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To summerize so far: For a hobbyist, pencil erasers are effective in removing tarnish from the metal on the surface of a printed circuit board prior to soldering. The technique is also applicable to switches and connectors.
Two issues with using erasers are:
Four common types of pencil erasers will be compared under the microscope to determine which produces the least scratching and least residue.
Magic Rub, Pink Pearl, plastic, and arrowhead cap erasers.
The tested erasers are:
Two other common types of erasers, art gum and kneaded, were not evaluated in these tests because I didn’t have any on hand. Ink erasers were not tested because they are grittier and therefore too aggressive.
The pencil top eraser was used to obtain the results on the prior page. So, the other three eraser types will be compared to the pencil top eraser.
For each test, the middle and right hand portion of a 0.1″ by 0.07″ tin/lead-plated commercial PCB pad was erased by hand with moderate pressure for approximately 5-10 full strokes. The left edge of the pad was not erased so that it could provide a visual comparison of before and after. The eraser residue was not blown or brushed away.
Printed circuit board pad cleaned with a Sanford Magic Rub eraser at 60x magnification.
The Magic Rub eraser appears to scratch less and it leaves far less residue (at least at this magnification) than the pencil top eraser. In fact, it appears that the big glob of Magic Rub eraser residue can simply be brushed away without requiring any additional cleaning.
The tarnish came off very well, except for a small stubborn patch that may be ink or a stain. Only one sample pad was tested. Perhaps this was just bad luck.
Other brands of white vinyl erasers can likely be substituted.
Printed circuit board pad cleaned with a Sanford Pink Pearl eraser at 60x magnification.
The Pink Pearl eraser also appears to be much gentler than the pencil top eraser. However, it leaves a lot of residue. To my standards, the tarnish came off the pad evenly and completely.
I’m not certain of the composition of the plastic eraser. The plastic eraser is firm (solid) and smooth (non-gritty).
Tarnish was not removed from a printed circuit board pad with a plastic eraser (60x magnification).
Although the plastic eraser might have wiped away some dirt or mechanical contaminants, the eraser did not appear to have any effect on the tarnish. There was a little scratching, which might have been caused by contaminants getting embedded into the eraser during usage.
The eraser residue was not as bad as the Pink Pearl or pencil top eraser, but not as clean as the Magic Rub.
When I need to repair a board in situ (in the original device) or when I’m cleaning a connector that can’t afford to lose plating, I'll select the Magic Rub eraser because it doesn’t appear to scratch and the residue appears to be easy to clean up.
If the board can be removed such that it can be rinsed after cleaning, the Pink Pearl may be slightly more thorough.
For more aggressive cleaning of a PCB shortly before soldering, the pencil top eraser digs the deepest.