechanical strain on the connection, but it certainly has many uses.

 

[precisionworks]

33 X 10 ^-6 ohm-cm, right?

You'd think that's the correct way to express 33 micro ohms, and the way I posted would mean 33 meg ohms. Hard to figure

 

[Blindasabat]

I tried to use some conductive silver epoxy a year ago on SMD resistors. Didn't work for me at all. It wasn't nearly viscous enough to work with. Let me know if yours works.
I it from Digikey. Not at home to copy the exact name. Cost me $20 for a tiny syringe.

At 0.38 ohm/cm, if your gap is only ~0.1mm (0.01cm) then your R should only be 0.0038 ohm.

 

[precisionworks]

At 0.38 ohm/cm, if your gap is only ~0.1mm (0.01cm) then your R should only be 0.0038 ohm.

The manufacturer shows 0.38 ohm-cm, which means 0.38 ohm per cubic centimeter. It's a volumetric measurement, not just thickness.

 

[mudman cj]

Ohm-cm is another notation for Ohm*cm or Ohms times centimeters. It is a unit of resistivity and you calculate resistance by multiplying resistivity times the distance over which the electricity must flow through the item having that resistivity divided by the area. So in a sense the volume does matter because both the length and area are involved.

This concept can help to give a better understanding of thermal design considerations such as choosing epoxy vs. soldering and the effects of adding additional thermal junctions as in the case of some cheap dropins I have seen. One reason why Malkoff dropins are better is that the design reduces the number of thermal interfaces.

Anyway, I want to help spread a greater understanding of the principles behind the lights we all enjoy - so if I come off like the guy that can't help but correct everyone then I'm sorry.

 

[Blindasabat]

cc means cubic centimeter. cm means centimeter

The manufacturer shows 0.38 ohm-cm, which means 0.38 ohm per cubic centimeter. It's a volumetric measurement, not just thickness.

 

[rpage53]

cc means cubic centimeter. cm means centimeter

True but a 1 cm long trace that is a molecule in width would have a very high resistance. A 1X1X1 cube would be dramatically less. The measure is actually called "volume resistivity".
http://www.astm.org/Standards/D2739.htm
http://composite.about.com/library/glossary/v/bldef-v5988.htm

At any rate, this epoxy has high resistance compared to solder and in a high current situation will overheat and melt.

Rick.

 

[saabluster]

True but a 1 cm long trace that is a molecule in width would have a very high resistance. A 1X1X1 cube would be dramatically less. The measure is actually called "volume resistivity".

At any rate, this epoxy has high resistance compared to solder and in a high current situation will overheat and melt.

Rick.

How about this one?

 

[LLCoolBeans]

At any rate, this epoxy has high resistance compared to solder and in a high current situation will overheat and melt.

What do you consider a high current situation to be?

 

[rpage53]

What do you consider a high current situation to be?

That completely depends on how thick the epoxy is. If you are using it for gap-filling then 1A is probably too high. If you read the specs of the data sheet you just posted, they recommend a very thin layer. "The cured bondline should be 0.8 to 1.2 mils"

Mind you, high current mods have frequently melted the soldered components if you don't have an excellent heat sink.

Rick.