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What is an Alloy?

  • Solder Alloys

  • An alloy is a metal which is comprised of two or more metals. These metals are stable and have some level of solubility together; otherwise, they would not form an alloy and would exist as a heterogeneous combination. Metals are combined in a variety of compositions to form an alloy. The variance in compositions leads to a variance in properties.

    Two alloys that are widely used as solders in the electronics industry are Sn63 and SAC305.  Sn63 refers to an alloy with the composition of 63%Sn and 37%Pb. This alloy is a homogeneous mixture of the two metals, so, when alloyed, the individual metals cannot be seen with the naked eye. SAC305 is a mixture of three different metals: 96.5%Sn, 3.0%Ag, and 0.5%Cu. The “305” in SAC305 comes from the 3.0% Ag (the 30 in 305) and the 0.5% Cu (the 5 in 305). The remaining balance of the alloy is Sn, which, in this case, is 96.5% of the alloy. However, "SAC" is a general term. So, when someone refers to SAC alloys, they would need to specify which SAC alloy they were referring to, as the composition of the Sn, Ag, and Cu can vary.

    The different metals (elements) used in the alloy dictate the alloy’s properties. For example, Bi is very brittle. So, when adding Bi to an alloy, it can become more brittle, but it will also lower the melting temperature, which is desirable for a lot of applications. There are pros and cons for each elemental addition which, depending on the application, can be accounted for by adjusting the alloy ratio.

    If you have more questions on what an alloy is please feel free to reach out to me or email