Soldering problems with bright Tin Plate

A. Dull Tin (no organics added) remains solderable longer, but fingerprints badly, so it depends.

Other possibilities: The bright tin bath may need a carbon treatment, or your pre-plate cycle may not be leaving a clean base metal. Do you strike first with cyanide copper ? Are you etching the brass before plating? I was going to write "over-etching", but you should not etch at all, the brass should stay bright in the pre-plate cleaning step, the cleaners could be too hot, the acid could be too concentrated.

A. You may try analyzing the tin plate bath for Copper, Zinc, Iron, etc. contamination. These contaminants are usually detrimental if over 500-1000 PPM.

good luck,

Dave
SUNNYvale, CA

A. How long between plating and soldering? If parts have been on the shelf for an extended period, especially if at elevated temperature or for more than six months, or if there is no barrier plate between brass and tin, zinc and/or copper diffusion can poison the tin. This usually shows as a dark discoloration of the tin deposit, but might also affect solderability. If freshly plated, ignore this line of reasoning.

Another problem you may have is conversion of the metal tin plating to intermetallic. If the plating is mostly intermetallic, solderability is greatly diminished.

Intermetallic conversion is a time and temperature dependent process. Has the material been plated for a long time, i.e. many months? Have the parts been through any elevated temperature processing after plating? Either of these factors will contribute to formation of intermetallics in the plating. Intermetallic formation can be prevented in most cases by a nickel flash between the copper or brass and the tin.

A. Hi Poshendra. We appended your inquiry to one of several threads about this problem. Note Tom's suggestion that bright tin is more difficult to solder than alkaline tin, and Larry's that intermetallics may have formed in storage.

Please search the site for "solder problem tin plated brass" to get some additional understanding of the possible causes for this problem, then get back to us with the details of your situation. Thanks!

Regards,