Sometimes I come across an old computer or some other electronic device that doesn't work and is very dirty in some way. Maybe because it had been thrown away in the woods and left there for weeks, maybe because something was spilled on it while its case cover was removed, maybe because it's one of my computers and it was forced to run in my dirty home for too long. No matter what the symptoms are; A dirty PCB can be the cause for almost any type of misfunctioning.
What inspired this post was the fact that one day, Fred refused to turn on again. This time I couldn't blame a cheap power supply. I decided to clean the whole server because it was sitting in a home with nondiscript renovation activities going on for months. It was visibly dirty. Some electronics are designed with all sorts of unusual envirements in mind. Most are not prepared to be exposed to the envirement I lived in at the time, for a prolonged period of time.
Without keeping one specific computer, a specific type of dirt or one specific instance of dirty electronics in mind, the following are the main steps that I consider when I decide to clean a very dirty piece of electronics (mainly PCs).
You may decide to skip any part or any tip if you think it will do no good or even harm your specific device. I wrote this whith the dirtiest computer that I have encountered in my life in mind to cover pretty much all cases.
Checkup And Prevention
To get an idea of how dense the dirt is in various places, you can blow on parts to take away the top layer of dust. I like to use a spray can of compressed gas (often called compressed air or air preassure can) to run not-so-dense dirt out of the corners in which it has been collecting so far. There are great differences in preassure and volume of compressed gas spray cans. From those commonly found at distributors in Germany, I like Balisto best. Any gas spray can with a high preassure will do though. If you have an air compressor you can use that instead. I don't like it because of the noise. But it is cheaper and easier on the enviroment if you do it a lot.
Some people claim that there is no use in blowing on dirty electronics because that will merely redistribute the dirt inside of the device. That is not true if more dirt is blown off of the electronics than there is in the air already. Yes, the dirt gets merely blown onto other surfaces. But those tend to be outside of the device and easier to clean. If you do this to a device regularly before denser dirt builds up, you can prevent having to apply the rest of the steps.
Also, with a smart air circulation concept and clean filters on entry points (sucking fans) dust buildup can be reduced noticably.
Cleaning the surrounding of the device regularly and not letting smokers or hairy pets into the room where the device is running also helps to prevent dirt buildup in the first place.
Notice that high air humidity and nearby plants can attract bugs and spiders, which is nice, but not for electronics. Even PCBs build for the use in the outdoors develop faults if many insects are taking a liking to the warm envirement in the case. That happens mostly if the device is left outside, not moved around much and there are a great variety of different wild plants nearby. Also humidity itself contributes to corrosion in contacts, traces and possibly even wires.
Taking The Device Apart
If it's really dirty, you'll have to take it apart, I'm afraid. You need to reach in all corners and be able to make sure that dirt doesn't get merely transfered into th hardest to reach place of the casing.
To remember which part goes where, you may want to make pictures of the arrangement in the case, of connectors, orientations and marking of things, clips, screws and labeling. If it's not straightforward, make more pictures than you think you'll need. You may realise when putting something back in that two parts look very similar except from one angle, or that the orientation of a connector is not clear. If necessary, label cables and put screws into labeled containers.
Do not forget to remove any batteries. You should do so definitely before applying any liquids. But moist dirt itself can also cause trouble when it touches the wrong spots (which is why the device has to be cleaned in the first place). Commonly in PCs there is a 3 V round cell battery in a clip holder that can easily be taken out. Older devices may have soldered on lithium batteries in various casings and form factors. In modern, small form factor PCs, especially in laptops, the lithium battery also may take various forms and may require soldering to be replaced.
First Brushing
The next step after blowing is brushing. First I take a large soft paint brush and take the majority of the dust off. Its hair are long and soft, so there is no danger to any sort of soldered parts. A few brushes in several directions while holding the board over a trash can should be enough.
