waterproof circuit boards

[srimannarayanakarthik]

hi
can any1 suggest me a method to make a ciruit board which doesnt get spoiled when it is dropped into water.actually i got the this idea because my mobile fell into water and was spoiled.
please dont give the ideas that to cover it with something.
i need a circiutboard or a water resistant method for electronic circiuts

 

[Paul Obrien]

Try liquid tape **broken link removed**

 

[dknguyen]

You mean like epoxying the board? That's pretty hardcore and impossible to make fixes to in the future for repairs (or to fix screwups while doing it).

You could just always spray or wipe a conformal coating onto the PCB. It won't make it waterproof, but it would make it water resistant. You'd have to google the differenet materials available and pick the one with the properties you want like silicon, acyrlic, or urethane.

 

[srimannarayanakarthik]

Try liquid tape **broken link removed**

ya thats really good.thanks a lot..are there any more suggestions.i mean a water resistant circuit board. i liked this but i am in india. it may not be deliver to me bcos of shipping problem.

 

[srimannarayanakarthik]

the above idea was good..any more suggestions

 

[dknguyen]

Search around for conformal coating rather than spray on liquid electrical tape (actually, it seems to be pretty hard to find liquid electrical tape, let alone the spray on versions unless you live in a very big city). Where I am, I can only get one kind of liquid tape.). YOu should come across some locally...eventually.

It's much easier to get liquid tape online I find.

 

[Oznog]

Liquid electrical tape actually doesn't make much of a bond with most surfaces. It bonds to itself and goes around an item, but water will creep in at least along the wire connections.

Potting causes a number of problems. First is that thermal dissipation can become quite low. Components may overheat at a fraction of their ratings.

Second, for rigid coating such as epoxy, there's a huge thermal expansion issue. Epoxy typically has a low thermal expansion coefficient, however, components, the board, etc have different coefficients. So expansion can create huge forces.

Sometimes the difference in dielectric properties of an encapsulant can change the circuit's operation too.

 

[mramos1]

Watching TV and did a double post. Sorry.

 

[mramos1]

Search around for conformal coating

This is what I use as well, it is very expensive. I spray everything that goes on our boats and patio with it (the circuit boards of course).

 

[zevon8]

As stated above, silicone conformal coating is made for this application. Spray or liquid form will do. Many come with a UV indicating dye so that you can see if you have complete coverage. It is flexible, repairable, and wont cause problems with components. If you cannot locate it at an electronic supplier, sometimes a similar product is available from automotive part suppliers, same use, waterproffing electrical connections on vehicles.

Here in Canada, a 340g spray can is about $18, quite abit of caoverage from one can.

here is a link: **broken link removed**

 

[Klaus]

There are certain items in a mobile phone which would be very difficult to make completely waterproof. The speaker, the microphone, the keyboard, internal connectors for example. You could easier make them splashproof as in getting rained on or somebody spilling coffee on it but waterproof, as you said happened with a dunking under water, is more difficult. Then there is the issue of water pressure, how deep do you expect to sink the mobile and still want it to remain waterproof?
Perhaps enquire for a military spec mobile phone instead?

 

[mramos1]

For a cell phone. Think ZIP LOCK bag.. I doubt you can seal it 100% and the phone still work.

Does anyone use a vacuum chamber to dry devices out that have took a dip? I have bought the parts to build one, just not assembled it yet..

 

[dknguyen]

My friend forgot his cellphone in his shorts when he went into a hottub and realized it 10 minutes later. It was still working when it dried out, just one of the extras for the address book was a bit funky now.

Perhaps it was the drop combined with the water that caused the failure? Rather than just the water alone.

 

[ParkingLotLust]

To waterproof a circuit board, why not try waxing it? As long as everything stays still when the wax is cooling then it will be watertight. Just put some wax in a double-boiler, heat it to melting, and dip the board. Let it cool and repeat until you have a thick coating. If you need to access the board, you can just melt the wax off.

 

[srimannarayanakarthik]

if v are trying to coat a film on a circuit,this may producea lot of heat.how about that.doesnt this effect the efficiecy on the electonic device

 

[ParkingLotLust]

Wax melts at approximately 45 degrees celsius. Im quite sure any electronic part could handle that.

 

[Nigel Goodwin]

Wax melts at approximately 45 degrees celsius. Im quite sure any electronic part could handle that.

Wax has commonly been used in electronics, often to fix air cored coils after adjustments (VHF radio etc.), it's normal for most of the front end to be covered in wax.

 

[ParkingLotLust]

Case and point.

 

[zevon8]

Many common petroleum ( ie paraffin ) waxes are brittle at room temperature. Not good for something exposed to flexing or serious vibration. Commercial waxes for this purpose are lower in molecular weight, and end up being the softer stickier stuff you see in RF work. Good luck buying a small quantity.

As for the melting point, that varies widely with formulation. 40C to nearly twice as much, depends on the level of refinement. The bigger issue is the environmental temperature when added to the heat of the electronics. Any power section is going to be melting many waxes all over the place.

Horses for courses, wax is OK in the RF section, but I would think power sections and areas subject to mechanical stress would be better suited to other materials.

 

[srimannarayanakarthik]

gereally why does a elecronic ciruit gets spoiled when it falls in water.is it because the electrical elements get shorted due the conduction propery of water or due to any other reason?