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topic 8899

Bright vs. matte for reflow


(2001)

We have experienced solderability problems with a brass pin with copper flash, 100uin min nickel plate, 200 µinmin 60/40 tin/lead plate (bright). The pin is subjected to a surface mount reflow process prior to wave soldering. It is during wave soldering that the problem occurs. We believe the main contributor is the bright tin/lead plate subjected to reflow. We received freshly plated pins both bright and matte and subjected them to a tyupical surface mount convection reflow profile. The bright pins darkened and appeared rough and showed non-wetting when solder dipped or wave soldered. The matte pins brightened up and showed good wetting when dipped even after five reflows.

I am looking for confimation that matte tin/lead plate is more appropriate than bright for a part that is subjected to convection reflow and then must be wave soldered. Also, for improved shelf life/solderability, would it be better to receive the pins already reflowed rather than sitting on the shelf waiting for reflow in our process? And is the shelf life of 90/10 significantly different than 60/40?

Pat Bailey
- Redwood Falls, MN, USA


(2001)

Pat -

You should have the parts reflowed before letting them sit on the shelf. A matte finish is typically more subject to contamination than a bright finish. If the bright parts you are using are a bright acid and not a reflow this could be causing problems because of the organic brighteners in the bath/tin lead.

John Bowers
- Everett, Massachusetts



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