Now that the majority of dust has come off, what stays is the stuff that needs more intensive cleaning. If common house dust was all that there was to get rid of and you don't care about looks, you can already power up the device again to see whether the fault has disappeared.
If a more intensive cleaning is necessary, liquid gets involved. There are two ways to continue. One is with a dishwasher (if you have one that allows for the necessary settings) and one without. The latter is more work, of course.
Wet Washing (Dish Washer)
Some people don't want to believe that this technique can be safe because it involves water. But water itself is not dangorous for the PCB, if it dries off before any voltage is applied and before anything starts to corrode. A run in the dishwasher is just the right thing for getting even oily substances or crusted food residue off completely.
The three dangers that dishwashers can pose to PCBs are:
- Water preassure - This only comes into play if you're using a special industrial dish washer and have certain delicate parts on the PCB. Water preassure is not a problem at all with household washers.
- Heat - The most important thing is that the dishwasher has a setting to disable drying. All dish washers nowadays dry the dishes after washing them in order to prevent water spots from building. The heat during the drying period may be too high for some parts on the PCB. Dish washers usually also heat up the water in order to be able to reduce the time the dishes have to be let sit wet. Some claim to maintain a water temperature of 95 °C. That may be too hot for some parts on the PCB. If you're not sure about every piece on the PCB, you should reside on the side of caution and not use the dish washer for that PCB. If the device is specified to continuesly operate at an surrounding temperature of 60 °C or more, and you trust that it's still up to that, and you're sure that neither the water nor the air inside the dish washer gets hotter than that, it should be safe enough. Most parts don't have a problem with being heated to that temperature for a short while. But you should make sure that the temperature really doesn't rise above what the setting suggests. There are enough reasons to forget about the dish washer and do it by hand if unsure. The usual advice is to only use a dish washer if it has an option to run a cold wash, without heating up the water. If it offers a run at 30 °C, then that generally is safe also. Note though that the cooler the water is the longer it has to sit to achieve the same effect.
- Hight/Dimensions - Lastly, of course the board has to fit into the dish washer. If your dish washer has a spindle at the top, make sure it can't collide with anything. The board should be oriented in a way in which the dirtiest or most difficult to clean by hand parts are facing the spindle that squirts out the water. If there are fiddly parts (like slot connector rows, deep heatsinks or forests of capacitors and coils) on both sides of the PCB then you may need to turn it around after one go and wash it again.
Usually PCBs don't have to be washed for as long as dishes with crusted food residue. That means that even without heated water the washing time doesn't have to be increased. But if there actually are crusts of dirt and gooey clumps on there, washing time needs to be significantly longer than it would be with hot water.
Wet Washing (No Dish Washer)
In order to save water, get a tub or a bowl or some similar container large enough to hold all the parts that you're going to wash. Wet the dirty parts with a shower head, catching the water in the tub/bowl. Use warm water no hotter than you would to wash yourself. Put some of the dirtly pieces into the bowl/tub. Add a drop or two of dish soap if you like. Don't use aggressive detergent. If the parts aren't covered with water completely, add more water.
Depending of the type and intensity of the dirt, you may want to keep the parts in water for an hour or even longer. Usually, a few minutes are enough though. When you think the dirt is soaked enough, remove the parts from the dirty water and rinse them with cold, clean water. A bit of preassure may be good. If you have an old shower with no preassure limiter, be careful not to damage sensitive parts, if there are any.
In most cases, PCBs, metal parts, plastic parts, cables and connectors are clean after that. Make sure to let everything dry sufficiantly (see below) before powering anything. If you find than some spots are still dirty, a second and possibly longer bath or a more thorough brushing may be needed.
Instead of letting the parts soak you can also try to brush them with a soft, wet brush, then rinse off the dirt and repeat until no more dirt is removed with the large, soft brush. This may be more convenient if all that is to be cleaned is one PCB. See below for more brushing tips.
