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Discoloration on pure tin product

I have been working in plating operation of an IC assembly company. Our product is SMD product with pure tin plating. I got feed back from my customer about discolor lead defect. The symptom is found near lead tip area only that was cut from lead frame by TNF process. I am quite sure that I could not see this problem after finishing assembly process but the problem shows when time passed.

I have did EDX analysis on the normal area and discolor area. The result shows copper at discolor area but none at normal area on the same lead. Could you please help to advise me why we found copper on discolor area and what should be the root cause of this problem?

Note: I have checked plating thickness on problematic area. The result is not low, about 500 to 600 microinches.

Kusuma Watcharasittichoke
Plating shop employee - Thailand
October 14, 2008

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Hi Kusuma,

Lead discoloration/tarnished is a form of oxidation. possible causes can be attributed to poor plating process control or handling problems when the plated parts are process in the backend operations. Post- plate process is the first item to check list.

regards and good luck

Joy de Luna
- Philippines
October 15, 2008

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Hi Kusuma,

The source of copper is likely to be from the copper impurities in a etching tank or plating tank. The root cause may excessively treated in a corrosive pre-cleaning/treatment process, in other words " improper cleaning process", since the expose copper may found in the cut area.

Regards,

Joy de Luna
- Philippines
October 16, 2008

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The Cu that you detected could be due to the Cu migration after the cutting process since it only happen at the lead area where it is cut. How long did they wait after cutting before they send the parts for assembly?

When Cu diffused and oxidized, it will create soldering problems.

Robin C.Y. Chua
- Singapore
December 4, 2008