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Removal of Carbon "smear" from contact pins prior to Ni Au Plating.

November 19, 2009

Hi all,
I am looking to improve our current process for removing carbon "smear" from the surface of assembled connector contact pins. The carbon is smeared onto the sides of the nickel alloy pins by a carbon alignment fixture, during its removal, after furnacing the connector at 1800 degrees F. Due to the configuration of the connector and location of the carbon, mechanical removal is problematic.
The contact pins are inspected at 10x after Ni Au plating and any visual evidence of remaining carbon is cause for rejection. Due to the shear volume and difficulty in inspecting during the pretreatment cycle, we are experiencing a much higher rejection rate than is acceptable.
Current process used with the goal of complete carbon removal as follows;
The connectors are racked in quantities of 12 - 30, depending on size.
Number of pins per connector can range from 2 - 200.
Periodic reverse electro-clean @ 4-6 V for 10-15 min. standard e-clean chemistry @ 155 f
Permanganate/hydroxide at 1.5 #s per gallon 200 F for 1 hour
Oxalic/sulfuric @ 130 F for 30 sec to 10 min to remove Perm residue.
Repeat above process if required until Pins are carbon free(impossible to verify in production)
Continue with subsequent plating.

This is a legacy process, given to us by the original manufacturer, and works fairly well on 80-90% of the production.

Any suggestions are welcome, the more the merrier.

Some of my thoughts, ultrasonics, acid dip prior to perm, vapor honing pins.....

Thanks for you interest and responses.

Steve Parkhurst
Job Shop Employee - San Diego, California, USA