Second Brushing
Before you get out the harder brushes or try to rub off remaining dirt with more preassure, inspect all PCBs that you want to brush to see if there are any parts that may be damaged by too much preassure. Pins can be bent, long legs of parts can be bent and even ripped off. Polished dies (heat intensive chips on which a heatsink will be placed) can take damage in the form of scratches. Sockets of modern CPUs need to be covered to protect their pins. If the socket can't be covered securely otherwise, consider just leaving the CPU in. Be careful around these spots and consider covering polished dies with a piece of packaging tape (or the original cover if you still have it and it doesn't cover too much other space).
Small areas of flat surfaces (like unpopulated areas on PCBs) can be cleaned with wet cotton sticks. I recommend them only for the removal of specific blobs of dirt. Cleaning more than a square centimeter or so takes too many sticks. If there are larger flat areas, like on casing parts or on modern ATX boards, use a cotton or microfiber cloth.
Any other area of a PCB, any area that is populated by anything or where there isn't much space bewteen two parts, is better cleaned with brushes. Start with a large, relatively soft brush to sweep and brush large areas at once. Then switch to a smaller, harder brush for any spot that is not sufficiently cleaned by the larger, softer one. That will be many spots. Practically any spot where there is no more than a few millimeters of space between parts. Depending on how dense, how high and in what shape parts are, I switch between the following brushes:
- Wide, soft paint brush - for larger areas with flat SMD parts only as well as the unpopulated back of a PCB.
- Narrow, soft paint brush with slightly shortened bristles - for areas between high parts (e.g. between large capacitors or between PCB slots).
- Small, hard paint brush with very short bristles - This is getting closer to scratching. I use this brush to get grundge out of corners, from under legs or from between flat SMD parts. Do not use this on sensitive connectors, like RAM slots or flat flex connectors unless you need to. If you do, be very careful and only brush in the direction the connector pads are oriented in.
- Medium-hard toothbrush with cross bristles - I use this one for light scrubbing around all sorts of areas. The crossed bristles really make a difference in getting general dirt out from the corners of tiny SMD parts and from under legs of through-hole parts. When I say scrubbing I mean with almost no preassure. The movemenet in varying directions is what matters.
- Hard toothbrush - If there are areas that require it, this harder brush continues the scrubbing, with very light preassure. Do not use the hard brush on sensitive connectors like RAM slots or flat flex connectors.
- Interdental brushes - Although I almost never do this, if you would want to bring the manual cleaning process to an extreme, you can go on using interdental brushes of various sizes to scrub inbween every other mm. On PCBs with many through-hole parts and a lot of solid dirt this may be necessary. But I reckon that if that much afterwork is necessary, the bathing and rinsing before wasn't done thoroughly enough.
After you're done with the process once, you know what sort of brushes you like and can prepare the right set for the next time. Shorten bristles according to your requirements to make paint brushes harder.
After brushing and possibly scrubbing every area of the board, rinse it in the shower again. Repeat brushing and rinsing if necessary.
Other guides on cleaning electronics often include the usage of alcohol and vinegar. So even though I rarely use them just to get off heavy dirt, I'll write about their role a bit. Vinegar is mostly useful to treat spots of light corrosion. Hopefully your board isn't that badly. If it is, cleaning might not be enough to get it working again. Cleaning alcohol (isopropanol with 90 or more % of alcohol) is useful to dissolve substances that don't dissolve easily in water. Depending on the type of extreme dirt you might try insect remover, dish soap, degreaser, silicon cleaner or diluted acid. Be aware though that anything more agressive than soap might attack some parts on the PCB or their casing. Cleaning alcohol has so far been the only thing besides soap to clean off even the most disgusting clumps or dirt. You might consider meths instead isopropanol alcohol because it's way cheaper. Denaturated alcohol will leave a residue of its additives, though. I'm not aware of any consequeces to electronics. I know it is often used as a cheaper alternative to isopropanol alcohol even in professional circles. But YouTubers tend to warn about using it to clean electronics. So, maybe they know why and you should reside on the safe side here. I don't and I'm not aware of any problems it may have caused me.
