Fibreglass pencils

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While eBay-crawling in search of some Stannol solder to try, I saw something called a fibreglass pencil. Apparently it's to be used to clean tracks and contacts.
Hmm... but doesn't it scratch these tracks and contacts? If you used this 'pencil', can you please share the experience?

[mikeselectricstuff]

They work pretty well for cleaning really dirty boards or removing solder resist however you end up with loads of fibreglass bits which irritate the skin like hell.
Wire brushes are nealy as effective without the nasty debris.

[david77]

Very usefull to clean corroded contacts & such, also works well to remove permanent marker and dirt of all descriptions. I always keep one in the workshop.

[Fraser]

I wouldn't be without one.

They are abrasive (they have to be to work) but plating damage is minimal.

When using such a glass fire pencil I advise the wearing of latex (or whatever you prefer) gloves and working on a disposable surface such as  a newspaper. Once you've completed the job, shake the debris out onto the paper, then bin it carefully. It is important to not get the tiny glass fibres (that are shed during cleaning) into your skin as has already been stated. If such occurs you will suffer very irritating itching of the site for days and it probably isn't a great health idea either. You may wish to wear a dust mask as well, though I have never found this to be needed.

In a sentence.... a great tool to have on hand but handle with suitable care to avoid unpleasantness afterwards !

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Thank you for the advice.
Call me stupid, but I just finished cleaning liquid damage to a Mac mini board, and I am having a hard time imagining how this fibreglass pencil with 4mm tip is even going to work on this board; 4mm looks huge next to tiny clearances on this densely packed board.
Is it possible to get different size tips, or there is pretty much only 1 size?

[Fraser]

STOP !

Please explain exactly what is on the board and what you are trying to clean.

I would not normally be using a FG pencil on a PC or MAC PCB. Fluid damage can be a killer as the worst damage often occurs under the IC's where it's very hard to examine or clean. Many fluid damaged PCBs can be soaked in warm distilled water or IPA to remove conductive contaminants. If rust has formed it is very bad news for the PCB. Any BIOS memory battery will be US, and any +ve tracks or IC pins connected to it will corrode heavily due to electrolytic action.

Please let us know the full story so that we can best advise you 

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Well, while what you are saying is true, in the past 10 years I brought back a fair number of liquid-damaged boards, assuming the damage occurred fairly recently and no major damage was done to components (and the customer is very lucky). My question isn't about how to clear liquid damage, really.
I am trying to understand the intended application of these fibreglass pencils which I have never seen in person, I just saw one for the first time in my life on eBay.
So you're saying that the pencil is of no use to me because I mainly rework and repair mobile phones, laptops, and such?

[IanB]

I have a fibreglass pencil that I picked up either at Radio Shack or Fry's (I don't remember which). It is like a felt tip pen with a thick fibreglass tip and a screw advance mechanism like on a glue stick. It works well for cleaning the oxide film from the surface of copper or other metal surfaces making it nice and shiny again without excessive abrasion. You just rub it gently on the surface to be cleaned until it is bright and ready for soldering.

I have not noticed the fibreglass bits problem that Mike mentioned; maybe this depends on the particular make of pencil?

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I have a fibreglass pencil that I picked up either at Radio Shack or Fry's (I don't remember which). It is like a felt tip pen with a thick fibreglass tip and a screw advance mechanism like on a glue stick. It works well for cleaning the oxide film from the surface of copper or other metal surfaces making it nice and shiny again without excessive abrasion. You just rub it gently on the surface to be cleaned until it is bright and ready for soldering.

I have not noticed the fibreglass bits problem that Mike mentioned; maybe this depends on the particular make of pencil?

Do these pencils come only in 1 size?

[Bored@Work]

I am trying to understand the intended application of these fibreglass pencils which I have never seen in person, I just saw one for the first time in my life on eBay.

They are sort of like tiny wire brushes. The fibers are much smaller than wires in a wire brush but still very hard. The tiny fibers give you finer control over the applied force to the surface, compared to a wire brush. And that allows not just to scrap hard stuff from a surface, but also to polish the surface to some extend.

 

[IanB]

I've only ever seen one size. It's about the same size as a flux pen.

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Probably I should get one of these and have some quality time with it and a dead board, see how it feels and what it does and go from there.
Thanks very much for your replies and advice.

[IanB]

I've found the best technique for using one is to keep the "brush" short and use a light touch. Don't force it, just let the abrasive tip do the work. They are good for fine control and small areas.

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I've found the best technique for using one is to keep the "brush" short and use a light touch. Don't force it, just let the abrasive tip do the work. They are good for fine control and small areas.

That's useful, thanks.
You mean you just 'sharpen' the pencil to suit the type of area you're working on?
If so, what do you sharpen it with?
How short do you recommend to keep the brush?

[IanB]

No, you don't sharpen it. Think more of a mechanism like a glue stick (a "Pritt Stick"). The brush advances out of a metal tube and as the end wears down you just advance it a bit more. You end up with a circular brush a few mm in diameter. You hold the pen vertical when you use it so the end of the brush is flat against the surface.

[IanB]

A product picture: