does copper wire become thinner when it dip to leadfree solder?

arnold: I did not say that Sn100 dissolved copper faster. The graph of dissolution rates [from the link above] shows that Sn100 dissolves copper slower than many of the other solders.

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Hello Arnold, Just to clarify the Sn100C discussion: Please note that SN100C is the Nihon Superior alloy composed of tin/.7copper/nickel. The key point in regard to SN100C is that Cu does not go directly into solution but first reacts to form an intermetallic layer. The rate of dissolution is then determined by how quickly that intermetallic dissolves and the Ni incorporated in that intermetallic in the SN100C stabilizes it and slows the dissolution rate.

Of course how close you are to saturation at a particular temperature is another factor. One of the factors in the high dissolution rate of SAC305 is that the Cu level is well below saturation. Increasing the Cu content or adjusting the Ag content to move the alloy towards a composition with a lower Cu saturation level does reduce the rate of dissolution a little but it is only when there is Ni present the rate of dissolution is brought to almost zero.

At higher temperatures the effect of the Ni is diminished and that is where the extra Cu in the SN100C3 and C4 plays a role.

Thanks, Bob

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