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Discoloration on Plated Leadframe

I do need expert advise for the following. Recently some of the silver plated leadframe with Ag plating of 0.3 to 0.4µm was facing discoloration problem after undergoing the die bond oven at 380°C for 1.5 sec approx. The color change from a Silver to "Algae" green. The thin Ag plating and diffusion were initially suspected to cause the color change (spec call for 0.5µm minimum) but this leadframe have been in production for over 8 years and this is the first time that we encountered discoloration.

Leadframe samples with Ag thickness between 0.2 to 0.3µm and 0.3 to 0.5µm have been sent to run and no discoloration was noted from this sample after undergoing the die bond oven. The leadframe base is copper.

Suriani A. Muhin
-Singapore
2003