What are the constituents of alloy solder ?

Solder is a metallic alloy primarily used for joining electrical wires and components due to its low melting point. Traditionally, the most common form of solder is an alloy composed of lead (Pb) and tin (Sn) [1]. The eutectic composition of this tin-lead alloy, specifically Sn63Pb37, has a melting point of approximately 183°C, which is significantly lower than the melting points of the individual constituent metals [4]. While modern environmental regulations like RoHS have led to the development of lead-free alternatives using elements such as copper (Cu), silver (Ag), and bismuth (Bi), the classic alloy solder remains defined by its lead and tin content [1]. Lead provides technical advantages in these alloys, including improved wetting characteristics and reduced melting temperatures [4]. Therefore, the primary constituents of traditional alloy solder are lead and tin.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > QUESTIONS > p. 54
2. [4] https://nepp.nasa.gov/docuploads/B04F2DB5-001E-4F16-9B0190ABB573BD95/Pb%20Free%20Solder%20Report%20Draft%20R3-71305.pdf