How can I remove graphite dust from a circuit board without wrecking the board?

Question

I have two circuit boards that I removed from a CNC machine. The machine shop where it is recently machined a block of graphite, which the shop owner now regrets. Graphite dust filled the air and got all over everything. It also got into a lot of electronics, which is bad since graphite is electrically conductive. Fortunately, the boards I removed hadn't exploded yet so I have some hope of repairing them. The first thing I need to do is remove the dust without further damaging the boards. I'm wondering if anyone out there has had experience with this and if so, what is a good solvent for this? Should I just use my usual soap and water?

thanks, deflagrated. that method works great for loose dust. this is actually stuck to the board. i'm not sure what is causing it to be so sticky, but it's probably some kind of oil, since this board is from an EDM machine in a machine shop. these boards were right above a cooling fan so the dust was blown onto the boards. the loose dust blew by, leaving only the sticky stuff for me to deal with.

Answer 1

see what you can do with canned air.
If you can't get everything off with air, rinsing with alcohol will be much better than rinsing with water as it will not cause rust and evaporate very quickly, leaving no moisture behind. Soap and water isn't good for any electronics.

Answer 2

What you can do is used compressed air to start out with, but the problem with that is it just blows the dust elsewhere in the computer and it can get very messy. What I do after that is completely take apart the computer and lay it on antistatic bags (the silver bags that the hardware is placed in when you take it out of the retail box). When you are done there should be nothing inside the case. Before touching any of the hardware again, make sure to discharge any static you built up, either by taping on the metal chassis of the computer case, or by wearing an antistatic strap sold at some computer stores. The next thing I do is take dry cotton swaps, rubbing all the dust and dirt from the fans, and I will even unscrew the fan off the heatsink of the CPU and wipe it off. After all the dust is out that I can with a dry cotton swab, I will get rubbing alcohol and dip the swab in that and get all the caked on dust you can't remove with the dry swab and clean all the hardware. I will wipe the case out with a damp cloth and use the air duster again to clean as much from the power supply as possible, but DON'T OPEN THE POWER SUPPLY!, just blow as much dust out of there as possible. Once everything is cleaned off as much as possible, go ahead and put it back in. It is suggested that you do this every 6 months. Speaking of which, if you really want to take care of your computer correctly, it is also suggested that when you do this, you also format your hard drive and start from scratch, by doing these two things at the same time, your computer will run like brand new. The process of cleaning the system will probably take a few hours, but there is nothing better than this, except for maybe getting your computer buddy to do it for you :) The formatting and installing the OS and software can take another few hours to a day. For a hint, once the system is together again and you have a fresh install, make a drive image using a program like Acronis True Image that will backup all the programs and files so you don't have to reinstall anything anymore, just run the program to restore and after an hour or so, depending on how much is backed up, you have a system ready to use. Also for your information, it isn't dust in itself that is dangerous for your computer at all, in fact it is harmless in that sense (except for the fan maybe if it prevents it from moving or blowing air), but it is actually the fact that dust makes a nice insulator which means the cooling mechanisms of your computer can't do their job because the dust is keeping the components warm, and warmth is what kills electronics.

Answer 3

I've cleaned grease, dirt and conductive metal chips from many circuit boards, so here is how I go about it. Don't use soap and water.

First, remove as much as you can with a brush (stiff paintbrush, or old toothbrush.) If you have a an air compressor, you can blow some of it off instead. If there is lots of it, start by holding the board upside down over the trash and tapping it sharply all over the bottom with the handle of brush.

Second, especially if there is grease or flux left over from soldering, use a special solvent to remove it, as it is sticky and will retain a lot of the dust. Go to Radio Shack and buy a pressurized can of cleaner/degreaser. DON'T just use any old solvent that you would use to degrease metal parts, because some solvents will dissolve the plastic insulation of components (like capacitors) and cause worse problems.

The graphite itself will not dissolve. What you are trying to do is to dissolve any lubricant or grease that might cause it to stick. The graphite particles themselves must be removed mechanically, either by brushing or flushing or blowing.

Use a hand lens and a good light to look at the board from the edges, to see whether there are any traces of the graphite, especialy between the pins of integrated circuits.

It will be up to you to test the circuit boards and to determine whether they were damaged by being powered up when the short circuit (the graphite dust) occurred. If you have a diagnostic bench set up with a current-limited power supply and you know how much current the board is supposed to draw, set the current limit on your bench power supply very close to that amount, just barely above it. Then, when you power the board on to test it, if there is any remaining short on the board, the excess current it draws from the power supply will cause the power supply to shut itself off instead of damaging components on the board.

If you have to put the board back in the machine to test it, be prepared to run the manufacturer's diagnostics or self-test routine (I presume they have one that came with the machine.) Also, be prepared to interrupt the power-on-test if there is any sign of trouble, to keep worse damage from happening!

Once you are sure that everything is working properly again, coat the board with a conformal silicone coating. (NOT the same as silicone caulking for your bathtub! That stuff gives off acetic acid which can cause shorts.) You can order conformal coating materials from electronics supply houses. (I don't think that Radio Shack carries them, but you can ask.)

What the coating does is to seal the circuits and protect them from environmental hazards such as the graphite dust. It will also protect the circuit board from water due to condensation or fire sprinklers, or dripping grease and solvents, or whatever other things might be in your shop. It can be peeled off in the event future repairs need to be done. (Naturally, you don't coat the plugs, jacks, edge connectors, etc. Just the components and the etched traces on the board.)

I'd stongly encourage you to take the extra time to do some annual preventative maintenance and coat the circuit boards in each one of your machines with a silicone conformal coating. With the way the graphite dust is so fine and blows around so easily, it may well have gotten into other machines and their circuit boards as well. Don't wait for them to break down! And buy pre-machined graphite EDM electrodes next time!

Hope this is sufficient. Good Luck!

21 NOV 06, 1616 hrs, GMT.

Answer 4

Use something that will blow the dust away. I think you'll find a vacuum less useful. If you don't have a compressor then ( I have no idea how large a job it is ) what comes to my mind is a kit I purchased for ear wax removal... there's a squeeze ball that fills with warm water that is used to irrigate the ear but .. it blows air of course with no water in. Maybe you have something handy that will do the job.

Answer 5

I would remove as much of the graphite as possible with a soft brush and/or a vacuum cleaner. Then clean the remaining graphite with contact cleaner and cotton swabs.

I sure miss good old trichloromethane.

JeffM

Answer 6

I would use a soft paint brush or even a vacuum cleaner. Using solvents or even water will probably do even more damage.

Answer 7

Try using compressed air.