Connectors are parts you should to look out for specially if after the first round of wet washing you still have hard dirt to brush away. Many modern connectors (their pins or their fixation) are easy to bent with a brush with hard bristles. Some can be ripped off more easily than one may assume. That is the reason I like to treat some connectors longer in a water tub or dish washer than, e.g. casing parts. Cables with flat sheath are best cleaned by soaking in in water for a while, then slowly wiping off dirt by swiping it through a cloth. Depending on the number of centuries the cable has been exposed to heavy dirt, the process might have to be repeated a couple of times for each centimeter of the cable from every angle. Especially wite cables might take a dozen or more times of swiping with 10 minutes of soaking in between. Mash cable sleees, if they are really dirty, might take some brusing with a hard brush with small bristles after they have been soaked in water enough.
Drying
Before the electronics can be powered they need to dry, of course. There are a few things that can be overlooked though. If a board looks dry on the surface that doesn't necessarily mean that every part of it is dry enough already.
Coils and some other parts can hold water for days if they were drenched. If there are any on the board, a day long dry should be the minimum; Two days if you want to be sure and don't apply any drying methods. Dense connectors can hold quite a lot of water even if the rest of the board already completely dry. It may be necessary to blow them dry even after a day of waiting.
Because of my work and living situation, I often don't come back to the device for days anyway. So I just leave it in a slightly ventilated spot for 5 days or a week until putting the device back together. If you don't want to wait that long, consider the following.
- Leave the parts in a well ventilated and dry spot in a position where only small surfaces/corners are touching anything other than air. Things will not dry otherwise and you may get a new problem with corrosion.
- Position a fan to blow on or past the parts, especially PCBs, in a way that it can be left unattended. Even a small computer fan at low speed does a lot. A room fan set to 11 does more. But don't use a room heater to blow hot air directly at the parts.
- Use a hair dryer on low or cold setting to blow parts dry quicker. This speeds up the drying process a lot. But don't expect wonders after one minute. You still need to give it some time. Don't come too close with a hot hair dryer and don't use the high setting unless you hold it apart a meter or so to dry a large bunch of parts.
- If the weather allows for it, you can use solar energy to dry parts quicker. If there is nothing among them that you don't want to be exposed to UV light a lot, leave them outside in the sun for a few hours. In really hot weather, check the temperatur of the surface first and regularly. It might be too hot for some parts. Don't use glass or mirrors to increase temperature.
- In general, what's best is slightly above room temperature (more heat doesn't do all that much but can damage some parts) and continued ventilation (the more the quicker).
To prevent water spotting make sure to use soft water (low amount of chalk in it), filter it if necessary. Cleaning alcohol can also help to prevent spots during the drying process.
If you grow impatient, make sure to withstand the idea to try and use a heater. Don't place the electronics on top of a heater, don't have a heatgut point directly, at it. If you use a radiator, use it to heat the room, not the electronics first.
Finishing And Testing
When you are happy with the result of the cleaning process and you are sure that all the parts have dried sufficiently, you might rush and power the PCB up to see how it does. But you also might want to take the time to check whether you have damaged anything, bent any radially mounted party or connector pins. Depending on the original finish and the age of the PCB the now perfectly clean part may look astonishingly well or boring. If you want to show off your machine or sell the PCB. you might want to apply your own finishing by spraying the board with silicon spray. There are oils that advertise being best for this purpose. But I don't agree. An evenly distributed silicon coat looks best in pictures and in person. A spray can with a good nozzle allows for an evenly distributed, thin coat. Don't allow for drops to form. If you can't get it evenly distributed or your can spits, apply a bit more than enough and use a large brush with soft bristles (the one you started out with for the manual cleaning process) and brush the board in random and all sorts of directions to make it look evenly distributed.