Hi

I pulled a connector out of its cavity where a part of a flexible circuit board bends in. The part which is bent in has few exposed copper areas where it makes contact with the corresponding pins in the connector.
The copper is getting dark, I think it is removable dirt. what is the best way to clean it? I do not want to use fine sand paper less it destroys the thin connecting areas of the flexible circuit board.
Should I use alcohol with a cotton swaps or something like that.

thx

 

Professionals make a glass brush (I am not sure you can buy them) for this purpose. They are very effective.

Find a fibreglass/resin rod or shaft about 1/4" diameter.

Cut or grind a flat at one end.

Form the brush by pressing the flat against the side of a hot soldering iron or other hot, but not glowing, iron and rub with a twisting motion.

This will melt out the resin in the end, exposing 1/8" to 1/4" of the ends of the glass fibres.

 

If it isn't really heavily oxidized I use a common clean pencil eraser, they work wonders.

 

Yep, common clean pencil erasers work great.

Another method one can use that's moderately hazardous is to dip the corroded end in muriatic acid (diluted hydrochloric acid; available at pool supply stores) for 20-30 seconds, and then immediately rinse thoroughly in clean cool water.

Note that muriatic acid is very harmful to breathe, and will destroy natural fibers (for example, jeans and cotton T-shirts) along with nylon and many synthetic materials. Only use it in a well ventilated area, preferably with a large fan blowing the fumes away from you. Keep a bucket of water (with some baking soda mixed in) handy in case you have any spillage. Immediate dilution of the acid with water and baking soda will minimize any damage.

The microwave-safe black plastic trays that Stouffer's frozen ready-to-eat entrees come packaged in (like lasagna and stuffed green peppers) seem to be immune to muriatic acid; and the square corners help when you're ready to pour it back into a container. I use these plastic trays for making small PCB's.