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February 17, 2015

Gold Edge Contact Rework

I am replating gold edge contact that need repair. After completing the bench-top replating process the board meets the required thickness specifications and passes a peel test. However, the electroplating process leaves slight dark residue on the gold contacts. Is this acceptable? Can it easily be removed?

T.T.

Experts Comments

This is a great question. Most people use a pencil eraser to 'polish' the gold surface. It doesn't make it look perfect, but it does a good job of getting rid of the black spots and inconsistencies. Just be aware of the composition of the eraser, as it can leave contaminates behind, as well as being overly abrasive. Pink Pearl works, but I'm sure there are better available. Also dark tarnishing after replating is often a sign of too high of DC voltage through the plating process. Try backing off a few volt or a two and see if it alleviates the tarnishing. 
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Avery Armes
IPC Training Coordinator
Adco Circuits Inc.
Mr. Armes is the Training Coordinator at Adco Circuits Inc. he has 21 years experience in surface mount and through hole assembly, test and inspection, with a focus on IPC 7711/7722 repair/rework techniques. IPC-A-610 C.I.T., J-STD-001E C.I.T., J-STD-001ES C.I.T.
The "residue" might actually be a surface condition caused by the plating conditions, usually by plating too quickly (too high current density). If this is the case, it is often possible to gently polish the contact using a soft pencil eraser (don't use an abrasive eraser meant for ink!). Gently rub the contact to burnish the area. After this process, wipe the contact with alcohol to remove any organic residues, and re-test the thickness.
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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
First we need to understand the nature of the residues. Are they a product of process control, equipment performance, board prep/cleanliness? The equipment vendor or application engineer will be able to assist you better with this issue.
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Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
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