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The goal of optimal soldering is to obtain create an intermetallic layer (the layer of bronze between the copper and the tin) of the optimal thickness. This has been empirically determined to be around 1μm. For most applications, this will be achieved when the solder is heated to the correct temperature, the solder flows across the copper to cover all the appropriate areasareas of the joint ("wetting"), and the joint is heated for around 2-5 seconds.
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