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Today, while I was cleaning a RAM module, I was thinking about this.

An eraser is really a easy way to clean gold/copper contacts in such modules.
And it is really tempting to do so.

I did it a few times with RAMs, network cards, graphic cards and other components.

But, my question is: is it safe at all to clean contacts with an eraser?
It at least works, since the module was perfectly working fine this time.

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    \$\begingroup\$ There are many eraser materials of which some build up quite some static. \$\endgroup\$ – PlasmaHH May 5 '15 at 9:42
  • \$\begingroup\$ @PlasmaHH Does a regular white eraser (to erase pencil on paper) causes that? \$\endgroup\$ – Ismael Miguel May 5 '15 at 9:45
  • \$\begingroup\$ I'm amazed you haven't blown RAM and/or other things doing that. I would buy made-for-purpose contact cleaner instead, and follow the instructions. Seriously! \$\endgroup\$ – CL22 May 5 '15 at 9:49
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    \$\begingroup\$ @IsmaelMiguel: there is no "regular" material those are made of, all can be different. \$\endgroup\$ – PlasmaHH May 5 '15 at 10:02
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    \$\begingroup\$ @IsmaelMiguel: Do it like with a wire... if you dont know if its live, are you going to touch it? \$\endgroup\$ – PlasmaHH May 5 '15 at 10:09
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It all depends on what you mean with safe.

To cut it short: if what you are doing is some sort of professional work, the answer is not at all. As @Jodes said in a comment, the right thing to do is to use some specialty chemical made for the job.

If, however, you are doing some hobbyist work and you are going to take some risks then your approach may work, but keep in mind that the results may not be very repeatable.

There are at least two things that may go wrong with your approach:

  • Electrostatic discharge (ESD) issues
  • Mechanical stress

Anytime you rub two objects against each other you have the chance of generating static electric charges on them. This phenomenon is called triboelectric effect. A problem with ESD is that it may not kill your chips rightaway (many chips today have protection circuitry that will handle a small amount of ESD), but it may degrade the performance of your devices (e.g. leakage currents or offset voltages may become permanently worse because of microscopic damages inside the semiconductor device). Therefore a RAM module, to take your example, may still work, but with intermittent failures or glitches (e.g. it may exhibit a higher error rate or it may work reliably only well below its rated maximum speed).

Whether your approach will work consistently in this respect will depend, besides sheer luck, on many parameters like ambient humidity, eraser and PCB materials, operator grounding, etc.

Mechanical stress is maybe a lesser concern, but it should be taken into account: if the eraser is hard, if you press too much while erasing, if the PCB tracks or pads are too thin, you may risk detaching one of these latter from the PCB and this will ruin your day most likely (repairing a multilayer PCB is not easy, is often expensive and sometimes is not even possible).

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  • \$\begingroup\$ Those are very interesting points. I never though about it. Sadly, it is for professional work. And I really can't get anything better than the eraser. \$\endgroup\$ – Ismael Miguel May 5 '15 at 10:51
  • \$\begingroup\$ @IsmaelMiguel Can't you order something online and make it delivered to you? From your profile I see you are from Portugal so you could shop online from here. I just searched for an affiliated distributor of one I use here in Italy (sadly not one of the cheapest, but fairly realiable), so I cannot tell you more details for your country. \$\endgroup\$ – Lorenzo Donati supports Monica May 5 '15 at 11:17
  • \$\begingroup\$ Since I don't have a credit card, it will be hard to buy it myself. I'll have to convince my boss to buy it. But that sounds like a really promissing website and I surely will look into it. \$\endgroup\$ – Ismael Miguel May 5 '15 at 11:27
  • \$\begingroup\$ Feel free to show your boss what you have found here on EE.SE (maybe search this site for the ESD tag, you'll learn a lot more). A professional firm should use professional tools, especially if it wants to keep its clients happy (and hopefully to gain more). \$\endgroup\$ – Lorenzo Donati supports Monica May 5 '15 at 11:31
  • \$\begingroup\$ That is actually a nice tip. My speciality is programming, but we do all the efforts to make our clients happy and to solve all their problems. I guess I did the right thing in asking here if it was safe or not. \$\endgroup\$ – Ismael Miguel May 5 '15 at 11:42
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Short answer: no point.

Longer answer: In the past many generic and certain purpose made erasers have been used to clean electrical contact (diamond coated plastic sheets were used on relay contacts at times).

That said the cleaning is intended to remove oxide layers and gold plated contacts should not have oxidation. Also the gold plating on modern contacts is as thin as they can make it and heavy mechanical abrasion will remove some of the gold. When the gold is no longer protecting the base metal beneath you will have oxides forming.

The binders of an eraser are no conductive, this is good and bad, good because the fine dust should not cause a short but bad because any residue left will form an insulating layer. Any hard abrasive particles on the contact surface will prevent contact unless they are displaced when the contact is remade.

