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Matte Sn discolouration

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Hi ,
we are using matte Sn over nickel underplate.
For the solderability application, the product sees a temperature in excess of 232C (Sn melting pt).
For cycles greater than 232C, I see the matte Sn discolour is shades of yellow to brown.

Could someone shed light as to the cause of the discolouration.

Ali

Sharaf Ali
electronics assembly - San Diego, California, USA

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Mr Sharaf Ali.

It is likely the plated Matte Tin solution is organically overloaded with either bult up impurities or excess brightener, both of which tend to co deposit and then oxidise to the brown you see,when exposed to high temperatures.

Warm the solution to 35 or 40 centigrade , Run 3 to 4 grams per liter carbon for 4 Hours and filter our by decantation or filtration. This removes excess brightener and most of the organic impurities.

It should help.

Regards

Asif Nurie Atlanta Global New Delhi, India