The role of lead in solder

- Mar 15, 2019-

Solder paste printing is the first process of PCB assembly. It affects the subsequent process of soldering, reflow soldering, cleaning, testing, etc., and directly determines the reliability and quality of the product. Then the effect of lead in the solder is analyzed by FASTPCBA.

The tin in the solder is alloyed with the base metal due to the metallurgical reaction during the soldering process, and the lead hardly participates in the reaction below 300 °C. However, when lead is added to tin, excellent properties which are not possessed by tin and lead are obtained, which are manifested in the following aspects.

PCB assembly

(1) Lowering the melting point for easy soldering. The melting point of tin is 231.9 ° C, the melting point of lead is 327.4 ° C, both of which are higher than the melting temperature of solder 183 ° C. If the two metal alloys of tin and lead are mixed, the melting point of the alloy is lower than the melting point of the two metals, so the welding The process is easy to operate.

(2) Improve mechanical properties. Due to the addition of lead, the mechanical properties of tin-lead metal, both tensile strength and shear strength, are more than doubled compared to their single component.

(3) Reduce the surface tension. The surface tension of the tin-lead alloy is lower than that of pure tin, which is beneficial to the wetting of the solder on the surface of the metal to be welded.

(4) Antioxidation. The incorporation of lead into tin increases the oxidation resistance of the solder and reduces the amount of oxidation.

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