silver/lead-free/copper soldering alloys

[metebalci]

Hi,

What is the effect of silver in soldering alloy ?
e.g. Sn62Pb36Ag02 (melting point: 179C-189C)

What is the effect of lead-free soldering alloy ?
e.g. Sn96Ag04 (melting point: 221C-229C)

What is the effect of copper in soldering alloy ?
e.g. Sn95.5Ag3.8Cu0.7 (melting point: 217C-221C)

Thanks so much.

MB

[jneutron]

Originally posted by metebalci
Hi,

What is the effect of silver in soldering alloy ?
e.g. Sn62Pb36Ag02 (melting point: 179C-189C)

What is the effect of lead-free soldering alloy ?
e.g. Sn96Ag04 (melting point: 221C-229C)

What is the effect of copper in soldering alloy ?
e.g. Sn95.5Ag3.8Cu0.7 (melting point: 217C-221C)

Thanks so much.

MB

InN the eutectic tin lead system, the silver causes the eutectic point to drop, from 183 C to 179 C.

Lead free is a result of lead based issues for human health. Pure tin is 232 C, the addition of silver brings it down to 221 C.

Copper: for the tin lead eutectic, the melt can support copper over approximately 4% contamination for typical pot temperatures, and then it will not dissolve any further. Problem is, that causes a very grainy surface, which can make it difficult to identify a cold solder joint. Some include it because they believe it reduces the scavenging of copper during the soldering operation.

In addition, the copper/tin alloy stuck in the melt will solidify about 2 degrees before the bulk of the pot. This allows one to scrape out the heavy copper tin contamination from the bottom of the pot once the pot has achieved 185 C. Not a very useful process, IMHO.

I assume the copper in tin silver will do approximately the same thing it does in tin lead, but have seen no publications to that effect.

All the additional alloy constituents cause the solid surface of the solder joint to appear non shiny. If shiny is the criteria for a good solder joint, it would have to be re-visited.

Cheers, John