For gold contacts I would clean with solvent, 90+% ethyl or iso-propyl alcohol are safe for most electronic devices (careful with keyboards, switches and relays and other devices with exposed contacts that may get dirt washed in or displays and sensors that may use adhesives in construction). The solvent cleaning is also a good idea after cleaning with an eraser to remove the binder residue. Limit eraser cleaning of gold contacts to a very limited number of occasions and only if there is visible contamination that does not want to come off with the solvent.

There are aerosol contact cleaners that contain various solvents that are available for more money than they are worth.

Here are some mechanical contact cleaning aids

http://www.eraser.com/fybrglass-brushes-and-erasers/

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  • \$\begingroup\$ Where can I get that? I can get ethylic alchool, but I would love to avoid any liquid in a RAM module or any computer part. But you made a nice point. I do make sure that there's no residue left. And I double and triple-check it before using. \$\endgroup\$ – Ismael Miguel May 5 '15 at 11:13
  • \$\begingroup\$ Pharmacy should be able to sell small qualities of the alcohol (ethyl is usually more expensive because it is taxed as liquor) I would stay away from methylated/denatured/rubbing alcohols as they contain adulterants, methy alcohol and water. Large qualtities from chemical supplier. With pure alcohols there is no danger in immersing the memories and then letting them dry. \$\endgroup\$ – KalleMP May 5 '15 at 11:18
  • \$\begingroup\$ Do you think that 96% of concentration is enough? I can scrub around and find 97%. One example, from a supermarket here: continente.pt/stores/continente/pt-pt/public/Pages/… (The important is the title, which simply says "Ethylic Alchool 96% volume"). \$\endgroup\$ – Ismael Miguel May 5 '15 at 11:30
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    \$\begingroup\$ The stuff you found looks fine. The purest ethyl alcohol is generally limited to 97% but then contains some not food safe chemicals needed to distil it to that point. Usually the best that can be achieved that is food safe is 92%. Both are fine for cleaning, anything above ~90% will evaporate with no residue (if you rinse all the dirt away). To test, put a big drop on a clean smooth surface, it should not leave a ring when dry. \$\endgroup\$ – KalleMP May 5 '15 at 11:46
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    \$\begingroup\$ Isopropyl Alcohol (or IPA) is pretty easy to get hold of in concentrations up to 99%. Most pharmacies sell it as to many many places online. \$\endgroup\$ – Tom Carpenter May 5 '15 at 13:36
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@Lorenzo Donati alredy gave a good answer. But also be aware that there are several types of erasers.

This soft, beige-colored erasers made of pure natural rubber only will not do any physical damage to your PCBs (except when you apply too much force)

But often, some abrasive material like pumice or quartz is added. For example, this common type of eraser contains some abrasive material in the red part and a lot in the blue, used to remove Indian ink.

enter image description here

Also, the rubbers of pencils usually contain some abrasive material.

While a slight grinding effect may be intended to remove oxides, you can easily remove too much, e.g. from the gold plating of the contacts. The contact will corrode very fast making it very unreliable.

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  • \$\begingroup\$ That isn't the type of eraser I have. I have one of the soft white types. Like this one: maped.com/en/products/school-supplies/erasers/technic-softy. But you made an interesting point there too! I don't get why they would put quartz in an eraser, but I'm not an eraser maker. \$\endgroup\$ – Ismael Miguel May 5 '15 at 10:54
  • \$\begingroup\$ I'd heard that rubbing contacts with erases was a no-no due to phosphorus. I don't know if there's any validity in that, however as a kid, I did try it several times on battery terminals. The net result was always more oxidization (and worse performance) after erasing. \$\endgroup\$ – rdtsc May 5 '15 at 12:03
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I don't use erasers any more, unless cleaning battery acid residue off a terminal. Common 70% or 90% rubbing alcohol and a soft cloth works so well, why risk it?

See also Contact Cleaner VS Alcohol

Please note that rubbing alcohol is partly water. Water, especially clean water, is meaningless to unpowered electronics. In production the cleaning step of those boards (these days, given environmental regulations) was likely water based anyway. Make sure it dries totally completely before powering back on.

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  • \$\begingroup\$ I'm sorry, but the "water is meaningless" part really scares me. I had a huge luck that none of the devices I've used the eraser to clean had a bit of residue stuck that stopped the contact. \$\endgroup\$ – Ismael Miguel May 7 '15 at 19:19
  • \$\begingroup\$ What Bryce means, is that it is OK to use water to clean the components, just make sure it has TOTALLY evaporated before applying power to the board. It is obvious that if the water used for cleaning has evaporated, then there is no water left on the board to cause any problems! \$\endgroup\$ – Guill May 8 '15 at 23:36
  • \$\begingroup\$ As mentioned many modern PCB cleaning regimes during manufacture are water based (with various surfactants and solvents, probably alcohols, mixed in). Total immersion or flood washing with pure water, most common alcohols and other proprietary PCB cleaners is usually safe if you do not have devices with hidden contacts and crevices (like speakers) that can trap liquid, weak inks and adhesives or power from standby batteries. All these must be removed so only the bare board is being washed. If you cannot remove sensitive parts you have to work more carefully with earbuds or similar. \$\endgroup\$ – KalleMP Nov 17 '17 at 20:55

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